JP2022172674A - Laminated polyester film, laminated film with cured resin layer and laminated metal film - Google Patents

Abstract

To provide a laminated polyester film that supports high-speed communication and has low dielectric properties and superior transparency, and a laminated film with a cured resin layer and a laminated metal film.SOLUTION: A laminated polyester film has two or more polyester layers. The film has, as at least one surface layer, at least one layer A of the polyester layers. The layer A has a thickness of 10-70% of the total thickness of the laminated polyester film, with the dielectric loss tangent at 28 GHz being 0.0060 or less.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a laminated polyester film, a laminated film with a cured resin layer, and a metal laminated film.

In recent years, as electrical and electronic equipment has become more sophisticated and functional, there has been a need for high-speed communication of information. For example, with the start of 5G (fifth generation mobile communication system) high-speed communication services for smartphones, high-speed communication services are spreading not only in the consumer sector but also in the industrial sector (factories, vehicles such as automobiles, etc.). be.
Radio waves in the “millimeter wave” (wavelength 1 to 10 mm, frequency 30 to 300 GHz) band are used for 5G high-speed, large-capacity data communication. Advantages of millimeter waves include that the amount of data that can be transmitted at one time is large, and that the resulting image can be of high definition.

On the other hand, when a high-frequency digital signal such as a millimeter wave is passed through a circuit board, a portion of the transmitted digital signal is consumed as heat on the wiring of the circuit board, causing dielectric loss, resulting in an attenuated digital signal. A so-called "transmission loss" occurs that reaches the receiver. Therefore, there is a situation in which measures to reduce transmission loss are required for the members used. The transmission loss is the sum of dielectric loss and conductor loss, and the dielectric loss _αd is calculated from the following equation (1).

Note that f is the frequency, c is the speed of light, _εr is the dielectric constant, and tan δ is the dielectric loss tangent.

For example, in FPCs (Flexible Printed Circuits), which are flexible circuit boards formed of a resin film and a copper foil, the resin film is required to reduce dielectric loss α _d in order to reduce transmission loss. More specifically, attempts have been made to lower _εr and tan δ, particularly tan δ.
Specifically, liquid crystal polymer (LCP), which has a dielectric loss of about 1/10, and cycloolefin polymer (COP), which has a dielectric loss of about 1/50, compared to polyimide (PI) used as a material for FPC ), and a fluororesin such as polytetrafluoroethylene (PTFE), which has a dielectric loss of about 1/100 (Non-Patent Document 1).

However, LCP and COP have the problem of low heat resistance, fluororesin has low adhesion strength to other members such as copper foil, and it is difficult to drill holes with a UV laser because it is a UV absorber. There's a problem. Furthermore, fluororesins are expensive. Therefore, a versatile resin film with low dielectric loss is desired.

A polyester film is mentioned as a resin film with high versatility. Polyester film is excellent in heat resistance, weather resistance, mechanical strength, transparency, etc., and is easily available in terms of price, so it is used for various applications such as packaging materials and optical applications. Low dielectric properties have not been studied much.

For example, Patent Document 1 discloses a laminated biaxially stretched polyester film containing 5 to 45% by volume of voids inside as a polyester film having excellent low dielectric properties. By containing cavities, voids (air) can be dispersed, achieving a low dielectric constant and a low dielectric loss tangent.

By the way, recently, a "transparent antenna film" in which an invisible ultrafine metal mesh wiring is formed on a transparent film is being studied, and is intended to reduce the dielectric loss of the film, more specifically, to lower the dielectric constant of the film. and low dielectric loss tangent.
Compared to conventional microwaves, millimeter waves are more susceptible to the effects of nearby products. has the problem of increasing the number of installed antennas.
The transparent antenna film that is being studied to address these issues does not impair the design, so it can be attached not only to mobile devices, but also to buildings such as window glass and glass of car bodies to receive 5G radio waves. can be done.

Japanese Patent Application Laid-Open No. 2006-352470

"Development Trends of High-Frequency Compatible Materials and Applications to 5G and Millimeter-Wave Radars", Technical Information Institute, Chapter 3, Section 2, p. 77-84 "Development trend of high-speed and high-frequency FPC and reduction of transmission loss"

In the void-containing laminated biaxially stretched polyester film described in Patent Document 1, different materials are mixed to form voids. In such a case, it is necessary to control the size of the voids or the dispersion state of the different materials. is difficult, and for example, when dispersing state of dissimilar materials is insufficient, desired low dielectric properties may not be obtained.
Furthermore, depending on the different materials used, the original transparency of the polyester film may not be obtained. In addition, there are cases where light is refracted at the interfaces of the cavities, resulting in a decrease in transparency.

The problem to be solved by the present invention is to solve the above problems and provide a laminated polyester film that is highly versatile and yet has excellent low dielectric properties and transparency.

The present inventors have completed the present invention as a result of earnest studies to achieve the above-mentioned problems. In one aspect of the present invention, the gist is the following [1] to [19].
[1] A laminated polyester film having two or more polyester layers, wherein at least one surface layer has at least one layer A of the polyester layer, and the thickness of the layer A is 10 of the total thickness of the laminated polyester film. ∼70% and a dielectric loss tangent at 28 GHz of 0.0060 or less.
[2] The laminated polyester film according to [1] above, wherein the layer A has a dielectric constant at 28 GHz of 3.0 or less.
[3] The laminated polyester film according to [1] or [2] above, wherein the layer A has a dielectric loss tangent at 28 GHz of 0.0050 or less.
[4] The above [ 1] The laminated polyester film according to any one of [3].
[5] The laminated polyester film according to [4] above, wherein the polycyclohexylene dimethylene terephthalate further has an isophthalic acid unit as the dicarboxylic acid component (a-1).
[6] The above [1]-[ 5], the laminated polyester film according to any one of the above.
[7] The laminated polyester film according to any one of [1] to [6] above, which has a haze of 4.0% or less.
[8] The laminated polyester film according to any one of [1] to [7] above, which has a total thickness of 1 to 300 μm.
[9] The laminated polyester film according to any one of [1] to [8] above has a cured resin layer on at least one surface layer, and the cured resin layer contains a cross-linking agent of 70 mass with respect to non-volatile components. % or more of a resin composition containing a cured resin layer.
[10] Curing according to the above [9], wherein the laminated polyester film has the cured resin layers on both surface layers, and the oligomer precipitation amount on the surface of at least one of the cured resin layers is 0.40 mg/m ² or less. Laminated film with a resin layer.
[11] A metal laminated film comprising a metal layer on the cured resin layer of the laminated film with a cured resin layer according to [9] or [10] above.
[12] The metal laminate film according to [11] above, wherein the metal layer is patterned.
[13] The metal laminate film according to [11] or [12] above, wherein the metal layer is made of copper or silver.
[14] The laminated polyester film according to any one of [1] to [8] above, which is used for high-speed communication circuits.
[15] The laminated polyester film according to [14] above, which is for a transparent antenna film.
[16] The laminated film with a cured resin layer according to the above [9] or [10], which is for high-speed communication circuits.
[17] The laminated film with a cured resin layer according to the above [16], which is for a transparent antenna film.
[18] The metal laminate film according to any one of [11] to [13] above, which is used for high-speed communication circuits.
[19] The metal laminate film according to [18] above, which is for a transparent antenna film.

The laminated polyester film, the laminated film with a cured resin layer, and the metal laminated film of the present invention have excellent low dielectric properties capable of high-speed communication.
Furthermore, the laminated polyester film, the laminated film with a cured resin layer, and the metal laminated film of the present invention are also excellent in transparency, so that they can be suitably used particularly for transparent antenna films.

1 is a schematic cross-sectional view showing an example of a microstripline; FIG.

The present inventor believes that when a high-frequency electric signal is passed through a circuit board such as one for high-speed communication circuits, the electric field strength is greatest immediately below the conductor wiring, which is the circuit board. We thought that the transmission loss could be efficiently reduced by lowering the dielectric properties, especially by lowering the dielectric loss tangent.
In addition, by making the layer A directly under the conductor wiring have low dielectric properties and efficiently reducing transmission loss, the excellent heat resistance, weather resistance, mechanical strength, and cost of polyester films typified by polyethylene terephthalate film can be achieved. We thought that we could provide a highly versatile laminated polyester film without impairing its performance.
The present invention will be described in detail below. However, the contents of the present invention are not limited to the embodiments described below.

<<Laminated polyester film>>
A laminated polyester film according to an example of the embodiment of the present invention (hereinafter also referred to as "the present laminated polyester film") is a laminated polyester film having two or more polyester layers, and at least one of the polyester layers on at least one surface layer It has one layer A, the thickness of the layer A is 10 to 70% of the total thickness of the laminated polyester film, and the dielectric loss tangent at 28 GHz is 0.0060 or less.
In the present invention, the laminated polyester film means a laminated polyester film having two or more polyester layers, and the surface layer means the layer arranged on the outermost surface side of the laminated polyester film. A cured resin layer, a metal layer, etc., which will be described later, can be arranged on the surface layer. It is distinguished from a laminated polyester film.

In the present laminated polyester film, the number of laminated polyester layers is preferably 10 or less. When the number of layers is 10 or less, the thickness of each layer is sufficient, so that the lamination property during film formation is sufficient, flow marks and the like are less likely to occur, and the quality of the film is sufficiently maintained. Among them, from the viewpoint of suppressing the manufacturing cost, two or more layers and three or less layers are most preferable.

The laminated polyester film has two or more polyester layers, and has at least one layer A of the polyester layers on at least one surface layer. For example, when another polyester layer other than layer A is used as layer B, the present laminated polyester film may have layers other than layer A and layer B, but the film formability and interlayer adhesion From this point of view, it is preferable that the layer A and the layer B be formed only.

In order to efficiently reduce transmission loss, a two-layer structure of layer A/layer B is sufficient. A three-layer structure of layer B/layer B is preferred.

Hereinafter, the polyester layers constituting the present laminated polyester film will be described in detail. , and a case in which only the layer A and the layer B are formed will be described.
Layers A and B may be layers made of the same polyester or layers made of different polyesters.

<Layer A>
Layer A is a polyester layer for imparting low dielectric properties to the laminated polyester film, and preferably has a dielectric loss tangent of 0.0050 or less at 28 GHz. If the dielectric loss tangent of the layer A is 0.0050 or less, the dielectric loss tangent of the entire laminated polyester film can be lowered, and a sufficient transmission loss reduction effect can be obtained. From the above viewpoints, the dielectric loss tangent of the layer A is more preferably 0.0045 or less, still more preferably 0.0040 or less. The lower limit is not particularly limited, but is 0.001 or more.
From the same point of view, the dielectric constant of layer A at 28 GHz is preferably 3.0 or less, more preferably 2.9 or less, and even more preferably 2.8 or less. The lower limit is not particularly limited, but is 2.0 or more.
The dielectric loss tangent and dielectric constant of Layer A are values measured by the method described in Examples.

The thickness of the layer A is 10-70% of the total thickness of the laminated polyester film. If the thickness of layer A is less than 10%, a sufficiently low dielectric property cannot be obtained. On the other hand, if the thickness of the layer A exceeds 70%, the heat resistance, weather resistance, mechanical strength, etc. will be poor, and versatility will be low, and the cost will be high.
From the above viewpoints, that is, from the viewpoint of good balance and versatility of heat resistance, weather resistance, mechanical strength, cost, etc., the thickness of layer A is 15 to 60% of the total thickness of the laminated polyester film. and more preferably 20 to 50%. The thickness of the layer A can be adjusted by the ratio of the discharge amount when extruding the polyester raw material when manufacturing the laminated polyester film.
The thickness of layer A is obtained by preparing an obliquely cut surface of the film by SAICAS (registered trade method) and using a time-of-flight secondary ion mass spectrometer (ToF-SIMS) to obtain the layer thickness from the ion peak intensity data. can be done.

The total thickness of the laminated polyester film is preferably 1 to 300 μm, more preferably 30 to 250 μm, even more preferably 50 to 200 μm.
If the total thickness is 1 μm or more, the film strength is maintained within a practical range. On the other hand, if the total thickness is 300 μm or less, it is easy to incorporate into a mobile device or the like.
The total thickness of this laminated polyester film is obtained by cutting out a substantially square sample piece having a side of 40 mm from this laminated polyester film, and using a dial gauge with a scale of 1/1000 mm, the thickness is measured at any five points in the film plane. and calculated the average value.

As mentioned above, layer A is a polyester layer with low dielectric properties and can be formed using polyester with low dielectric properties.
Moreover, as the polyester having low dielectric properties, it is particularly preferable to use a polyester having a cyclic structure such as a naphthalene ring or a cyclohexane ring as a skeleton. It is presumed that the mechanism of having excellent low dielectric properties by having the above-mentioned ring structure as a skeleton is because the dipole motion can be suppressed by stacking the ring structure, and a low dielectric loss tangent can be achieved.

Examples of the polyester having a naphthalene ring include dicarboxylic acid components such as 1,2-naphthalenedicarboxylic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1, Polyesters containing 6-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid and the like can be mentioned.
Moreover, it is preferable that the dicarboxylic acid component of the polyester having the naphthalene ring is the main component of the dicarboxylic acid component constituting the polyester.
Incidentally, the main component means the component with the highest content ratio among all the dicarboxylic acid components constituting the polyester, preferably 50 mol% or more of all the dicarboxylic acid components, more preferably 70 mol% or more of all the dicarboxylic acid components. A component that accounts for mol % or more.
However, the polyester having a naphthalene ring is not limited to those described above, and may have a naphthalene ring in the diol component, for example.

Polyesters having a cyclohexane ring include, for example, diol components such as 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, and 1,3-cyclohexane. Mention may be made of polyesters including dimethanol, 1,4-cyclohexanedimethanol, and the like.
Moreover, it is preferable that the diol component of the polyester having the cyclohexane ring is the main component of the diol component constituting the polyester.
Incidentally, the main component means the component with the highest content ratio among all the diol components constituting the polyester, preferably 50 mol% or more of all diol components, more preferably 70 mol% or more of all diol components. A component that occupies
However, the polyester having a cyclohexane ring is not limited to those described above, and for example, a dicarboxylic acid component may have a cyclohexane ring.

As the polyester having low dielectric properties, among others, from the viewpoint of interlayer adhesion with Layer B and low dielectric properties described later, a terephthalic acid unit as a dicarboxylic acid component (a-1) and a diol component (a- Polycyclohexylene dimethylene terephthalate having a 1,4-cyclohexanedimethanol unit is preferable as 2), and from the viewpoint of improving stretching processability, the polycyclohexylene dimethylene terephthalate is further used as a dicarboxylic acid component (a-1). , isophthalic acid units.
In addition, since the layer A contains the polycyclohexylene dimethylene terephthalate, it is effective in suppressing deterioration in visibility due to whitening of the film appearance caused by precipitation and crystallization of the oligomer.

From the viewpoint of interlayer adhesion with layer B, the dicarboxylic acid component (a-1) preferably contains 50 mol% or more of terephthalic acid units, still more preferably 60 mol% or more, and particularly preferably 70 mol%. More preferably, 80 mol % or more of the dicarboxylic acid component is the terephthalic acid unit.
From the viewpoint of stretching processability, the dicarboxylic acid component (a-1) preferably further contains 3 mol% or more of an isophthalic acid unit, more preferably 5 mol% or more, and still more preferably 8 mol% or more. be. From the viewpoint of crystallinity, the upper limit of the isophthalic acid unit is preferably 25 mol % or less, more preferably 20 mol % or less.

The dicarboxylic acid component (a-1) other than terephthalic acid and isophthalic acid constituting the polycyclohexylene dimethylene terephthalate includes phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6 -naphthalenedicarboxylic acid, 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, 3,4-furandicarboxylic acid, benzophenonedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 3,3'-diphenyldicarboxylic acid , 4,4'-diphenyl ether dicarboxylic 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 dicarboxylic acid and the like. Among these, 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, and 3,4-furandicarboxylic acid are preferable from the viewpoint of moldability. These dicarboxylic acid components can be used singly or in combination of two or more.
The content of dicarboxylic acid components other than terephthalic acid and isophthalic acid is preferably 10 mol % or less in all dicarboxylic acid components including terephthalic acid and isophthalic acid.

From the viewpoint of heat resistance and stretching processability, it is more preferable that the diol component (a-2) contains 80 mol% or more of 1,4-cyclohexanedimethanol unit, more preferably 90 mol% or more, particularly Preferably 95 mol % or more, particularly preferably all (100 mol %) of the diol component (a-2) are 1,4-cyclohexanedimethanol units.

The diol component (a-2) other than 1,4-cyclohexanedimethanol constituting the polycyclohexylene dimethylene terephthalate includes 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, ethylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, hydroquinone, bisphenol , spiroglycol, 2,2,4,4,-tetramethylcyclobutane-1,3-diol, isosorbide and the like. Among these, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,3-cyclohexanedimethanol are preferred from the viewpoint of moldability. These diol components can be used singly or in combination of two or more.
The content of diol components other than 1,4-cyclohexanedimethanol is preferably 10 mol % or less in all diol components including 1,4-cyclohexanedimethanol.

The polyester polymerization catalyst is not particularly limited, and conventionally known compounds can be used, such as titanium compounds, germanium compounds, antimony compounds, manganese compounds, aluminum compounds, magnesium compounds and calcium compounds.

In order to suppress the precipitation amount of the oligomer component, the film may be produced using a polyester having a low content of the oligomer component as a raw material. As a method for producing a polyester having a low content of oligomer components, various known methods can be used.
The polyester may also be obtained by subjecting the polyester to esterification or transesterification, followed by melt polycondensation under reduced pressure at a higher reaction temperature.

In addition, the layer A may contain other resins than 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, polylactic acid resins, polybutylene succinate resins, polycarbonate resins, polyamide resins ( aramid resin), polyacetal resin, acrylic resin, ethylene-vinyl acetate copolymer, polymethylpentene resin, polyvinyl alcohol resin, cyclic olefin resin, polyacrylonitrile resin, polyethylene oxide resin, cellulose resin, polyimide resin, polyurethane resin, polyphenylene sulfide resin, polyphenylene ether resin, polyvinyl acetal resin, polybutadiene resin, polybutene resin, polyamideimide resin, polyamide bismaleimide resin, polyetherimide resin , polyetheretherketone-based resins, polyetherketone-based resins, polyethersulfone-based resins, polyketone-based resins, polysulfone-based resins, fluorine-based resins, and the like.

Layer A may contain particles for the main purpose of imparting lubricity and preventing scratching in each step. The type of particles is not particularly limited as long as it can impart easy lubricity, and specific examples include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples include inorganic particles such as magnesium, kaolin, aluminum oxide and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenol resin, epoxy resin, and benzoguanamine resin.
Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

On the other hand, the shape of the particles to be used is not particularly limited either, and any of spherical, massive, rod-like, flattened and the like may be used.
Moreover, there are no particular restrictions on its hardness, specific gravity, color, and the like. One of these series of particles may be used alone, or two or more of them may be used in combination, if necessary.

The average particle diameter of the particles used is preferably 5 μm or less, more preferably in the range of 0.01 to 3 μm. When the thickness is 5 μm or less, the surface roughness of the film does not become excessively large, and problems do not occur when various surface functional layers are formed in subsequent steps. Moreover, the transparency of the film becomes sufficient, which is preferable.
The average particle size of the particles is calculated from the particle size (d50) at a cumulative volume fraction of 50% in the equivalent spherical distribution measured using a centrifugal sedimentation particle size distribution analyzer.

Furthermore, the particle content in Layer A is generally preferably less than 5% by mass, more preferably in the range of 0.0003 to 3% by mass. If there are no particles or if there are few particles, the transparency of the film will be high and the film will be good in terms of transparency, but the slipperiness may be insufficient, so particles should be added to the coating layer. Therefore, it may be necessary to take measures such as improving slipperiness. On the other hand, if the particle content is less than 5% by mass, the transparency of the film will be good.

A method for adding particles to the layer A is not particularly limited, and conventionally known methods can be employed. For example, it can be added at any stage of production of the polyester constituting each layer, but it is preferably added after the completion of the esterification or transesterification reaction.

In addition to the particles described above, known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, and the like can be added to the layer A as necessary.

<Layer B>
The polyester constituting the layer B is not particularly limited, and examples thereof include the following dicarboxylic acid component (b-1) and diol component (b-2).
Examples of the dicarboxylic acid component (b-1) 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, ester-forming derivatives thereof, and the like.

Examples of the diol component (b-2) include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol and 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, dimethylolpropion acid potassium, and the like.
From the above compounds, one or more may be appropriately selected, and a polyester may be synthesized by a conventional polycondensation reaction.

The polyester constituting the layer B may be the same as the polyester constituting the layer A, or may be different.

Among the above polyesters, from the viewpoint of balance of heat resistance, weather resistance, mechanical strength, cost, etc. and improvement of versatility, a terephthalic acid unit is used as the dicarboxylic acid component (b-1), and ethylene as the diol component (b-2). It preferably contains polyethylene terephthalate having glycol units.
From the viewpoint of crystallinity and heat resistance, the dicarboxylic acid component (b-1) preferably contains 60 mol% or more, more preferably 80 mol% or more, and particularly preferably 90 mol% or more, of terephthalic acid units. Most preferably, all (100 mol %) of the dicarboxylic acid component (b-1) are terephthalic acid units.
From the same viewpoint, the diol component (b-2) preferably contains 60 mol% or more of ethylene glycol units, still more preferably 80 mol% or more, particularly preferably 90 mol% or more, and most preferably All (100 mol %) of the diol component (b-2) are ethylene glycol units.

The polyester polymerization catalyst is not particularly limited, and conventionally known compounds can be used, such as titanium compounds, germanium compounds, antimony compounds, manganese compounds, aluminum compounds, magnesium compounds and calcium compounds.

In order to suppress the precipitation amount of the oligomer component, the film may be produced using a polyester having a low content of the oligomer component as a raw material. As a method for producing a polyester having a low content of oligomer components, various known methods can be used.
The polyester may also be obtained by subjecting the polyester to esterification or transesterification, followed by melt polycondensation under reduced pressure at a higher reaction temperature.

As in layer A, particles, ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, and the like can be added to layer B as well.

<Method for producing laminated polyester film>
A method for producing the present laminated polyester film will be described. However, the following description is an example of a method for producing a laminated polyester film, and the laminated polyester film of the present invention is not limited to the laminated polyester film produced by such a production method.

For example, in the case of producing a biaxially oriented film, the above-mentioned raw material polyester is extruded as a molten sheet from a die using a plurality of extruders, and cooled and solidified with a rotating cooling drum to obtain an unstretched laminated sheet. preferable. In this case, it is preferable to increase the adhesion between the laminated sheet and the rotating cooling drum in order to improve the flatness of the laminated sheet, and the electrostatic application adhesion method and/or the liquid coating adhesion method are preferably employed. Thus, an unstretched laminate sheet is obtained.
In addition, the polyester used as a raw material is preferably dried as pellets or the like, and then supplied to the extruder. Particles, ultraviolet absorbers, other additives, and the like may also be blended into the pellets as appropriate.

Next, the unstretched laminated sheet obtained by the above method is stretched in one direction by a roll or tenter type stretching machine. The stretching temperature is usually 70 to 120° C., preferably 80 to 110° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times.
Next, the film is stretched in a direction perpendicular to the stretching direction of the first stage. In this case, the stretching temperature is usually 70 to 170° C., and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times. be.

Subsequently, heat treatment is performed at a temperature of 180 to 270° C. under tension or under relaxation of 30% or less to obtain a biaxially stretched film. In the above stretching, a method of stretching in one direction in two or more stages can also be employed. In that case, it is preferable to carry out so that the stretching ratios in the two directions finally fall within the above ranges.

A simultaneous biaxial stretching method can also be employed for the production of the laminated polyester film. The simultaneous biaxial stretching method is a method of simultaneously stretching and orienting the unstretched sheet in the longitudinal direction and the width direction while the temperature is controlled at usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is is 4 to 50 times, preferably 7 to 35 times, more preferably 10 to 25 times in area magnification.
Subsequently, heat treatment is performed at a temperature of 170 to 250° C. under tension or under relaxation of 30% or less to obtain a stretched and oriented film. Conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be used for the simultaneous biaxial stretching apparatus that employs the above-described stretching methods.

The longitudinal direction (MD) of the film refers to the direction in which the film advances in the film manufacturing process, that is, the winding direction of the film roll. The width direction (TD) is the direction parallel to the film surface and perpendicular to the longitudinal direction, ie, the direction parallel to the central axis of the film roll.

<Physical properties of laminated polyester film>
The dielectric loss tangent of this laminated polyester film at 28 GHz is 0.0060 or less. If the dielectric loss tangent exceeds 0.0060, a sufficient transmission loss reduction effect cannot be obtained. From the above viewpoints, the dielectric loss tangent of the laminated polyester film is more preferably 0.0058 or less, even more preferably 0.0056 or less. The lower limit is not particularly limited, but is 0.001 or more.
When the dielectric loss tangent of the present laminated polyester film is within such a range, the present laminated polyester film has good low dielectric properties and can be suitably used for high-speed communication circuits.
In addition, the dielectric loss tangent can be adjusted by the polyester used for the layers A and B, and the film-forming and stretching conditions of the laminated polyester film.

The dielectric constant at 28 GHz of the laminated polyester film is preferably 3.5 or less, more preferably 3.3 or less, and even more preferably 3.1 or less. The lower limit is not particularly limited, but is 2.0 or more.
If the dielectric constant of the present laminated polyester film is within such a range, the present laminated polyester film has good low dielectric properties and can be suitably used for high-speed communication circuits.
The dielectric loss tangent and dielectric constant of the laminated polyester film are values measured by the methods described in Examples.

The haze of the laminated polyester film is preferably 4.0% or less, more preferably 3.0% or less, even more preferably 2.5% or less, and 2.0% or less. is particularly preferred, 1.5% or less is particularly preferred, and 1.0% or less is most preferred. The lower limit is not particularly limited, but is 0.1% or more.
If the haze is within the range, it can be said that the present laminated polyester film has good transparency, and can be suitably used particularly for transparent antenna films.
The haze is a value measured by the method described in Examples.

The thermal shrinkage of the laminated polyester film after heat treatment at 150 ° C. for 30 minutes is preferably −5 to 5% in both the longitudinal direction (MD) and the width direction (TD), and is −3 to 3%. It is more preferably -2% to 2%. If the heat shrinkage ratio is in the range, the film has sufficient flatness and heat resistance. The thermal shrinkage rate is measured by the method described in Examples, and a positive value indicates a shrinkage rate, and a negative value indicates an expansion rate.

(Transmission loss reduction rate (%))
The transmission loss reduction rate (%) when using this laminated polyester film was calculated as follows using the transmission loss (dB) obtained from the simulation described in Examples.
[Transmission loss reduction rate (%)] = (1-[Transmission loss (dB) when using this laminated polyester film]/[Transmission loss (dB) when using polyethylene terephthalate film]) × 100
The transmission loss reduction rate is preferably 5% or more, more preferably 7% or more, and even more preferably 10% or more. The higher the transmission loss reduction rate, the better, but if it is 5% or more, the transmission loss can be efficiently reduced by using this laminated polyester film in which the layer A placed directly under the conductor wiring has low dielectric properties. It can be said that

<<Laminated film with cured resin layer>>
The laminated polyester film of the present invention may optionally have a cured resin layer on at least one surface layer of the laminated polyester film for the purpose of improving adhesion to the metal layer. It is preferably formed from a resin composition containing 70% by mass or more of a cross-linking agent based on the non-volatile components. Above all, it is more preferable to provide cured resin layers on both surface layers of the laminated polyester film. Here, the laminated polyester film having a cured resin layer is referred to as a laminated film with a cured resin layer, as described above.
In addition, another layer may be provided between the laminated polyester film and the cured resin layer.

As the cross-linking agent, various known cross-linking agents can be used, and examples thereof include oxazoline compounds, melamine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, silane coupling compounds and the like.
Among these, when providing a metal layer on a cured resin layer, an oxazoline compound is preferably used from the viewpoint of improving durable adhesion.
A melamine compound is preferably used from the viewpoint of preventing precipitation of oligomers on the film surface due to heating and improving the durability of the cured resin layer.

(oxazoline compound)
An oxazoline compound is a compound having an oxazoline group in its molecule, and a polymer containing an oxazoline group is particularly preferable. Addition polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline and the like can be mentioned, and one or a mixture of two or more thereof can be used. Among these, 2-isopropenyl-2-oxazoline is suitable because it is easily available industrially.
Other monomers are not limited as long as they are copolymerizable with addition-polymerizable oxazoline group-containing monomers. , n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group and cyclohexyl group); acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, Unsaturated carboxylic acids such as styrenesulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); Unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-alkyl (Meth)acrylamide and N,N-dialkyl(meth)acrylamide (as alkyl groups, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl 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; vinyl chloride and vinylidene chloride halogen-containing α,β-unsaturated monomers such as; α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene; be able to.
From the viewpoint of improving the durability of the coating film, the oxazoline group content of the oxazoline compound is preferably in the range of 0.5 to 10 mmol/g, more preferably 3 to 9 mmol/g, still more preferably 5 to 8 mmol/g.

(melamine compound)
A melamine compound is a compound having a melamine skeleton in the compound, and examples thereof include alkylolated melamine derivatives, compounds obtained by reacting alkylolated melamine derivatives with alcohol to partially or completely etherify them, and mixtures thereof. can be used. Methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol and the like are preferably used as the alcohol used for etherification.
Moreover, the melamine compound may be either a monomer or a polymer of dimers or higher, or a mixture thereof. Further, 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.

(epoxy compound)
Epoxy compounds are compounds having an epoxy group in the molecule, and include condensates with hydroxyl groups and amino groups such as epichlorohydrin, ethylene glycol, polyethylene glycol, glycerin, polyglycerin and bisphenol A, and polyepoxy compounds. , diepoxy compounds, monoepoxy compounds, glycidylamine compounds, and the like.
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 poly glycidyl ether and the like. 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, and polypropylene glycol diglycidyl ether. Ether and polytetramethylene glycol diglycidyl ether and the like. 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, 1,3 -Bis(N,N-diglycidylamino)cyclohexane and the like.

(isocyanate compound)
An isocyanate compound is a compound having an isocyanate derivative structure represented by isocyanate or blocked isocyanate. Examples of isocyanates include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate and naphthalene diisocyanate; aliphatic isocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate and hexamethylene diisocyanate; Examples include alicyclic isocyanates. Polymers and derivatives of these isocyanates such as buret products, isocyanurate products, uretdione products and carbodiimide modified products are also included. These may be used alone or in combination of multiple types. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferable than aromatic isocyanates in order to avoid yellowing due to ultraviolet rays.

When used in the state of blocked isocyanate, the blocking agent includes, for example, bisulfites, phenolic compounds such as phenol, cresol and ethylphenol; alcoholic compounds such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol and ethanol. Compounds; 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; ε-caprolactam, δ-valerolactam and the like amine compounds such as diphenylaniline, aniline and ethyleneimine; acid amide compounds of acetanilide and acetic acid amide; These may be used alone or in combination of two or more.

Also, the isocyanate compound may be used alone, or may be used as a mixture or combination with various polymers. From the viewpoint of improving the dispersibility and crosslinkability of the isocyanate compound, it is preferable to use a mixture or combination with a polyester resin or a urethane resin.

(carbodiimide compound)
A carbodiimide compound is a compound having a carbodiimide structure, and is a compound having one or more carbodiimide structures in the molecule. More preferred is a polycarbodiimide compound having

A carbodiimide compound can be synthesized by a conventionally known technique, and generally a condensation reaction of a diisocyanate compound is used. The diisocyanate compound is not particularly limited, and both aromatic and aliphatic compounds can be used. methylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate and dicyclohexylmethane diisocyanate;

The content of the carbodiimide group contained in the carbodiimide compound is usually 100 to 1000, preferably 250 to 700, more preferably 300 to 300, in terms of carbodiimide equivalent (weight [g] of the carbodiimide compound to give 1 mol of carbodiimide group). 500 range. By using it in the above range, the durability of the coating film is improved.

Furthermore, in order to improve the water-solubility and water-dispersibility of the polycarbodiimide compound, a surfactant may be added, polyalkylene oxide, a quaternary ammonium salt of a dialkylamino alcohol, and a hydroxy Hydrophilic monomers such as alkylsulfonates may be added and used.

(Silane coupling compound)
A silane coupling compound is an organosilicon compound having an organic functional group and a hydrolyzable group such as an alkoxy group in one molecule. For example, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4- epoxy group-containing compounds such as ethyltrimethoxysilane; vinyl group-containing compounds such as vinyltrimethoxysilane and vinyltriethoxysilane; styryl group-containing compounds such as p-styryltrimethoxysilane and p-styryltriethoxysilane; 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, etc. (Meth) acrylic group-containing compounds; 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)- 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-triethoxysilyl-N Amino group-containing compounds such as -(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane; tris(trimethoxysilylpropyl) Isocyanurate, isocyanurate group-containing compounds such as tris(triethoxysilylpropyl) isocyanurate; and mercapto group-containing compounds such as ethoxysilane.

These cross-linking agents may be used alone or in combination of two or more. By using two or more in combination, adhesion to the metal layer provided on the cured resin layer and prevention of precipitation of oligomers after heating are improved. can be improved. Among these, a combination of an oxazoline compound that can improve the adhesion to the metal layer on the cured resin layer and a melamine compound that has a good ability to prevent precipitation of oligomers after heating is preferable.

Further, in order to further improve the adhesion to the metal layer on the cured resin layer, it is more preferable to combine three or more cross-linking agents. A melamine compound is preferably selected as the cross-linking agent for combination with the melamine compound, and an oxazoline compound and an epoxy compound, and a carbodiimide compound and an epoxy compound are more preferable as the cross-linking agent to be combined with the melamine compound.

The ratio of the cross-linking agent to the total nonvolatile components in the resin composition forming the cured resin layer according to the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. If it is 70% by mass or more, the adhesiveness to the metal layer provided on the cured resin layer and the oligomer precipitation prevention property after heating are improved.

The resin composition may contain a binder resin in order to improve the appearance of the cured resin layer, improve adhesion with the metal layer provided on the cured resin layer, etc., within the scope of the present invention. It is possible.
As the binder resin, conventionally known ones can be used, but polyester resins, acrylic resins, and urethane resins are preferably used from the viewpoint of improving adhesion to the layer provided on the cured resin layer.

In addition, the resin composition may contain particles for the purpose of blocking and improving slipperiness. From the viewpoint of film transparency, the average particle size is preferably 1.0 μm or less, more preferably 0.5 μm or less, and even more preferably 0.2 μm or less. On the other hand, in order to improve slipperiness more effectively, the thickness is preferably 0.01 μm or more, more preferably 0.03 μm or more, and particularly preferably larger than the film thickness of the cured resin layer.
Specific examples of particles include silica, alumina, kaolin, calcium carbonate, organic particles, and the like.

Furthermore, the resin composition may optionally contain a cross-linking catalyst, an antifoaming agent, a coatability improver, a thickener, an organic lubricant, an antistatic agent, and an ultraviolet absorber, as long as the gist of the present invention is not compromised. Agents, antioxidants, foaming agents, dyes, pigments, etc. can be used in combination.

The film thickness (after drying) of the cured resin layer is preferably 0.003 to 1.0 μm, more preferably 0.005 to 0.5 μm, even more preferably 0.01 to 0.2 μm. When the film thickness is 1.0 μm or less, the appearance and blocking resistance of the cured resin layer are sufficient. On the other hand, when the film thickness is 0.003 μm or more, the amount of oligomer precipitated from the film is small and the film is good.

The resin composition is generally preferably diluted with water, an organic solvent, or a mixture thereof. It may be formed by coating as and drying.

If necessary, the surface of the laminated polyester film may be coated, and the cured resin layer may be formed by coating. Methods for forming the cured resin layer include in-line coating and off-line coating, and in-line coating is preferred. In-line coating is a method of coating in the process of manufacturing a laminated polyester film. Specifically, coating is performed at any stage from melt extrusion of the raw material polyester to stretching, heat setting, and winding. The method. Usually, it is coated on any of unstretched laminated sheet obtained by melting and quenching, stretched uniaxially stretched film, biaxially stretched film before heat setting, and laminated polyester film after heat setting and before winding up. A method of coating a uniaxially stretched film stretched in the longitudinal direction (machine direction) and then stretching it in the width direction (horizontal direction) is preferred.

<Physical properties of laminated film with cured resin layer>
The cured resin layer according to the present invention is effective not only in improving adhesion to the metal layer, but also in preventing precipitation of oligomers onto the film surface due to heating. By reducing the precipitation of oligomers, it is possible to suppress deterioration in visibility due to whitening of the film appearance caused by precipitation and whitening of oligomers.
In the laminated film with a cured resin layer of the present invention, in an embodiment having cured resin layers on both surface layers of the laminated polyester film, the amount of oligomer (ester cyclic trimer) precipitated on at least one surface of the cured resin layer is 0.40 mg. /m ² or less, more preferably 0.35 mg/m ² or less, even more preferably 0.30 mg/m ² or less, particularly 0.25 mg/m ² or less. preferable. If the oligomer deposition amount is 0.40 mg/m ² or less, the oligomer will precipitate and crystallize on the surface, resulting in deterioration of visibility due to whitening of the film appearance, occurrence of defects in post-processing, and contamination of processes and members. It is preferable because there is no Although the lower limit is not particularly limited, it is 0.01 mg/m ² or more.
The amount of oligomer precipitated on the surface of the cured resin layer can be adjusted from the polyester used and the layer structure of the laminated polyester film.
Further, when the amount of oligomer precipitated on the surface of the cured resin layer on the layer A is less than the amount of oligomer precipitated on the surface of the cured resin layer on the layer B, from the viewpoint of suppressing visibility deterioration, the layer A / A three-layer structure of layer A/layer B/layer A is preferable to a two-layer structure of layer B or a three-layer structure of layer A/layer B/layer B.
The amount of precipitated oligomer is a value obtained by the method described in Examples.

<<Metal laminated film>>
The metal laminated film of the present invention may have a metal layer on the cured resin layer. In addition, another layer may be provided between the cured resin layer and the metal layer.
A metal layer is a layer containing a metal as a main component. Here, the main component means that the metal accounts for 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more of the metal layer.
Metals to be used include copper, copper alloys, silver, stainless steel, nickel, nickel alloys, aluminum, aluminum alloys, titanium, and titanium alloys. Copper is more preferable from the viewpoint of flexibility (flexibility).

From the viewpoint of maintaining the transparency of the laminated polyester film and the laminated film with a cured resin layer, the metal layer is preferably patterned, for example, in a mesh shape or a wire shape.

The thickness of the metal layer is preferably 2-30 μm, more preferably 3-25 μm. When the thickness of the metal layer is at least the above lower limit value, the conductivity is sufficiently ensured, and when it is at most the above upper limit value, visibility can be reduced when the metal layer is provided.
The thickness of the metal layer can be measured by observing the cross section of the sample with an electron microscope.

<<Usage>>
The laminated polyester film, laminated film with a cured resin layer, and metal laminated film of the present invention have excellent low dielectric properties without impairing transparency.
Therefore, it can be suitably used for high-speed communication circuits. Applications for high-speed communication circuits include FPC (Flexible Printed Circuits), which are flexible circuit boards made of resin film and copper foil, and transparent antenna films, which are made by forming invisible ultra-fine metal mesh wiring on a transparent film. mentioned. Among others, it can be suitably used as a transparent antenna film for which high transparency is required.

<<Description of terms, etc.>>
In the present invention, the term "film" includes the "sheet", and the term "sheet" includes the "film".
In the present invention, when "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it means "X or more and Y or less" and "preferably larger than X" or "preferably larger than Y". It also includes the meaning of "small".
In addition, when described as "X or more" (X is any number), unless otherwise specified, it includes the meaning of "preferably greater than X", and when described as "Y or less" (Y is any number) , also includes the meaning of "preferably smaller than Y" unless otherwise specified.

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples described below.

<Evaluation method>
(1) Intrinsic Viscosity of Polyester 1 g of polyester was precisely weighed, dissolved in 100 ml of a mixed solvent of phenol/tetrachloroethane=50/50 (mass ratio), and measured at 30°C.

(2) Dielectric loss tangent and dielectric constant of laminated polyester film For the laminated polyester films obtained in Examples and Comparative Examples, a dielectric constant measurement system (cavity resonator (TE mode), control software , and vector network analyzer MS46122B (manufactured by Anritsu Corporation), according to JIS R1641, the dielectric loss tangent and dielectric constant at a frequency of 28 GHz were measured.

(3) Dielectric Loss Tangent and Relative Permittivity of Layer A The raw material of Layer A was charged into a small twin-screw extruder and melt-extruded at 300° C. to obtain an unstretched sheet with a thickness of 200 μm. The obtained unstretched sheet was stretched at a magnification of 3.0×3.0 at 100° C. with a small batch-type biaxial stretching machine to obtain a biaxially stretched film sample. The dielectric loss tangent and dielectric constant of layer A at a frequency of 28 GHz were measured for the obtained film sample using the same method as described above.

(4) Haze Measured using a haze meter DH-2000 manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K7136.

(5) Heat shrinkage A sample film of 1.5 cm x 15 cm was heat-treated for 30 minutes in a hot air oven maintained at a predetermined temperature (150°C) in a non-tensioned state, and the length of the sample film before and after that was measured. It was calculated by the following formula. The measurements were made in each of the longitudinal direction (MD) and the width direction (TD) of the film.
Thermal shrinkage rate (%) = {(Sample length before heat treatment) - (Sample length after heat treatment)} / (Sample length before heat treatment) x 100

(6) Evaluation of transmission loss by simulation An electromagnetic field for obtaining an appropriate line width (50Ω line width) and transmission loss (insertion loss, S21) for a characteristic impedance of 50Ω using a microstrip line as a pattern on a film circuit board. A simulation was performed.
As a simulation model, the thickness of the polyester film (substrate) was set to 125 μm. Table 1 shows the dielectric constant and dielectric loss tangent at 28 GHz of each polyester layer used in the simulation.
Also, a simulation model was prepared by laminating a metal layer (copper foil, thickness 18 μm, surface roughness (Rz) 1.0 μm, line length 100 mm) on a substrate.
The electromagnetic field simulation was performed under the conditions of a characteristic impedance of 50Ω and a frequency of 28 GHz.

FIG. 1 is a cross-sectional view showing an example of a microstripline. The microstrip line 10 has a substrate 11, a microstrip line 12 made of a metal layer, and a ground plane 13 made of a metal layer.

(7) Oligomer (ester cyclic trimer) precipitation amount on cured resin layer surface by heating For the laminated films with cured resin layers obtained in Examples and Comparative Examples, a sample having a size of 300 mm in length and 225 mm in width was prepared. (180° C.) in a hot air oven for 120 minutes. After the heat treatment, a box shape with an open top measuring 200 mm long and 125 mm wide was produced with the measurement surface as the inner surface.
Then, after putting 10 mL of DMF (dimethylformamide) in the above box shape and leaving it for 3 minutes, DMF was recovered and subjected to liquid chromatography (manufactured by Shimadzu Corporation: LC-7A Mobile phase A: acetonitrile, mobile Phase B: 2% acetic acid aqueous solution, column: "MCI GEL ODS 1HU" manufactured by Mitsubishi Chemical Corporation, column temperature: 40°C, flow rate: 1 mL/min, detection wavelength: 254 nm), and the ester cyclic triethylamine in DMF. The amount of the oligomer was determined, and this value was divided by the area of the film contacted with DMF to obtain the amount (mg/m ² ) of the oligomer (ester cyclic trimer) on the surface of the cured resin layer. The ester cyclic trimer in DMF was obtained from the peak area ratio of the standard sample peak area and the measurement sample peak area (absolute calibration curve method).
The standard sample was prepared by accurately weighing the ester cyclic trimer collected in advance and dissolving it in accurately weighed DMF.

<Materials used>
[Polyester raw material]
Raw material A: polycyclohexylene dimethylene terephthalate (dicarboxylic acid component: terephthalic acid/isophthalic acid (molar ratio) = 92/8, diol component: 1,4-cyclohexanedimethanol 100 mol%) (intrinsic viscosity = 0.80 dL/ g)
Raw material B: homopolyethylene terephthalate (intrinsic viscosity = 0.64 dL/g)

[Cured resin layer]
As the resin composition for forming the cured resin layer, the following was used.
(A1): Hexamethoxymethylolmelamine (A2): Epocross, an oxazoline compound (manufactured by Nippon Shokubai Co., Ltd.) Oxazoline group amount 7.7 mmol/g
(A3): Polyglycerol polyglycidyl ether (B1): Silica particles having an average particle diameter of 0.07 μm Table 2 shows the compositions of the coating liquids used in the examples.

(Example 1)
The raw material A was used as the raw material for the layer A, and the raw material B was used as the raw material for the layer B. Then, the raw material A as the raw material for the surface layer, the raw material B as the raw material for the intermediate layer, and the raw material B as the raw material for the other surface layer are separately put into a twin-screw extruder. Co-extrusion was carried out at 280° C., and cooling and solidification was performed on a cooling roll set at 15° C. to obtain an unstretched laminated sheet of two kinds and three layers of Layer A/Layer B/Layer B.
Then, the obtained unstretched laminated sheet was stretched 3.0 times at 88° C. in the longitudinal direction (MD) with a roll stretching machine. Furthermore, after preheating at 120° C. in a tenter, the film was stretched in the width direction (TD) at 130° C. to 3.7 times. Finally, heat treatment was performed at 250° C. to obtain a biaxially stretched laminated polyester film having a thickness of 125 μm (layer A/layer B/layer B=50/50/25 (μm)).
The properties of the obtained laminated polyester film were evaluated by the methods described above. Table 3 shows the evaluation results.

(Example 2)
After stretching in the longitudinal direction (MD) of Example 1 and before stretching in the width direction (TD), the coating liquid was applied to both sides of the uniaxially stretched laminated polyester film, and the film thickness (after drying) was 0.04 μm. A biaxially stretched laminated polyester film having a layer (laminated film with a cured resin layer) was obtained.
Table 4 below shows the evaluation results of the obtained laminated film with a cured resin layer.

(Example 3)
In Example 1, the thickness was 125 µm (layer A/layer B/layer B = 25/75/25 (layer A/layer B/layer B = 25/75/25 ( μm)) to obtain a biaxially stretched laminated polyester film.
The properties of the obtained laminated polyester film were evaluated by the methods described above. Table 3 shows the evaluation results.

(Example 4)
After stretching in the longitudinal direction (MD) of Example 3 and before stretching in the width direction (TD), the coating liquid was applied to both sides of the uniaxially stretched laminated polyester film, and the film thickness (after drying) was 0.04 μm. A biaxially stretched laminated polyester film having a layer (laminated film with a cured resin layer) was obtained.
Table 4 below shows the evaluation results of the obtained laminated film with a cured resin layer.

(Example 5)
The raw material A was used as the raw material for the layer A, and the raw material B was used as the raw material for the layer B. Then, the raw material A as the raw material for both surface layers and the raw material B as the raw material for the intermediate layer are separately put into a twin screw extruder, and the layer A is co-extruded at 290 ° C. and the layer B is co-extruded at 280 ° C. C. to obtain an unstretched laminated sheet of two kinds and three layers of layer A/layer B/layer A by cooling and solidifying on a cooling roll set at .degree.
Then, the obtained unstretched laminate sheet was stretched 3.0 times at 90° C. in the longitudinal direction (MD) with a roll stretching machine. Furthermore, after preheating at 120° C. in a tenter, the film was stretched in the width direction (TD) at 130° C. to a ratio of 3.8. Finally, heat treatment was performed at 250° C. to obtain a biaxially stretched laminated polyester film having a thickness of 125 μm (layer A/layer B/layer A=25/75/25 (μm)).
The properties of the obtained laminated polyester film were evaluated by the methods described above. Table 3 shows the evaluation results.

(Example 6)
After stretching in the longitudinal direction (MD) and before stretching in the width direction (TD) in Example 5, the coating liquid was applied to both sides of the uniaxially stretched laminated polyester film, and the film thickness (after drying) was 0.04 μm. A biaxially stretched laminated polyester film having a layer (laminated film with a cured resin layer) was obtained.
Table 4 below shows the evaluation results of the obtained laminated film with a cured resin layer.

(Comparative example 1)
Raw material B was charged into a twin screw extruder, extruded at 280°C, and solidified by cooling on a cooling roll set at 20°C to obtain an unstretched sheet.
Then, the obtained unstretched sheet was stretched 3.2 times at 85° C. in the longitudinal direction (MD) with a roll stretching machine. Furthermore, after preheating at 110° C. in a tenter, the film was stretched in the width direction (TD) at 140° C. to 4.3 times. Finally, heat treatment was performed at 240° C. to obtain a biaxially stretched polyester film having a thickness of 125 μm.
The properties of the obtained polyester film were evaluated by the methods described above. Table 3 shows the evaluation results.

(Comparative example 2)
After stretching in the longitudinal direction (MD) of Comparative Example 1 and before stretching in the width direction (TD), the coating liquid is applied to both sides of the uniaxially stretched polyester film, and the cured resin layer having a film thickness (after drying) of 0.04 μm. A biaxially stretched polyester film having
The evaluation results of the obtained film with a cured resin layer are shown in Table 4 below.

In Table 3 below, TPA is terephthalic acid, IPA is isophthalic acid, CHDM is 1,4-cyclohexanedimethanol, and EG is ethylene glycol.
In Tables 3 and 4, the top surface is the surface on which the microstrip line is provided, and the bottom surface is the surface on which the ground plane is provided. becomes.

From the results of Examples 1, 3, and 5, the laminated polyester film of the present invention has a high transmission loss reduction rate, and even with a film structure using polyethylene terephthalate, which is a general-purpose resin, it is a low dielectric property film. This result suggests a possibility. Also, the haze is low and the transparency is excellent. Furthermore, since it is a structure using polyethylene terephthalate, it is excellent in heat resistance, weather resistance, mechanical properties and workability, and is also advantageous in terms of cost.
Moreover, in the laminated film with a cured resin layer, from the results of Examples 2, 4, and 6, having the cured resin layer on the layer A can reduce the amount of oligomer precipitated on the surface of the cured resin layer. Therefore, the laminated polyester film and the laminated film with a cured resin layer of the present invention have good visibility and are particularly suitable for use as a transparent antenna film.

The laminated polyester film and the laminated film with a cured resin layer of the present invention have excellent low dielectric properties and transparency, so they are very useful for high-speed communication circuit applications, especially for transparent antenna films that require high transparency. be.

10 microstrip line 11 substrate 12 microstrip line 13 ground plane

Claims (19)

A laminated polyester film having two or more polyester layers, wherein at least one surface layer has at least one layer A of the polyester layer,
The thickness of the layer A is 10 to 70% of the total thickness of the laminated polyester film,
A laminated polyester film having a dielectric loss tangent of 0.0060 or less at 28 GHz. 2. The laminated polyester film according to claim 1, wherein the layer A has a dielectric constant at 28 GHz of 3.0 or less. 3. The laminated polyester film according to claim 1, wherein the layer A has a dielectric loss tangent at 28 GHz of 0.0050 or less. Claims 1 to 3, wherein the layer A comprises polycyclohexylene dimethylene terephthalate having terephthalic acid units as the dicarboxylic acid component (a-1) and 1,4-cyclohexanedimethanol units as the diol component (a-2). The laminated polyester film according to any one of the above. The laminated polyester film according to claim 4, wherein the polycyclohexylene dimethylene terephthalate further has an isophthalic acid unit as the dicarboxylic acid component (a-1). Any one of claims 1 to 5, wherein a layer other than the layer A contains polyethylene terephthalate having a terephthalic acid unit as the dicarboxylic acid component (b-1) and an ethylene glycol unit as the diol component (b-2). The laminated polyester film according to Item. The laminated polyester film according to any one of claims 1 to 6, which has a haze of 4.0% or less. The laminated polyester film according to any one of claims 1 to 7, which has a total thickness of 1 to 300 µm. It has a cured resin layer on at least one surface layer of the laminated polyester film according to any one of claims 1 to 8, and the cured resin layer contains 70% by mass or more of a cross-linking agent with respect to non-volatile components. A laminated film with a cured resin layer formed from a resin composition. The laminate with a cured resin layer according to claim 9, wherein the cured resin layer is provided on both surface layers of the laminated polyester film, and the oligomer precipitation amount on the surface of at least one cured resin layer is 0.40 mg/m ² or less. the film. A metal laminated film comprising a metal layer on the cured resin layer of the laminated film with a cured resin layer according to claim 9 or 10. 12. The metal laminate film of claim 11, wherein said metal layer is patterned. 13. The metal laminate film according to claim 11 or 12, wherein said metal layer is made of copper or silver. The laminated polyester film according to any one of claims 1 to 8, which is used for high-speed communication circuits. 15. The laminated polyester film according to claim 14, which is for a transparent antenna film. The laminated film with a cured resin layer according to claim 9 or 10, which is for high-speed communication circuits. 17. The laminated film with a cured resin layer according to claim 16, which is for a transparent antenna film. The metal laminated film according to any one of claims 11 to 13, which is used for high-speed communication circuits. 19. The metal laminate film according to claim 18, which is for a transparent antenna film.

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