JP2020072204A - Resin film, metal layer integrated resin film, and film capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin film capable of suppressing a decrease rate of an insulation resistance value (IR) in a life test of a capacitor element. SOLUTION: A volume resistance calculated from a current value after 1 minute has passed by containing a crystalline thermoplastic resin as a main component and applying a voltage so as to have a potential gradient of 200 V / μm in an atmosphere of 23 ° C. A voltage was applied so that the product [ρV23 ° C. × εr23 ° C.] of the rate ρV23 ° C. and the relative permittivity εr23 ° C. was 1 × 1016 Ω · cm or more and the potential gradient was 200 V / μm in an atmosphere of 100 ° C. A resin film having a product [ρV100 ° C. × εr100 ° C.] of a volumetric resistance ρV100 ° C. and a relative permittivity εr100 ° C. calculated from the current value after 1 minute of 1 minute of 1 × 1014 Ω · cm or more. [Selection diagram] None

Description

  The present invention relates to a resin film, a metal layer-integrated resin film, and a film capacitor.

  The polypropylene film has excellent electrical characteristics such as high withstand voltage and low dielectric loss characteristics, and also has high humidity resistance. Therefore, it is widely used in electronic devices and electric devices. Specifically, it is used as a film used in, for example, high voltage capacitors, various switching power supplies, filter capacitors (for example, converters, inverters, etc.), smoothing capacitors, and the like.

  In recent years, further miniaturization and higher capacity of capacitors have been required. In order to improve the capacitance without changing the volume of the capacitor, it is preferable to make the film as a dielectric thin. Therefore, there is a demand for a film having a thinner thickness.

  In recent years, polypropylene films have begun to be widely used as capacitors for inverter power supply devices that control drive motors of electric vehicles, hybrid vehicles, and the like. Capacitors for inverter power supplies used in automobiles, etc. are required to have small size, light weight, high capacity, and high withstand voltage over a wide temperature range (for example, -40 ° C to 90 ° C) for a long period of time. ..

Patent Document 1 describes a polypropylene film having a volume resistivity at 110 ° C. of 5 × 10 ¹⁴ Ω · cm or more (see claim 5). Further, there is a description that reliability may be impaired when the volume resistivity at 110 ° C. is less than 5 × 10 ¹⁴ Ω · cm (see paragraph [0028]). Further, regarding the reliability evaluation, there is a description that the capacitor element was disassembled and the state of destruction was examined to evaluate the reliability (paragraph [0147]). Specifically, it is stepwise at 50 VDC / 1 min. It is evaluated whether or not penetrating destruction is observed after increasing the voltage until the capacitance decreases to 10% or less of the initial value by repeatedly increasing the applied voltage with. (Paragraphs [0141], [0147] -paragraph [0151]). Generally, as an index showing the electrical insulation property, it can be roughly classified into "dielectric breakdown" that occurs when a voltage is applied and "insulation deterioration" that gradually progresses by applying a voltage for a long time. In Patent Document 1, since a high voltage is applied and evaluated in a short time, it is considered that the penetrating breakdown indicates dielectric breakdown, and it is considered that the former characteristic is good. .. That is, Patent Document 1 describes that when the volume resistivity at 110 ° C. is set to a predetermined value or more, the penetration-like dielectric breakdown is suppressed and the dielectric strength in a short time is good. Conceivable.

International Publication No. 2016/182003

  On the other hand, the present inventors are investigating a highly reliable capacitor that can withstand long-term use, and for example, even if it is possible to suppress a decrease in capacitance in a 1000-hour life test, the long-term use is not always guaranteed. We have found that it cannot be said to be usable. In other words, in the life test of the capacitor, it is impossible to perform the test under the same conditions as the actual usage conditions and for the same time as the actual usage, so it is considered that the load is somewhat higher than the actual usage conditions. After that, the measurement is stopped in a shorter time than the actually expected service life (for example, 1000 hours), and it is judged at this point whether or not it can withstand long-term use. It was found that even if the decrease in electrostatic capacity could be suppressed in the 1000-hour life test, it could not be said that it could withstand long-term use.

  The present inventors diligently studied the above findings. As a result, they have found that by suppressing the rate of decrease in the insulation resistance value (IR) of the capacitor element in the life test, a highly reliable capacitor that can withstand long-term use can be obtained. More specifically, for example, in the life test, even if the decrease in the capacitance of the capacitor element can be suppressed, the insulation resistance value (IR) of the capacitor element is greatly decreased compared to the initial value. I realized there were cases. In such a case, if the test is continued thereafter, the amount of heat generated increases due to the decrease in the insulation resistance value (IR) of the capacitor element, and the capacitance of the capacitor element decreases exponentially. As a result, the performance will drop sharply. In other words, the inventors of the present invention evaluate the degree of deterioration of the capacitance of the capacitor element in the life test during the life test period, and clarify how the performance after the life test becomes. I thought that it was not something I could grasp. On the other hand, the reduction amount (reduction rate) of the insulation resistance value (IR) of the capacitor element is an index that can evaluate the degree of deterioration within the life test period, and also an index that can evaluate the degree of deterioration progress after the life test. I thought. That is, if the decrease rate of the insulation resistance value (IR) of the capacitor element is large during the life test period, if the test is continued after that, the capacitance will decrease exponentially and the performance will decrease sharply. Therefore, it was considered that this is an index that can also evaluate the degree of deterioration progress after the life test.

  However, it has been unclear how to suppress the decrease of the insulation resistance value (IR) in the life test of the capacitor element.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a resin film capable of suppressing a decrease rate of an insulation resistance value (IR) of a capacitor element in a life test. The present invention also provides a metal layer-integrated resin film having the resin film, and a film capacitor having the metal layer-integrated resin film.

  The present inventors diligently studied this point. As a result, it has been surprisingly found that the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test can be suppressed by setting the product of the volume resistivity and the relative permittivity of the resin film to a predetermined value or more. The present invention has been completed.

  Incidentally, conventionally, in the life test of the capacitor element, it is generally considered that it can be evaluated that there is no problem in the performance of the capacitor as long as the decrease in the capacitance can be suppressed, and the insulation resistance value (IR) is If there is no problem with the initial value, detailed examination of the subsequent decline rate has not been performed.

  Further, as described above, in Patent Document 1, when the volume resistivity of the film at 110 ° C. is set to a predetermined value or more, it is possible to suppress the capacitance decrease of the capacitor element, and when a high voltage is applied. It is thought that it is described that short-term dielectric breakdown can be prevented, but by setting the value of the volume resistivity of the film or the product of the volume resistivity and the relative dielectric constant to a predetermined value or more, the life test There is no description that the reduction rate of the insulation resistance value (IR) of the capacitor element can be suppressed.

  Although the details will be described later, the method for measuring the volume resistivity of the film in Patent Document 1 is different from the method for measuring the volume resistivity of the film of the present invention. In the method of measuring volume resistivity in Patent Document 1, it is not possible to obtain a correlation between the value of volume resistivity and the rate of decrease in insulation resistance value (IR) of the capacitor element in the life test. Therefore, even if a resin film having a volume resistivity of not less than a predetermined value obtained by the method for measuring volume resistivity in Patent Document 1 is obtained, the resin film has an insulation resistance value (IR) of a capacitor element in a life test. It does not mean that the rate of decrease in

The resin film according to the present invention,
Contains crystalline thermoplastic resin as the main component,
The product of the volume resistivity ρ _{V23 °} C. at 23 ° C. measured by the following measuring method (1) and the relative dielectric constant ε _{r23 °} C. at 23 ° C. measured by the following measuring method (2) [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more,
The product of the volume resistivity ρ _{V100 °} C. at 100 ° C. measured by the following measuring method (3) and the relative dielectric constant ε _{r100 °} C. at 100 ° C. measured by the following measuring method (4) [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more.
<Measurement method>
(1) A voltage is applied in an atmosphere of 23 ° C. so that the potential gradient is 200 V / μm, and the value is calculated from the current value at the time when one minute has elapsed by the following formula.
ρ _{V23 ° C.} = [(effective electrode area) × (applied voltage)] / [(thickness of resin film) × (current value)]
(2) A conductive paste is applied to both sides of the resin film and dried to form electrodes, and a conductive wire is attached to the obtained electrodes using the conductive paste, and the capacitance C of the obtained test capacitor is set to 23 ° C. It is measured in an atmosphere, and ε _{r23 ° C.} is calculated using the following formula.
(Capacitance C) = (ε _{r23 ° C.} ) × (vacuum dielectric constant ε ₀ ) × [(electrode area) / (resin film thickness)]
(3) A voltage is applied so that the potential gradient becomes 200 V / μm in an atmosphere of 100 ° C., and the value is calculated from the current value at the time when 1 minute has elapsed by the following formula.
ρ _{V100 ° C.} = [(effective electrode area) × (applied voltage)] / [(thickness of resin film) × (current value)]
(4) A conductive paste is applied to both sides of the resin film and dried to form an electrode, a conductor is attached to the obtained electrode using the conductive paste, and the capacitance C of the obtained test capacitor is set to 100 ° C. It is measured in an atmosphere, and ε _{r100 ° C.} is calculated using the following formula.
(Capacitance C) = (ε _{r100 ° C.} ) × (vacuum dielectric constant ε ₀ ) × [(electrode area) / (resin film thickness)]

Conventionally, in a general method for measuring a volume resistivity of a film, the number of digits is a reliable value as the accuracy of the measured value, and a value more detailed than the number of digits is regarded as an error range. However, the volume resistivity of the film measured with an accuracy of the order of magnitude cannot obtain a clear correlation with the reduction rate of the insulation resistance value (IR) in the life test of the capacitor element manufactured from the film.
On the other hand, in the present invention, the volume resistivity ρ _{V23 °} C at 23 ° _C is measured by the above measuring method (1), and the volume resistivity _{ρV100 °} C at 100 ° _C is measured by the above measuring method (3). Thereby, the volume resistivity of the film can be obtained with higher accuracy than the order of magnitude. In the volume resistivity measuring method of the present invention, one of the reasons for improving accuracy is that the potential gradient is constant (200 V / μm in the present invention).
In general, within the range where Ohm's law holds, the volume resistivity becomes constant regardless of the voltage (regarding the potential gradient). However, in the region where the Ohm's law does not hold (high electric field region), the volume resistivity differs depending on the voltage at the time of measurement. Specifically, the higher the voltage at the time of measurement (the higher the potential gradient), the lower the volume resistivity is measured. Therefore, it is important to compare the volume resistivities of the films under the condition that the potential gradients are uniform.
In the present invention, in order to obtain the volume resistivity while keeping the potential gradient constant, for example, when the volume resistivity of a plurality of types of films is measured, in the conventional method, since the number of digits is the same, the volume resistivity is almost the same. It is possible to make the values that were evaluated as "clearly different". Then, as can be seen from the examples, there is a good correlation between the volume resistivity of the film obtained by the method for measuring the volume resistivity of the present invention and the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test. can get. The relative permittivity is a value peculiar to the molecular structure and crystal form of the resin film. Therefore, the product of the volume resistivity and the relative permittivity in the present invention also has a good correlation with the reduction rate of the insulation resistance value (IR) in the life test.
From the above, the higher the volume resistivity of the film in the present invention, the more the decrease rate of the insulation resistance value (IR) of the capacitor element in the life test is suppressed.
If the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, it can withstand actual long-term use in a 23 ° C. (normal temperature) atmosphere.
Further, if the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more, it can withstand actual long-term use in a 100 ° C. (high temperature) atmosphere.
When the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, it is assumed that the product [ρ _V100 can be used for a long period of time under an atmosphere of 23 ° C. (normal temperature). _{[° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more, it can be said that it can withstand actual long-term use in a 100 ° C. (high temperature) atmosphere as an evaluation criterion in a life test. If the value is more than the above value, it is assumed that the possibility of withstanding actual long-term use is extremely high.

In the present invention, the volume resistivity [rho _V23 instead _{° C.,} using a product _{[ρ V23 ℃ × ε r23 ℃} ] of the volume resistivity [rho _{V23 ° C.} and a relative dielectric constant ^{_{ε r23 ℃, 1 × 10 16}} Ω · cm The reason is as follows.
As described above, the higher the volume resistivity of the film in the present invention, the more the decrease rate of the insulation resistance value (IR) of the capacitor element in the life test is suppressed. Therefore, the larger the volume resistivity, the more preferable.
On the other hand, the larger the relative permittivity, the higher the ability to store electricity. That is, if the electrode area is the same, the larger the relative permittivity, the larger the capacitance as a capacitor. Therefore, the larger the relative dielectric constant, the more preferable.
Here, when considering resin materials, various materials such as those having a relatively large volume resistivity but a relatively small relative permittivity, and those having a relatively small volume resistivity but a relatively large relative permittivity are used. Exists.
When examining such various materials, for those with a relatively large volume resistivity of the film, the leakage current of the capacitor element during the life test period is suppressed small, as a result of suppressing the heat generation of the capacitor element, Since the decrease in insulation resistance (IR) will be further suppressed, it is expected that the degree of progress of deterioration will be slower. Therefore, even if the relative permittivity is relatively small, it is considered that the device can withstand actual long-term use in terms of performance.
On the other hand, in the case where the film has a relatively low volume resistivity, the insulation resistance (IR) of the capacitor element tends to decrease as compared with the film having a relatively high volume resistivity, and the degree of deterioration progresses slightly faster. is expected. However, when the relative permittivity is relatively large, the ability to store electricity is originally high. Therefore, (A) the film area (electrode area) required to obtain the target capacitance can be reduced, or (B) the film thickness can be increased while maintaining the film area. As a result, the leakage current of the capacitor element during the life test period can be reduced and heat generation can be suppressed.
This point will be described in more detail.
It is assumed that capacitors having the same capacitance are manufactured by using films having different relative dielectric constants. Under this assumption, using a film having a relatively large relative dielectric constant is advantageous in that it can be selected from the following three ways (1) to (3) as an option for achieving reduction of leakage current. Is.
(1) The film area used is reduced while maintaining the film thickness.
(2) Make the film thick without changing the film area.
(3) Taking advantage of the former two, make the film a little thicker and make the film area a little smaller.
From the above, it is considered that the decrease in the insulation resistance (IR) of the capacitor element is further suppressed, and the capacitor element can withstand actual long-term use.
Therefore, we decided to use the product of volume resistivity and relative permittivity as an index of whether or not it can withstand actual long-term use.

Further, as described above, the relative dielectric constant is a value peculiar to the molecular structure (conformation or packing) of the resin film, but the conventional relative dielectric constant measuring method accurately measures the relative dielectric constant of a thin film. It was difficult to do.
On the other hand, in the present invention, the relative dielectric constant ε _{r23 °} C. at 23 ° _C. is measured by the above measuring method (2), and the relative dielectric constant ε _{r100 °} C. at 100 ° _C. is measured by the above measuring method (4). This makes it possible to measure the relative permittivity easily and with good reproducibility even with a thin resin film.
From the above, more accurate values can be obtained for the value of the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] and the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ].
As a result, a more accurate value can be obtained as an index of whether or not it can withstand actual long-term use.

In Patent Document 1, a voltage of 100 V is applied for 1 minute, and the volume resistivity is calculated from the volume resistance value after 1 minute has elapsed (see paragraph [0137]). The film thickness is not taken into consideration when applying the voltage. For example, the film of Example 8 has a thickness of 2.3 μm, but the potential gradient is about 43.5 V / μm (100 V / 2.3 μm). On the other hand, the film of Example 9 has a thickness of 5.8 μm, but the potential gradient is about 17.2 V / μm (100 V / 5.8 μm). As described above, in the region where the Ohm's law does not hold (high electric field region), the volume resistivity is different depending on the voltage at the time of measurement. Therefore, in the volume resistivity measuring method as disclosed in Patent Document 1, I have to say that the accuracy is low.
Therefore, even if the volume resistivity is measured by the method of Patent Document 1, it is not possible to obtain a clear correlation with the rate of decrease in the insulation resistance value (IR) of the capacitor element in the life test.
In the first place, in Patent Document 1, the volume resistivity is intended to suppress the through-like breakdown of the film when a high voltage is applied and to have good initial characteristics, and to evaluate the quality of the capacitor element in long-term use. Not intended. Therefore, it must be said that Patent Document 1 has no motivation to use the value of the volume resistivity to perform an evaluation that can withstand long-term use of the capacitor element.

  In the present specification, the "life test" is an accelerated test that promotes deterioration of the capacitor element under a condition where a temperature or voltage that is more severe than the actual operating conditions is applied, and the actually expected useful service time is A test in which measurement is discontinued in a shorter time (for example, 1000 hours), and whether or not it can withstand long-term use is estimated and evaluated by evaluation at this point.

Furthermore, in the resin film according to the present invention, the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, and the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10. ^{Since it is 14} Ω · cm or more and the decrease in the insulation resistance (IR) of the capacitor element is suppressed, the decrease in the capacitance C is also suppressed. As a result, the decrease in (C · IR) is also suppressed.
It is generally known that when the capacitance C of a capacitor is large (for example, the electrode area is large and the thickness of the dielectric is thin), the insulation resistance (IR) is small (current easily leaks). ing. In general, “CR product (electrostatic capacity × insulation resistance)” is used as an index for fairly comparing capacitors even if the electrostatic capacity C is different. (C · IR) in this specification is synonymous with this CR product, and is excellent in that capacitors can be compared fairly even if the electrostatic capacitance C is different.

  The resin film having the above-described structure preferably has a thickness within the range of 0.8 to 6 μm.

When the thickness is 6 μm or less, the decrease in capacitance can be further suppressed. Further, since the decrease in capacitance can be further suppressed, the decrease rate (%) of (C · IR) can be further suppressed.
Further, when the thickness of the resin film is 6 μm or less, the capacitance per unit volume of the capacitor element can be increased, so that it can be suitably used for capacitors. In addition, it is preferable that the thickness of the resin film is 0.8 μm or more from the viewpoint of film forming stability.

  The resin film having the above structure is preferably for capacitors.

The resin film having a product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] and a product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] equal to or greater than a predetermined value suppresses the reduction rate of the insulation resistance value (IR) in the life test of the capacitor element. Therefore, it can be suitably used for capacitors.

  The resin film having the above structure is preferably biaxially stretched.

When biaxially stretched, it is easy to _obtain a resin film having a product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] and a product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] of a predetermined value or more.

  The resin film having the above-described structure preferably has a thickness within a range of 0.8 to 22 μm.

  When the thickness is in the range of 0.8 to 22 μm, the electrostatic capacity can be increased, so that it can be suitably used for capacitors.

  In the resin film having the above structure, the crystalline thermoplastic resin has (a) a main chain of an aliphatic hydrocarbon, (b) an amide bond in the main chain, (c) an ether bond in the main chain, Of these, it is preferable to satisfy at least one.

  A crystalline thermoplastic resin satisfying at least one of (a) the main chain is an aliphatic hydrocarbon, (b) having an amide bond in the main chain, and (c) having an ether bond in the main chain, Melting point is relatively high. Therefore, when the crystalline thermoplastic resin satisfies at least one of the above (a) to (c), it has excellent heat resistance.

  In the resin film having the above structure, it is also preferable that at least one hydrogen atom is bonded to each carbon atom forming the main chain of the crystalline thermoplastic resin.

  When at least one hydrogen atom is bonded to each carbon atom forming the main chain of the crystalline thermoplastic resin, it is suitable as a dielectric. For example, when only a chlorine atom or a fluorine atom is bonded to a carbon atom constituting the main chain, and a hydrogen atom is not bonded, it may become a ferroelectric substance, and when a voltage is applied, a film due to an inverse piezoelectric effect is formed. Deformation (distortion) is a concern. It should be noted that even a ferroelectric material cannot be used for a capacitor.

In the resin film having the above structure, the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more,
The product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more,
The relative permittivity ε _{r100 ° C.} is preferably 2 or more and 5 or less.

The product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more, and the ratio is When the dielectric constant ε _{r100 ° C.} is 2 or more and 5 or less, the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test is further suppressed.

In the resin film having the above structure, it is preferable that log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )] is 5 or less.

When the log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )] is 5 or less, the insulation resistance in the life test is 23 ° C. (normal temperature) and 100 ° C. (high temperature). It can be said that the difference in the rate of decrease in the value (IR) is small. That is, the log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )] can be used as an index showing heat resistance, and when this index is 5 or less, It can be said that it has excellent heat resistance.

  In the resin film having the above structure, the crystalline thermoplastic resin is preferably a polypropylene resin.

  Since the polypropylene resin is a resin having a relatively high volume resistivity, when the crystalline thermoplastic resin is a polypropylene resin, it is possible to suitably suppress the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test. ..

  The ash content in the resin forming the resin film is preferably 5 ppm or more and 35 ppm or less.

  When the ash content in the resin (raw material resin) forming the resin film is 5 ppm or more and 35 ppm or less, the electrical characteristics of the capacitor can be improved while suppressing the generation of polar low-molecular components.

  In the resin film having the above structure, the heptane-insoluble content is preferably 96% or more and 99.5% or less.

  The more heptane-insoluble matter, the higher the stereoregularity of the resin. When the heptane insoluble content (HI) of the resin film is 96% or more and 99.5% or less, the crystallinity of the resin is appropriately improved due to the moderately high stereoregularity, and the withstand voltage property at high temperature is increased. improves. On the other hand, the rate of solidification (crystallization) at the time of forming the cast raw sheet becomes appropriate, and it has an appropriate stretchability.

  In the resin film having the above structure, the molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] is preferably 5 or more and 12 or less.

  When the molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the resin film is within the above range, proper resin fluidity can be obtained during biaxial stretching, and ultrathinization without unevenness in thickness can be achieved. It becomes easy to obtain the biaxially stretched polypropylene film. In addition, by adjusting the distribution structure of the high molecular weight component and the low molecular weight component, it is possible to further improve the withstand voltage of the capacitor formed using the biaxially stretched resin film.

  In the resin film having the above structure, the crystallite size obtained by using the Scherrer's formula from the half-value width of the reflection peak of the α crystal (040) plane measured by the wide-angle X-ray diffraction method is 9 nm or more and 15 nm or less. Preferably.

  When the crystallite size of the resin film is 15 nm or less, the leakage current becomes small, and the withstand voltage property at room temperature or high temperature is preferably improved. On the other hand, the crystallite size of 9 nm or more is preferable from the viewpoint of maintaining the mechanical strength and melting point of the resin film (particularly polypropylene film).

  In the resin film having the above structure, the plane orientation coefficient is preferably 0.010 to 0.016.

  It is preferable that the plane orientation coefficient of the resin film is within the above range because the dielectric breakdown under high temperature and high voltage can be further reduced.

  The melting point of the resin film having the above structure is preferably 170 ° C. or higher and 176 ° C. or lower.

  When the melting point of the resin film is 170 ° C. or higher, the withstand voltage property at high temperature and the thermal dimensional stability are excellent. On the other hand, when the temperature is 176 ° C. or lower, the rigidity of the film becomes appropriate and the stretched film can be easily formed.

  In the resin film having the above structure, the melting enthalpy is preferably 90 J / g or more and 125 J / g or less.

  It is preferable that the resin film has a enthalpy of fusion of 90 J / g or more because the crystallite becomes strong. On the other hand, when it is 125 J / g or less, the crystallite size is appropriately reduced, which is preferable.

In addition, the metal layer integrated resin film according to the present invention,
With the resin film,
It has a metal layer laminated on one side or both sides of the resin film.

According to the above configuration, since the resin film has the metal layer laminated on one side or both sides, the resin film can be used as a dielectric and the metal film can be used as a film capacitor. The product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, and the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more. Since it has the resin film, the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test is suppressed.

  Further, the film capacitor according to the present invention is characterized by having the wound metal layer-integrated resin film or having a configuration in which a plurality of the metal layer-integrated resin films are laminated.

  ADVANTAGE OF THE INVENTION According to this invention, the resin film which can suppress the fall rate of the insulation resistance value (IR) of the capacitor element in a life test can be provided. Further, it is possible to provide a metal layer-integrated resin film having the resin film, and a film capacitor having the metal layer-integrated resin film.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to these embodiments.

  In this specification, the expressions "containing" and "including" include the concepts of "containing", "including", "consisting essentially of" and "consisting solely of".

  In this specification, "element", "capacitor", "capacitor element" and "film capacitor" mean the same thing.

The resin film according to the present embodiment,
Contains crystalline thermoplastic resin as the main component,
The product of the volume resistivity ρ _{V23 °} C. at 23 ° C. measured by the following measuring method (1) and the relative dielectric constant ε _{r23 °} C. at 23 ° C. measured by the following measuring method (2) [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more,
The product of the volume resistivity ρ _{V100 °} C. at 100 ° C. measured by the following measuring method (3) and the relative dielectric constant ε _{r100 °} C. at 100 ° C. measured by the following measuring method (4) [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more.
<Measurement method>
(1) A voltage is applied in an atmosphere of 23 ° C. so that the potential gradient is 200 V / μm, and the value is calculated from the current value at the time when one minute has elapsed by the following formula.
ρ _{V23 ° C.} = [(effective electrode area) × (applied voltage)] / [(thickness of resin film) × (current value)]
(2) A conductive paste is applied to both sides of the resin film and dried to form electrodes, and a conductive wire is attached to the obtained electrodes using the conductive paste, and the capacitance C of the obtained test capacitor is set to 23 ° C. It is measured in an atmosphere, and ε _{r23 ° C.} is calculated using the following formula.
(Capacitance C) = (ε _{r23 ° C.} ) × (vacuum dielectric constant ε ₀ ) × [(electrode area) / (resin film thickness)]
(3) A voltage is applied so that the potential gradient becomes 200 V / μm in an atmosphere of 100 ° C., and the value is calculated from the current value at the time when 1 minute has elapsed by the following formula.
ρ _{V100 ° C.} = [(effective electrode area) × (applied voltage)] / [(thickness of resin film) × (current value)]
(4) A conductive paste is applied to both sides of the resin film and dried to form an electrode, a conductor is attached to the obtained electrode using the conductive paste, and the capacitance C of the obtained test capacitor is set to 100 ° C. It is measured in an atmosphere, and ε _{r100 ° C.} is calculated using the following formula.
(Capacitance C) = (ε _{r100 ° C.} ) × (vacuum dielectric constant ε ₀ ) × [(electrode area) / (resin film thickness)]

The measurement method (1) will be described in detail. In the following description, measurement conditions not particularly described are based on JIS C2139.
First, a volume resistivity measuring jig (hereinafter, also simply referred to as “jig”) is placed in a constant temperature bath of 23 ° C. environment. The structure of the volume resistivity measuring jig is as follows. A DC power supply and a DC ammeter are connected to each electrode of the jig.
<Jig for measuring volume resistivity>
Main electrode (diameter 50mm)
Counter electrode (85 mm diameter)
Ring-shaped guard electrode surrounding the main electrode (outer diameter 80 mm, inner diameter 70 mm)
Each electrode is made of gold-plated copper, and conductive rubber is attached to the surface in contact with the sample. The conductive rubber used was EC-60BL (W300) manufactured by Shin-Etsu Silicone Co., Ltd., which was attached so that the glossy surface of the conductive rubber was in contact with the gold-plated copper.

  Next, the resin film (hereinafter, also referred to as a sample) is placed in an environment of 23 ° C. and 50% RH for 24 hours. Then, the sample is set in a jig in a constant temperature bath. Specifically, the main electrode and the guard electrode are brought into close contact with one surface of the sample, the counter electrode is brought into close contact with the other surface, and the sample and the respective electrodes are brought into close contact with a load of 5 kgf. Then, let stand for 30 minutes.

  Next, a voltage is applied to the sample so that the potential gradient becomes 200 V / μm.

After applying the voltage, the current value at the time when one minute has elapsed is read, and the volume resistivity is calculated by the following formula. In addition, 2290-10 (DC power supply) manufactured by Keithley is used for voltage application, and 2635B (DC ammeter) manufactured by Keithley is used for measurement of current value.
Volume resistivity = [(effective electrode area) × (applied voltage)] / [(thickness of sample) × (current value)]

Here, the effective electrode area is obtained by the following formula.
(Effective electrode area) = π × [[[(diameter of main electrode) + (inner diameter of guard electrode)] / 2] / 2] ²

  In the present embodiment, the effective electrode area is not the area of the main electrode, and in the separated portion between the main electrode and the guard electrode, a portion that is the same as or closer to the main electrode is the effective electrode area. .. This enables more accurate current value measurement.

  The measurement method (1) has been described above.

Next, the measuring method (2) will be described in detail.
First, a mold having a diameter of 30 mm is applied to one surface of a resin film (hereinafter, also referred to as a sample), and the conductive paste is applied. After the solvent is sufficiently volatilized and the conductive paste does not flow out even if the mold is removed, the mold is removed and left for half a day. This forms an electrode. Next, an electrode is formed in the same manner on the other surface of the sample so as to sandwich the film and overlap with the previous electrode. As described above, a capacitor having electrodes with a diameter of 30 mm on each side is obtained.

  In order to connect the prepared capacitor to the measuring device, a conductive wire is connected to each electrode portion of the capacitor with a conductive paste. At this time, if the conductors face each other across the film, capacitance is also formed in the conductor portions, so the conductors are connected at positions as far apart as possible. The conductive wire is not particularly limited, but tin-plated copper may be used.

Next, each conductor is connected to a measuring device, and the capacitance C of the produced capacitor is measured. The measurement is carried out under the following conditions after standing still for 30 minutes in a constant temperature bath set at 23 ° C.
<Measurement conditions>
Applied voltage: 1V
Measurement frequency: 1 kHz

Then, the relative permittivity _{εr23 ° C.} is calculated using the following formula.
(Capacitance C) = (ε _{r23 ° C.} ) × (vacuum dielectric constant ε ₀ ) × [(electrode area) / (resin film thickness)]

  The measurement method (2) has been described above.

  The details of the above measuring method (3) are the same as the above measuring method (1) except that the temperature of the constant temperature bath is 100 ° C. Therefore, detailed description is omitted here.

  The details of the measuring method (4) are the same as the measuring method (2) except that the temperature of the constant temperature bath is 100 ° C. Therefore, detailed description is omitted here.

Conventionally, in a general method for measuring a volume resistivity of a film, the number of digits is a reliable value as the accuracy of the measured value, and a value more detailed than the number of digits is regarded as an error range. However, the volume resistivity of the film measured with an accuracy of the order of magnitude cannot obtain a clear correlation with the reduction rate of the insulation resistance value (IR) in the life test of the capacitor element manufactured from the film.
On the other hand, in the present embodiment, the volume resistivity ρ _{V23 °} C. at 23 ° _C. is measured by the above measuring method (1), and the volume resistivity ρ _{V100 °} C. at 100 ° _C. is measured by the above measuring method (3). .. Thereby, the volume resistivity of the film can be obtained with higher accuracy than the order of magnitude. In the method of measuring the volume resistivity in the present embodiment, one of the reasons for improving the accuracy is that the potential gradient is constant (200 V / μm in the present embodiment).
In general, within the range where Ohm's law holds, the volume resistivity becomes constant regardless of the voltage (regarding the potential gradient). However, in the region where the Ohm's law does not hold (high electric field region), the volume resistivity differs depending on the voltage at the time of measurement. Specifically, the higher the voltage at the time of measurement (the higher the potential gradient), the lower the volume resistivity is measured. Therefore, it is important to compare the volume resistivities of the films under the condition that the potential gradients are uniform.
In the present embodiment, in order to obtain the volume resistivity while keeping the potential gradient constant, for example, when the volume resistivity of a plurality of types of films is measured, in the conventional method, since the number of digits is the same, the volume resistivity is almost the same. It is possible that the values that were evaluated to be certain have different values. Then, as can be seen from the examples, the volume resistivity of the film obtained by the method of measuring the volume resistivity in the present embodiment and the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test have a good correlation. Is obtained. The relative permittivity is a value specific to the molecular structure (conformation or packing) of the resin film. Therefore, the product of the volume resistivity and the relative permittivity in this embodiment also has a good correlation with the reduction rate of the insulation resistance value (IR) in the life test.
Further, in the present embodiment, when calculating the volume resistivity from the measured current value, the effective electrode area is not the area of the main electrode, and the same as the main electrode in the separated portion between the main electrode and the guard electrode. , Or a portion closer to the main electrode is the effective electrode area. This enables more accurate current value measurement.
From the above, the higher the volume resistivity in the present embodiment, the more the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test is suppressed.
If the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, it can withstand actual long-term use in a 23 ° C. (normal temperature) atmosphere.
Further, if the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more, it can withstand actual long-term use in a 100 ° C. (high temperature) atmosphere.
When the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, it is assumed that the product [ρ _V100 can be used for a long period of time under an atmosphere of 23 ° C. (normal temperature). _{[° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more, it can be said that it can withstand actual long-term use in a 100 ° C. (high temperature) atmosphere as an evaluation criterion in a life test. If the value is more than the above value, it is assumed that the possibility of withstanding actual long-term use is extremely high.

Further, in the present embodiment, the volume resistivity [rho _V23 instead _{° C.,} using a product _{[ρ V23 ℃ × ε r23 ℃} ] of the volume resistivity [rho _{V23 ° C.} and a relative dielectric constant ^{_{ε r23 ℃, 1 × 10 16}} Ω · The reason why it is not less than cm is as follows.
As described above, the larger the volume resistivity of the film in the present embodiment, the more the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test is suppressed. Therefore, the larger the volume resistivity, the more preferable.
On the other hand, the larger the relative permittivity, the higher the ability to store electricity. That is, the larger the relative permittivity, the larger the capacitance as a capacitor. Therefore, the larger the relative dielectric constant, the more preferable.
Here, when considering resin materials, various materials such as those having a relatively large volume resistivity but a relatively small relative permittivity, and those having a relatively small volume resistivity but a relatively large relative permittivity are used. Exists.
When examining such various materials, for those with a relatively large volume resistivity of the film, the leakage current of the capacitor element during the life test period is suppressed small, as a result of suppressing the heat generation of the capacitor element, Since the decrease in insulation resistance (IR) will be further suppressed, it is expected that the degree of progress of deterioration will be slower. Therefore, even if the relative permittivity is relatively small, it is considered that the device can withstand actual long-term use in terms of performance.
On the other hand, in the case where the film has a relatively low volume resistivity, the insulation resistance (IR) of the capacitor element tends to decrease as compared with the film having a relatively high volume resistivity, and the degree of deterioration progresses slightly faster. is expected. However, when the relative permittivity is relatively large, the ability to store electricity is originally high. Therefore, (A) the film area (electrode area) required to obtain the target capacitance can be reduced, or (B) the film thickness can be increased while maintaining the film area. As a result, the leakage current of the capacitor element during the life test period can be reduced and heat generation can be suppressed.
This point will be described in more detail.
It is assumed that capacitors having the same capacitance are manufactured by using films having different relative dielectric constants. Under this assumption, using a film having a relatively large relative dielectric constant is advantageous in that it can be selected from the following three ways (1) to (3) as an option for achieving reduction of leakage current. Is.
(1) The film area used is reduced while maintaining the film thickness.
(2) Make the film thick without changing the film area.
(3) Taking advantage of the former two, make the film a little thicker and make the film area a little smaller.
From the above, it is considered that the decrease in the insulation resistance (IR) of the capacitor element is further suppressed, and the capacitor element can withstand actual long-term use.
Therefore, we decided to use the product of volume resistivity and relative permittivity as an index of whether or not it can withstand actual long-term use.

Further, as described above, the relative dielectric constant is a value peculiar to the molecular structure (conformation or packing) of the resin film, but the conventional relative dielectric constant measuring method accurately measures the relative dielectric constant of a thin film. It was difficult to do.
On the other hand, in the present embodiment, the relative permittivity ε _{r23 °} C. at 23 ° _C. is measured by the above measuring method (2), and the relative permittivity ε _{r100 °} C. at 100 ° _C. is measured by the above measuring method (4). .. This makes it possible to measure the relative permittivity easily and with good reproducibility even with a thin resin film.
From the above, more accurate values can be obtained for the value of the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] and the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ].
As a result, a more accurate value can be obtained as an index of whether or not it can withstand actual long-term use.

As described above, the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] of the resin film according to the present embodiment is 1 × 10 ¹⁶ Ω · cm or more. The product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is preferably 2 × 10 ¹⁶ Ω · cm or more, more preferably 3 × 10 ¹⁶ Ω · cm or more. Further, the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is preferably as large as possible, but can be, for example, 1 × 10 ²² Ω · cm or less and 1 × 10 ²¹ Ω · cm or less.

Moreover, as described above, the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] of the resin film according to the present embodiment is 1 × 10 ¹⁴ Ω · cm or more. The product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is preferably 2 × 10 ¹⁴ Ω · cm or more, more preferably 3 × 10 ¹⁴ Ω · cm or more, and 1 × 10 ¹⁵ Ω · cm or more. Is more preferable, 2 × 10 ¹⁵ Ω · cm or more is still more preferable, and 3 × 10 ¹⁵ Ω · cm or more is particularly preferable. Further, the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is preferably as large as possible, but can be, for example, 5 × 10 ¹⁹ Ω · cm or less and 1 × 10 ¹⁹ Ω · cm or less.

The volume resistivity ρ _{V23 ° C.} is preferably 1 × 10 ¹⁵ Ω · cm or more, more preferably 5 × 10 ¹⁵ Ω · cm or more. When the volume resistivity ρ _{V23 ° C.} is 1 × 10 ¹⁵ Ω · cm or more, the decrease rate of the insulation resistance value (IR) at 23 ° C. (normal temperature) is further suppressed. The volume resistivity ρ _{V23 ° C.} is preferably as large as possible, but may be, for example, 5 × 10 ²¹ Ω · cm or less and 5 × 10 ²⁰ Ω · cm or less.

The relative dielectric constant ε _{r23 ° C.} is preferably 2.0 or more, and more preferably 2.2 or more. When the relative permittivity ε _{r23 ° C.} is 2.0 or more, the capacitance as a capacitor can be increased. The relative permittivity ε _{r23 ° C.} is preferably as large as possible, but may be 9.0 or less and 5.0 or less, for example.

The volume resistivity ρ _{V100 ° C.} is preferably 5 × 10 ¹³ Ω · cm or more, more preferably 5 × 10 ¹⁴ Ω · cm or more. When the volume resistivity ρ _{V100 ° C.} is 5 × 10 ¹³ Ω · cm or more, the reduction rate of the insulation resistance value (IR) at 100 ° C. (high temperature) is further suppressed. The volume resistivity ρ _{V100 ° C.} is preferably as high as possible, but may be, for example, 3 × 10 ¹⁹ Ω · cm or less and 5 × 10 ¹⁸ Ω · cm or less.

The relative permittivity ε _{r100 ° C.} is preferably 2.0 or more, and more preferably 2.2 or more. When the relative permittivity ε _{r100 ° C.} is 2.0 or more, the capacitance as a capacitor can be further increased. The relative permittivity ε _{r100 ° C.} is preferably as high as possible, but can be, for example, 9.0 or less and 5.0 or less.

Among the resin films, the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, and the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁵ Ω. It is preferable that it is cm or more and the relative permittivity ε _{r100 ° C.} is 2 or more and 5 or less. The product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁵ Ω · cm or more, and the ratio is When the dielectric constant ε _{r100 ° C.} is 2 or more and 5 or less, the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test is further suppressed.

In the resin film, log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )] is preferably 5 or less, more preferably 3 or less, and preferably 2 or less. Is more preferable.

When the log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )] is 5 or less, a capacitor element in a life test at 23 ° C. (normal temperature) and 100 ° C. (high temperature) It can be said that there is little difference in the reduction rate of the insulation resistance value (IR). That is, the log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )] can be used as an index showing heat resistance, and when this index is 5 or less, It can be said that it has excellent heat resistance. The log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )] is preferably as small as possible, but is, for example, 0.01 or more, 0.1 or more, 0.5 or more.

The [ρ _{V23 ° C.} × ε _{r23 ° C.} ], the [ρ _{V100 ° C.} × ε _{r100 ° C.} ], and the log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )] are , (I) type selection of resin (raw material resin) constituting the resin film, stereoregularity, ash content, and molecular weight distribution, (ii) content of the resin with respect to the entire resin film, (iii) at the time of stretching Longitudinal and transverse stretching ratios, and transverse stretching angle, (iv) crystallinity and crystallite size of the resin film, (v) presence or absence of poling treatment of the resin and applied voltage in the treatment, (vi) additive ( In particular, it can be appropriately adjusted by selecting the type of the inorganic filler) and its content.
In this specification, the transverse stretching angle is as follows.
Lateral stretching angle: Both ends of the first line segment constituting the resin film width at the lateral stretching start point are defined by the first end and the second end, and the second line segment constituting the resin film width at the lateral stretching end point. When both ends are defined by a third end and a fourth end, and it is defined that the first end and the third end are located on one side of a reference virtual straight line extending from the midpoint of the first line segment along the flow direction, An angle formed by a first virtual straight line connecting the first end and the third end and a second virtual straight line extending along the flow direction from the first end (the angle is less than 90 °). The lateral stretching angle is preferably 8.5 ° or more, more preferably 9.0 ° or more. The transverse stretching angle is preferably 13.0 ° or less, more preferably 12.0 ° or less. When the transverse stretching angle is increased, [ρ _{V23 ° C.} × ε _{r23 ° C.} ] and [ρ _{V100 ° C.} × ε _{r100 ° C.} ] tend to be increased.

  The reduction rate of the insulation resistance value (IR) in the life test of the capacitor element manufactured using the resin film is preferably 50% or less, more preferably 25% or less, and further preferably 20% or less. , 15% or less is even more preferable, and 10% or less is particularly preferable. Further, the lowering rate of the insulation resistance value (IR) is preferably as small as possible, but may be, for example, −1000% or more, −500% or more, −100% or more. The decrease rate of the insulation resistance value (IR) is a value calculated by the following formula. The method for measuring the insulation resistance value of the capacitor element and the method for measuring the insulation resistance value after the life test are as follows.

<Measurement of insulation resistance value of capacitor element, measurement of insulation resistance value after life test, and calculation of decrease rate of insulation resistance value (IR)>
The insulation resistance value of the capacitor element is evaluated using a super insulation resistance meter DSM8104 manufactured by Hioki Electric Co., Ltd. The rate of decrease of the insulation resistance value is obtained by the following procedure. After allowing the capacitor element to stand at 23 ° C. for 24 hours, apply a voltage to the capacitor element with a potential gradient of 250 V / μm (however, 500 V when the film thickness is 2 μm or more), and insulate 1 minute after application. Measure the resistance. This is defined as the insulation resistance value before the life test. Next, the capacitor element is removed from the super insulation resistance meter, and the voltage is continuously applied (loaded) to the capacitor element with a DC high voltage power source at a potential gradient of 280 V / μm for 1000 hours in a thermostatic chamber at 105 ° C. After the lapse of 1000 hours, the capacitor element is removed, and then a discharge resistor is connected to the capacitor element to eliminate the charge. Then, the capacitor element is allowed to stand at 23 ° C. for 24 hours, after which the insulation resistance value of the capacitor element is measured. This is the insulation resistance value after the life test. Then, the reduction rate of the insulation resistance value is calculated. The reduction rate of the insulation resistance value is evaluated by the average value of two capacitors.
[Insulation resistance decrease rate (%)] = [[(insulation resistance value before life test)-(insulation resistance value after life test)] / ((insulation resistance value before life test)] * 100

The reduction rate of (C · IR) in the life test of the capacitor element manufactured using the resin film is preferably 50% or less, more preferably 30% or less, and 20% or less. It is more preferably 10% or less. The decrease rate (%) of (C · IR) is a value calculated by the following formula. When the (C / IR) decrease rate (%) is 50% or less, the self-heating of the capacitor element during the life test is suppressed to a low level, so that the deterioration of the resin film slows down and the capacitor can withstand long-term use. It is a highly reliable capacitor.
[(C · IR) decrease rate (%)] = [[(capacity of capacitor before life test) x (insulation resistance value before life test)-(capacitor capacity after life test) x (after life test) Insulation resistance value)] / [(capacity of capacitor before life test) x (insulation resistance value before life test)]] x 100

  The ash content in the resin constituting the resin film is preferably 35 ppm or less, more preferably 30 ppm or less, and further preferably 25 ppm or less. The ash content is preferably 5 ppm or more, more preferably 10 ppm or more, further preferably 15 ppm or more, further preferably 20 ppm or more. The ash content refers to a value obtained by the method described in Examples when a resin film containing no additive (see the description of an additive described later) is used as the resin film. On the other hand, when a resin film containing an additive is used as the resin film, it means a value obtained by the method described in the examples using a resin film for ash content measurement prepared only with the raw material resin.

  The ash content in the resin (raw material resin) forming the resin film is preferably 5 ppm or more and 35 ppm or less in order to improve the electrical characteristics of the capacitor while suppressing the generation of polar low-molecular components.

  The heptane-insoluble content of the resin film is preferably 96% or more and 99.5% or less, more preferably 97.0% or more and 99.3% or less, and 97.5% or more and 99.0%. The following is more preferable. The heptane-insoluble matter is measured by the method described in Examples.

  The more heptane-insoluble matter, the higher the stereoregularity of the resin. When the heptane insoluble content (HI) of the resin film is 96% or more and 99.5% or less, the crystallinity of the resin is appropriately improved due to the moderately high stereoregularity, and the withstand voltage property at high temperature is increased. improves. On the other hand, the rate of solidification (crystallization) at the time of forming the cast raw sheet becomes appropriate, and it has an appropriate stretchability.

  The weight average molecular weight Mw of the resin film and the number average molecular weight Mn of the resin film are not particularly limited.

  The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the resin film is preferably 5 or more and 12 or less, more preferably 5.2 or more and 10.5 or less. It is more preferably 5 or more and 9 or less.

  When the molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the resin film is within the above numerical range, appropriate resin fluidity can be obtained when the stretching step is performed, and there is no thickness unevenness. It is preferable because it is easy to obtain a film. It is also preferable from the viewpoint of withstand voltage when used as a capacitor.

  In the present specification, the weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the resin film are values measured using a gel permeation chromatograph (GPC) device. is there. More specifically, it is a value measured using HLC-8121GPC-HT (trade name), a high temperature GPC measuring instrument with a built-in differential refractometer (RI) manufactured by Tosoh Corporation. As a GPC column, three TSKgel GMHHR-H (20) HT manufactured by Tosoh Corporation are connected and used. The column temperature is set to 140 ° C. and trichlorobenzene as an eluent is flowed at a flow rate of 1.0 ml / 10 minutes to obtain measured values of Mw and Mn. A calibration curve for the molecular weight M is prepared using standard polystyrene manufactured by Tosoh Corporation, and the measured value is converted into a polystyrene value to obtain Mw and Mn. Here, the logarithm of the base 10 of the molecular weight M of standard polystyrene is referred to as logarithmic molecular weight (“Log (M)”).

  It is preferable that the resin film has a crystallite size of 9 nm or more and 15 nm or less, which is determined from the half-value width of the reflection peak of the α crystal (040) plane measured by the wide-angle X-ray diffraction method using the Scherrer's equation. The thickness is more preferably 10 nm or more and 13.5 nm or less, further preferably 11 nm or more and 12.2 nm or less, and particularly preferably 11.3 nm or more and 12.0 nm or less. The crystallite size is measured according to the method described in Examples.

  When the crystallite size of the resin film is 15 nm or less, the leakage current becomes small, and the withstand voltage property at room temperature or high temperature is preferably improved. On the other hand, the crystallite size of 9 nm or more is preferable from the viewpoint of maintaining the mechanical strength and melting point of the resin film (particularly polypropylene film).

  The surface orientation coefficient of the resin film is preferably 0.010 to 0.016, more preferably 0.011 to 0.0155, and further preferably 0.0115 to 0.015. 0.0121 to 0.0134 are even more preferable, and 0.0125 to 0.0131 are particularly preferable.

  It is preferable that the plane orientation coefficient of the resin film is within the above range because the dielectric breakdown under high temperature and high voltage can be further reduced.

<Plane orientation coefficient ΔP>
In the present specification, the “plane orientation coefficient ΔP” means a plane orientation coefficient ΔP (where ΔP = ΔP = calculated from the values of birefringence values ΔNyz and ΔNxz in the thickness direction of the resin film obtained by optical birefringence measurement). (ΔNyz + ΔNxz) / 2).
In the specification, the “birefringence value ΔNyz” in the thickness direction of the resin film means the birefringence value ΔNyz in the thickness direction obtained by optical birefringence measurement. More specifically, the principal axis in the in-plane direction of the film is the x-axis and the y-axis, and the thickness direction of the film (direction normal to the in-plane direction) is the z-axis. When the slow axis in the higher direction is the x-axis, the birefringence value ΔNyz is the value obtained by subtracting the three-dimensional refractive index in the z-axis direction from the three-dimensional refractive index in the y-axis direction.

  In the present specification, the “birefringence value ΔNxz” in the thickness direction of the resin film means the birefringence value ΔNxz in the thickness direction obtained by optical birefringence measurement, and more specifically, the x-axis. The value obtained by subtracting the three-dimensional refractive index in the z-axis direction from the three-dimensional refractive index in the (slow axis) direction is the birefringence value ΔNxz.

  The value of the birefringence value ΔNyz and / or ΔNxz can be used as an index of the orientation strength of the film. When the orientation strength of the film is strong, the in-plane refractive index, that is, the three-dimensional refractive index in the y-axis direction and / or the three-dimensional refractive index in the x-axis direction increases, and Since the three-dimensional refractive index is low, the birefringence values ΔNyz and / or ΔNxz are large.

  In this embodiment, in order to measure the “birefringence value ΔNyz” in the thickness direction of the resin film, specifically, a phase difference measuring device RE-100 manufactured by Otsuka Electronics Co., Ltd. is used. The measurement of retardation (phase difference) is performed using a tilt method. More specifically, the principal axis in the in-plane direction of the film is the x-axis and the y-axis, and the thickness direction of the film (direction normal to the in-plane direction) is the z-axis. The slow axis in the higher direction is the x axis. Retardation values are obtained when the x-axis is tilted by 10 ° with respect to the z-axis in the range of 0 ° to 50 °. From the obtained retardation value, the y-axis direction with respect to the thickness direction (z-axis direction) was used using the method described in Non-Patent Document "Yu Awaya, Introduction to Polarizing Microscopes for Polymer Materials, pp. 105-120, 2001". The birefringence ΔNyz of is calculated. First, for each inclination angle φ, R / d obtained by dividing the measured retardation value R by the inclination-corrected thickness d is obtained. For each R / d of φ = 10 °, 20 °, 30 °, 40 °, 50 °, obtain the difference from the R / d of φ = 0 °, and divide them by sin2r (r: refraction angle). The birefringence ΔNzy at each φ is set, and the positive and negative signs are reversed to obtain the birefringence value ΔNyz. The birefringence value ΔNyz is calculated as the average value of ΔNyz at φ = 20 °, 30 °, 40 °, and 50 °. In the successive stretching method, for example, when the stretching ratio in the TD direction (width direction) is higher than the stretching ratio in the MD direction (flow direction), the TD direction becomes the slow axis (x axis) and the MD direction becomes y. It becomes an axis. When polypropylene is used, the value of the refraction angle r at each tilt angle for polypropylene is that described on page 109 of the above document.

  Further, in the present embodiment, the “birefringence value ΔNxz” with respect to the thickness direction of the resin film is obtained as described above from the value obtained by dividing the retardation value R measured at the inclination angle φ = 0 ° by the thickness d. The birefringence value ΔNxz is calculated by dividing ΔNzy.

  When orientation is given in the plane direction (x-axis direction and / or y-axis direction) of the resin film, the refractive index Nz in the thickness direction changes, the birefringence value ΔNyz and / or ΔNxz increases, and the withstand voltage property increases. Improve (higher breakdown voltage). This is considered to be due to the following reasons. When the molecular chains of the resin (for example, polypropylene) are oriented in the plane direction, the refractive index Nz in the thickness direction becomes low. The electrical conductivity in the film thickness direction is low because it is transmitted between molecular chains. Therefore, when the resin molecular chain (for example, polypropylene molecular chain) is oriented in the plane direction (the birefringence value ΔNyz and / or ΔNxz is large), the electrical conductivity in the film thickness direction can be transferred between the molecular chains. It is considered that the withstand voltage is improved as compared with the case where the molecular chains of the resin are not oriented in the plane direction (the birefringence values ΔNyz and / or ΔNxz are small).

  Generally, it is possible to control the "birefringence value ΔNyz" and / or the "birefringence value ΔNxz" by changing the orientation of the molecular chains of the resin by changing the film forming conditions (such as adjustment of the draw ratio). .. Further, the “birefringence value ΔNyz” and / or the “birefringence value ΔNxz” can be controlled by changing the characteristics of the resin (molecular weight, degree of polymerization, molecular weight distribution, etc.).

The “plane orientation coefficient ΔP” is obtained by substituting the birefringence values ΔNyz and ΔNxz into the formula: ΔP = (ΔNyz + ΔNxz) / 2. In the present invention, the “plane orientation coefficient ΔP” calculated by taking into consideration not only the orientation strength in the y-axis direction represented by the birefringence value ΔNyz but also the orientation strength in the x-axis direction represented by the birefringence value ΔNxz. There is one feature in the point of paying attention to. For example, even if the birefringence value ΔNyz is very large, the plane orientation coefficient ΔP has a relatively small value if the birefringence value ΔNxz is extremely small. Assuming a case where there is a large difference between the long axis and the short axis of the cross section of the site where the resin has a branched chain, one of the birefringence values is extremely small, and thus the long axis direction approaches the film thickness direction ( It is considered that in this case, the electric conductivity in the film thickness direction is increased and the withstand voltage is decreased. Therefore, it is considered that both the birefringence value ΔNyz and the birefringence value ΔNxz are not extremely low values, and because the plane orientation coefficient ΔP is equal to or higher than a certain value, the withstand voltage property is improved.
The specific measurement method of the plane orientation coefficient is according to the method described in the examples.

  The melting point of the resin film is preferably 170 ° C. or higher and 176 ° C. or lower, more preferably 171 ° C. or higher and 175.5 ° C. or lower, and further preferably 171.5 ° C. or higher and 175 ° C. or lower, 172 It is particularly preferable that the temperature is not less than 0 ° C and not more than 174.5 ° C.

  When the melting point of the resin film is 170 ° C. or higher, the withstand voltage property at high temperature and the thermal dimensional stability are excellent. On the other hand, when the temperature is 176 ° C. or lower, the rigidity of the film becomes appropriate and the stretched film can be easily formed. The melting point is measured by the method described in Examples.

  The melting enthalpy of the resin film is preferably 90 J / g or more and 125 J / g or less, more preferably 100 J / g or more and 123 J / g or less, and further preferably 108 J / g or more and 122 J / g or less. preferable.

  It is preferable that the resin film has a enthalpy of fusion of 90 J / g or more because the crystallite becomes strong. On the other hand, when it is 125 J / g or less, the crystallite size becomes appropriately small, which is preferable. The method of measuring the enthalpy of fusion is according to the method described in Examples.

  The resin film preferably has a thickness within a range of 0.8 to 22 μm, more preferably within a range of 1.2 to 12.0 μm, and within a range of 1.4 to 6.0 μm. Is more preferable, 1.5 to 4.0 μm is still more preferable, 1.5 to 3.0 μm is still more preferable, and 1.5 to 2.9 μm is particularly preferable.

  When the thickness is 22 μm or less, the electrostatic capacity can be increased, and therefore, it can be suitably used for capacitors. From the viewpoint of manufacturing, the thickness can be 0.8 μm or more.

It is particularly preferable that the resin film has a thickness in the range of 0.8 to 6 μm. When the capacitor element generates heat, the temperature of the resin film inside the capacitor element also rises, causing a decrease in the insulation resistance value (IR). Therefore, if the thickness of the resin film is reduced, the capacitor element can be downsized even with the same capacitance, so that the specific surface area of the capacitor element is increased, which is advantageous for heat dissipation. Therefore, when the thickness is 6 μm or less, the decrease in capacitance can be further suppressed. Further, since the decrease in capacitance can be further suppressed, the decrease rate (%) of (C · IR) can be further suppressed.
Further, when the thickness of the resin film is 6 μm or less, the capacitance per unit volume of the capacitor element can be increased, so that it can be suitably used for capacitors. Further, from the viewpoint of film forming stability of the film, the thickness of the resin film is preferably 0.8 μm or more.
This point will be described in detail below.
The thinner the resin film, the larger the electrostatic capacity per unit volume. More specifically, the capacitance C is expressed as follows using the permittivity ε, the electrode area S, and the dielectric thickness d (resin film thickness d).
C = εS / d
Here, in the case of a film capacitor, the thickness of the electrode is three digits or more thinner than the thickness of the resin film (dielectric), so if the volume of the electrode is ignored, the volume V of the capacitor is expressed as follows. To be done.
V = Sd
Therefore, from the above two equations, the electrostatic capacity C / V per unit volume is expressed as follows.
C / V = ε / d ²
As can be seen from the above formula, the capacitance (C / V) per unit volume is inversely proportional to the square of the resin film thickness. Further, the dielectric constant ε is determined by the material used. Then, it is understood that the capacitance per unit volume (C / V) can be improved only by reducing the thickness unless the material is changed.
The electrode area does not affect the electrostatic capacity (C / V) per unit volume. This point will be described below.
It is assumed that a capacitor is manufactured by winding a film having the same material and the same thickness. For example, it is assumed that the number of turns (number of turns) is increased and the number of turns is ten times longer (the electrode area is ten times larger). Then, the capacitance is increased by 10 times, but the volume is also increased by 10 times, so that the capacitance per unit volume (C / V) does not change even if the electrode area changes.
The above description has been idealized for ease of understanding. That is, in practice, for example, there may be a slight gap between the films, the influence of the fringe effect at the electrode end, and the like, so that the capacitance per unit volume (C In some cases, there may be some changes in the value of / V). However, it can be understood that generally, the capacitance per unit volume (C / V) is determined by the resin film thickness.
From the above, it is preferable that the thickness of the resin film is as thin as possible within the range where the film-forming stability is ensured. Therefore, the thickness of the resin film is preferably 6 μm or less.

  The thickness of the resin film is a value measured according to JIS-C2330, except that it is measured at 100 ± 10 kPa using a paper thickness measuring instrument MEI-11 manufactured by Citizen Seimitsu Co., Ltd.

  The resin film may be a biaxially stretched film, a uniaxially stretched film, or an unstretched film. Among them, the biaxially stretched film is preferable from the viewpoint of increasing the plane orientation coefficient.

  As described above, the resin film contains a crystalline thermoplastic resin as a main component. In the present specification, containing a crystalline thermoplastic resin as a main component means that the crystalline thermoplastic resin is 50% by mass or more with respect to the entire resin film (when the entire resin film is 100% by mass). It means to contain. The content of the crystalline thermoplastic resin with respect to the entire resin film is preferably 75% by mass or more, and more preferably 90% by mass or more. The upper limit of the content of the crystalline thermoplastic resin is, for example, 100% by mass or 98% by mass based on the entire resin film.

The crystalline thermoplastic resin is at least one of (a) the main chain is an aliphatic hydrocarbon, (b) has an amide bond in the main chain, and (c) has an ether bond in the main chain. Resins satisfying the above are preferable.
Examples of the crystalline thermoplastic resin (a) whose main chain is an aliphatic hydrocarbon include polypropylene resin, polyethylene resin, polyvinylidene fluoride (PVDF) resin and the like.
In addition, in this specification, an aliphatic hydrocarbon means both a saturated hydrocarbon and an unsaturated hydrocarbon.
Examples of the crystalline thermoplastic resin (b) having an amide bond in the main chain include 6-nylon (PA6) and 66-nylon (PA66).
Examples of the (c) crystalline thermoplastic resin having an ether bond in the main chain include polyether ether ketone (PEEK) resin and polyacetal (POM) resin.
The crystalline thermoplastic resin may be a copolymer that satisfies two or more of the above (a) to (c).

Further, the crystalline thermoplastic resin may be a resin in which at least one hydrogen atom is bonded to each carbon atom constituting the main chain of the crystalline thermoplastic resin.
As the crystalline thermoplastic resin in which at least one hydrogen atom is bonded to each carbon atom constituting the main chain, polypropylene resin, polyethylene resin, polyphenylene sulfide (PPS) resin, polyether ether ketone (PEEK) resin, Examples thereof include polyacetal (POM) resin.
In the present specification, at least one hydrogen atom is bonded to each carbon atom constituting the main chain, and when the main chain contains a benzene ring, at least one hydrogen atom is contained in the benzene ring. Means that are bound. Further, when the main chain has atoms other than carbon atoms, it means that hydrogen atoms may or may not be bonded to atoms other than the carbon atoms.

  As the crystalline thermoplastic resin, one type of crystalline thermoplastic resin may be used alone, or two or more types of crystalline thermoplastic resin may be used in combination. As the crystalline thermoplastic resin, it is particularly preferable to use two or more crystalline thermoplastic resins in combination.

  Among these, the crystalline thermoplastic resin is preferably a polypropylene resin. Since the polypropylene resin is a resin having a relatively high volume resistivity, when the crystalline thermoplastic resin is a polypropylene resin, it is possible to suitably suppress the reduction rate of the insulation resistance value (IR) of the capacitor element in the life test. ..

  The weight average molecular weight Mw of the polypropylene resin is preferably 250,000 or more and 450,000 or less, and more preferably 250,000 or more and 400,000 or less. When the weight average molecular weight Mw of the polypropylene resin is 250,000 or more and 450,000 or less, the resin fluidity becomes appropriate. As a result, the thickness of the cast original fabric sheet can be easily controlled, and a thin stretched film can be easily produced. In addition, it is possible to impart appropriate stretchability to the cast original fabric sheet. When two or more polypropylene resins are used, it is preferable to use the polypropylene resin having the Mw of 250,000 or more and less than 330,000 and the polypropylene resin having the Mw of 330,000 or more and 450,000 or less in combination.

  The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the polypropylene resin is preferably 5 or more and 12 or less, more preferably 5 or more and 11 or less, and 5 or more and 10 or less. Is more preferable. When two or more polypropylene resins are used, it is preferable to use the polypropylene resin having a molecular weight distribution of 5 or more and less than 8.5 and the polypropylene resin having a molecular weight distribution of 8.5 or more and 11 or less in combination.

  In the present specification, the weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the polypropylene resin are values measured using a gel permeation chromatograph (GPC) device. is there. More specifically, it is a value measured using HLC-8121GPC-HT (trade name), a high temperature GPC measuring instrument with a built-in differential refractometer (RI) manufactured by Tosoh Corporation. As a GPC column, three TSKgel GMHHR-H (20) HT manufactured by Tosoh Corporation are connected and used. The column temperature is set to 140 ° C. and trichlorobenzene as an eluent is flowed at a flow rate of 1.0 ml / 10 minutes to obtain measured values of Mw and Mn. A calibration curve for the molecular weight M is prepared using standard polystyrene manufactured by Tosoh Corporation, and the measured value is converted into a polystyrene value to obtain Mw and Mn. Here, the logarithm of the base 10 of the molecular weight M of standard polystyrene is referred to as logarithmic molecular weight (“Log (M)”).

The differential distribution value difference D _{M of the} polypropylene resin is preferably −5% or more and 14% or less, more preferably −4% or more and 12% or less, and −4% or more and 10% or less. More preferable. Here, the “differential distribution value difference D _M ” is the differential distribution value when the logarithmic molecular weight Log (M) = 4.5 to the differential distribution value when Log (M) = 6.0 in the molecular weight differential distribution curve. Is the difference obtained by subtracting.
In addition, "the differential distribution value difference _DM is -5% or more and 14% or less" means that a component having a molecular weight of 10,000 to 100,000 on the lower molecular weight side than the value of Mw of the polypropylene resin (hereinafter, "low (Also referred to as “molecular weight component”) having a logarithmic molecular weight of Log (M) = 4.5 as a typical distribution value and a high molecular weight component having a molecular weight of about 1,000,000 (hereinafter, also referred to as “high molecular weight component”). When comparing the components around Log (M) = 6.0 as a typical distribution value, the low molecular weight component is more when the difference is positive, and the higher molecular weight component is the difference when the difference is negative. Understand that there are many.

  That is, even though the molecular weight distribution Mw / Mn is 5 to 12, it merely represents the breadth of the molecular weight distribution, and the quantitative relationship between the high molecular weight component and the low molecular weight component therein is unknown. Absent. Therefore, from the viewpoint of stable film-forming property and thickness uniformity of the cast original sheet, the polypropylene resin has a wide molecular weight distribution and, at the same time, has a molecular weight of 10,000 to 100,000 in order to appropriately contain a low molecular weight component. It is preferable to use the polypropylene resin so that the component has a differential distribution value difference of −5% or more and 14% or less as compared with the component having a molecular weight of 1,000,000.

  The differential distribution value is a value obtained as follows using GPC. A curve showing intensity against time (generally also referred to as "elution curve") obtained by a GPC differential refraction (RI) detector is used. Using the calibration curve obtained using standard polystyrene, the elution curve is converted into a curve showing the intensity with respect to Log (M) by converting the time axis into logarithmic molecular weight (Log (M)). Since the RI detection intensity is proportional to the component concentration, an integral distribution curve for the logarithmic molecular weight Log (M) can be obtained when the total area of the intensity curve is 100%. The differential distribution curve is obtained by differentiating this integral distribution curve by Log (M). Therefore, the "differential distribution" means the differential distribution of the concentration fraction with respect to the molecular weight. From this curve, the differential distribution value at a specific Log (M) is read.

  The heptane insoluble content (HI) of the polypropylene resin is preferably 96.0% or more, more preferably 97.0% or more. Further, the heptane-insoluble content (HI) of the polypropylene resin is preferably 99.5% or less, more preferably 99.0% or less. Here, it is indicated that the larger the amount of heptane-insoluble matter, the higher the stereoregularity of the resin. When the heptane-insoluble matter (HI) is 96.0% or more and 99.5% or less, the crystallinity of the resin is appropriately improved due to the moderately high stereoregularity, and the withstand voltage property at high temperature is improved. To do. On the other hand, the rate of solidification (crystallization) at the time of forming the cast raw sheet becomes appropriate, and it has an appropriate stretchability. The heptane-insoluble matter (HI) is measured by the method described in Examples.

  The melt flow rate (MFR) of the polypropylene resin is preferably 1.0 to 8.0 g / 10 min, more preferably 1.5 to 7.0 g / 10 min, and 2.0 to 6.0 g. More preferably, it is / 10 min. The method for measuring the melt flow rate of the polypropylene resin is according to the method described in Examples.

  The polypropylene resin can be manufactured using a generally known polymerization method. Examples of the polymerization method include a gas phase polymerization method, a bulk polymerization method, and a slurry polymerization method.

  The polymerization may be a single-stage (single-stage) polymerization using one polymerization reactor or a multi-stage polymerization using two or more polymerization reactors. The polymerization may be carried out by adding hydrogen or a comonomer as a molecular weight modifier into the reactor.

  A generally known Ziegler-Natta catalyst can be used as a catalyst for the polymerization, and it is not particularly limited as long as the polypropylene resin can be obtained. The catalyst may include a promoter component and a donor. The molecular weight, molecular weight distribution, stereoregularity, etc. can be controlled by adjusting the catalyst and the polymerization conditions.

  The molecular weight distribution and the like of the polypropylene resin can be adjusted by resin mixing (blending). For example, there may be mentioned a method of mixing two or more kinds of resins having different molecular weights or molecular weight distributions. In general, a mixture of two types of polypropylene having a main resin of 55% by mass or more and 90% by mass or less, where 100% by mass of the entire resin is a resin having a higher average molecular weight or a resin having a lower average molecular weight. The system is preferable because it is easy to adjust the amount of low molecular weight components.

  When the above-mentioned mixing adjustment method is adopted, the melt flow rate (MFR) may be used as a measure of the average molecular weight. In this case, the difference in MFR between the main resin and the added resin is preferably about 1 to 30 g / 10 minutes from the viewpoint of convenience in adjustment.

  The method for mixing the resins is not particularly limited, but a polymer powder of the main resin and the added resin, or a pellet, a method of dry blending using a mixer or the like, a polymer powder of the main resin and the added resin, or pellets. Is supplied to a kneader and melt-kneaded to obtain a blended resin.

  The mixer and the kneader are not particularly limited. The kneader may be a single screw type, a twin screw type, or a multi-screw type more than that. In the case of a screw type having two or more shafts, either kneading type rotating in the same direction or rotating in different directions may be used.

  In the case of blending by melt-kneading, the kneading temperature is not particularly limited as long as a good kneaded product can be obtained. Generally, it is in the range of 200 ° C to 300 ° C, and 230 ° C to 270 ° C is preferable from the viewpoint of suppressing deterioration of the resin. Further, in order to suppress deterioration at the time of kneading and mixing the resin, the kneading machine may be purged with an inert gas such as nitrogen. The melt-kneaded resin may be pelletized to an appropriate size using a generally known granulator. As a result, mixed polypropylene raw material resin pellets can be obtained.

  The total ash content resulting from the polymerization catalyst residue and the like contained in the polypropylene raw material resin is preferably 50 ppm or less based on the polypropylene resin (100 parts by weight).

  The total ash content (total ash content in the polypropylene raw material resin) is preferably 5 ppm or more and 35 ppm or less, and 5 ppm or more and 30 ppm or less, in order to improve the electrical characteristics of the capacitor while suppressing the generation of polar low-molecular components. The following is more preferable, and 10 ppm or more and 25 ppm or less is further preferable.

  Hereinafter, each polypropylene resin when two or more polypropylene resins are used will be described.

When two or more polypropylene resins are used, the following polypropylene resin A-1 and the following polypropylene resin B-1, the following polypropylene resin A-2 and the following polypropylene resin B-2, or the following polypropylene resin A-3 and the following polypropylene resin The combination of B-3 is mentioned as a suitable thing. In the present embodiment, the expression polypropylene resin A includes the concepts of polypropylene resin A-1, polypropylene resin A-2 and polypropylene resin A-3. The expression polypropylene resin B includes the concepts polypropylene resin B-1, polypropylene resin B-2 and polypropylene resin B-3. The polypropylene resins A, A-1, A-2, A-3 and the polypropylene resins B, B-1, B-2, B-3 are all preferably linear polypropylene resins.
<Polypropylene resin A>
(Polypropylene resin A-1)
A polypropylene resin having a differential distribution value difference D _M of 8.0% or more.
(Polypropylene resin A-2)
A polypropylene resin having a heptane insoluble content (HI) of 98.5% or less.
(Polypropylene resin A-3)
A polypropylene resin having a melt flow rate (MFR) at 230 ° C. of 4.0 to 10.0 g / 10 min.
<Polypropylene resin B>
(Polypropylene resin B-1)
A polypropylene resin having a differential distribution value difference D _M of less than 8.0%.
(Polypropylene resin B-2)
Polypropylene resin with a heptane insoluble content (HI) exceeding 98.5%.
(Polypropylene resin B-3)
A polypropylene resin having a melt flow rate (MFR) at 230 ° C. of 0.1 to 3.9 g / 10 min.

  The weight average molecular weight Mw of the polypropylene resin A is preferably 250,000 or more and 450,000 or less, more preferably 250,000 or more and 400,000 or less, and further preferably 250,000 or more and 340,000 or less. When the weight average molecular weight Mw of the polypropylene resin A is 250,000 or more and 450,000 or less, the resin fluidity becomes appropriate. As a result, the thickness of the cast original fabric sheet can be easily controlled, and a thin biaxially oriented polypropylene film can be easily produced. Further, it is preferable that the cast original sheet and the biaxially stretched polypropylene film are less likely to be uneven in thickness, and appropriate stretchability can be obtained.

  The molecular weight distribution Mw / Mn of the polypropylene resin A is preferably 8.5 or more and 12.0 or less, more preferably 8.5 or more and 11.0 or less, and 9.0 or more and 11.0 or less. Is more preferable.

  When the molecular weight distribution Mw / Mn of the polypropylene resin A is within the above-mentioned preferred range, unevenness is less likely to occur in the thickness of the cast raw fabric sheet and the biaxially stretched polypropylene film, and appropriate stretchability is obtained, which is preferable.

The differential distribution value difference D _M of the polypropylene resin A is preferably 8.0% or more, more preferably 8.0% or more and 18.0% or less, and 8.5% or more and 17.0% or less. Is more preferable, and particularly preferably 9.0% or more and 16.0% or less.

When the differential distribution value difference D _M is 8.0% or more and 18.0% or less, the low molecular weight component is included in a large amount in the ratio of 8.0% or more and 18.0% or less when compared with the high molecular weight component. Therefore, the frequency of breakage in the stretching step can be reduced, and the continuous film forming property is improved, which is preferable.

  The heptane-insoluble content (HI) of the polypropylene resin A is preferably 96.0% or more, more preferably 97.0% or more. Further, the heptane-insoluble content (HI) of the polypropylene resin A is preferably 99.5% or less, more preferably 98.5% or less, and further preferably 98.0% or less.

  The melt flow rate (MFR) at 230 ° C. of the polypropylene resin A is preferably 1.0 to 15.0 g / 10 min, more preferably 2.0 to 10.0 g / 10 min. It is more preferably 10.0 g / 10 min, and particularly preferably 4.3 to 6.0 g / 10 min. When the MFR at 230 ° C. of the polypropylene resin A is within the above range, the flow characteristics in the molten state are excellent, and thus unstable flow such as melt fracture is unlikely to occur, and breakage during stretching is suppressed. Therefore, since the film thickness uniformity is good, there is an advantage that formation of a thin portion where dielectric breakdown easily occurs is suppressed.

  The content of the polypropylene resin A is preferably 55% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 85% by mass or less, and 60% by mass or more based on the entire biaxially stretched polypropylene film. It is more preferably 80% by mass or less.

  The weight average molecular weight Mw of the polypropylene resin B is preferably 300,000 or more and 400,000 or less, more preferably 330,000 or more and 380,000 or less, and further preferably 350,000 or more and 380,000 or less.

  The molecular weight distribution Mw / Mn of the polypropylene resin B is preferably 6.0 or more and less than 8.5, more preferably 6.5 or more and 8.4 or less, and 7.0 or more and 8.3 or less. Is more preferable.

  When the molecular weight distribution Mw / Mn of the polypropylene resin B is within the above-mentioned preferable range, unevenness in the thickness of the cast raw fabric sheet and the biaxially stretched polypropylene film is less likely to occur, and appropriate stretchability is obtained, which is preferable.

The differential distribution value difference D _M of the polypropylene resin B is preferably less than 8.0%, more preferably −20.0% or more and less than 8.0%, and −10.0% or more and 7.9. % Or less, more preferably -5.0% or more and 7.5% or less.

  The heptane-insoluble content (HI) of the polypropylene resin B is preferably 97.5% or more, more preferably 98% or more, further preferably 98.5% or more, and particularly preferably 98.6%. That is all. The heptane-insoluble matter (HI) of the polypropylene resin B is preferably 99.5% or less, more preferably 99% or less.

  The melt flow rate (MFR) of the polypropylene resin B at 230 ° C. is preferably 0.1 to 6.0 g / 10 min, more preferably 0.1 to 5.0 g / 10 min, and More preferably, it is 3.9 g / 10 min.

  When the polypropylene resin B is used as the polypropylene resin, the content of the polypropylene resin B is preferably 10% by mass or more and 45% by mass or less, and 15% by mass or more and 40% by mass or less, when the polypropylene resin is 100% by mass. Is more preferable, and 20% by mass or more and 40% by mass or less is further preferable.

  When polypropylene resin A and polypropylene resin B are used together as the polypropylene resin, if the total polypropylene resin is 100% by mass, it contains 55 to 90% by weight of polypropylene resin A and 45 to 10% by weight of polypropylene resin B. It is preferable that 60 to 85% by weight of the polypropylene resin A and 40 to 15% by weight of the polypropylene resin B are contained more preferably, 60 to 80% by weight of the polypropylene resin A and 40 to 20% by weight of the polypropylene resin. It is particularly preferable to include B.

  When the polypropylene resin contains the polypropylene resin A and the polypropylene resin B, the biaxially stretched polypropylene film is in a finely mixed state (phase separation state) of the polypropylene resin A and the polypropylene resin B, and thus has a high voltage resistance at high temperature. Is improved.

  Heretofore, each polypropylene resin when two or more polypropylene resins are used has been described.

The resin film has a product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] of 1 × 10 ¹⁶ Ω · cm or more, and a product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] of 1 × 10 ¹⁴ Ω · cm or more. Inside, other resin different from the crystalline thermoplastic resin may be included.
Examples of the other resin include an amorphous thermoplastic resin.
Examples of the non-crystalline thermoplastic resin include polyamide imide (PAI) and polycarbonate (PC).

The resin film may include an additive. By including an additive in the resin film, the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ], the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ], the log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / The value of (ρ _{V100 ° C.} × ε _{r100 ° C.} )] can be adjusted.

Examples of the additives include antioxidants, chlorine absorbers, ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, inorganic fillers and organic fillers. Examples of the inorganic filler include barium titanate, strontium titanate, and aluminum oxide.
The resin film preferably does not contain a crystal nucleating agent (in particular, an α crystal nucleating agent). As the crystal nucleating agent, there are one that is soluble in the resin (dissolution type nucleating agent) and one that is insoluble in the resin (dispersion type nucleating agent). Examples of the dissolution-type nucleating agent include nonitol-type nucleating agent and sorbitol-type nucleating agent, and the molecular weight of the dissolution-type nucleating agent is extremely smaller than that of the thermoplastic resin. Therefore, the dissolution type nucleating agent added to the thermoplastic resin easily causes bleed-out on the film surface during the manufacturing process of the resin film, and gradually contaminates the surface of the manufacturing equipment (particularly the metal roll that contacts the film). Will end up. When the pollution is accumulated, it is necessary to stop the manufacturing facility and remove the pollution, which may deteriorate productivity. On the other hand, examples of the dispersion-type nucleating agent include talc, mica, phosphoric acid ester metal salt-based nucleating agent, and carboxylic acid metal salt-based nucleating agent, but the interface between the thermoplastic resin and the dispersion-type nucleating agent is conductive. Since it easily becomes a pass, the withstand voltage may be lowered. Furthermore, if the ionic substance contained in the film increases due to the reason that the crystal nucleating agent, the thermal decomposition product of the crystal nucleating agent, or any of the impurities contained in the crystal nucleating agent is an ionic substance, This causes an increase in ionic electric conduction and deteriorates the volume resistivity. For these reasons, it is preferable that the resin film does not contain a crystal nucleating agent (in particular, an α crystal nucleating agent).

  When the resin film is a biaxially stretched resin film, a cast original fabric sheet before stretching for producing the biaxially stretched resin film can be produced as follows.

First, a crystalline thermoplastic resin pellet, a dry mixed crystalline thermoplastic resin pellet, or a mixed crystalline thermoplastic resin pellet prepared by melt kneading in advance is supplied to an extruder and heated and melted.
The extruder rotation speed during heating and melting is preferably 5 to 40 rpm, more preferably 10 to 30 rpm.
The temperature of melt-kneading varies depending on the type of thermoplastic resin, but in the case of polypropylene resin, the set temperature of the extruder during heating and melting is preferably 220 to 280 ° C, more preferably 230 to 270 ° C. The resin temperature during heating and melting is preferably 220 to 280 ° C, more preferably 230 to 270 ° C. The resin temperature at the time of heating and melting is a value measured by a thermometer inserted in the extruder.
The extruder rotation speed during heating and melting, the extruder set temperature, and the resin temperature are selected in consideration of the physical properties of the crystalline thermoplastic resin used. It is also possible to suppress the deterioration of the resin by setting the resin temperature during heating and melting within the above numerical range.

Next, the molten resin is extruded into a sheet shape using a T die, and cooled and solidified by at least one metal drum to form an unstretched cast raw sheet.
The surface temperature of the metal drum (the temperature of the metal drum that first comes into contact after extrusion) is preferably 50 to 100 ° C, more preferably 60 to 80 ° C. The surface temperature of the metal drum can be determined according to the physical properties of the crystalline thermoplastic resin used.

In the case of polypropylene resin, the melt flow rate (MFR) of the cast raw sheet is preferably 1.0 to 9.0 g / 10 min, more preferably 2.0 to 8.0 g / 10 min, More preferably, it is 3.0 to 7.0 g / 10 min. The method for measuring the melt flow rate of the polypropylene film is according to the method described in Examples.
The thickness of the cast raw fabric sheet is not particularly limited as long as the resin film can be obtained, but is usually preferably 0.05 mm to 2 mm, and 0.1 mm to 1 mm. Is more preferable.

  The resin film can be produced by subjecting the resin cast original sheet to a stretching treatment. The stretching is preferably biaxial stretching in which the film is oriented biaxially in the machine and transverse directions, and the sequential biaxial stretching method is preferred as the stretching method. As a sequential biaxial stretching method, for example, first, a cast raw fabric sheet is maintained at a temperature of 100 to 170 ° C., and is passed between rolls having a speed difference and stretched 3 to 7 times in the flow direction. Subsequently, the sheet is guided to a tenter and stretched in the transverse direction 3 to 11 times. After that, relaxation and heat fixation are applied by 2 to 10 times. By the above, a biaxially stretched resin film is obtained.

  The resin film may be subjected to a corona discharge treatment online or offline after the stretching and heat-setting processes for the purpose of enhancing the adhesive property in a post-process such as a metal deposition process. The corona discharge treatment can be performed using a known method. It is preferable to use air, carbon dioxide gas, nitrogen gas, or a mixed gas thereof as the atmosphere gas.

  In order to process it as a capacitor, a metal layer may be laminated on one or both sides of the resin film to form a metal layer-integrated resin film. The metal layer functions as an electrode. Examples of the metal used in the metal layer include zinc, lead, silver, chromium, aluminum, copper, nickel, and other such metal simple substances, a mixture of a plurality of types thereof, and alloys thereof. Considering economical efficiency and capacitor performance, zinc and aluminum are preferable.

  Examples of the method for laminating the metal layer on one side or both sides of the resin film include a vacuum vapor deposition method and a sputtering method. From the viewpoint of productivity and economic efficiency, the vacuum vapor deposition method is preferable. As the vacuum vapor deposition method, generally, a crucible method, a wire method, etc. can be exemplified, but there is no particular limitation, and an optimum method can be appropriately selected.

  The margin pattern when depositing the metal layer by vapor deposition is not particularly limited, but a pattern including a so-called special margin such as a fishnet pattern or a T margin pattern is used in order to improve the characteristics such as the security of the capacitor. It is preferably applied on one side of the film. It is also effective from the standpoint of enhancing safety and preventing capacitor destruction and short circuits.

  As a method of forming a margin, a generally known method such as a tape method or an oil method can be used without any limitation.

  The metal layer-integrated resin film can be laminated by a conventionally known method or wound to form a film capacitor.

  Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

[Crystalline thermoplastic resin]
Table 1 shows the crystalline thermoplastic resins used for producing the resin films of Examples and Comparative Examples.
Table 1 shows the types of resin. In Table 1, PP represents a linear polypropylene resin.
Resin A shown in Table 1 is a product manufactured by Prime Polymer Co., Ltd. Resin B is HPT-1 manufactured by Korea Yuka Co., Ltd. Resin C is HC300BF manufactured by Borealis. Resin D is HF500N from Basell. Resin E is HP400R manufactured by Basell. Resin F is HP501L manufactured by Basell.
Table 1 shows the number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) of Resins A to F. These values are in the form of raw resin pellets. The measuring method is as follows.

<Measurement of number average molecular weight (Mn) of resin, weight average molecular weight (Mw), molecular weight distribution (Mw / Mn), and differential distribution value difference D _M >
The number average molecular weight (Mn), the weight average molecular weight (Mw), the molecular weight distribution (Mw / Mn), and the differential distribution value difference D _M of the resin were measured using GPC (gel permeation chromatography) under the following conditions.
An HLC-8121GPC-HT type, which is a high temperature GPC device with a built-in differential refractometer (RI) manufactured by Tosoh Corporation, was used. As a column, three TSKgel GMHHR-H (20) HT manufactured by Tosoh Corporation were connected and used. It was measured by flowing trichlorobenzene as a eluent at a column temperature of 140 ° C. at a flow rate of 1.0 ml / min. A calibration curve was prepared using standard polystyrene manufactured by Tosoh Corporation, and the measured molecular weight value was converted into a polystyrene value to obtain a number average molecular weight (Mn) and a weight average molecular weight (Mw). .. A molecular weight distribution (Mw / Mn) was obtained using the values of Mw and Mn.
Further, the differential distribution value difference D _M was obtained by the following method. First, a time curve (elution curve) of the intensity distribution detected using an RI detector is converted into a distribution curve with respect to the molecular weight M (Log (M)) of standard polystyrene using a calibration curve prepared using the above standard polystyrene. Converted Next, after obtaining an integral distribution curve for Log (M) in the case where the total area of the distribution curve is 100%, a derivative distribution with respect to Log (M) is obtained by differentiating this integral distribution curve with Log (M). The curve was obtained. From this differential distribution curve, the differential distribution values at Log (M) = 4.5 and Log (M) = 6.0 were read. The difference between the differential distribution value when Log (M) = 4.5 and the differential distribution value when Log (M) = 6.0 was defined as the differential distribution value difference D _M. The series of operations until obtaining the differential distribution curve was performed using the analysis software built in the used GPC measurement device. The results are shown in Table 1.

<Measurement of heptane insoluble matter (HI)>
Resin A to resin F were press-molded into 10 mm × 35 mm × 0.3 mm to prepare a measurement sample of about 3 g. Next, about 150 mL of heptane was added and Soxhlet extraction was performed for 8 hours. The heptane-insoluble matter was calculated from the sample mass before and after extraction. The results are shown in Table 1.

<Measurement of melt flow rate (MFR)>
The melt flow rate (MFR) of each resin in the form of raw material resin pellets was measured using a melt indexer manufactured by Toyo Seiki Co., Ltd. according to JIS K 7210 condition M. Specifically, first, a sample weighed to 4 g was inserted into a cylinder at a test temperature of 230 ° C., and preheated for 3.5 minutes under a load of 2.16 kg. After that, the weight of the sample extruded through the bottom hole was measured for 30 seconds, and the MFR (g / 10 min) was determined. The above measurement was repeated 3 times, and the average value was used as the measured value of MFR. The results are shown in Table 1.

  Using the above-mentioned resins, resin films of Examples and Comparative Examples were produced and their physical properties were evaluated.

<Production of resin film>
(Example 1)
Resin A and resin B were dry blended. The mixing ratio was (resin A) :( resin B) = 66.7: 33.3 in terms of mass ratio. Thereafter, the dry-blended resin was melted at a resin temperature of 250 ° C., then extruded using a T die, wound around a metal drum whose surface temperature was kept at 95 ° C., and solidified to prepare a cast original sheet. The obtained unstretched cast raw fabric sheet was kept at a temperature of 130 ° C., passed between rolls having a speed difference, stretched 4.5 times in the flow direction, and immediately cooled to room temperature. Subsequently, the stretched film is guided to a tenter, stretched 8 times in the width direction at a temperature of 158 ° C. at a stretching angle of 9 °, then relaxed, heat-set and wound, and aged in an atmosphere of about 40 ° C. A biaxially oriented polypropylene film was obtained by treatment. In this way, a resin film was obtained. The thickness of the obtained resin film was as shown in Table 2 (2.32 μm).

(Example 2)
A resin film having a thickness of 4.94 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed by using the resin C.

(Example 3)
A resin film having a thickness of 1.95 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed.

(Example 4)
A resin film having a thickness of 2.51 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed.

(Example 5)
A resin film having a thickness of 2.07 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed and the stretching ratio in the width direction was changed to 8.1 times.

(Example 6)
A resin film having a thickness of 2.55 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed and the stretching ratio in the flow direction was changed to 4.6 times.

(Example 7)
A resin film having a thickness of 2.54 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed and the draw ratio in the flow direction was changed to 4.4 times.

(Example 8)
A resin film having a thickness of 2.31 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed and the stretching ratio in the flow direction was stretched to 4.3 times.

(Example 9)
Using Resin C, adding a filler (barium titanate, average particle size 80 nm (number average value of n = 100 observed with a transmission electron microscope) of 60,000 ppm, and changing the discharge amount of the resin composition A resin film having a thickness of 4.90 μm was obtained in the same manner as in Example 1 except for the above.

(Comparative Example 1)
A resin film having a thickness of 4.90 μm was obtained in the same manner as in Example 1 except that the resin D was used and the discharge amount of the resin composition was changed.

(Comparative example 2)
A resin film having a thickness of 5.20 μm was obtained in the same manner as in Example 1 except that the resin E was used and the discharge amount of the resin composition was changed.

(Comparative example 3)
A resin film having a thickness of 5.00 μm was obtained in the same manner as in Example 1 except that the resin F was used and the discharge amount of the resin composition was changed.

(Comparative example 4)
A resin film having a thickness of 1.96 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed and the stretching ratio in the width direction was changed to 8.4 times.

(Comparative example 5)
A resin film having a thickness of 2.07 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed and the stretching ratio in the width direction was changed to 8.7 times.

(Comparative example 6)
A resin film having a thickness of 1.96 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed and the stretching ratio in the flow direction was changed to 4.0 times.

(Comparative Example 7)
A resin film having a thickness of 2.31 μm was obtained in the same manner as in Example 1 except that the discharge amount of the resin composition was changed and the stretching ratio in the flow direction was changed to 4.2 times.

  The thickness of the resin film was the micrometer thickness described in JIS-C2330. However, as the measuring instrument, a paper thickness measuring instrument MEI-11 manufactured by Citizen Seimits Co., Ltd. was used.

<Measurement of volume resistivity ρ _{V23 ° C} >
The specific procedure for measuring the volume resistivity is described below, but the conditions not particularly described were measured according to JIS C 2139.
First, a volume resistivity measuring jig (hereinafter, also simply referred to as “jig”) was placed in a constant temperature bath of 23 ° C. environment. The structure of the volume resistivity measuring jig is as follows. A DC power supply and a DC ammeter are connected to each electrode of the jig.
<Jig for measuring volume resistivity>
Main electrode (diameter 50mm)
Counter electrode (85 mm diameter)
Ring-shaped guard electrode surrounding the main electrode (outer diameter 80 mm, inner diameter 70 mm)
Each electrode is made of gold-plated copper, and conductive rubber is attached to the surface in contact with the sample. The conductive rubber used is EC-60BL (W300) manufactured by Shin-Etsu Silicone Co., Ltd., and is attached so that the glossy surface of the conductive rubber is in contact with gold-plated copper.

  Next, the resin films of Examples and Comparative Examples (hereinafter, also referred to as samples) were placed in an environment of 23 ° C. and 50% RH for 24 hours. Then, the sample was set in a jig in a constant temperature bath. Specifically, the main electrode and the guard electrode were brought into close contact with one surface of the sample, the counter electrode was brought into close contact with the other surface, and the sample and each electrode were brought into close contact with a load of 5 kgf. Then, it left still for 30 minutes.

  Next, a voltage was applied to the sample so that the potential gradient was 200 V / μm.

After applying the voltage, the current value after 1 minute was read, and the volume resistivity was calculated by the following formula. In addition, 2290-10 (DC power supply) manufactured by Keithley was used for voltage application, and 2635B (DC ammeter) manufactured by Keithley was used for measurement of current value.
Volume resistivity = [(effective electrode area) × (applied voltage)] / [(thickness of sample) × (current value)]

Here, the effective electrode area was calculated by the following formula.
(Effective electrode area) = π × [[[(diameter of main electrode) + (inner diameter of guard electrode)] / 2] / 2] ²

<Measurement of relative permittivity _{εr23 ° C} >
First, a conductive film (Dotite D-500 manufactured by Fujikura Kasei Co., Ltd.) was prepared by applying a mold having a diameter of 30 mm to one surface of each of the resin films of Examples and Comparative Examples (hereinafter, also referred to as a sample). Was applied with a brush. After the solvent was sufficiently volatilized and the conductive paste did not flow out even if the mold was removed, the mold was removed and left for half a day. This formed the electrode. Next, an electrode was similarly formed on the other surface of the sample so as to sandwich the sample and overlap with the previous electrode. As described above, a capacitor having electrodes each having a diameter of 30 mm on both surfaces was obtained.

  In order to connect the produced capacitor to the measuring device, a conductor wire (tin-plated copper wire) was connected to each electrode portion of the capacitor with a conductive paste. At this time, if the conductors face each other across the film, capacitance is also formed in the conductor portions, so the conductors were connected at positions as far apart as possible.

Next, each conducting wire was connected to a measuring device (LCR HiTester 3522-50, manufactured by Hioki Electric Co., Ltd.), and the capacitance C of the produced capacitor was measured. The measurement was carried out under the following conditions after standing still for 30 minutes in a constant temperature bath set at 23 ° C.
<Measurement conditions>
Applied voltage: 1V
Measurement frequency: 1 KHz

Then, the relative permittivity _{εr23 ° C.} was calculated using the following formula. The vacuum dielectric constant ε ₀ was 8.55 × 10 ⁻¹² F / m. The results are shown in Table 2. The product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] was also calculated. The results are shown in Table 2. In Table 2, the notation in the “E + n” format such as “E + 16” indicates an index. For example, “E + 16” means 10 to the 16th power. In addition, the number on the left side of E such as “2.44E + 16” is a coefficient, and for example, “2.44E + 16” means 2.44 × 10 ¹⁶ .
(Capacitance C) = (ε _{r23 ° C.} ) × (vacuum dielectric constant ε ₀ ) × [(electrode area) / (resin film thickness)]

<Measurement of volume resistivity ρ _{V100 ° C} >
The volume resistivity ρ _{V100 ° C.} of the resin films of Examples and Comparative Examples was measured in the same manner as the measurement of the volume resistivity ρ _{V23 ° C.} , except that the temperature of the constant temperature bath was 100 ° C. The results are shown in Table 2.

<Measurement of relative permittivity ε _{r 100 ° C.} >
Except that the temperature of the thermostatic chamber and 100 ° C., as in the measurement of the dielectric constant epsilon _{r23 ° C.,} Example, were measured relative dielectric constant epsilon _{r100 ° C.} of the resin films of Comparative Examples. The results are shown in Table 2. Also, the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] was calculated. The results are shown in Table 2.

< _{Calculation of} log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )]>
Using the above measurement results, log ₁₀ [(ρ _{V23 ° C.} × ε _{r23 ° C.} ) / (Ρ _{V100 ° C.} × ε _{r100 ° C.} )] of the resin films of Examples and Comparative Examples was calculated. The results are shown in Table 2.

<Measurement of ash>
The resin films of Examples and Comparative Examples were measured according to JIS-K 7250-1 (2006). Specifically, ashing treatment was performed at 800 ° C. for 40 minutes, and the ratio (ppm) of the obtained ash was measured. The results are shown in Table 2.

<Measurement of heptane insoluble matter (HI)>
About the resin film of an Example and a comparative example, the sample for a measurement of about 3g was produced. Next, about 150 mL of heptane was added and Soxhlet extraction was performed for 8 hours. The heptane-insoluble matter was calculated from the sample mass before and after extraction. The results are shown in Table 2.

<Measurement of molecular weight distribution (Mw / Mn) of resin film>
With respect to the resin films of Examples and Comparative Examples, the molecular weight distribution (Mw / Mn) was measured and calculated in the same manner as in Resin A to Resin F. As a result, Example 1 was 7.3, Example 2 was 7.7, Example 3 was 7.4, Example 4 was 7.3, Example 5 was 7.3, and Example 6 was 7.3. Example 7 is 7.3, Example 8 is 7.3, Example 9 is 7.7, Comparative Example 1 is 4.0, Comparative Example 2 is 3.5, Comparative Example 3 is 6.1, Comparative Example 4 was 7.3, Comparative Example 5 was 7.3, Comparative Example 6 was 7.3, and Comparative Example 7 was 7.3.

<Measurement of crystallite size of resin film>
The crystallite sizes of the resin films according to Examples and Comparative Examples were measured under the following conditions using an XRD (wide angle X-ray diffraction) device.
Measuring machine: Rigaku X-ray diffractometer "MiniFlex 300"
X-ray generation output: 30kV, 10mA
Irradiated X-ray: Monochromator monochromatic CuKα ray (wavelength 0.15418 nm)
Detector: Scintillation counter Goniometer scanning: 2θ / θ interlocking scanning

  From the obtained data, the full width at half maximum of the diffraction reflection peak of the α crystal (040) plane was calculated using an integrated powder X-ray analysis software PDXL attached to the apparatus standard using an analysis computer. The crystallite size was determined from the half width using the Scherrer's formula (D = K × λ / (β × Cosθ)). The results are shown in Table 2.

  In the Scherrer's equation, D is a crystallite size (nm), K is a constant (form factor: 0.94 is used in this example), λ is a used X-ray wavelength (nm), and β is a half obtained. The valence width, θ is the diffraction Bragg angle. 0.15418 nm was used as λ.

<Measurement of plane orientation coefficient>
<Retardation value>
First, the retardation values of the resin films according to Examples and Comparative Examples were measured by the tilt method as described below.
Measuring instrument: Retardation measuring device RE-100 manufactured by Otsuka Electronics Co., Ltd.
Light source: LED light source with wavelength of 550 nm Measuring method: The angle dependence of retardation value was measured by the following tilt method. The x-axis and y-axis are the main axes in the in-plane direction of the film, and the z-axis is the film thickness direction (direction normal to the in-plane direction). When the axis is the x-axis and the x-axis is the tilt axis, each retardation value was obtained when tilted by 10 ° with respect to the z-axis in the range of 0 ° to 50 °. For example, in the successive stretching method, when the stretching ratio in the TD direction (width direction) is higher than the stretching ratio in the MD direction (flow direction), the TD direction becomes the slow axis (x axis) and the MD direction becomes the y axis. ..

<Birefringence value and plane orientation coefficient ΔP>
From the retardation value, the plane orientation coefficient ΔP was calculated as described in Non-Patent Document “Yu Awaya, Introduction to Polarizing Microscopes of Polymer Materials, pp. 105 to 120, 2001”.
First, for each tilt angle φ, the measured retardation value R was divided by the tilt-corrected thickness d to obtain R / d. For each R / d of φ = 10 °, 20 °, 30 °, 40 °, 50 °, obtain the difference from the R / d of φ = 0 °, and divide them by sin2r (r: refraction angle). The birefringence .DELTA.Nzy for each .phi. Was set, and the positive and negative signs were reversed to obtain the birefringence value .DELTA.Nyz. The birefringence value ΔNyz was calculated as the average value of ΔNyz at φ = 20 °, 30 °, 40 °, and 50 °.
Next, the retardation value R measured at the inclination angle φ = 0 ° was divided by the thickness d to obtain the birefringence value ΔNxz by dividing ΔNzy obtained above.
Finally, the birefringence values ΔNyz and ΔNxz were substituted into the formula: ΔP = (ΔNyz + ΔNxz) / 2 to obtain ΔP. As for the value of the refraction angle r at each inclination angle φ of polypropylene, the value described on page 109 of the non-patent document was used. The results are shown in Table 2.

<Measurement of melting point and enthalpy of fusion>
The melting points and melting enthalpies of the resin films obtained in Examples and Comparative Examples were obtained by the following procedure using an input compensation type DSC Diamond DSC manufactured by Perkin Elmer. First, about 5 mg of a resin film was weighed, packed in an aluminum sample holder, and set in a DSC device. Under a nitrogen flow, the temperature was raised (fast run) from 30 ° C to 280 ° C at a rate of 20 ° C / min, and the melting curve was measured. As a result of the DSC measurement, at least one or more melting peaks can be obtained between 100 ° C. and 190 ° C., and the peak top (apex) temperature of the melting peak curve on the highest temperature side was evaluated as the melting point. Moreover, the enthalpy of fusion was determined from the results of the first run. The results are shown in Table 2.

<Measurement of decrease rate of insulation resistance value (IR) of capacitor element in life test>
Capacitor elements were manufactured as follows using the resin films obtained in the examples and comparative examples. A metallized film containing a metal film on one surface of the above film was obtained by subjecting the resin film to aluminum vapor deposition with a T margin vapor deposition pattern at a vapor deposition resistance of 15 Ω / □. After slitting to a width of 60 mm, the two metallized films were put together, and using the automatic winding machine 3KAW-N2 manufactured by Minato Manufacturing Co., Ltd., the vapor deposition film was wound around a core of φ20 mm at a winding tension of 250 g. The capacitance of the wound and completed capacitor element is 75 μF (Example 1, Example 3, Example 4, Example 5-8, Comparative Examples 4 to 7) or 50 μF (Example 2, Example 5, Example). The winding was performed by adjusting the number of winding turns so as to be 9). The wound element was heat-treated at 120 ° C. for 15 hours while pressing, and then zinc metal was sprayed on the end face of the element to obtain a flat capacitor. A lead wire was soldered to the end face of the flat type capacitor and then sealed with an epoxy resin.

  The insulation resistance value of the obtained capacitor element is evaluated using a super insulation resistance meter DSM8104 manufactured by Hioki Electric Co., Ltd. The reduction rate of the insulation resistance value was obtained by the following procedure. After allowing the capacitor element to stand at 23 ° C. for 24 hours, apply a voltage to the capacitor element with a potential gradient of 250 V / μm (however, 500 V when the film thickness is 2 μm or more), and insulate 1 minute after application. The resistance value was measured. This was taken as the insulation resistance value before the life test.

Next, the capacitor element was removed from the super insulation resistance meter, and the voltage was continuously applied (loaded) to the capacitor element with a DC high voltage power source at a potential gradient of 280 V / μm for 1000 hours in a constant temperature bath of 105 ° C. Specifically, the DC voltage was determined by the following formula.
[DC voltage applied in life test (V)] = 750 × [film thickness (μm)] ÷ εr _{100 ° C.} −50
That is, the applied voltage is 707 V in the first embodiment, 1561 V in the second embodiment, 586 V in the third embodiment, 768 V in the fourth embodiment, 1717 V in the fifth embodiment, 625 V in the sixth embodiment, 782 V in the seventh embodiment, and the embodiment. 8 is 778 V, Example 9 is 703 V, Example 10 is 1031 V, Comparative Example 1 is 1548 V, Comparative Example 2 is 1646 V, Comparative Example 3 is 1580 V, Comparative Example 4 is 589 V, Comparative Example 5 is 625 V, and Comparative Example 6 is 589V and 703V in Comparative Example 7.

After 1000 hours had passed, the capacitor element was removed, and then a discharge resistor was connected to the capacitor element to eliminate the charge. Next, the capacitor element was allowed to stand at 23 ° C. for 24 hours, after which the insulation resistance value of the capacitor element was measured. This was defined as the insulation resistance value after the life test (hereinafter sometimes referred to as "IR ₁₀₀₀ "). Then, the reduction rate of the insulation resistance value was calculated. The reduction rate of the insulation resistance value was evaluated by the average value of two capacitors. The results are shown in Table 2.
[Insulation resistance decrease rate (%)] = [[(insulation resistance value before life test)-(insulation resistance value after life test)] / ((insulation resistance value before life test)] * 100

<Measurement of capacitance change rate ΔC>
The capacitance before and after the life test was measured, and the change rate ΔC of the capacitance was calculated by the following formula. The results are shown in Table 2.
[Change rate of electrostatic capacitance ΔC (%)] = [[(capacity of capacitor before life test)-(capacitor capacity after life test)] / ((capacitor capacity before life test)] × 100
Table 2 also shows the reduction rate (%) of (C · IR).

(result)
From Table 2, the product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more, and the product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more. It can be seen that the film suppresses the reduction rate (%) of the insulation resistance value (IR) of the capacitor element.
Further, a resin film having a product [ρ _{V23 ° C.} × ε _{r23 ° C.} ] of 1 × 10 ¹⁶ Ω · cm or more and a product [ρ _{V100 ° C.} × ε _{r100 ° C.} ] of 1 × 10 ¹⁴ Ω · cm or more is , (C · IR) decrease rate (%) is 50% or less, and it is understood that the (C · IR) decrease rate (%) is suppressed.

<Verification of measurement accuracy of volume resistivity>
It was verified that the measurement accuracy of the volume resistivity measuring method according to the present disclosure is higher than that of Patent Document 1 (International Publication No. 2016/182003). This will be described below.
Reference Example 1 is a test example assuming the method for measuring the volume resistivity in Patent Document 1. Reference Example 2 is a test example for confirming how the measurement accuracy changes in comparison with Reference Example 1 when the potential gradient is set higher than that of Reference Example 1.

(Reference example 1)
The jig for measuring the volume resistivity, the DC power supply, and the DC ammeter used in the above-described examples were prepared.
Next, a 2.3 μm biaxially oriented polypropylene film having the same thickness as that of Example 1 of Patent Document 1 (different from the biaxially oriented polypropylene film of Example 1 described in Patent Document 1, biaxial manufactured by Oji Holdings Co., Ltd. The stretched polypropylene film) was set on the jig and held at 120 ° C. for 30 minutes. Then, a voltage of 100V was applied. That is, the potential gradient was 43 V / μm. As a result, a minute current of 0.1 to 0.5 nA level was measured 1 minute after the voltage application.
Using the results of this voltage and current, the volume resistance value when the diameter of the electrode area was assumed to be 10 mm was calculated and found to be 6.8 × 10 ¹⁴ Ω · cm. This value is the average value of the reproduction test (n = 4). The volume resistance value was calculated when the diameter of the electrode area was assumed to be 10 mm because the diameter of the electrode area was set to 10 mm in the method for measuring the volume resistivity of Patent Document 1, and this is to be adjusted. is there.
This volume resistance value (6.8 × 10 ¹⁴ Ω · cm) was a value close to 6.5 × 10 ¹⁴ Ω · cm, which is the value of Example 1 of Patent Document 1. Therefore, it can be seen that the measurement method of Reference Example 1 is appropriate as a test assuming the measurement method of Patent Document 1.
Next, the standard deviation was obtained from the variation in the measured current value in the reproduction test (n = 4). As a result, the standard deviation was 1.2 × 10 ¹⁴ Ω · cm. The coefficient of variation (Coefficient of variation) was calculated to be about 18%.
The coefficient of variation is a value obtained by the following.
(Coefficient of variation) = (standard deviation) / (average value)
Here, in Patent Document 1, the measurement is performed at 110 ° C., while in Reference Example 1, the measurement is performed at 120 ° C. This is for the following reason.
When measured at 110 ° C. in the test method of Reference Example 1, the measured current value was smaller than that in Patent Document 1. Therefore, in order to reproduce the measurement method of Patent Document 1 more accurately, in Reference Example 1, the measurement was performed at 120 ° C. The reason why the measured current value does not become the same current value as in Patent Document 1 when measured at 110 ° C. in the test method of Reference Example 1 is that the biaxially oriented polypropylene film used for measurement is the same as that in Patent Document 1. It is believed that this is not the case.

(Reference example 2)
Similar to Reference Example 1, the jig for measuring the volume resistivity, the DC power supply, and the DC ammeter used in the above-described Examples were prepared.
Next, the same biaxially oriented polypropylene film as used in Reference Example 1 was set on the above jig and held at 120 ° C. for 30 minutes. Then, in Reference Example 2, a voltage of 200 V was applied. That is, in Reference Example 2, the potential gradient was set to 87 V / μm. The current value was measured in the same manner as in Reference Example 1 except for the potential gradient. As a result, a current of 11 to 12 nA was measured.
Using the results of this voltage and current, the volume resistance value when the diameter of the electrode area was assumed to be 10 mm was calculated to be 5.9 × 10 ¹³ Ω · cm. This value is the average value of the reproduction test (n = 4).
Next, the standard deviation was obtained from the variation in the measured current value in the reproduction test (n = 4). As a result, the standard deviation was 3.3 × 10 ¹² Ω · cm. In addition, the coefficient of variation (Coefficient of variation) was calculated to be about 6%.

(Discussion)
According to the volume resistivity measuring method of Patent Document 1, as in Reference Example 1, the obtained current is at the pA (picoampere) level and the value is not stable, but the current at the nA (nanoampere) level is the same as in Reference Example 2. It can be seen that the value stabilizes when measured as.
In Reference Example 2, when the potential gradient is 87 V / μm, it is shown that the value is stable as compared with Reference Example 1 in which the potential gradient is 43 V / μm. Therefore, the potential gradient of 200 V / μm In this case (when the present volume resistivity measurement method is used), it can be seen that the value is more stable than the volume resistivity measurement method of Patent Document 1.
From the above, it can be seen that the present method of measuring volume resistivity has high accuracy.

Claims (10)

Contains crystalline thermoplastic resin as the main component,
The product of the volume resistivity ρ _{V23 °} C. at 23 ° C. measured by the following measuring method (1) and the relative dielectric constant ε _{r23 °} C. at 23 ° C. measured by the following measuring method (2) [ρ _{V23 ° C.} × ε _{r23 ° C.} ] is 1 × 10 ¹⁶ Ω · cm or more,
The product of the volume resistivity ρ _{V100 °} C. at 100 ° C. measured by the following measuring method (3) and the relative dielectric constant ε _{r100 °} C. at 100 ° C. measured by the following measuring method (4) [ρ _{V100 ° C.} × ε _{r100 ° C.} ] is 1 × 10 ¹⁴ Ω · cm or more.
<Measurement method>
(1) A voltage is applied in an atmosphere of 23 ° C. so that the potential gradient is 200 V / μm, and the value is calculated from the current value at the time when one minute has elapsed by the following formula.
ρ _{V23 ° C.} = [(effective electrode area) × (applied voltage)] / [(thickness of resin film) × (current value)]
(2) A conductive paste is applied to both sides of the resin film and dried to form electrodes, and a conductive wire is attached to the obtained electrodes using the conductive paste, and the capacitance C of the obtained test capacitor is set to 23 ° C. It is measured in an atmosphere, and ε _{r23 ° C.} is calculated using the following formula.
(Capacitance C) = (ε _{r23 ° C.} ) × (vacuum dielectric constant ε ₀ ) × [(electrode area) / (resin film thickness)]
(3) A voltage is applied so that the potential gradient becomes 200 V / μm in an atmosphere of 100 ° C., and the value is calculated from the current value at the time when 1 minute has elapsed by the following formula.
ρ _{V100 ° C.} = [(effective electrode area) × (applied voltage)] / [(thickness of resin film) × (current value)]
(4) A conductive paste is applied to both sides of the resin film and dried to form an electrode, a conductor is attached to the obtained electrode using the conductive paste, and the capacitance C of the obtained test capacitor is set to 100 ° C. It is measured in an atmosphere, and ε _{r100 ° C.} is calculated using the following formula.
(Capacitance C) = (ε _{r100 ° C.} ) × (vacuum dielectric constant ε ₀ ) × [(electrode area) / (resin film thickness)]   The resin film according to claim 1, having a thickness within a range of 0.8 to 6 μm.   It is for capacitors, The resin film of Claim 1 or 2 characterized by the above-mentioned.   The resin film according to any one of claims 1 to 3, which is biaxially stretched.   The crystalline thermoplastic resin has at least one of (a) a main chain of which is an aliphatic hydrocarbon, (b) an amide bond in the main chain, and (c) an ether bond in the main chain. The resin film according to any one of claims 1 to 4, which is satisfied.   The resin film according to any one of claims 1 to 5, wherein the crystalline thermoplastic resin is a polypropylene resin.   The melting point of the resin film is 170 ° C. or higher and 176 ° C. or lower, and the resin film according to claim 1.   The melting enthalpy is 90 J / g or more and 125 J / g or less, and the resin film according to claim 1. A resin film according to any one of claims 1 to 8,
A resin film integrated with a metal layer, comprising a metal layer laminated on one side or both sides of the resin film.   A film capacitor having the metal layer-integrated resin film according to claim 9 that is wound or a structure in which a plurality of the metal layer-integrated resin films according to claim 8 are laminated.