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

Abstract

To provide a biaxially oriented film having sufficiently low dielectric properties.SOLUTION: A biaxially oriented film contains two or more polyesters, at least one of which is a polybutylene naphthalate resin (A), with the dielectric loss tangent at 28 GHz being 0.0040 or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, the increasing performance and functionality of electrical and electronic devices has created a need for high-speed information communication. For example, with the launch of 5G (fifth generation mobile communication system) high-speed communication services for smartphones, high-speed communication services are becoming widespread not only in the consumer sector but also in the industrial sector (factories, automobiles, and other vehicles). 5G's high-speed, large-capacity data communications use radio waves in the "millimeter wave" band (wavelength 1-10 mm, frequency 30-300 GHz). Advantages of millimeter waves include the large amount of data that can be transmitted at one time and the high-resolution images that can be obtained.

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

[0004]

number

[0005] where f is frequency, c is the speed of light, and ε r is the relative permittivity, and tan δ is the dielectric loss tangent.

[0006] For example, in FPC (Flexible Printed Circuits), which is a flexible circuit board made of resin film and copper foil, the resin film has a dielectric loss α dMore specifically, a reduction in ε r Attempts have been made to reduce the tan δ, especially to reduce the tan δ.

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

[0008] Polyester films are a versatile resin film that has excellent heat resistance, weather resistance, mechanical strength, transparency, and other properties, and is readily available at a reasonable price. As a result, polyester films are used in a variety of applications, including packaging materials and optical applications, but their low dielectric properties have not been extensively studied.

[0009] For example, Patent Document 1 discloses a laminated biaxially oriented polyester film containing 5 to 45% by volume of voids inside as a polyester film with excellent low dielectric properties. The inclusion of voids allows voids (air) to be dispersed, thereby achieving a low dielectric constant and a low dielectric loss tangent. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open 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 Low Transmission Loss" Summary of the Invention [Problem to be solved by the invention]

[0012] The void-containing laminated biaxially stretched polyester film described in Patent Document 1 is formed by mixing different materials to form the voids. In such cases, it is difficult to control the size of the voids 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 object of the present invention is to solve the above problems and to provide a biaxially oriented polyester film having excellent low dielectric properties without voids. [Means for solving the problem]

[0014] The present inventors have conducted extensive research to achieve the above object, and as a result have completed the present invention. In one aspect, the present invention is summarized as follows [1] to

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

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

[11] The biaxially stretched film according to

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

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

[11] , which has a film thickness of 40 to 150 μm.

[13] A film with a cured resin layer, comprising the biaxially stretched film according to any one of [1] to

[12] above, and a cured resin layer on at least one surface layer, the cured resin layer being formed from a resin composition containing a crosslinking agent in an amount of 70% by mass or more relative to the non-volatile components.

[14] A metal laminated film comprising a metal layer on the cured resin layer of the film with a cured resin layer described in

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

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

[18] The biaxially stretched film according to

[17] above, which is used as a substrate film for a transparent antenna.

[19] The film with a cured resin layer according to

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

[20] The film with a cured resin layer according to

[19] above, which is used as a substrate film for a transparent antenna.

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

[14] to

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

[22] The metal laminated film according to

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

[0015] The biaxially stretched 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 stretched 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. DETAILED DESCRIPTION OF THE INVENTION

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

[0017] <<Biaxially oriented film>> A biaxially stretched film according to one 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 at 28 GHz of 0.0040 or less. Since the present film is a biaxially stretched film, it can be made thin, and has low dielectric properties because the dielectric loss tangent is adjusted to fall within a specific range using a specific blend of polyesters. Furthermore, because the crystallization rate of this film is controlled by using a specific blend of polyesters, it is also excellent for extrusion molding and stretching, which are difficult to do with PBN resin (A) alone.

[0018] 1. Physical properties First, the physical properties of the present film will be described.

[0019] (1) Dielectric tangent The dielectric loss tangent of the present film at 28 GHz is 0.0040 or less, preferably 0.0039 or less, more preferably 0.0038 or less, particularly preferably 0.0035 or less, and particularly 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 polyester to be mixed, the stretching conditions, etc. The dielectric loss tangent was measured by the method described in the examples.

[0020] (2) Dielectric constant The dielectric constant of the present film at 28 GHz is preferably 3.15 or more and 3.25 or less, 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. If the dielectric constant is within this range, 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 by the type and content of the polyester to be mixed, the stretching conditions, etc. The dielectric constant was measured by the method described in the examples.

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

[0022] In the present invention, the machine direction (MD) of the film refers to the direction in which the film travels during the film production process, that is, the winding direction of the film roll. The transverse direction (TD) of the film refers to the direction parallel to the film surface and perpendicular to the longitudinal direction, that is, the direction parallel to the central axis of the roll of the film. The longitudinal direction (MD) is also called the machine direction or longitudinal direction, and the transverse direction (TD) is also called the cross direction.

[0023] (4) Storage modulus The storage modulus measured by dynamic viscoelasticity at 23°C is preferably 3.5 GPa or more in both the machine direction (MD) and the transverse direction (TD). It is more preferably 3.6 GPa or more, even more preferably 3.7 GPa or more, and particularly preferably 3.8 GPa or more. There is no particular upper limit, but it is usually 10 GPa or less, preferably 8.0 GPa or less. If the storage modulus of the present film is 3.5 GPa or more, the film will have good stiffness, be less prone to wrinkles, and be easy to handle. The storage modulus is a value determined by the method described in the examples.

[0024] (5) Tensile properties after wet heat test After being left standing for 96 hours in an environment of 120°C and 85% RH, and then further left standing for 18 hours at room temperature (23°C), the tensile strength at break in both the machine direction (MD) and the cross 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. The upper limit is not particularly limited, but is usually 300 MPa or less, preferably 250 MPa or less. If the tensile strength at break of the present film after the wet heat test is 100 MPa or more, the film will have excellent hydrolysis resistance and sufficient weather resistance. Furthermore, after leaving the film standing in an environment of 120°C and 85% RH for 96 hours, and then leaving it standing at room temperature (23°C) for 18 hours, the strength retention in both the machine direction (MD) and the cross direction (TD) is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, and particularly preferably 65% ​​or more. The upper limit is not particularly limited, but is 100% or less. If the strength retention rate of the present film after the wet heat test is 50% or more, the film has sufficient weather resistance.

[0025] (6) Haze The haze of the present 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 the present film is the above upper limit or less, it can be said to have good transparency. The lower limit is not particularly limited, but is usually 0.01% or more.

[0026] (7) Heat shrinkage rate The heat shrinkage of the present film when heated at 150° C. for 30 minutes is preferably 5.0% or less in both the machine direction (MD) and the transverse direction (TD). With a heat shrinkage of 5.0% or less, the present film has excellent heat resistance, particularly dimensional stability at high temperatures, and can be used practically without problems. From this viewpoint, the heat shrinkage of the present film is more preferably 4.0% or less, further 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 the present film is preferably 1 to 250 μm, more preferably 5 to 200 μm, and even more preferably 10 to 150 μm. By making it 1 μm or more, the film strength is maintained within a practical range. By making it 250 μm or less, it can be easily incorporated into mobile devices and the like, and can be suitably used for high-speed communication circuits. In particular, when used as a substrate film for a transparent antenna, the thickness of the present film is preferably 40 to 150 μm. The lower limit of the thickness is more preferably 50 μm, even more preferably 75 μm, and particularly preferably 100 μm. The upper limit of the thickness is preferably 140 μm, even more preferably 130 μm. The thickness can be adjusted by adjusting the film-forming and stretching conditions.

[0028] 2. Ingredients Next, the components constituting the present film will be described.

[0029] The present film contains two or more polyesters, at least one of which is a PBN resin (A). Although the mechanism by which this film contains PBN resin (A) and thus has excellent low dielectric properties is unclear, it is assumed that this is because the stacking of aromatic rings suppresses the movement of dipoles. Generally, when a dielectric is placed in an electric field, the dipoles become oriented. Then, the dipoles rotate and flip to follow the phase of the AC electric field. This rotation and flip motion of the dipoles creates friction, which causes dielectric loss. Therefore, it is presumed that suppressing the movement of dipoles leads to excellent low dielectric properties.

[0030] More specifically, from the viewpoint of suppressing dipole motion by stacking of aromatic rings, it is believed that stronger stacking leads to a greater suppression effect, and more specifically, it is believed that having a naphthalene skeleton rather than a benzene skeleton can exhibit better low dielectric properties. Therefore, from the viewpoint of low dielectric properties, it is preferable that the aromatic ring be a naphthalene skeleton rather than a benzene skeleton.

[0031] <Polybutylene naphthalate resin (A)> The PBN resin (A) constituting the present 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), and is preferably composed mainly of 2,6-naphthalenedicarboxylic acid and 1,4-butanediol, i.e., it contains 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. Preferably, 2,6-naphthalenedicarboxylic acid accounts for 92 mol% or more of the dicarboxylic acid component (a-1), more preferably 94 mol% or more, even more preferably 96 mol% or more, and even more preferably 98 mol% or more. Most preferably, all (100 mol%) of the dicarboxylic acid component (a-1) is 2,6-naphthalenedicarboxylic acid. By including 90 mol% or more of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component (a-1), the glass transition temperature and crystallinity of the PBN resin (A) are improved, thereby improving the heat resistance and mechanical properties of the film. Furthermore, by including 90 mol% or more of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component (a-1), the content of naphthalene skeletons is increased, enhancing the effect of inhibiting dipole motion due to stacking. This, in turn, results in improved low dielectric properties.

[0033] The PBN resin (A) may be copolymerized with an acid component other than 2,6-naphthalenedicarboxylic acid for the purpose of improving moldability and heat resistance. Specific examples include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, 3,4-furandicarboxylic acid, benzophenonedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 3,3'-diphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic 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-furandicarboxylic acid, 2,4-furandicarboxylic acid, and 3,4-furandicarboxylic acid are preferred from the viewpoint of moldability. Among these, from the viewpoint of low dielectric properties, acid components having a naphthalene skeleton with strong stacking are preferred, and for example, acid components having a benzene skeleton such as terephthalic acid and isophthalic acid are preferably contained in an amount 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 alone or in combination of two or more. The content of the acid components other than 2,6-naphthalenedicarboxylic acid is preferably 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), 1,4-butanediol preferably 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, and most preferably all (100 mol%) of the diol component (a-2) is 1,4-butanediol. By using 1,4-butanediol at 90 mol% or more as the diol component (a-2), compatibility with the polyester to be mixed is improved, and further the glass transition temperature and crystallinity of the PBN resin (A) are improved, thereby improving the heat resistance and mechanical properties of the present film.

[0035] The PBN resin (A) may be copolymerized with a diol component other than 1,4-butanediol to improve moldability and heat resistance. Specific 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, and isosorbide. 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 may be used alone or in combination of two or more. The content of the diol components other than 1,4-butanediol is preferably 10 mol % or less of all the 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 stretched film is taken as 100% by mass. When the content is 5% by mass or more, the low dielectric properties of the PBN resin (A) are exhibited. Furthermore, when the content is 70% by mass or less, an appropriate amount of at least one polyester, as described below, can be ensured, thereby improving the extrusion moldability and stretchability during film formation while achieving a good balance between low dielectric properties, mechanical properties, and weather resistance.

[0037] Among these, from the viewpoint of achieving 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 particularly preferably 50% by mass or more and 60% by mass or less.

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

[0039] <At least one type of polyester> The present film is composed of a polyester mixture containing at least one polyester in addition to the PBN resin (A).

[0040] The at least one polyester is not particularly limited, and examples thereof include those composed of a dicarboxylic acid component and a diol component as shown below. Examples of the dicarboxylic acid component 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 sulfoisophthalic 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, trimellitic acid monopotassium salt, and ester-forming derivatives thereof.

[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-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, and potassium dimethylolpropionate. One or more compounds may be appropriately selected from the above compounds and subjected to a conventional polycondensation reaction to synthesize a polyester. The at least one polyester includes a polyester corresponding 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 PBN resin (A) with the crystalline polyester (B), the crystallization rate of the PBN resin (A) can be controlled, and a film with excellent extrusion moldability and stretch processability can be obtained. Furthermore, since the crystalline polyester (B) has a higher glass transition temperature than the PBN resin (A), a resin composition having a higher glass transition temperature than the PBN resin (A) alone can be obtained, resulting in good heat resistance. Furthermore, by mixing the crystalline polyester (B), high crystallinity can be maintained, and a film having an excellent balance of low dielectric properties, mechanical properties, and weather resistance can be obtained.

[0044] The crystalline polyester (B) is preferably a polyethylene naphthalate resin, a polycyclohexylene dimethylene terephthalate resin, or the like, and more preferably contains a polyethylene naphthalate (hereinafter also referred to as "PEN") resin from the viewpoint of improving the balance between low dielectric properties, mechanical properties, and weather resistance. Because polyethylene naphthalate resin has a naphthalene skeleton in its structure, it has a significant effect of suppressing dipole movement due to stacking of aromatic rings, and can further improve the low dielectric properties of the present film.

[0045] (Polyethylene naphthalate resin) The PEN resin may be a homopolyester or a copolymer polyester, but it is preferable that the amount of an 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 components. Alternatively, all of the dicarboxylic acid components (100 mol %) may be 2,6-naphthalenedicarboxylic acid without containing any other copolymer components. Among these, homopolyesters are preferred from the viewpoint of maintaining high crystallinity, and also from the viewpoint of increasing the content of naphthalene skeletons to enhance the effect of suppressing dipole motion due to stacking and to facilitate improvement of low dielectric properties. A homopolyester and a copolymer polyester may be blended together, but when a homopolyester and one copolymer polyester are blended together, it is considered that two types of the crystalline polyester (B) are used.

[0046] When the PEN resin is made of a homopolyester, it is obtained by polycondensing 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 is made of a copolymer polyester, 2,6-naphthalenedicarboxylic acid is an essential component of the dicarboxylic acid component (b-1), and other copolymer components may be added thereto as required. Other copolymerization components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, 3,4-furandicarboxylic acid, benzophenonedicarboxylic 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-furandicarboxylic acid, 2,4-furandicarboxylic acid, and 3,4-furandicarboxylic acid are preferred from the perspective of moldability. Furthermore, among these, copolymerization components having a naphthalene skeleton with strong stacking are preferred from the perspective of low dielectric properties. These copolymerization components can be used alone or in combination of two or more.

[0048] The diol component (b-2) is essentially ethylene glycol, and as necessary, other copolymerization components may be used, such as 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, dimer diol, and bisphenols (bisphenol compounds such as bisphenol A, bisphenol F, and bisphenol S, or derivatives thereof, or ethylene oxide adducts thereof), of which 1,4-cyclohexanedimethanol, polytetramethylene ether glycol, dimer diol, and bisphenols are preferred. In particular, from the viewpoint of maintaining the strength of the film, it is preferable to use bisphenols. As the bisphenol, it is preferable to use an adduct of bisphenol A and ethylene oxide. These copolymerization components can be used alone or in combination of two or more.

[0049] The copolymer 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 copolymer polyester preferably contains 0 mol % or more and 10 mol % or less, more preferably 0 mol % or more and 8 mol % or less, even more preferably 0 mol % or more and 6 mol % or less, particularly preferably 0 mol % or more and 4 mol % or less, and especially preferably 0 mol % or more and 2 mol % or less of other copolymer components in the dicarboxylic acid component. By adjusting the content of the other copolymerization component in the dicarboxylic acid component to fall within the above range, the glass transition temperature and crystallinity of the copolymerized polyester are improved, and the heat resistance and mechanical properties of the present film are also improved. As described above, a particularly preferred embodiment is to use a copolymerization component having a naphthalene skeleton with strong stacking as the other copolymerization component. For example, the amount of an 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 copolymer polyester contains 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component in an amount of preferably 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, and all of the dicarboxylic acid component (100 mol%) may be 2,6-naphthalenedicarboxylic acid. By adjusting the content of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component within the above range, the glass transition temperature and crystallinity of the copolymer polyester are improved, thereby improving the heat resistance and mechanical properties of the film. Furthermore, by adjusting the content of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component within the above range, the content of naphthalene skeletons is increased, enhancing the effect of suppressing dipole motion due to stacking. As a result, the low dielectric properties are improved.

[0052] The copolymer polyester contains other copolymer components in the diol component in an amount of 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 %. By adjusting the content of the other copolymerization component in the diol component to fall within the above range, the glass transition temperature of the copolymerized polyester is improved, and the heat resistance of the present film is also improved. Furthermore, since the crystallinity can be controlled, the crystallization rate can be slowed down, and the extrusion moldability and stretchability of the film can be improved. Furthermore, if the content is 70 mol % or less, the melting point will not be too high, and therefore there is no need to set the molding temperature high, and there is no risk of thermal decomposition.

[0053] The copolymer polyester contains ethylene glycol in the diol component in an amount of 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 adjusting the content of ethylene glycol in the diol component to fall within the above range, the crystallinity of the copolymerized polyester is maintained, thereby improving the heat resistance of the present film.

[0054] From the viewpoint of a balance between low dielectric properties, mechanical properties, weather resistance, and moldability, the content of the crystalline polyester (B) such as PEN resin is preferably 50 parts by mass or more and 1,000 parts by mass or less, 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, per 100 parts by mass of PBN resin (A). When the content of the crystalline polyester (B) in the present film is 50 parts by mass or more, the crystallization rate can be slowed down, and therefore extrusion moldability and stretch processability during film formation can be improved. Furthermore, when the amount is 50 parts by mass or more, the glass transition temperature is increased, and the heat resistance of the present film can be improved. On the other hand, if the content of the crystalline polyester (B) is 1,000 parts by mass or less, the balance between 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 between the dielectric properties, mechanical properties, and weather resistance.

[0055] Among these, from the viewpoint of achieving 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, 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 particularly preferably 65 parts by mass or more and 110 parts by mass or less, per 100 parts by mass of the PBN resin (A).

[0056] For example, when a PEN resin is used as the crystalline polyester (B), both the PBN resin (A) and the PEN resin have a naphthalene skeleton, but as the amount of the PBN resin (A) increases, the dielectric loss tangent decreases, resulting in better low dielectric properties. The reason for this is thought to be related to density. The dielectric constant is a parameter that indicates the degree of polarization, and since the total sum of dipoles increases as the number of molecules per unit volume increases, it is thought that the higher the density, the greater the dielectric constant. On the other hand, the dielectric loss tangent is a parameter that indicates the degree of energy loss that occurs when dipoles vibrate when an AC voltage is applied. From this, it is thought that when the density is high, the energy loss, i.e., the dielectric loss tangent, decreases as the dipoles vibrate and cancel each other out. That is, when the present film contains the PBN resin (A) and the PEN resin, the density increases as the content of the PBN resin (A) increases, and therefore the dielectric loss tangent is effectively reduced.

[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 temperature between the PBN resin (A) and the crystalline polyester (B) is equal to or greater than the above lower limit, the glass transition temperature of the present film falls within a suitable range, and a film having excellent heat resistance and extrusion moldability can be obtained. The upper limit of the difference in glass transition temperature 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. or higher and 200° C. or lower, more preferably 75° C. or higher and 190° C. or lower, and even more preferably 80° C. or higher and 180° C. If the glass transition temperature of the crystalline polyester (B) is within this range, the glass transition temperature of the present film will be in 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> The present film may contain other resins in addition to the PBN resin (A) and the at least one polyester, as long as the effects of the present invention are not impaired. Examples of 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, polyamideimide resins, polyamide bismaleimide resins, polyetherimide resins, polyether ether ketone resins, polyether ketone resins, polyethersulfone resins, polyketone resins, polysulfone resins, aramid resins, and fluorine-based resins.

[0060] <Particle> The present film may contain particles for the primary purposes of imparting lubricity and preventing scratches during each process. The type of particles to be added is not particularly limited as long as they are capable of imparting lubricity. 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 a metal compound such as a catalyst during the production process of a polymer such as polyester can also be used.

[0061] <Additives> The film may also contain additives that are commonly used, such as recycled resins generated from trimming losses such as selvage, pigments such as titanium oxide and carbon black, flame retardants, weather stabilizers, heat stabilizers, antistatic agents, melt viscosity modifiers, crosslinking agents, lubricants, nucleating agents, plasticizers, antioxidants, antioxidants, light stabilizers, UV absorbers, neutralizers, anti-fogging agents, anti-blocking agents, slip agents, and colorants, which are added for the purpose of improving or adjusting moldability, productivity, and various physical properties of the porous film.

[0062] 3. Manufacturing method Next, a method for producing the present film will be described.

[0063] A method for producing the biaxially stretched film of the present invention will be described below. However, the following description is an example of a method for producing the present film, and the present film is not limited to films produced by this production method.

[0064] The method for producing the present film according to one embodiment of the present invention is a method for producing a film by forming a resin composition containing the PBN resin (A) and at least one polyester into a film and biaxially stretching the film.

[0065] The method for kneading the PBN resin (A), at least one polyester, other resins, and additives to obtain a resin composition is not particularly limited, but in order to obtain the resin composition as simply as possible, it is preferable to produce it by melt-kneading using an extruder. In order to uniformly mix the raw materials that constitute the resin composition, it is preferable to melt-knead using a co-rotating twin-screw extruder. The kneading temperature is preferably equal to or higher than the glass transition temperature (Tg) of all polymers used, and for crystalline resins, equal to or higher than the crystalline melting temperature (Tm) of the polymer. A kneading temperature as high as possible relative to the glass transition temperature (Tg) or crystalline melting temperature (Tm) of the polymer used facilitates transesterification of a portion of the polymer, improving compatibility. However, an unnecessarily high kneading temperature is undesirable because it can cause resin decomposition. For this reason, the kneading temperature is preferably 255°C or higher and 340°C or lower, more preferably 260°C or higher and 330°C or lower, even more preferably 270°C or higher and 320°C or lower, and particularly preferably 280°C or higher and 310°C or lower. A kneading temperature within this range can improve compatibility and melt moldability without causing polymer decomposition.

[0066] The obtained resin composition can be molded into a biaxially stretched film by a general molding method, such as extrusion molding, injection molding, blow molding, vacuum molding, pressure molding, press molding, etc. In each molding method, the apparatus and processing conditions are not particularly limited. The present film is preferably produced, for example, by the following method.

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

[0068] Next, the unstretched film is stretched in the longitudinal direction (MD) of the film and in the transverse direction (TD) perpendicular to the MD, usually by 1.1 to 5.0 times in at least one direction, preferably by 1.1 to 5.0 times in each of the longitudinal and transverse directions, in terms of stretching effect, film strength, etc.

[0069] As a biaxial stretching method, any of the conventionally known stretching methods 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 case of tenter-type sequential biaxial stretching, an unstretched film can be produced by heating the unstretched film to a temperature range of Tg to Tg + 60°C, where Tg is the glass transition temperature of the resin composition, stretching the film in the longitudinal direction by 1.1 to 5.0 times, preferably 1.5 to 4.5 times, and more preferably 2.0 to 4.0 times, using a roll-type longitudinal stretching machine, and then stretching the film in the transverse direction by 1.1 to 5.0 times, preferably 1.5 to 4.8 times, and more preferably 2.0 to 4.6 times, within a temperature range of Tg to Tg + 60°C using a tenter-type transverse stretching machine. Within this range of stretching ratio, the film can be uniformly stretched, and oriented crystallization can be induced, resulting in a film strength suitable for display applications. In the case of tenter-type simultaneous biaxial stretching or tubular-type simultaneous biaxial stretching, the film can be produced by simultaneously stretching the film in both the longitudinal and transverse directions by 1.1 to 5.0 times in the temperature range of Tg to Tg+60°C.

[0070] The biaxially stretched film stretched by the above method is subsequently heat-set. Heat-setting can impart dimensional stability at room temperature. In this case, the treatment temperature is preferably selected in the range of Tm-1 to Tm-80°C, which is the crystalline melting temperature of the resin composition. If the heat-setting temperature is within the above range, heat-setting is sufficiently carried out, stress during stretching is alleviated, sufficient heat resistance and mechanical properties are obtained, and an excellent film can be obtained without problems such as breakage or whitening of the film surface.

[0071] In the present invention, in order to alleviate the stress of crystallization shrinkage due to heat setting, it is preferable to perform relaxation in the width direction during heat setting by 0 to 15%, preferably 3 to 10%. By performing sufficient relaxation and uniformly relaxing the film 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 relaxation follows the film shrinkage, there is no sagging of the film, no flapping in the tenter, and no film breakage.

[0072] 4.Applications The biaxially stretched 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 a resin film and copper foil, and transparent antennas in which invisible ultrafine metal mesh wiring is formed on a transparent film. In particular, when the present film has high transparency, it can be suitably used as a substrate film for transparent antennas, which require high transparency.

[0073] Furthermore, since the transparent antenna does not impair the design, it can be attached not only to mobile devices but also to buildings such as window glass, car glass, etc. to receive 5G radio waves. If the film also has sufficient weather resistance, it can also be preferably used outdoors.

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

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

[0076] (1) Amount of oligomer (ester cyclic trimer) precipitated The cured resin layer of the present invention not only improves adhesion to the metal layer, but also prevents oligomer precipitation on the film surface due to heating. By reducing oligomer precipitation, it is possible to suppress the deterioration of visibility due to whitening of the film appearance caused by oligomer precipitation. In the cured resin layer-attached film of the present invention, in an embodiment in which cured resin layers are provided on both surface layers of a biaxially stretched film, the amount of oligomer (ester cyclic trimer) precipitated on the surface of at least one of the cured resin layers is 0.50 mg / m 2 Preferably, it is 0.40 mg / m or less. 2 More preferably, it is 0.30 mg / m or less. 2 More preferably, it is 0.20 mg / m or less. 2 It is particularly preferred that: Oligomer precipitation amount: 0.50mg / m 2 If the content is less than this, it is preferable because it prevents the deterioration of visibility due to whitening of the film appearance caused by precipitation and crystallization of oligomers on the surface, the occurrence of defects in post-processing, and contamination of the process and components. 2 That's all. The amount of precipitated oligomer is a value obtained by the method described in the Examples.

[0077] (2) Thickness The thickness of the cured resin layer (after drying) is preferably 0.003 to 1.0 μm, more preferably 0.005 to 0.5 μm, and even 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 precipitated from the film is small, resulting in a good appearance.

[0078] 2. Ingredients Next, the components constituting the cured resin layer will be described.

[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> As the crosslinking agent, various known crosslinking agents can be used, and examples thereof include oxazoline compounds, melamine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, and silane coupling compounds. Among these, when a metal layer is provided on a cured resin layer, oxazoline compounds are preferably used from the viewpoint of improving durable adhesion. Furthermore, from the viewpoints of preventing oligomer precipitation on the film surface due to heating and improving the durability of the cured resin layer, melamine compounds are preferably used.

[0081] (Oxazoline compounds) An oxazoline compound is a compound having an oxazoline group in the molecule. A polymer containing an oxazoline group is particularly preferred. The compound can be prepared by polymerizing an addition-polymerizable oxazoline group-containing monomer alone or with other monomers. Examples of the addition-polymerizable oxazoline group-containing monomer 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. These monomers can be used alone or in combination. Among these, 2-isopropenyl-2-oxazoline is preferred because it is readily available industrially. The other monomer is not limited as long as it is copolymerizable with the addition-polymerizable oxazoline group-containing monomer, and examples thereof include (meth)acrylic acid esters such as alkyl(meth)acrylate (the alkyl group can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid, and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-alkyl( Examples of the monomer include unsaturated amides such as (meth)acrylamide and N,N-dialkyl(meth)acrylamide (the alkyl group can be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a 2-ethylhexyl group, a cyclohexyl group, and the like); 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, and 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 compounds) The melamine compound is a compound having a melamine skeleton, and examples thereof include alkylolated melamine derivatives, compounds obtained by reacting alkylolated melamine derivatives with alcohols to partially or completely etherify them, and mixtures thereof. Suitable alcohols for etherification include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, and isobutanol. The melamine compound may be a monomer or a dimer or higher polymer, or a mixture thereof. Furthermore, melamine may be partially co-condensed with urea or the like, and a catalyst may be used to increase the reactivity of the melamine compound.

[0083] (epoxy compounds) Epoxy compounds are compounds having an epoxy group in the molecule, and examples thereof include condensation products of epichlorohydrin, ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A, etc. with a hydroxyl group or an amino group, polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, etc. 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, and examples of glycidylamine compounds include N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylamino)cyclohexane.

[0084] (Isocyanate compounds) The isocyanate compound refers to a compound having an isocyanate or an isocyanate derivative structure, such as a blocked isocyanate. Examples of the isocyanate include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl 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 isopropylidenedicyclohexyl diisocyanate. Further examples include polymers and derivatives of these isocyanates, such as biuretized products, isocyanurated products, urethodionated products, and carbodiimide-modified products. These may be used alone or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferred than aromatic isocyanates in order to prevent yellowing due to ultraviolet rays.

[0085] When used in the form of a blocked isocyanate, examples of the blocking agent include bisulfites, phenolic compounds such as phenol, cresol, and ethylphenol; alcohol 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, acetaldoxime, acetone oxime, methyl ethyl ketone oxime, and cyclohexanone oxime, which may be used alone or in combination of two or more.

[0086] The isocyanate compound may be used alone or as a mixture or bond with various polymers. In order to improve the dispersibility and crosslinkability of the isocyanate compound, it is preferable to use a mixture or bond with a polyester resin or a urethane resin.

[0087] (Carbodiimide compounds) A carbodiimide compound is a compound having a carbodiimide structure, and is a compound having one or more carbodiimide structures in the molecule. For better adhesion, etc., a polycarbodiimide compound having two or more carbodiimide structures in the molecule is more preferred.

[0088] Carbodiimide compounds can be synthesized by conventionally known techniques, and generally involve the condensation reaction of a diisocyanate compound. The diisocyanate compound is not particularly limited, and either an aromatic or aliphatic diisocyanate can be used. Specific 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 content of carbodiimide groups contained in the carbodiimide compound, in terms of carbodiimide equivalent (weight [g] of the carbodiimide compound required to provide 1 mol of carbodiimide groups), is usually in the range of 100 to 1000, preferably 250 to 700, and more preferably 300 to 500. Use within the above range improves the durability of the cured resin layer.

[0090] Furthermore, within the scope of the present invention, in order to improve the water solubility or water dispersibility of the polycarbodiimide compound, a surfactant may be added, or a hydrophilic monomer such as a polyalkylene oxide, a quaternary ammonium salt of a dialkylamino alcohol, or a hydroxyalkyl sulfonate may be added.

[0091] (Silane coupling compounds) A silane coupling compound is an organosilicon compound that contains an organic functional group and a hydrolyzable group such as an alkoxy group in one 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, and N-2-(aminoethyl)- Examples of suitable compounds 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 alone or in combination of two or more, but by using two or more in combination, it is possible to improve adhesion to a metal layer provided on the cured resin layer and to prevent oligomer precipitation after heating. Among them, a combination of an oxazoline compound, which can improve adhesion to a metal layer on the cured resin layer, and a melamine compound, which has good properties of 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 more preferable to combine three or more types of crosslinking agents. When combining three or more types of crosslinking agents, it is suitable to select a melamine compound as one of the crosslinking agents. As the counterpart crosslinking agent to be combined with the melamine compound, an oxazoline compound and an epoxy compound, or a carbodiimide compound and an epoxy compound are more preferable.

[0094] When such a crosslinking agent is contained, a component for promoting crosslinking, such as a crosslinking catalyst, can be used in combination.

[0095] The crosslinking agent preferably accounts for 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more of the total nonvolatile components in the resin composition forming the cured resin layer of the present invention. A content of 70% by mass or more improves adhesion to a metal layer provided on the cured resin layer and prevents oligomer precipitation after heating.

[0096] <Binder resin> The resin composition may contain a binder resin to improve the appearance of the cured resin layer and to improve adhesion to a metal layer formed on the cured resin layer, within the scope of the present invention. As the binder resin, any known binder resin can be used, but from the viewpoint of improving adhesion with layers provided on the cured resin layer, it is preferable to use polyester resin, acrylic resin, or urethane resin.

[0097] <Particle> The resin composition may also contain particles for the purpose of preventing blocking and improving slippage. 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, to more effectively improve slippage, the average particle size is preferably 0.01 μm or more, more preferably 0.03 μm or more, and particularly preferably in a range larger 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, within the scope of the present invention, the resin composition may be used in combination with a crosslinking catalyst, an antifoaming agent, a coatability improver, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, an antioxidant, a foaming agent, a dye, a pigment, or the like, as needed.

[0099] The various compounds (components) in the cured resin layer can be analyzed by, for example, TOF-SIMS, ESCA, fluorescent X-rays, or the like.

[0100] 3. Manufacturing method Next, a method for forming the cured resin layer will be described.

[0101] A method for forming a cured resin layer will be described below, but the following description is an example of a method for forming a cured resin layer, and the present invention is not limited to this formation method.

[0102] The resin composition is generally preferably diluted with water, an organic solvent, or a mixture thereof, and the cured resin layer may be formed by coating the diluted resin composition on the surface of the film as a coating liquid and drying it. Examples of a method for applying the coating liquid to the film include 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, calendar coating, and extrusion coating. In order to improve the coatability and adhesion of the coating agent (coating liquid) to the film, the film may be subjected to chemical treatment, corona discharge treatment, plasma treatment, or the like before coating.

[0103] A coating can be applied to the film surface as needed, and the cured resin layer can be formed by coating. Methods for forming the cured resin layer include inline coating and offline coating, with inline coating being preferred. Inline coating is a method of coating within the film production process, specifically, a method of coating at any stage from melt extrusion of the raw material polyester to stretching, heat setting, and winding up. Typically, the coating is applied to an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, or a biaxially stretched film after heat setting and before winding up. A particularly preferred method is to coat a uniaxially stretched film stretched in the longitudinal direction (longitudinal direction) and then stretch it in the width direction (transverse direction). When forming a cured resin layer by inline coating, it is preferable to use a coating liquid prepared by preparing an aqueous solution or aqueous dispersion of the above-mentioned compounds and adjusting the solids concentration to approximately 0.1 to 50% by mass. Furthermore, within the scope of the present invention, the coating liquid may contain a small amount of one or more organic solvents for the purposes of improving dispersibility in water, 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 forming a cured resin layer by offline coating, the heat treatment is preferably carried out at 80 to 200°C for 3 to 40 seconds, and more preferably at 100 to 180°C for 3 to 40 seconds. On the other hand, when the cured resin layer is provided by in-line coating, the heat treatment is preferably carried out at 70 to 280° C. for 3 to 200 seconds.

[0105] Regardless of whether off-line coating or in-line coating is used, heat treatment and irradiation with active energy rays such as ultraviolet rays 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 the precipitation of oligomers, and therefore can also suppress a decrease in visibility due to whitening of the film appearance. Therefore, the film with a cured resin layer 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 a resin film and copper foil, and transparent antennas in which invisible ultrafine metal mesh wiring is formed on a transparent film. In particular, it can be suitably used as a substrate film for transparent antennas, which require high transparency.

[0107] <<Metal laminated film>> The metal laminated film of the present invention may have a metal layer on the cured resin layer, and may have another layer 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, more preferably 3 to 25 μm. When the thickness of the metal layer is equal to or greater than the lower limit, electrical conductivity is sufficiently ensured, and when the thickness is equal to or less than the upper limit, a decrease in visibility can be suppressed when the metal layer is provided. The thickness of the metal layer can be measured by observing the cross section of a sample with an electron microscope.

[0110] 2. Ingredients Next, the components constituting the metal layer will be described.

[0111] The metal layer is a layer containing a metal as a main component, which means that the metal accounts for 50% by mass or more of the metal layer, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Examples of metals that can be used include copper, copper alloys, silver, stainless steel, nickel, nickel alloys, aluminum, aluminum alloys, titanium, and titanium alloys. From the viewpoint of electromagnetic wave shielding properties, copper and silver are preferred, and from the viewpoint of pliability (flexibility), copper is more preferred.

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

[0113] 3.Applications As described above, the metal laminated film of the present invention does not impair 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 a resin film and copper foil, and transparent antennas in which invisible ultrafine metal mesh wiring is formed on a transparent film. In particular, it can be suitably used as a substrate film for transparent antennas, which require high transparency.

[0114] <<Explanation of terms, etc.>> In the present invention, the term "film" includes the term "sheet", and the term "sheet" includes the term "film". In the present invention, when it is stated that "X to Y" (X and Y are any numbers), unless otherwise specified, it means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y". Furthermore, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified. [Example]

[0115] Examples are shown below, but the present invention is not limited by these examples.

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

[0117] (2) Tensile breaking strength The tensile strength of the films obtained in the examples and comparative examples was measured using a tensile tester (tensile tester AG-1kNXplus manufactured by Shimadzu Corporation) according to JIS K 7127:1999. Test specimens were prepared by cutting the films into rectangles measuring 100 mm in the measurement direction and 10 mm in width. Both ends of the test specimen in the longitudinal direction were chucked with a chuck distance of 40 mm and pulled at a pulling rate of 200 mm / min. The stress at the breaking point was measured three times as the tensile strength, and the average value was calculated. The tensile test was carried out in both the machine direction (MD) and the transverse direction (TD) of the film.

[0118] (3) Storage modulus by viscoelasticity measurement The dynamic viscoelasticity of the tensile deformation of the films obtained in the Examples and Comparative Examples was measured using a dynamic viscoelasticity measuring device (model name: "DMS6100", manufactured by SII Nanotechnology Co., Ltd.) according to a method in accordance with JIS K7244-1: 1998. The test was carried out by 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 tensile-deformed 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 and comparative examples were cut into rectangles measuring 100 mm in length and 10 mm in width in the measurement direction and subjected to a moist heat test in accordance with JIS C 60068-2-66:2001. The moist heat test was performed using a highly accelerated life tester (EHS-221M) manufactured by Espec Corporation. The specimens were left to stand at 120°C and 85% RH for 96 hours, followed by an additional 18 hours at room temperature (23°C). After the moist heat test, the specimens were subjected to tensile strength measurement in accordance with JIS K 7127:1999 using a tensile tester (AG-1kNXplus tensile tester manufactured by Shimadzu Corporation). The specimens were clamped at both ends in the longitudinal direction with a chuck distance of 40 mm and pulled at a pulling rate of 200 mm / min. The stress at break was measured three times as the tensile strength, and the average value was calculated according to the following formula: The tensile test was carried out in both the machine direction (MD) and the transverse direction (TD) of the film. Strength retention rate = ([tensile breaking strength after wet heat test] / [tensile breaking strength measured in (2)]) × 100

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

[0121] (6) Crystal melting temperature The films obtained in the examples and comparative examples were heated to the melting temperature at a heating rate of 10°C / min and then cooled at a cooling rate of 10°C / min in accordance with JIS K7121 (2012) using a DSC8000 (manufactured by PerkinElmer Japan Co., Ltd.), and the crystalline melting temperature during the heating process at a heating rate of 10°C / min was measured.

[0122] (7) Formability In extrusion molding, when the film was cooled and solidified using a cast roll to obtain a pre-stretched sheet, if a transparent film was obtained without crystallization and whitening, it was evaluated as ○, and if a crystallization and whitening film was obtained, it was evaluated as ×.

[0123] (8) Heat shrinkage rate This film was cut into a rectangle 120 mm long and 10 mm wide in the measurement direction, and a mark was made 100 mm from the edge. These test pieces were hung by clamping the edge with clips 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. The measurements were carried out in both the machine direction (MD) and the transverse direction (TD).

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

[0125] (10) Film thickness The thickness of this film was measured at five random locations within the surface using a 1 / 1000 mm dial gauge, and the average 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. Then, sections prepared by ultrathin sectioning 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 100 kV).

[0127] (12) Amount of oligomer (ester cyclic trimer) precipitated on the surface of the cured resin layer due to heating The film with the cured resin layer obtained in the examples was cut into a sample measuring 300 mm in length and 225 mm in width and heat-treated for 120 minutes in a hot air oven maintained at a predetermined temperature (180°C). After the heat treatment, a box-shaped sample measuring 200 mm in length and 125 mm in width and with an open top was prepared with the measurement surface facing the inner surface. Next, 10 mL of DMF (dimethylformamide) was placed in the box-shaped container and allowed to stand for 3 minutes. The DMF was then recovered and fed 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 trimer in the DMF. This value was divided by the area of ​​the film that had come into contact with the DMF to determine the amount of oligomer (ester cyclic trimer) (mg / m) on the surface of the cured resin layer. 2 The amount of ester cyclic trimer in DMF was determined from the peak area ratio between the peak area of ​​the standard sample and the peak area of ​​the measured sample (absolute calibration curve method). The standard sample was prepared by accurately weighing a previously separated ester cyclic trimer and dissolving it in an accurately weighed amount of 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)] The PBN resin (A) used was a homo-PBN consisting of 100 mol% dicarboxylic acid component (a-1) 2,6-naphthalenedicarboxylic acid and 100 mol% diol component (a-2) 1,4-butanediol. The glass transition temperature (Tg(A)) of the PBN resin was 77°C.

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

[0131] [Polyethylene terephthalate film] The PET film used was a biaxially stretched PET film having a thickness of 50 μm ("Diafoil T100-50" manufactured by Mitsubishi Chemical Corporation).

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

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

[0134] The compositions of the coating solutions used in the examples are as shown in Table 1. More specifically, the resin compositions obtained by stirring and mixing the compositions shown in Table 1 below were diluted with water to prepare the coating solutions.

[0135] [Table 1]

[0136] Example 1 Pelletized (B) was added at a ratio of 90% by mass to 10% by mass of pelletized (A) (900 parts by mass of (B) to 100 parts by mass of (A)), dry-blended, and then melt-kneaded in a Φ40 mm twin-screw extruder set at 285°C. The mixture was extruded as a film from a T-die with a gap of 1.0 mm, taken up by a cast roll at 105°C, cooled and solidified, and a film-like material (cast film) with a thickness of approximately 450 μm was obtained. The resulting cast film was then passed through a longitudinal stretching machine and heated with an infrared heater (temperature near the heater: 170°C) to be stretched 2.8 times in the machine direction (MD). The resulting longitudinally stretched film was then passed through a transverse stretching machine (tenter) to be 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 relaxed 5% in the width direction (TD) while being heat set in the tenter. The obtained film was subjected to measurements, and the results are shown in Table 2.

[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 added to 80% by mass of pelletized (B) (400 parts by mass of (B) per 100 parts by mass of (A)), and the cast roll temperature was set to 100°C. The resulting cast film was then passed through a longitudinal stretching machine and heated with an infrared heater (temperature near the heater: 160°C) to be stretched 2.8 times in the machine direction (MD).Then, the resulting longitudinally stretched film was passed through a transverse stretching machine (tenter) to be 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.The film was then relaxed by 5% in the tenter. The obtained film was subjected to measurements, and the results are shown in Table 2.

[0138] Example 3 A cast film was obtained in the same manner as in Example 1, except that 30% by mass of pelletized (A) was added to 70% by mass of pelletized (B) (233 parts by mass of (B) per 100 parts by mass of (A)), and the cast roll temperature was set to 95°C. The resulting cast film was then passed through a longitudinal stretching machine and heated with an infrared heater (temperature near the heater: 155°C) to be stretched 2.8 times in the machine direction (MD).Then, the resulting longitudinally stretched film was passed through a transverse stretching machine (tenter) to be 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.The film was then relaxed by 5% in the tenter. The obtained film was subjected to measurements, and the results are shown in Table 2.

[0139] Example 4 A cast film was obtained in the same manner as in Example 1, except that pellet-form (B) was added in a ratio of 60 mass% to 40 mass% of pellet-form (A) (150 mass parts of (B) per 100 mass parts of (A)), dry blended, and the cast roll temperature was set to 90°C. The resulting cast film was then passed through a longitudinal stretching machine and heated with an infrared heater (temperature near the heater: 145°C) to be stretched 2.8 times in the machine direction (MD).Then, the resulting longitudinally stretched film was passed through a transverse stretching machine (tenter) to be 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.The film was then relaxed by 5% in the tenter. The obtained film was subjected to measurements, and the results are shown in Table 2.

[0140] Example 5 A cast film was obtained in the same manner as in Example 1, except that 50% by mass of pelletized (A) was added to 50% by mass of pelletized (B) (100 parts by mass of (B) per 100 parts by mass of (A)), and the cast roll temperature was set to 81°C. The resulting cast film was then passed through a longitudinal stretching machine and heated with an infrared heater (temperature near the heater: 135°C) to be stretched 2.8 times in the machine direction (MD).Then, the resulting longitudinally stretched film was passed through a transverse stretching machine (tenter) to be 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.Then, the film was relaxed by 5% in the tenter. The obtained film was subjected to measurements, and the results are shown in Table 2.

[0141] Example 6 A cast film was obtained in the same manner as in Example 1, except that 60% by mass of pelletized (A) was added to 40% by mass of pelletized (B) (67 parts by mass of (B) per 100 parts by mass of (A)), and the cast roll temperature was set to 70°C. The resulting cast film was then passed through a longitudinal stretching machine and heated with an infrared heater (temperature near the heater: 133°C) to be stretched 2.8 times in the machine direction (MD).Then, the resulting longitudinally stretched film was passed through a transverse stretching machine (tenter) to be 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.The film was then relaxed by 5% in the tenter. The obtained film was subjected to measurements, and the results are shown in Table 2.

[0142] Example 7 After the longitudinal direction (MD) stretching of Example 6 and before the transverse direction (TD) stretching, the coating liquid was applied to both sides of the uniaxially stretched film to obtain a biaxially stretched 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 film was stretched 3.0 times in the machine direction (MD) at 100°C. After preheating at 100°C in a tenter, it was stretched 4.5 times in the transverse direction (TD) at 110°C. Finally, it was heat-treated at 200°C, and a biaxially stretched film having a thickness of 125 μm was produced. The obtained film with a cured resin layer was subjected to measurements, and the results are shown in Table 2. The results of evaluation of the amount of oligomer precipitation on the surface of the cured resin layer by heating the obtained film with the cured resin layer are shown in Table 3 below.

[0143] (Comparative Example 1) When an attempt was made to produce a cast film in the same manner as in Example 1, except that 100% by mass of pelletized (A) was used and the temperature of the casting roll was set to 75°C, whitening, which is thought to be due to crystallization, occurred, and the film had a poor appearance and uneven thickness due to poor adhesion to the casting roll, and it was not possible to obtain an amorphous film that could be stretched. Therefore, the moldability in Table 2 was marked as 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 casting roll was set to 110°C. The resulting cast film was then passed through a longitudinal stretching machine and heated with an infrared heater (temperature near the heater: 175°C) to be stretched 2.6 times in the machine direction (MD).Then, the resulting longitudinally stretched film was passed through a transverse stretching machine (tenter) to be 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.Then, the film was relaxed by 5% in the tenter. The obtained film was subjected to measurements, and the results are shown in Table 2.

[0145] (Comparative Example 3) The results of evaluation of the biaxially stretched PET film are shown in Table 2.

[0146] [Table 2]

[0147] [Table 3]

[0148] In Table 3, 0.17 / 0.17 indicates that the amount of oligomer precipitated on one side is 0.17 mg / m 2The amount of oligomer precipitation on the other side was 0.17 mg / m 2 This means that

[0149] Furthermore, Table 4 below shows the dielectric loss tangents and dielectric constants 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 stretched film of the present invention has low dielectric properties in the high-frequency band, resulting in low transmission loss and making it applicable to 5G high-speed, large-capacity data communications. Furthermore, its high tensile strength at break provides sufficient mechanical properties. Furthermore, its high storage modulus provides the film with strong stiffness and good handleability. Furthermore, its good tensile strength at break and strength retention after a wet heat test indicate excellent hydrolysis resistance and sufficient weather resistance. Additionally, its low heat shrinkage rate and excellent heat resistance are also excellent, with low haze and excellent transparency. In addition to these properties, the polyester film is highly versatile, which 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 stretched film, the amount of oligomer precipitation on the surface of the cured resin layer can be reduced. Therefore, the film with a cured resin layer of the present invention has good visibility and can be suitably used as a substrate film for a transparent antenna, which requires particularly high transparency. [Industrial Applicability]

[0153] The biaxially stretched film, film with a cured resin layer, and metal laminated film of the present invention have excellent low dielectric properties and are therefore suitable for use in high-speed communication circuits, particularly flexible printed circuits (FPCs), which are flexible circuit boards formed from a resin film and copper foil, and transparent antennas in which invisible ultrafine metal mesh wiring is formed on a transparent film. Among these, when the biaxially stretched film, the film with a cured resin layer, and the metal laminated film of the present invention have high transparency, they can be preferably used as the transparent antenna substrate film. In particular, when the biaxially stretched film, film with a cured resin layer, and 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-mentioned applications.

Claims

1. Contains two or more polyesters, At least one of them is a polybutylene naphthalate resin (A), The dielectric loss tangent at 28 GHz is 0.0040 or less, Biaxially oriented film for high-speed communication circuits.

2. 2. The biaxially stretched film according to claim 1, having a dielectric constant at 28 GHz of 3.15 or more and 3.25 or less.

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

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

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

6. The biaxially stretched film according to any one of claims 1 to 5, wherein the strength retention rate in both the machine direction (MD) and the width direction (TD) is 50% or more when the film is 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.

7. The biaxially stretched 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. The biaxially stretched film according to any one of claims 1 to 7, comprising a crystalline polyester (B).

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

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

11. The biaxially stretched film according to claim 10, wherein the polyethylene naphthalate resin contains 5 mol% or less of an acid component having a benzene skeleton as a copolymerization component other than 2,6-naphthalenedicarboxylic acid, based on all dicarboxylic acid components.

12. The biaxially stretched film according to any one of claims 1 to 11, having a film thickness of 40 to 150 µm.

13. A polyester composition comprising two or more polyesters, At least one of them is a polybutylene naphthalate resin (A), A biaxially stretched film having a dielectric loss tangent of 0.0040 or less at 28 GHz, A film with a cured resin layer, comprising the biaxially stretched film and a cured resin layer on at least one surface layer thereof, the cured resin layer being formed from a resin composition containing a crosslinking agent in an amount of 70% by mass or more relative to the non-volatile components.

14. A metal laminated film comprising the cured resin layer-attached film according to claim 13, and a metal layer on the cured resin layer.

15. The metal laminate film of claim 14 , wherein the metal layer is patterned.

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

17. A film with a cured resin layer as described in claim 13, containing 35 mass% or more and 70 mass% or less of the polybutylene naphthalate resin (A).

18. The biaxially stretched film according to any one of claims 1 to 12, which is used as a substrate film for a transparent antenna.

19. The film with a cured resin layer according to claim 13 or 17, which is for use in high-speed communication circuits.

20. The film with a cured resin layer according to claim 19, which is used as a substrate film for a transparent antenna.

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

22. The metal laminated film according to claim 21, which is used as a substrate film for a transparent antenna.

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