阅读说明：本技术 双轴拉伸聚丙烯薄膜、金属化薄膜、金属化薄膜卷和薄膜电容器 (Biaxially stretched polypropylene film, metallized film roll, and film capacitor ) 是由 奥山佳宗 富永刚史 藤城义和 石渡忠和 于 2019-08-28 设计创作，主要内容包括：一种双轴拉伸聚丙烯薄膜,其厚度为1.0μm～3.5μm,第一方向上的135℃的拉伸断裂应力为70MPa以上,第一方向上的125℃的拉伸断裂应力与第一方向上的135℃的拉伸断裂应力之差为0MPa以上且15MPa以下。(A biaxially stretched polypropylene film having a thickness of 1.0 to 3.5 [ mu ] m, a tensile stress at break at 135 ℃ in the first direction of 70MPa or more, and a difference between the tensile stress at break at 125 ℃ in the first direction and the tensile stress at break at 135 ℃ in the first direction of 0MPa or more and 15MPa or less.)

1. A biaxially stretched polypropylene film having a thickness of 1.0 to 3.5 μm,

a tensile breaking stress at 135 ℃ in the first direction of 70MPa or more,

the difference between the tensile breaking stress at 125 ℃ in the first direction and the tensile breaking stress at 135 ℃ in the first direction is 0MPa or more and 15MPa or less.

2. The biaxially stretched polypropylene film according to claim 1, wherein the dimensional change rate in the first direction at 135 ℃ is-3.2% or more.

3. The biaxially stretched polypropylene film according to claim 1 or 2, wherein the difference between the rate of change in dimension in the first direction at 125 ℃ and the rate of change in dimension in the first direction at 135 ℃ is 0% or more and 1.5% or less.

4. The biaxially stretched polypropylene film according to any one of claims 1 to 3, wherein the crystallite size is 12.20nm or less.

5. The biaxially stretched polypropylene film according to any one of claims 1 to 4, which is used for capacitors.

6. A metallized film, comprising:

the biaxially stretched polypropylene film according to any one of claims 1 to 5; and the combination of (a) and (b),

and a metal layer laminated on one or both surfaces of the biaxially stretched polypropylene film.

7. A roll of metallized film obtained by winding the metallized film according to claim 6.

8. A film capacitor having the metallized film of claim 6 wound or having a constitution in which a plurality of layers of the metallized film of claim 6 are laminated.

Technical Field

The present disclosure relates to biaxially stretched polypropylene films, metallized films, rolls of metallized films, and film capacitors.

Background

Biaxially stretched polypropylene films have excellent electrical characteristics such as high voltage resistance and low dielectric loss characteristics, and have high moisture resistance, and therefore, are used as dielectrics for film capacitors. For example, the derivative is used as a thin film capacitor in an inverter constituting a power control unit of a hybrid vehicle/electric vehicle.

As shown in fig. 1, a metallized film 5 constituting a film capacitor includes: a biaxially stretched polypropylene film 10; and a metal layer 30 provided on the biaxially stretched polypropylene film 10. A metal layer 30 is provided on one of both surfaces of the biaxially stretched polypropylene film 10. Fig. 1 is a sectional view taken along line I-I in fig. 2.

As shown in fig. 2, an insulating boundary 21 extending continuously in the MD direction D1 is provided on one end 51 of the metallized film 5 in the TD direction D2. Typically, the insulating boundary 21 is formed as follows: before the metal deposition is performed on the biaxially stretched polypropylene film 10, a predetermined position of the biaxially stretched polypropylene film 10 is covered with oil. Note that reference numeral 52 denotes the other end portion of the metalized film 5 in the TD direction D2, reference numeral 31 denotes a heavy-edge portion, and reference numeral 32 denotes a movable portion.

To produce such a metallized film 5, for example, the following steps are performed: extruding the melted polypropylene resin in a T die head in a sheet shape to obtain a casting blank sheet; biaxially stretching the casting blank sheet to obtain a biaxially stretched polypropylene film; the biaxially stretched polypropylene film was unwound, oil was blown to perform metal deposition, and the metallized film 6 (see fig. 3) before slitting was wound up on a winding roll (hereinafter, this may be referred to as "deposition step"). As shown in fig. 3, the metallized film 6 before slitting has a plurality of insulating borders 21 extending continuously in the MD direction D1. The metallized film 5 can be obtained by cutting the pre-slit metallized film 6 into a plurality of pieces by a cutting blade in the TD direction D2 while being unwound. In the vapor deposition step, oil at 100 to 150 ℃ is blown to the biaxially stretched polypropylene film. The metal used for metal evaporation is generally heated to 600 ℃ or higher in an evaporation source. The biaxially stretched polypropylene film 10 after the oil blowing was passed between the evaporation source and the cooling roll to evaporate the metal. In fig. 3, reference numeral 300 denotes a metal layer of the metallized film 6 before dicing, which is formed by vapor deposition.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 63-310954

Disclosure of Invention

Problems to be solved by the invention

In the vapor deposition step, the biaxially stretched polypropylene film may be affected by heat from an oil for forming an insulating boundary, a vapor deposited metal, or an evaporation source, thereby causing heat loss (wrinkles and sagging). This heat loss may cause wrinkles when the metallized film is wound up before slitting after vapor deposition, or may cause unevenness in the vapor deposited film due to wrinkles or slackness. In particular, in a biaxially stretched polypropylene film which is thin as in a biaxially stretched polypropylene film for capacitors, the occurrence of defects due to heat loss, specifically, the occurrence of wrinkle defects and vapor deposition film unevenness is significant. Such defects adversely affect the subsequent steps (dicing step, capacitor element winding step, film capacitor manufacturing step, etc.), and thus defective portions are discarded.

Therefore, since the film capacitor is used in a hybrid vehicle, an electric vehicle, or the like, it is desired that the capacitance is not easily decreased and short-circuiting is not easily caused even in a severe environment of high temperature and high voltage.

The object of the present disclosure is to provide a biaxially stretched polypropylene film: the biaxially stretched polypropylene film has a small thickness, but can suppress the occurrence of wrinkle defects in the wound form after the vapor deposition step and the occurrence of vapor deposition film unevenness, and in both limit tests (temperature limit test and voltage limit test), a film capacitor can be produced which has a small decrease in electrostatic capacity with the passage of time and a long time to short circuit.

Means for solving the problems

The disclosed biaxially stretched polypropylene film has a thickness of 1.0 to 3.5 [ mu ] m, a tensile stress at break at 135 ℃ in a first direction of 70MPa or more, and a difference between the tensile stress at break at 125 ℃ in the first direction and the tensile stress at break at 135 ℃ in the first direction of 0MPa or more and 15MPa or less.

In the biaxially stretched polypropylene film of the present disclosure, although the biaxially stretched polypropylene film is thin, the occurrence of wrinkle failure in the wound form after the vapor deposition step can be suppressed, and the occurrence of vapor deposition film unevenness can be suppressed. The biaxially stretched polypropylene film of the present disclosure can produce a film capacitor which has a small decrease in electrostatic capacity with the passage of time and a long time to short-circuit in two kinds of limit tests (temperature limit test and voltage limit test). Further, since the biaxially stretched polypropylene film is thin, the capacitance of the film capacitor and the capacitance per unit volume are large.

The reason why the wrinkle failure and the deposition film unevenness in the winding form after the deposition step can be suppressed is estimated as follows.

The first factor that causes the wrinkle failure and the vapor deposition film unevenness in the wound form after the vapor deposition step is that the temperature rises at the portion where the oil for forming the insulation boundary adheres, and this portion is easily elongated in the MD direction by the tension during transportation, and the other portion (the portion where the oil does not adhere) is not easily elongated, and the second factor is that when the biaxially stretched polypropylene film passes near the vapor deposition source, the film temperature rises as it gets closer to the vapor deposition source and receives heat from the adhered vapor deposition metal or the vapor deposition source, and therefore the portion near the vapor deposition source is easily elongated in the MD direction by the tension during transportation, and the portion far from the vapor deposition source is not easily elongated.

In contrast, it is considered that the biaxially stretched polypropylene film of the present disclosure can suppress temperature unevenness (high temperature in the portion where oil is adhered and low temperature in the portion where oil is not adhered) which may be caused by oil for forming an insulation boundary in the past, and wrinkle failure in a wound form and unevenness of a vapor-deposited film which are caused by rapid temperature change of the biaxially stretched polypropylene film due to adhesion of a vapor-deposited metal and heat from a vapor-deposition source. This will be described in detail below.

First, it is considered that the biaxially stretched polypropylene film of the present disclosure can suppress the wrinkle failure in the wound form and the unevenness of the vapor deposition film, which may have been caused by the temperature unevenness (high temperature in the portion where the oil is adhered and low temperature in the portion where the oil is not adhered) which may be caused by the oil for forming the insulation boundary.

As described above, the reason why the wrinkle failure and the vapor deposited film unevenness can be suppressed is that, first, the tensile breaking stress at 135 ℃ in the first direction is 70MPa or more, and therefore, the portion to which the oil for forming the insulating boundary adheres can be suppressed from being elongated in the MD direction by the tension at the time of transportation. For another reason, the difference between the tensile breaking stress at 125 ℃ in the first direction and the tensile breaking stress at 135 ℃ in the first direction is 0MPa or more and 15MPa or less, and therefore, the TD-directional unevenness in strength can be reduced due to the temperature unevenness in the plane of the biaxially stretched polypropylene film, and thus the TD-directional unevenness in MD-directional elongation can be suppressed.

As described above, it is considered that the biaxially stretched polypropylene film of the present disclosure can stabilize transportation in the vapor deposition step by suppressing both elongation in the MD of the portion to which the oil for forming an insulating boundary adheres and variation in the TD of the MD elongation.

As a result, the biaxially stretched polypropylene film of the present disclosure can suppress the temperature unevenness, the wrinkle failure in the wound form, and the unevenness of the vapor deposition film, which may have been caused by the oil for forming the insulating boundary.

Secondly, the biaxially stretched polypropylene film of the present disclosure can suppress the wrinkle failure in the wound form and the unevenness of the vapor-deposited film, which may be caused by the rapid temperature change of the biaxially stretched polypropylene film due to the adhesion of the vapor-deposited metal and the heat from the vapor-deposition source.

As described above, the reason why the wrinkle failure and the vapor deposited film unevenness can be suppressed is that, first, the tensile breaking stress at 135 ℃ in the first direction is 70MPa or more, and therefore, when the biaxially stretched polypropylene film receives heat from the vapor deposited metal or the evaporation source attached in the metal vapor deposition step, the biaxially stretched polypropylene film can be suppressed from being elongated in the MD direction by the tension during transportation. For another reason, the difference between the tensile breaking stress at 125 ℃ in the first direction and the tensile breaking stress at 135 ℃ in the first direction is 0MPa or more and 15MPa or less, so that variation in strength due to temperature change can be reduced, and thus, variation in elongation in the MD due to tension during transportation can be suppressed.

As described above, it is considered that the biaxially stretched polypropylene film of the present disclosure can stabilize the transportation in the vapor deposition step by suppressing both the stretching of the biaxially stretched polypropylene film in the MD direction due to the heat from the vapor deposition metal or the evaporation source and the unevenness of the MD direction elongation due to the temperature change.

As a result, it is considered that the biaxially stretched polypropylene film of the present disclosure can suppress wrinkle defects in the wound form and unevenness of the vapor-deposited film, which may have been conventionally caused by rapid temperature changes of the biaxially stretched polypropylene film due to adhesion of the vapor-deposited metal and heat from the vapor-deposition source.

According to such a principle, the biaxially stretched polypropylene film of the present disclosure has a small thickness, but can suppress temperature unevenness which may be caused by an oil for forming an insulating boundary in the past, and wrinkle defects in a wound form and vapor deposition film unevenness which are caused by a rapid temperature change of the biaxially stretched polypropylene film due to adhesion of a vapor deposition metal and heat from a vapor deposition source.

On the other hand, patent document 1 discloses that the rigidity is improved and the generation of wrinkles at the time of vapor deposition is suppressed, but not only the rigidity at high temperature of the biaxially stretched polypropylene film but also the strength of the rigidity against temperature unevenness and temperature change at high temperature have not been studied. Further, the biaxially stretched polypropylene film is also thick, and thin films have not been studied. From this fact, it is considered that the biaxially stretched polypropylene film of patent document 1 is difficult to suppress both the wrinkle failure and the vapor deposition film unevenness in the wound form of the thin film.

The reason why the biaxially stretched polypropylene film of the present disclosure can produce a film capacitor having a small reduction in electrostatic capacity and a long time to short circuit in two limit tests (temperature limit test and voltage limit test) is presumed as follows.

First, it is considered that the tensile breaking stress at 135 ℃ in the first direction is 70MPa or more, and therefore, the internal structure of the biaxially stretched polypropylene film of the present disclosure is strong even at high temperatures (specifically, 115 ℃ in the temperature limit test and 105 ℃ in the voltage limit test).

Secondly, since the difference between the tensile breaking stress at 125 ℃ in the first direction and the tensile breaking stress at 135 ℃ in the first direction is 0MPa or more and 15MPa or less, and the change in tensile breaking stress is small with respect to the temperature change, the internal structure is not easily disintegrated by heating to the test temperature for the temperature limit test and the voltage limit test (specifically, 115 ℃ in the temperature limit test and 105 ℃ in the voltage limit test), and a strong structure can be maintained even at the test temperature. As a result, it is considered that the biaxially stretched polypropylene film of the present disclosure can suppress the decrease in electrostatic capacity with the passage of time and can suppress the occurrence of short circuits in the temperature limit test and the voltage limit test.

It is noted that the biaxially stretched polypropylene film of the present disclosure can be used for capacitors.

Further, the present disclosure also relates to a metallized film, which may have: a biaxially stretched polypropylene film of the present disclosure; and a metal layer laminated on one or both surfaces of the biaxially stretched polypropylene film.

The present disclosure also relates to a roll of metallized film, which may be wound from the metallized film of the present disclosure.

The present disclosure also relates to a film capacitor, which may have the metalized film of the present disclosure wound or have a constitution in which a plurality of layers of the metalized film of the present disclosure are laminated.

ADVANTAGEOUS EFFECTS OF INVENTION

The biaxially stretched polypropylene film of the present disclosure can suppress wrinkle defects in a wound form after a vapor deposition step and can suppress the occurrence of vapor deposition film unevenness, although it is thin, and can produce a film capacitor having a long time to short-circuit with a reduced electrostatic capacity with the passage of time in two kinds of limit tests (a temperature limit test and a voltage limit test).

Drawings

FIG. 1 is a simplified cross-sectional view of a metallized membrane, and more particularly, a simplified cross-sectional view taken along line I-I in FIG. 2.

Fig. 2 is a schematic top view of a metallized film.

Fig. 3 is a schematic plan view of a metallized film before slitting unwound from a take-up roll.

Detailed Description

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

In the present specification, expressions "including" and "including" include concepts of "including", "consisting essentially of … …", and "consisting of … … only".

In this specification, the expression "capacitor" includes the concepts of "capacitor", "capacitor element", and "film capacitor".

The biaxially stretched polypropylene film of the present embodiment is not a microporous film and therefore does not have a large number of pores.

The biaxially stretched polypropylene film of the present embodiment may be composed of a plurality of layers of 2 or more layers, and preferably is composed of a single layer.

In the present specification, polypropylene is sometimes referred to simply as PP, and polypropylene resin is sometimes referred to simply as PP resin.

First, the direction described in the present embodiment will be explained. In the present embodiment, the first direction means a longitudinal direction of the biaxially stretched polypropylene film, that is, the same direction as the longitudinal direction. The longitudinal direction is sometimes referred to as the roll take-up direction. In the present embodiment, the first direction may be the same direction as the machine direction (hereinafter, referred to as "MD direction"). The MD direction is sometimes referred to as the flow direction, machine axis direction, etc. Hereinafter, the first direction is mainly referred to as MD direction. However, in the present invention, the first direction is not limited to the embodiment in which the first direction is the same as the longitudinal direction, and is not limited to the embodiment in which the first direction is the same as the MD direction. On the other hand, the second direction means the same direction as the width direction of the biaxially stretched polypropylene film. In the present embodiment, the second direction may be the same direction as the TransverseDirection (hereinafter referred to as "TD direction"). Hereinafter, the second direction is mainly referred to as TD direction. However, in the present invention, the second direction is not limited to the mode of referring to the same direction as the width direction, and is not limited to the mode of referring to the same direction as the TD direction.

In the biaxially stretched polypropylene film of the present embodiment, the tensile breaking stress at 135 ℃ in the first direction is 70MPa or more, preferably 80MPa or more, and more preferably 85MPa or more. If the tensile breaking stress of the biaxially stretched polypropylene film is less than 70MPa, the strength of the portion subjected to heat to the tensile force during transportation may be insufficient when the film is subjected to heat from an oil for forming an insulation boundary, a vapor-deposited metal, or a vapor deposition source. Further, if the tensile breaking stress is less than 70MPa, the internal structure of the biaxially stretched polypropylene film may be insufficient. The tensile breaking stress at 135 ℃ in the first direction is preferably 120MPa or less, more preferably 110MPa or less, still more preferably 105MPa or less, and particularly preferably 100MPa or less. The reason why 120MPa or less is preferred is that if the tensile breaking stress at 135 ℃ in the first direction is too high, the film forming stability (the ease of breakage of the film) of the biaxially stretched polypropylene film is insufficient. In the present specification, the tensile breaking stress at 135 ℃ is sometimes referred to as σ_b135。

Tensile stress at break (σ) of 135 ℃ in a first direction_b135) Can be adjusted according to the MD stretching ratio. The MD stretching ratio is a ratio when the green sheet is stretched in the MD direction. However, a tensile breaking stress (σ) of 135 ℃ in the first direction_b135) The temperature of the MD preheat roller group located upstream of the MD stretch roller group, the time of adhesion to the MD preheat roller group, the temperature of the MD stretch roller group, the time of adhesion to the MD stretch roller group, the temperature of the MD relax roller group located downstream of the MD stretch roller group, and the time of adhesion to the MD relax roller group also affect the performance of the device.

In the biaxially stretched polypropylene film of the present embodiment, the tensile breaking stress at 125 ℃ in the first direction and the tensile breaking stress at 135 ℃ in the first direction (σ)_b135) The difference is 0MPa or more and 15MPa or less, preferably 3MPa or more and 15MPa or less, more preferably 5MPa or more and 14MPa or less, and further preferably 6MPa or more and 14MPa or less. The difference may be obtained by subtracting the tensile breaking stress (σ) at 135 ℃ in the first direction from the tensile breaking stress at 125 ℃ in the first direction_b135) And obtaining the compound. If the difference exceeds 15MPa, it can be said that temperature unevenness due to the oil for forming the insulating boundary, temperature change due to passage near the evaporation source, and insufficient strength TD direction unevenness are small, and the internal structure is likely to be disintegrated by heating at test temperatures for reaching the temperature limit test and the voltage limit test (specifically, 115 ℃ in the temperature limit test and 105 ℃ in the voltage limit test). In the present specification, the tensile breaking stress at 125 ℃ is sometimes referred to as σ_b125. In the present specification, the tensile breaking stress (. sigma.) at 125 ℃ in the first direction is defined_b125) And a tensile breaking stress (σ) of 135 ℃ in the first direction_b135) The difference in tensile breaking stress is sometimes referred to as the difference in σ_b125-σ_b135。

Tensile breaking stress difference (sigma)_b125-σ_b135) The adjustment can be made by the temperature of the MD preheat roll group located upstream of the MD stretch roll group, the adhesion time to the MD preheat roll group, the temperature of the MD stretch roll group, the adhesion time to the MD stretch roll group, the temperature of the MD relax roll group located downstream of the MD stretch roll group, and the adhesion time to the MD relax roll group. However, tensile breaking stressDifference (sigma)_b125-σ_b135) Is also affected by the MD stretch ratio.

The thickness of the biaxially stretched polypropylene film of the present embodiment is in the range of 1.0 μm to 3.5. mu.m. The thickness of the biaxially stretched polypropylene film of the present embodiment is preferably 1.0 μm or more, more preferably 1.5 μm or more, and further preferably 2.0 μm or more. The thickness of the biaxially stretched polypropylene film of the present embodiment is preferably 3.5 μm or less, more preferably 3.0 μm or less, and still more preferably 2.8 μm or less. The biaxially stretched polypropylene film of the present embodiment can be suitably used as a capacitor because the electrostatic capacity per unit volume when a capacitor element is produced can be increased if the thickness is 3.5 μm or less.

In the case of the polypropylene film, the thinner the thickness is, the larger the capacitance per unit volume can be. More specifically, the capacitance C is represented by the dielectric constant ∈, the electrode area S, and the dielectric thickness d (thickness d of the polypropylene film) as follows.

C＝εS/d

Here, in the case of the film capacitor, since the thickness of the electrode is thinner by 3 orders or more than the thickness of the polypropylene film (dielectric), if the volume of the electrode is disregarded, the volume V of the capacitor is expressed as follows.

V＝Sd

Therefore, according to the above 2 formulae, the capacitance per unit volume C/V is represented as follows.

C/V＝ε/d²

From the above formula, the electrostatic capacity (C/V) per unit volume is inversely proportional to the square of the thickness of the polypropylene film. In addition, the dielectric constant ε is determined by a material to be used. As can be seen, the capacitance per unit volume (C/V) cannot be improved unless the material is changed and the thickness is reduced.

The foregoing thickness of the biaxially stretched polypropylene film means the following value: measured at a temperature of 23. + -. 2 ℃ and a humidity of 50. + -. 5% RH using a Citizen Seimitsu Co., Ltd., a paper thickness measuring instrument MEI-11 (measurement pressure 100kPa, lowering speed 3 mm/sec, measurement terminal. phi. 16mm, measurement force 20.1N). The sample was cut out from the roll in a state of being overlapped by 10 sheets or more, and the operation was performed so that the film did not enter wrinkles or air at the time of cutting. For 10 superimposed samples, 5 measurements were made, and the thickness was calculated by dividing the average of 5 measurements by 10.

In the biaxially stretched polypropylene film of the present embodiment, the tensile breaking stress at 23 ℃ in the first direction is preferably 155MPa or more, more preferably 160MPa or more. When the tensile breaking stress of the biaxially stretched polypropylene film is 155MPa or more, the internal structure of the biaxially stretched polypropylene film is sufficiently strengthened, the dielectric breakdown voltage of the film is further improved, and the withstand voltage of the capacitor element can be further improved. The tensile breaking stress at 23 ℃ in the first direction is preferably 300MPa or less, more preferably 280MPa or less, and further preferably 250MPa or less. When the tensile breaking stress of the biaxially stretched polypropylene film is 300MPa or less, the biaxially stretched polypropylene film is more excellent in film forming stability (film breakage resistance). In the present specification, the tensile breaking stress at 23 ℃ in the MD direction is sometimes referred to as σ_b23。

In the biaxially stretched polypropylene film of the present embodiment, the heat shrinkage rate in the first direction at 125 ℃ is preferably 7.0% or less, more preferably 6.5% or less. When the heat shrinkage ratio in the first direction at 125 ℃ is 7.0% or less, the film can be prevented from excessively shrinking when used as a capacitor element at high temperatures. As a result, the capacitor element can be prevented from being deformed due to the change in the gap between the films, and the deterioration of the withstand voltage performance of the capacitor element can be suppressed. The heat shrinkage ratio in the first direction at 125 ℃ is preferably 3.0% or more, more preferably 4.0% or more, and still more preferably 5.0% or more.

In the present embodiment, the heat shrinkage rate in the first direction at 125 ℃ can be controlled depending on the stretching conditions and the like. For example, when the first direction is the MD direction, the MD heat shrinkage tends to increase as the MD stretching magnification increases, and the MD heat shrinkage tends to increase as the temperature in the MD preheating, stretching, and relaxing step decreases. In the present specification, the heat shrinkage rate at 125 ℃ in the MD direction is sometimes referred to as S_b125。

In the biaxially stretched polypropylene film of the present embodiment, the heat shrinkage rate in the first direction at 135 ℃ is preferably 9.0% or less, more preferably 8.5% or less, and still more preferably 8.0% or less. When the heat shrinkage ratio in the first direction at 135 ℃ is 9.0% or less, the film can be prevented from excessively shrinking when used as a capacitor element at high temperatures. As a result, the capacitor element can be prevented from being deformed due to the change in the gap between the films, and the deterioration of the withstand voltage performance of the capacitor element can be suppressed. The heat shrinkage ratio in the first direction at 135 ℃ is preferably 3.0% or more, more preferably 4.0% or more, and still more preferably 5.0% or more.

In the present embodiment, the heat shrinkage rate in the first direction at 135 ℃ can be controlled depending on the stretching conditions and the like. For example, when the first direction is the MD direction, the MD heat shrinkage tends to increase as the MD stretching magnification increases, and the MD heat shrinkage tends to increase as the temperature in the MD preheating, stretching, and relaxing step decreases. In the present specification, the heat shrinkage rate at 135 ℃ in the MD direction is sometimes referred to as S_b135。

The aforementioned S_b125And the aforementioned S_b135Difference (i.e., S)_b125-S_b135) Preferably not less than 4.0% and not more than 0%, more preferably not less than 3.0% and not more than 0.1%, still more preferably not less than 2.5% and not more than 0.5%, and particularly preferably not less than 2.2% and not more than 1.0%. When the difference is within the above-described preferable range, the TD directional unevenness in strength due to temperature unevenness caused by the oil for forming the insulating boundary, temperature change caused when passing through the vicinity of the evaporation source, and the like can be further sufficiently reduced.

In the biaxially stretched polypropylene film of the present embodiment, the dimensional change rate in the first direction at 125 ℃ is preferably-2.2% or more, more preferably-2.0% or more. When the dimensional change rate in the first direction at 125 ℃ is-2.2% or more, excessive increase in shrinkage of the film can be suppressed when the film is used as a capacitor element at high temperatures. As a result, the capacitor element can be prevented from being deformed due to the change in the gap between the films, and the deterioration of the withstand voltage performance of the capacitor element can be suppressed. The dimensional change rate in the first direction at 125 ℃ is preferably 1.0% or less, more preferably 0.5% or less, and still more preferably 0.0% or less.

In the present embodiment, the rate of change in the dimension in the first direction at 125 ℃ can be controlled depending on the stretching conditions and the like. For example, when the first direction is the MD direction, the MD dimension change rate tends to become larger in the negative direction as the MD stretching magnification is higher (that is, the MD dimension change rate tends to become lower). For example, when the first direction is the MD direction, the MD dimension change rate tends to become larger in the negative direction as the temperature in the preheating, stretching, and relaxing step in the MD is lower (that is, the value as the MD dimension change rate tends to become lower).

The dimensional change rate in the first direction at 125 ℃ is a value measured by the TMA method, and is based on the method described in examples in more detail. In the present specification, the dimensional change rate in the first direction at 125 ℃ is sometimes referred to as D_b125。

In the biaxially stretched polypropylene film of the present embodiment, the dimensional change rate in the first direction at 135 ℃ is preferably-3.2% or more, more preferably-3.0% or more. When the dimensional change rate in the first direction at 135 ℃ is-3.2% or more, excessive increase in shrinkage of the film can be suppressed when the film is used as a capacitor element at high temperatures. As a result, the capacitor element can be prevented from being deformed due to the change in the gap between the films, and the deterioration of the withstand voltage performance of the capacitor element can be suppressed. The dimensional change rate in the first direction at 135 ℃ is preferably 1.0% or less, more preferably 0.5% or less, and still more preferably 0.0% or less.

In the present embodiment, the rate of change in the dimension in the first direction at 135 ℃ can be controlled depending on the stretching conditions and the like. For example, when the first direction is the MD direction, the MD dimension change rate tends to increase in the negative direction as the MD stretching magnification increases, and the MD dimension change rate tends to increase in the negative direction as the temperature in the preheating, stretching, and relaxing step in the MD decreases.

The dimensional change rate in the first direction at 135 ℃ is a value measured by the TMA method, and is based on the method described in examples in more detail. In the present specification, the dimensional change rate in the first direction at 135 ℃ is sometimes referred to as D_b135。

D above_b125And the foregoing D_b135Difference (i.e., D)_b125-D_b135) Preferably 0% or more and 1.5% or less, more preferably 0.1% or more and 1.0% or less, further preferably 0.2% or more and 0.9% or less, and particularly preferably 0.3% or more and 0.8% or less. When the difference is within the above-described preferable range, the TD directional unevenness in strength due to temperature unevenness caused by the oil for forming the insulating boundary, temperature change caused when passing through the vicinity of the evaporation source, and the like can be further sufficiently reduced.

In the biaxially stretched polypropylene film of the present embodiment, the crystallite size of the (040) plane as measured by wide-angle X-ray diffractometry is preferably 12.20nm or less, more preferably 12.00nm or less. As the crystallite size decreases, the leak current decreases, and structural failure due to joule heat generation becomes less likely to occur, and therefore, heat resistance, voltage resistance, and heat resistance and voltage resistance over a long period of time are preferably improved. However, if the mechanical strength and the like are considered and the thickness of the sheet (folded crystal) of the polymer chain is considered, the lower limit of the crystallite size is generally 10.00nm, preferably 11.00 nm.

In the present embodiment, the crystallite size can be controlled according to the cooling conditions, the stretching conditions, and the like when obtaining a cast ingot. The crystallite size tends to be smaller as the casting temperature is lower, the crystallite size tends to be smaller as the draw ratio is higher, and the crystallite size tends to be smaller as the draw temperature is lower.

In the biaxially stretched polypropylene film of the present embodiment, when a capacitor element is produced by the method described in examples and a temperature limit test is performed, the time required for the rate of change in electrostatic capacity to be + 5% or more or-5% or less is preferably 500 hours or more.

In the biaxially stretched polypropylene film of the present embodiment, when a capacitor element is produced by the method described in examples and subjected to a voltage limit test, the time required for the rate of change in electrostatic capacity to be + 5% or more or-5% or less is preferably 500 hours or more.

Next, suitable raw materials and production methods of the biaxially stretched polypropylene film of the present embodiment will be described below. However, the raw material and the production method of the biaxially stretched polypropylene film of the present embodiment are not limited to the following descriptions.

The biaxially stretched polypropylene film comprises a polypropylene resin. The content of the polypropylene resin is preferably 90% by mass or more, more preferably 95% by mass or more, based on the whole biaxially stretched polypropylene film (when the whole biaxially stretched polypropylene film is 100% by mass). The upper limit of the content of the polypropylene resin is, for example, 100 mass% or 98 mass% with respect to the whole biaxially stretched polypropylene film. The polypropylene resin may contain one kind of polypropylene resin alone, or two or more kinds of polypropylene resins.

When two or more kinds of polypropylene resins are contained in the biaxially stretched polypropylene film, the polypropylene resin having a large content is referred to as "polypropylene resin of main component" in the present specification. In addition, when the polypropylene resin contained in the biaxially stretched polypropylene film is one type, the polypropylene resin is referred to as "polypropylene resin of the main component" in the present specification.

Hereinafter, in the present specification, when the term "polypropylene resin" is used without particularly specifying whether or not the polypropylene resin is a main component, the term refers to both the polypropylene resin as a main component and the polypropylene resins other than the main component unless otherwise specified. For example, the "weight average molecular weight Mw of the polypropylene resin is preferably 25 to 45 ten thousand. "the weight average molecular weight Mw of the polypropylene resin as the main component is preferably 25 to 45 ten thousand, and the weight average molecular weight Mw of the polypropylene resin other than the main component is preferably 25 to 45 ten thousand.

The weight average molecular weight Mw of the polypropylene resin is preferably 25 to 45 ten thousand, more preferably 25 to 40 ten thousand. When the weight average molecular weight Mw of the polypropylene resin is 25 to 45 ten thousand, the resin flowability becomes appropriate. As a result, the thickness of the green sheet can be easily controlled, and a thin stretched film can be easily produced.

The molecular weight distribution (Mw/Mn) of the polypropylene resin is preferably 5 or more and 12 or less, more preferably 5 or more and 11 or less, and further preferably 5 or more and 10 or less.

In the present specification, the weight average molecular weight (Mw), the number average molecular weight (Mn), and the molecular weight distribution (Mw/Mn) of the polypropylene resin are values measured by a Gel Permeation Chromatography (GPC) apparatus. More specifically, it is a value measured using HLC-8321GPC-HT (trade name) of a high temperature GPC measurement machine with a built-in differential Refractometer (RI), manufactured by Tosoh corporation. As the GPC column, 1 TSKgel guard columnHHR (30) HT (7.5 mmI.D.. times.7.5 cm) and 3 TSKgel GMHHR-H (20) HT, manufactured by Tosoh corporation, were connected and used. The column temperature was set to 140 ℃ to prepare a standard curve, which was a 5-fold approximation curve of standard polystyrene manufactured by Tosoh corporation measured by allowing trichlorobenzene as an eluent to flow at a flow rate of 1.0ml/10 minutes. Wherein the molecular weight is converted to the molecular weight of polypropylene by Q-factor. From the obtained calibration curve and SEC chromatogram, the weight average molecular weight (Mw) and number average molecular weight (Mn) were obtained by analytical software for a measuring apparatus.

Differential distribution value difference D of polypropylene resin_MPreferably-5% or more and 14% or less, more preferably-4% or more and 12% or less, and further preferably-4% or more and 10% or less. Here, the "differential distribution value difference D_M"is a difference obtained by subtracting a differential distribution value at log (m) of 6.0 from a differential distribution value at log molecular weight log (m) of 4.5 in a molecular weight differential distribution curve.

Note that the "differential distribution value difference D_MThe phrase "at least 5% and at most 14% means that when the log molecular weight log (m) which is a representative distribution value of a component having a molecular weight of 1 to 10 ten thousand on the low molecular weight side (hereinafter also referred to as" low molecular weight component ") is compared with a component having a molecular weight of about 100 ten thousand on the high molecular weight side (hereinafter also referred to as" high molecular weight component ") and a log (m) which is a representative distribution value of about 6.0, the difference is positive, the number of low molecular weight components is large, and the number of high molecular weight components is large when the difference is negative, depending on the Mw value of the polypropylene resin.

That is, even if the molecular weight distribution Mw/Mn is 5 to 12, the width of the molecular weight distribution is merely expressed, and the relationship between the amounts of the high molecular weight component and the low molecular weight component is not known. Therefore, from the viewpoint of stabilizing the film-forming property and the thickness uniformity of the green sheet, it is preferable that the polypropylene resin is used so that the difference in the differential distribution value is from-5% to 14% in the component having a molecular weight of 1 to 10 ten thousand to the component having a molecular weight of 100 ten thousand in order to have a wide molecular weight distribution and to appropriately contain the low-molecular-weight component.

Differential distribution value difference D_MThe values obtained below. First, an SEC chromatogram was obtained in the same manner as described above. The chromatogram was converted into a differential molecular weight distribution curve using analysis software built into the measuring apparatus used. From the differential molecular weight distribution curve, values of the differential molecular weight distribution at log (m) of 4.5 and log (m) of 6.0 were read. Differential distribution value difference D_MThe value of the differential molecular weight distribution at log (m) of 6.0 was subtracted from the value of the differential molecular weight distribution at log (m) of 4.5.

The heptane-insoluble matter (HI) of the polypropylene resin is preferably 96.0% or more, more preferably 97.0% or more. The heptane-insoluble matter (HI) of the polypropylene resin is preferably 99.5% or less, more preferably 99.0% or less. Here, the more 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 moderately improved and the voltage resistance at high temperature is improved due to moderately high stereoregularity. On the other hand, the solidification (crystallization) speed at the time of molding the green casting web becomes moderate, and the green casting web has moderate stretchability.

The meso pentad fraction ([ mmmm ]) of the polypropylene resin is preferably 94.0% or more, more preferably 94.5% or more, and still more preferably 95.0% or more. The meso pentad fraction of the polypropylene resin is preferably less than 98.0%, more preferably 97.5% or less, and still more preferably 97.0% or less. By using such a polypropylene resin, crystallinity of the resin is moderately improved by moderately high stereoregularity, and initial voltage resistance and voltage resistance over a long period of time are improved. On the other hand, the desired stretchability can be obtained according to an appropriate solidification (crystallization) speed at the time of molding into a green sheet for casting.

The meso pentad fraction ([ mmmm ]) is an index of stereoregularity which can be obtained by high temperature Nuclear Magnetic Resonance (NMR) measurement. In the present specification, the meso pentad fraction ([ mmmm ]) is a value measured by a high-temperature fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR) manufactured by japan electronics corporation and JNM-ECP 500. The observation core was 13C (125MHz), the measurement temperature was 135 ℃, and a solvent for dissolving the polypropylene resin was o-dichlorobenzene (ODCB: a mixed solvent of ODCB and deuterated ODCB (mixing ratio: 4/1)) was used as the solvent for measuring the polypropylene resin, and the measurement method by high-temperature NMR was carried out, for example, by referring to the method described in "Japan analytical chemistry and Polymer analysis research, eds., New edition handbook of Polymer analysis, Ji Yi House, 1995, p.610".

The Melt Flow Rate (MFR) of the polypropylene resin is preferably 1.0 to 8.0g/10 min, more preferably 1.5 to 7.0g/10 min, and still more preferably 2.0 to 6.0g/10 min.

The polypropylene resin can be generally produced by a known polymerization method. As the polymerization method, for example, a gas phase polymerization method, a bulk polymerization method, and a slurry polymerization method can be exemplified. On the other hand, as the polypropylene resin, a commercially available product is also used.

In order to improve the electrical characteristics, the total ash content derived from the polymerization catalyst residue and the like contained in the polypropylene raw material resin is preferably as small as possible. The total ash content is preferably 50ppm or less, more preferably 40ppm or less, and particularly preferably 30ppm or less, based on the polypropylene resin (100 parts by weight).

The polypropylene resin or polypropylene resin composition may contain additives. Examples of the additives include antioxidants, chlorine absorbers, ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, and nucleating agents (e.g., melt-type nucleating agents). The polypropylene resin or polypropylene resin composition may contain additives in an amount not adversely affecting the biaxially stretched polypropylene film. The melt-type nucleating agent is preferably substantially not contained in the polypropylene resin or the polypropylene resin composition.

Next, each polypropylene resin when 2 or more polypropylene resins are used will be explained.

When 2 or more kinds of polypropylene resins are used, preferable examples include a combination of the following linear polypropylene resin A-1 and the following linear polypropylene resin B-1, the following linear polypropylene resin A-2 and the following linear polypropylene resin B-2, the following linear polypropylene resin A-3 and the following linear polypropylene resin B-3, or the following linear polypropylene resin A-4 and the following linear polypropylene resin B-4. In the present embodiment, the expression "linear polypropylene resin A" includes concepts of "linear polypropylene resin A-1", "linear polypropylene resin A-2", "linear polypropylene resin A-3" and "linear polypropylene resin A-4". The expression called the linear polypropylene resin B includes concepts called the linear polypropylene resin B-1, the linear polypropylene resin B-2, the linear polypropylene resin B-3 and the linear polypropylene resin B-4.

< Linear Polypropylene resin A >

(Linear Polypropylene resin A-1)

Differential distribution value difference D_M8.0% or more of a linear polypropylene resin.

(Linear Polypropylene resin A-2)

The heptane-insoluble matter (HI) is 98.5% or less of the linear polypropylene resin.

(Linear Polypropylene resin A-3)

A linear polypropylene resin having a Melt Flow Rate (MFR) at 230 ℃ of 4.0g/10 min or more and 10.0g/10 min or less.

(Linear Polypropylene resin A-4)

A linear polypropylene resin having a weight average molecular weight (Mw) of 25 to less than 34.5 ten thousand.

< Linear Polypropylene resin B >

(Linear Polypropylene resin B-1)

Differential distribution value difference D_MLess than 8.0% of linear polypropylene resin.

(Linear Polypropylene resin B-2)

Heptane Insolubles (HI) over 98.5% of linear polypropylene resin.

(Linear Polypropylene resin B-3)

A linear polypropylene resin having a Melt Flow Rate (MFR) at 230 ℃ of 0.1g/10 min or more and less than 4.0g/10 min.

(Linear Polypropylene resin B-4)

A linear polypropylene resin having a weight average molecular weight (Mw) of 34.5 to 45 ten thousand.

In the present embodiment, the linear polypropylene resin a may be a polypropylene resin as a main component, the linear polypropylene resin B may be a polypropylene resin as a main component, and a polypropylene resin with the linear polypropylene resin a as a main component is preferable.

The weight average molecular weight Mw of the linear polypropylene resin a is preferably 25 to 45 ten thousand, more preferably 25 to 40 ten thousand, and still more preferably 25 to less than 34.5 ten thousand. When the weight average molecular weight Mw of the linear polypropylene resin a is 25 to 45 ten thousand, the resin flowability becomes appropriate. As a result, the thickness of the green sheet can be easily controlled, and a thin biaxially stretched polypropylene film can be easily produced. Further, the thickness of the green sheet and the biaxially stretched polypropylene film is not likely to vary, and appropriate stretchability can be obtained, which is preferable.

The molecular weight distribution Mw/Mn of the linear 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 further preferably 9.0 or more and 11.0 or less.

When the molecular weight distribution Mw/Mn of the linear polypropylene resin A is within the above-described preferred range, the thickness of the green sheet and the biaxially stretched polypropylene film becomes less likely to vary, and appropriate stretchability can be obtained, which is preferred.

Differential distribution value difference D of Linear Polypropylene resin A_MPreferably 8.0% or more, more preferably 8.0% or more and 18.0% or less, further preferably 9.0% or more and 17.0% or less, and particularly preferably 10.0% or more and 16.0% or less.

Differential distribution value difference D_MWhen the content is 8.0% to 18.0%, the low-molecular-weight component is contained in a larger amount of 8.0% to 18.0% than the high-molecular-weight component. Therefore, the surface of the biaxially stretched polypropylene film in the present embodiment is preferably easily obtained.

The heptane-insoluble matter (HI) of the linear polypropylene resin a is preferably 96.0% or more, more preferably 97.0% or more. The heptane-insoluble matter (HI) of the linear polypropylene resin a is preferably 99.5% or less, more preferably 98.5% or less, and still more preferably 98.0% or less.

The linear polypropylene resin A has a Melt Flow Rate (MFR) at 230 ℃ of preferably 1.0 to 15.0g/10 min, more preferably 2.0 to 10.0g/10 min, still more preferably 4.0 to 10.0g/10 min, particularly preferably 4.3 to 6.0g/10 min. When the MFR at 230 ℃ of the linear polypropylene resin A is within the above range, the flow characteristics in a molten state are excellent, so that unstable flow such as melt fracture is less likely to occur, and the fracture at the time of stretching is suppressed. Therefore, the film thickness uniformity is good, and therefore, there is an advantage that the formation of a thin portion which easily causes insulation breakdown is suppressed.

The content of the linear polypropylene resin a is preferably 55 mass% to 90 mass%, more preferably 60 mass% to 85 mass%, and still more preferably 60 mass% to 80 mass% of the whole biaxially stretched polypropylene film.

The weight average molecular weight Mw of the linear polypropylene resin B is preferably 30 to 40 ten thousand, more preferably 33 to 38 ten thousand, and further preferably 35 to 38 ten thousand. The weight average molecular weight Mw of the linear polypropylene resin B is also preferably 34.5 to 45 ten thousand.

The molecular weight distribution Mw/Mn of the linear 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 further preferably 7.0 or more and 8.3 or less.

When the molecular weight distribution Mw/Mn of the linear polypropylene resin B is within the above-described preferred range, the thickness of the green sheet and the biaxially stretched polypropylene film becomes less likely to vary, and appropriate stretchability can be obtained, which is preferred.

Differential distribution value difference D of Linear Polypropylene resin B_MPreferably less than 8.0%, more preferably-20.0% or more and less than 8.0%, further preferably-10.0% or more and 7.9% or less, particularly preferably-5.0% or more and 7.5% or less.

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

The linear polypropylene resin B has a Melt Flow Rate (MFR) at 230 ℃ of preferably 0.1 to 6.0g/10 min, more preferably 0.1 to 5.0g/10 min, still more preferably 0.1 to 10 min but less than 4.0g/10 min, particularly preferably 0.1 to 10 min but not more than 3.9g/10 min.

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

When the linear polypropylene resin a and the linear polypropylene resin B are used in combination as the polypropylene resin, the polypropylene resin preferably contains 55 to 90% by weight of the linear polypropylene resin a and 45 to 10% by weight of the linear polypropylene resin B, more preferably 60 to 85% by weight of the linear polypropylene resin a and 40 to 15% by weight of the linear polypropylene resin B, and particularly preferably 60 to 80% by weight of the linear polypropylene resin a and 40 to 20% by weight of the linear polypropylene resin B, when the total amount of the polypropylene resin is 100% by mass.

When the polypropylene resin contains the linear polypropylene resin a and the linear polypropylene resin B, the biaxially stretched polypropylene film is in a finely mixed state (phase-separated state) of the linear polypropylene resin a and the linear polypropylene resin B, and therefore, the withstand voltage at high temperatures is improved.

The above description is of each polypropylene resin when 2 or more polypropylene resins are used.

The biaxially stretched polypropylene film may contain other resins (hereinafter also referred to as "other resins") than the polypropylene resin. Examples of the other resin include polyolefins other than polypropylene, such as polyethylene, poly (1-butene), polyisobutylene, poly (1-pentene), and poly (1-methylpentene); copolymers of α -olefins such as ethylene-propylene copolymers, propylene-butene copolymers, and ethylene-butene copolymers; vinyl monomer-diene monomer random copolymers such as styrene-butadiene random copolymers; and vinyl monomer-diene monomer-vinyl monomer random copolymers such as styrene-butadiene-styrene block copolymers. The biaxially stretched polypropylene film may contain such other resins in an amount within a range not adversely affecting the biaxially stretched polypropylene film. The biaxially stretched polypropylene film is preferably substantially free of such other resins.

The pre-stretched green sheet for producing the biaxially stretched polypropylene film can be suitably produced as follows. However, the method for producing the biaxially stretched polypropylene film of the present disclosure is not limited to the method described below.

First, a polypropylene resin composition (for example, polypropylene resin pellets after dry mixing, or mixed polypropylene resin pellets prepared by melting and kneading in advance) is supplied to an extruder and heated and melted.

The extruder temperature during heating and melting is preferably 220 to 280 ℃, more preferably 230 to 270 ℃. The resin temperature during heating and melting is preferably 220 to 280 ℃, more preferably 230 to 270 ℃. The resin temperature during heating and melting was measured by a thermometer inserted into the extruder.

The extruder setting temperature and the resin temperature at the time of heating and melting are selected in consideration of the physical properties of the polypropylene resin used. By setting the resin temperature at the time of heating and melting to such a numerical range, deterioration of the resin can be suppressed.

Next, the molten resin composition is extruded into a sheet form using a T-die, and cooled and solidified on at least 1 or more metal drums to form an unstretched green sheet.

The surface temperature of the metal drum (the temperature of the metal drum after extrusion and in initial contact) is preferably 50 to 100 ℃, more preferably 90 to 100 ℃. The surface temperature of the metal drum can be determined according to the physical properties of the polypropylene resin used. If the surface temperature of the metal drum is too high or too low in the above-described preferable range, the degree of surface roughening of the polypropylene film may be affected, and therefore, the repairability (safety) of the capacitor element may be lowered, and the voltage resistance of the capacitor element may be lowered.

The biaxially stretched polypropylene film can be produced by subjecting a green sheet to biaxial stretching treatment. As the biaxial stretching method, a sequential biaxial stretching method is preferable.

In the sequential biaxial stretching method, for example, the following can be performed: the web of the cast raw material was preheated in the MD set of the preheat rolls located upstream of the MD set of the stretch rolls, and then the web of the preheated cast raw material was stretched in the MD direction in the MD set of the stretch rolls, and then the web stretched in the MD direction was relaxed in the MD set of the relax rolls located downstream of the MD set of the stretch rolls, and stretched in the TD direction in a tenter. Hereinafter, stretching in the MD may be referred to as MD stretching or longitudinal stretching, and stretching in the TD may be referred to as TD stretching or transverse stretching.

The temperature of the uppermost stream preheating roll in the MD preheating roll group, i.e., the preheating roll in the first stage is preferably lower than the temperature of the second stage and the subsequent preheating rolls, for example, preferably 60 to 95 c, more preferably 75 to 95 c. If the temperature of the first-stage preheating roll is too high or too low relative to the above-described preferred range, local air entrainment may occur between the green sheet and the first-stage preheating roll, and the flatness of the sheet may be affected.

The temperature of the second stage and the preheating rolls thereafter is preferably 115 ℃ to 138 ℃, more preferably 120 ℃ to 138 ℃. The higher the temperature of the preheating rolls in and after the second stage, the difference in tensile breaking stress (. sigma.)_b125-σ_b135) The smaller the tendency becomes. When the temperature of the second stage and the subsequent preheating rolls is too high, it is difficult to adjust the tensile breaking stress at 135 ℃ to 70MPa or more, or to adjust the difference in tensile breaking stress (. sigma.) (_b125-σ_b135) The pressure is adjusted to 0MPa to 15 MPa. If the temperature of the second stage and the subsequent preheating rolls is too low, it becomes difficult to stress the tension at breakDifference (sigma)_b125-σ_b135) The pressure is adjusted to 0MPa to 15 MPa.

The adhesion time to the MD preheat roll group is preferably 5 seconds to 10 seconds. The longer the adhesion time is, the lower the tensile breaking stress (sigma)_b125-σ_b135) The smaller the tendency becomes. If the adhesion time is too long, it becomes difficult to adjust the tensile breaking stress at 135 ℃ to 70MPa or more, or to adjust the difference in tensile breaking stress (. sigma.). The_b125-σ_b135) The pressure is adjusted to 0MPa to 15 MPa. If the adhesion time is too short, it becomes difficult to reduce the tensile breaking stress difference (. sigma.)_b125-σ_b135) The pressure is adjusted to 0MPa to 15 MPa. The adhesion time to the MD preheat roll group means the length of time during which any portion of the cast green sheet is actually adhered to the MD preheat rolls constituting the MD preheat roll group, and does not include the time during which any MD preheat roll is not adhered between adjacent MD preheat rolls.

The temperature of the MD draw roll group is preferably 130 ℃ to 150 ℃. The higher the temperature of the MD draw roll group, the lower the tensile break stress (σ)_b125-σ_b135) The smaller the tendency becomes. When the temperature of the MD drawing roller group is too high, it is difficult to adjust the tensile breaking stress at 135 ℃ to 70MPa or more, or to adjust the tensile breaking stress difference (sigma)_b125-σ_b135) The pressure is adjusted to 0MPa to 15 MPa. If the temperature of the MD drawing roller group is too low, it is difficult to reduce the tensile breaking stress difference (sigma)_b125-σ_b135) The pressure is adjusted to 0MPa to 15 MPa.

The time for adhesion to the MD drawing roller group is preferably 1 to 2 seconds. The longer the adhesion time is, the lower the tensile breaking stress (sigma)_b125-σ_b135) The smaller the tendency becomes. If the adhesion time is too long, it becomes difficult to adjust the tensile breaking stress at 135 ℃ to 70MPa or more, or to adjust the difference in tensile breaking stress (. sigma.). The_b125-σ_b135) The pressure is adjusted to 0MPa to 15 MPa. If the adhesion time is too short, it becomes difficult to reduce the tensile breaking stress difference (. sigma.)_b125-σ_b135) The pressure is adjusted to 0MPa to 15 MPa. The time period for which the MD stretch roller group is in contact with the cast raw web is the length of time for which any part of the cast raw web is in contact with the MD stretch rollers constituting the MD stretch roller group, and is not included in the time period between adjacent MD stretch rollersTime between MD stretching rollers without any MD stretching rollers.

The MD stretching magnification is preferably 4.5 to 6.0 times. The higher the MD stretch ratio, the higher the tensile breaking stress (sigma) at 135 DEG C_b135) The higher the tensile breaking stress difference (. sigma.)_b125-σ_b135) The larger the tendency becomes. If the MD stretching ratio is too high, the orientation of the polypropylene film after MD stretching becomes too high, and stretching breakage may occur in the TD stretching step. If the MD stretch ratio is too low, it becomes difficult to adjust the tensile stress at break at 135 ℃ to 70MPa or more.

The temperature of the MD relaxation roller group is preferably 120-128 ℃. The higher the temperature of the set of MD relax rolls, the lower the tensile break stress (σ)_b125-σ_b135) The smaller the tendency becomes. If the temperature of the MD relaxation roller group is too high, it is difficult to adjust the tensile breaking stress at 135 ℃ in the first direction to 70MPa or more. If the temperature of the MD relaxation roller group is too low, the heat shrinkage rate and dimensional change rate in the first direction at high temperature become large, and the gaps between the films change to cause deformation of the capacitor element, and the withstand voltage performance of the capacitor element may be lowered.

The adhesion time to the MD relaxation roller group is preferably 1 second to 2 seconds. The longer the adhesion time is, the lower the tensile breaking stress (sigma)_b125-σ_b135) The smaller the tendency becomes. If the adhesion time is too short, it becomes difficult to reduce the tensile breaking stress difference (. sigma.)_b125-σ_b135) The pressure is adjusted to 0MPa to 15 MPa. If the adhesion time is too long, it becomes difficult to control the tensile breaking stress at 135 ℃ to 70MPa or more. The adhesion time to the MD relaxation roller group means the length of time during which an arbitrary portion of the cast green sheet actually adheres to the MD relaxation rollers constituting the MD relaxation roller group, and does not include the time during which any MD relaxation roller does not adhere to the adjacent MD relaxation rollers.

The polypropylene film after MD stretching by the MD relaxation roller group is introduced into a tenter, and TD stretching is preferably performed at 155 to 170 ℃ to 3 to 11 times.

And (3) performing relaxation and heat fixation on the TD stretched polypropylene film. Thus, a biaxially stretched polypropylene film can be obtained.

In the biaxially stretched polypropylene film, for the purpose of improving the adhesion characteristics in the subsequent steps such as the vapor deposition step, after the stretching and heat-fixing step is completed, corona discharge treatment may be performed on-line or off-line. The corona discharge treatment may be performed by a known method. It is preferable to use air, carbon dioxide gas, nitrogen gas, or a mixed gas thereof as the atmosphere gas.

An oil having a pattern corresponding to the pattern of the insulating boundary is applied to one surface of a biaxially stretched polypropylene film to form an oil mask for the insulating boundary, and metal deposition is performed on the oil mask to obtain a metallized film before slitting. The insulating boundary oil mask is used to prevent metal particles from adhering to a portion of the biaxially stretched polypropylene film which is to be an insulating boundary due to metal vapor deposition. The oil mask for insulation boundary may be formed as follows: the oil for forming the insulating boundary stored in the oil tank is gasified, and the oil is blown to the biaxially stretched polypropylene film from a nozzle provided in the tank. The oil is blown out at 100 to 150 ℃ to the biaxially stretched polypropylene film. The biaxially stretched polypropylene film with the insulating boundary oil mask formed thereon was passed between an evaporation source and a cooling roll to form a metal layer. In the evaporation source, the metal used for metal evaporation is generally heated to 600 ℃ or higher and evaporated. The metal vapor is released to the surface of the biaxially stretched polypropylene film on which the oil mask for insulation boundary is formed, out of both surfaces of the biaxially stretched polypropylene film on which the oil mask for insulation boundary is formed. The chill roll can be maintained at a temperature of typically-30 ℃ to-20 ℃. Examples of the metal used for the metal vapor deposition include simple metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, various mixtures thereof, and alloys thereof. In the case where the boundary pattern is provided in the movable portion of the metal layer, the pattern oil mask may be formed on the surface of the biaxially stretched polypropylene film on which the insulating boundary oil mask is formed, between the formation of the insulating boundary oil mask and the metal vapor deposition, that is, after the formation of the insulating boundary oil mask and before the metal vapor deposition. The oil mask for pattern is generally formed on a plate roll. The temperature of the oil used for forming the oil mask for patterning is lower than that of the oil mask for forming the insulating boundary. The oil used for forming the oil mask for patterning is applied to the biaxially stretched polypropylene film at room temperature (40 ℃ or lower, as an example).

The metallized film before slitting and the metallized film obtained by dividing the metallized film before slitting, which are obtained as described above, will be described below with reference to the drawings.

As shown in fig. 3, the pre-slit metallized film 6 includes a plurality of insulating borders 21 continuously extending in the MD direction D1, and a metal layer 300 continuously extending in the MD direction D1. Before dicing, the insulating boundaries 21 and the metal layers 300 are alternately arranged in the TD direction D2 in the metallized film 6. Each metal layer 300 includes two movable portions 32 and a heavy edge portion 31 located between the movable portions 32. That is, in each metal layer 300, the first movable portion 32, the heavy edge portion 31, and the second movable portion 32 are arranged in this order in the TD direction D2. In this way, the first movable portion 32 extends in the TD direction D2 from one end of the heavy portion 31 in the TD direction D2, and the second movable portion 32 extends in the TD direction D2 from the other end of the heavy portion 31 in the TD direction D2. The first and second movable portions 32 extend continuously in the MD direction D1. The heavy-side portion 31 also extends continuously in the MD direction D1. In the example shown in fig. 3, the insulating boundaries 21 are provided at both ends of the metallized film 6 in the TD direction D2 before slitting, but the metal layer 300 may be provided at both ends or at one of both ends. A boundary pattern (not shown) may be formed in the first and second movable portions 32.

In the dicing step of the pre-dicing metallized film 6, a dicing blade is inserted into the center (hereinafter, sometimes referred to as "TD center") and the TD center of each heavy edge portion 31 along the TD direction D2 in each insulating boundary 21, the pre-dicing metallized film 6 is divided into a plurality of pieces along the TD direction D2, and the metallized films 5 (see fig. 1 and 2) are wound around the core. Fig. 3 shows an example of the position and cutting direction of the cutting blade, which is indicated by a bar-shaped arrow. The metallized film may be stored in the form of a roll of metallized film wound into a roll. A roll of metallized film (also referred to simply as a film roll) may or may not have a roll core (core). The roll of metallized film preferably has a roll core (core). The winding core is preferably cylindrical. The material of the winding core of the metallized film roll is not particularly limited. Examples of the material include paper (paper tube), resin, Fiber Reinforced Plastic (FRP), and metal. Examples of the resin include polyvinyl chloride, polyethylene, polypropylene, phenol resin, epoxy resin, acrylonitrile-butadiene-styrene copolymer, and the like. Examples of the plastic constituting the fiber-reinforced plastic include polyester resins, epoxy resins, vinyl ester resins, phenol resins, thermoplastic resins, and the like. Examples of the fibers constituting the fiber-reinforced plastic include glass fibers, aramid fibers (Kevlar (registered trademark) fibers), carbon fibers, poly (p-phenylene benzoxazole) fibers (Zylon (registered trademark) fibers), polyethylene fibers, and boron fibers. Examples of the metal include iron, aluminum, and stainless steel. The core of the metallized film roll also includes a core in which the paper tube is impregnated with the resin. In this case, the material of the core is classified as resin.

As shown in fig. 1 and 2, the metallized film 5 thus obtained includes a biaxially stretched polypropylene film 10 and a metal layer 30 provided on one surface of the biaxially stretched polypropylene film 10. The thickness of the metal layer 30 preferably falls within the range of 1nm to 200 nm.

In the metalized film 5, an insulating boundary 21 continuously extending in the MD direction D1 is provided at one end 51 in the TD direction D2. The length of the insulating border 21 is greater than the width of the insulating border 21.

The metal layer 30 is located laterally in the TD direction D2 of the insulating boundary 21. The metal layer 30 extends from the other end 52 in the TD direction D2 to the insulating boundary 21. Although not shown, the metal layer 30 extends continuously between both ends of the metalized film 5 in the MD direction D1. That is, the metal layer 30 continuously extends from one end portion in the MD direction D1 in the metallized film 5 to the other end portion in the MD direction D1 in the metallized film 5. The width of the metal layer 30 is greater than the width of the insulating boundary 21. For example, the width of the metal layer 30 is preferably 1.5 to 300 times the width of the insulating boundary 21. Here, the width of the metal layer 30 is a value measured regardless of the boundary pattern.

The metal layer 30 of the metallized film 5 includes a heavy-edge portion 31. The heavy-side portion 31 is located at the end portion 52 of the metalized film 5 in the TD direction D2. The heavy-side portion 31 extends continuously in the MD direction D1. More specifically, the heavy edge portion 31 extends continuously between both ends of the metalized film 5 in the MD direction D1. That is, the heavy-edge portion 31 continuously extends from one end portion in the MD direction D1 in the metallized film 5 to the other end portion in the MD direction D1 in the metallized film 5. The thickness of the heavy edge portion 31 is greater than that of the movable portion 32.

The metal layer 30 of the metallized film 5 includes a movable portion 32. The movable portion 32 extends continuously in the MD direction D1. In more detail, the movable portion 32 extends continuously between both ends of the metallized film 5 in the MD direction D1. That is, the movable portion 32 extends continuously from one end portion in the MD direction D1 in the metallized film 5 to the other end portion in the MD direction D1 in the metallized film 5. The movable portion 32 may have a boundary pattern, for example, a T-boundary pattern, formed thereon. The film resistance of the metal layer 30 is usually about 1. omega./□ to 8. omega./□, preferably about 1. omega./□ to 5. omega./□.

The metallized film 5 may be laminated or wound by a conventionally known method to form a film capacitor. For example, 2 sheets of 1 pair of metallized films 5 are stacked and wound so that the metal layers 30 in the metallized films 5 and the biaxially stretched polypropylene films 10 are alternately laminated and the insulating boundaries 21 are on the opposite sides. In this case, 2 sheets of the metallized films 5 in 1 pair are preferably stacked with a shift of 1mm to 2mm in the TD direction D2. The winder to be used is not particularly limited, and for example, an automatic winder 3KAW-N2 type manufactured by Du Teng Kao, K.K., can be used. In the case of manufacturing a flat capacitor, after winding, the obtained wound product is usually pressed. Crimping/capacitor element formation of the film capacitor is facilitated by pressing. From the viewpoint of controlling the interlayer gap and stabilizing the interlayer gap, the optimum value of the applied pressure varies depending on the thickness of the biaxially stretched polypropylene film 10, but is, for example, 2kg/cm²～20kg/cm². Then, the film capacitor was obtained by thermally spraying metal onto both end surfaces of the wound product and providing thermally sprayed metal (Metallikon) electrodes.

As described above, the film capacitor may have a structure in which a plurality of metallized films 5 are laminated, or may have a rolled metallized film 5. Such a film capacitor can be suitably used for a capacitor for an inverter-power supply device for controlling a drive motor of an electric vehicle, a hybrid vehicle, or the like. In addition, the solar photovoltaic panel can be suitably used for railway vehicles, wind power generation, solar power generation, general household appliances, and the like.

In fig. 1 to 2, the metallized film 5 in which the metal layer 30 is provided on one side of the biaxially stretched polypropylene film 10 is described, but the metallized film of the present invention is not limited to the metallized film 5 having such a structure. For example, the metallized film of the present invention may be provided with a metal layer on both sides of a biaxially stretched polypropylene film.

In this embodiment, the metallized film having the heavy-edge portion is described, but the metallized film may not have the heavy-edge portion.

Examples

The present invention will be described more specifically with reference to examples, which are provided for the purpose of illustrating the present invention and are not intended to limit the present invention in any way. In the examples, "part(s)" and "%" represent "part(s) by mass" and "% by mass", respectively, unless otherwise specified.

< PP resin >

The PP resin a used for producing the biaxially stretched polypropylene films of the respective examples was Prime Polymer co., ltd., and the PP resin B was manufactured by korea oil chemical industries co. The PP resin A and the PP resin B are straight chain homo-polypropylene.

< determination of weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) >)

The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw/Mn) of the PP resin were measured by GPC (gel permeation chromatography) under the following conditions.

Specifically, a HLC-8321GPC-HT model, manufactured by Tosoh corporation, which is a differential Refractometer (RI) built-in high temperature GPC apparatus, was used. As a column, 1 TSKgel guard columnHHR (30) HT (7.5 mmI.D.. times.7.5 cm) and 3 TSKgel GMHHR-H (20) HT from Tosoh corporation were used in a linked manner. Trichlorobenzene as an eluent was flowed and measured at a flow rate of 1.0 ml/min at a column temperature of 140 ℃. A calibration curve was prepared using a standard polystyrene manufactured by Tosoh corporation, which was approximated 5 times. Wherein the molecular weight is converted to the molecular weight of polypropylene by using Q-factor. From the obtained calibration curve and SEC chromatogram, the weight average molecular weight (Mw) and number average molecular weight (Mn) were obtained using analysis software for a measuring apparatus.

< differential distribution value difference D_MMeasurement of

Differential distribution value difference D_MObtained in the following manner. First, an SEC chromatogram was obtained in the same manner as described above. The chromatogram was converted into a differential molecular weight distribution curve using analysis software incorporated in the measurement apparatus used. From the differential molecular weight distribution curve, values of the differential molecular weight distribution at log (m) ═ 4.5 and log (m) ═ 6.0 were read. Differential distribution value difference D_MThe value of the differential molecular weight distribution at log (m) of 6.0 was subtracted from the value of the differential molecular weight distribution at log (m) of 4.5.

< determination of meso pentad fraction ([ mmmm) >)

The PP resin was dissolved in a solvent, and the solution was measured by a high temperature fourier transform nuclear magnetic resonance apparatus (high temperature FT-NMR) under the following conditions.

High-temperature Nuclear Magnetic Resonance (NMR) apparatus: high temperature Fourier transform Nuclear magnetic resonance device (high temperature FT-NMR) JNM-ECP500 manufactured by Japan Electron Ltd

And (3) observing a nucleus:¹³C(125MHz)

measuring temperature: 135 deg.C

Solvent: o-dichlorobenzene (ODCB: mixed solvent of ODCB and deuterated ODCB (mixing ratio: 4/1))

Measurement mode: signal single-pulse proton broadband decoupling ring

Pulse amplitude: 9.1 musec (45 degree pulse)

Pulse interval: 5.5 seconds

Cumulative number of times: 4500 times

Displacement reference: CH (CH)₃(mmmm)＝21.7ppm

The pentad fraction indicating the tacticity was calculated as a percentage (%) from the intensity integrated value of each signal derived from a combination (mmmm, mrrm, etc.) of 5 cell groups (pentads) of a cell group "meso (m)" aligned in the same direction and a cell group "racemic (r)" aligned in a different direction. For attribution of each signal originating from mmmm, mrrm, etc., for example, the description of the spectrum of "t.hayashi et al, Polymer, volume 29, page 138 (1988)" etc. is referred to.

< determination of Heptane Insolubility (HI) >

About 3g of a sample for measurement was prepared by press molding each PP resin to a thickness of 10 mm. times.35 mm. times.0.3 mm. Next, about 150mL 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 the extraction.

< determination of Melt Flow Rate (MFR) >)

For each PP resin, the Melt Flow Rate (MFR) in the form of raw material resin pellets was measured by a melt index meter of tokyo seiki, in accordance with condition M of JIS K7210. Specifically, first, a sample weighed 4g was inserted into a cylinder set at a test temperature of 230 ℃ and preheated for 3.5 minutes under a load of 2.16 kg. Then, the weight of the sample extruded from the bottom hole within 30 seconds was measured to determine MFR (g/10 min). The measurement was repeated 3 times, and the average value was defined as the measured value of MFR.

< example 1 >

[ production of a sheet for casting blank ]

The PP resin A [ Mw: 32 ten thousand, Mw/Mn: 9.3, differential distribution value difference D_M11.2 meso pentad fraction [ mmmm]95%, 97.3%, 4.9g/10 min MFR, Prime Polymer co, ltd, PP resin B [ Mw 35 ten thousand, Mw/Mn 7.7 ], differential distribution value difference D_M7.2 meso pentad fraction [ mmmm]96.5%, HI 98.6%, MFR 3.8g/10 min, manufactured by Korea oil industries Ltd.): (resin B) ═ 60: 40 was measured continuously, and the mixed dry blend was fed to an extruder, melted at a resin temperature of 255 ℃, extruded through a T-die, wound around a metal drum having a surface temperature of 95 ℃ and solidified to prepare a green casting sheet.

[ production of biaxially stretched Polypropylene film ]

The green sheet was preheated in the MD preheat roll group, then stretched in the MD direction in the MD stretch roll group, and then relaxed in the MD relax roll group. This was stretched 10-fold in the TD direction at 163 ℃ in a tenter, subjected to relaxation and heat setting, and a biaxially stretched polypropylene film having a thickness of 2.3 μm was taken up.

The MD stretching magnification was 4.5 times, the temperature of the preheating roll in the first stage was 85 ℃, the temperature of the preheating roll in the second stage and thereafter was 130 ℃, the temperature of the MD stretch roll group was 146 ℃, the temperature of the MD relax roll group was 125 ℃, the adhesion time to the MD preheating roll group was 7.4 seconds, the adhesion time to the MD stretch roll group was 1.1 seconds, and the adhesion time to the MD relax roll group was 1.1 seconds.

[ production of metallized film before slitting ]

The biaxially stretched polypropylene film was unwound, and an oil mask for an insulating boundary was formed on the biaxially stretched polypropylene film. Next, a pattern oil mask having a pattern corresponding to the electrode pattern was formed on the biaxially stretched polypropylene film on which the insulation boundary oil mask was formed. Next, a metal vapor deposition was performed on the biaxially stretched polypropylene film on which the oil mask for patterning was formed. The biaxially stretched polypropylene film after metal deposition was wound around a bakelite core (core) as a winding core. This gives a roll of metallized film before slitting.

In order to form the oil mask for insulation boundary, Fomblin oil vapor at about 120 ℃ was blown through a nozzle slit onto one of both surfaces of a biaxially stretched polypropylene film. The entire surface of the biaxially stretched polypropylene film was formed in a striped pattern using an oil mask for an insulation boundary (see fig. 3).

The oil mask for pattern was formed by a plate roll. The oil mask for patterning is formed in a pattern substantially corresponding to the electrode pattern of the metal vapor-deposition electrode in the region of the entire biaxially stretched polypropylene film where the oil mask for insulating boundary is not formed.

In the metal deposition, aluminum is first deposited. The aluminum vapor deposition was performed on the entire surface of the biaxially stretched polypropylene film on which the oil mask for insulation boundary and the oil mask for pattern were formed (hereinafter referred to as "oil mask formation surface"). Subsequently, zinc is vapor-plated to form the heavy-edge portion. Zinc is vapor-deposited on the oil mask formation surface in a region where the heavy-side portion is to be formed. The metal deposition was carried out while cooling the biaxially stretched polypropylene film on a cooling roll maintained at-24 ℃. In this way, the biaxially stretched polypropylene film was passed between the cooling roll and the evaporation source for metal vapor deposition, and aluminum and zinc were vapor-deposited.

< example 2 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed from 4.6 times to 4.5 times, and the adhesion time to the MD preheat roll group was changed from 7.8 seconds to 7.4 seconds. The foregoing changes relating to the adhesion time to the MD preheat roll group were made by changing the casting speed from example 1.

< example 3 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed from 4.8 times to 4.5 times, and the adhesion time to the MD preheat roll group was changed from 8.1 seconds to 7.4 seconds. The foregoing changes relating to the adhesion time to the MD preheat roll group were made by changing the casting speed from example 1.

< example 4 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed to 5.0 times instead of 4.5 times, and the adhesion time to the MD preheat roll group was changed to 8.4 seconds instead of 7.4 seconds. The foregoing changes relating to the adhesion time to the MD preheat roll group were made by changing the casting speed from example 1.

< example 5 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed from 4.6 times to 4.5 times, the temperature of the preheat roll in the second stage and thereafter was changed from 125 ℃ to 130 ℃, the temperature of the MD stretch roll group was changed from 135 ℃ to 146 ℃, and the adhesion time to the MD preheat roll group was changed from 5.5 seconds to 7.4 seconds. The foregoing changes relating to the adhesion time to the MD preheat roll group were made by changing the casting speed from example 1.

< example 6 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed from 4.6 times to 4.5 times, the temperature of the MD stretching roller group was changed from 143 ℃ to 146 ℃, and the adhesion time to the MD preheating roller group was changed from 7.5 seconds to 7.4 seconds. The foregoing changes relating to the adhesion time to the MD preheat roll group were made by changing the casting speed from example 1.

< example 7 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed from 4.6 times to 4.5 times, the temperature of the MD stretching roller group was changed from 140 ℃ to 146 ℃, and the adhesion time to the MD preheating roller group was changed from 7.5 seconds to 7.4 seconds. The foregoing changes relating to the adhesion time to the MD preheat roll group were made by changing the casting speed from example 1.

< example 8 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was set to 5.5 times instead of 4.5 times, the temperature of the preheating roll in the second stage and thereafter was set to 135 ℃ instead of 130 ℃, the adhesion time to the MD preheating roll group was set to 9.5 seconds instead of 7.4 seconds, the adhesion time to the MD stretching roll group was set to 1.8 seconds instead of 1.1 seconds, and the adhesion time to the MD relaxation roll group was set to 1.8 seconds instead of 1.1 seconds. The above-described respective adhesion times were changed by changing the casting speed from example 1.

< example 9 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1 except that the thickness of the biaxially stretched polypropylene film was set to 2.5. mu.m.

< comparative example 1 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed from 4.6 times to 4.5 times, the temperature of the MD stretching roller group was changed from 128 ℃ to 146 ℃, and the adhesion time to the MD preheating roller group was changed from 7.5 seconds to 7.4 seconds. The foregoing changes relating to the adhesion time to the MD preheat roll group were made by changing the casting speed from example 1.

< comparative example 2 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching ratio was changed to 4.6 times instead of 4.5 times, the temperature of the preheating roll in the first stage was changed to 70 ℃ instead of 85 ℃, the temperature of the preheating roll in the second stage and thereafter was changed to 110 ℃ instead of 130 ℃, and the adhesion time to the MD preheating roll group was changed to 7.5 seconds instead of 7.4 seconds. The foregoing changes relating to the adhesion time to the MD preheat roll group were made by changing the casting speed from example 1.

< comparative example 3 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed from 4.6 times to 4.5 times, the adhesion time to the MD preheat roll group was changed from 4.5 seconds to 7.4 seconds, the adhesion time to the MD stretch roll group was changed from 0.8 seconds to 1.1 seconds, and the adhesion time to the MD relax roll group was changed from 0.8 seconds to 1.1 seconds. The above-described respective adhesion times were changed by changing the casting speed from example 1.

< comparative example 4 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed from 4.4 to 4.5, the temperature of the preheating roll in the first stage was changed from 70 ℃ to 85 ℃, the temperature of the preheating roll in the second stage and thereafter was changed from 110 ℃ to 130 ℃, the temperature of the MD stretching roll group was changed from 128 ℃ to 146 ℃, the adhesion time to the MD preheating roll group was changed from 4.1 seconds to 7.4 seconds, the adhesion time to the MD stretching roll group was changed from 0.8 seconds to 1.1 seconds, and the adhesion time to the MD relaxation roll group was changed from 0.8 seconds to 1.1 seconds. The above-described respective adhesion times were changed by changing the casting speed from example 1.

< comparative example 5 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was 6.0 times instead of 4.5 times, the adhesion time to the MD preheat roll group was 4.5 seconds instead of 7.4 seconds, the adhesion time to the MD stretch roll group was 0.8 seconds instead of 1.1 seconds, and the adhesion time to the MD relax roll group was 0.8 seconds instead of 1.1 seconds. The above-described respective adhesion times were changed by changing the casting speed from example 1.

< comparative example 6 >

In the same manner as in example 1, production of a biaxially stretched polypropylene film and a metallized film before slitting was attempted except that the biaxial stretching conditions were changed. Specifically, the production of a metallized film before slitting was attempted under the same conditions as in example 1 except that the MD stretching magnification was changed to 6.5 times, the adhesion time to the MD preheat roll group was changed to 7.5 seconds instead of 7.4 seconds, the adhesion time to the MD stretch roll group was changed to 0.7 seconds instead of 1.1 seconds, and the adhesion time to the MD relax roll group was changed to 0.7 seconds instead of 1.1 seconds. The above-described respective adhesion times were changed by changing the casting speed from example 1.

However, when biaxially stretched, specifically, when the green cast sheet is stretched in the MD direction, the sheet is broken, and therefore, a biaxially stretched polypropylene film cannot be produced.

< comparative example 7 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the adhesion time to the MD preheat roll group was set to 10.8 seconds instead of 7.4 seconds, the adhesion time to the MD stretch roll group was set to 1.6 seconds instead of 1.1 seconds, and the adhesion time to the MD relax roll group was set to 1.6 seconds instead of 1.1 seconds. The above-described respective adhesion times were changed by changing the casting speed from example 1.

< comparative example 8 >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1, except that the biaxial stretching conditions were changed. Specifically, a metallized film before slitting was produced under the same conditions as in example 1 except that the MD stretching magnification was changed from 4.6 times to 4.5 times, the adhesion time to the MD preheat roll group was changed from 13.7 seconds to 7.4 seconds, the adhesion time to the MD stretch roll group was changed from 2.1 seconds to 1.1 seconds, and the adhesion time to the MD relax roll group was changed from 2.1 seconds to 1.1 seconds. The above-described respective adhesion times were changed by changing the casting speed from example 1.

< reference comparative example >

A biaxially stretched polypropylene film and a metallized film before slitting were produced in the same manner as in example 1 except that the thickness of the biaxially stretched polypropylene film was set to 4.6. mu.m. Except for using this before-slitting metallized film, when a capacitor was produced in the same manner as in example 1 (that is, when a capacitor was produced in the same manner as described in the item < production of capacitor and measurement of capacitance > described later), the capacitance per unit volume of this capacitor theoretically stayed 0.25 times the capacitance per unit volume of the capacitor obtained in example 1. Therefore, the biaxially stretched polypropylene film of this reference comparative example was significantly inferior to the biaxially stretched polypropylene films of examples 1 to 9 in terms of the capacitance of the capacitor and the capacitance per unit volume.

< measurement of thickness >

The measurement was carried out at a temperature of 23. + -. 2 ℃ and a humidity of 50. + -. 5% RH using a paper thickness measuring instrument MEI-11 (measurement pressure 100kPa, lowering speed 3 mm/sec, measurement terminal. phi. 16mm, measurement force 20.1N), manufactured by Ltd. The samples were directly stacked at 10 sheets or more, cut out from a roll, and the cut out was performed so that wrinkles and air did not enter the film. For 10 superimposed samples, 5 measurements were made, and the thickness was calculated by dividing the average of 5 measurements by 10.

Tensile stress at break (σ) of < 125 ℃ in MD_b125)＞

Tensile stress at break (. sigma.) at 125 ℃ in MD_b125) According to JIS K7127: 1999. First, rectangular samples having a length of 150mm and a width of 10mm were cut out from the biaxially stretched polypropylene films of examples and comparative examples. At this time, the sample was cut out so that the MD direction became the longitudinal direction. The sample was mounted on a tensile tester with an oven at a chuck pitch of 50mm (A)&D co, ltd, Tensilon universal tester RTG-1210) heated to 125 ℃. Next, the sample was preheated for 1 minute, and a tensile test was conducted at a test speed of 300 mm/minute. The value of the load at the maximum strain in the tensile test was divided by the cross-sectional area of the sample before the tensile test (thickness of the sample before the tensile test × width 10mm), to calculate the tensile breaking stress (σ) at 125 ℃_b125). Tensile tests were carried out 5 times each. The average values are shown in table 1. It should be noted that the tensile breaking stress is sometimes defined byReferred to as tensile break strength, tensile break stress, tensile break strength.

Tensile stress at break (σ) of < 135 ℃ in MD_b135)＞

The tensile breaking stress (sigma) of 125 ℃ was used in place of the temperature of 125 ℃ in the oven_b125) A tensile test was carried out in the same manner as above to calculate the tensile breaking stress (. sigma.) at 135 ℃_b135). Tensile tests were carried out 5 times each. The average values are shown in table 1.

[ Table 1]

Tensile stress at break (σ) of < 23 ℃ in MD_b23)＞

The tensile breaking stress (sigma) of 125 ℃ was used in place of the temperature of 125 ℃ in the oven_b125) A tensile test was carried out in the same manner as above to calculate the tensile breaking stress (. sigma.) at 23 ℃_b23). The tensile test was performed 5 times each. The average values are shown in Table 2.

(ii) heat shrinkage in MD (< 125 ℃ C.) >

The biaxially stretched polypropylene films of examples and comparative examples were cut into a rectangular shape having a width of 20mm and a length of 130mm to prepare measurement samples. At this time, the sample was cut out so that the longitudinal direction of the sample coincides with the MD direction. 3 pieces of the measurement samples were prepared. Next, a 100mm long portion was measured with a ruler, and a mark line was marked at the portion. Then, the 3 measurement samples were suspended in a hot air circulation type thermostatic bath at 125 ℃ without load and held for 15 minutes. Then, the sheet was cooled at room temperature (23 ℃), the interval between the mark lines was measured with a ruler, and the heat shrinkage (%) in the MD direction was calculated by the following formula.

Heat shrinkage (%) [ (interval of marking line before heating-interval of marking line after heating)/(interval of marking line before heating) ] × 100

The average value of the measured values of 3 bars was defined as the heat shrinkage (%) in the MD direction.

The measurement conditions other than those described herein were measured in accordance with JIS C2151: 2019, "25. size change". The results are shown in Table 2.

(ii) heat shrinkage in MD (< 135 ℃ C.) >

The heat shrinkage in the MD direction at 125 ℃ was measured in the same manner as in the hot air circulation type thermostatic bath except that the temperature was set at 135 ℃ instead of 125 ℃. The results are shown in Table 2.

(ii) a ratio of change in dimension in MD at 125 ℃ and a ratio of change in dimension in MD at 135 >

The dimensional change rate in the MD direction was determined by temperature modulation TMA measurement using a thermo-mechanical analyzer ("SS-6000", manufactured by Seiko Instruments inc.).

From the biaxially stretched polypropylene films of examples and comparative examples, a strip was cut out so as to have a width of 30mm in the measurement direction and 4mm in the direction orthogonal to the measurement direction, to prepare samples. 3 pieces of the measurement samples were prepared. At this time, the sample was cut out so that the measurement direction of the sample coincides with the MD direction. The measurement conditions were as follows: the distance between the chucks was set to 15mm, the measurement temperature ranged from 25 ℃ to 150 ℃, the temperature rise rate was set to 10 ℃/min, and the tensile load continuously applied to the sample piece was set to 20 mN. The dimensional change rate in the MD direction was determined from the chuck pitch (mm) at a furnace temperature of 125 ℃ and the chuck pitch (mm) at a furnace temperature of 135 ℃ by the following equation.

[ dimensional change in MD at 125 [ (%) ] [ (chuck spacing at 125 ℃ C. -chuck spacing at 25 ℃ C.)/chuck spacing at 25 ℃ C. ]. times.100

[ dimensional change in MD at 135 [ (% ]) [ ((chuck spacing at 135 ℃ C. -chuck spacing at 25 ℃ C.)/chuck spacing at 25 ℃) X100

The average of the measured values of 3 specimens was defined as the percentage change (%) in the MD at 125 ℃ and the percentage change (%) in the MD at 135 ℃.

The dimensional change rate is positive (+) when the film size increases (expands) with an increase in temperature, and negative (-) when the film size decreases (contracts) with an increase in temperature. The results are shown in Table 2.

< measurement of crystallite size >

The crystallite size of the biaxially stretched polypropylene films of examples and comparative examples was measured by XRD (wide-angle X-ray diffraction) under the following conditions in a state in which 15 films were stacked.

A measuring machine: x-ray diffraction apparatus "MiniFlex 300" manufactured by Rigaku Corporation "

X-ray power: 30kV and 10mA

Irradiation with X-rays: monochromator monochromatized CuK alpha ray (wavelength 0.15418nm)

A detector: scintillation counter

Scanning by a goniometer: 2 theta/theta linked scanning

From the obtained data, the half-value width of the diffraction reflection peak of the α -crystal (040) plane was calculated by optimizing the data by a split-type pseudo-Voight function using PDXL (Ver.2.1.3.4) integrated powder X-ray analysis software with equipment standard by an analysis computer. The crystallite size was determined from the half-value width using the Scherrer equation (D ═ K × λ/(β × cos θ)).

In the Scherrer equation, D is the crystallite size (nm), K is a constant (shape factor: 0.94 in this example), λ is the wavelength (nm) of the X-ray used, β is the half-value width obtained, and θ is the diffraction bragg angle. 0.15418nm was used as λ. The results are shown in Table 2.

[ Table 2]

< production of capacitor and measurement of Electrostatic capacitance >

The pre-slit metallized films (metal layer-integrated polypropylene films) prepared in examples and comparative examples were slit into 60mm wide pieces. Subsequently, 2 metal layer-integrated polypropylene films were laminated to each other. The polypropylene film integrated with the metal layer was wound using an automatic winder 3KAW-N2 type manufactured by Du vine Ltd under a winding tension of 250g, a contact pressure of 880g, and a winding speed of 4 m/secAnd (4) winding. The biaxially stretched polypropylene film was subjected to 1137-strand winding when the thickness was 2.3 μm, and to 1076-strand winding when the thickness was 2.5 μm. For the wound component, the load was 5.9kg/cm²The press was then heat treated at 120 ℃ for 15 hours. And finally, spraying zinc metal on the end surface of the element. As the spraying conditions, spraying was carried out so that the feeding speed was 15 mm/sec, the spraying voltage was 22V, and the spraying pressure was 0.3MPa, and the thickness was 0.7 mm. Thus, a flat type capacitor was obtained. A lead wire is soldered to an end face of the flat capacitor. After that, the flat capacitor is sealed with an epoxy resin. The epoxy resin was cured by heating at 90 ℃ for 2.5 hours and then at 120 ℃ for 2.5 hours. The capacitance of the capacitor element was 75 μ F (+ -2 μ F).

< evaluation of wrinkle Defect in winding form >

The state of the rolled state was evaluated by visually observing the state of the film roll of the metallized film before slitting (also referred to as the rolled state) in examples and comparative examples. Specifically, it is determined whether or not a fold wrinkle is present in the film roll of the metallized film before slitting. The results are shown in Table 3.

< evaluation of unevenness of vapor deposition film >

From 1 full width film of 1 circumference of the roll-shaped before-slit metallized film peeling roller of the examples and comparative examples, whether the vapor deposition film was uniformly deposited on the whole before-slit metallized film was evaluated by visual observation by irradiating the lower side of the peeled before-slit metallized film with light from a fluorescent lamp. If the state of vapor deposition is observed so that the vapor deposition film has a corrugated shape, or the state of shielding of the vapor deposition film thickness, or both states are observed, it is determined that the film is defective. The results are shown in Table 3.

Capacitor elements were produced using the pre-slit metallized films produced in examples and comparative examples, and two limit tests (temperature limit test and voltage limit test) were performed on the capacitor elements to measure the rate of change in capacitance with the passage of time. In each of the examples in which the winding-form wrinkle defect and the vapor deposition film unevenness occurred, the capacitor element was produced at a normal portion other than the portion where the vapor deposition defect occurred, and the test was performed. The method for manufacturing the capacitor element is as described in the section "manufacturing the capacitor and measuring the capacitance" above.

< temperature Limit test (115 ℃, 700V) >)

After the capacitor element was preheated at 115 ℃ for 1 hour, the electrostatic capacity was measured by LCR Hi TESTER 3522-50 manufactured by Nissan electric Motor Co. This capacitance is hereinafter referred to as initial capacitance, also referred to as C₀. Subsequently, the capacitor element was continuously applied with a voltage of 700V DC for 100 hours in a thermostatic bath at 115 ℃. Then, the capacitance after the voltage was continuously applied for 100 hours (the capacitance is also referred to as the capacitance after 100 hours had elapsed and is also referred to as C)₁₀₀). The rate of change in capacitance (rate of change in capacitance after 100 hours had elapsed) was calculated. The rate of change is calculated by the following equation.

Rate of change of electrostatic capacity after 100 hours

(electrostatic capacity after 100 hours-initial electrostatic capacity)/initial electrostatic capacity ] × 100

The rate of change in capacitance after the lapse of 100 hours is also referred to as Δ C, and Δ C { (C)₁₀₀-C₀)/C₀}×100。

The capacitor element was returned to the thermostatic bath, a voltage of 700V DC was continuously applied to the capacitor element for 50 hours, and then the capacitor element was taken out, and the capacitance was measured to calculate the initial capacitance (C)₀) The rate of change of (c). This series of operations is repeated until the rate of change falls outside the range of-5% to + 5%. Thus, the time lapse (hereinafter, sometimes referred to as "failure time") when the rate of change falls outside the range of-5% to + 5% is determined.

The rate of change (Δ C) after 100 hours was evaluated from the average value of 5 capacitor elements. When the change rate (Δ C) after 100 hours had passed was out of the range of-5% to + 5%, it was judged to be defective. The failure time was evaluated as a time outside the range of-5% to + 5% at the fastest rate of change in the capacitor elements 5. When the failure time was 450 hours or less, the evaluation was determined to be defective. When only one of the 5 capacitor elements is short-circuited, it is determined to be defective.

The change rate (Δ C) of the electrostatic capacity and the failure time after 100 hours elapsed are shown in table 3.

< Voltage Limit test (105 ℃, 800V) >

The rate of change of electrostatic capacity (Δ C) and the failure time were measured by the same method as the temperature limit test except that the preheating of the capacitor element was changed to 105 ℃ instead of 115 ℃, the thermostat was changed to 105 ℃ instead of 115 ℃, and the voltage applied to the capacitor element was changed to 800V instead of 700V.

[ Table 3]

In examples 1 to 9, neither a wrinkle failure nor a non-uniform vapor deposition film was observed in the wound form, and the failure time exceeded 450 hours in both the temperature limit test and the voltage limit test. On the other hand, in comparative examples 1 to 5, both of the wrinkle defect and the vapor deposition film unevenness were observed. In comparative example 3, the failure time in the voltage limit test was as short as 350 hours. In comparative example 4, short circuit failure was caused in the voltage limit test.

Tensile breaking stress (. sigma.) at 135 ℃ in comparative example 3 and comparative example 1_b135) The two cases were the same, but in the limit tests of the two cases, the failure time of example 3 was longer than that of comparative example 1. The reason for this is considered to be that the tensile breaking stress difference (. sigma.) in example 3_b125-σ_b135) The tensile breaking stress was less than that of comparative example 1, and thus in example 3, the internal structure of the biaxially stretched polypropylene film was less likely to disintegrate by heating to the test temperature (115 ℃ in the temperature limit test and 105 ℃ in the voltage limit test), and therefore, the decrease in electrostatic capacity was less likely to progress.

Tensile stress at break (σ) of 135 ℃ of example 4_b135) Higher than 85MPa in example 7 and 93MPa, in the limit test of the two, the examplesThe failure time of 4 is also longer than that of embodiment 7. It is considered that the biaxially stretched polypropylene film of example 4 has a stronger internal structure than that of the biaxially stretched polypropylene film of example 7. Thus, from a comparison of example 4 with example 7, it can be interpreted as a tensile breaking stress (σ) of 135 ℃_b135) The higher the correlation, the more strongly the internal structure of the biaxially stretched polypropylene film.

In contrast, in example 8, the tensile breaking stress (σ) at 135 ℃ is_b135) The pressure was higher than 95MPa and 106MPa in example 5, but in the limit test of both, the failure time in example 8 was shorter than that in example 5. This is considered to imply a tensile breaking stress (. sigma.) at 135 ℃_b135) Tensile stress at break (sigma) of about 106MPa at 135 DEG C_b135) The correlation with the strength of the internal structure of the biaxially stretched polypropylene film begins to break.

Comparative example 3 tensile breaking stress (. sigma.) at 135 ℃_b135) 70MPa or more, but the failure time in the voltage limit test is as short as 350 hours. This is considered to be because comparative example 3 has a difference in tensile breaking stress (σ)_b125-σ_b135) Since the pressure is as high as 17MPa, the internal structure of the biaxially stretched polypropylene film is easily disintegrated by heating at a test temperature (105 ℃) for reaching the voltage limit test, and the decrease in the electrostatic capacity is easily advanced.

Description of the reference numerals

5 metallized film

6 metallized film before slitting

10 biaxially stretched polypropylene film

21 insulating boundary

30 metal layer

31 heavy edge part

32 movable part

51 one end portion of the metallized film

52 metallizing the other end portion of the film

300 metal layer