WO2019049922A1

WO2019049922A1 - Base material film for flat cables and insulating film for flat cables using same

Info

Publication number: WO2019049922A1
Application number: PCT/JP2018/033000
Authority: WO
Inventors: 晴紀安田
Original assignee: 倉敷紡績株式会社
Priority date: 2017-09-08
Filing date: 2018-09-06
Publication date: 2019-03-14
Also published as: JPWO2019049922A1; JP7116732B2

Abstract

[Problem] To provide: a base material film for flat cables, which is used for the purpose of efficiently transmitting high frequency signals; and an insulating film for flat cables, which uses this base material film for flat cables. [Solution] A base material film (10) for flat cables has a relative dielectric constant of 2.5 or less and a dielectric loss tangent of 0.001 or less at a temperature of 23°C, at a relative humidity of 50% and at a frequency of 10GHz, while containing a syndiotactic polystyrene resin and being biaxially oriented. An insulating film (1) for flat cables is provided with: this base material film (10) for flat cables; and an adhesive layer (12) that is provided on this base material film.

Description

Substrate film for flat cable and insulating film for flat cable using the same

The present invention relates to a substrate film for flat cable and an insulating film for flat cable using the same.

There is known a flat cable which is closed with a plurality of conductors sandwiched between an insulating film provided with a base film and an adhesive layer provided on the surface thereof such that the adhesive layers face each other. This flat cable is used for wiring of various electronic devices because of its compactness and dense wiring. Further, with the development of electronic devices, it is also required to propagate high frequency electric signals to flat cables.

On the other hand, attenuation (transmission loss) of the electric signal flowing through the flat cable becomes a problem by increasing the frequency. The transmission loss can be expressed by the sum of the conductor loss and the dielectric loss, and the conductor loss and the dielectric loss increase as the frequency of the electric signal increases. And, the dielectric loss is proportional to the square root of the dielectric constant of the insulating film and the dielectric loss tangent as well as the frequency.
Heretofore, dielectric loss due to an insulating film has been dealt with, for example, by lowering the dielectric constant and dielectric loss tangent of the adhesive layer that wraps the conductor, as in Patent Document 1. And as a base film of an insulation film, generally the polyethylene terephthalate (PET) was used from the processability being excellent.
However, while further increase in capacity is required, in order to further suppress dielectric loss, a substrate film having a lower relative dielectric constant and a lower dielectric loss tangent is required.

For example, Patent Document 2 is made of a biaxially oriented polyarylene sulfide film, and has a dielectric loss of 0 to 0.01 at a temperature of 25 ° C. and a frequency of 1 GHz, and a tensile elongation at break of 100 to 250 in the longitudinal direction and the width direction. % Insulating films are disclosed.
Patent Document 3 further includes a foamed polyester resin insulating layer having a relative dielectric constant of 2.4 to 3.0, and a polyolefin adhesive layer having a relative dielectric constant of 2.1 to 2.7, A flat cable is disclosed in which the relative permittivity of the adhesive layer is smaller than the relative permittivity of the insulating layer.

Patent No. 6064378 JP 2007-250245 A JP 2012-64478 A

An object of the present invention is to provide a flat cable substrate film for efficiently transmitting high frequency signals and an insulating film for flat cable using the same.

The base film for flat cables of the present invention has a relative dielectric constant of 2.5 or less, a dielectric loss tangent of 0.005 or less at a temperature of 23 ° C., a relative humidity of 50%, and a frequency of 10 GHz, and a syndiotactic polystyrene type It is characterized in that it contains a resin (SPS resin) and is biaxially oriented.
In the present specification, the relative dielectric constant and the dielectric loss tangent of the base film are determined by the cavity resonator perturbation method based on ASTMD2520. The relative dielectric constant and dielectric loss tangent of the base film at a temperature of 23 ° C., a relative humidity of 50%, and a frequency of 10 GHz, after leaving the base film (test piece) in an environment of a temperature of 23 ° C. and a relative humidity of 50%, It is a value measured in a test environment at a temperature of 23 (± 2) ° C. and a relative humidity of 50 (± 5)%.

Since the substrate film for flat cables of the present invention has a relative dielectric constant of 2.5 or less and a dielectric loss tangent of 0.005 or less, the dielectric loss is small. Also, the propagation speed of the signal flowing through the flat cable conductor is inversely proportional to the square root of the relative permittivity of the insulating film, so the signal propagation speed is high. Furthermore, since the SPS resin has a low water absorption rate, it is difficult to deteriorate the quality due to humidity. In other words, water molecules, which are polar molecules absorbed by the base film, are largely moved by the electric field generated by the high frequency signal, and thus have a great influence on the dielectric constant and dielectric loss tangent of the insulating film, but SPS resin has a water absorption coefficient Because of the low property, the flat cable using this substrate film can maintain its electrical characteristics even when used in a humid environment. Furthermore, it is excellent in hydrolysis resistance.

The base film for flat cables of the present invention preferably has a relative dielectric constant of 2.5 or less and a dielectric loss tangent of 0.005 or less at a temperature of 60 ° C., a relative humidity of 90%, and a frequency of 10 GHz. The relative dielectric constant and dielectric loss tangent of the base film at a temperature of 60 ° C., a relative humidity of 90%, and a frequency of 10 GHz after leaving the base film (test piece) in an environment of a temperature of 60 ° C. and a relative humidity of 90% for 48 hours It is a value measured in a test environment at a temperature of 23 (± 2) ° C. and a relative humidity of 50 (± 5)%. The measurement was carried out within 20 minutes from the environment of temperature 60 ° C. and relative humidity 90%. Since the relative dielectric constant of the substrate film is small even in an environment with a temperature of 60 ° C and a relative humidity of 90%, the flat cable using this substrate film has a signal propagation speed even when used in a high temperature and high humidity environment You can keep In addition, dielectric loss can also be suppressed.
In particular, the rate of change of the relative dielectric constant of the base film at a temperature of 60 ° C., a relative humidity of 90%, and a frequency of 10 GHz relative to the relative dielectric constant of the base film at a temperature of 23 ° C. and a relative humidity of 50% and a frequency of 10 GHz. It is preferable when it is 0% or less.

It is preferable that the base film for flat cables of the present invention has a nominal strain at break of tensile failure of 15% or more at room temperature. In this case, if the nominal strain at break is less than 15%, the flexibility as a flat cable can not be sufficiently provided.
In this specification, the nominal strain on tensile fracture of the film is based on JIS K 7127 (1999) when the specimen type 2 (10 mm × 100 mm strip) is pulled at a speed of 200 mm / min. Say the growth rate of

It is the base film for flat cables of this invention, Comprising: That whose glass transition point is 140 degreeC or more is preferable. Since heat treatment such as heating and pressing to thermally bond adhesive layers in the process of drying the adhesive layer in the manufacturing process of the insulating film or flat cable can be performed at a relatively high temperature, the selectivity of the material of the primer layer and the adhesive layer Is high.
In addition, in this specification, a glass transition point is calculated | required from the thermomechanical-analysis (TMA) measurement result obtained based on JISK7197 (1991).

In the base film for flat cables of the present invention, one having a thermal expansion coefficient of 80 ppm / ° C. or less is preferable. When the coefficient of thermal expansion exceeds 80 ppm / ° C., the heat resistant dimensional stability decreases.
In this specification, the coefficient of thermal expansion is obtained by suspending the test piece (2 mm × 25 mm) so that the longitudinal direction is in the vertical direction, and applying a tensile load of 5 gf / 2 mm width to the lower end of the test piece. It is a coefficient of thermal expansion when the ambient temperature is raised from 50 ° C. to 100 ° C. at a heating rate of 10 ° C./min.

The insulating film for flat cables of the present invention is characterized by having the base film for flat cables of the present invention and an adhesive layer provided on the base film. Moreover, what provided the primer layer between the base film and the adhesive layer is preferable.
Since the insulating film for flat cables of this invention has a low dielectric constant and dielectric loss tangent of a base film, it can construct a flat cable with small dielectric loss.

FIG. 1a is a side cross-sectional view showing one embodiment of the flat cable insulating film of the present invention, and FIG. 1b is a side cross-sectional view showing another embodiment of the flat cable insulating film of the present invention.

The insulating film 1 for flat cables of FIG. 1a has a base film 10, a primer layer 11 provided on the base film, and an adhesive layer 12 provided on the primer layer. The primer layer 11 is a resin layer which suppresses peeling of the base film 10 and the adhesive layer 12. The adhesive layer 12 is a resin layer having heat sealability. The relative permittivity and dielectric loss tangent of the primer layer 11 and the adhesive layer 12 are preferably equal to or smaller than that of the base film 10.

The base film 10 contains syndiotactic polystyrene (hereinafter, SPS) resin and is biaxially oriented.
The biaxial orientation means that polymers are oriented in two different directions in the plane direction. The two different directions are preferably oriented in two directions substantially perpendicular to each other (the film extrusion direction (MD) and the direction perpendicular to the extrusion direction (TD)). Toughness (elongation and tensile strength) can be imparted to the film by biaxial orientation.
Biaxial orientation is achieved by biaxially orienting the unoriented precursor film. For example, a simultaneous biaxial stretching system, a sequential biaxial stretching system, etc. are mentioned, and a simultaneous biaxial stretching system is preferable. The unstretched precursor film is obtained by melting the resin material and forming it into a film. For example, an extrusion molding method, a calendar molding method, a casting method and the like can be mentioned, and the extrusion molding method is preferable.
The thickness of the base film 10 is 5 to 300 μm, preferably 5 to 100 μm, and particularly preferably 10 to 75 μm.

The base film 10 has a relative dielectric constant of 2.5 or less at a temperature of 23 ° C., a relative humidity of 50%, and a frequency of 10 GHz. Preferably, it is 2.4 or less, particularly preferably 2.3 or less. When the relative dielectric constant is higher than 2.5, the signal transmission speed is reduced and the dielectric loss is increased at a temperature of 23 ° C. and a relative humidity of 50%. In the case of a base film mainly composed of SPS resin, the relative dielectric constant never falls below 1.5.

The base film 10 has a relative dielectric constant of 2.5 or less at a temperature of 60 ° C., a relative humidity of 90%, and a frequency of 10 GHz. Preferably, it is 2.4 or less, particularly preferably 2.35 or less. When the relative dielectric constant is higher than 2.5, the temperature is 60 ° C., the relative humidity is 90%, the signal transmission speed is reduced, and the dielectric loss is increased. In the case of a base film mainly composed of SPS resin, the relative dielectric constant never falls below 1.5.
In addition, since the base film absorbs the moisture although it is minute by leaving the base film in an environment of temperature 60 ° C. and relative humidity 90%, the ratio of the base film at temperature 60 ° C., relative humidity 90% and frequency 10 GHz The dielectric constant is slightly higher than the dielectric constant of the base film at a temperature of 23 ° C., a relative humidity of 50%, and a frequency of 10 GHz. The rate of change is less than 3.0%. Preferably it is 2.0% or less, especially preferably 1.5% or less. And the rate of change never falls below 0.1%.
Thus, the rate of change of the relative dielectric constant of the base film 10 with a frequency of 10 GHz in an environment of 60 ° C. and 90% relative humidity is the base film 10 with a frequency of 10 GHz in an environment of 23 ° C. and 50% relative humidity. Because the relative dielectric constant of the flat cable is 3.0% or less, the change in the electrical characteristics of the flat cable is small even by environmental changes.

The dielectric loss tangent of the base film 10 is 0.005 or less at a temperature of 23 ° C., a relative humidity of 50%, and a frequency of 10 GHz. Preferably, it is 0.002 or less, particularly preferably 0.001 or less. When the dielectric loss tangent of the base film is larger than 0.005, the dielectric loss is large at a temperature of 23 ° C. and a relative humidity of 50%. In the case of a base film mainly composed of SPS resin, the dielectric loss tangent never falls below 0.00005.

The dielectric loss tangent of the base film 10 is 0.005 or less at a temperature of 60 ° C., a relative humidity of 90%, and a frequency of 10 GHz. Preferably, it is 0.002 or less, particularly preferably 0.001 or less. When the dielectric loss tangent of the base film is larger than 0.005, the dielectric loss becomes large at a temperature of 60 ° C. and a relative humidity of 90%. In the case of a base film mainly composed of SPS resin, the dielectric loss tangent never falls below 0.00005.
In addition, since the base film absorbs moisture although it is minute by leaving the base film in an environment at a temperature of 60 ° C. and a relative humidity of 90%, the dielectric of the base film at a temperature of 60 ° C., a relative humidity of 90% and a frequency of 10 GHz The tangent is slightly higher than the dielectric loss tangent of the base film at a temperature of 23 ° C., a relative humidity of 50% and a frequency of 10 GHz. The rate of change is less than 30%. It is preferably at most 25%, particularly preferably at most 20%. The rate of change never falls below 5%.

Nominal strain at break of base film 10, preferably 15% or more, more preferably 35% or more, particularly preferably 50% or more at room temperature, in any direction of MD direction and TD direction . Nominal strain at room temperature is related to the flexibility of the flat film. If the tensile strain at nominal temperature at room temperature is too small, the film is likely to be damaged during handling and use. There is no particular problem even if the tensile strain at nominal temperature at room temperature is large, but in the case of the base film 10 containing an SPS-based resin as a main component, it usually does not exceed 200%.

The glass transition temperature of the base film 10 is 140 ° C. or more, preferably 180 ° C. or more, and particularly preferably 200 ° C. or more. If the glass transition point is low, the quality may be degraded in the production process of the insulating film and / or the production process of the flat cable. There is no particular problem even if the glass transition temperature is large, but in the case of the base film 10 mainly composed of SPS resin, it does not usually exceed 250 ° C.

The base film 10 is substantially made of SPS resin. However, the base film 10 may contain a synthetic resin other than the SPS-based resin, as long as the base film 10 does not affect the electrical characteristics, tensile strain at break, and glass transition temperature of the base film 10.
Moreover, the base film 10 is an antioxidant, an ultraviolet absorber, a light stabilizer, a lubricant, an antistatic agent, an inorganic filler, a coloring agent, a crystal nucleating agent, a flame retardant etc. in the range which can exhibit the effect of this invention. You may contain an additive.

The SPS-based resin is a styrenic polymer having a syndiotactic structure. The syndiotactic structure means a steric structure in which a phenyl group or a substituted phenyl group which is a side chain relative to a main chain formed from a carbon-carbon bond is alternately located in the opposite direction.

The degree of tacticity (tacticity) of the SPS resin can be quantified by nuclear magnetic resonance ( ¹³ C-NMR) with isotope carbon. The tacticity of SPS-based resin measured by ¹³ C-NMR method is a chain consisting of several monomer units, for example, dyads in the case of two, triads in the case of three, triads in the case of five, and pentads in the case of five. It can be shown by the proportion of reverse syndiotactic configuration (racemic dyad etc.). The SPS-based resin in the present invention is usually at least 75%, preferably at least 85% in racemic dyad, or at least 60%, preferably at least 75% in racemic triad, or at least 30%, preferably 50% in racemic pentad. It is a styrenic polymer having the above syndiotacticity.

Types of styrene-based polymers as SPS-based resins include polystyrene, poly (alkylstyrene), poly (halogenated styrene), poly (halogenated alkylstyrene), poly (alkoxystyrene), poly (vinyl benzoate), These hydrogenated polymers etc. and these mixtures, or the copolymer which has these as a main component are mentioned. Examples of poly (alkylstyrenes) include poly (methylstyrene), poly (ethylstyrene), poly (isopropylstyrene), poly (tertiary butylstyrene), poly (phenylstyrene), poly (vinyl naphthalene), poly (vinyl styrene) Etc.). Examples of poly (halogenated styrene) include poly (chlorostyrene), poly (bromostyrene), poly (fluorostyrene) and the like. Examples of poly (halogenated alkylstyrene) include poly (chloromethylstyrene) and the like. Examples of poly (alkoxystyrene) include poly (methoxystyrene) and poly (ethoxystyrene).

The weight average molecular weight of the SPS resin is 10,000 to 3,000,000, preferably 30,000 to 1,500,000, and particularly preferably 50,000 to 500,000.

The melting point of the SPS resin is 200 to 320 ° C., preferably 220 to 280 ° C. The melting point is a value measured according to JIS K 7121 (1987).
The water absorption rate of the SPS resin is 0.005% to 0.20%, preferably 0.01% to 0.20%, particularly preferably 0.05% to 0.15%. The water absorption is a value measured using a 100 mm × 100 mm square test piece based on the 6.2A method of JIS K 7209 (2000).

The thermal expansion coefficient of the SPS resin is 80 ppm / ° C. or less, preferably 75 ppm / ° C. or less, particularly preferably 70 ppm / ° C. or less, in any of the MD direction and the TD direction. The smaller the thermal expansion coefficient, the better, but in the case of the base film 10 containing an SPS-based resin as a main component, it does not usually fall below 10 ppm / ° C. The absolute value of the difference between the MD direction and the TD direction of the thermal expansion coefficient is 50 ppm / ° C. or less, preferably 40 ppm / ° C. or less, particularly preferably 20 ppm / ° C. or less.

The absolute value of the thermal contraction rate of the SPS resin at 150 ° C. is 4.0% or less, preferably 2.0% or less, particularly preferably 1.5% or less in any of the MD direction and the TD direction. It is. The thermal contraction rate at 150 ° C is measured for 30 minutes at a temperature of 150 ° C and a length in the MD direction and TD direction after leaving a test piece of 200 mm × 200 mm for 2 hours at a temperature of 23 ° C. and a relative humidity of 50%. After leaving it to stand, it is a ratio of the amount of change with respect to the length before the test by determining the amount of change between the MD direction and the length in the TD direction after leaving for 2 hours under an environment of temperature 23 ° C. and relative humidity 50%.

Next, the manufacturing method of a base film, an insulation film, and a flat cable is shown.
First, SPS resin pellets are melted, kneaded, and extrusion molded to form an unstretched precursor film. This precursor film is simultaneously biaxially stretched or sequentially biaxially stretched to produce a substrate film for flat cable. In addition, it is preferable to perform a relaxation heat treatment in which the heat treatment is carried out by relaxing the tension at the time of biaxial stretching treatment after biaxial stretching. The stretching ratio, stretching temperature and stretching speed of biaxial stretching can be selected according to the desired coefficient of thermal expansion and tensile strain at break. The temperature and relaxation rate of relaxation heat treatment can be selected according to the heat shrinkage rate.
Next, the primer layer 11 and the adhesive layer 12 are laminated on one surface of the flat cable base film 10 to produce the flat cable insulating film 1 of FIG. 1 (a). An electromagnetic wave shield layer or the like may be provided on the other surface of the base film 10. The adhesive layer 12 may be provided directly on the base film 10 as in the insulating film 1 of FIG. 1 (b).
A flat cable is manufactured by preparing two insulating films 1, facing each other with an adhesive layer 12, sandwiching a conductor, bonding them while heating, and heat-sealing.

Example 1
SPS resin (made by Idemitsu Kosan Co., Ltd., Zarek, glass transition temperature 93 ° C, melting point 272 ° C), melt extruded at 320 ° C using an extruder with a T-die attached to the tip, and cooled to give a precursor A film (about 250 μm) was obtained. This precursor film is simultaneously biaxially stretched in the MD direction and TD direction at 110 ° C. at a drawing speed of 500% / min and a draw ratio of 3.3 × 3.4 (MD × TD), and then at 230 ° C. and a relaxation rate A relaxation heat treatment was performed at 94% × 96% (MD × TD) to obtain a 25 μm-thick base film (Example 1).
Example 2
SPS resin (made by Idemitsu Kosan Co., Ltd., Zarek, glass transition point 95 ° C, melting point 247 ° C), melt extruded at 320 ° C using an extruder equipped with a T-die at the tip, and cooled to give a precursor A film (about 500 μm) was obtained. This precursor film is simultaneously biaxially stretched in the MD direction and TD direction at 110 ° C. at a drawing speed of 500% / min and a draw ratio of 3.3 × 3.4 (MD × TD), and then at 230 ° C. and a relaxation rate A relaxation heat treatment was performed at 94% × 96% (MD × TD) to obtain a 50 μm thick base film (Example 2).

Comparative Example 1
A base film (made by Toray DuPont Co., Ltd., Kapton) made of a thermosetting polyimide resin having a thickness of 25 μm was prepared.
Comparative Example 2
A base film (Lumirror, manufactured by Toray Industries, Inc.) made of biaxially oriented polyethylene terephthalate (hereinafter, PET) resin having a thickness of 25 μm was prepared.
Comparative Example 3
Melt extrusion of SPS resin (made by Idemitsu Kosan Co., Ltd., Zarek, glass transition point 95 ° C, melting point 247 ° C) at 320 ° C using an extruder with a T-die attached to the tip, cooling and unstretching A base film (about 50 μm) was obtained.

[Measurement of dielectric constant and dielectric loss tangent at 1 GHz]
The base films of Examples 1 and 2 and Comparative Examples 1 and 2 were cut into a width of 1.5 mm and a length of 60 mm, and left for 48 hours under an environment of a temperature of 23 ° C. and a relative humidity of 50%. Thereafter, the relative dielectric constant and the dielectric loss tangent were measured twice at a frequency of 1 GHz in a test environment of a temperature of 23 (± 2) ° C. and a relative humidity of 50 (± 5)%, and the average value was determined. . As a measurement apparatus, PNA-L network analyzer N5230A manufactured by Agilent Technologies, Inc. and CP431 for cavity resonator 1 GHz manufactured by Kanto Electronics Application Development Co., Ltd. were used. The results are shown in Table 1.

The base film for flat cables of the present invention exhibited excellent values both in relative dielectric constant and dielectric loss tangent at a frequency of 1 GHz under an environment of a temperature of 23 ° C. and a relative humidity of 50%.

"Measurement of dielectric constant and dielectric loss tangent at 10 GHz"
The base films of Examples 1 and 2 and Comparative Examples 1 and 2 were cut into a width of 1.5 mm and a length of 60 mm, and left for 48 hours under an environment of a temperature of 23 ° C. and a relative humidity of 50%. Thereafter, the relative dielectric constant and the dielectric loss tangent were measured twice each at a frequency of 10 GHz in a test environment with a temperature of 23 (± 2) ° C. and a relative humidity of 50 (± 5)%, and the average value was determined. . As a measurement apparatus, PNA-L network analyzer N5230A manufactured by Agilent Technologies, Inc. and CP 531 for cavity resonator 10 GHz manufactured by Kanto Electronics Application Development Co., Ltd. were used.
Similarly, the base films of Examples 1 and 2 and Comparative Examples 1 and 2 were cut into a width of 1.5 mm and a length of 60 mm, and left for 48 hours under the environment of 60 ° C. and 90% relative humidity. After removing each base film from the above environment, the frequency is 10 GHz in a test environment with a temperature of 23 (. +-. 2) .degree. C. and a relative humidity of 50 (. +-. 5)% for 10 minutes to 15 minutes. Each relative dielectric constant and dielectric loss tangent were measured twice each, and the average value was calculated. The results of relative dielectric constant are shown in Table 2, and the results of dielectric loss tangent are shown in Table 3.

As shown in Table 2, the relative dielectric constants of Examples 1 and 2 were as excellent as 2.5 or less under any environment. Furthermore, the rate of change was only 1.3%.

As shown in Table 2, the dielectric loss tangents of Examples 1 and 2 were as excellent as 0.002 or less under any environment.

Physical properties of the base films of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 4. In addition, tensile fracture stress, tensile fracture nominal strain, tensile elastic modulus, coefficient of thermal expansion, and coefficient of thermal contraction show values in the MD direction and TD direction (MD / TD). The tensile breaking stress and the tensile modulus of elasticity were determined under the same conditions as tensile breaking nominal strain (JIS K 7127, test piece type 2, 200 mm / min). The heat shrinkage rate (200 ° C.) was determined under the same conditions as the heat shrinkage rate (150 ° C.) except that the heat shrinkage rate (200 ° C.) was left for 30 minutes.

* 1: The unstretched substrate film of Comparative Example 3 was broken without yielding.

"An endurance test"
The base films of Example 1 and Comparative Example 2 were cut out to have a width of 100 mm and a length of 150 mm. The test pieces of the base film of Example 1 and Comparative Example 2 were left to stand for 50 hours, 100 hours, 150 hours, and 200 hours, respectively, in a suspended state under an environment of a temperature of 120 ° C. and a relative humidity of 100%. The state of each base film in each condition was confirmed. The results are shown in Table 5.

○: not broken even when bent :: broken when bent ×: broken when touched * Stopped at 2: 150 hours

The base film of Comparative Example 2 was degraded by hydrolysis only when it was left under an environment of a temperature of 120 ° C. and a relative humidity of 100% for 50 hours. On the other hand, in the base film of Example 1, no change was observed in the film even after being left under the above environment for 200 hours. It turns out that the base film of Example 1 is superior to the base film of Comparative Example 2 in hydrolysis resistance.

1 insulating film 10 substrate film 11 primer layer 12 adhesive layer

Claims

At a temperature of 23 ° C., a relative humidity of 50%, and a frequency of 10 GHz, the dielectric constant is 2.5 or less, and the dielectric loss tangent is 0.005 or less,
Biaxially oriented, containing syndiotactic polystyrene based resin
Substrate film for flat cables.
At a temperature of 60 ° C., a relative humidity of 90%, and a frequency of 10 GHz, the relative dielectric constant is 2.5 or less, and the dielectric loss tangent is 0.005 or less.
The base film for flat cables according to claim 1.
The rate of change of the relative dielectric constant of the base film at a temperature of 60 ° C., a relative humidity of 90% and a frequency of 10 GHz relative to the relative dielectric constant of the base film at a temperature of 23 ° C. and a relative humidity of 50% and a frequency of 10 GHz Less than
The base film for flat cables according to claim 2.
Nominal strain at break is 15% or more at room temperature
The base film for flat cables according to any one of claims 1 to 3.
The glass transition point is 140 ° C. or higher,
The base film for flat cables according to any one of claims 1 to 4.
The coefficient of thermal expansion is 80 ppm / ° C. or less
The base film for flat cables according to any one of claims 1 to 5.
An insulating film for flat cable, comprising the substrate film for flat cable according to any one of claims 1 to 6 and an adhesive layer provided on the substrate film.