CN111801373A

CN111801373A - Biaxially stretched polypropylene film, metallized film, film capacitor, and film roll

Info

Publication number: CN111801373A
Application number: CN201980016778.2A
Authority: CN
Inventors: 末葭道子; 富永刚史; 石田立治; 石渡忠和
Original assignee: Oji Holdings Corp
Current assignee: Oji Holdings Corp
Priority date: 2018-03-07
Filing date: 2019-03-07
Publication date: 2020-10-20
Anticipated expiration: 2039-03-07
Also published as: JP7261389B2; KR20200130245A; CN111801373B; JP2020041120A; WO2019172390A1

Abstract

A biaxially stretched polypropylene film having a thickness of 1.0 to 3.0 μm, wherein the difference between the thermal shrinkage rate in a first direction at 140 ℃ and the thermal shrinkage rate in the first direction at 130 ℃ is 0% or more and less than 2.0%, and the difference between the thermal shrinkage rate in a second direction perpendicular to the first direction at 140 ℃ and the thermal shrinkage rate in the second direction at 130 ℃ is 0% or more and less than 2.3%.

Description

Biaxially stretched polypropylene film, metallized film, film capacitor, and film roll

Technical Field

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

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.

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

As shown in fig. 2, in metalized film 5, an insulating margin (insulation margin)21 extending continuously in longitudinal direction D1 is provided at one end 51 in width direction D2. Generally, the insulating margin 21 is formed by covering a predetermined position of the biaxially stretched polypropylene film 10 with oil before the biaxially stretched polypropylene film 10 is subjected to metal deposition.

The metal layer 30 is located beside the insulating edge 21 (beside in the width direction D2). The metal layer 30 extends from the other end 52 in the width direction D2 to the insulating edge 21. The area of the metal layer 30 is larger than the area of the insulating rim 21.

The thickness of the metal layer 30 is large at the end portion 52 of the metallized film 5. Such a thick portion 31 of the metal layer 30 is sometimes referred to as a heavy edge (heavy edge) portion. The portion 31 will be referred to as heavy edge portion 31 hereinafter. The heavy edge portion 31 is continuous and extends in the longitudinal direction D1. The heavy edge 31 is provided to firmly bond the metallized film 5 and the sprayed metal electrode. On the other hand, in the metal layer 30, a portion 32 between the heavy edge portion 31 and the insulating edge 21 is sometimes referred to as an active (active) portion. The portion 32 will be referred to as the active portion 32 hereinafter. The thickness of the active portion 32 is smaller than that of the heavy edge portion 31.

In order to produce such a metallized film 5, for example, a molten polypropylene resin may be extruded in a sheet form by a T-die to obtain a green casting sheet; biaxially stretching the green sheet, heat-setting, and winding to obtain a biaxially stretched polypropylene film; the metallized film 6 before slitting (see fig. 3) is produced by adhering oil to a biaxially stretched polypropylene film and performing metal deposition thereon.

As shown in fig. 3, the metallized film 6 before slitting includes a plurality of insulating edges 21 extending continuously in the longitudinal direction D1 and a plurality of metal layers 300 having heavy edges 31 extending continuously in the longitudinal direction D1. In this manner, in the metallized film 6 before slitting, the insulating edges 21 and the metal layers 300 are alternately arranged in the width direction D2. Each metal layer 300 includes two active portions 32 and a heavy edge portion 31 located between the active portions 32. That is, in each metal layer 300, the first active portions 32, the heavy edge portions 31, and the second active portions 32 are arranged in this order in the width direction D2.

A cutting blade is placed at the center in the width direction of each insulating margin 21 (center in the width direction D2) and at the center in the width direction of each heavy edge portion 31 in the before-slit metallized film 6, and the before-slit metallized film 6 is divided into a plurality of sheets in the width direction D2 (hereinafter referred to as "slit process"), whereby the metallized film 5 can be obtained. If this procedure is followed, the width of insulating border 21 in metallized film 5 (the width in width direction D2) forms half the width of insulating border 21 in metallized film 6 before slitting. The width of the heavy edge portion 31 in the metallized film 5 (the width in the width direction D2) is also formed to be half the width of the heavy edge portion 31 in the metallized film 6 before slitting. Here, the bar-shaped arrows shown in fig. 3 indicate the position and cutting direction of the cutting blade.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-195367

Disclosure of Invention

Problems to be solved by the invention

The metallized film obtained by such a step preferably has an insulating edge having a width equal to one end in the longitudinal direction (e.g., a slit start end) and the other end in the longitudinal direction (e.g., a slit end). This is because the metallized film having the insulating edge with a width largely different between one end and the other end may have no predetermined influence on the film capacitor.

However, when the thickness of the biaxially stretched polypropylene film is 1.0 μm or more and 3.0 μm or less, the width of the insulating margin is likely to be deviated at one end in the longitudinal direction and the other end in the longitudinal direction in the metallized film after the slitting step. This is because the heat shrinkage rate increases as the thickness of the biaxially stretched polypropylene film is smaller.

An object of the present disclosure is to provide a biaxially stretched polypropylene film which can suppress a deviation in width of an insulating edge (hereinafter, sometimes referred to as "insulating edge width deviation") at one end in the longitudinal direction and the other end in the longitudinal direction in a metallized film after a slitting process, even though the biaxially stretched polypropylene film is thin.

Means for solving the problems

The biaxially stretched polypropylene film of the present disclosure of item 1 (item 1, the biaxially stretched polypropylene film of the present invention) has a thickness of 1.0 μm to 3.0 μm, a difference between the thermal shrinkage rate at 140 ℃ in the first direction and the thermal shrinkage rate at 130 ℃ in the first direction is 0% or more and less than 2.0%, and a difference between the thermal shrinkage rate at 140 ℃ in the second direction perpendicular to the first direction and the thermal shrinkage rate at 130 ℃ in the second direction is 0% or more and less than 2.3%.

The biaxially stretched polypropylene film of the present disclosure of the 2 nd (the biaxially stretched polypropylene film of the 2 nd invention) has a thickness of 1.0 μm to 3.0. mu.m, a width in the second direction of 1200mm or less,

a biaxially stretched polypropylene film having a difference of less than 6 DEG between the maximum value and the minimum value of the slow axis angle obtained by the following methods (1) to (3).

< method for determining difference between maximum value and minimum value of slow axis angle >

(1) When the total length in the width direction was defined as 100%, a sample for measurement of 50mm × 50mm centered at positions spaced every 10% from both ends thereof was cut out,

(2) the second direction of the measurement sample was set to 0 degrees, the acute angle between the second direction and the slow axis of each measurement sample was measured,

(3) the difference between the maximum and minimum angles measured in the above (2) was obtained for 9 samples for measurement.

The principles of the present inventors as conceived are thus explained for the biaxially stretched polypropylene film of the present disclosure.

< 1 st original patent Commission and its invention (invention 1) >

The inventors of the present invention have made intensive studies on the cause of the deviation in width of the insulating edge between one end in the longitudinal direction and the other end in the longitudinal direction in the metallized film after the slitting process, and they have first thought that the cause is that the temperature of the biaxially stretched polypropylene film increases at the portion where the oil for forming the insulating edge adheres, the thermal shrinkage is large at the portion, and the thermal shrinkage is small at the portion where the oil does not adhere. This is considered to be because the oil is directly adhered to the biaxially stretched polypropylene film, generally vaporized, and adhered at about 130 ℃ to 140 ℃.

As another cause of the deviation of the insulating margin width, it is considered that the temperature of the biaxially stretched polypropylene film locally increases due to the metal vapor (for example, zinc vapor) for forming the heavy margin portion, and a temperature distribution occurs in the plane, and a portion having a large thermal shrinkage and a portion having a small thermal shrinkage occur. The reason for this is that the metal vapor has a high temperature, for example, about 600 ℃.

However, considering the specific heat of oil and the specific heat of metal, the present inventors considered that oil has a greater influence on localized temperature increases in the biaxially stretched polypropylene film than metal vapor. Further, the present inventors considered that the oil had a greater influence than the metal vapor, because the surface of the biaxially stretched film facing the surface to which the metal vapor adheres was strongly cooled by the cooling roll in the step of adhering the metal vapor.

Thus, in order to suppress the deviation of the insulating edge width, the present inventors paid attention to the reduction in the thermal shrinkage rate at 130 ℃ in the first direction and the thermal shrinkage rate at 130 ℃ in the second direction orthogonal to the first direction, with reference to the temperature of the insulating edge forming oil.

However, the present inventors have found that the insulating edge width deviation does not necessarily depend on the heat shrinkage rate of 130 ℃ in the first direction and the second direction.

More specifically, the present inventors have found that the deviation in the width of the insulating margin greatly depends on the difference between the thermal shrinkage rate in the first direction at 140 ℃ and the thermal shrinkage rate in the first direction at 130 ℃, and the difference between the thermal shrinkage rate in the second direction at 140 ℃ and the thermal shrinkage rate in the second direction at 130 ℃.

Based on these findings, the present inventors have conceived the biaxially stretched polypropylene film of the present disclosure of item 1.

Among the above features, the biaxially stretched polypropylene film is preferred

A heat shrinkage ratio S of 140 ℃ in the second direction_TD140A heat shrinkage ratio S of 140 ℃ to the first direction_MD140Is a ratio of_TD140/S_MD140Is 0.200 to 0.325 inclusive.

The aforementioned ratio S_TD140/S_MD140In the case of the above range, the in-plane thermal shrinkage in the 140 ℃ region is well balanced (the thermal shrinkage in the first direction and the second direction becomes uniform), so that the thickness unevenness accuracy is more excellent and the insulating edge width deviation can be further suppressed.

The width in the second direction is 1200mm or less,

the difference between the maximum value and the minimum value of the slow axis angle obtained by the following techniques (1) to (3) is less than 6 °.

When the difference is less than 6 degrees, the thickness variation accuracy of the biaxially stretched polypropylene film is more excellent. When a metallized film is produced from the biaxially stretched polypropylene film, the film is less likely to suffer from uneven shrinkage in the in-plane direction, and wrinkles and sagging are suppressed, and the film can be suitably used.

It is to be noted that the biaxially stretched polypropylene film of the present disclosure of the 1 st aspect can be used for capacitors.

Further, the disclosure of 1 st also relates to a metallized film, and the metallized film of 1 st of the disclosure may have the biaxially stretched polypropylene film of 1 st of the disclosure, and a metal layer laminated on one side or both sides of the biaxially stretched polypropylene film.

The present disclosure of 1 st also relates to a film capacitor, and the film capacitor of 1 st of the present disclosure may have a structure in which a1 st metalized film of the present disclosure is wound or a1 st metalized film of the present disclosure is laminated in plural.

The present disclosure of 1 st also relates to a film roll, and the film roll of 1 st of the present disclosure may be formed in a structure in which the biaxially stretched polypropylene film of 1 st of the present disclosure is wound in a roll shape.

< 2 nd original patent Commission and its invention (invention 2) >

The present inventors studied the effect of oil in the same manner as described in fig. 1. The present inventors have also paid attention to the slow axis angle of a biaxially stretched polypropylene film in order to suppress the width deviation of the insulating edge. As a result, the present inventors have found that the deviation of the insulating edge width greatly depends on the difference between the maximum value and the minimum value of the slow axis angle. Based on these findings, the present inventors have conceived the biaxially stretched polypropylene film of the present disclosure of item 2.

A heat shrinkage ratio S of 140 ℃ in the second direction_TD140A heat shrinkage ratio S of 140 ℃ to the first direction_MD140Is a ratio of_TD140/S_MD140Is 0.200 to 0.325 inclusive. The reason is the same as in the case of the invention 1.

The difference between the thermal shrinkage rate at 140 ℃ in the first direction and the thermal shrinkage rate at 130 ℃ in the first direction is 0% or more and less than 2.0%, and the difference between the thermal shrinkage rate at 140 ℃ in the second direction perpendicular to the first direction and the thermal shrinkage rate at 130 ℃ in the second direction is 0% or more and less than 2.3%.

It is to be noted that the biaxially stretched polypropylene film of the present disclosure of the 2 nd can be used for capacitors.

Further, the disclosure of 2 nd also relates to a metallized film, and the metallized film of 2 nd of the disclosure may have the biaxially stretched polypropylene film of 2 nd of the disclosure, and a metal layer laminated on one side or both sides of the biaxially stretched polypropylene film.

The disclosure of claim 2 also relates to a film capacitor, and the film capacitor of claim 2 may have a structure in which a rolled metallized film of claim 2 or a plurality of metallized films of claim 2 are stacked.

The disclosure of 2 nd relates also to a film roll, and the film roll of 2 nd of the disclosure may be formed in a structure in which the biaxially stretched polypropylene film of 2 nd of the disclosure is wound in a roll shape.

ADVANTAGEOUS EFFECTS OF INVENTION

With the biaxially stretched polypropylene film of the present disclosure (the present disclosure of 1 st and the present disclosure of 2 nd), although the thickness of the biaxially stretched polypropylene film is thin, in the metallized film after the slitting process, the insulating edge width deviation can be suppressed.

Drawings

Fig. 1 is a cross-sectional view of a metalized film, and more particularly, a cross-sectional view taken along line I-I in fig. 2.

Fig. 2 is a top view of a metallized membrane.

Fig. 3 is a top view of a metallized film prior to slitting.

Fig. 4 is a top view of the metallized film before slitting made in example and comparative example.

Detailed Description

The following describes embodiments of the present invention. The present invention is not limited to these embodiments.

In the present specification, expressions "including" and "comprising" include concepts of "including", "comprising", "substantially including" and "containing only".

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

The biaxially stretched polypropylene film of the present embodiment does not have many pores because it is not a microporous film.

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

The biaxially stretched polypropylene film of the present embodiment achieves the above-described problems when the thickness is very small (thin) and 1.0 to 3.0 μm. The biaxially stretched polypropylene film of the present embodiment is not supposed to have a large (thick) thickness such as 4.5 μm or 5 μm.

First, two directions appearing in the present embodiment will be explained. In the present embodiment, the first direction refers to the same direction as the longitudinal direction of the biaxially stretched polypropylene film. In the present embodiment, the first Direction is also the same Direction as a Machine Direction (hereinafter referred to as "MD Direction"). The first direction is hereinafter mainly referred to as MD direction. However, in the present invention, the first direction is not limited to the mode of referring to the same direction as the longitudinal direction, and is not limited to the mode of referring to the same direction 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 is also the same Direction as a Transverse Direction (hereinafter referred to as "TD Direction"). The second direction will be mainly referred to as TD direction hereinafter. However, in the present invention, the second direction is not limited to the same direction as the width direction, and is not limited to the same direction as the TD direction.

< embodiment of the invention 1 >

The thickness (thickness) of the biaxially stretched polypropylene film of the present embodiment is in the range of 1.0 to 3.0. mu.m. The thickness of the biaxially stretched polypropylene film of the present embodiment is preferably 1.2 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 less than 3.0. mu.m, more preferably 2.9 μm or less, still more preferably 2.8 μm or less, and particularly preferably 2.5 μm or less. When the thickness of the biaxially stretched polypropylene film of the present embodiment is within the above ranges including the preferred ranges, the excellent effect of suppressing the deviation of the insulating margin width in the metallized film after the slitting process even if the thickness of the biaxially stretched polypropylene film is thin can be enjoyed to the maximum, and a film capacitor with a reduced size and a large capacitance can be obtained.

Further, since the polypropylene film has a thickness of 3.0 μm or less, the electrostatic capacitance per unit volume when forming a capacitor element can be increased, and thus the polypropylene film can be suitably used as a capacitor.

This will be described in detail below.

The capacitance per unit volume can be increased as the thickness of the polypropylene film is decreased, and more specifically, the capacitance C is expressed as follows using a dielectric constant, an electrode area S, and a dielectric thickness d (thickness d of the polypropylene film).

C＝S/d

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

V＝Sd

Therefore, the capacitance C/V per unit volume is expressed by the above 2 equations as follows.

C/V＝/d²

From the above formula, the capacitance per unit volume (C/V) is inversely proportional to the square of the thickness of the polypropylene film. In addition, the dielectric constant is determined by the material used. Therefore, it is known that the electrostatic capacitance per unit volume (C/V) cannot be improved unless the thickness is made thin without changing the material.

That is, if it is assumed that film capacitors are made of the same material, (1) when film capacitors of the same size are made, a film capacitor having a large capacitance is obtained when a thin polypropylene film is used. In addition, (2) when a film capacitor having the same capacitance is manufactured, a film capacitor having a small size can be obtained by using a thin polypropylene film, and space saving can be achieved.

The thickness of the biaxially stretched polypropylene film is measured at 100. + -. 10kPa using a paper thickness measuring instrument MEI-11 manufactured by CITIZEN SEIMITSU, and is measured in accordance with JIS-C2330.

In the biaxially stretched polypropylene film of the present embodiment, the difference between the heat shrinkage rate at 140 ℃ in the MD and the heat shrinkage rate at 130 ℃ in the MD (hereinafter referred to as "MD heat shrinkage rate difference") is 0% or more and less than 2.0%, and the difference between the heat shrinkage rate at 140 ℃ in the TD and the heat shrinkage rate at 130 ℃ in the TD (hereinafter referred to as "TD heat shrinkage rate difference") is 0% or more and less than 2.3%. In the present specification, the heat shrinkage rate at 140 ℃ in the MD direction is sometimes referred to as S_MD140The heat shrinkage at 130 ℃ in the MD is called S_MD130The thermal shrinkage in the TD direction at 140 ℃ is designated as S_TD140The thermal shrinkage at 130 ℃ in the TD direction is designated as S_TD130. The difference in MD heat shrinkage in this specification may be referred to as S_MD140-S_MD130Difference in TD thermal shrinkageIs called S_TD140-S_TD130。

The biaxially stretched polypropylene film of the present embodiment is thin and has a thickness in the range of 1.0 μm to 3.0. mu.m, but in the metallized film after the slitting step, the width deviation of the insulating margin can be suppressed at one end in the longitudinal direction and the other end in the longitudinal direction. The width of the insulating edge was measured in the width direction of the biaxially stretched polypropylene film.

The reason why the deviation of the insulating edge width can be suppressed is presumed as follows.

When the insulating edge is formed on the biaxially stretched polypropylene film, it is considered that the insulating edge-forming oil causes temperature unevenness in the surface of each insulating edge.

It is considered that such temperature unevenness can be roughly classified into temperature unevenness in the TD direction and temperature unevenness in the MD direction.

Regarding the temperature unevenness in the TD direction, it is considered that the temperature at the center portion in the TD direction is higher than the temperatures at both end portions in the TD direction at each insulation edge. This is considered to be because the oil vapor for forming the insulating edge is ejected in a fan shape from the slit of the nozzle, and therefore the amount of oil is larger in the center portion in the TD direction of the insulating edge than in the both end portions in the TD direction.

On the other hand, regarding the occurrence of the temperature unevenness in the MD direction, it is considered that the oil vapor for forming the insulating edge is adjusted so as to be jetted at a constant potential, but it cannot be assumed that the potential is strictly constant, and the potential slightly varies, and it is estimated that the temperature unevenness in the MD direction occurs due to such variation.

Further, it is considered that the temperature range of the temperature unevenness in each insulating edge surface is about 130 ℃ to about 140 ℃. This is considered to be because the oil vapor for forming the insulating margin is generally injected at about 130 ℃ to about 140 ℃. Hereinafter, a region that can be regarded as about 140 ℃ (a region that is regarded as a relatively large amount of oil) may be referred to as a 140 ℃ region or a high temperature region, and a region that can be regarded as about 130 ℃ (a region that is regarded as a relatively small amount of oil) may be referred to as a 130 ℃ region.

The biaxially stretched polypropylene film of the present embodiment is considered to be capable of suppressing wrinkles and sagging which may occur conventionally due to such temperature unevenness. This is considered to be because, in the biaxially stretched polypropylene film of the present embodiment, the heat shrinkage rate at 140 ℃ which may correspond to the temperature of the high temperature region of the insulating edge and the heat shrinkage rate at 130 ℃ which may correspond to the temperature of the 130 ℃ region of the insulating edge are close to each other in the direction perpendicular to each other. That is, when a temperature distribution is generated in each insulating edge due to the oil for forming the insulating edge, the heat shrinkage rates at 130 ℃ and 140 ℃ of the biaxially stretched polypropylene film do not have a large distribution, that is, the heat shrinkage rates at 130 ℃ and 140 ℃ of the biaxially stretched polypropylene film are close to each other, and therefore, it is considered that wrinkles and sagging can be suppressed.

As a result of suppressing such wrinkles and slackening, it is presumed that the biaxially stretched polypropylene film of the present embodiment can suppress the deviation of the insulating edge width.

Heat shrinkage (S) in the TD direction (second direction) at 140 DEG C_TD140) Heat shrinkage (S) of 140 ℃ from MD direction (first direction)_MD140) Is the ratio of (A) to (B), i.e. S_TD140/S_MD140Preferably 0.200 or more, more preferably 0.240 or more, further preferably 0.280 or more, and particularly preferably 0.290 or more. In addition, S_TD140/S_MD140Preferably 0.385 or less, more preferably 0.360 or less, further preferably 0.330 or less, further more preferably 0.325 or less, particularly preferably 0.320 or less, and particularly preferably 0.315 or less. In addition, S_TD140/S_MD140The range defining the upper limit and the lower limit is preferably 0.200 or more and 0.385 or less, more preferably 0.240 or more and 0.360 or less, and further preferably 0.280 or more and 0.320 or less. S_TD140/S_MD140In the case of the above range, the in-plane heat shrinkage in the 140 ℃ region is well balanced (the heat shrinkage in the TD direction and the MD direction becomes uniform), so the thickness unevenness accuracy is more excellent, and the insulating edge width deviation can be further suppressed.

Thermal shrinkage (S) at 130 ℃ in TD direction_TD130) Heat shrinkage (S) at 130 ℃ from MD_MD130) Is the ratio of (A) to (B), i.e. S_TD130/S_MD130Preferably 0.140 or less, more preferably0.070 to 0.130, more preferably 0.080 to 0.100. S_TD130/S_MD130In the case of the above range, the in-plane heat shrinkage in the 130 ℃ region is well balanced (the heat shrinkage in the TD direction and the MD direction becomes uniform), so the thickness unevenness accuracy is more excellent, and the insulating edge width deviation can be further suppressed.

TD Heat shrinkage Rate Difference (S)_TD140-S_TD130) Difference in thermal shrinkage from MD (S)_MD140-S_MD130) Is (S)_TD140-S_TD130)/(S_MD140-S_MD130) Preferably 0.920 or more and 1.350 or less, preferably 0.930 or more and 1.200 or less, and more preferably 0.960 or more and 1.080 or less. (S)_TD140-S_TD130)/(S_MD140-S_MD130) In the case of the above range, the in-plane heat shrinkage in the region of 130 to 140 ℃ is well balanced (the heat shrinkage in the TD direction and the MD direction is uniform), so that the thickness variation accuracy is more excellent and the insulating edge width deviation can be further suppressed.

Difference in thermal shrinkage for MD (S)_MD140-S_MD130) Difference in TD thermal shrinkage ratio (S)_TD140-S_TD130) Both of these are affected by the speed of a drawing roll (hereinafter referred to as "drawing speed") for taking up the biaxially stretched polypropylene film downstream of the tenter and the speed of conveyance of the polypropylene film in the MD direction in the tenter stretching section (hereinafter referred to as "film forming line speed"), and also by the heat-setting temperature. They are explained in detail in the explanation of biaxial stretching.

Difference in MD Heat shrinkage (S)_MD140-S_MD130) Preferably 0.1% or more, more preferably 0.5% or more, further preferably 1.0% or more, and particularly preferably 1.5% or more. The difference in MD heat shrinkage is preferably 1.9% or less, more preferably 1.8% or less.

On the other hand, TD thermal shrinkage ratio is poor (S)_TD140-S_TD130) Preferably 0.1% or more, more preferably 0.5% or more, further preferably 1.0% or more, and particularly preferably 1.5% or more. The difference in TD thermal shrinkage is preferably 2.2% or less, more preferably 2.0% or less, and still more preferablyPreferably 1.9% or less, particularly preferably 1.8% or less.

Heat shrinkage (S) in MD at 140 ℃_MD140) Preferably 10.0% or less, more preferably 9.0% or less, and further preferably 8.5% or less. Heat shrinkage (S) in MD at 140 ℃_MD140) Preferably 1.0% or more, more preferably 3.0% or more, further preferably 5.0% or more, and particularly preferably 7.0% or more.

Thermal shrinkage (S) in TD direction at 140 ℃_TD140) Preferably 5.0% or less, more preferably 4.0% or less, further preferably 3.5% or less, and particularly preferably 2.7% or less. The heat shrinkage ratio in the TD direction at 140 ℃ is preferably 0.1% or more, more preferably 0.5% or more, still more preferably 1.0% or more, and particularly preferably 2.0% or more.

The width of the biaxially stretched polypropylene film in the TD direction (second direction) is not particularly limited. However, when the difference between the maximum value and the minimum value of the slow axis angle obtained by the following techniques (1) to (3) is less than 6 °, the width in the TD direction (second direction) is preferably 1200mm or less.

That is, the above biaxially stretched polypropylene film is preferred

The width in the TD direction (second direction) is 1200mm or less,

the difference between the maximum value and the minimum value of the slow axis angle obtained by the following techniques (1) to (3) is less than 6 °. This will be explained below.

The slow axis is explained here.

In the biaxially stretched polypropylene film of the present embodiment, stretching is performed biaxially in a first direction and a second direction orthogonal thereto. Since the polymer is oriented in the plane by the biaxial stretching, the biaxially stretched film has birefringence. The orientation in which the refractive index is maximized in the film plane is called a slow axis because the light traveling speed is slow (the phase is slow).

For example, when a sequential biaxial stretching method is used, the green cast web is first stretched in the flow direction (MD) and then the sheet is stretched in the Transverse Direction (TD). In this case, the slow axis of the biaxially stretched polypropylene film tends to have a refractive index in the transverse direction of the second direction larger than the refractive index in the flow direction of the first direction. Here, the transverse direction of the second direction forms a slow axis.

In the stretching in the transverse direction (TD direction), when the stretching is completely performed in the transverse direction (when the stretching is completely performed in the direction orthogonal to the flow direction), the slow axis angle defined in the present specification is 0 °. However, in the practice, poisson contraction stress, mechanical external force, thermoplasticity of the film, and the like act during stretching, and the film cannot be stretched completely in the transverse direction (TD direction), and the slow axis angle tends to be larger than 0 °. In the sequential biaxial stretching method, the slow axis angle tends to be larger as the film is stretched at both ends.

In the present embodiment, it can be said that the smaller the difference between the maximum value and the minimum value of the slow axis angle, the smaller the deviation of the optical orientation axis from the orientation in two directions orthogonal to the flow direction (MD direction) in the first direction and the transverse direction (TD direction) in the second direction. Therefore, when a metallized film is produced, the shrinkage in the oblique direction during heating is reduced, and the thermal shrinkage in the first direction and the second direction is easily uniform. As a result, wrinkles and slackening during processing are suppressed, and the film can be suitably used. Further, when the film is stretched, the film is deformed in the transverse direction (TD direction) in which a tensile stress acts, and therefore the obtained film is excellent in the accuracy of thickness variation.

In addition, when the maximum value of the slow axis angle is smaller, the deformation force in the oblique direction different from the transverse direction (TD direction) is more difficult to be applied in the film formation of the biaxially stretched polypropylene film, and therefore, the tensile fracture is reduced, and the continuous film forming property tends to be excellent. In particular, the biaxially stretched polypropylene film of the present embodiment has a thickness of 1.0 to 3.0 μm and is very small (thin), and therefore, the effect is remarkably exhibited.

The difference between the maximum value and the minimum value of the slow axis angle in the present embodiment does not indicate anisotropy of the optical alignment strength due to birefringence or the like, that is, the magnitude and direction of the alignment itself, but indicates the width-wise variation width of the slow axis angle, which is the angle formed by the maximum value and the minimum value of the second direction and the slow axis. In the present embodiment, it is preferable to control the difference to be small.

The reason why the difference is preferably small is that, even if the polypropylene, which is a soft material, is provided with orientation strength by biaxial stretching to provide constant mechanical processing strength, the amount of dimensional change of heat generated during metal vapor deposition processing is not sufficiently reduced, and it is obvious that the result that suppressing deviation or variation in orientation direction is useful for suppressing shrinkage unevenness in the in-plane direction is obtained.

Further, the polypropylene film of the present embodiment has a very small (thin) thickness of 1.0 to 3.0 μm, and is greatly affected by the temperature of the metal deposition process. Therefore, uniformity of orientation accompanying the heat shrinkage rate is also important. In the present embodiment, by reducing the width-directional variation range of the slow axis angle, the alignment of the thermal shrinkage can be maintained.

The difference between the maximum value and the minimum value of the slow axis angle is preferably less than 6 °, more preferably 5.5 ° or less, further preferably 5 ° or less, and particularly preferably 4.5 ° or less. When the difference is less than 6 degrees, the thickness variation accuracy of the biaxially stretched polypropylene film is more excellent. Further, when a metallized film is produced from the biaxially stretched polypropylene film, the film is less likely to suffer from uneven shrinkage in the in-plane direction, and wrinkles and sagging are suppressed, and therefore, the film can be suitably used.

The maximum value of the slow axis angle is preferably less than 15 °, more preferably 14.5 ° or less, further preferably 13 ° or less, and particularly preferably 12 ° or less. When the maximum value is within the above numerical range, the film tends to have less breakage and excellent continuous productivity when a biaxially stretched polypropylene film is formed.

When the difference between the maximum value and the minimum value of the slow axis angle is less than 6 °, the width in the TD direction (second direction) is preferably 1200mm or less, more preferably 1100mm or less, and still more preferably 1000mm or less. When the difference is less than 6 °, the width in the TD direction (second direction) may be 500mm or more, 550mm or more, 600mm or more, or the like.

The measurement device and the measurement conditions for obtaining the difference between the maximum value and the minimum value of the slow axis angle are as follows.

< measuring apparatus, measuring conditions >

A measuring device: otsuka electronic corporation delay amount measuring device RE-100

Light source: laser luminous diode (LED)

Band-pass filter: 550nm (measuring wavelength)

Measurement interval: 0.1sec (seconds)

Cumulative number of times: 10time (second)

Measuring the number of points: 15point (Point)

Gain: 10dB

And (3) measuring environment: the temperature is 23 ℃ and the humidity is 60%

The difference between the maximum value and the minimum value of the slow axis angle tends to increase when the heat setting temperature is lowered, and tends to increase when the ratio of the take-up speed to the film forming linear speed is raised.

The maximum value of the slow axis angle tends to be increased when the heat setting temperature is lowered, and tends to be increased when the ratio of the take-up speed to the deposition linear speed is raised.

The biaxially stretched polypropylene film and the metallized film are each wound in a roll form, and preferably in the form of a film roll. The aforementioned film rolls may or may not have a roll core (core). The aforementioned film roll preferably has a roll core (core). The material of the winding core of the 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, and acrylonitrile-butadiene-styrene copolymer. 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, polyparaphenylene benzoxazole fibers (ZYLON (registered trademark)) fibers, polyethylene fibers, and boric acid fibers. Examples of the metal include iron, aluminum, and stainless steel. The winding core of the film roll also includes a winding core formed by impregnating a paper tube with the resin. At this time, the material of the core is classified as resin.

Next, preferred raw materials and a production method 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 contains a polypropylene resin. The content of the polypropylene resin is preferably 75% by mass or more, more preferably 90% by mass or more, and further 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 and the biaxially stretched polypropylene film of the present embodiment may contain one kind of polypropylene resin alone or two or more kinds of polypropylene resins.

The weight average molecular weight Mw of the polypropylene resin is preferably 28 to 45 ten thousand, more preferably 28 to 40 ten thousand. The resin flowability is suitable when the weight average molecular weight Mw of the polypropylene resin is from 28 to 45 ten thousand. 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, more preferably 6.1 or more, further preferably 6.5 or more, further more preferably 7.2 or more, and particularly preferably 7.5 or more. The molecular weight distribution of the polypropylene resin is preferably 12 or less, more preferably 11 or less, still more preferably 10 or less, and particularly preferably 9.5 or less. The ranges defining the upper limit and the lower limit of the molecular weight distribution of the polypropylene resin are preferably 5 to 12 inclusive, more preferably 5 to 11 inclusive, and still more preferably 5 to 10 inclusive.

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 using a Gel Permeation Chromatography (GPC) apparatus. More specifically, the value was measured using HLC-8121GPC-HT (trade name) from a differential Refractometer (RI) built-in high temperature GPC measurement machine manufactured by Tosoh corporation. As a GPC column, 3 TSKgel GMHHR-H (20) HT (available from Tosoh corporation) was used in combination. The column temperature was set at 140 ℃ and trichlorobenzene as an eluent was flowed at a flow rate of 1.0ml/10 minutes to obtain measured values of Mw and Mn. A calibration curve for the molecular weight M was prepared using a standard polystyrene available from Tosoh corporation, and the Mw and Mn were obtained by converting the measured values into polystyrene values. Here, the base 10 logarithm of the molecular weight M of standard polystyrene is referred to as the logarithmic molecular weight ("log (M)").

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 still more preferably-4% or more and 10% or less. Here, the "differential distribution value difference D_M"means a difference obtained by subtracting a differential distribution value at log (m) of 6.0 from a differential distribution value at 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) of 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 ") in terms of the Mw value of the polypropylene resin, if the difference is positive, the low molecular weight component is large, and the difference is negative, the log (m) is compared with the component having a distribution value of about 6.0In this case, it is understood that the high molecular weight component is contained in a large amount.

That is, even if the molecular weight distribution Mw/Mn is 5 to 12, the width of the molecular weight distribution width is simply expressed, and the quantitative relationship between the high molecular weight component and the low molecular weight component is unknown. Therefore, from the viewpoint of stabilizing the film-forming property and the thickness uniformity of the green sheet, the following polypropylene resins are preferably used as the polypropylene resin: the composition has a wide molecular weight distribution and, in order to appropriately contain low-molecular-weight components, a differential distribution value difference of-5% to 14% is obtained by comparing a component having a molecular weight of 1 to 10 ten thousand with a component having a molecular weight of 100 ten thousand.

The differential distribution value is obtained by GPC as follows. A curve showing intensity versus time (also commonly referred to as "dissolution curve") obtained by differential Refractometry (RI) detection by GPC was used. The dissolution curve was converted to a curve representing intensity versus log (m) using a standard curve obtained with standard polystyrene, converting the time axis to a logarithmic molecular weight (log (m)). Since the RI detection intensity is proportional to the component concentration, an integral distribution curve with respect to the log molecular weight log (m) can be obtained when the total area of the curve representing the intensity is 100%. The differential profile is obtained by differentiating the integral profile by log (m). Therefore, the "differential distribution" refers to a differential distribution of concentration fraction with respect to molecular weight. From this curve, the differential distribution value at a specific log (m) is read.

The meso pentad fraction ([ mmmm ]) of the polypropylene resin is preferably 94% or more, more preferably 95% or more, further preferably more than 95%, particularly preferably 95.5% or more, and particularly preferably more than 96%. The meso pentad fraction of the polypropylene resin is preferably 98.5% or less, more preferably 98.4% or less, still more preferably 98% or less, particularly preferably less than 98.0%, particularly preferably 97.5% or less, and particularly preferably 97.0% or less. The meso pentad fraction of the polypropylene resin is preferably 94% or more and 99% or less, and more preferably 95% or more and 98.5% or less. By using such a polypropylene resin, crystallinity of the resin is moderately improved due to 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 depending on an appropriate solidification (crystallization) speed at the time of forming into a green sheet.

The meso pentad fraction ([ mmmm ]) is an index of stereoregularity which can be obtained by high temperature Nuclear Magnetic Resonance (NMR) measurement. Specifically, the measurement can be carried out, for example, by using a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR) manufactured by Nippon electronic Co., Ltd., or JNM-ECP 500. The observation core was 13C (125MHz), the measurement temperature was 135 ℃, and the solvent for dissolving the polypropylene resin was o-dichlorobenzene (ODCB: a mixed solvent of ODCB and deuterated ODCB (mixing ratio: 4/1)), 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, Jiez House, 1995, p.610".

The measurement mode may be single-pulse proton broadband decoupling, pulse width 9.1 μ sec (45 ° pulse), pulse interval 5.5sec, cumulative number 4500 times, and displacement reference CH₃(mmmm)＝21.7ppm。

The pentad fraction indicating the stereoregularity is calculated as a percentage based on the integrated value of the intensity of each signal derived from the combination (mmmm, mrrm, etc.) of 5 cell groups (pentads) of the cell group "meso (m)" arranged in the same direction and the cell group "racemic (r)" arranged in a different direction. Signals originating from mmmm and mrrm et al can be attributed, for example, with reference to "t.hayashi et al, Polymer, volume 29, page 138 (1988)", and the like.

The heptane-insoluble content (HI) of the polypropylene resin is preferably 96.0% or more, more preferably 97.0% or more. The heptane-insoluble content (HI) of the polypropylene resin is preferably 99.5% or less, more preferably 99.0% or less. Here, the more heptane-insoluble component, the higher the stereoregularity of the resin. When the heptane-insoluble fraction (HI) is 96.0% or more and 99.5% or less, crystallinity of the resin is moderately improved by moderately high stereoregularity, and voltage resistance at high temperature is improved. On the other hand, the solidification (crystallization) rate at the time of molding the green casting web is moderate, and the green casting web has moderate stretchability.

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 can be used.

In order to improve the electrical characteristics, the total ash content due to the polymerization catalyst residue and the like contained in the polypropylene raw material resin or the biaxially stretched polypropylene film of the present embodiment 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 100 parts by weight of the polypropylene resin.

The polypropylene resin may contain additives. Examples of the additive include an antioxidant, a chlorine absorber, an ultraviolet absorber, a lubricant, a plasticizer, a flame retardant, and an antistatic agent. The polypropylene resin may contain additives in an amount not to adversely affect the biaxially stretched polypropylene film.

From now on, the respective polypropylene resins in the case of using 2 or more polypropylene resins will be explained.

In the case of using 2 or more kinds of polypropylene resins, 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 combination of the following linear polypropylene resin A-4 and the following linear polypropylene resin B-4 can be cited as preferable examples. In the present embodiment, the expression called the linear polypropylene resin A includes concepts called the linear polypropylene resin A-1, the linear polypropylene resin A-2, the linear polypropylene resin A-3 and the 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. However, in the present invention, the polypropylene resin is not limited to the following resins.

< 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)

A linear polypropylene resin having a heptane-insoluble content (HI) of 98.5% or less.

(Linear Polypropylene resin A-3)

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

(Linear Polypropylene resin A-4)

A linear polypropylene resin having a weight average molecular weight Mw of 28 to 34 ten thousand.

< Linear Polypropylene resin B >

(Linear Polypropylene resin B-1)

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

(Linear Polypropylene resin B-2)

A linear polypropylene resin having a heptane insoluble content (HI) of more than 98.5%.

(Linear Polypropylene resin B-3)

A linear polypropylene resin having a Melt Flow Rate (MFR) of 0.1 to 3.9g/10 min at 230 ℃.

(Linear Polypropylene resin B-4)

A linear polypropylene resin having a weight average molecular weight Mw of more than 34 ten thousand.

The weight average molecular weight Mw of the linear polypropylene resin a is preferably 28 ten thousand or more. The weight average molecular weight Mw of the linear polypropylene resin a is preferably 45 ten thousand or less, more preferably 40 ten thousand or less, further preferably 35 ten thousand or less, and particularly preferably 34 ten thousand or less. When the weight average molecular weight Mw of the linear polypropylene resin a is 28 to 45 ten thousand, the resin flowability is moderate. 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 is 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-mentioned preferred range, the thickness of the green sheet and the biaxially stretched polypropylene film is less likely to vary, and appropriate stretchability is 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% or more and 18.0% or less, the content is much more than 8.0% and 18.0% or less when the low molecular weight component and the high molecular weight component are compared. Therefore, the surface of the biaxially stretched polypropylene film in the present embodiment is easily obtained, and is therefore preferable.

The meso pentad fraction ([ mmmm ]) of the linear polypropylene resin a is preferably 99.8% or less, more preferably 99.5% or less, and still more preferably 99.0% or less. The meso pentad fraction is preferably 94.0% or more, more preferably 94.5% or more, and still more preferably 95.0% or more. When the meso pentad fraction is within the above numerical range, crystallinity of the resin is improved appropriately by appropriately high stereoregularity, and the voltage resistance at high temperature is improved. On the other hand, the cast sheet has a moderate solidification (crystallization) rate and a moderate elongation during molding.

The heptane-insoluble content (HI) of the linear polypropylene resin a is preferably 96.0% or more, more preferably 97.0% or more. The heptane-insoluble content (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 of the linear polypropylene resin A at 230 ℃ is within the above range, the flow characteristics in the molten state are excellent, so that unstable flow such as melt fracture is less likely to occur, and the breakage during stretching is suppressed. Therefore, the film thickness uniformity is good, and there is an advantage that the formation of a thin portion in which dielectric breakdown is likely to occur is suppressed.

The content of the linear polypropylene resin a is preferably 55% by mass or more, more preferably 60% by mass or more, based on the whole biaxially stretched polypropylene film. The content of the linear polypropylene resin a is preferably 99.9% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less, and particularly preferably 80% by mass or less, based on 100% by mass of the entire polypropylene resin in the polypropylene film.

The weight average molecular weight Mw of the linear polypropylene resin B is preferably 30 ten thousand or more, more preferably 33 ten thousand or more, further preferably more than 34 ten thousand, further more preferably 35 ten thousand or more, particularly preferably more than 35 ten thousand. The weight average molecular weight Mw of the linear polypropylene resin B is preferably 40 ten thousand or less, more preferably 38 ten thousand or less.

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, further preferably 7.0 or more and 8.3 or less, and particularly preferably 7.2 or more and 8.2 or less.

When the molecular weight distribution Mw/Mn of the linear polypropylene resin B is within the above-mentioned preferred range, the thickness of the green sheet or the biaxially stretched polypropylene film is less likely to vary, and appropriate stretchability is 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 meso pentad fraction ([ mmmm ]) of the linear polypropylene resin B is preferably less than 99.8%, more preferably 99.5% or less, and still more preferably 99.0% or less. The meso pentad fraction is preferably 94.0% or more, more preferably 94.5% or more, and still more preferably 95.0% or more. When the meso pentad fraction is within the above numerical range, crystallinity of the resin is improved appropriately by appropriately high stereoregularity, and the voltage resistance at high temperature is improved. On the other hand, the cast sheet has a moderate solidification (crystallization) rate and a moderate elongation during molding.

The heptane-insoluble content (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 content (HI) of the linear polypropylene resin B is preferably 99.5% or less, more preferably 99% or less.

The linear polypropylene resin B preferably has a Melt Flow Rate (MFR) at 230 ℃ of 0.1 to 6.0g/10 min, more preferably 0.1 to 5.0g/10 min, and further preferably 0.1 to 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% by mass or more, more preferably 15% by mass or more, and still more preferably 20% by mass or more, based on 100% by mass of the entire polypropylene resin in the polypropylene film. Similarly, the content of the linear polypropylene resin B is preferably 45% by mass or less, more preferably 40% by mass or less, assuming that the entire polypropylene resin in the polypropylene film is 100% by mass.

When the linear polypropylene resin a and the linear polypropylene resin B are used in combination as the polypropylene resin, the polypropylene resin is preferably composed of 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 composed of 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 composed of 60 to 80% by weight of the linear polypropylene resin a and 40 to 20% by weight of the linear polypropylene resin B, based on 100% by mass of the whole polypropylene resin.

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 voltage resistance (particularly, the voltage resistance at high temperatures) is improved, and the capacitance when used as a film capacitor element is improved.

The above description is of each polypropylene resin in the case of using 2 or more polypropylene resins.

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 of the present embodiment is preferably made of a polypropylene resin as a resin.

The pre-stretched green sheet for producing the biaxially stretched polypropylene film can be produced as follows.

First, polypropylene resin pellets after dry blending, or mixed polypropylene resin pellets prepared by melting and kneading in advance are supplied to an extruder and heated and melted.

The rotation speed of the extruder during heating and melting is preferably 5 to 40rpm, more preferably 10 to 30 rpm. The extruder set 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 at the time of heating and melting is a value measured with a thermometer inserted into the extruder.

The extruder rotation speed, the extruder set temperature, and the resin temperature at the time of heating and melting are also selected in consideration of the physical properties of the crystalline thermoplastic resin to be 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.

Then, the molten resin is extruded into a sheet form by 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.

The biaxially stretched polypropylene film can be produced by subjecting a green sheet to a stretching treatment. The stretching is preferably biaxial stretching in which orientation is carried out biaxially in the longitudinal and transverse directions, and as the stretching method, sequential biaxial stretching is preferred. As the sequential biaxial stretching method, for example, a green cast web is first stretched 3 to 7 times in the flow direction (MD direction) by passing between rollers provided with a speed difference. Then, the sheet is introduced into a tenter and stretched 3 to 11 times in the transverse direction (TD direction). The temperature at the time of stretching in the flow direction (also referred to as a longitudinal stretching temperature) is preferably 130 to 150 ℃. The temperature during the stretching in the width direction (also referred to as transverse stretching temperature) is preferably 155 to 170 ℃. Then, the sheet was relaxed, heat-set, and wound around a take-up roll. From the above, a biaxially stretched polypropylene film was obtained.

Both of the MD heat shrinkage difference and TD heat shrinkage difference of the biaxially stretched polypropylene film are affected by the speed (drawing speed) of the drawing roll for winding the biaxially stretched polypropylene film downstream of the tenter and the transfer speed (film forming line speed) of the polypropylene film in the MD direction in the tenter stretching section, as described above. The difference between the maximum value and the minimum value of the slow axis angle and the maximum value of the slow axis angle are affected by the pulling speed and the film deposition linear speed. Therefore, the ratio of the drawing speed to the film forming linear speed (drawing speed/film forming linear speed) will be described. This ratio is preferably 1.01 to 1.20, more preferably 1.02 to 1.18, still more preferably 1.03 to 1.15, and particularly preferably 1.05 to 1.09. By adjusting this ratio to 1.20 or less, the roll can be positioned directly above the pulling rollIn the case of the biaxially stretched polypropylene film, the tension is suppressed to such a low level that the film is not bent, and the thermal dimensional strain can be suitably suppressed to a small level. The reason why the thermal dimensional deformation can be suppressed is considered to be because the progress of the orientation of the polymer molecular chains can be suppressed. By adjusting this ratio to 1.20 or less, the polypropylene film after biaxial stretching can be suitably prevented from breaking even immediately above the drawing roll. If the ratio of the drawing speed to the film forming linear speed (drawing speed/film forming linear speed) is increased (raised), S is present_MD140-S_MD130、S_TD140-S_TD130And S_TD140/S_MD140Both tend to be high, and S is present when the ratio is lowered (lowered)_MD140-S_MD130、S_TD140-S_TD130And S_TD140/S_MD140The tendency is reduced.

Both of the MD heat shrinkage difference and the TD heat shrinkage difference are affected not only by the ratio of the drawing speed to the film forming line speed but also by the heat setting temperature in heat setting after biaxial stretching. In addition, the difference between the maximum value and the minimum value of the slow axis angle and the maximum value of the slow axis angle are affected by the heat-setting temperature. Therefore, the heat-setting temperature is explained. The present inventors considered that such a phenomenon that the mobility of the polymer molecular chain changes depending on the temperature affects the temperature dependence of the thermal shrinkage rate. That is, the present inventors presume that both the MD heat shrinkage difference and the TD heat shrinkage difference are affected by the heat setting temperature, because the mobility of the polymer molecular chain changes with respect to the temperature change due to the heat setting temperature. The heat-setting temperature is preferably 159 ℃ to 169 ℃, more preferably 161 ℃ to 167 ℃, further preferably 162 ℃ to 166 ℃, particularly preferably 162 ℃ to 164 ℃. The difference in MD heat shrinkage is preferably less than 2.0% and the difference in TD heat shrinkage is preferably less than 2.3% at 169 ℃. It is also preferably 169 ℃ or lower in order to suppress the polypropylene film from breaking immediately above the drawing roll after biaxial stretching and to form a film with good thickness unevenness accuracy. Here, the thickness variation accuracy means that the thickness in the TD direction in the biaxially stretched polypropylene film is uniformTo the extent of (c). If the heat-setting temperature in heat-setting after biaxial stretching is increased (raised), S is present_MD140-S_MD130、S_TD140-S_TD130And S_TD140/S_MD140Both of them tend to be reduced, and when the heat-setting temperature is lowered (lowered), S is present_MD140-S_MD130、S_TD140-S_TD130And S_TD140/S_MD140Both in an elevated tendency.

Thus, the biaxially stretched polypropylene film is heat-set at 159 to 169 ℃ and is further wound up at a ratio of a take-up speed to a film forming line speed of 1.01 to 1.20, whereby the MD heat shrinkage difference can be favorably made less than 2.0% and the TD heat shrinkage difference can be made less than 2.3%.

In the biaxially stretched polypropylene film, for the purpose of improving the adhesion characteristics in the subsequent steps such as the metal vapor deposition process, corona discharge treatment may be performed on-line or off-line after the stretching and heat-setting steps. The corona discharge treatment may be performed by a known method. The atmosphere gas is preferably air, carbon dioxide gas, nitrogen gas, or a mixture thereof.

An oil mask for insulating edge was formed by applying an oil corresponding to the pattern of the insulating edge pattern to one surface of a biaxially stretched polypropylene film, and metal deposition was performed thereon to obtain a metallized film before slitting. The insulating edge oil mask is used to prevent metal particles from adhering to a portion where an insulating edge of a biaxially stretched polypropylene film is formed in a vapor deposition process. The oil mask for the insulating edge may be formed by directly applying oil stored in an oil tank to a biaxially stretched polypropylene film from a nozzle provided in the oil tank by gasifying the oil. Here, "direct coating" refers to spraying oil from a slit of a nozzle to adhere the oil to a biaxially stretched polypropylene film. On the other hand, metal vapor deposition is performed when the biaxially stretched polypropylene film after the formation of the insulating edge oil mask passes through a cooling roll. The cooling roll is maintained at, for example, -30 ℃ to-20 ℃. That is, metal deposition is performed while a biaxially stretched polypropylene film having an insulating edge oil mask is passed through a space between a cooling roll and an evaporation source for metal deposition. In this way, in the space, the metal vapor is released toward the surface of the biaxially stretched polypropylene film on which the oil mask for insulating edge is formed, and adheres to the biaxially stretched polypropylene film. The cooling roll is used to prevent the biaxially stretched polypropylene film from being deformed by the heat of the metal vapor. Examples of the metal used for the metal vapor deposition include simple metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, mixtures of a plurality of these metals, and alloys thereof, but it is preferable to use aluminum for the active portion and zinc and aluminum for the heavy edge portion in consideration of the environment, the economy, the thin film capacitor performance, and the like. Such a metal layer is formed by, for example, depositing aluminum on both the region where the active portion is to be formed and the region where the heavy edge portion is to be formed in the biaxially stretched polypropylene film having the oil mask for insulating edge, and further depositing zinc on the region where the heavy edge portion is to be formed. Alternatively, for example, the active portion may be formed by depositing aluminum only in a region where the active portion is to be formed, and by depositing zinc only in a region where the heavy edge portion is to be formed. In the case where the edge pattern is provided in the active portion, the oil mask for pattern may be formed on one of both surfaces of the biaxially stretched polypropylene film, on which the oil mask for insulating edge is formed, during the formation of the oil mask for insulating edge and the metal vapor deposition, that is, after the formation of the oil mask for insulating edge and before the metal vapor deposition. The oil mask for patterning is generally formed by a plate roller. The temperature of the oil used for forming the oil mask for patterning is lower than the temperature of the oil mask for forming the insulating edge. The oil for forming the oil mask for patterning is applied to the biaxially stretched polypropylene film at room temperature (for example, 40 ℃ or lower).

The metallized film before slitting thus obtained and the metallized film obtained by dividing the metallized film before slitting will be described with reference to the drawings.

As shown in fig. 3, the metallized film 6 before slitting includes a plurality of insulating edges 21 that are continuous and extend in the MD direction D1, and a metal layer 300 that is continuous and extends in the MD direction D1. In the metallized film 6 before slitting, the insulating edges 21 and the metal layers 300 are alternately arranged in the TD direction D2. Each metal layer 300 includes two active portions 32 and a heavy edge portion 31 located between the active portions 32. That is, in each metal layer 300, the first active portions 32, the heavy edge portions 31, and the second active portions 32 are arranged in this order in the TD direction D2. Thus, the first active portions 32 extend in the TD direction D2 from one end of the heavy edge portion 31 in the TD direction D2, and the second active portions 32 extend in the TD direction D2 from the other end of the heavy edge portion 31 in the TD direction D2. The first and second active portions 32 are continuous and extend in the MD direction D1. The heavy edge portion 31 also continues and extends in the MD direction D1. In the example shown in fig. 3, the insulating edges 21 are provided at both ends of the metallized film 6 in the TD direction D2 before slitting, but the heavy edge portions 31 may be provided at both ends or one of both ends.

In the dicing step of the pre-dicing metallized film 6, a dicing blade is placed at the center of the insulating margin 21 in the TD direction D2 (hereinafter, sometimes referred to as "TD direction center") and at the center of the heavy margin portion 31 in the TD direction, and the pre-dicing metallized film 6 is divided into a plurality of pieces in the TD direction D2, thereby obtaining metallized films 5 (see fig. 1 and 2). Specifically, before slitting, metallized film 6 formed in a roll shape is unwound, and cut by placing a cutting blade at the center in the TD direction of each insulating margin 21 and at the center in the TD direction of each heavy margin 31, and metallized film 5 is wound in a roll shape. Thereby, a plurality of metallized films 5 can be obtained. The width of the insulating edge 21 in the metallized film 5 is half the width of the insulating edge 21 in the metallized film 6 before slitting. The width of the heavy edge portion 31 in the metallized film 5 is also half the width of the heavy edge portion 31 in the metallized film 6 before slitting. Note that the metallized film 5 has a capacitor element width.

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 is preferably 1 to 200 nm.

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

The metal layer 30 is located in the transverse direction in the TD direction D2 of the insulating edge 21. The metal layer 30 extends from the other end 52 in the TD direction D2 to the insulating edge 21. Although not illustrated, the metal layer 30 is continuous and extends between both ends in the MD direction D1 in the metallized film 5. That is, the metal layer 30 is continuous from one end portion in the MD direction D1 in the metallized film 5 and extends 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 edge 21. For example, the width of the metal layer 30 is preferably 1.5 to 300 times the width of the insulating edge 21. Here, the width of the metal layer 30 refers to a value measured regardless of the edge pattern. The width of the metal layer 30 is measured in the TD direction D2 of the metallized film 5.

The metal layer 30 of the metallized film 5 includes a heavy edge portion 31. The heavy edge portion 31 is located at the end portion 52 of the metalized film 5 in the TD direction D2. The heavy edge portion 31 is continuous and extends in the MD direction D1. More specifically, the heavy edge portion 31 is continuous and extends between both ends in the MD direction D1 in the metallized film 5. That is, the heavy edge portion 31 is continuous from one end portion in the MD direction D1 in the metallized film 5 and extends to the other end portion in the MD direction D1 in the metallized film 5. The thickness of the heavy edge portion 31 is larger than that of the active portion 32. The heavy edge portion 31 may have, for example, an aluminum film provided on the biaxially stretched polypropylene film 10 and a zinc portion provided on the aluminum film. In such a heavy edge portion 31, the aluminum film may be located between the biaxially stretched polypropylene film 10 and the zinc portion.

The metal layer 30 of the metallized film 5 includes an active portion 32. The active portions 32 are continuous and extend in the MD direction D1. More specifically, the active portions 32 are continuous and extend between both ends of the metallized film 5 in the MD direction D1. That is, the active portion 32 is continuous 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 active portion 32 may have an aluminum film. The aluminum film of the active portion 32 is continuous with the aluminum film of the heavy edge portion 31. An edge pattern, for example, a T-edge pattern, or the like may be formed in the active portion 32. The film resistance of the heavy edge portion 31 is usually about 1 to 8 Ω/□, preferably about 1 to 5 Ω/□.

The metallized film 5 may be laminated by a conventionally known method, orThe film capacitor is formed by winding. For example, 2 sheets of 1 pair of metallized films 5 are stacked and wound so that the metal layers 30 in the metallized film 5 and the biaxially stretched polypropylene film 10 are alternately stacked and the insulating edge 21 is formed on the opposite side. In this case, 2 sheets of the metallized films 5 in 1 pair are preferably stacked with a1 to 2mm shift in the TD direction D2. The winder used is not particularly limited, and for example, an automatic winder 3KAW-N2 type manufactured by Duty cane K.K., can be used. In the case of manufacturing a flat capacitor, the resultant wound product is usually pressurized after winding. The winding of the film capacitor and the formation of the capacitor element are promoted by pressing. From the viewpoint of controlling and stabilizing the interlayer gap, the optimum value of the pressure to be applied varies depending on the thickness of the biaxially stretched polypropylene film 10, and is, for example, 2 to 20kg/cm². After the pressurization, both end surfaces of the wound body were subjected to thermal spraying to form thermal spraying electrodes, thereby producing a film capacitor.

As described above, the film capacitor may have a structure in which a plurality of metalized films 5 are stacked, or may have a rolled metalized 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 present invention can be suitably used for railway vehicles, wind power generation, solar power generation, general household electrical appliances, and the like.

In fig. 1 to 3, 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 it goes without saying that 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 formed by providing a metal layer on both surfaces of a biaxially stretched polypropylene film.

In the present embodiment, the metallized film having the heavy edge portion is described, but it goes without saying that the metallized film may not have the heavy edge portion.

< embodiment of the invention of the 2 nd >

The following describes an embodiment of the present invention according to claim 2. In the biaxially stretched polypropylene film according to embodiment 2 of the present invention, the difference between the heat shrinkage rate at 140 ℃ in the first direction and the heat shrinkage rate at 130 ℃ in the first direction is not necessarily 0% or more and less than 2.0%, and the difference between the heat shrinkage rate at 140 ℃ in the second direction perpendicular to the first direction and the heat shrinkage rate at 130 ℃ in the second direction is not necessarily 0% or more and less than 2.3%.

The polypropylene film according to embodiment 2 of the present invention (hereinafter also referred to as "embodiment 2") has a thickness of 1.0 to 3.0 μm and a width in the second direction of 1200mm or less, and the difference between the maximum value and the minimum value of the slow axis angle obtained by the following methods (1) to (3) is less than 6 °.

(3) the difference between the maximum and minimum angles measured in the above (2) was obtained for 9 samples for measurement. The biaxially stretched polypropylene film according to embodiment 2 of the present invention is excellent in the accuracy of thickness variation. When a metallized film is produced from the biaxially stretched polypropylene film, the shrinkage in the in-plane direction is less uneven, and wrinkles and sagging are suppressed.

In the above feature, the biaxially stretched polypropylene film preferably has a difference between a heat shrinkage ratio in a first direction at 140 ℃ and a heat shrinkage ratio in the first direction at 130 ℃ of 0% or more and less than 2.0%, and a difference between a heat shrinkage ratio in a second direction perpendicular to the first direction at 140 ℃ and a heat shrinkage ratio in the second direction at 130 ℃ of 0% or more and less than 2.3%. Other preferable heat shrinkage ratios of the biaxially stretched polypropylene film of the present embodiment, and the ratio between the difference in heat shrinkage ratios and the heat shrinkage ratio are the same as those described in the section "embodiment 1 of the present invention". Therefore, the description is omitted here. In embodiment 2 of the present invention, the term "embodiment 1 of the present invention" may be cited here for reasons of correction, technical explanation, and the like.

The preferred embodiment of the biaxially stretched polypropylene film of the present embodiment is the same as that of "embodiment 1 of the present invention". For example, the descriptions of (1) the film properties (for example, thickness, total ash content, etc.), (2) the types, properties, ratios, combinations, etc. of the polypropylene resins contained, (3) the types, properties, ratios, combinations, etc. of the polypropylene resins other than the polypropylene resins contained, (4) the method for producing the biaxially stretched polypropylene film of the present embodiment, and the like are the same as those in the section of "embodiment of the present invention of the 1 st embodiment". The physical properties, structure, and manufacturing method of the metallized film (5) and the physical properties, structure, and manufacturing method of the film capacitor (6) in the present embodiment are the same as those in the item of "embodiment 1 of the present invention". Therefore, the description is omitted here. In embodiment 2 of the present invention, the term "embodiment 1 of the present invention" may be cited here for reasons of correction, technical explanation, and the like.

Examples

Next, the present invention (the present invention of the 1 st and the present invention of the 2 nd) will be specifically described by examples, but these examples are for explaining the present invention and do not limit the present invention at all. In the examples, "part(s)" and "%" represent "part(s) by mass" and "% by mass", respectively, unless otherwise specified.

< determination of weight average molecular weight (Mw), molecular weight distribution (Mw/Mn), and differential distribution value of Polypropylene resin >

The measurement was performed by GPC (gel permeation chromatography) under the following conditions, and the calculation was performed.

A measuring device: tosoh corporation, differential Refractometer (RI) built-in high temperature GPC HLC-8121GPC/HT type

Column: tosoh corporation, 3 TSKgel GMHhr-H (20) HT

Column temperature: 145 ℃.

Eluent: trichlorobenzene

Flow rate: 1.0 ml/min

A calibration curve was prepared using a standard polystyrene manufactured by Tosoh corporation, and the value of the measured molecular weight was converted into a value of polystyrene to obtain a weight average molecular weight (Mw) and a number average molecular weight (Mn). The molecular weight distribution (Mw/Mn) was obtained from the values of Mw and Mn.

The differential distribution value is obtained in the following manner. First, a time curve (dissolution curve) of the intensity distribution detected by an RI detector, which is a distribution curve of the molecular weight M (Log (M)) relative to the standard polystyrene using the standard curve prepared using the standard polystyrene, is converted into a distribution curve. Next, an integral distribution curve with respect to log (m) is obtained when the total area of the distribution curve is 100%, and then the integral distribution curve is differentiated by log (m), so that a differential distribution curve with respect to log (m) can be obtained. From the differential distribution curve, differential distribution values at log (m) of 4.5 and log (m) of 6.0 are read. A series of operations up to obtaining the differential distribution curve is performed by using analysis software built in the GPC measurement apparatus used.

< meso pentad fraction >

The polypropylene 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: single pulse proton broadband decoupling

Pulse amplitude: 9.1 musec (45 degree pulse)

Pulse interval: 5.5sec

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.hayashiet al, Polymer, volume 29, page 138 (1988)" and the like is referred to.

< determination of Melt Flow Rate (MFR) >)

For each resin, the Melt Flow Rate (MFR) in the form of raw material resin pellets was measured using 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.

< determination of heptane insoluble fraction (HI) >

About 3g of a sample for measurement was prepared by press molding each resin at 10 mm. times.35 mm. times.0.3 mm. Followed by Soxhlet extraction with heptane, about 150mL, for 8 hours. The heptane-insoluble fraction was calculated from the mass of the sample before and after the extraction.

< example 1 >

[ production of a sheet for casting blank ]

PP resin A1[ Mw: 32 ten thousand, Mw/Mn: 9.3, differential distribution value difference D_M11.2 meso pentad fraction [ mmmm]95%, 97.3%, MFR 4.9g/10 min, Prime Polymer co., ltd]And PP resin B1[ Mw 35 ten thousand, Mw/Mn 7.7, differential distribution value difference D_M7.2 meso pentad fraction [ mmmm]96.5%, 98.6%, 3.8g/10 min MFR, and made into Korean oil]Supplied to an extruder at a ratio of 65:35, melted at a resin temperature of 250 ℃, extruded through a T die, and wound while maintaining a surface temperature of the extruded material at 250 ℃And (4) rolling and solidifying the metal at 95 ℃ to prepare a casting blank sheet.

[ production of biaxially stretched Polypropylene film ]

The obtained cast green sheet was stretched 4.5 times in the flow direction by passing between rolls provided with a speed difference while maintaining the temperature at 140 ℃ and immediately cooled to room temperature, and then the stretched film was guided to a tenter and stretched 10 times in the width direction at 160 ℃, followed by relaxation and heat setting, and a biaxially stretched polypropylene film having a thickness of 2.3 μm was wound around a drawing roll at the outlet of the tenter. The heat-setting temperature at the heat-setting was set to 164 ℃. The speed of the take-up roll was 1.09 times the film-forming linear speed. That is, the ratio of the take-up speed to the film forming linear speed (take-up speed/film forming linear speed) was set to 1.09.

[ production of metallized film before slitting ]

The biaxially stretched polypropylene film was drawn out from the roll, and an oil mask for insulating edge 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 insulating edge oil mask was formed. Then, the biaxially stretched polypropylene film on which the oil mask for pattern was formed was subjected to metal vapor deposition. Thereby obtaining a metallized film before slitting.

In order to form an oil mask for an insulating edge, a nozzle slit was used to eject Fomblin oil vapor on one of both surfaces of a biaxially stretched polypropylene film. The insulating edge oil mask was formed in a stripe shape (stripe shape) over the entire surface of the biaxially stretched polypropylene film (see fig. 4).

The pattern oil mask is formed by using a plate roll. The pattern oil mask 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 stripe-shaped insulating edge oil mask is not formed.

In 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 insulating edge oil mask and the pattern oil mask were formed (hereinafter referred to as "oil mask formation surface"). Subsequently, zinc is vapor-deposited to form a heavy edge portion. The zinc is vapor-deposited on the region of the oil mask formation surface where the heavy edge portion is to be formed. Metal deposition, i.e., aluminum deposition and zinc deposition, is performed while cooling a biaxially stretched polypropylene film with a cooling roll maintained at-30 ℃ to-20 ℃. That is, when the biaxially stretched polypropylene film is passed through a space between a cooling roll and an evaporation source for metal deposition, aluminum is deposited, followed by zinc deposition.

The metallized film before slitting thus obtained will be described with reference to fig. 4. As shown in fig. 4, the pre-slit metallized film (pre-slit metallized film 6) includes three insulating edges 21 that are continuous and extend in the MD direction D1, and two metal layers 300 that are continuous and extend in the MD direction D1. Each insulating margin 21 is continuous from one end portion in the MD direction D1 in the pre-slit metallized film 6 and extends to the other end portion in the MD direction D1 in the pre-slit metallized film 6. Each metal layer 300 is also continuous from one end portion in the MD direction D1 in the pre-slit metallized film 6 and extends to the other end portion in the MD direction D1 in the pre-slit metallized film 6. In the metallized film 6 before slitting, the insulating edges 21 and the metal layers 300 are alternately arranged in the TD direction D2. Each metal layer 300 includes two active portions 32 and a heavy edge portion 31 located between the active portions 32. That is, in each metal layer 300, the first active portions 32, the heavy edge portions 31, and the second active portions 32 are arranged in this order in the TD direction D2. The first and second active portions 32 are continuous and extend in the MD direction D1. The heavy edge portion 31 also continues and extends in the MD direction D1.

When evaluating the edge accuracy of metallized film 6 before slitting, among three insulating edges 21, insulating edge 21 located at the center in TD direction D2 was set to a cutting blade, and the insulating edge width was measured.

< example 2 >

A biaxially stretched polypropylene film and a pre-slit metallized film produced therefrom were obtained in the same manner as in example 1 except that the thickness of the biaxially stretched polypropylene film was 2.4. mu.m.

< example 3 >

A biaxially stretched polypropylene film and a pre-slit metallized film produced therefrom were obtained in the same manner as in example 1 except that the thickness of the biaxially stretched polypropylene film was 2.5. mu.m.

< example 4 >

A biaxially stretched polypropylene film and a pre-slit metallized film produced therefrom were obtained in the same manner as in example 1 except that the thickness of the biaxially stretched polypropylene film was 2.8. mu.m.

< example 5 >

A biaxially stretched polypropylene film and a pre-slit metallized film produced therefrom were obtained in the same manner as in example 1, except that the heat-setting temperature was 162 ℃ and the speed of the take-up roll was 1.05 times the film-forming line speed.

< example 6 >

A biaxially stretched polypropylene film and a pre-slit metallized film produced therefrom were obtained in the same manner as in example 4, except that the heat-setting temperature was set to 166 ℃ and the speed of the take-up roll was set to 1.15 times the film-forming line speed.

< example 7 >

A biaxially stretched polypropylene film and a metallized film before slitting produced therefrom were obtained in the same manner as in example 1 except that the heat-setting temperature was 161 ℃ and the speed of the take-up roll was 1.02 times the film forming line speed.

< example 8 >

Instead of the polypropylene resin B1, a polypropylene resin B2(Mw 38 ten thousand, Mw/Mn 8.3, D) was used_M0.6, meso pentad fraction [ mmmm]A green casting sheet was produced in the same manner as in example 1 except that the composition was changed to 96.7%, HI was 98.8%, and MFR was 2.3g/10 min. A biaxially stretched polypropylene film and a metallized film before slitting made of the biaxially stretched polypropylene film were obtained in the same manner as in example 1 except that the above cast green sheet was used.

< example 9 >

A biaxially stretched polypropylene film and a pre-slit metallized film produced therefrom were obtained in the same manner as in example 4, except that the heat-setting temperature was set to 166 ℃ and the speed of the take-up roll was set to 1.12 times the film-forming line speed.

< comparative example 1 >

A biaxially stretched polypropylene film and a metallized film before slitting produced therefrom were obtained in the same manner as in example 3 except that the heat-setting temperature was 158 ℃ and the speed of the take-up roll was 1.10 times the film forming line speed.

< comparative example 2 >

A biaxially stretched polypropylene film and a metallized film before slitting produced therefrom were obtained in the same manner as in example 1 except that the heat-setting temperature was 160 ℃ and the speed of the take-up roll was 1.21 times the film forming line speed.

< comparative example 3 >

A biaxially stretched polypropylene film and a metallized film before slitting produced therefrom were obtained in the same manner as in example 4 except that the heat-setting temperature was 160 ℃ and the speed of the take-up roll was 1.21 times the film forming line speed.

< comparative example 4 >

A biaxially stretched polypropylene film and a metallized film before slitting produced therefrom were obtained in the same manner as in example 8, except that the heat-setting temperature was 160 ℃ and the speed of the take-up roll was 1.21 times the film forming line speed.

< comparative example 5 >

A biaxially stretched polypropylene film and a metallized film before slitting produced therefrom were obtained in the same manner as in example 1 except that the heat-setting temperature was set to 170 ℃ and the speed of the take-up roll was set to 1.22 times the film forming line speed.

< comparative example 6 >

Instead of the polypropylene resin a1, a polypropylene resin a2(Mw 27 ten thousand, Mw/Mn 5.7, D) was used_M8.8, HI 97.8%, MFR 5.6g/10 min), instead of the polypropylene resin B1, a polypropylene resin B2(Mw 38 ten thousand, Mw/Mn 8.3, D) was used_M0.6, meso pentad fraction [ mmmm]A green casting sheet was produced in the same manner as in example 1 except that the composition was changed to 96.7%, HI was 98.8%, and MFR was 2.3g/10 min. A biaxially stretched polypropylene film and a metallized film before slitting made of the biaxially stretched polypropylene film were obtained in the same manner as in example 1 except that the above cast green sheet was used.

< measurement of thickness >

The thickness of the biaxially stretched polypropylene film was measured in accordance with JIS-C2330 except that the thickness was measured at 100. + -. 10kPa using a paper thickness measuring instrument MEI-11 manufactured by CITIZEN SEIMITSU.

< continuous productivity >

The production of a biaxially stretched polypropylene film was started using a biaxial stretching apparatus set to a predetermined thickness, and the time during which continuous film formation was possible until the biaxially stretched polypropylene film broke (hereinafter referred to as "continuous film formation time") was measured from the time when the thickness of the obtained biaxially stretched polypropylene film reached the target thickness ± 2%. When the thickness reached the target thickness. + -.2%, a sample was cut from the center in the width direction of the biaxially stretched polypropylene film, and the thickness of the sample was measured and confirmed by using a micrometer (JIS-B7502) according to JIS-C2330. Based on the obtained continuous film forming time, the continuous productivity was evaluated according to the following evaluation criteria.

A: even if the time exceeds 8 hours, the film can be formed without tensile failure.

B: the film can be formed without tensile failure in more than 1 hour and less than 8 hours.

C: the film was not broken within 1 hour, and film formation could not be carried out for more than 1 hour.

< precision of unequal thickness >

First, a sample was cut out from a biaxially stretched polypropylene film, and the thickness of the sample was measured by a micrometer (JIS-B7502) according to JIS-C2330 to determine the average and standard deviation of 30 points in the width direction. Then, the variation coefficient is calculated based on the formula A. Based on the obtained variation coefficient, the thickness unevenness accuracy was evaluated according to the following evaluation criteria.

Coefficient of variation is standard deviation/average x 100 formula a

(evaluation criteria for thickness variation accuracy)

A: less than 0.9 percent

B: more than 0.9 percent and less than 1.5 percent

C: 1.5% or more

Thermal shrinkage rate of < 130 ℃ >

First, in order to measure the heat shrinkage in the MD direction, a biaxially stretched polypropylene film was cut into a 20mm × 130 mm-sized rectangle, and a 100mm mark was marked with a ruler to obtain a sample. For this sample, the 130mm side extends in the MD direction. The upper end of the sample was held by a clip, suspended in a drier, and heat-treated at 130 ℃ for 15 minutes. The sample was taken out from the dryer, the interval between the marked lines was measured with a ruler, and the heat shrinkage was calculated using the following formula.

Heat shrinkage factor (reticle spacing before heat treatment-reticle spacing after heat treatment)/reticle spacing before heat treatment × 100

A sample for measuring the thermal shrinkage in the TD direction was also prepared, and the thermal shrinkage was calculated by performing the above-described heat treatment. This sample was the same as the sample for MD measurement except that the 130mm side extended in the TD direction.

Thermal shrinkage rate of < 140 >

The heat treatment temperature was 140 ℃ instead of 130 ℃, except that the heat shrinkage was measured by the same method as that for 130 ℃.

Thermal shrinkage rate of < 120 ℃ >

The heat treatment temperature was 120 ℃ instead of 130 ℃, except that the heat shrinkage was measured by the same method as that of 130 ℃.

< edge precision >

The pre-slit metallized film was unwound from the pre-slit metallized film roll, and an insulating margin having a width of 2.0mm was cut at the center by a cutting blade, and a metallized film having an insulating margin having a width of 1.0mm at either of the left and right ends and having a capacitor element width of 60mm was wound in a roll shape. After cutting 3000m, the width of the insulating edge was measured, and the width of the deviation from the width of 1.0mm was determined by difference calculation. Based on the deviation width, the edge accuracy was evaluated according to the following evaluation criteria.

(evaluation criterion of edge accuracy)

AA: the offset width is less than 0.1mm

A: the offset width exceeds 0.1mm and is less than 0.2mm

B: the offset width exceeds 0.2mm and is 0.3mm or less

C: the offset width exceeds 0.3mm

< difference between maximum and minimum values of slow axis angle >

The biaxially stretched polypropylene films produced in examples and comparative examples were divided (slit) into equal portions so as to form rolls having a width of 1200 mm.

Of the obtained rolls having a width of 1200mm, the widthwise outermost end of the roll before slitting was defined as roll 1.

Of the obtained rolls having a width of 1200mm, a roll including the central portion (any roll adjacent to the central portion when the central portion and slitting are repeated) was defined as the roll 2.

For the roll 1 and the roll 2, the difference between the maximum value and the minimum value of the slow axis angle is obtained by the following method of obtaining the difference between the maximum value and the minimum value of the slow axis angle. The measurement apparatus and the measurement conditions are as follows.

< measuring apparatus, measuring conditions >

Light source: laser luminous diode (LED)

Band-pass filter: 550nm (measuring wavelength)

Measurement interval: 0.1sec

Cumulative number of times: 10time

Measuring the number of points: 15point

Gain: 10dB

(1) When the total length in the width direction was defined as 100%, 50mm × 50mm samples for measurement were cut out with the center at positions spaced by 10% from both ends. That is, a total of 9 measurement samples of 50mm × 50mm centered at one end (1200/9) mm, ([1200/9] × 2) mm, ([1200/9] × 3) mm, ([1200/9] × 4) mm, ([1200/9] × 5) mm, ([1200/9] × 6) mm, ([1200/9] × 7) mm, ([1200/9] × 8) mm, and (1200/9 ] × 9) mm of the self-wound coil were cut.

(2) Next, the second direction of the measurement sample was set to 0 °, and the acute angle between the second direction and the slow axis of each measurement sample (total of 9 measurement samples) was measured.

(3) Finally, the difference between the maximum and minimum angles measured in the above (2) was determined among 9 measurement samples. The results are shown in Table 5. Table 5 also shows the maximum and minimum values.

In the present example, when the biaxially stretched polypropylene film had a width of 1200mm, the difference between the maximum value and the minimum value of the slow axis angle was less than 6 °. It is understood that the difference is smaller as the width (width in the TD direction) is narrower. Therefore, although the present example shows the case where the biaxially stretched polypropylene film has a width of 1200mm, it is obvious that the difference is not less than 6 ° even in the case where the width is 1200mm or less (for example, the width is 600 mm).

< measurement of Ash >

The biaxially stretched polypropylene films of examples and comparative examples were measured as follows.

About 200g of the sample was weighed, transferred to a platinum dish, and ashed at 800 ℃ for 40 minutes. The ash ratio (ppm) was determined from the obtained ash residue.

As a result, the ash content of the biaxially stretched polypropylene films of examples and comparative examples was 20 ppm.

[ production of capacitor ]

The pre-slit metallized film produced in the examples was slit to a width of 60 mm. Then, 2 sheets of metallized films were laminated. The laminated metallized film was wound up at 1137 revolutions using an automatic winder 3KAW-N2 made by Du Teng, K.K., at a winding tension of 250g, a contact pressure of 880g, and a winding speed of 4 m/s. The load applied to the edge of the wound element was 5.9kg/cm²The heat treatment was carried out at 120 ℃ for 15 hours while pressing the plate. And then the end face of the element is sprayed with zinc metal. As the spraying conditions, spraying was carried out at a feed rate of 15mm/s, a spraying voltage of 22V, a spraying pressure of 0.3MPa and a thickness of 0.7 mm. Thus, a flat capacitor is obtained. The lead wire is soldered to the end face of the flat capacitor, and then the flat capacitor is sealed with an epoxy resin. The epoxy resin is cured inHeating at 90 ℃ for 2.5 hours, and further heating at 120 ℃ for 2.5 hours. The electrostatic capacity of the completed film capacitor was 75 μ F.

[ Table 1]

MD Direction

[ Table 2]

In the TD direction

[ Table 3]

[ Table 4]

[ Table 5]

Description of the reference numerals

5 metallized film

6 metallized film before slitting

10 biaxially stretched polypropylene film

21 insulating edge

30 metal layer

31 heavy edge part

32 active part

51 one end of the metallized film

52 another end of the metallized film

300 metal layer

Claims

1. A biaxially stretched polypropylene film having a thickness of 1.0 to 3.0. mu.m,

the difference between the thermal shrinkage rate at 140 ℃ in the first direction and the thermal shrinkage rate at 130 ℃ in the first direction is 0% or more and less than 2.0%,

the difference between the thermal shrinkage rate at 140 ℃ in a second direction perpendicular to the first direction and the thermal shrinkage rate at 130 ℃ in the second direction is 0% or more and less than 2.3%.

2. The biaxially stretched polypropylene film of claim 1, wherein the second direction has a heat shrinkage S of 140 ℃_TD140A heat shrinkage ratio S of 140 ℃ to the first direction_MD140Is a ratio of_TD140/S_MD140Is 0.200 to 0.325 inclusive.

3. The biaxially stretched polypropylene film according to claim 1 or 2, wherein the width in the second direction is 1200mm or less,

the difference between the maximum value and the minimum value of the slow axis angle obtained by the following methods (1) to (3) is less than 6 DEG and < the method for determining the difference between the maximum value and the minimum value of the slow axis angle >

(3) the difference between the maximum and minimum angles measured in the above (2) was determined among 9 samples for measurement.

4. The biaxially stretched polypropylene film according to any one of claims 1 to 3, which is used for capacitors.

5. A metallized film comprising the biaxially stretched polypropylene film according to any one of claims 1 to 4, and

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

6. A film capacitor having a structure in which the metallized film according to claim 5 is wound or a plurality of the metallized films according to claim 5 are stacked.

7. A film roll obtained by winding the biaxially stretched polypropylene film according to any one of claims 1 to 4 in a roll form.