Biaxially oriented film, film with cured resin layer, and metal laminated film

Abstract

The objective is to provide a biaxially oriented film with excellent low dielectric properties. [Solution] A biaxially oriented film containing two or more types of polyester, at least one of which is polybutylene naphthalate resin (A), and having a dielectric loss tangent of 0.0040 or less at 28 GHz.

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented film, a film with a cured resin layer, and a metal laminated film. [Background technology]

[0002] In recent years, with the increasing performance and functionality of electrical and electronic devices, there has been a growing need for high-speed information communication. For example, with the launch of 5G (fifth-generation mobile communication system) high-speed communication services for smartphones, these services are becoming widespread not only in the consumer sector but also in the industrial sector (factories, automobiles, etc.). 5G's high-speed, high-capacity data communication utilizes "millimeter wave" radio waves (wavelengths of 1-10 mm, frequencies of 30-300 GHz). Advantages of millimeter waves include the ability to transmit large amounts of data at once and the potential for high-resolution images.

[0003] On the other hand, when a high-frequency digital signal such as millimeter waves is passed through a circuit board, dielectric loss occurs where a portion of the transmitted digital signal is consumed as heat on the wiring of the circuit board, resulting in a so-called "transmission loss" where the digital signal reaches the receiving side attenuated. Therefore, measures to reduce transmission loss are required in the materials used. The aforementioned transmission loss is the sum of dielectric loss and conductor loss, and the dielectric loss α d It is calculated from the following formula (1).

[0004]

number

[0005] Note that f is frequency, c is the speed of light, and ε r is the relative permittivity, and tanδ is the dielectric loss tangent.

[0006] For example, in FPCs (Flexible Printed Circuits), which are flexible circuit boards formed from resin film and copper foil, the resin film has dielectric loss α to reduce transmission loss. dA reduction in ε is required. More specifically, r Attempts have been made to lower tanδ, particularly to reduce tanδ.

[0007] Various materials have been proposed to lower the dielectric constant and dielectric loss tangent of resin films, but among them, fluororesins, particularly polytetrafluoroethylene (PTFE), have low dielectric constant and dielectric loss tangent, and are widely used as insulating layers for various electrical components that handle high-frequency signals (Non-Patent Literature 1). However, fluororesins have many limitations in terms of mechanical properties, processability, and cost, and there is a demand for more versatile resin films.

[0008] Polyester film is a highly versatile resin film. Polyester film excels in heat resistance, weather resistance, mechanical strength, and transparency, and is also readily available at a reasonable price. Therefore, it is used in various applications such as packaging materials and optical applications, but its low dielectric properties have not been given much consideration.

[0009] For example, Patent Document 1 discloses a laminated biaxially oriented polyester film containing 5 to 45 volume percent of voids inside, as a polyester film having excellent low dielectric properties. By containing voids, air gaps can be dispersed, achieving a low dielectric constant and low dielectric loss tangent. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2006-352470 [Non-patent literature]

[0011] [Non-Patent Document 1] "Development Trends of High-Frequency Compatible Materials and Their Applications to 5G and Millimeter-Wave Radar," Technical Information Association, Chapter 3, Section 2, pp. 77-84, "Development Trends of High-Speed, High-Frequency Compatible FPCs and Reduction of Transmission Loss" [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] The cavity-containing laminated biaxially oriented polyester film described in Patent Document 1 above is formed by mixing different materials to create cavities. However, in such cases, it is difficult to control the size of the cavities or the dispersion state of the different materials. For example, if the dispersion state of the different materials is insufficient, the desired low dielectric properties may not be obtained.

[0013] The problem that this invention aims to solve is to provide a biaxially oriented polyester film that has excellent low dielectric properties even without having cavities, by solving the above-mentioned problems. [Means for solving the problem]

[0014] The inventors of this invention have diligently studied and conducted research to achieve the above objectives, and as a result, have completed this invention. In one aspect, the gist of this invention is as follows [1] to

[10] . The gist of this invention is as follows: [1] A biaxially oriented film comprising two or more polyesters, at least one of which is polybutylene naphthalate resin (A), and having a dielectric loss tangent of 0.0040 or less at 28 GHz. [2] The biaxially oriented film described in [1] above, wherein the dielectric constant at 28 GHz is 3.15 or more and 3.25 or less. [3] The biaxially oriented film according to [1] or [2] above, wherein the tensile breaking strength in both the longitudinal direction (MD) and the width direction (TD) is 150 MPa or more. [4] A biaxially oriented film according to any of [1] to [3] above, wherein the storage modulus measured by dynamic viscoelasticity at 23°C is 3.5 GPa or more in both the longitudinal direction (MD) and the width direction (TD). [5] The biaxially stretched film according to any one of [1] to [4] above, wherein the tensile break strength in the machine direction (MD) and the transverse direction (TD) when left standing in an environment of 120 °C and 85% RH for 96 hours and then further left standing at room temperature (23 °C) for 18 hours is 100 MPa or more in both directions. [6] The biaxially stretched film according to any one of [1] to [5] above, wherein the strength retention rates in the machine direction (MD) and the transverse direction (TD) when left standing in an environment of 120 °C and 85% RH for 96 hours and then further left standing at room temperature (23 °C) for 18 hours are 50% or more in both directions. [7] The biaxially stretched film according to any one of [1] to [6] above, which contains 35% by mass or more and 70% by mass or less of the polybutylene naphthalate resin (A). [8] The biaxially stretched film according to any one of [1] to [7] above, which contains a crystalline polyester (B). [9] The biaxially stretched film according to [8] above, wherein the glass transition temperature of the crystalline polyester (B) is higher than that of the polybutylene naphthalate resin (A).

[10] The biaxially stretched film according to [8] or [9] above, wherein the crystalline polyester (B) is a polyethylene naphthalate resin.

[11] The biaxially stretched film according to

[10] above, wherein the polyethylene naphthalate resin has an acid component having a benzene skeleton as another copolymerization component other than 2,6-naphthalenedicarboxylic acid of 5 mol% or less in all dicarboxylic acid components.

[12] The biaxially stretched film according to any one of [1] to

[11] above, having a film thickness of 40 to 150 μm.

[13] A film with a cured resin layer, having a cured resin layer on at least one surface layer of the biaxially stretched film according to any one of [1] to

[12] above, wherein the cured resin layer is formed from a resin composition containing 70% by mass or more of a crosslinking agent with respect to the non-volatile components.

[14] A metal laminated film, having a metal layer on the cured resin layer of the film with a cured resin layer according to

[13] above.

[15] The metal laminated film according to

[14] above, wherein the metal layer is patterned.

[16] The metal laminated film according to

[14] or

[15] above, wherein the metal layer is made of copper or silver.

[17] A biaxially oriented film according to any of [1] to

[12] above, for use in high-speed communication circuits.

[18] The biaxially oriented film described in

[17] above, used as a base film for transparent antennas.

[19] A film with a cured resin layer as described in

[13] above, for use in high-speed communication circuits.

[20] A film with a cured resin layer as described in

[19] above, used as a base film for a transparent antenna.

[21] A metal laminated film according to any of the above

[14] to

[16] , for use in high-speed communication circuits.

[22] The metal laminated film described in

[21] above, which is used as a base film for a transparent antenna. [Effects of the Invention]

[0015] The biaxially oriented film, the film with a cured resin layer, and the metal laminated film of the present invention have excellent low dielectric properties. Therefore, the biaxially oriented film, the film with a cured resin layer, and the metal laminated film of the present invention can be suitably used for high-speed communication circuits. [Modes for carrying out the invention]

[0016] The present invention will be described in detail below. However, the present invention is not limited to the embodiments described below.

[0017] <<Biaxially oriented film>> A biaxially oriented film according to an example of an embodiment of the present invention (hereinafter sometimes referred to as "this film") contains two or more polyesters, at least one of which is a polybutylene naphthalate (hereinafter also referred to as "PBN") resin (A), and has a dielectric loss tangent of 0.0040 or less at 28 GHz. Because this film is a biaxially oriented film, it can be made into a thin film, and because the dielectric loss tangent is adjusted to a specific range using a particular blend of polyesters, it has low dielectric properties. Furthermore, because this film uses a specific blend of polyesters to control the crystallization rate, it is also excellent for extrusion molding and stretching, which are difficult with PBN resin (A) alone.

[0018] 1. Physical properties First, let me explain the physical properties of this film.

[0019] (1) Dielectric loss tangent The film has a dielectric loss tangent of 0.0040 or less at 28 GHz, preferably 0.0039 or less, more preferably 0.0038 or less, particularly preferably 0.0035 or less, and especially preferably 0.0030 or less. The lower limit is not particularly limited, but is 0.0010 or more, preferably 0.0015 or more, more preferably 0.0020 or more, and even more preferably 0.0025 or more. If the dielectric loss tangent is 0.0040 or less, the film can be said to have excellent low dielectric properties and can be suitably used for high-speed communication circuits. The dielectric loss tangent can be adjusted by the type and content of the polyesters mixed, the stretching conditions, etc. The dielectric loss tangent was measured using the method described in the examples.

[0020] (2) Dielectric constant The dielectric constant of this film at 28 GHz is preferably 3.15 or more and 3.25 or less. The upper limit is more preferably 3.24 or less, even more preferably 3.23 or less, particularly preferably 3.22 or less, and especially preferably 3.21 or less. Within the range of the dielectric constant, the film can be said to have excellent low dielectric properties and can be suitably used for high-speed communication circuits. The dielectric constant can be adjusted depending on the type and content of the polyesters mixed, the stretching conditions, etc. The dielectric constant was measured using the method described in the examples.

[0021] (3) Tensile breaking strength The tensile breaking strength in both the longitudinal direction (MD) and the width direction (TD) of this film is preferably 150 MPa or higher. More preferably 154 MPa or higher, even more preferably 170 MPa or higher, particularly preferably 173 MPa or higher, and especially preferably 175 MPa or higher. There is no particular upper limit, but both the longitudinal direction (MD) and the width direction (TD) are usually 500 MPa or lower, preferably 300 MPa or lower. If the tensile breaking strength of this film is 150 MPa or higher, sufficient mechanical properties can be obtained. The tensile breaking strength can be adjusted by the type and content of polyester mixed, the stretching conditions, etc. The tensile breaking strength was measured using the method described in the examples.

[0022] In this invention, the longitudinal direction (MD) of the film refers to the direction in which the film progresses during the film manufacturing process, that is, the winding direction of the film roll. Furthermore, the width direction (TD) of the film refers to the direction parallel to the film surface and perpendicular to the longitudinal direction; in other words, it is the direction parallel to the central axis of the roll when the film is in a roll form. The above-mentioned longitudinal direction (MD) is also called the machine direction or vertical direction, and the above-mentioned width direction (TD) is also called the horizontal direction.

[0023] (4) Storage modulus The storage modulus measured by dynamic viscoelasticity at 23°C is preferably 3.5 GPa or higher in both the longitudinal (MD) and widthwise (TD) directions. More preferably 3.6 GPa or higher, even more preferably 3.7 GPa or higher, and particularly preferably 3.8 GPa or higher. There is no particular upper limit, but it is usually 10 GPa or lower, preferably 8.0 GPa or lower. If the storage modulus of this film is 3.5 GPa or higher, the film will have good stiffness, be less prone to wrinkling, and have excellent handling properties. The storage modulus is the value obtained by the method described in the examples.

[0024] (5) Tensile properties after wet heat test After standing for 96 hours in an environment of 120°C and 85%RH, and then standing for another 18 hours at room temperature (23°C), the tensile breaking strength in the longitudinal direction (MD) and the width direction (TD) is preferably 100 MPa or more, more preferably 105 MPa or more, even more preferably 110 MPa or more, particularly preferably 120 MPa or more, and especially preferably 130 MPa or more. There is no particular upper limit, but it is usually 300 MPa or less, preferably 250 MPa or less. If the tensile breaking strength of this film after a wet heat test is 100 MPa or higher, it will be a film with excellent hydrolysis resistance and sufficient weather resistance. Furthermore, after standing for 96 hours in an environment of 120°C and 85%RH, and then standing for another 18 hours at room temperature (23°C), the strength retention rate in the longitudinal direction (MD) and the width direction (TD) is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, and particularly preferably 65% ​​or more. There is no particular upper limit, but it should be 100% or less. If the strength retention rate of this film after a humid heat test is 50% or higher, it has sufficient weather resistance as a film.

[0025] (6) Hayes The haze of this film is preferably 3.0% or less, more preferably 2.0% or less, even more preferably 1.0% or less, and particularly preferably 0.5% or less. If the haze of this film is below the above upper limit, it can be said to have good transparency. While there is no specific lower limit, it is usually 0.01% or higher.

[0026] (7) Thermal shrinkage When this film is heated at 150°C for 30 minutes, the thermal shrinkage rate is preferably 5.0% or less in both the longitudinal direction (MD) and the width direction (TD). A thermal shrinkage rate of 5.0% or less allows the film to exhibit excellent heat resistance, particularly dimensional stability at high temperatures, and to be used without practical problems. From this perspective, the thermal shrinkage rate of this film is more preferably 4.0% or less, even more preferably 3.0% or less, and particularly preferably 2.5% or less. There is no particular lower limit, but it is usually 0.01% or more.

[0027] (8) Thickness The thickness of this film is preferably 1 to 250 μm, more preferably 5 to 200 μm, and even more preferably 10 to 150 μm. A thickness of 1 μm or more ensures that the film strength is within a practical range. A thickness of 250 μm or less makes it easy to incorporate into mobile devices and other applications, and is suitable for use in high-speed communication circuits. In particular, when used as a base film for transparent antennas, the thickness of the film is preferably 40 to 150 μm. The lower limit of this thickness is more preferably 50 μm, even more preferably 75 μm, and particularly preferably 100 μm. The upper limit of this thickness is preferably 140 μm, and even more preferably 130 μm. The thickness can be adjusted by the film formation and stretching conditions.

[0028] 2. Ingredients Next, we will explain the components that make up this film.

[0029] This film contains two or more types of polyester, at least one of which is PBN resin (A). The mechanism by which this film, by containing PBN resin (A), exhibits excellent low dielectric properties is not entirely clear, but it is presumed that this is due to the suppression of dipole motion by the stacking of aromatic rings. Generally, when a dielectric material is placed in an electric field, its dipoles orient themselves. Then, the dipoles rotate and reverse direction in accordance with the phase of the alternating electric field. This rotational and reversal motion of the dipoles generates friction, resulting in dielectric loss. Therefore, it is hypothesized that suppressing the motion of the dipole leads to excellent low dielectric properties.

[0030] More specifically, from the perspective of suppressing dipole motion through aromatic ring stacking, it is thought that stronger stacking leads to a greater suppression effect, and more specifically, having a naphthalene skeleton rather than a benzene skeleton is thought to result in better low dielectric properties. Therefore, from the viewpoint of low dielectric properties, it is preferable for the aromatic ring to have a naphthalene skeleton rather than a benzene skeleton.

[0031] <Polybutylene naphthalate resin (A)> The PBN resin (A) constituting this film is a polyester containing 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (a-1) and 1,4-butanediol as the diol component (a-2), preferably mainly composed of 2,6-naphthalenedicarboxylic acid and 1,4-butanediol, that is, preferably containing 50 mol% or more of 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (a-1) and 50 mol% or more of 1,4-butanediol as the diol component (a-2). In particular, the PBN resin (A) used in the present invention more preferably contains 90 mol% or more of 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (a-1) and 90 mol% or more of 1,4-butanediol as the diol component (a-2).

[0032] The dicarboxylic acid component (a-1) constituting the PBN resin (A) contains 2,6-naphthalenedicarboxylic acid, and of the dicarboxylic acid component (a-1), it is more preferable that 2,6-naphthalenedicarboxylic acid is 92 mol% or more, even more preferable that it is 94 mol% or more, particularly preferable that it is 96 mol% or more, especially preferable that it is 98 mol% or more, and most preferably that all (100 mol%) of the dicarboxylic acid component (a-1) is 2,6-naphthalenedicarboxylic acid. By setting the dicarboxylic acid component (a-1) to 90 mol% or more of 2,6-naphthalenedicarboxylic acid, the glass transition temperature and crystallinity of the PBN resin (A) are improved, and consequently the heat resistance and mechanical properties of the film are improved. Furthermore, by setting the dicarboxylic acid component (a-1) to 90 mol% or more of 2,6-naphthalenedicarboxylic acid, the naphthalene skeleton content is increased, and the effect of suppressing dipole motion due to stacking is enhanced. As a result, the low dielectric properties are improved.

[0033] The PBN resin (A) may be copolymerized with acid components other than 2,6-naphthalenedicarboxylic acid for the purpose of improving moldability and heat resistance. Specifically, examples include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-frandicarboxylic acid, 2,4-frandicarboxylic acid, 3,4-frandicarboxylic acid, benzophenone dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 3,3'-diphenyldicarboxylic acid, and 4,4'-diphenylether dicarboxylic acid; and aliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. Among these, isophthalic acid, 2,5-frandicarboxylic acid, 2,4-frandicarboxylic acid, and 3,4-frandicarboxylic acid are preferred from the viewpoint of moldability. Furthermore, from the viewpoint of low dielectric properties, acid components having a naphthalene skeleton with strong stacking properties are preferred among these. For example, acid components having a benzene skeleton, such as terephthalic acid and isophthalic acid, are preferably present in amounts of 5 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less. These acid components can be used individually or in combination of two or more. Furthermore, it is preferable that the content of acid components other than 2,6-naphthalenedicarboxylic acid be 10 mol% or less of the total acid components including 2,6-naphthalenedicarboxylic acid.

[0034] The diol component (a-2) constituting the PBN resin (A) contains 1,4-butanediol, and of the diol component (a-2), it is more preferable that 1,4-butanediol accounts for 92 mol% or more, even more preferably 94 mol% or more, particularly preferably 96 mol% or more, and especially preferably 98 mol% or more, with the most preferable being that all (100 mol%) of the diol component (a-2) is 1,4-butanediol. By setting the diol component (a-2) to 90 mol% or more of 1,4-butanediol, the compatibility with the polyester to be mixed is improved, further improving the glass transition temperature and crystallinity of the PBN resin (A), and consequently improving the heat resistance and mechanical properties of the film.

[0035] The PBN resin (A) may be copolymerized with diol components other than 1,4-butanediol to improve moldability and heat resistance. Specifically, examples include 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, ethylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, hydroquinone, bisphenol, spiroglycol, 2,2,4,4-tetramethylcyclobutane-1,3-diol, isosorbide, etc. Among these, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol are preferred from the viewpoint of moldability. These diol components can be used individually or in combination of two or more. Furthermore, it is preferable that the content of diol components other than 1,4-butanediol is 10 mol% or less of the total diol components including 1,4-butanediol.

[0036] The content of the PBN resin (A) is preferably 5% by mass or more and 70% by mass or less, when the biaxially oriented film is considered to be 100% by mass. If the content is 5% by mass or more, the low dielectric properties of the PBN resin (A) are exhibited. If the content is 70% by mass or less, an appropriate amount of at least one type of polyester, as described later, can be secured, thereby improving the extrusion moldability and stretchability during film formation while achieving a good balance of low dielectric properties, mechanical properties, and weather resistance.

[0037] In particular, from the viewpoint of achieving even better low dielectric properties, the content of the PBN resin (A) is preferably 35% by mass or more and 70% by mass or less, more preferably 40% by mass or more and 65% by mass or less, even more preferably 45% by mass or more and 62% by mass or less, and especially preferably 50% by mass or more and 60% by mass or less.

[0038] The glass transition temperature (Tg(A)) of PBN resin (A) is preferably 50°C to 130°C, more preferably 58°C to 125°C, and even more preferably 65°C to 120°C. A glass transition temperature (Tg(A)) within this range provides an excellent balance between heat resistance and extrusion moldability. The glass transition temperature (Tg(A)) can be measured by the method described in the examples.

[0039] <At least one type of polyester> This film is made of a mixed polyester containing at least one type of polyester in addition to the PBN resin (A) mentioned above.

[0040] The aforementioned at least one polyester is not particularly limited, and examples include those consisting of a dicarboxylic acid component and a diol component as described below. Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfisoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, monopotassium salt of trimellitic acid, and their ester-forming derivatives.

[0041] Examples of diol components include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethylol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol, methylolpropionic acid, glycerin, trimethylolpropane, sodium methylolethylsulfonate, potassium methylolpropionate, and the like. From the above compounds, one or more can be appropriately selected, and polyesters can be synthesized by conventional polycondensation reactions. The at least one polyester mentioned above includes a polyester equivalent to the PBN resin (A) described above, but in the mixed polyester of the present invention, the at least one polyester used is different from the PBN resin (A) described above.

[0042] The at least one polyester is preferably a crystalline polyester (B), and more preferably the crystalline polyester (B) has a higher glass transition temperature than the PBN resin (A).

[0043] By mixing the crystalline polyester (B) with the PBN resin (A), the crystallization rate of the PBN resin (A) can be controlled, and a film with excellent extrusion moldability and stretchability can be obtained. Furthermore, because the crystalline polyester (B) has a higher glass transition temperature than the PBN resin (A), a resin composition with a higher glass transition temperature than PBN resin (A) alone can be obtained, resulting in good heat resistance. Furthermore, by mixing in the aforementioned crystalline polyester (B), high crystallinity can be maintained, resulting in a film with an excellent balance of low dielectric properties, mechanical properties, and weather resistance.

[0044] The crystalline polyester (B) is preferably polyethylene naphthalate resin, polycyclohexylene dimethylene terephthalate resin, etc., and more preferably contains polyethylene naphthalate (hereinafter also referred to as "PEN") resin from the viewpoint of improving the balance of low dielectric properties, mechanical properties and weather resistance. Since polyethylene naphthalate resin has a naphthalene skeleton in its structure, it has a great effect of suppressing the movement of dipoles by stacking aromatic rings, which can make the low dielectric properties of this film even better.

[0045] (Polyethylene naphthalate resin) The PEN resin may be a homopolyester or a copolymerized polyester, but it is preferable that the acid component having a benzene skeleton as a copolymer component other than 2,6-naphthalenedicarboxylic acid is 5 mol% or less of the total dicarboxylic acid component. Alternatively, it may contain no other copolymer components, and all of the dicarboxylic acid component (100 mol%) may be 2,6-naphthalenedicarboxylic acid. Among these, homopolyester is preferred from the viewpoint of maintaining high crystallinity. Furthermore, homopolyester is preferred from the viewpoint of increasing the naphthalene skeleton content to enhance the effect of suppressing dipole motion through stacking, thereby making it easier to improve low dielectric properties. Furthermore, homopolyester and copolymerized polyester may be blended, but if homopolyester and one type of copolymerized polyester are blended, it shall be considered as if two types of crystalline polyester (B) were used.

[0046] When the PEN resin is made of homopolyester, it is obtained by polycondensation of 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (b-1) and ethylene glycol as the diol component (b-2).

[0047] On the other hand, when the PEN resin consists of copolymerized polyester, 2,6-naphthalenedicarboxylic acid is an essential component as the dicarboxylic acid component (b-1), and other copolymer components may be added as needed. Other copolymer components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-frandicarboxylic acid, 2,4-frandicarboxylic acid, 3,4-frandicarboxylic acid, benzophenone dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 3,3'-diphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid; aliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dimer acid; and oxycarboxylic acids such as p-oxybenzoic acid. Among these, isophthalic acid, 2,5-frandicarboxylic acid, 2,4-frandicarboxylic acid, and 3,4-frandicarboxylic acid are preferred from the viewpoint of moldability. Furthermore, from the viewpoint of low dielectric properties, copolymer components having a naphthalene skeleton with strong stacking properties are preferred. These copolymer components can be used individually or in combination of two or more.

[0048] Ethylene glycol is an essential component of the diol component (b-2), and other copolymer components may be used as needed, including 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, propylene glycol, polyalkylene glycol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, hydroquinone, spiroglycol, 2,2,4,4-tetramethylcyclobutane-1,3-diol, isosorbide, 1,4-cyclohexanedimethanol, polytetramethylene ether glycol, dimergol, bisphenols (bisphenol compounds such as bisphenol A, bisphenol F, or bisphenol S, or their derivatives, or their ethylene oxide adducts), among which 1,4-cyclohexanedimethanol, polytetramethylene ether glycol, dimergol, and bisphenols are preferred. In particular, from the viewpoint of maintaining film strength, it is preferable to use bisphenols. Furthermore, it is preferable to use bisphenol A-ethylene oxide adducts as the bisphenol compounds. These copolymer components can be used individually or in combination of two or more.

[0049] The copolymerized polyester constituting the PEN resin preferably contains 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (b-1), and ethylene glycol and a bisphenol A-ethylene oxide adduct as the diol component (b-2).

[0050] The copolymerized polyester contains, preferably, 0 mol% to 10 mol%, more preferably 0 mol% to 8 mol%, even more preferably 0 mol% to 6 mol%, particularly preferably 0 mol% to 4 mol%, and especially preferably 0 mol% to 2 mol% of other copolymerized components in the dicarboxylic acid component. By keeping the content of other copolymer components in the dicarboxylic acid component within the above numerical range, the glass transition temperature and crystallinity of the copolymerized polyester are improved, and consequently, the heat resistance and mechanical properties of the film are improved. A particularly preferred configuration is, as described above, the use of a copolymer component having a naphthalene skeleton with strong stacking properties as another copolymer component. For example, the acid component having a benzene skeleton, such as terephthalic acid or isophthalic acid, is preferably 5 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less.

[0051] The copolymerized polyester preferably contains 90 mol% or more, more preferably 92 mol% or more, even more preferably 94 mol% or more, particularly preferably 96 mol% or more, and especially preferably 98 mol% or more of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component, and all (100 mol%) of the dicarboxylic acid component may be 2,6-naphthalenedicarboxylic acid. By keeping the content of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component within the above numerical range, the glass transition temperature and crystallinity of the copolymerized polyester are improved, and consequently, the heat resistance and mechanical properties of the film are enhanced. Furthermore, keeping the content of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component within the above numerical range increases the naphthalene skeleton content, which enhances the effect of suppressing dipole motion due to stacking. As a result, the low dielectric properties are improved.

[0052] The copolymerized polyester contains, preferably, 4 mol% to 70 mol%, more preferably 4.2 mol% to 60 mol%, even more preferably 4.4 mol% to 50 mol%, particularly preferably 4.6 mol% to 40 mol%, and especially preferably 4.8 mol% to 30 mol% of other copolymerized components in the diol component. By keeping the content of other copolymer components in the diol component within the above numerical range, the glass transition temperature of the copolymerized polyester is improved, and consequently, the heat resistance of this film is improved. Furthermore, because crystallinity can be controlled, the crystallization rate can be slowed, improving the extrusion and stretchability of the film. Furthermore, if the content is 70 mol% or less, the melting point will not become too high. Therefore, there is no need to set a high molding temperature, and there is no concern about thermal decomposition.

[0053] The copolymerized polyester contains ethylene glycol in the diol component, preferably 30 mol% to 96 mol%, more preferably 40 mol% to 95.8 mol%, even more preferably 50 mol% to 95.6 mol%, particularly preferably 60 mol% to 95.4 mol%, and especially preferably 70 mol% to 95.2 mol%. By keeping the ethylene glycol content in the diol component within the above numerical range, the crystallinity of the copolymerized polyester is maintained, and consequently, the heat resistance of this film is improved.

[0054] The content of the crystalline polyester (B), such as PEN resin, is preferably 50 parts by mass or more and 1000 parts by mass or less per 100 parts by mass of PBN resin (A), more preferably 55 parts by mass or more and 980 parts by mass or less, even more preferably 60 parts by mass or more and 950 parts by mass or less, and particularly preferably 65 parts by mass or more and 900 parts by mass or less, from the viewpoint of balancing low dielectric properties, mechanical properties, weather resistance and moldability. If the content of the crystalline polyester (B) in this film is 50 parts by mass or more, the crystallization rate can be slowed down, thereby improving the extrusion moldability and stretchability during film manufacturing. Furthermore, if the amount is 50 parts by mass or more, the glass transition temperature will improve, thereby enhancing the heat resistance of this film. On the other hand, if the content of the crystalline polyester (B) is 1,000 parts by mass or less, the balance of the low dielectric properties, mechanical properties, and weather resistance of the PBN resin (A) is not significantly impaired, and the resulting film has a good balance of dielectric properties, mechanical properties, and weather resistance.

[0055] In particular, from the viewpoint of achieving even better low dielectric properties, the content of the crystalline polyester (B), such as PEN resin, is preferably 50 parts by mass or more and 185 parts by mass or less per 100 parts by mass of PBN resin (A), more preferably 55 parts by mass or more and 150 parts by mass or less, even more preferably 60 parts by mass or more and 125 parts by mass or less, and especially preferably 65 parts by mass or more and 110 parts by mass or less.

[0056] For example, when PEN resin is used as the crystalline polyester (B), both the PBN resin (A) and the PEN resin are resins having a naphthalene skeleton. However, as the amount of PBN resin (A) increases, the dielectric loss tangent decreases, and the low dielectric properties can be improved. This is thought to be related to density. The dielectric constant is a parameter that indicates the degree of polarization. As the number of molecules per unit volume increases, the sum of dipoles increases, so it is thought that the dielectric constant increases with higher density. On the other hand, the dielectric loss tangent is a parameter that indicates the degree of energy loss caused by the vibration of dipoles when an AC voltage is applied. From this, it is thought that when the density is high, the vibrations of the dipoles cancel each other out, resulting in a smaller energy loss, i.e., a smaller dielectric loss tangent. In other words, when this film contains the PBN resin (A) and the PEN resin, the density increases as the PBN resin (A) content increases, so the dielectric loss tangent effectively decreases.

[0057] Furthermore, the crystalline polyester (B) used in the present invention has a higher glass transition temperature than the PBN resin (A), and the difference in their glass transition temperatures is preferably 20°C or more, more preferably 30°C or more, and even more preferably 40°C or more. When the difference in glass transition temperatures between the PBN resin (A) and the crystalline polyester (B) is greater than or equal to the lower limit mentioned above, the glass transition temperature of the film falls within a suitable range, resulting in a film with excellent heat resistance and extrusion moldability. The upper limit of the difference in glass transition temperatures between the PBN resin (A) and the crystalline polyester (B) is not particularly limited, but is usually 150°C or less, and preferably 100°C or less.

[0058] The glass transition temperature (Tg(B)) of the crystalline polyester (B) is preferably 70°C to 200°C, more preferably 75°C to 190°C, and even more preferably 80°C to 180°C. If the glass transition temperature of the crystalline polyester (B) is within this range, the glass transition temperature of the film will be within a suitable range, and a film with excellent heat resistance and extrusion moldability can be obtained. The glass transition temperature can be measured by the method described in the examples.

[0059] <Other resins> This film may contain PBN resin (A) and other resins other than the at least one polyester, as long as the effects of the present invention are not impaired. Other resins include polystyrene resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polycarbonate resins, polyamide resins, polyacetal resins, acrylic resins, ethylene vinyl acetate copolymers, polymethylpentene resins, polyvinyl alcohol resins, cyclic olefin resins, polylactic acid resins, polybutylene succinate resins, polyacrylonitrile resins, polyethylene oxide resins, cellulose resins, polyimide resins, polyurethane resins, polyphenylene sulfide resins, polyphenylene ether resins, polyvinyl acetal resins, polybutadiene resins, polybutene resins, polyamide-imide resins, polyamide-bismaleimide resins, polyetherimide resins, polyetherether ketone resins, polyethersulfone resins, polyketone resins, polysulfone resins, aramid resins, and fluorine resins.

[0060] <particle> This film may contain particles primarily for the purpose of providing slipperiness and preventing scratches during each process. The type of particles to be added is not particularly limited as long as they can provide slipperiness. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide; and organic particles such as acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin. Furthermore, precipitated particles obtained by precipitating and finely dispersing a portion of metal compounds such as catalysts during the polymer manufacturing process, such as polyester, can also be used.

[0061] <Additives> Furthermore, this film may contain commonly used additives as appropriate. Examples of such additives include recycled resins generated from trimming losses such as edges, pigments such as titanium dioxide and carbon black, flame retardants, weather stabilizers, heat stabilizers, antistatic agents, melt viscosity modifiers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, antioxidants, light stabilizers, ultraviolet absorbers, neutralizing agents, anti-fogging agents, anti-blocking agents, slip agents, and colorants, which are added for the purpose of improving and adjusting moldability, productivity, and various physical properties of the porous film.

[0062] 3. Manufacturing method Next, the manufacturing method of this film will be explained.

[0063] The following description concerns a method for manufacturing the biaxially oriented film of the present invention. However, the following description is merely one example of a method for manufacturing the film, and the film is not limited to films manufactured by this method.

[0064] One example of an embodiment of the present invention is a method for manufacturing the film, in which a resin composition containing PBN resin (A) and at least one polyester is formed into a film and then biaxially stretched.

[0065] The method for obtaining a resin composition by kneading PBN resin (A), at least one type of polyester, other resins, and additives is not particularly limited, but in order to obtain the resin composition as simply as possible, it is preferable to manufacture it by melt kneading using an extruder. In order to uniformly mix the raw materials constituting the resin composition, it is preferable to melt knead using a coaxial twin-screw extruder. The mixing temperature is preferably above the glass transition temperature (Tg) of all polymers used, and for crystalline resins, it is preferably above the crystal melting temperature (Tm) of the polymer. While a higher mixing temperature relative to the glass transition temperature (Tg) or crystal melting temperature (Tm) of the polymers used makes it easier for some of the polymers to undergo transesterification and improves compatibility, excessively high mixing temperatures are undesirable because they cause decomposition of the resin. For this reason, the mixing temperature is preferably between 255°C and 340°C, more preferably between 260°C and 330°C, even more preferably between 270°C and 320°C, and particularly preferably between 280°C and 310°C. Within the range of the mixing temperature, compatibility and melt moldability can be improved without causing decomposition of the polymers.

[0066] The obtained resin composition can be molded into a biaxially oriented film by general molding methods, such as extrusion molding, injection molding, blow molding, vacuum molding, pressure molding, or press molding. The apparatus and processing conditions are not particularly limited in each molding method. This film is preferably manufactured by, for example, the following method.

[0067] A substantially amorphous and unoriented film (hereinafter also referred to as "unstretched film") is produced by extrusion from the resin composition obtained by mixing. This unstretched film can be produced, for example, by extruding the raw materials in an extruder, extruding them through a flat die or annular die, and then rapidly cooling to produce a flat or annular unstretched film. In this case, a laminated structure using multiple extruders may be used.

[0068] Next, the unstretched film described above is stretched in at least one direction, usually 1.1 to 5.0 times, and preferably 1.1 to 5.0 times each in the longitudinal direction (MD) and the width direction (TD) perpendicular thereto, from the viewpoint of stretching effect, film strength, etc.

[0069] As for the biaxial stretching method, any conventionally known stretching method can be used, such as tenter-type sequential biaxial stretching, tenter-type simultaneous biaxial stretching, and tubular-type simultaneous biaxial stretching. For example, in the tenter-type sequential biaxial stretching method, the unstretched film is heated to a temperature range of Tg to Tg+60°C, with the glass transition temperature of the resin composition being Tg, stretched in the longitudinal direction by 1.1 to 5.0 times, preferably 1.5 to 4.5 times, more preferably 2.0 to 4.0 times using a roll-type longitudinal stretcher, and then stretched in the transverse direction by 1.1 to 5.0 times, preferably 1.5 to 4.8 times, more preferably 2.0 to 4.6 times, using a tenter-type transverse stretcher within the temperature range of Tg to Tg+60°C. Within the stretching ratio range, the film can be stretched uniformly, orientation crystallization is induced, and the strength of the film can be brought to a range suitable for display applications. Furthermore, in the case of Tenter-type simultaneous biaxial stretching or tubular-type simultaneous biaxial stretching methods, for example, the material can be manufactured by stretching it by 1.1 to 5.0 times in each axial direction simultaneously in the longitudinal and transverse directions within a temperature range of Tg to Tg + 60°C.

[0070] The biaxially oriented film stretched by the above method is subsequently heat-set. Heat-setting provides dimensional stability at room temperature. In this case, the processing temperature is preferably selected from the range of the crystal melting temperature Tm-1 to Tm-80°C of the resin composition. If the heat-setting temperature is within the above range, sufficient heat-setting is performed, the stress during stretching is relieved, sufficient heat resistance and mechanical properties are obtained, and an excellent film is obtained that is free from problems such as breakage and whitening of the film surface.

[0071] In this invention, in order to alleviate the stress of crystallization shrinkage due to heat setting, it is preferable to perform relaxation in the width direction by 0 to 15%, preferably 3 to 10%, during heat setting. When sufficient relaxation is performed and the film is relaxed uniformly in the width direction, the shrinkage rate in the width direction becomes uniform, and a film with excellent dimensional stability at room temperature is obtained. Furthermore, since the relaxation follows the shrinkage of the film, there is no sagging of the film, flapping in the tenter, and no film breakage.

[0072] 4.Applications The biaxially oriented film of the present invention has excellent low dielectric properties. Therefore, it can be suitably used for high-speed communication circuits. Examples of high-speed communication circuit applications include FPCs (Flexible Printed Circuits), which are flexible circuit boards formed from resin film and copper foil, and transparent antennas, which have invisible ultra-fine metal mesh wiring formed on a transparent film. In particular, when this film has high transparency, it can be suitably used as a base film for transparent antennas where high transparency is required.

[0073] Furthermore, since the transparent antenna described above does not impair the aesthetic design, it can be attached not only to mobile devices but also to windows and other glass surfaces of buildings and vehicles to receive 5G radio waves. If the film also has sufficient weather resistance, it can be preferably used for outdoor applications as well.

[0074] <<Film with a cured resin layer>> The biaxially oriented film of the present invention may optionally have a cured resin layer on at least one surface layer of the biaxially oriented film for the purpose of improving adhesion to a metal layer, and it is preferable that the cured resin layer is formed from a resin composition containing 70% by mass or more of a crosslinking agent relative to the non-volatile components. In particular, it is more preferable to provide cured resin layers on both surface layers of the biaxially oriented film. Here, a biaxially oriented film having a cured resin layer is referred to as a film with a cured resin layer and is distinguished from a biaxially oriented film. Note that other layers may be provided between the biaxially stretched film and the cured resin layer.

[0075] 1. Physical properties First, the physical properties of the film with the cured resin layer of the present invention will be described.

[0076] (1) Amount of oligomer (ester cyclic trimer) precipitation The cured resin layer according to the present invention is effective not only in improving the adhesion to the metal layer but also in preventing the precipitation of oligomers on the film surface by heating. By reducing the precipitation of oligomers, it is possible to suppress the decrease in visibility due to the whitening of the film appearance caused by the precipitation and whitening of oligomers. In the film with the cured resin layer of the present invention, in the aspect where the cured resin layers are provided on both surface layers of the biaxially stretched film, the amount of oligomer (ester cyclic trimer) precipitation on the surface of at least one of the cured resin layers is preferably 0.50 mg / m 2 or less, more preferably 0.40 mg / m 2 or less, still more preferably 0.30 mg / m 2 or less, particularly preferably 0.20 mg / m 2 or less. If the amount of oligomer precipitation is 0.50 mg / m 2 or less, it is preferable because there is no decrease in visibility due to the whitening of the film appearance caused by the precipitation and crystallization of oligomers on the surface, no occurrence of defects in post-processing, and no contamination in the process or of components. The lower limit is not particularly limited, but it is 0.01 mg / m 2 or more. Note that the amount of oligomer precipitation is a value obtained by the method described in the examples.

[0077] (2) Thickness The thickness (after drying) of the cured resin layer is preferably 0.003 to 1.0 μm, more preferably 0.005 to 0.5 μm, and still more preferably 0.01 to 0.2 μm. If the thickness is 1.0 μm or less, the appearance and blocking resistance of the cured resin layer are sufficient. On the other hand, if the thickness is 0.003 μm or more, the amount of oligomer precipitation from the film is small, which is favorable.

[0078] 2. Ingredients Next, we will explain the components that make up the cured resin layer.

[0079] As described above, the cured resin layer is preferably formed from a resin composition containing a crosslinking agent in an amount of 70% by mass or more relative to the non-volatile components.

[0080] <Crosslinking agent> Various known crosslinking agents can be used as the aforementioned crosslinking agent, including, for example, oxazoline compounds, melamine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, silane coupling compounds, and the like. Among these, when a metal layer is provided on a cured resin layer, oxazoline compounds are preferably used from the viewpoint of improving durability and adhesion. Furthermore, melamine compounds are preferably used from the viewpoint of preventing oligomer precipitation on the film surface due to heating and improving the durability of the cured resin layer.

[0081] (Oxazoline compounds) Oxazoline compounds are compounds having an oxazoline group in their molecule, and polymers containing an oxazoline group are particularly preferred. These can be produced by polymerization of an addition-polymerizable oxazoline group-containing monomer alone or with other monomers. Examples of addition-polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline. One or more of these can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is readily available industrially. Other monomers are not limited as long as they are copolymerizable with addition-polymerizable oxazoline group-containing monomers, for example (meth)acrylic acid esters such as alkyl (meth)acrylates (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid and their salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-alkyl( Examples of unsaturated amides such as meth)acrylamide and N,N-dialkyl(meth)acrylamide (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α,β-unsaturated monomers such as vinyl chloride and vinylidene chloride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene. One or more of these monomers can be used. From the viewpoint of improving the durability of the cured resin layer, the amount of oxazoline groups in the oxazoline compound is preferably in the range of 0.5 to 10 mmol / g, more preferably 3 to 9 mmol / g, and even more preferably 5 to 8 mmol / g.

[0082] (Melamine compound) Melamine compounds are compounds that have a melamine skeleton in the compound. For example, alkylolated melamine derivatives, compounds that have been partially or completely etherified by reacting alkylolated melamine derivatives with alcohol, and mixtures thereof can be used. Suitable alcohols for etherification include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, and isobutanol. Furthermore, the melamine compound may be a monomer, a polymer of two or more commensals, or a mixture thereof. In addition, a compound in which urea or the like is co-condensed with a portion of the melamine can be used, and a catalyst can be used to increase the reactivity of the melamine compound.

[0083] (Epoxy compound) Epoxy compounds are compounds that have an epoxy group in their molecule. Examples include condensates of epichlorohydrin, ethylene glycol, polyethylene glycol, glycerin, polyglycerin, and bisphenol A with hydroxyl or amino groups, as well as polyepoxy compounds, diepoxy compounds, monoepoxy compounds, and glycidylamine compounds. Examples of polyepoxy compounds include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris(2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether. Examples of diepoxy compounds include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polytetramethylene glycol diglycidyl ether. Examples of monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether, while examples of glycidylamine compounds include N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylamino)cyclohexane.

[0084] (Isocyanate compounds) Isocyanate compounds are compounds having an isocyanate derivative structure, such as isocyanates or blocked isocyanates. Examples of isocyanates include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylenediphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; aliphatic isocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic isocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic isocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylenebis(4-cyclohexyl isocyanate), and isopropylidene dicyclohexyl diisocyanate. Furthermore, polymers and derivatives of these isocyanates, such as biuretized, isocyanurateized, uretdioneized, and carbodiimide-modified products, are also mentioned. These may be used individually or in combination of multiple types. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferred than aromatic isocyanates in order to avoid yellowing due to ultraviolet light.

[0085] When used in the form of blocked isocyanates, examples of blocking agents include phenolic compounds such as bisulfites, phenol, cresol, and ethylphenol; alcoholic compounds such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, and ethanol; active methylene compounds such as methyl isobutanoylacetate, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone; mercaptan compounds such as butyl mercaptan and dodecyl mercaptan; lactam compounds such as ε-caprolactam and δ-valerolactam; amine compounds such as diphenylaniline, aniline, and ethyleneimine; acid amide compounds such as acetanilide and acetic acid amide; and oxime compounds such as formaldehyde, acetaldehyde oxime, acetone oxime, methyl ethyl ketone oxime, and cyclohexanone oxime. These may be used individually or in combination of two or more.

[0086] Furthermore, isocyanate compounds may be used alone or as mixtures or binders with various polymers. It is preferable to use mixtures or binders with polyester resins or urethane resins to improve the dispersibility and crosslinking properties of the isocyanate compounds.

[0087] (Carbodiimide compounds) A carbodiimide compound is a compound having a carbodiimide structure, specifically a compound having one or more carbodiimide structures within its molecule. However, polycarbodiimide compounds having two or more carbodiimide structures within their molecule are more preferable for better adhesion and other properties.

[0088] Carbodiimide compounds can be synthesized using conventionally known techniques, and generally, condensation reactions of diisocyanate compounds are employed. The diisocyanate compounds are not particularly limited and can be either aromatic or aliphatic. Specifically, examples include tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, and dicyclohexylmethane diisocyanate.

[0089] The amount of carbodiimide groups contained in a carbodiimide compound is typically in the range of 100 to 1000, preferably 250 to 700, and more preferably 300 to 500, in terms of carbodiimide equivalents (weight [g] of the carbodiimide compound required to give 1 mol of carbodiimide groups). Using the compound within this range improves the durability of the cured resin layer.

[0090] Furthermore, to the extent that it does not impair the spirit of the present invention, surfactants may be added, or hydrophilic monomers such as polyalkylene oxides, quaternary ammonium salts of dialkylamino alcohols, and hydroxyalkyl sulfonates may be added to improve the water solubility and water dispersibility of the polycarbodiimide compound.

[0091] (Silane coupling compounds) Silane coupling compounds are organosilicon compounds that contain both an organic functional group and a hydrolysis group such as an alkoxy group within a single molecule. For example, epoxy group-containing compounds such as 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; vinyl group-containing compounds such as vinyltrimethoxysilane and vinyltriethoxysilane; styryl group-containing compounds such as p-styryltrimethoxysilane and p-styryltriethoxysilane; (meth)acrylic group-containing compounds such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)- Examples include amino group-containing compounds such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane; isocyanurate group-containing compounds such as tris(trimethoxysilylpropyl)isocyanurate and tris(triethoxysilylpropyl)isocyanurate; and mercapto group-containing compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane.

[0092] These crosslinking agents may be used individually or in combination of two or more, but using two or more in combination can improve adhesion to the metal layer provided on the cured resin layer and prevent oligomer precipitation after heating. Among these, a combination of an oxazoline compound, which can improve adhesion to the metal layer on the cured resin layer, and a melamine compound, which has good properties for preventing oligomer precipitation after heating, is particularly preferred.

[0093] Furthermore, in order to further improve the adhesion between the cured resin layer and the metal layer, it is preferable to combine three or more crosslinking agents. As for the combination of three or more crosslinking agents, it is preferable to select a melamine compound as one of the crosslinking agents, and as the other crosslinking agents to be combined with the melamine compound, it is even more preferable to combine an oxazoline compound and an epoxy compound, or a carbodiimide compound and an epoxy compound.

[0094] When such a crosslinking agent is included, components that promote crosslinking, such as a crosslinking catalyst, can be used in combination.

[0095] The crosslinking agent is preferably present in an amount of 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total nonvolatile components in the resin composition forming the cured resin layer according to the present invention. If the amount is 70% by mass or more, good adhesion to the metal layer provided on the cured resin layer and good prevention of oligomer precipitation after heating are achieved.

[0096] <Binder resin> The resin composition may also contain a binder resin, to the extent that it does not impair the spirit of the present invention, in order to improve the appearance of the cured resin layer or to improve adhesion with the metal layer provided on the cured resin layer. While conventionally known binder resins can be used, it is preferable to use polyester resin, acrylic resin, or urethane resin from the viewpoint of improving adhesion with the layer provided on the cured resin layer.

[0097] <Particle> Furthermore, the resin composition may also contain particles for the purpose of blocking and improving slipperiness. From the viewpoint of film transparency, the average particle size is preferably 1.0 μm or less, more preferably 0.5 μm or less, and even more preferably 0.2 μm or less. On the other hand, in order to more effectively improve slipperiness, it is preferably 0.01 μm or more, more preferably 0.03 μm or more, and particularly preferably in a range greater than the film thickness of the cured resin layer. Specific examples of particles include silica, alumina, kaolin, calcium carbonate, and organic particles.

[0098] <Other> Furthermore, to the extent that the spirit of the present invention is not impaired, the resin composition may optionally contain crosslinking catalysts, defoaming agents, coating properties improvers, thickeners, organic lubricants, antistatic agents, ultraviolet absorbers, antioxidants, foaming agents, dyes, pigments, and the like.

[0099] Furthermore, the analysis of various compounds (components) in the cured resin layer can be performed, for example, by TOF-SIMS, ESCA, or X-ray fluorescence.

[0100] 3. Manufacturing method Next, we will explain the method for forming the cured resin layer.

[0101] The following description will explain a method for forming a cured resin layer. However, this description is merely one example of a method for forming a cured resin layer and is not limited to this method.

[0102] The resin composition is generally preferably diluted with water, an organic solvent, or a mixture thereof. The cured resin layer is formed by coating the surface of the film with the diluted resin composition as a coating solution and then drying it. Conventional coating methods can be used to apply the coating solution to the film, such as air doctor coating, blade coating, rod coating, bar coating, knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss roll coating, cast coating, spray coating, curtain coating, calender coating, and extrusion coating. Furthermore, in order to improve the applicability and adhesion of the coating agent (coating liquid) to the film, the film may be subjected to chemical treatment, corona discharge treatment, plasma treatment, etc., before coating.

[0103] The film surface can be coated as needed, and the coating is used to form the cured resin layer. There are in-line coating and off-line coating methods for forming the cured resin layer, but in-line coating is preferred. In-line coating is a method of coating within the film manufacturing process, and specifically, it is a method of coating at any stage from melting and extruding the polyester raw material to stretching, heat fixing, and winding. Usually, the coating is applied to an unstretched sheet obtained by melting and rapidly cooling, a stretched uniaxially oriented film, a biaxially oriented film before heat fixing, or a biaxially oriented film after heat fixing and before winding, but it is particularly preferred to coat a uniaxially oriented film stretched in the longitudinal direction (vertical direction) and then stretch it in the width direction (horizontal direction). When providing a cured resin layer by in-line coating, it is preferable to use a coating solution prepared by adjusting the solid content concentration to approximately 0.1 to 50% by mass using the above-mentioned series of compounds as an aqueous solution or aqueous dispersion. Furthermore, within the limits that do not impair the spirit of the present invention, the coating solution may contain a small amount of one or more organic solvents for the purpose of improving dispersibility in water, improving film-forming properties, etc.

[0104] The drying and curing conditions when forming a cured resin layer on a film are not particularly limited. For example, when providing a cured resin layer by offline coating, it is preferable to perform heat treatment at 80-200°C for 3-40 seconds, and more preferably at 100-180°C for 3-40 seconds. On the other hand, when a cured resin layer is provided by in-line coating, it is preferable to perform heat treatment at 70 to 280°C for approximately 3 to 200 seconds.

[0105] Furthermore, regardless of whether it is offline coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as needed.

[0106] 4.Applications As described above, the film with a cured resin layer of the present invention can reduce oligomer precipitation, thereby suppressing the reduction in visibility due to whitening of the film's appearance. Therefore, the film with a cured resin layer of the present invention maintains transparency and has excellent low dielectric properties. Therefore, it can be suitably used for high-speed communication circuits. Examples of high-speed communication circuit applications include FPCs (Flexible Printed Circuits), which are flexible circuit boards formed from resin film and copper foil, and transparent antennas, which have invisible, ultra-fine metal mesh wiring formed on a transparent film. In particular, it can be suitably used as a base film for transparent antennas where high transparency is required.

[0107] <<Laminated metal film>> In the metal laminated film of the present invention, a metal layer may be provided on the cured resin layer. Furthermore, other layers may be provided between the cured resin layer and the metal layer.

[0108] 1. Physical properties First, the physical properties of the metal laminated film of the present invention will be described.

[0109] (1) Thickness The thickness of the metal layer is preferably 2 to 30 μm, and more preferably 3 to 25 μm. If the thickness of the metal layer is above the lower limit, sufficient conductivity is ensured, and if it is below the upper limit, the reduction in visibility when the metal layer is provided can be suppressed. The thickness of the metal layer can be measured by observing the cross-section of the sample with an electron microscope.

[0110] 2. Ingredients Next, we will explain the components that make up the metal layer.

[0111] The metal layer is a layer that contains metal as its main component. Here, "main component" means that metal accounts for 50% or more by mass, more preferably 70% or more by mass, even more preferably 80% or more by mass, and particularly preferably 90% or more by mass of the metal layer. Regarding the metals to be used, examples include copper, copper alloys, silver, stainless steel, nickel, nickel alloys, aluminum, aluminum alloys, titanium, and titanium alloys. However, from the viewpoint of electromagnetic wave shielding properties, copper and silver are preferred, and from the viewpoint of flexibility, copper is more preferred.

[0112] From the viewpoint of maintaining the transparency of the biaxially oriented film and the film with the cured resin layer, it is preferable that the metal layer be patterned, for example, in a mesh shape or a wire shape.

[0113] 3.Applications As described above, the metal laminated film of the present invention has excellent low dielectric properties without impairing transparency. Therefore, it can be suitably used for high-speed communication circuits. Examples of high-speed communication circuit applications include FPCs (Flexible Printed Circuits), which are flexible circuit boards formed from resin film and copper foil, and transparent antennas, which have invisible, ultra-fine metal mesh wiring formed on a transparent film. In particular, it can be suitably used as a base film for transparent antennas where high transparency is required.

[0114] <<Explanation of terms and phrases>> In this invention, the term "film" includes "sheets," and the term "sheet" includes "film." In this invention, when "X~Y" (where X and Y are any numbers) is written, unless otherwise specified, it includes the meaning of "X or greater and Y or less," as well as "preferably greater than X" or "preferably less than Y." Furthermore, when "X or greater" (where X is any number) is written, unless otherwise specified, it includes the meaning of "preferably greater than X," and when "Y or less" (where Y is any number) is written, unless otherwise specified, it also includes the meaning of "preferably less than Y." [Examples]

[0115] Examples are shown below, but these do not limit the present invention in any way.

[0116] 1. Evaluation Method (1) Dielectric loss tangent and dielectric constant For the films obtained in the examples or comparative examples, the dielectric loss tangent and dielectric constant were measured at frequencies of 10 GHz, 28 GHz, and 40 GHz in accordance with JIS R1641 using a dielectric constant measurement system manufactured by AET Co., Ltd. (cavity resonator (TE mode), control software, and vector network analyzer MS46122B (manufactured by Anritsu Corporation)).

[0117] (2) Tensile breaking strength The tensile breaking strength of the films obtained in the examples or comparative examples was measured using a tensile testing machine (Shimadzu Corporation AG-1kNXplus) in accordance with JIS K 7127:1999. The test specimens were made by cutting the film into rectangles with a length of 100 mm and a width of 10 mm in the measurement direction. Both ends of the test specimen in the longitudinal direction were chucked with a chuck distance of 40 mm, and the specimen was pulled at a tensile speed of 200 mm / min. The stress at the breaking point was measured three times as the tensile breaking strength, and the average value of each measurement was calculated. The tensile tests described above were performed in both the longitudinal (MD) and widthwise (TD) directions of the film.

[0118] (3) Storage modulus measured by viscoelasticity The dynamic viscoelasticity of the films obtained in the examples or comparative examples was measured using a dynamic viscoelasticity measuring device (model name: "DMS6100", manufactured by SII Nanotechnology Co., Ltd.) in accordance with the method specified in JIS K7244-1:1998. The test involved raising the temperature from -70°C to 300°C at a rate of 3°C / min, and determining the storage modulus at 23°C when the film was deformed in tensile deformation at a frequency of 10 Hz and a strain of 0.07%.

[0119] (4) Tensile breaking strength and strength retention rate after wet heat test The films obtained in the examples or comparative examples were cut into rectangles with a length of 100 mm and a width of 10 mm in the measurement direction, and a moist heat test was performed in accordance with JIS C60068-2-66:2001. The moist heat test was performed using an ESPEC Corporation accelerated life tester (EHS-221M), where the specimens were left to stand for 96 hours in an environment of 120°C and 85% RH, and then left to stand for another 18 hours at room temperature (23°C). The tensile breaking strength of the specimens after the moist heat test was measured using a tensile testing machine (Shimadzu Corporation AG-1kNXplus) in accordance with JIS K 7127:1999. Both ends of the specimen in the longitudinal direction were chucked with a chuck distance of 40 mm, and the specimen was pulled at a tensile speed of 200 mm / min. The stress at the breaking point was measured three times as the tensile breaking strength, and the average value was calculated. The strength retention rate was calculated according to the following formula. The tensile tests described above were performed in both the longitudinal (MD) and widthwise (TD) directions of the film. Strength retention rate = ([Tensile breaking strength after moist heat test] / [Tensile breaking strength measured in (2)]) × 100

[0120] (5) Glass transition temperature For the films obtained in the examples or comparative examples, the temperature was raised to the melting temperature once at a heating rate of 10°C / min and then cooled down at a cooling rate of 10°C / min using a DSC8000 (manufactured by PerkinElmer Japan) in accordance with JIS K7121 (2012). Subsequently, the glass transition temperature during the heating process at a heating rate of 10°C / min was measured.

[0121] (6) Crystal melting temperature For the films obtained in the examples or comparative examples, the temperature was raised to the melting temperature once at a heating rate of 10°C / min in accordance with JIS K7121 (2012) using a DSC8000 (manufactured by PerkinElmer Japan), and then cooled at a cooling rate of 10°C / min. Subsequently, the crystal melting temperature during the heating process at a heating rate of 10°C / min was measured.

[0122] (7) Formability In the extrusion molding process, when obtaining a pre-stretched sheet by cooling and solidifying with a cast roll, a "○" was given if a transparent film was obtained without crystallization and whitening, and a "×" was given if a film that had crystallized and whitened was obtained.

[0123] (8) Thermal shrinkage The film was cut into rectangles with a length of 120 mm and a width of 10 mm in the measurement direction, and marked 100 mm from the edge. These test pieces were suspended by clipping the edges and heated at 150°C for 30 minutes. After cooling, the length from the edge of the test piece to the mark was measured to determine the thermal shrinkage rate. Measurements were taken in both the longitudinal (MD) and transverse (TD) directions.

[0124] (9) Hayes Using a haze meter NDH-7000II (manufactured by Nippon Denshoku Industries Co., Ltd.), the total light transmittance and diffuse transmittance were measured in accordance with JIS K7136 (2000), and the haze was calculated using the following formula. [Haze] = ([Diffuse transmittance] / [Total light transmittance]) × 100

[0125] (10) Film thickness The thickness of this film was determined by measuring it at five unspecified points within the surface using a 1 / 1000 mm dial gauge, and the average of these measurements was taken as the thickness.

[0126] (11) Thickness of the cured resin layer The surface of the cured resin layer was stained with RuO4 and embedded in epoxy resin. Subsequently, sections prepared by the ultrathin sectioning method were stained with RuO4, and the cross-section of the cured resin layer was measured using a transmission electron microscope (TEM) (Hitachi High-Technologies Corporation, H-7650, accelerating voltage 100kV).

[0127] (12) Amount of oligomer (ester cyclic trimer) precipitated on the surface of the cured resin layer due to heating The cured resin-coated film obtained in the example was heat-treated for 120 minutes in a hot-air oven maintained at a predetermined temperature (180°C) as a sample measuring 300 mm in length and 225 mm in width. After heat treatment, a box-shaped object with an open top measuring 200 mm in length and 125 mm in width was fabricated with the measurement surface as the inner surface. Next, 10 mL of DMF (dimethylformamide) was placed in the box-shaped container described above and left for 3 minutes. After the DMF was recovered, it was supplied to a liquid chromatograph (Shimadzu Corporation: LC-7A, mobile phase A: acetonitrile, mobile phase B: 2% aqueous acetic acid solution, column: Mitsubishi Chemical Corporation "MCI GEL ODS 1HU", column temperature: 40°C, flow rate: 1 mL / min, detection wavelength: 254 nm) to determine the amount of ester cyclic trimers in the DMF. This value was then divided by the film area in contact with the DMF to determine the amount of oligomers (ester cyclic trimers) on the surface of the cured resin layer (mg / m²). 2 The ester cyclic trimers in DMF were determined from the peak area ratio of the standard sample peak area to the measured sample peak area (absolute calibration curve method). The standard sample was prepared by accurately weighing a pre-parate ester cyclic trimer and dissolving it in accurately weighed DMF.

[0128] 2.Material The polyester raw materials and polyester films used in the examples and comparative examples are as follows:

[0129] [PBN resin (A)] As PBN resin (A), homo-PBN was used, with dicarboxylic acid component (a-1): 2,6-naphthalenedicarboxylic acid = 100 mol% and diol component (a-2): 1,4-butanediol = 100 mol%. The glass transition temperature (Tg(A)) of this PBN resin was 77°C.

[0130] [PEN resin] At least one type of polyester used was a crystalline polyester (B), homo-PEN with a dicarboxylic acid component of 2,6-naphthalenedicarboxylic acid = 100 mol% and a diol component of ethylene glycol = 100 mol%. The glass transition temperature (Tg) of this PEN resin was 121°C. Hereafter, the PEN resin will be referred to as (B).

[0131] [Polyethylene terephthalate film] A biaxially oriented PET film with a thickness of 50 μm (Mitsubishi Chemical Corporation's "Diafoil T100-50") was used as the PET film.

[0132] Furthermore, the following resin composition was used to form the cured resin layer.

[0133] [Resin composition] (A1): Hexamethoxymethylolmelamine (A2): Epocross (manufactured by Nippon Shokubai Co., Ltd.), an oxazoline compound. Oxazoline base content: 7.7 mmol / g (A3): Polyglycerol polyglycidyl ether (B1): Silica particles with an average particle size of 0.07 μm

[0134] The composition of the coating solution used in the examples is shown in Table 1. More specifically, the resin composition obtained by stirring and mixing the components shown in Table 1 below was diluted with water to prepare the coating solution.

[0135] [Table 1]

[0136] (Example 1) Pellet-shaped (A) was mixed with pellet-shaped (B) at a ratio of 90% by mass to 10% by mass of pellet-shaped (A) (900 parts by mass of (B) for every 100 parts by mass of (A)). After dry blending, the mixture was melt-kneaded in a Φ40 mm twin-screw extruder set to 285°C, extruded as a film through a T-die with a gap of 1.0 mm, taken up by a cast roll at 105°C, cooled and solidified to obtain a film-like material (cast film) with a thickness of approximately 450 μm. Next, the obtained cast film was passed through a longitudinal stretcher and heated with an infrared heater (heater vicinity temperature: 170°C) to stretch it 2.8 times in the longitudinal direction (MD). Subsequently, the obtained longitudinally stretched film was passed through a transverse stretcher (tenter) and stretched 4.0 times in the width direction (TD) at a preheating temperature of 130°C, a stretching temperature of 135°C, and a heat-setting temperature of 190°C. After that, the film was heat-set in the tenter and relaxed by 5% in the width direction (TD). Table 2 shows the results of measurements performed on the obtained films.

[0137] (Example 2) A cast film was obtained in the same manner as in Example 1, except that 20% by mass of pelletized (A) was mixed with 80% by mass of pelletized (B) (400 parts by mass of (B) for every 100 parts by mass of (A)), and after dry blending, the cast roll temperature was set to 100°C. Next, the obtained cast film was passed through a longitudinal stretcher and heated with an infrared heater (heater vicinity temperature: 160°C) to stretch it 2.8 times in the longitudinal direction (MD). Subsequently, the obtained longitudinally stretched film was passed through a transverse stretcher (tenter) and stretched 3.9 times in the width direction (TD) at a preheating temperature of 120°C, a stretching temperature of 125°C, and a heat setting temperature of 190°C. After that, the film was relaxed by 5% inside the tenter. Table 2 shows the results of measurements performed on the obtained films.

[0138] (Example 3) A cast film was obtained in the same manner as in Example 1, except that 70% by mass of pelletized (B) was added to 30% by mass of pelletized (A) (233 parts by mass of (B) for every 100 parts by mass of (A)), and after dry blending, the cast roll temperature was set to 95°C. Next, the obtained cast film was passed through a longitudinal stretcher and heated with an infrared heater (heater vicinity temperature: 155°C) to stretch it 2.8 times in the longitudinal direction (MD). Subsequently, the obtained longitudinally stretched film was passed through a transverse stretcher (tenter) and stretched 3.9 times in the width direction (TD) at a preheating temperature of 115°C, a stretching temperature of 120°C, and a heat setting temperature of 190°C. After that, the film was relaxed by 5% inside the tenter. Table 2 shows the results of measurements performed on the obtained films.

[0139] (Example 4) A cast film was obtained in the same manner as in Example 1, except that 60% by mass of pelletized (B) was added to 40% by mass of pelletized (A) (150 parts by mass of (B) for every 100 parts by mass of (A)), and after dry blending, the cast roll temperature was set to 90°C. Next, the obtained cast film was passed through a longitudinal stretcher and heated with an infrared heater (heater vicinity temperature: 145°C) to stretch it 2.8 times in the longitudinal direction (MD). Subsequently, the obtained longitudinally stretched film was passed through a transverse stretcher (tenter) and stretched 3.8 times in the width direction (TD) at a preheating temperature of 105°C, a stretching temperature of 110°C, and a heat setting temperature of 190°C. After that, the film was relaxed by 5% inside the tenter. Table 2 shows the results of measurements performed on the obtained films.

[0140] (Example 5) A cast film was obtained in the same manner as in Example 1, except that 50% by mass of pelletized material (B) was added to 50% by mass of pelletized material (A) (100 parts by mass of (A) and 100 parts by mass of (B)), and after dry blending, the cast roll temperature was set to 81°C. Next, the obtained cast film was passed through a longitudinal stretcher and heated with an infrared heater (heater vicinity temperature: 135°C) to stretch it 2.8 times in the longitudinal direction (MD). Subsequently, the obtained longitudinally stretched film was passed through a transverse stretcher (tenter) and stretched 4.0 times in the width direction (TD) at a preheating temperature of 95°C, a stretching temperature of 100°C, and a heat setting temperature of 190°C. After that, the film was relaxed by 5% inside the tenter. Table 2 shows the results of measurements performed on the obtained films.

[0141] (Example 6) A cast film was obtained in the same manner as in Example 1, except that 40% by mass of pelletized (B) was added to 60% by mass of pelletized (A) (67 parts by mass of (B) for every 100 parts by mass of (A)), and after dry blending, the cast roll temperature was set to 70°C. Next, the obtained cast film was passed through a longitudinal stretcher and heated with an infrared heater (heater vicinity temperature: 133°C) to stretch it 2.8 times in the longitudinal direction (MD). Subsequently, the obtained longitudinally stretched film was passed through a transverse stretcher (tenter) and stretched 3.7 times in the width direction (TD) at a preheating temperature of 95°C, a stretching temperature of 100°C, and a heat setting temperature of 190°C. After that, the film was relaxed by 5% inside the tenter. Table 2 shows the results of measurements performed on the obtained films.

[0142] (Example 7) In Example 6, after stretching in the longitudinal direction (MD) and before stretching in the width direction (TD), the coating solution was applied to both sides of the uniaxially oriented film to obtain a biaxially oriented film (film with a cured resin layer) having a cured resin layer with a thickness (after drying) of 0.04 μm. In Example 7, the material was stretched 3.0 times in the longitudinal direction (MD) at 100°C. Furthermore, after preheating in a tenter at 100°C, it was stretched 4.5 times in the width direction (TD) at 110°C. Finally, it was heat-treated at 200°C to produce a biaxially oriented film with a thickness of 125 μm. Table 2 shows the results of measurements performed on the obtained film with a cured resin layer. Furthermore, the evaluation results of the amount of oligomer precipitation on the surface of the cured resin layer upon heating of the obtained cured resin layer-coated film are shown in Table 3 below.

[0143] (Comparative Example 1) When attempting to produce a cast film using the same method as in Example 1, except that 100% by mass of pelletized (A) was used and the temperature of the cast roll was set to 75°C, whitening, likely due to crystallization, occurred, resulting in poor adhesion to the cast roll, a poor appearance, and a film with uneven thickness. As a result, it was not possible to obtain a stretchable amorphous film. Therefore, the moldability in Table 2 was marked with an "X".

[0144] (Comparative Example 2) A cast film was obtained in the same manner as in Example 1, except that 100% by mass of pelletized (B) was used and the temperature of the cast roll was set to 110°C. Next, the obtained cast film was passed through a longitudinal stretcher and heated with an infrared heater (heater vicinity temperature: 175°C) to stretch it 2.6 times in the longitudinal direction (MD). Subsequently, the obtained longitudinally stretched film was passed through a transverse stretcher (tenter) and stretched 3.8 times in the width direction (TD) at a preheating temperature of 125°C, a stretching temperature of 130°C, and a heat setting temperature of 190°C. After that, the film was relaxed by 5% inside the tenter. Table 2 shows the results of measurements performed on the obtained films.

[0145] (Comparative Example 3) Table 2 shows the results of the evaluation of biaxially oriented PET film.

[0146] [Table 2]

[0147] [Table 3]

[0148] Note that in Table 3, 0.17 / 0.17 indicates that the amount of oligomer precipitated on one side is 0.17 mg / m². 2The amount of oligomer precipitated on the other side was 0.17 mg / m². 2 It means that.

[0149] Furthermore, Table 4 below shows the dielectric loss tangent and dielectric constant at 10 GHz and 40 GHz for the films of Examples 1 to 7 and Comparative Examples 2 and 3.

[0150] [Table 4]

[0151] As is clear from Examples 1 to 6 above, the biaxially oriented film of the present invention has low dielectric properties in the high-frequency band, resulting in low transmission loss and making it applicable to high-speed, high-capacity 5G data communication. Furthermore, it has sufficient mechanical properties due to its high tensile breaking strength. In addition, its high storage modulus gives the film high rigidity and good handling properties. Moreover, its good tensile breaking strength and strength retention rate after wet heat testing indicate excellent hydrolysis resistance and sufficient weather resistance. In addition, it has a low thermal shrinkage rate, excellent heat resistance, low haze, and excellent transparency. In addition to these characteristics, the fact that it is a highly versatile polyester film makes it cost-effective and easy to manufacture.

[0152] In the film with a cured resin layer of the present invention, the results of Example 7 show that by having a cured resin layer on at least one surface layer of the biaxially oriented film, the amount of oligomer precipitation on the surface of the cured resin layer can be reduced. Therefore, the cured resin layered film of the present invention has good visibility and can be suitably used as a base film for transparent antennas where particularly high transparency is required. [Industrial applicability]

[0153] The biaxially oriented film, the film with a cured resin layer, and the metal laminated film of the present invention have excellent low dielectric properties and can therefore be suitably used for high-speed communication circuits, particularly for flexible printed circuits (FPCs) formed from a resin film and copper foil, and for transparent antennas in which ultra-fine metal mesh wiring that is not visible is formed on a transparent film. In particular, the biaxially oriented film, the film with a cured resin layer, and the metal laminated film of the present invention can be preferably used as the base film for the transparent antenna when they have high transparency. In particular, if the biaxially oriented film, the film with a cured resin layer, and the metal laminated film of the present invention have an excellent balance of low dielectric properties, mechanical properties, and weather resistance, they can be suitably used outdoors among the above applications.

Claims

1. Contains two or more types of polyester, At least one of them is polybutylene naphthalate resin (A), A biaxially oriented film having a dielectric loss tangent of 0.0040 or less at 28 GHz.

2. The biaxially oriented film according to claim 1, wherein the dielectric constant at 28 GHz is 3.15 or more and 3.25 or less.

3. The biaxially oriented film according to claim 1 or 2, wherein the tensile breaking strength in both the longitudinal direction (MD) and the width direction (TD) is 150 MPa or more.

4. A biaxially oriented film according to any one of claims 1 to 3, wherein the storage modulus measured by dynamic viscoelasticity at 23°C is 3.5 GPa or more in both the longitudinal direction (MD) and the width direction (TD).

5. A biaxially oriented film according to any one of claims 1 to 4, wherein the tensile breaking strength in both the longitudinal direction (MD) and the width direction (TD) is 100 MPa or more after being left to stand for 96 hours in an environment of 120°C and 85% RH, and then left to stand for another 18 hours at room temperature (23°C).

6. A biaxially oriented film according to any one of claims 1 to 5, wherein the strength retention rate in both the longitudinal direction (MD) and the width direction (TD) is 50% or more after being left to stand for 96 hours in an environment of 120°C and 85% RH, and then left to stand for a further 18 hours at room temperature (23°C).

7. A biaxially oriented film according to any one of claims 1 to 6, containing 35% by mass or more and 70% by mass or less of the polybutylene naphthalate resin (A).

8. A biaxially oriented film according to any one of claims 1 to 7, comprising a crystalline polyester (B).

9. The biaxially oriented film according to claim 8, wherein the crystalline polyester (B) has a higher glass transition temperature than the polybutylene naphthalate resin (A).

10. The biaxially oriented film according to claim 8 or 9, wherein the crystalline polyester (B) is polyethylene naphthalate resin.

11. The polyethylene naphthalate resin is a biaxially oriented film according to claim 10, wherein the acid component having a benzene skeleton as a copolymer component other than 2,6-naphthalenedicarboxylic acid is 5 mol% or less of the total dicarboxylic acid component.

12. A biaxially oriented film according to any one of claims 1 to 11, wherein the film thickness is 40 to 150 μm.

13. A film with a cured resin layer, having a cured resin layer on at least one surface layer of a biaxially oriented film according to any one of claims 1 to 12, wherein the cured resin layer is formed from a resin composition containing 70% by mass or more of a crosslinking agent relative to a non-volatile component.

14. A metal laminated film comprising a metal layer on the cured resin layer of a film with a cured resin layer according to claim 13.

15. The metal laminated film according to claim 14, wherein the metal layer is patterned.

16. The metal laminated film according to claim 14 or 15, wherein the metal layer is made of copper or silver.

17. A biaxially oriented film according to any one of claims 1 to 12, for use in high-speed communication circuits.

18. A biaxially oriented film according to claim 17, used as a base film for a transparent antenna.

19. A film with a cured resin layer according to claim 13, for use in high-speed communication circuits.

20. A film with a cured resin layer according to claim 19, used as a base film for a transparent antenna.

21. A metal laminated film according to any one of claims 14 to 16, for use in high-speed communication circuits.

22. A metal laminated film according to claim 21, used as a base film for a transparent antenna.

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