Biaxially stretched polypropylene film, metallized film and capacitor

Abstract

Provided are: a biaxially stretched polypropylene film exhibiting high dielectric breakdown strength even at high temperatures; a metallized film using the biaxially stretched polypropylene film; and a capacitor. Specifically provided is a biaxially stretched polypropylene film which is characterized by containing a linear polypropylene resin A and a branched polypropylene resin B. (1) The mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is 99.0: 1.0-85.0: 15.0, and the mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is 0.5: 1.0-85.0: 15.0. (2) the molecular weight distribution (Mw / Mn) of the weight-average molecular weight Mw and the number-average molecular weight Mn of the linear polypropylene resin A is 7.0-9.3 inclusive, and (3) the storage modulus (E ') of the biaxially stretched polypropylene film at a vibration frequency of 1 Hz and a temperature of 160 DEG C is 22.50-31.00 MPa inclusive.

Description

Technical Field

[0001] The invention relates to a biaxially stretched polypropylene film, a metallized film and a capacitor. Background Art

[0002] Conventionally, biaxially stretched polypropylene films have been used in electrical equipment and the like, and have been used as dielectric films for capacitors because of their excellent electrical properties such as withstand voltage.

[0003] A capacitor manufactured using the above-described capacitor dielectric film can be used, for example, in an inverter constituting a power control unit of a hybrid vehicle, an electric vehicle, or the like.

[0004] The biaxially stretched polypropylene film used for manufacturing such a capacitor must be thinned due to the recent miniaturization and high capacitance of capacitors, and is required to show high dielectric breakdown strength even with a thin thickness.

[0005] For example, Patent Document 1 discloses a polypropylene film in which a polypropylene resin has a melting peak in a specific range as a polypropylene film used for capacitor applications.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2007-084813 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] However, the polypropylene film described in Patent Document 1 has a problem in that the heat resistance is not sufficient.

[0011] The capacitors described above are used in environments where the temperature in the engine room rises or the capacitors themselves generate heat, and therefore require high heat resistance at high temperatures of about 120°C (e.g., 100°C to 125°C). In other words, the capacitors are required to not cause short circuits even at high temperatures and to maintain insulation and electrostatic capacitance.

[0012] The biaxially stretched polypropylene film used for producing such a capacitor is required to show high dielectric breakdown strength even at high temperatures.

[0013] Therefore, there is a demand for the development of a biaxially stretched polypropylene film that exhibits high dielectric breakdown strength even at high temperatures and a metallized film using the biaxially stretched polypropylene film, and for the development of a capacitor that can maintain insulation and electrostatic capacitance even at high temperatures.

[0014] An object of the present invention is to provide a biaxially stretched polypropylene film showing high dielectric breakdown strength even at high temperatures, and a metallized film and a capacitor using the biaxially stretched polypropylene film.

[0015] Solutions for solving problems

[0016] The present inventors have conducted intensive studies to solve the above problems and have found that the above objects can be achieved by using a biaxially stretched polypropylene film, which contains a linear polypropylene resin A and a branched polypropylene resin B, wherein the mass ratio of the linear polypropylene resin A to the branched polypropylene resin B and the molecular weight distribution (Mw / Mn) of the linear polypropylene resin A are within specific ranges, and the biaxially stretched polypropylene film has a specific storage modulus. The present invention has been completed.

[0017] That is, the present invention relates to the following biaxially stretched polypropylene film, metallized film and capacitor.

[0018] 1. A biaxially stretched polypropylene film, characterized in that it contains a linear polypropylene resin A and a branched polypropylene resin B,

[0019] (1) the mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is the linear polypropylene resin A: the branched polypropylene resin B = 99.0:1.0 to 85.0:15.0,

[0020] (2) the molecular weight distribution (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn of the linear polypropylene resin A is 7.0 or more and 9.3 or less,

[0021] (3) The storage modulus (E') of the biaxially stretched polypropylene film at a vibration frequency of 1 Hz and a temperature of 160° C. is 22.50 MPa or more and 31.00 MPa or less.

[0022] 2. The biaxially stretched polypropylene film according to item 1 above, wherein the mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is the linear polypropylene resin A:the branched polypropylene resin B=96.9:3.1 to 85.0:15.0.

[0023] 3. The biaxially stretched polypropylene film according to the above item 1 or 2, wherein the branched polypropylene resin B has a melt flow rate at 230° C. of 2.0 g / 10 min or more.

[0024] 4. The biaxially stretched polypropylene film according to any one of items 1 to 3 above, wherein the branched polypropylene resin B has a melt tension of 9 g / cm at 230°C.3 Above and 20g / cm 3 the following.

[0025] 5. The biaxially stretched polypropylene film according to any one of Items 1 to 4 above, wherein the storage modulus (E′) is 22.97 MPa to 27.53 MPa.

[0026] 6. The biaxially stretched polypropylene film according to any one of the above items 1 to 5, wherein the linear polypropylene resin A contains a linear polypropylene resin having a heptane-insoluble matter (HI) of 98.5% or more.

[0027] 7. The biaxially stretched polypropylene film according to any one of items 1 to 6 above, wherein the linear polypropylene resin A contains two types of linear polypropylene resin A1 and linear polypropylene resin A2, the meso pentad fraction of the linear polypropylene resin A1 is lower than 98.0%, and the meso pentad fraction of the linear polypropylene resin A2 is 98.0% or more.

[0028] 8. The biaxially stretched polypropylene film according to any one of items 1 to 7, wherein the biaxially stretched polypropylene film has a dielectric breakdown strength at a direct current voltage at 120° C. (DCES120° C.) of 448 V / μm or more.

[0029] 9. The biaxially stretched polypropylene film according to any one of items 1 to 8 above, wherein in differential scanning calorimetry, the biaxially stretched polypropylene film has a melting peak temperature of 166° C. to 188° C. when initially heated from 30° C. to 280° C. at 20° C. / min in a nitrogen atmosphere.

[0030] 10. The biaxially stretched polypropylene film according to any one of the above items 1 to 9, wherein in differential scanning calorimetry, the biaxially stretched polypropylene film has a crystallization peak temperature of 112°C or higher and lower than 120°C when the temperature is initially increased from 30°C to 280°C at a rate of 20°C / min, maintained at 280°C for 5 minutes, and then initially cooled to 30°C at a temperature reduction rate of 20°C / min in a nitrogen atmosphere.

[0031] 11. The biaxially stretched polypropylene film according to any one of items 1 to 10, wherein in the cast sheet before biaxial stretching, the ratio of β crystals to the total of α crystals and β crystals, i.e., β crystal fraction, is 10% or more.

[0032] 12. The biaxially stretched polypropylene film according to any one of items 1 to 11 above, which is used for capacitors.

[0033] 13. A metallized film comprising a metal layer on at least one surface of the biaxially stretched polypropylene film according to any one of items 1 to 12 above.

[0034] 14. The metallized film according to item 13 above, which has a thickness of 1.8 μm or more and 3.0 μm or less.

[0035] 15. A capacitor comprising the metallized film according to item 13 or 14 above.

[0036] Effects of the Invention

[0037] The biaxially stretched polypropylene film of the present invention can show high dielectric breakdown strength even at high temperatures. In addition, the present invention can provide a metallized film and a capacitor using the biaxially stretched polypropylene film. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a graph showing the relationship between the storage modulus (horizontal axis) and the dielectric breakdown strength at 120° C. (vertical axis) of each biaxially stretched polypropylene film produced in Examples and Comparative Examples.

[0039] Figure 2 The figure shows the relationship between the storage modulus (horizontal axis) and the improvement rate of the dielectric breakdown strength at 120° C. (vertical axis) of each biaxially stretched polypropylene film produced in the examples and comparative examples. It should be noted that Examples 1 to 7 show the improvement rate relative to Comparative Example 1, and Examples 8 to 9 show the improvement rate relative to Comparative Example 2. DETAILED DESCRIPTION

[0040] In this specification, the "to" of the numerical range means above and below. That is, the expression of α to β means above α and below β, or above β and below α, and as a range, α and β are included. In addition, when multiple lower limits and multiple upper limits are recorded respectively, any lower limit and upper limit can be selected and connected with "to".

[0041] In this specification, the expressions “comprise” and “include” include concepts such as “comprises”, “includes”, “consists essentially of” and “consists only of”.

[0042] In this specification, the expression "capacitor" includes concepts such as "capacitor", "capacitor element" and "film capacitor".

[0043] In this specification, the directions of the biaxially stretched polypropylene film are as follows. First, the machine direction of the film is the Machine Direction (hereinafter, also referred to as the "MD direction"). The MD direction is sometimes referred to as the length direction or the flow direction. Next, the transverse direction of the film is the Transverse Direction (hereinafter, also referred to as the "TD direction"). The TD direction is sometimes referred to as the width direction.

[0044] 1. Biaxially stretched polypropylene film

[0045] The biaxially stretched polypropylene film of the present invention is characterized by comprising a linear polypropylene resin A and a branched polypropylene resin B.

[0046] (1) the mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is the linear polypropylene resin A: the branched polypropylene resin B = 99.0:1.0 to 85.0:15.0,

[0047] (2) the molecular weight distribution (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn of the linear polypropylene resin A is 7.0 or more and 9.3 or less,

[0048] (3) The storage modulus (E') of the biaxially stretched polypropylene film at a vibration frequency of 1 Hz and a temperature of 160° C. is 22.50 MPa or more and 31.00 MPa or less.

[0049] The biaxially stretched polypropylene film of the present invention having the above-mentioned characteristics can show high dielectric breakdown strength even at high temperatures.

[0050] The effect of the present invention is not yet clear, but it is speculated that the biaxially stretched polypropylene film of the present invention contains a linear polypropylene resin A and a branched polypropylene resin B, and

[0051] (1) the mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is the linear polypropylene resin A: the branched polypropylene resin B = 99.0:1.0 to 85.0:15.0, and

[0052] (2) the molecular weight distribution (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn of the linear polypropylene resin A is 7.0 or more and 9.3 or less,

[0053] Thereby, the "entanglement effect (pseudo cross-linking effect)" and the "crystallization effect" of the molecular chains of the polypropylene constituting the biaxially stretched polypropylene film are promoted, which affects the action of the present invention.

[0054] For example, the molecular weight distribution (Mw / Mn) of the linear polypropylene resin A in the specific range of 7.0 or more and 9.3 or less contributes to promoting the "entanglement effect" of the molecular chains of polypropylene. In addition, by making the molecular weight distribution (Mw / Mn) of the linear polypropylene resin A in the specific range of 7.0 or more and 9.3 or less, it is easy to obtain the effect of high mechanical strength (tensile stress suitable for promoting oriented crystallization) by utilizing the effect of molecular fluidity.

[0055] In addition, the branched polypropylene resin B has the function of a crystal nucleating agent, and the inclusion of the branched polypropylene resin B in a specific blending amount also helps to promote the "entanglement effect" and "crystallization effect" of the molecular chain of polypropylene. On the other hand, if the branched polypropylene resin B is excessively blended, although crystallization and physical crosslinking are promoted, "crystallization" is hindered, so there is a tendency for the storage modulus to exceed the specified range (storage modulus (E') at a vibration frequency of 1 Hz and a temperature of 160°C is 22.50 MPa or more and 31.00 MPa or less), and it becomes difficult to obtain the effect of improving the dielectric breakdown strength at high temperature. Therefore, in order to make the storage modulus within the specified range, so as to obtain high dielectric breakdown strength at high temperature as a synergistic effect of the "entanglement effect" and "crystallization effect" of the molecular chain of polypropylene, the mass ratio of the above-mentioned linear polypropylene resin A and the above-mentioned branched polypropylene resin B must be the mass ratio of the above-mentioned linear polypropylene resin A: the above-mentioned branched polypropylene resin B = 99.0:1.0 to 85.0:15.0.

[0056] Furthermore, by containing the branched polypropylene resin B, a large amount of β crystals are formed in the cast sheet before biaxial stretching. By stretching the cast sheet containing β crystals, the β crystals are transformed into α crystals. Therefore, due to the difference in density between the β crystals and the α crystals, (roughly) arc-shaped concavities and convexities are formed in the polypropylene film obtained by stretching, and the surface can be appropriately roughened. From the above viewpoints, the biaxially stretched polypropylene film of the present invention is also suitable as a material for a dielectric film for a capacitor.

[0057] The storage modulus (E') of the biaxially stretched polypropylene film of the present invention at a vibration frequency of 1Hz and a temperature of 160°C is as long as it is 22.50MPa or more and 31.00MPa or less, wherein it is preferably 26.00MPa or more and 31.00MPa or less, and more preferably 26.00MPa or more and 29.00MPa or less. By being within the above range, it becomes easy to obtain a high dielectric breakdown strength at high temperature. For example, even at a high temperature of 120°C, a high dielectric breakdown strength of more than 440Vdc / μm (preferably more than 470Vdc / μm) can be shown. It should be noted that the determination methods of the storage modulus (E') and the dielectric breakdown strength are based on the methods described in the embodiments, respectively.

[0058] For such a biaxially stretched polypropylene film of the present invention, in differential scanning calorimetry (DSC), the melting peak temperature when the temperature is initially increased from 30°C to 280°C at 20°C / min in a nitrogen atmosphere is preferably 166°C or more and 188°C or less. In addition, for the biaxially stretched polypropylene film of the present invention, in differential scanning calorimetry, the crystallization peak temperature when the temperature is initially increased from 30°C to 280°C at 20°C / min in a nitrogen atmosphere, maintained at 280°C for 5 minutes, and then initially cooled to 30°C at a cooling rate of 20°C / min is preferably 112°C or more and less than 120°C (119.9°C or less). It should be noted that the method for measuring the melting peak temperature at the initial heating and the crystallization peak temperature at the initial cooling in DSC is based on the method described in the examples. Hereinafter, in the present specification, the above-mentioned initial heating and initial cooling are also collectively referred to as the first run.

[0059] Hereinafter, the biaxially stretched polypropylene film of the present invention will be described in detail.

[0060] The biaxially stretched polypropylene film of the present invention contains a linear polypropylene resin A and a branched polypropylene resin B.

[0061] (1) the mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is the linear polypropylene resin A: the branched polypropylene resin B = 99.0:1.0 to 85.0:15.0, and

[0062] (2) The molecular weight distribution (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn of the linear polypropylene resin A is 7.0 or more and 9.3 or less.

[0063] The thickness of the biaxially stretched polypropylene film of the present invention is preferably 6.0 μm or less, more preferably 5.5 μm or less, further preferably 3.5 μm or less, particularly preferably 3.0 μm or less, and most preferably 2.8 μm or less from the viewpoint of further improving the miniaturization and high capacity of the capacitor when used in the capacitor. In addition, from the viewpoint of manufacturing, the lower limit is preferably 0.8 μm or more, more preferably 1.0 μm or more, further preferably 1.8 μm or more, and particularly preferably 2.0 μm or more. The method for measuring the thickness of the biaxially stretched polypropylene film in this specification is based on the method described in the examples.

[0064] The density of the biaxially stretched polypropylene film is not particularly limited, but is preferably 919 kg / m 3 Above and 930kg / m 3 the following.

[0065] The biaxially stretched polypropylene film of the present invention comprises a linear polypropylene resin A and a branched polypropylene resin B. The linear polypropylene resin A has a molecular weight distribution (Mw / Mn) of 7.0 to 9.3, preferably 8.1 to 9.3.

[0066] Here, in the relationship between the linear polypropylene resin A and the branched polypropylene resin B, the linear polypropylene resin A having a larger content is referred to as "main component polypropylene resin" or "base resin". In addition, the branched polypropylene resin B having a relatively smaller content is referred to as "blended resin".

[0067] It should be noted that the linear polypropylene resin A may be a single resin or a mixed resin of two or more (particularly two). For example, the linear polypropylene resin A may be a single linear polypropylene resin A1 described later, or a mixed resin of the linear polypropylene resin A1 and the linear polypropylene resin A2 described later. In this case, the linear polypropylene resin A1 having a large content is referred to as a "base resin", and the linear polypropylene resin A2 having a relatively small content is referred to as a "blended resin".

[0068] (Linear polypropylene resin A1)

[0069] In the biaxially stretched polypropylene film of the present invention, the linear polypropylene resin A may be composed of one of the linear polypropylene resins A1 described in this item. The linear polypropylene resin A1 may be crystalline polypropylene such as isotactic polypropylene and syndiotactic polypropylene.

[0070] The weight average molecular weight Mw of the linear polypropylene resin A1 is preferably 250,000 to 360,000, more preferably 280,000 to 350,000, further preferably 300,000 to 350,000, and particularly preferably 300,000 to less than 350,000. When the weight average molecular weight Mw of the linear polypropylene resin A1 is within the above range, in the production process of the biaxially stretched polypropylene film, it is easier to control the thickness of the cast sheet before biaxial stretching, and thickness unevenness is less likely to occur.

[0071] It should be noted that the weight average molecular weight Mw of the linear polypropylene resin A1 is a characteristic of the linear polypropylene resin A1 as a raw material resin. In addition, the number average molecular weight Mn, Z average molecular weight Mz, molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn), melt flow rate at 230° C. (MFRA1), melt tension at 230° C., meso pentad fraction ([mmmm]), and heptane insoluble matter (HI) of the linear polypropylene resin A1 described later are also characteristics of the linear polypropylene resin A1 as a raw material resin.

[0072] The number average molecular weight Mn of the linear polypropylene resin A1 is preferably 30,000 to 54,000, more preferably 33,000 to 52,000, and further preferably 33,000 to 47,000. When the number average molecular weight Mn of the linear polypropylene resin A1 is within the above range, the heat resistance of the produced capacitor is further improved.

[0073] The Z average molecular weight Mz of the linear polypropylene resin A1 is preferably 1,000,000 to 2,000,000, more preferably 1,250,000 to 1,800,000. When the Z average molecular weight Mz of the linear polypropylene resin A1 is within the above range, the dielectric breakdown strength of the biaxially stretched polypropylene film at high temperatures is further improved.

[0074] The molecular weight distribution (Mw / Mn) of the linear polypropylene resin A1 is 7.0 or more and 9.3 or less. The lower limit can be set preferably to 7.2 or more, more preferably 7.3 or more, and further preferably 8.1 or more. In addition, the upper limit can be set preferably to 9.0 or less, and more preferably 8.2 or less. When Mw / Mn is within the above range, the stretchability of the polypropylene film is further improved, and a thinner biaxially stretched polypropylene film can be produced. In addition, it becomes easy to set the storage modulus of the biaxially stretched polypropylene film to a specified range.

[0075] The molecular weight distribution (Mz / Mn) of the linear polypropylene resin A1 is preferably 10 to 100, more preferably 15 to 70, and further preferably 15 to 60. When Mz / Mn is within the above range, the stretchability of the polypropylene film is further improved, and a thinner biaxially stretched polypropylene film can be produced.

[0076] The melt flow rate (MFRA1) of the linear polypropylene resin A1 at 230°C is preferably 3.0 g / 10 minutes or more, more preferably 3.5 g / 10 minutes or more. In addition, the melt flow rate (MFRA1) of the linear polypropylene resin A1 at 230°C is preferably 10.0 g / 10 minutes or less, more preferably 8.0 g / 10 minutes or less, further preferably 6.0 g / 10 minutes or less, and particularly preferably 5.0 g / 10 minutes or less. By setting the melt flow rate (MFRA1) of the linear polypropylene resin A1 at 230°C to the above range, the dielectric breakdown strength of the biaxially stretched polypropylene film at high temperature is further improved. It should be noted that the method for measuring the melt flow rate (MFR) of the resin at 230°C in this specification is based on the method described in the examples.

[0077] The melt tension of the linear polypropylene resin A1 at 230°C is preferably 1.0 g or less, and more preferably less than 1.0 g. When the melt tension of the linear polypropylene resin A1 at 230°C is within the above range, the flow characteristics in the molten state are excellent, and unstable flow such as melt fracture is not likely to occur. As a result, the film thickness uniformity is good, and therefore, there is an advantage that a thin-walled portion that easily causes dielectric breakdown is not likely to be formed. It should be noted that the method for measuring the melt tension of the resin at 230°C in this specification is based on the method described in the Examples.

[0078] The meso pentad fraction ([mmmm]) of the linear polypropylene resin A1 is preferably 99.8% or less, more preferably 99.5% or less, further preferably 99.0% or less, and most preferably less than 98.0%. In addition, the above-mentioned meso pentad fraction is preferably 94.0% or more, more preferably 94.5% or more, and further preferably 95.0% or more. If the meso pentad fraction is within the above range, the crystallinity of the polypropylene resin is improved by utilizing moderately high stereoregularity, and the voltage resistance of the biaxially stretched polypropylene film at high temperature is further improved. In addition, the speed of solidification (crystallization) during cast sheet molding becomes moderate, and moderate stretchability can be shown. It should be noted that the method for determining the meso pentad fraction ([mmmm]) of the resin in this specification is based on the method described in the examples.

[0079] The heptane insoluble matter (HI) of the linear polypropylene resin A1 is preferably 97.0% or more, more preferably 97.5% or more, further preferably 98.0% or more, and particularly preferably 98.5% or more. In addition, the heptane insoluble matter is preferably 99.5% or less, more preferably 99.0% or less. It should be noted that the more heptane insoluble matter there is, the higher the stereoregularity of the resin. If the heptane insoluble matter is within the above range, the crystallinity of the polypropylene resin in the polypropylene film is moderately improved by utilizing the moderately high stereoregularity, and the dielectric breakdown strength at high temperature is improved. Furthermore, in the manufacturing process of the polypropylene film, the rate of solidification (crystallization) during the casting film molding before biaxial stretching becomes moderate, and has moderate stretchability. It should be noted that the method for determining the heptane insoluble matter (HI) of the resin in this specification is based on the method described in the examples.

[0080] Typical commercial products of the linear polypropylene resin A1 include, for example, HC300BF manufactured by Borealis and HPT-1 manufactured by Hankook Petrochemical Corporation.

[0081] (Linear polypropylene resin A2)

[0082] In the biaxially stretched polypropylene film of the present invention, as another embodiment, the linear polypropylene resin A may be composed of a mixed resin comprising the linear polypropylene resin A1 as a base resin and the linear polypropylene resin A2 as a blending resin. The linear polypropylene resin A2 may be a crystalline polypropylene such as isotactic polypropylene and syndiotactic polypropylene, similarly to the linear polypropylene resin A1.

[0083] In the linear polypropylene resin A, the mixing ratio of the linear polypropylene resin A1 (base resin) and the linear polypropylene resin A2 (blended resin) is not limited as long as the content of the blended resin is small. When the linear polypropylene resin A is 100 mass%, the content of the linear polypropylene resin A2 is preferably less than 50 mass%, more preferably 49 mass% or less, and further preferably 40 mass% or less. In addition, when the linear polypropylene resin A is 100 mass%, the content of the linear polypropylene resin A2 is preferably 10 mass% or more, more preferably 15 mass% or more, further preferably 25 mass% or more, and particularly preferably 30 mass% or more.

[0084] The weight average molecular weight Mw of the linear polypropylene resin A2 is preferably 300,000 or more, more preferably 350,000 or more, further preferably 360,000 or more, and particularly preferably more than 360,000. In addition, the weight average molecular weight Mw of the linear polypropylene resin A2 is preferably 550,000 or less, more preferably 450,000 or less, and further preferably 420,000 or less. When the weight average molecular weight Mw of the linear polypropylene resin A2 is within the above range, in the production process of the biaxially stretched polypropylene film, it is easier to control the thickness of the cast sheet before biaxial stretching, and it is less likely to cause uneven thickness.

[0085] It should be noted that the weight average molecular weight Mw of the linear polypropylene resin A2 is a characteristic of the linear polypropylene resin A2 as a raw material resin. In addition, the number average molecular weight Mn, Z average molecular weight Mz, molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn), melt flow rate at 230° C. (MFRA2), melt tension at 230° C., MFRA1-MFRA2, meso pentad fraction ([mmmm]) and heptane insoluble matter (HI) of the linear polypropylene resin A2 described later are also characteristics of the linear polypropylene resin A2 as a raw material resin.

[0086] The number average molecular weight Mn of the linear polypropylene resin A2 is preferably 35,000 to 54,000, more preferably 37,000 to 50,000, and further preferably 38,000 to 48,000. When the number average molecular weight Mn of the polypropylene resin A is within the above range, the heat resistance of the manufactured capacitor is further improved.

[0087] The Z average molecular weight Mz of the linear polypropylene resin A2 is preferably greater than 1.35 million and less than 2 million, more preferably greater than 1.4 million and less than 1.9 million. When the Z average molecular weight Mz of the linear polypropylene resin A2 is within the above range, the dielectric breakdown strength of the biaxially stretched polypropylene film at high temperatures is further improved.

[0088] The molecular weight distribution (Mw / Mn) of the linear polypropylene resin A2 is 7.0 or more and 9.3 or less. Among them, the lower limit can be set preferably to 8.1 or more, more preferably 8.2 or more, and further preferably 8.3 or more. In addition, the upper limit can be set preferably to 9.2 or less, and more preferably 9.1 or less. When Mw / Mn is in the above range, the stretchability of the polypropylene film is further improved, and a thinner biaxially stretched polypropylene film can be manufactured. In addition, it becomes easy to set the storage modulus of the biaxially stretched polypropylene film to a specified range.

[0089] The molecular weight distribution (Mz / Mn) of the linear polypropylene resin A2 is preferably 30 to 40, more preferably 33 to 37. When Mz / Mn is within the above range, the stretchability of the polypropylene film is further improved, and a thinner biaxially stretched polypropylene film can be produced.

[0090] The melt flow rate (MFRA2) of the linear polypropylene resin A2 at 230°C is preferably 4.0 g / 10 min or less, more preferably 3.5 g / 10 min or less, further preferably 3.2 g / 10 min or less, and particularly preferably less than 3.0 g / 10 min. The melt flow rate (MFRA2) of the linear polypropylene resin A2 at 230°C is preferably 0.1 g / 10 min or more, more preferably 0.5 g / 10 min or more, and further preferably 1.5 g / 10 min or more.

[0091] It should be noted that the difference MFRA1-MFRA2 between the MFR (MFRA1) of the linear polypropylene resin A1 as the base resin and the MFR (MFRA2) of the linear polypropylene resin A2 as the blended resin is preferably 0.8 g / 10 minutes or more. That is, MFRA1 is preferably greater than MFRA2. The above MFRA1-MFRA2 is preferably 1.0 g / 10 minutes or more, more preferably 1.5 g / 10 minutes or more, and further preferably 1.7 g / 10 minutes or more. When the above MFRA1-MFRA2 is less than 0.5 g / 10 minutes (the lower than 0.5 g / 10 minutes also includes negative values), in the manufacturing process of the polypropylene film, the sea-island phase separation structure at the time of casting before biaxial stretching cannot be formed, or even if the island size is formed, it is very small, so there is a concern that it will become difficult to finally obtain a polypropylene film with excellent dielectric breakdown strength at high temperatures. In particular, even if the difference between MFRA1 and MFRA2 is large, when MFRA2 is large (when the above-mentioned MFRA1-MFRA2 is negative), the size of the islands in the sea-island phase separation structure becomes extremely small.

[0092] The melt tension of the linear polypropylene resin A2 at 230°C is preferably 1.0 g or less, and more preferably less than 1.0 g. When the melt tension of the linear polypropylene resin A2 at 230°C is within the above range, the flow characteristics in the molten state are excellent, and unstable flow such as melt fracture is not easily generated. As a result, the uniformity of the film thickness is good, and therefore, there is an advantage that a thin-walled portion that easily causes dielectric breakdown is not easily formed. It should be noted that the method for measuring the melt tension of the resin at 230°C in this specification is based on the method described in the Examples.

[0093] The meso pentad fraction ([mmmm]) of the linear polypropylene resin A2 is preferably 99.8% or less, more preferably 99.5% or less, and further preferably 99.0% or less. In addition, the meso pentad fraction is preferably 94.0% or more, more preferably 94.5% or more, further preferably 95.0% or more, and most preferably 98.0% or more. If the meso pentad fraction is within the above range, the crystallinity of the polypropylene resin is improved by utilizing moderately high stereoregularity, and the voltage resistance of the biaxially stretched polypropylene film at high temperature is further improved. In addition, the speed of solidification (crystallization) during cast sheet molding becomes moderate, and moderate stretchability can be exhibited. It should be noted that when the linear polypropylene resin A contains both linear polypropylene resin A1 and linear polypropylene resin A2 (preferably, when the linear polypropylene resin A1 and the linear polypropylene resin A2 are mixed), the meso pentad fraction of the linear polypropylene resin A1 can be set to less than 98.0%, and the meso pentad fraction of the linear polypropylene resin A2 can be set to 98.0% or more.

[0094] The heptane insoluble matter (HI) of the linear polypropylene resin A2 is preferably 97.5% or more, more preferably 98.0% or more, further preferably 98.5% or more, and particularly preferably 98.6% or more. In addition, the heptane insoluble matter is preferably 99.5% or less, more preferably 99.0% or less. It should be noted that the heptane insoluble matter (HI) of both the linear polypropylene resin A1 and the linear polypropylene resin A2 may be set to 98.5% or more.

[0095] Typical commercial products of the linear polypropylene resin A2 include, for example, S802M manufactured by Han'an Petrochemical Corporation and HPT-S manufactured by Han'an Petrochemical Corporation.

[0096] (Branched polypropylene resin B)

[0097] The biaxially stretched polypropylene film of the present invention contains a branched polypropylene resin B in addition to the linear polypropylene resin A. The mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is 99.0:1.0 to 85.0:15.0.

[0098] Among the branched polypropylene resins B, the branched polypropylene resins B obtained by polymerizing propylene with a metallocene catalyst are preferred. The biaxially stretched polypropylene film contains the branched polypropylene resin B in addition to the linear polypropylene resin A, so that a large amount of β crystals are formed in the cast sheet before biaxial stretching. By stretching the cast sheet containing β crystals, the β crystals are transformed into α crystals, and therefore, (roughly) arc-shaped concavities and convexities are formed in the polypropylene film obtained by stretching due to the difference in density between β crystals and α crystals, and the surface can be appropriately roughened. From the above viewpoints, the biaxially stretched polypropylene film of the present invention is also suitable as a material for a dielectric film for capacitors.

[0099] When a branched polypropylene resin B obtained by crosslinking modification based on peroxide is used instead of a branched polypropylene resin B polymerized with a metallocene catalyst as the branched polypropylene resin B, the formation of α crystals in the cast sheet before biaxial stretching is promoted and the formation of β crystals is suppressed by the α crystal nucleation effect of the branched polypropylene resin B obtained by crosslinking modification based on peroxide. Even if the cast sheet containing α crystals is stretched, it is not easy to cause the transformation of microcrystals and it is not easy to form unevenness. Therefore, in order to roughen the biaxially stretched polypropylene film, a branched polypropylene resin B polymerized with a metallocene catalyst can be used appropriately. In this regard, when a branched polypropylene resin B polymerized with a metallocene catalyst is used, the β crystal fraction (that is, the ratio of β crystals to the total of α crystals and β crystals) in the cast sheet before biaxial stretching is preferably 10% or more, more preferably 13% or more, further preferably 15% or more, further preferably 17% or more, and most preferably 19% or more. It should be noted that the method for determining the β crystal fraction in this specification is based on the method described in the examples.

[0100] In addition, the metallocene catalyst is generally a metallocene compound that forms a polymerization catalyst for generating an olefin macromonomer. The branched polypropylene resin B obtained by polymerizing propylene with a metallocene catalyst has a moderate branch length and branch interval of the polypropylene, further improves the compatibility with the linear polypropylene, and is easy to obtain a more uniform composition and a more uniform surface shape, so it is preferred.

[0101] Typical commercial products of the branched polypropylene resin B include WAYMAX-EX6000 manufactured by Japan Polypropylene Corporation, WAYMAX-MFX6 manufactured by Japan Polypropylene Corporation, WAYMAX-MFX3 manufactured by Japan Polypropylene Corporation, WAYMAX-EX8000 manufactured by Japan Polypropylene Corporation, and WAYMAX-EX4000 manufactured by Japan Polypropylene Corporation.

[0102] The melt tension of the branched polypropylene resin B at 230°C is preferably 3 g / cm 3 Above and 25g / cm 3 Below, more preferably 5g / cm 3 Above and 20g / cm 3 Below, more preferably 9g / cm 3 Above and 20g / cm 3 Below, particularly preferably 9g / cm3 Above and 17g / cm 3 When the melt tension is within the above range, the dielectric breakdown strength of the biaxially stretched polypropylene film at high temperatures is further improved.

[0103] The melt flow rate of the branched polypropylene resin B at 230°C is preferably 0.1 to 12.0 g / 10 minutes, more preferably 1.0 to 6.0 g / 10 minutes, more preferably 1.5 to 4.0 g / 10 minutes, and further preferably 2.0 to 3.5 g / 10 minutes. Thus, the melt flow rate of the branched polypropylene resin B at 230°C can also be set to 2.0 g / 10 minutes or more. By having the melt flow rate at 230°C in 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 further suppressed. Therefore, the uniformity of the film thickness is better, thereby suppressing the formation of thin-walled parts that are prone to dielectric breakdown, and the dielectric breakdown strength of the biaxially stretched polypropylene film at high temperatures is further improved.

[0104] The weight average molecular weight Mw of the branched polypropylene resin B is preferably 150,000 to 600,000, more preferably 200,000 to 500,000, further preferably 250,000 to 500,000, and particularly preferably 350,000 to 480,000. If the weight average molecular weight Mw of the branched polypropylene resin B is within the above range, the resin fluidity becomes more appropriate, the thickness of the cast sheet is easier to control, and it becomes easier to make a thin stretched film. In addition, the thickness of the cast sheet and the stretched film becomes less likely to be uneven, and more appropriate stretchability can be obtained.

[0105] The number average molecular weight Mn of the branched polypropylene resin B is preferably 100,000 to 300,000, more preferably 100,000 to 250,000, and further preferably 100,000 to 200,000. When the number average molecular weight Mn of the branched polypropylene resin B is within the above range, the heat resistance of the manufactured capacitor is further improved.

[0106] The molecular weight distribution (Mw / Mn) of the branched polypropylene resin B is preferably 1.5 to 4.5, more preferably 1.8 to 4.5, and further preferably 2.0 to 4.2. When Mw / Mn is within the above range, the stretchability of the polypropylene film is further improved, and a thinner biaxially stretched polypropylene film can be produced.

[0107] The Z average molecular weight Mz of the branched polypropylene resin B is preferably greater than 700,000 and less than 2,000,000, more preferably greater than 800,000 and less than 1,700,000. When the Z average molecular weight Mz of the branched polypropylene resin B is within the above range, the dielectric breakdown strength of the biaxially stretched polypropylene film at high temperatures is further improved.

[0108] The molecular weight distribution (Mz / Mn) of the branched polypropylene resin B is preferably 4 to 30, more preferably 5 to 20. When Mz / Mn is within the above range, the stretchability of the polypropylene film is further improved, and a thinner biaxially stretched polypropylene film can be produced.

[0109] The molecular weight, molecular weight distribution and the like of the branched polypropylene resin B can be controlled by adjusting the catalyst and polymerization conditions.

[0110] The content of the branched polypropylene resin B may be such that the mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is 99.0:1.0 to 85.0:15.0, and preferably 96.9:3.1 to 85.0:15.0. In such a mass ratio, for example, when the total amount of the linear polypropylene resin A and the branched polypropylene resin B is 100 mass%, and the linear polypropylene resin A is a mixture of the resin A1 and the resin A2, the content of the linear polypropylene resin A1 is preferably 55 mass% to 65 mass%, the content of the linear polypropylene resin A2 is preferably 30 mass% to 40 mass%, and the content of the branched polypropylene resin B is preferably 2 mass% to 10 mass%. By setting such a compounding ratio, it is easy to obtain a high dielectric breakdown strength even at a high temperature compared with conventional products.

[0111] (Other resins)

[0112] The biaxially stretched polypropylene film of the present invention may also contain other resins (hereinafter also referred to as "other resins") other than the aforementioned linear polypropylene resin A and the aforementioned branched polypropylene resin B. "Other resins" are not particularly limited as long as they are resins other than the aforementioned linear polypropylene resin A and the aforementioned branched polypropylene resin B and can obtain the target biaxially stretched polypropylene film. As the other resins, for example, other polyolefins other than polypropylene such as polyethylene, poly (1-butene), polyisobutylene, poly (1-pentene), poly (1-methylpentene) can be cited; copolymers of α-olefins such as ethylene-propylene copolymers, propylene-butene copolymers, and ethylene-butene copolymers; random copolymers of vinyl monomers-diene monomers such as styrene-butadiene random copolymers; random copolymers of vinyl monomers-diene monomers-vinyl monomers such as styrene-butadiene-styrene block copolymers, etc. It should be noted that when other resins are contained, the total amount of the aforementioned linear polypropylene resin A and the aforementioned branched polypropylene resin B is preferably 95% by mass or more, more preferably 98% by mass or more in the total 100% by mass of the resin component. That is, the content of other resins in 100% by mass of the entire resin component is preferably 5% by mass or less, and more preferably 2% by mass or less.

[0113] (additive)

[0114] The biaxially stretched polypropylene film of the present invention may further contain additives, such as antioxidants, chlorine absorbers, ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, colorants, and the like.

[0115] (Characteristics of biaxially stretched polypropylene film)

[0116] The storage modulus (E') of the biaxially stretched polypropylene film of the present invention at a vibration frequency of 1 Hz and a temperature of 160°C is 22.50 MPa to 31.00 MPa, preferably 22.50 MPa to 28.00 MPa, and more preferably 22.97 MPa to 27.53 MPa. By being within the above range, it becomes easy to obtain high dielectric breakdown strength at high temperature.

[0117] The dielectric breakdown strength of the biaxially stretched polypropylene film of the present invention at a DC voltage at 120° C. (DCES120° C.) is 440 Vdc / μm or more, preferably 448 Vdc / μm or more, further preferably 460 V / μm or more, and particularly preferably 470 V / μm or more. The higher the upper limit of the dielectric breakdown strength at a DC voltage at 120° C., the more preferred, for example, 650 V / μm, 630 V / μm, etc.

[0118] For the biaxially stretched polypropylene film of the present invention, the β crystal fraction (that is, the ratio of β crystal to the total of α crystal and β crystal) in the cast sheet before biaxial stretching is preferably 10% or more, more preferably 13% or more, further preferably 15% or more, further preferably 17% or more, and most preferably 19% or more. The larger the upper limit of the β crystal fraction, the more preferred it is, for example, 50%, 40%, etc. By setting the β crystal fraction in the cast sheet to 10% or more in this way, (roughly) arc-shaped concavities and convexities are formed on the surface of the biaxially stretched polypropylene film of the present invention, the surface can be appropriately roughened, and the usefulness as a dielectric film for capacitors can be improved.

[0119] For the biaxially stretched polypropylene film of the present invention, in differential scanning calorimetry (DSC), the melting peak temperature when the temperature is initially increased from 30°C to 280°C at 20°C / min under a nitrogen atmosphere is preferably 166°C or more and 188°C or less. The lower limit is preferably 166°C or more, more preferably 168°C or more, and further preferably 169°C or more. If the melting peak temperature at the initial temperature increase is 166°C or more, the thickness of the sheet required to maintain the strength of dielectric breakdown becomes. In addition, the upper limit is preferably 188°C or less, more preferably 187°C or less, and further preferably 185°C or less. The upper limit of the melting peak temperature at the initial temperature increase is below the equilibrium melting point of polypropylene (the melting point when the thickness of the sheet is infinite), and from the viewpoint of molding processability, it is preferably 187°C or less. The aforementioned melting peak temperature is a value measured in the first round of differential scanning calorimetry, and in detail, it is based on the method described in the embodiment.

[0120] For the biaxially stretched polypropylene film of the present invention, in differential scanning calorimetry, the melting enthalpy when the temperature is initially increased from 30°C to 280°C at 20°C / min under a nitrogen atmosphere is 105 J / g or more and 150 J / g or less. The lower limit is preferably 105 J / g or more, more preferably 110 J / g or more, and further preferably 115 J / g or more. If the melting enthalpy at the initial temperature increase is 105 J / g or more, it becomes the crystallinity required to maintain the strength of dielectric breakdown. In addition, the upper limit is preferably 150 J / g or less, more preferably 140 J / g or less, and further preferably 130 J / g or less. If the melting enthalpy at the initial temperature increase is 150 J / g or less, it has appropriate film stretchability. The aforementioned melting enthalpy is a value measured in the first round of differential scanning calorimetry, and is specifically based on the method described in the embodiment.

[0121] For the biaxially stretched polypropylene film of the present invention, in a differential scanning calorimetry, the crystallization peak temperature when the temperature is initially raised from 30°C to 280°C at 20°C / min in a nitrogen atmosphere, maintained at 280°C for 5 minutes, and then initially cooled to 30°C at a cooling rate of 20°C / min is preferably 112°C or more and lower than 120°C (119.9°C or less). The lower limit is preferably 112°C or more, more preferably 114°C or more, and further preferably 116°C or more. If the crystallization peak temperature during initial cooling is 112°C or more, the size of the spherulites generated in the cooling process of the resin sheet obtained by melt extrusion can be controlled to be smaller, and the generation of insulation defects generated in the stretching process can be suppressed to be lower. In addition, the upper limit is preferably 120°C or less (119.9°C or less), more preferably 119°C or less, and further preferably 118°C or less. If the crystallization peak temperature during initial cooling is 120°C or less, a rough surface based on crystal transformation may be formed. The aforementioned crystallization peak temperature is a value measured in the first run of differential scanning calorimetry, and specifically, is based on the method described in Examples.

[0122] For the biaxially stretched polypropylene film of the present invention, in a differential scanning calorimetry, the crystallization enthalpy when the temperature is initially raised from 30°C to 280°C at 20°C / min under a nitrogen atmosphere, maintained at 280°C for 5 minutes, and then initially cooled to 30°C at a cooling rate of 20°C / min is preferably -150 J / g or more and -96 J / g or less. The lower limit is preferably -150 J / g or more, more preferably -130 J / g or more, further preferably -120 J / g or more, and particularly preferably -110 J / g or more. If the crystallization enthalpy during initial cooling is -150 J / g or more, it has appropriate film stretchability. In addition, the upper limit is preferably -96 J / g or less, more preferably -98 J / g or less, and further preferably -100 J / g or less. If the crystallization enthalpy during initial cooling is -96 J / g or less, it becomes the crystallinity required to maintain the strength of dielectric breakdown. The above-mentioned crystallization enthalpy is a value measured in the first run of differential scanning calorimetry, and is specifically based on the method described in Examples.

[0123] 2. Method for producing biaxially stretched polypropylene film

[0124] The method for producing the biaxially stretched polypropylene film of the present invention is not particularly limited, and can be produced, for example, by the following production method, comprising the steps of: subjecting a polypropylene resin composition containing at least a linear polypropylene resin A and a branched polypropylene resin B to a temperature of preferably 225° C. to 270° C. and a shear rate of 2000 s -1 Above and 15000s -1 The above-mentioned production method will be described below by way of example.

[0125] According to the above-mentioned manufacturing method, a biaxially stretched polypropylene film showing good dielectric breakdown strength at high temperature can be provided. The reason why a biaxially stretched polypropylene film showing good dielectric breakdown strength can be provided is believed to be due to the sea-island phase separation structure (especially the appropriate island size) of the cast sheet formed by using two specific different polypropylene resins.

[0126] There are no particular restrictions on the method for mixing the resins used in the above-mentioned manufacturing method, and the following methods can be cited: a method of dry mixing the base resin and the polymer powder or pellets of the blended resin using a mixer or the like; a method of supplying the base resin and the polymer powder or pellets of the blended resin to a kneader, performing melt kneading, and obtaining a mixed product.

[0127] The mixer and kneader are not particularly limited. The kneader may be a single screw type, a twin screw type, or a multi-screw type having three or more screws. In the case of a twin screw or more screw type, the kneader may be a co-rotating or counter-rotating type.

[0128] In the case of mixing based on melt mixing, there is no particular restriction on the mixing temperature as long as a good mixed material is obtained. It is usually in the range of 200°C to 300°C, and from the viewpoint of suppressing the degradation of the resin, it is preferably 230°C to 270°C. In addition, in order to suppress the degradation of the resin during mixing, an inert gas such as nitrogen can be purged into the mixer. The resin after melt mixing can usually be granulated into a suitable size using a known granulator. Thus, mixed polypropylene raw resin pellets can be prepared.

[0129] The polypropylene resin composition may contain additives. As additives, the same additives as those described in the biaxially stretched polypropylene film of the present invention may be used. The polypropylene resin composition may contain the additives in an amount that does not adversely affect the biaxially stretched polypropylene film.

[0130] In the method for producing the biaxially stretched polypropylene film, first, polypropylene resin pellets, dry-blended polypropylene resin pellets, or mixed polypropylene resin pellets prepared by melt kneading in advance are supplied to an extruder and heated and melted.

[0131] The polypropylene resin composition is preferably melted at 170° C. to 320° C. Specifically, the extruder setting temperature during the heating and melting of the polypropylene resin composition is set to 225° C. to 270° C. Thus, a sea-island phase separation structure is formed during the casting sheet molding described later, and a biaxially stretched polypropylene film having excellent dielectric breakdown strength at high temperatures can be produced.

[0132] The polypropylene resin composition is preferably heated at a temperature of 225°C to 270°C and at a shear rate of 2000 s. -1 Above and 15000s -1 The following is melted. Thus, the sea-island phase separation structure is formed during the casting process described later, and a polypropylene film with excellent dielectric breakdown strength at high temperature can be produced. If the shear rate is less than 2000s -1 If the shear rate is higher than 15000s, the extrusion rate will not be constant, and there is a concern that the shape and size of the blank sheet will become irregular or fluctuate regularly, and there is a concern that the blank sheet will be easily broken during transportation or during stretching. -1 , there are concerns that: due to a phenomenon called crushing in the extruder, unmelted material is extruded, and a uniform billet sheet cannot be obtained, which may easily cause breakage during stretching; or excessive heat generation during the tip gap may cause significant degradation of the polypropylene resin composition, and even if a uniform billet sheet is obtained, the dielectric breakdown strength of the film obtained by stretching may be reduced. The shear rate can be adjusted by the barrel diameter of the extruder, the screw speed, and the groove depth of the screw.

[0133] The above shear rate is preferably 2000s -1 More than 10000s -1 Below, more preferably 2000s -1 Above and 2300s -1 When the shear rate is within the above range, a biaxially stretched polypropylene film having a weight fraction w of 2.6% to 4.0% can be easily obtained, and the heat resistance of a film capacitor using the biaxially stretched polypropylene film as a capacitor dielectric is further improved.

[0134] Next, the molten polypropylene resin composition is extruded into a sheet by a T-die, cooled and solidified on at least one metal drum, and can be formed into an unstretched cast sheet. The surface temperature of the metal drum (the temperature of the metal drum first contacted after extrusion) is preferably above 10°C and below 105°C, more preferably above 15°C and below 100°C. The surface temperature of the metal drum can be determined based on the physical properties of the polypropylene resin used. If the surface temperature of the metal drum is lower than 10°C, it is difficult to obtain good sheet formability of the blank sheet, and therefore, there is a concern that uneven stretching and breakage are likely to occur during stretching film formation.

[0135] The thickness of the cast sheet is not particularly limited, but is preferably 0.05 mm to 2 mm, and more preferably 0.1 mm to 1 mm.

[0136] The biaxially stretched polypropylene film can be manufactured by biaxially stretching the above-mentioned cast sheet. The stretching is preferably biaxial stretching in which the film is oriented in both the longitudinal and transverse directions. As a stretching method, a sequential biaxial stretching method is preferred. As the above-mentioned sequential biaxial stretching method, for example, first, the cast sheet is maintained at a temperature of 100°C or more and 180°C or less (preferably 120°C or more and 170°C or less), and is stretched in the flow direction between rollers with a speed difference. The stretching ratio in the flow direction is preferably 3.0 times or more and 7.0 times or less, more preferably 4.0 times or more and 6.0 times or less. Then, the sheet is introduced into a tenter and stretched in the transverse direction. The temperature during transverse stretching is preferably 160°C or more and 180°C or less, and the transverse stretching ratio is preferably 3.0 times or more and 11.0 times or less. Then, after transverse stretching, relaxation, heat setting and winding are implemented.

[0137] By the production method described above, a biaxially stretched polypropylene film can be produced.

[0138] For the above-mentioned biaxially stretched polypropylene film, from the viewpoint of further improving the adhesive properties in subsequent processes such as the metal vapor deposition process, after the stretching and heat setting process are completed, a corona discharge treatment can be carried out online or offline. The corona discharge treatment can be carried out using a known method. As the atmosphere gas, it is preferably carried out using air, carbon dioxide gas, nitrogen or a mixed gas thereof.

[0139] The biaxially stretched polypropylene film of the present invention manufactured by the above-mentioned manufacturing method has excellent dielectric breakdown strength when a DC voltage is applied at a high temperature of about 120°C (100°C to 125°C) and dielectric breakdown strength when an AC voltage is applied, even when the thickness of the film is as thin as 6.0 μm or less, and thermal shrinkage is suppressed at a temperature of about 120°C, which is the above-mentioned high temperature, and excellent heat shrinkage resistance can be shown in this respect. As a result, the thermal shrinkage (deformation) of the capacitor is suppressed during repeated use between the above-mentioned high and low temperatures assumed in the engine room, and excellent heat shock resistance is also shown in this respect. Therefore, the biaxially stretched polypropylene film of the present invention is suitable for capacitor use, and can preferably be used as a dielectric of a capacitor constituting an inverter in a hybrid vehicle / electric vehicle.

[0140] 3. Metallized film, capacitor and method for manufacturing the same

[0141] The metallized film of the present invention is a metallized film having a metal layer on at least one surface of the biaxially stretched polypropylene film.

[0142] The metal layer functions as an electrode. As the metal used in the metal layer, for example, single metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, a mixture of multiple thereof, and alloys thereof can be used. Among these, zinc and aluminum are preferred in terms of environmental load, economy, and excellent capacitor performance.

[0143] The method of laminating the metal layer on at least one side (one side or both sides) of the biaxially stretched polypropylene film is not particularly limited, and examples thereof include vacuum evaporation method, sputtering method, etc. From the viewpoint of excellent productivity and economic efficiency, vacuum evaporation method is preferred. As vacuum evaporation method, crucible method, wire method, etc. can be mentioned, and the best one can be appropriately selected.

[0144] The edge pattern when laminating the metal layer by vapor deposition is not particularly limited. From the viewpoint of further improving the safety of the capacitor and further suppressing the destruction and short circuit of the capacitor, it is preferred to apply a pattern containing so-called special edges such as a fishnet pattern and a T-shaped edge pattern to a single surface of the biaxially stretched polypropylene film.

[0145] The method for forming the edge is not particularly limited, and the edge may be formed by a known method such as a tape method or an oil method.

[0146] The thickness of the metallized film of the present invention is not particularly limited, but is preferably 1.8 μm to 3.0 μm, and more preferably 2.0 μm to 2.8 μm.

[0147] The capacitor of the present invention is a capacitor including the metallized film. The metallized film disclosed in the present invention can be stacked or wound by a conventionally known method to form a film capacitor.

[0148] The film capacitor may have a structure in which a plurality of metallized films are stacked, or may have a wound metallized film. Such a film capacitor may be suitable for use as a capacitor for inverter power supply equipment for controlling a drive engine of an electric vehicle, a hybrid vehicle, etc. In addition, it may also be suitable for use in applications such as railway vehicles, wind power generation, solar power generation, and general household appliances.

[0149] Example

[0150] Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples.

[0151] In addition, Table 1 shows the raw materials used in Examples and Comparative Examples.

[0152] [Table 1]

[0153]

[0154] [Examples 1 to 9 and Comparative Examples 1 to 7]

[0155] <Manufacturing of biaxially stretched polypropylene film>

[0156] The raw materials shown in Table 1 were dry-blended at the mixing ratio (mass ratio) shown in Table 2. Then, the raw materials were supplied to an extruder, melted at a resin temperature of 230°C, extruded using a T-die, and wound on a metal drum whose surface temperature was maintained at 20°C for solidification to produce an unstretched cast sheet having a thickness of about 300 μm. Then, the unstretched cast sheet was stretched to 5 times in the flow direction at a temperature of 165°C using a KARO IV intermittent biaxial stretching machine manufactured by Brueckner, and then stretched to 10 times in the transverse direction to produce a biaxially stretched polypropylene film having a thickness of 6.0 μm.

[0157] <Measurement method>

[0158] About each Example and Comparative Example, various characteristics were evaluated according to the following measurement conditions.

[0159] (1) Evaluation of resin properties

[0160] (Determination of number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn) and differential distribution values ​​of polypropylene) The number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn) and differential distribution values ​​of the distribution curve of polypropylene were determined by GPC (gel permeation chromatography) under the following conditions.

[0161] HLC-8121GPC-HT type, a high temperature GPC device with built-in differential refractometer (RI) manufactured by Tosoh Corporation, was used. Three TSK gel GMHHR-H(20)HT columns manufactured by Tosoh Corporation were connected, and one TSK gelguard column HHR(30) was used. At a column temperature of 140°C, 0.05 wt% of 2,6-di-tert-butyl-p-cresol (common name: BHT) in 1,2,4-trichlorobenzene was allowed to flow at a flow rate of 1.0 ml / min as an eluent to obtain the number average molecular weight (Mn), weight average molecular weight (Mw) and z average molecular weight (Mz). The molecular weight distribution (Mz / Mn) was obtained using the values ​​of Mz and Mn, and the molecular weight distribution (Mw / Mn) was obtained using the values ​​of Mw and Mn.

[0162] The measurement conditions are as follows.

[0163] GPC device: HLC-8121GPC / HT (made by Tosoh)

[0164] Light scattering detector: DAWN EOS (Wyatt Technology),

[0165] Column: TSK gel guard column HHR (30) (7.8 mm ID × 7.5 cm) × 1 + TSK gel GMHHR-H (20) HT (7.8 mm ID × 30 cm) × 3 (made by Tosoh)

[0166] Eluent: 0.05 wt% BHT in 1,2,4-trichlorobenzene

[0167] Flow rate: 1.0mL / min

[0168] Sample concentration: 2mg / mL

[0169] Injection volume: 300μL

[0170] Column temperature: 140°C

[0171] System temperature: 40℃

[0172] Pretreatment: Accurately weigh the sample, add the eluent, shake and dissolve it at 140°C for 1 hour, and perform hot filtration using a 0.5μm sintered metal filter.

[0173] Calibration curve: A calibration curve was prepared using a fifth-order approximation curve of standard polystyrene manufactured by Tosoh Corporation. The molecular weight was converted to the molecular weight of polypropylene using the Q-factor.

[0174] Based on the obtained standard curve and SEC chromatogram, the molecular weight (logarithmic value) is plotted on the horizontal axis and the integral value of the concentration fraction is plotted on the vertical axis using the analytical software for the measuring device to obtain an integrated molecular weight distribution curve. In addition, the differential value of the integrated molecular weight distribution curve at each molecular weight (the slope of the integrated molecular weight distribution curve) is obtained, and the molecular weight (logarithmic value) is plotted on the horizontal axis and the differential value is plotted on the vertical axis to obtain a differential molecular weight distribution curve.

[0175] From these curves, the number average molecular weight Mn, the weight average molecular weight Mw and the Z average molecular weight Mz are obtained. The molecular weight distribution (Mw / Mn) is obtained using the values ​​of Mw and Mn. In addition, the molecular weight distribution (Mz / Mn) is obtained using the values ​​of Mz and Mn.

[0176] (Heptane insoluble matter (HI))

[0177] Each polypropylene resin used as a raw material in the examples and comparative examples was pressed into a shape of 10 mm × 35 mm × 0.3 mm to prepare a sample for measurement of about 3 g. Then, about 150 mL of heptane was added and Soxhlet extraction was performed for 8 hours. The heptane insoluble matter was calculated from the sample mass before and after extraction.

[0178] (Meso pentad component rate)

[0179] Each polypropylene resin as a raw material used in Examples and Comparative Examples was dissolved in a solvent, and the meso pentad fraction was measured under the following conditions using a high temperature Fourier transform nuclear magnetic resonance apparatus (high temperature FT-NMR).

[0180] High temperature nuclear magnetic resonance (NMR) device: manufactured by JEOL Ltd., high temperature Fourier transform nuclear magnetic resonance device (high temperature FT-NMR), model: JNM-ECP500

[0181] Observation nucleus: 13C (125MHz)

[0182] Measuring temperature: 135℃

[0183] Solvent: o-dichlorobenzene (ODCB: a mixed solvent of ODCB and deuterated ODCB (mixing ratio = 4 / 1))

[0184] Measurement mode: Single pulse proton broadband decoupling

[0185] Pulse width: 9.1μsec (45° pulse)

[0186] Pulse interval: 5.5sec

[0187] Cumulative times: 4500 times

[0188] Shift standard: CH3(mmmm)=21.7ppm

[0189] The pentad ratio indicating stereoregularity is calculated as a percentage (%) based on the intensity integral value of each signal of the combination of pentads (mmmm, mrrm, etc.) derived from the unit group "meso (m)" arranged in the same direction and the unit group "racemic (r)" arranged in an opposite direction. For the attribution of each signal derived from mmmm, mrrm, etc., for example, the description of the spectrum in "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)" and the like is used as a reference.

[0190] (Melt tension)

[0191] The raw material resins used in Examples and Comparative Examples were extruded into a rope shape using a capillary rheometer 1B manufactured by TOYO SEIKI CO., LTD. under the following conditions, and the tension detected by a pulley when winding the rope around a roll was taken as the melt tension.

[0192] Capillary: diameter 2.0mm, length 40mm

[0193] Barrel diameter: 9.55mm

[0194] Barrel extrusion speed: 20mm / min

[0195] Coiling speed: 4.0m / min

[0196] Temperature: 230℃

[0197] When the melt tension was extremely high, the resin might break at a pulling speed of 4.0 m / min. In such a case, the pulling speed was reduced to obtain the highest pulling speed as the melt tension.

[0198] (Dynamic viscoelasticity (storage modulus (E')))

[0199] The measurement conditions and measurement procedures are as follows.

[0200] As a dynamic viscoelasticity measuring machine, a "viscoelasticity measuring device (model: DMS6100)" manufactured by Seiko Instruments Inc. was used. Cast sheets extruded at the respective compounding ratios shown in Table 2 were used as measuring samples, cut into strips of 40 mm in the longitudinal direction and 8 mm in the transverse direction, and the temperature dependence of the cast sheets was measured under the measuring conditions shown below in accordance with JIS-K7244 (1999 edition).

[0201] Test mode: tensile mode

[0202] Chuck spacing: 20mm

[0203] Vibration frequency: 1Hz

[0204] Strain amplitude: 10μm

[0205] Tension gain: 1.2

[0206] Initial force amplitude: 100mN

[0207] Temperature range: -60~170℃

[0208] Heating rate: 5℃ / min

[0209] Measurement atmosphere: Nitrogen

[0210] Measuring thickness: 300μm

[0211] The storage modulus (E') at a temperature distribution of 160° C. was determined from the measurement results.

[0212] (Melt Flow Rate (MFR))

[0213] The melt flow rate (MFR) of the raw resin pellets used in the examples and comparative examples was measured using a melt indexer from TOYO SEIKI CO., LTD. in accordance with condition M of JIS K 7210. Specifically, first, a sample weighing 4 g was inserted into a barrel set at a test temperature of 230°C, and preheated for 3.5 minutes under a load of 2.16 kg. Thereafter, the weight of the sample extruded from the bottom hole within 30 seconds was measured to determine the MFR (unit: g / 10 minutes or g / 10min). The above measurement was repeated 3 times, and the average value was taken as the measured value of the MFR.

[0214] (2) Evaluation of properties of biaxially stretched polypropylene films

[0215] (Determination of dielectric breakdown strength: direct current (DC))

[0216] The dielectric breakdown voltage (BDV) of the biaxially stretched polypropylene film at 120°C was measured 16 times under the following test conditions using the electrode configuration described in JIS C2151 (2006) 17.2.2 (flat electrode method). It should be noted that the applied voltage when the leakage current of the upper limit reference value described below is detected during the boost is taken as BDV. The BDV is divided by the thickness (μm) of the film, and the average of the 12 values ​​excluding the highest 2 values ​​and the lowest 2 values ​​in the 16 measurement results is taken as the dielectric breakdown strength DCES (V / μm).

[0217] Test piece: about 150mm×150mm

[0218] Conditioning of test piece: 30 minutes under atmospheric conditions

[0219] Power supply: DC

[0220] Atmosphere: 120℃ in air

[0221] Testing machine: DC withstand voltage / insulation resistance testing machine TOS9213AS manufactured by Kikusui Electronics Corp.

[0222] Voltage rise speed: 100V / s

[0223] Current detection response speed: MID

[0224] Upper limit reference value: 5mA

[0225] (Melting peak temperature at the first heating)

[0226] A 5 mg sample was cut out from a biaxially stretched polypropylene film, sealed in an aluminum pan, and subjected to power-compensated differential scanning calorimetry using a differential scanning calorimeter (Diamond DSC manufactured by Perkin-Elmer Co., Ltd.). During the measurement, the temperature was initially raised from 30°C to 280°C at 20°C / min in a nitrogen atmosphere. The melting peak temperature was determined from the result of the initial temperature increase.

[0227] (Enthalpy of melting at first heating)

[0228] A 5 mg sample was cut out from the biaxially stretched polypropylene film, sealed in an aluminum pan, and subjected to power-compensated differential scanning calorimetry using a differential scanning calorimeter (Diamond DSC manufactured by Perkin-Elmer Co., Ltd.). During the measurement, the temperature was initially raised from 30°C to 280°C at 20°C / min in a nitrogen atmosphere. The melting enthalpy was determined from the result of the initial temperature increase.

[0229] (Determination of crystallization peak temperature during initial cooling)

[0230] In the first run, after being held at 280° C. for 5 minutes, the sample was primarily cooled to 30° C. at a temperature drop rate of 20° C. / min and then held at 30° C. for 5 minutes. The crystallization peak temperature was determined from the result of the primary cooling.

[0231] (Determination of crystallization enthalpy during initial cooling)

[0232] In the first run, after being held at 280°C for 5 minutes, the sample was cooled to 30°C at a temperature drop rate of 20°C / min and then held at 30°C for 5 minutes. The crystallization enthalpy was determined from the result of the first cooling.

[0233] (Thickness of film)

[0234] In an environment with a temperature of 23±2°C and a humidity of 50±5%RH, the paper thickness was measured using a paper thickness measuring instrument MEI-11 manufactured by CITIZEN SEIMITSU CO., LTD. (measuring pressure 100 kPa, descending speed 3 mm / sec, measuring terminal The thickness of the biaxially stretched polypropylene film was measured with a measuring force of 20.1 N. The sample was cut from the roll in a manner that 10 or more sheets were overlapped, and the film was cut in a manner that no wrinkles were generated and no air was trapped in the film. For the sample with 10 sheets overlapped, 5 measurements were performed, and the average value of the 5 measurements was divided by 10 to calculate the thickness.

[0235] (Measurement of β-Crystal Fraction of Cast Sheet Before Biaxial Stretching)

[0236] The β crystal fraction was evaluated using the K value obtained by X-ray diffraction intensity measurement. The X-ray diffraction intensity measurement conditions were as follows.

[0237] Measurement device: X-ray diffraction device RINT-2200 manufactured by Rigaku Corporation

[0238] X-ray source: CuKα rays

[0239] Irradiation output: 40KV-40mA

[0240] Scattering slit: 1deg

[0241] Light receiving slit: 0.3mm

[0242] Scanning speed: 1deg / minute

[0243] From the obtained intensity curve, the K value was calculated from the ratio of the sum of the heights of the three diffraction peaks derived from the α crystal to the one diffraction peak derived from the β crystal using the following formula.

[0244] K value (intensity ratio %) = Hβ / (Hβ+HαI+HαII+HαIII)×100〔wherein, Hβ is the intensity (height) of the peak of crystalline diffraction corresponding to β crystal (2θ=16deg), HαI is the intensity (height) of the peak of crystalline diffraction corresponding to α crystal (110) plane, HαII is the intensity (height) of the peak of crystalline diffraction corresponding to α crystal (040) plane, and HαIII is the intensity (height) of the peak of crystalline diffraction corresponding to α crystal (130) plane. The intensities (heights) after subtracting amorphous scattering are all used.〕

[0245] Table 2 shows the results of the above-mentioned various property evaluations of Examples and Comparative Examples.

[0246] [Table 2]

[0247]

[0248] From the results in Table 2, it is clear that:

[0249] (1) The mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is the linear polypropylene resin A: the branched polypropylene resin B = 99.0:1.0 to 85.0:15.0,

[0250] (2) the molecular weight distribution (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn of the linear polypropylene resin A is 7.0 or more and 9.3 or less,

[0251] (3) The storage modulus (E') of the biaxially stretched polypropylene film at a vibration frequency of 1 Hz and a temperature of 160°C is 22.50 MPa or more and 31.00 MPa or less

[0252] The biaxially stretched polypropylene films of Examples 1 to 8, which are the characteristics of the present invention, have high dielectric breakdown strength even at high temperatures. The advantageous effects of the present invention can be understood, for example, by comparing Examples 1 to 7 using one linear polypropylene resin A with Comparative Example 1, and it can be seen that the improvement rate of dielectric breakdown strength at 120° C. in Examples 1 to 7 exceeds 10.0% compared with Comparative Example 1. In addition, for example, by comparing Examples 8 to 9 using a mixture of two linear polypropylene resins A with Comparative Example 2, it can be seen that the improvement rate of dielectric breakdown strength at 120° C. in Examples 8 to 9 exceeds 13.0% compared with Comparative Example 2.

Claims

1. A biaxially stretched polypropylene film, characterized in that: Contains linear polypropylene resin A and branched polypropylene resin B, (1) The mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is the linear polypropylene resin A: the branched polypropylene resin B = 99.0:1.0 to 85.0:15.0, (2) the molecular weight distribution (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn of the linear polypropylene resin A is 7.0 or more and 9.3 or less, (3) The biaxially stretched polypropylene film has a storage modulus (E') of 22.50 MPa to 31.00 MPa at a vibration frequency of 1 Hz and a temperature of 160°C.

2. The biaxially stretched polypropylene film according to claim 1, wherein The mass ratio of the linear polypropylene resin A to the branched polypropylene resin B is the linear polypropylene resin A: the branched polypropylene resin B=96.9:3.1 to 85.0:15.

0.

3. The biaxially stretched polypropylene film according to claim 1 or 2, wherein: The branched polypropylene resin B has a melt flow rate at 230° C. of 2.0 g / 10 min or more.

4. The biaxially stretched polypropylene film according to claim 1 or 2, wherein: The branched polypropylene resin B has a melt tension of 9 g / cm at 230°C. 3 Above and 20g / cm 3 the following.

5. The biaxially stretched polypropylene film according to claim 1 or 2, wherein: The storage modulus (E') is 22.97 MPa or more and 27.53 MPa or less.

6. The biaxially stretched polypropylene film according to claim 1 or 2, wherein: The linear polypropylene resin A contains a linear polypropylene resin having a heptane insoluble matter (HI) of 98.5% or more.

7. The biaxially stretched polypropylene film according to claim 1 or 2, wherein: The linear polypropylene resin A includes two types of linear polypropylene resin A1 and linear polypropylene resin A2. The meso pentad fraction of the linear polypropylene resin A1 is lower than 98.0%, and the meso pentad fraction of the linear polypropylene resin A2 is greater than 98.0%.

8. The biaxially stretched polypropylene film according to claim 1 or 2, wherein: The biaxially stretched polypropylene film has a dielectric breakdown strength under a direct current voltage at 120° C. (DCES120° C.) of 448 V / μm or more.

9. The biaxially stretched polypropylene film according to claim 1 or 2, wherein: In differential scanning calorimetry, the biaxially stretched polypropylene film has a melting peak temperature of 166° C. to 188° C. when the temperature is initially increased from 30° C. to 280° C. at 20° C. / min in a nitrogen atmosphere.

10. The biaxially stretched polypropylene film according to claim 1 or 2, wherein: In differential scanning calorimetry, the biaxially stretched polypropylene film has a crystallization peak temperature of 112° C. or higher and lower than 120° C. when the temperature is initially increased from 30° C. to 280° C. at a rate of 20° C. / min in a nitrogen atmosphere, maintained at 280° C. for 5 minutes, and then initially cooled to 30° C. at a rate of 20° C. / min.

11. The biaxially stretched polypropylene film according to claim 1 or 2, wherein: In the biaxially stretched polypropylene film, in a cast sheet before biaxial stretching, a β crystal fraction, which is a ratio of β crystals to a total of α crystals and β crystals, is 10% or more.

12. The biaxially stretched polypropylene film according to claim 1 or 2, which is used for capacitors.

13. A metallized film comprising a metal layer on at least one surface of the biaxially stretched polypropylene film according to claim 1 or 2. 14 . The metallized film according to claim 13 , having a thickness of 1.8 μm to 3.0 μm.

15. A capacitor comprising the metallized film according to claim 13.

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