Polypropylene film, metal-layer-integrated polypropylene film, and film capacitor

Abstract

To provide a polypropylene film that has enhanced dielectric breakdown resistance while having excellent continuous productivity.SOLUTION: A polypropylene film comprises multiple layers including a first layer and a second layer adjacent to the first layer, wherein a difference between a crystallization temperature 1 of a constituent resin 1 of the first layer and a crystallization temperature 2 of a constituent resin 2 of the second layer is 3.0°C or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polypropylene film, a metal layer-integrated polypropylene film, a film capacitor, etc. [Background technology]

[0002] Polypropylene film has excellent electrical properties, such as high voltage resistance and low dielectric loss, as well as high moisture resistance. Therefore, it is widely used in electronic and electrical devices. Specifically, it is used as a film for high-voltage capacitors, various switching power supplies, filter capacitors (e.g., converters, inverters, etc.), smoothing capacitors, etc.

[0003] In particular, in recent years, polypropylene films have begun to be widely used as capacitors for inverter power supplies that control drive motors in electric vehicles, hybrid vehicles, etc. Capacitors for inverter power supplies used in automobiles, etc., are required to be small, lightweight, high-capacity, and highly reliable. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-156939 [Patent Document 2] Patent No. 6992929 [Patent Document 3] Japanese Patent Application Publication No. 2019-44171 Summary of the Invention [Problem to be solved by the invention]

[0005] Improving voltage resistance is an important means of ensuring high reliability. It is believed that electricity flows through amorphous parts along molecular chains. Therefore, attempts have been made to make it more difficult for electricity to flow (to increase voltage resistance) by highly controlling the orientation of molecular chains (Patent Document 1), increasing tie molecules to reduce the mobility of amorphous chains (Patent Document 2), or increasing the crystallinity (Patent Document 3). However, all of these methods tend to reduce stretchability, which can lead to breakage during stretching and impair continuous productivity. Thus, it has traditionally been difficult to achieve both high voltage resistance and continuous productivity.

[0006] An object of the present invention is to provide a polypropylene film that has higher voltage resistance and can be continuously produced with excellent productivity. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that the above-mentioned problems can be solved by a polypropylene film consisting of multiple layers including a first layer and a second layer adjacent to the first layer, in which the difference between the crystallization temperature 1 of the constituent resin 1 of the first layer and the crystallization temperature 2 of the constituent resin 2 of the second layer is 3.0°C or more. Based on this finding, the present inventors have conducted further research and have completed the present invention. That is, the present invention encompasses the following aspects.

[0008] Item 1. A polypropylene film consisting of multiple layers including a first layer and a second layer adjacent to the first layer, in which the difference between the crystallization temperature 1 of the constituent resin 1 of the first layer and the crystallization temperature 2 of the constituent resin 2 of the second layer is 3.0°C or more.

[0009] Item 2. The polypropylene film according to Item 1, wherein the difference is 5.0°C or more.

[0010] Item 3. The polypropylene film according to Item 1 or 2, wherein the difference is 25.0°C or less.

[0011] Item 4. The polypropylene film according to any one of Items 1 to 3, wherein the constituent resin 1 and the constituent resin 2 contain a linear polypropylene resin.

[0012] Item 5. The constituent resin 1 and the constituent resin 2 differ in at least one selected from the group consisting of the concentration of a nucleating agent, the concentration of a branched polypropylene resin, and the molecular weight distribution and / or heptane insoluble content of a linear polypropylene resin, and / or The concentration ratio of propylene homopolymer to propylene copolymer is different between the constituent resin 1 and the constituent resin 2. Item 5. The polypropylene film according to item 4.

[0013] Item 6. The polypropylene film according to any one of Items 1 to 5, which includes a third layer adjacent to the second layer, and wherein the difference between the crystallization temperature 2 of the constituent resin 2 of the second layer and the crystallization temperature 3 of the constituent resin 3 of the third layer is 3.0°C or more.

[0014] Item 7. The polypropylene film according to any one of Items 1 to 6, which consists of five or less layers.

[0015] Item 8. The polypropylene film according to any one of Items 1 to 7, which is a biaxially stretched polypropylene film.

[0016] Item 9. The polypropylene film according to any one of Items 1 to 8, having a thickness of 1.4 μm or more and 6.0 μm or less.

[0017] Item 10. The polypropylene film according to any one of Items 1 to 9, which is for use in a capacitor.

[0018] Item 11. A metal layer-integrated polypropylene film comprising the polypropylene film according to any one of items 1 to 10 and a metal layer laminated on one or both sides of the polypropylene film.

[0019] Item 12. A film capacitor comprising the metal layer-integrated polypropylene film according to Item 11. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a polypropylene film that has higher voltage resistance and excellent continuous productivity. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram of the apparatus used to measure the cumulative breakdown density at 550 VDC. DETAILED DESCRIPTION OF THE INVENTION

[0022] In this specification, the expressions "contain" and "comprise" include the concepts of "contain", "include", "consist essentially of" and "consist only of".

[0023] In this specification, based on the ranges consisting of the upper and / or lower limits described for each parameter, ranges in which the upper and / or lower limits are arbitrarily interchanged or arbitrarily combined between multiple ranges are also exemplified.

[0024] The polypropylene film of the present invention is A polypropylene film consisting of multiple layers including a first layer and a second layer adjacent to the first layer, wherein the difference between the crystallization temperature 1 of the constituent resin 1 of the first layer and the crystallization temperature 2 of the constituent resin 2 of the second layer is 3.0°C or more; It is characterized by:

[0025] The first and second layers are disposed adjacent to each other, i.e., there are no other layers between them, and one side of the first layer is in contact with one side of the second layer.

[0026] By ensuring that the difference between crystallization temperature 1 and crystallization temperature 2 is 3°C or more, it is possible to improve voltage resistance. Although a restrictive interpretation is not desired, it is believed that when the difference in crystallization temperature of the constituent resins is at least a certain level, a difference in crystal diameter between the first layer and the second layer is generated at least a certain level, which results in the formation of a clear interface between the first layer and the second layer, which acts as a barrier making it difficult for electricity to flow, thereby improving voltage resistance.

[0027] The difference between crystallization temperature 1 and crystallization temperature 2 is preferably 4.0° C. or more, more preferably 5.0° C. or more, even more preferably 6.0° C. or more, still more preferably 6.5° C. or more, particularly preferably 7.0° C. or more, especially more preferably 7.5° C. or more, especially more preferably 8.0° C. or more, and particularly preferably 8.3° C. or more. There is no particular upper limit to the temperature difference, but it is, for example, 25.0° C. or less, preferably 20.0° C. or less, more preferably 15.0° C. or less, even more preferably 12.0° C. or less, and still more preferably 10.0° C. or less.

[0028] There is no particular limitation on the difference between crystallization temperature 1 and crystallization temperature 2. Crystallization temperature 1 may be higher than crystallization temperature 2, or crystallization temperature 2 may be higher than crystallization temperature 1.

[0029] The polypropylene film of the present invention preferably includes a third layer adjacent to the second layer, and the difference between the crystallization temperature 2 of the constituent resin 2 of the second layer and the crystallization temperature 3 of the constituent resin 3 of the third layer is 3.0°C or more. This further improves the voltage resistance. In this embodiment, the polypropylene film of the present invention includes a laminate structure in which the first layer, second layer, and third layer are arranged in this order.

[0030] The preferred range of the difference between crystallization temperature 2 and crystallization temperature 3 is the same as the above-mentioned range of the difference between crystallization temperature 1 and crystallization temperature 2.

[0031] There are no particular limitations on the level of crystallization temperature 2 and crystallization temperature 3. Crystallization temperature 2 may be higher than crystallization temperature 3, or crystallization temperature 3 may be higher than crystallization temperature 2. In a preferred embodiment of the present invention, when crystallization temperature 1 is higher than crystallization temperature 2, it is preferable that crystallization temperature 3 is higher than crystallization temperature 2, and when crystallization temperature 2 is higher than crystallization temperature 1, it is preferable that crystallization temperature 2 is higher than crystallization temperature 3. In a particularly preferred embodiment of the present invention, crystallization temperature 1 and crystallization temperature 3 are higher than crystallization temperature 2.

[0032] The crystallization temperature of the constituent resin is not particularly limited, but is, for example, 90.0°C or higher and 130.0°C or lower, preferably 95.0°C or higher and 125.0°C or lower, more preferably 100.0°C or higher and 125.0°C or lower, even more preferably 105.0°C or higher and 125.0°C or lower, and still more preferably 105.0°C or higher and 120.0°C or lower.

[0033] The crystallization temperature of the constituent resin is a value measured according to or in accordance with the method of (3) in the Examples described below.

[0034] The number of layers constituting the polypropylene film of the present invention is not particularly limited, and may be, for example, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, or 5 or less. From the viewpoint that the interface between the layers becomes clearer and the effect of improving voltage resistance can be easily obtained even when the polypropylene film of the present invention is relatively thin, the number of layers is preferably as small as possible, and 5 or less is particularly preferred.

[0035] The polypropylene film of the present invention preferably has a thickness of 9.5 μm or less, more preferably 6.0 μm or less, even more preferably 3.0 μm or less, even more preferably 2.9 μm or less, particularly preferably 2.8 μm or less, and particularly preferably 2.5 μm or less. The thickness of the polypropylene film of the present invention is preferably 0.8 μm or more, more preferably 1.0 μm or more, even more preferably 1.4 μm or more, even more preferably 1.5 μm or more, and particularly preferably 1.8 μm or more. A thickness within the range of 1.4 to 6.0 μm, 1.5 to 3.0 μm, or 1.5 to 2.9 μm is particularly preferred, since the polypropylene film is very thin but has excellent processability in the slitting process, excellent suppression of blocking during the vapor deposition process, and excellent processability for winding elements.

[0036] The thickness is a value measured according to the method described in (4) of the Examples below.

[0037] The thickness of the first and second layers of the polypropylene film of the present invention (and the thickness of the third layer if the film contains a third layer) is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 0.6 μm or more, from the viewpoint of making the interface between the layers clearer and easily achieving an improved effect in voltage resistance. The upper limit of the thickness is not particularly limited, but is, for example, 8.0 μm or less, 5.0 μm or less, or 2.0 μm or less.

[0038] The polypropylene film of the present invention may be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film. From the viewpoint that the difference in continuous productivity is likely to be more significant compared to conventional techniques (e.g., Patent Documents 1 to 3), the polypropylene film of the present invention is preferably a stretched film, and particularly preferably a biaxially stretched film.

[0039] In this specification, the term "polypropylene film" refers to a film in which each layer (comprising a constituent resin), including the first and second layers, contains a polypropylene resin as the main component. In this specification, "containing a polypropylene resin as the main component" means that each layer of the polypropylene film of the present invention contains 50% by mass or more of polypropylene resin relative to the total constituent resins (when the total constituent resins are taken as 100% by mass). The content of the polypropylene resin relative to the total constituent resins is preferably 75% by mass or more, and more preferably 90% by mass or more. The upper limit of the content of the polypropylene resin relative to the total constituent resins is, for example, 100% by mass, 98% by mass, etc.

[0040] The polypropylene resin is not particularly limited, and one type may be used alone, or two or more types may be used in combination.

[0041] The polypropylene resin may contain one or both of a linear polypropylene resin and a branched polypropylene resin, and may also contain one or both of a propylene homopolymer obtained by polymerizing only propylene and a propylene copolymer obtained by copolymerizing propylene with other monomers.

[0042] The weight-average molecular weight Mw of the linear polypropylene resin is preferably 250,000 or more. Furthermore, the weight-average molecular weight Mw of the linear polypropylene resin is preferably 450,000 or less. When the weight-average molecular weight Mw of the linear polypropylene resin is 250,000 or more and 450,000 or less, the resin fluidity becomes appropriate. As a result, it is easy to control the thickness of the cast sheet, and it becomes easy to produce a thin stretched film. Furthermore, it is preferable because unevenness in the thickness of the cast sheet and stretched film is less likely to occur, and appropriate stretchability can be obtained.

[0043] The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the linear polypropylene resin is preferably 5.0 or more and 11.0 or less, more preferably 6.0 or more and 10.0 or less, even more preferably 7.0 or more and 10.0 or less, and particularly preferably 7.8 or more and 9.7 or less.

[0044] When the molecular weight distribution of the linear polypropylene resin is within the above-mentioned preferred range, the thickness of the cast sheet and stretched film is less likely to be uneven, and appropriate stretchability can be obtained, which is preferable.

[0045] The heptane insoluble fraction (HI) of the linear polypropylene resin is preferably 96.0% or more, more preferably 97.0% or more. The heptane insoluble fraction (HI) of the linear polypropylene resin is preferably 99.5% or less, more preferably 99.0% or less. Here, the higher the heptane insoluble fraction, the higher the stereoregularity of the resin. When the heptane insoluble fraction (HI) is 96.0% or more and 99.5% or less, the moderately high stereoregularity leads to a moderate improvement in the crystallinity of the resin, thereby improving the voltage resistance at high temperatures. On the other hand, the solidification (crystallization) rate during cast sheet molding is moderate, resulting in moderate stretchability.

[0046] The linear polypropylene resin can be produced by a generally known polymerization method. There are no particular limitations as long as a linear polypropylene resin that can be used for polypropylene films can be produced. Examples of such polymerization methods include gas phase polymerization, bulk polymerization, and slurry polymerization.

[0047] The polymerization may be a single-stage polymerization using one polymerization reactor, or a multi-stage polymerization using at least two polymerization reactors. Furthermore, hydrogen or a comonomer may be added to the reactor as a molecular weight modifier.

[0048] The catalyst used in the polymerization can be any commonly known Ziegler-Natta catalyst, and is not particularly limited as long as it can produce a linear polypropylene resin. The catalyst may contain a co-catalyst component or a donor. By adjusting the catalyst and polymerization conditions, it is possible to control the molecular weight, molecular weight distribution, stereoregularity, etc.

[0049] The molecular weight, molecular weight distribution, differential distribution value difference, etc. of the linear polypropylene resin can be adjusted by appropriately selecting, for example, (i) the polymerization method and the conditions during polymerization, such as temperature and pressure, (ii) the shape of the reactor during polymerization, (iii) the presence or absence, type and amount of additives used, and (iv) the type and amount of catalyst used.

[0050] Specifically, the molecular weight, molecular weight distribution, etc. of the linear polypropylene resin can be adjusted, for example, by a multi-stage polymerization reaction. Examples of the multi-stage polymerization reaction include the following methods.

[0051] First, in the first polymerization step, propylene and a catalyst are supplied to a first polymerization reactor. Hydrogen, acting as a molecular weight modifier, is mixed with these components in an amount necessary to achieve the desired polymer molecular weight. For example, in the case of slurry polymerization, the reaction temperature is approximately 70 to 100°C, and the residence time is approximately 20 to 100 minutes. Multiple reactors can be used in series, for example. In this case, the polymerization product of the first step is continuously sent to the next reactor together with additional propylene, catalyst, and molecular weight modifier, followed by a second polymerization in which the molecular weight is adjusted to a lower or higher molecular weight than in the first polymerization step. By adjusting the yields (production amounts) of the first and second reactors, the composition (configuration) of the high-molecular-weight and low-molecular-weight components can be adjusted.

[0052] The molecular weight, molecular weight distribution, etc. of the linear polypropylene resin can also be adjusted by peroxidation decomposition, for example, by a peroxidation treatment using a decomposing agent such as hydrogen peroxide or an organic peroxide.

[0053] When peroxide is added to a degradable polymer such as polypropylene, a hydrogen abstraction reaction occurs from the polymer, and some of the resulting polymer radicals recombine and undergo crosslinking reactions, but most of the radicals undergo secondary decomposition (β-scission), splitting into two polymers with lower molecular weights. In other words, the higher the molecular weight component, the higher the probability of decomposition. This increases the amount of low molecular weight components, allowing the molecular weight distribution to be adjusted.

[0054] When adjusting the content of low molecular weight components by blending (resin mixing), it is preferable to dry mix or melt mix at least two or more resins with different molecular weights. Generally, a two-polypropylene blend system in which a main resin is mixed with an additive resin having a higher or lower average molecular weight in an amount of about 1 to 40 mass % is preferably used because it is easy to adjust the amount of low molecular weight components.

[0055] In this mixing adjustment, the melt flow rate (MFR) may be used as a guide for the average molecular weight. In this case, the difference in MFR between the main resin and the additive resin should be about 1 to 30 g / 10 min from the viewpoint of convenience during adjustment.

[0056] As the linear polypropylene resin, commercially available products can also be used.

[0057] Among branched polypropylene resins, branched polypropylene resins obtained by polymerizing propylene using a metallocene catalyst are preferred. Specifically, when the branched polypropylene resin is contained in the polypropylene resin, a large amount of β crystals is formed in the cast sheet. Then, 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, (approximately) arc-shaped irregularities are formed in the polypropylene film obtained by stretching, and the surface can be suitably roughened.

[0058] In addition, if a long-chain branched polypropylene resin obtained by crosslinking with a peroxide is used instead of a branched polypropylene resin polymerized using a metallocene catalyst, the α-crystal nucleating effect of the long-chain branched polypropylene resin obtained by crosslinking with a peroxide will promote the formation of α-crystals in the cast sheet and significantly suppress the formation of β-crystals. Even if a cast sheet containing α-crystals is stretched, crystallite transition does not occur, so unevenness is unlikely to form. Therefore, a branched polypropylene resin polymerized using a metallocene catalyst is suitable for roughening the surface of a polypropylene film.

[0059] Metallocene catalysts are generally metallocene compounds that form polymerization catalysts that produce olefin macromers. Branched polypropylene resins obtained by polymerizing propylene using a metallocene catalyst are preferred because they have appropriate branch chain length and branch chain spacing, resulting in excellent compatibility with linear polypropylene. They are also preferred because they provide a uniform composition and surface morphology. In the production of branched polypropylene resins, other conditions besides the type and amount of catalyst used, such as (i) the polymerization method and temperature and pressure conditions during polymerization, (ii) the reactor configuration during polymerization, and (iii) the presence or absence, type, and amount of additives, can be the same as those described in the section on the production method of linear polypropylene resins, taking into account the molecular weight, molecular weight distribution, and differential distribution value difference of the branched polypropylene resin to be produced.

[0060] The weight-average molecular weight Mw of the branched polypropylene resin is preferably 150,000 or more and 600,000 or less, more preferably 200,000 or more and 500,000 or less, even more preferably 250,000 or more and 450,000 or less, and particularly preferably 350,000 or more and 420,000 or less. When the weight-average molecular weight Mw of the branched polypropylene resin is 150,000 or more and 600,000 or less, the resin fluidity becomes appropriate. As a result, it is easy to control the thickness of the cast sheet, and it is easy to produce a thin stretched film. In addition, it is preferable because unevenness in the thickness of the cast sheet and stretched film is less likely to occur, and appropriate stretchability can be obtained.

[0061] The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the branched polypropylene resin is preferably 1.5 or more and 4.5 or less, more preferably 1.8 or more and 4.2 or less, even more preferably 2.0 or more and 4.0 or less, particularly preferably 2.1 or more and 3.9 or less, and particularly preferably 2.2 or more and 3.0 or less.

[0062] As described above, the molecular weight, molecular weight distribution, etc. of the branched polypropylene resin can be controlled by adjusting the catalyst and polymerization conditions.

[0063] The heptane insoluble fraction (HI) of the branched polypropylene resin is preferably 98.0% or more, more preferably 98.2% or more, and even more preferably 98.5% or more. The heptane insoluble fraction (HI) of the branched polypropylene resin is preferably 99.5% or less, more preferably 99.0% or less. When the HI of the branched polypropylene resin is within the above-mentioned preferred range, β crystals are more suitably formed in the cast sheet, resulting in a suitable roughening of the surface of the polypropylene film.

[0064] The content of the branched polypropylene resin is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, particularly preferably 2% by mass or more, and even more particularly preferably 2.5% by mass or more, based on 100% by mass of the resins constituting the layer. The content of the branched polypropylene resin is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, particularly preferably 7% by mass or less, and even more particularly preferably 5% by mass or less, based on 100% by mass of the resins constituting the layer.

[0065] Representative commercially available branched chain polypropylene resins include, for example, MFX3 and MFX6 manufactured by Japan Polypropylene Corporation, and MFX8 manufactured by Japan Polypropylene Corporation.

[0066] The propylene copolymer may be any copolymer such as a random copolymer, a block copolymer, or a graft copolymer. Among these, a random copolymer is preferred. The propylene copolymer is preferably a copolymer of propylene and an olefin other than propylene, and more preferably a propylene-ethylene copolymer.

[0067] The content of ethylene units in the propylene-ethylene copolymer is not particularly limited, but is, for example, 0.05 mol% or more, 0.1 mol% or more, 1 mol% or more, 2 mol% or more, 4 mol% or more, or 6 mol% or more, and the content of ethylene units is, for example, 20 mol% or less, 10 mol% or less, 9 mol% or less, or 8 mol% or less.

[0068] The weight average molecular weight (Mw) of the propylene-ethylene copolymer is preferably 250,000 or more and 800,000 or less, and more preferably 450,000 or more and 700,000 or less.

[0069] The molecular weight distribution (Mw / Mn) of the propylene-ethylene copolymer is preferably 3 or more and 12 or less, more preferably 4 or more and 11 or less, even more preferably 5 or more and 10 or less, even more preferably 5 or more and 8 or less, and particularly preferably 5 or more and 6.9 or less.

[0070] The above-mentioned physical properties of the polypropylene resin are values ​​measured according to the method described in (1) of the Examples below.

[0071] The constituent resins of the layers constituting the polypropylene film of the present invention may contain other resins besides polypropylene resin (hereinafter also referred to as "other resins"). The "other resins" are resins other than polypropylene resin, which is generally considered to be the main resin, and are not particularly limited as long as the desired polypropylene film can be obtained. Examples of other resins include polyolefins other than polypropylene, such as polyethylene, poly(1-butene), polyisobutene, poly(1-pentene), and poly(1-methylpentene); copolymers of α-olefins, such as ethylene-propylene copolymers, propylene-butene copolymers, and ethylene-butene copolymers; random copolymers of vinyl monomers and diene monomers, such as styrene-butadiene random copolymers; and random copolymers of vinyl monomers, diene monomers, and vinyl monomers, such as styrene-butadiene-styrene block copolymers. The constituent resins of the layers may contain preferably 10 parts by mass or less of the other resin per 100 parts by mass of polypropylene resin, more preferably 5 parts by mass or less, even more preferably 2 parts by mass or less, even more preferably 1 part by mass or less, and particularly preferably 0.1 parts by mass or less.

[0072] The resins constituting the layers constituting the polypropylene film of the present invention may further contain at least one additive in addition to the resin components. The "additive" refers to an additive generally used in polypropylene, and is not particularly limited as long as the desired polypropylene film can be obtained. Examples of additives include nucleating agents (α-crystal nucleating agents, β-crystal nucleating agents), antioxidants, necessary stabilizers such as chlorine absorbers and UV absorbers, lubricants, plasticizers, flame retardants, antistatic agents, inorganic fillers, organic fillers, etc. Examples of inorganic fillers include barium titanate, strontium titanate, and aluminum oxide. When using such additives, they can be contained in an amount that does not adversely affect the desired polypropylene film.

[0073] The "nucleating agent" is not particularly limited as long as it is commonly used in polypropylene and can provide the desired polypropylene film.

[0074] Examples of the nucleating agent include an α-crystal nucleating agent that preferentially nucleates α-crystals and a β-crystal nucleating agent that preferentially nucleates β-crystals.

[0075] Among α-crystal nucleating agents, organic nucleating agents include dispersion-type nucleating agents and solution-type nucleating agents. Examples of dispersion-type nucleating agents include phosphate ester metal salt-based nucleating agents, carboxylate metal salt-based nucleating agents, and rosin metal salt-based nucleating agents. Examples of solution-type nucleating agents include sorbitol-based nucleating agents, nonitol-based nucleating agents, xylitol-based nucleating agents, and amide-based nucleating agents.

[0076] Examples of the β-crystal nucleating agent include amide-based nucleating agents, di- or polycarboxylic acid metal salt-based nucleating agents, quinacridone-based nucleating agents, aromatic sulfonic acid-based nucleating agents, phthalocyanine-based nucleating agents, and tetraoxaspiro compound-based nucleating agents.

[0077] The nucleating agent can be dry-blended or melt-blended with the polypropylene raw material and pelletized before use, or can be fed into an extruder together with polypropylene pellets before use. The surface roughness of the film can be adjusted to a desired level by using a nucleating agent. A typical example of a commercially available nucleating agent is NJSTAR NU-100 manufactured by New Japan Chemical Co., Ltd., which is a β-crystal nucleating agent. When the polypropylene film contains a β-crystal nucleating agent, the content thereof is preferably 1 to 4,000 ppm by mass, more preferably 50 to 3,000 ppm by mass, relative to the mass of the resin component (mass of the entire resin component).

[0078] "Antioxidants" are generally referred to as antioxidants and are not particularly limited as long as they are used in polypropylene to obtain the desired polypropylene film. Antioxidants are generally used for two purposes. One purpose is to suppress thermal and oxidative degradation in the extruder, and the other purpose is to contribute to suppressing degradation over long-term use as a capacitor film and improving capacitor performance. Antioxidants that suppress thermal and oxidative degradation in the extruder are also called "primary agents," while antioxidants that contribute to improving capacitor performance are called "secondary agents."

[0079] Two types of antioxidants may be used for these two purposes, or one type of antioxidant may be used for both purposes.

[0080] An example of a primary agent is 2,6-di-tertiary-butyl-para-cresol (general name: BHT). Primary agents can usually be added to the polypropylene resin composition during preparation, as described later in the polypropylene film production method, for the purpose of suppressing thermal and oxidative degradation in the extruder. Most of the antioxidant added to the polypropylene resin composition for this purpose is consumed during the molding process in the extruder, and almost none remains in the film after film formation. Therefore, when the polypropylene film contains a primary agent, the content thereof is usually less than 100 ppm by mass relative to the mass of the resin components (mass of the resin components as a whole).

[0081] The secondary agent may be a hindered phenol-based antioxidant having a carbonyl group.

[0082] The "hindered phenol antioxidant having a carbonyl group" is generally understood to be a hindered phenol antioxidant having a carbonyl group, and is not particularly limited as long as the desired polypropylene film can be obtained.

[0083] Examples of the hindered phenol antioxidant having a carbonyl group include triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] (trade name: Irganox 245), 1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 259), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1010), 2,2-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1011), Examples of suitable hydroxyl groups include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1035), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1076), and N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide) (trade name: Irganox 1098). Of these, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is particularly preferred due to its high molecular weight, excellent compatibility with polypropylene, low volatility, and excellent heat resistance.

[0084] The polypropylene film may contain one or more types of hindered phenol-based antioxidants (secondary agents) having a carbonyl group for the purpose of suppressing deterioration that progresses over time during long-term use. When the polypropylene film contains one or more types of hindered phenol-based antioxidants having a carbonyl group, the content thereof is preferably 4000 ppm by mass to 6000 ppm by mass, more preferably 4500 ppm by mass to 6000 ppm by mass, relative to the mass of the resin component (mass of the resin component as a whole). From the viewpoint of achieving an appropriate effect, it is preferable that the content of the hindered phenol-based antioxidants having a carbonyl group in the film is 4000 ppm by mass to 6000 ppm by mass.

[0085] A polypropylene film containing an optimum specific range of amount of a hindered phenol-based antioxidant having a carbonyl group, which has good compatibility with polypropylene at the molecular level, is preferred because it improves long-term durability.

[0086] The term "chlorine absorbent" is generally used in polypropylene and is not particularly limited as long as it can be used to obtain the desired polypropylene film. Examples of chlorine absorbents include metal soaps such as calcium stearate. When such a chlorine absorbent is used, it can be contained in an amount that does not adversely affect the desired polypropylene film.

[0087] In each layer of the polypropylene film of the present invention, the constituent resins including constituent resin 1 and constituent resin 2 preferably contain a linear polypropylene resin, more preferably a linear propylene homopolymer. The content of this component is, for example, 50% by mass or more, preferably 75% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to 100% by mass of the constituent resins.

[0088] There are no particular limitations on the means for adjusting the crystallization temperature of the resins constituting the layers. For example, the crystallization temperature can be increased by adding a nucleating agent, or by adding a branched polypropylene resin. The crystallization temperature can also be adjusted by adjusting the type and content of the α-olefin to be copolymerized. For example, propylene copolymers (e.g., propylene-ethylene copolymers) tend to have lower crystallization temperatures than propylene homopolymers. Furthermore, even between linear polypropylene resins (particularly propylene homopolymers), the crystallization temperature can be adjusted by adjusting the molecular weight distribution and heptane insoluble content.

[0089] In a preferred embodiment of the present invention (for example, when constituent resin 1 and constituent resin 2 contain linear polypropylene resins), Constituent Resin 1 and Constituent Resin 2 differ in at least one selected from the group consisting of the concentration of a nucleating agent, the concentration of a branched polypropylene resin, and the molecular weight distribution and / or heptane-insoluble content of a linear polypropylene resin; and / or The concentration ratio of propylene homopolymer to propylene copolymer is different between constituent resin 1 and constituent resin 2. It is preferable.

[0090] The different concentrations refer to both cases where the concentration in one constituent resin is 0 (does not contain the component) and the concentration in the other constituent resin is greater than 0 (contains the component), and cases where the concentrations in both constituent resins are greater than 0.

[0091] The concentration ratio of the propylene homopolymer to the propylene copolymer is the ratio of the masses of these two polymers in the constituent resin.

[0092] The different concentration ratios refer to both cases where the concentration of one of the propylene homopolymer and propylene copolymer in one or both of the constituent resins is 0 (the component is not contained), and cases where the concentration of each of the propylene homopolymer and propylene copolymer in both of the constituent resins is greater than 0 (the component is contained).

[0093] In a particularly preferred embodiment of the present invention, Constituent resin 1 and constituent resin 2 contain a linear polypropylene resin (preferably a linear propylene homopolymer) (preferably, based on 100% by mass of the constituent resin, the content is, for example, 50% by mass or more, preferably 75% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more), The concentration of the branched polypropylene resin differs between constituent resin 1 and constituent resin 2, and more preferably the concentration in one constituent resin is 0 (the component is not contained) and the concentration in the other constituent resin is greater than 0 (from the viewpoint of voltage resistance, preferably 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 2% by mass or more, or 2.5% by mass or more, and 10% by mass or less, 7% by mass or less, 5% by mass or less, 4% by mass or less, or 3.5% by mass or less, relative to 100% by mass of the constituent resins).

[0094] When the polypropylene film of the present invention includes a third layer, the preferred embodiments of the above-mentioned constituent resins 1 and 2 can also be applied to constituent resins 2 and 3.

[0095] The polypropylene film of the present invention has excellent continuous productivity and also has a higher voltage resistance. For example, the polypropylene film of the present invention has a voltage resistance of 550V as measured by the method of (5) in the Examples described later. DC / μm (unit: pieces / cm 2 ) is lower, preferably 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.15 or less. The lower limit of the density is not particularly limited, and is, for example, 0, 0.01, 0.02, or 0.05.

[0096] The method for producing the polypropylene film of the present invention is not particularly limited, but examples thereof include the following method. The polypropylene film of the present invention can be produced by the following steps: a melting step of melting a resin component containing a polypropylene resin to obtain a molten resin composition; A lamination step of laminating multiple layers (two or more layers) of the molten resin composition to obtain a molten laminate; A discharge step of discharging the molten laminate to obtain a film. It can be suitably produced by a method comprising the steps of:

[0097] In the melting step, a resin component containing a polypropylene resin and various additives such as an antioxidant, which are added as needed, are melt-kneaded to obtain a molten resin composition. (1) A method in which a resin component and various additives are kneaded to produce pellets of a resin composition, and the pellets of the resin composition are melt-kneaded in a kneader; (2) A method in which a resin component and various additives are pre-mixed to produce masterbatch pellets, and the masterbatch pellets and resin pellets are melt-mixed in a kneader; or (3) A method in which the resin components and various additives are dry-blended without making a masterbatch, and then melt-kneaded in a kneader. The above method (1) or (2) is preferred because it allows the vicinity of the extrusion kneader to be kept in a clean environment. As a mixing device for dry blending, a batch type such as a tumbler or wing mixer, or a continuous type metering mixer can be used.

[0098] The melt-kneading temperature is usually 200 to 300°C, and preferably 240 to 280°C. When the melt-kneading temperature is within the above range, the insulating properties of the film are less likely to deteriorate due to thermal degradation of the resin components, and kneading is carried out sufficiently, allowing the film components to be mixed uniformly. In order to suppress deterioration during resin kneading, an inert gas such as nitrogen may be purged into the extrusion kneader.

[0099] The extrusion kneader is not particularly limited, and a single-screw type, twin-screw type, or multi-screw type can be used as appropriate. In the case of a twin or more screw type, either a co-rotating or counter-rotating kneading type can be used by adjusting the kneading conditions so as not to cause significant resin degradation, but a single-screw type or a co-rotating twin-screw type is preferred because it is less likely to cause thermal degradation of the resin.

[0100] Before melt-kneading the resin component, a treatment to remove moisture contained in the resin component may be performed. The method for removing moisture is not particularly limited, but examples thereof include heat treatment. The temperature for such heat treatment is, for example, 100°C or higher, preferably 130°C or higher, and more preferably 150°C or higher, from the viewpoint of sufficiently removing moisture, and is, for example, 350°C or lower, from the viewpoint of suppressing thermal decomposition of the resin component. The heat treatment time is, for example, 1 hour or higher, preferably 2 hours or higher, from the viewpoint of sufficiently removing moisture, and is usually 24 hours or shorter, for example, 10 hours or shorter, from the viewpoint of suppressing thermal decomposition of the resin component. This treatment can suppress hydrolysis of the resin component due to moisture.

[0101] In the lamination step, the molten resin composition obtained in the melting step is laminated into a plurality of layers to obtain a molten laminate. In the lamination step, two or more layers of the molten resin composition are laminated.

[0102] In the lamination step, the method for laminating the molten resin composition to obtain a molten laminate is not particularly limited, but for example, a molten laminate can be obtained by co-extrusion using a multi-manifold or a feed block.

[0103] When the lamination process is performed using a multi-manifold, a multi-manifold is used that has manifolds in the number equal to or greater than the desired number of layers. The molten resin composition introduced into the multi-manifold is divided and flows into each manifold, spreading in the width direction of the multi-manifold. In this case, it is preferable that the shapes and cross-sectional areas of all the manifolds are the same. If the shapes and cross-sectional areas of all the manifolds are the same, the thicknesses of the layers included in the resulting capacitor film will be uniform. The molten resin compositions flowing through the manifolds then join together near the end of the multi-manifold and are laminated, resulting in a molten laminate having the desired number of layers.

[0104] On the other hand, when the lamination process is performed using a feed block, the molten resin composition is introduced into the feed block. The molten resin composition introduced into the feed block is first passed through a multiplier block. This multiplier block has m (m is an integer of 2 or more) divided flow paths arranged to divide the molten resin composition. The m divided molten resin compositions are then laminated in the thickness direction and widened to form a molten laminate of m layers.

[0105] Furthermore, a molten laminate of m × n layers can be formed by passing the laminated m-layer molten laminate through another multiplier block having n (n is an integer of 2 or more) divided flow paths. By repeating the same operation, a molten laminate having the desired number of layers can be obtained.

[0106] Here, the multi-manifold and feed block used in the present invention are preferably provided with a heating means, for example, a heater. The position where the heating means is provided is not particularly limited as long as it can heat the molten resin composition.

[0107] The heating temperature in this case is usually 200 to 300°C, and preferably 240 to 280°C. In the case of polystyrene resin, it is usually 170 to 340°C, and preferably 180 to 330°C. In the case of polyethylene terephthalate resin, it is usually 250 to 320°C, and preferably 270 to 310°C. When the heating temperature is within the above range, the insulating properties of the film are less likely to deteriorate due to thermal degradation of the resin components, and kneading is carried out sufficiently, allowing the film components to be mixed uniformly.

[0108] In the extrusion step, the molten laminate obtained in the lamination step is extruded to obtain a film. The molten laminate is extruded from a die (preferably a T-die) connected to a multi-manifold or a feed block, etc., to form a film. The film can be formed into an unstretched cast raw sheet by cooling and solidifying it on at least one metal drum. The temperature of the metal drum (casting temperature) is usually 40 to 140°C, preferably 60 to 120°C, more preferably 80 to 110°C, and even more preferably 90 to 100°C. The thickness of the cast raw sheet is usually 40 μm to 2000 μm, preferably 50 μm to 1800 μm, more preferably 60 μm to 1400 μm, even more preferably 70 μm to 900 μm, particularly preferably 80 μm to 800 μm, and even more preferably 90 μm to 600 μm.

[0109] The method for producing the polypropylene film of the present invention may further include a stretching step of stretching the film (cast raw sheet). The stretching step can be carried out by uniaxial or biaxial stretching, but is preferably carried out by biaxial stretching from the viewpoint of thickness uniformity in the width direction.

[0110] When biaxially stretching is performed, the film (cast raw sheet) can be biaxially stretched according to a conventional method. Biaxial stretching involves biaxial orientation in both the longitudinal and transverse directions. Examples of stretching methods include simultaneous or sequential biaxial stretching, with sequential biaxial stretching being preferred. In the case of polypropylene, for example, sequential biaxial stretching involves first maintaining the film at a temperature of preferably 100 to 180°C (more preferably 100 to 170°C, and even more preferably 120 to 165°C) and passing it between rolls with a speed difference to stretch it 3 to 7 times in the machine direction. Subsequently, the stretched film is introduced into a tenter and stretched 3 to 11 times (e.g., 6 to 11 times, preferably 8 to 11 times) in the width (transverse) direction at a temperature of preferably 150°C or higher, more preferably 150 to 180°C, followed by relaxation, heat setting, and winding. The wound film can be subjected to an aging treatment in an atmosphere of, for example, about 20 to 45°C, and then cut to a desired product width.

[0111] Furthermore, heat treatment for crystal orientation may be performed while both ends of the film are fixed with clips, etc. The heat treatment temperature is, for example, 150 to 300°C, preferably 180 to 280°C, and more preferably 200 to 260°C, and the heat treatment time is, for example, 1 second to 3 minutes, preferably 5 seconds to 1 minute, and more preferably 10 seconds to 40 seconds.

[0112] Such a stretching process results in a film with excellent mechanical strength and rigidity, and the surface irregularities are more clearly defined, resulting in a finely roughened stretched film. It is preferable to impart a suitable surface roughness to the surface of the stretched film to improve winding suitability and also to improve capacitor performance.

[0113] The polypropylene film of the present invention preferably has a surface roughness of 0.01 μm to 0.20 μm in centerline average roughness (Ra) on at least one surface, and is preferably finely roughened to 0.1 μm to 1.5 μm in maximum height (Rz, Rmax as defined by the old JIS). When Ra and Rz are within the above-mentioned preferred ranges, the surface can be finely roughened, and during capacitor processing, wrinkles are less likely to occur during winding, allowing the element to be wound up smoothly. Furthermore, uniform contact between films is possible, which can improve the voltage resistance and long-term voltage resistance of the capacitor.

[0114] Here, "Ra" and "Rz" (Rmax defined in the old JIS) are, for example, "Ra" and "Rz" refer to values ​​measured using a commonly used stylus surface roughness meter (for example, a stylus surface roughness meter using a diamond stylus, etc.) in accordance with the method specified in JIS-B0601:2001, etc. More specifically, "Ra" and "Rz" can be determined using, for example, a three-dimensional surface roughness meter, Surfcom 1400D-3DF-12, manufactured by Tokyo Seimitsu Co., Ltd., in accordance with the method specified in JIS-B0601:2001.

[0115] Various known roughening methods, such as embossing and etching, can be used to impart fine irregularities to the film surface. Among these methods, roughening methods using β-crystals, which do not require the inclusion of impurities, are preferred. The proportion of β-crystals produced can generally be controlled by changing the casting temperature and casting speed. Furthermore, the proportion of β-crystals melting / transition can be controlled by the roll temperature in the longitudinal stretching process. A finely roughened surface can be obtained by selecting optimal manufacturing conditions for these two parameters, β-crystal production and its melting / transition.

[0116] The film obtained by the above method may have another layer laminated on one or both sides of the film. The method for laminating the other layer is not particularly limited, but examples include a method in which a resin layer is formed by applying a coating liquid containing a resin and drying or heating the coating, and a method in which the other layer (film) is laminated, if necessary, using an adhesive (e.g., an acrylic adhesive, a silicone adhesive, an olefin adhesive), etc. By laminating the other layer, the oxygen gas permeability coefficient (Cmu) and Cmo / Cmu of the resulting laminated film can be adjusted. The lamination of the other layer may be performed before or after biaxial stretching. When the other layer is laminated before biaxial stretching, the other layer can also be stretched during biaxial stretching.

[0117] The polypropylene film of the present invention can be subjected to corona discharge treatment online or offline after the stretching and heat setting processes in order to improve adhesive properties in subsequent processes such as metal deposition. Corona discharge treatment can be performed using a known method. The atmospheric gas used is preferably air, carbon dioxide, nitrogen, or a mixture thereof.

[0118] In another embodiment of the present invention, a metal layer-integrated polypropylene film is provided, comprising the polypropylene film of the present invention and a metal layer laminated on one or both sides of the polypropylene film. In the process of producing the metal layer-integrated polypropylene film, a metal vapor-deposited film is formed on one or both sides of the polypropylene film of the present invention. Methods for forming the metal vapor-deposited film include, for example, vacuum deposition and sputtering, with vacuum deposition being preferred from the standpoints of productivity and economy. When forming a metal vapor-deposited film by vacuum deposition, a known method such as a crucible method or a wire method can be appropriately selected. The metal constituting the metal vapor-deposited film can be a single metal such as zinc, lead, silver, chromium, aluminum, copper, or nickel, or a mixture or alloy of multiple metals selected from these metals. From the standpoints of environmental considerations, economy, and film capacitor performance, particularly the temperature and frequency characteristics of capacitance and insulation resistance, it is preferable to use a single metal, metal mixture, or alloy selected from zinc and aluminum as the metal constituting the metal vapor-deposited film.

[0119] From the viewpoint of the electrical characteristics of the capacitor, the film resistance of the metal vapor deposition film (metal film) is preferably 1 to 150 Ω / □. Even within this range, a higher resistance is desirable from the viewpoint of self-healing properties, and a film resistance of 5 Ω / □ or more is more preferable, and 10 Ω / □ or more is even more preferable. Furthermore, from the viewpoint of safety as a capacitor, the film resistance is more preferably 100 Ω / □ or less, even more preferably 50 Ω / □ or less, and particularly preferably 20 Ω / □ or less. The film resistance of the metal vapor deposition film can be measured during metal deposition, for example, by a two-terminal method known to those skilled in the art. The film resistance of the metal vapor deposition film can be adjusted, for example, by adjusting the output of the evaporation source to control the amount of evaporation. The above-mentioned range of film resistance of the metal vapor deposition film is suitable, for example, for solid deposition or transferring a special margin. In the case of oblique deposition, deposition may be performed by varying the thickness of the deposited film to a film resistance of approximately 50 to 100 Ω / □. The thickness of the metal film is not particularly limited, but is preferably 1 to 200 nm.

[0120] When forming a metal vapor-deposited film on one or both sides of the film, it is preferable to leave a certain width from one end of the film undeposited to form an insulating margin so that the film will become a capacitor when rolled up. Furthermore, to strengthen the bond between the metal layer-integrated polypropylene film and the metallikon electrode, it is preferable to form a heavy edge structure on the end opposite the insulating margin, and the film resistance of the heavy edge is usually 2 to 8 Ω / □, preferably 3 to 6 Ω / □.

[0121] There are no particular restrictions on the margin pattern of the metal vapor deposition film to be formed, but from the perspective of the safety of the film capacitor, a pattern including a so-called special margin, such as a fishnet pattern or a T-margin pattern, is preferred. Forming a metal vapor deposition film on one or both sides of the film in a pattern including a special margin improves the safety of the resulting film capacitor and prevents damage and short circuits of the film capacitor, which is preferable. As a method for forming the margin, any known method can be used without any restrictions, such as a tape method in which tape is used for masking during vapor deposition, or an oil method in which oil is used for masking.

[0122] In another embodiment of the present invention, there is also provided a capacitor (also referred to as a capacitor element, a film capacitor element, or simply an element) comprising the above-mentioned metal layer-integrated polypropylene film. The capacitor can be manufactured using the above-mentioned metal layer-integrated polypropylene film. For example, a film capacitor element can be manufactured by stacking two metal layer-integrated polypropylene films prepared as described above as a pair, overlapping and winding them so that the metal vapor deposition film and the polypropylene film of the present invention are alternately laminated, and then forming a pair of metallikon electrodes on both end surfaces by metal spraying.

[0123] When producing a capacitor element, two metal layer-integrated polypropylene films are usually stacked and wound with the insulating margins facing opposite sides. The two metal layer-integrated polypropylene films are preferably stacked with a 0.5 to 2 mm offset. The winding machine used is not particularly limited, and an automatic winding machine, Model 3KAW-N2, manufactured by Kaito Seisakusho Co., Ltd., can be used, for example.

[0124] After winding, the resulting wound product is usually subjected to a heat treatment (hereinafter sometimes referred to as "heat pressing") while applying pressure. If the film capacitor element is properly tightened and its crystal structure is appropriately changed by the heat pressing, mechanical and thermal stability can be obtained. However, if the element is excessively tightened or its crystal structure is excessively changed by the heat pressing, the film may be thermally damaged and shrink, resulting in problems such as thermal wrinkles and molding defects. From this point of view, the optimum pressure to be applied varies depending on the thickness of the polypropylene film of the present invention, but is preferably 10 × 10 4 ~450×10 4 Pa is preferred, and 15×10 4 ~300×10 4 Pa, more preferably 20 × 10 4 ~150×10 4 Pa. The heat treatment temperature is preferably 100 to 120° C. The heat treatment time is preferably 5 hours or more, more preferably 10 hours or more, from the viewpoint of obtaining mechanical and thermal stability, but is preferably 20 hours or less, more preferably 15 hours or less, from the viewpoint of preventing molding defects such as heat wrinkles and molding.

[0125] Next, metal is sprayed onto both end surfaces of the wound material to form metallikon electrodes, producing a film capacitor element. Electrode terminals are typically joined to the metallikon electrodes. The joining method for the electrode terminals is not particularly limited, but can be performed by welding, ultrasonic welding, or soldering, for example. Furthermore, to provide weather resistance and, in particular, to prevent humidity degradation, the capacitor element is preferably encapsulated in a case and sealed with a resin such as epoxy resin. [Example]

[0126] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0127] (1) Preparation of materials The linear propylene homopolymers used to produce the polypropylene films of the Examples and Comparative Examples are listed in Table 1. Mn is the number average molecular weight, Mw is the weight average molecular weight, and these units are kDa. HI is the heptane insoluble fraction.

[0128] [Table 1]

[0129] Furthermore, linear propylene-ethylene copolymers were used to produce the polypropylene films of the examples and comparative examples. The details of the resins are shown in Table 2.

[0130] [Table 2]

[0131] Furthermore, to produce the polypropylene films of the Examples and Comparative Examples, MFX6 manufactured by Japan Polypropylene Corporation was used as the branched chain polypropylene resin. The details of this resin are shown in Table 3.

[0132] [Table 3]

[0133] Two types of nucleating agents were used to produce the polypropylene films of the Examples and Comparative Examples. The details of these nucleating agents are shown in Table 4.

[0134] [Table 4]

[0135] Furthermore, polyethylene resin (PE, Ethylene F-300SP manufactured by Prime Polymer Co., Ltd.) was used to produce the film of the comparative example.

[0136] The physical properties shown in Tables 1 to 3 were measured as follows.

[0137] <Measurement of average molecular weight and molecular weight distribution of various linear polypropylene resins> Using SEC (size exclusion chromatography), various average molecular weights and various molecular weight distributions were measured under the following conditions. Apparatus: HLC-8321GPC / HT (detector: differential refractometer (RI)) (manufactured by Tosoh Corporation) Column: TSKgel guard column H HR (30)HT(7.5mmI.D.×7.5cm)×1 + TSKgel GMH HR -H(20)HT(7.8mmI.D.×30cm)×3 (Tosoh Corporation) Eluent: 1,2,4-trichlorobenzene (Fujifilm Wako Pure Chemical Industries, Ltd., for GPC) + dibutylhydroxytoluene (0.05%) Flow rate: 1.0mL / min Detection condition: polarity=(-) Injection volume: 300μL Column temperature: 140℃ System temperature: 40°C Sample concentration: 1 mg / mL Pretreatment: The samples were weighed, added with a solvent (1,2,4-trichlorobenzene with 0.1% dibutylhydroxytoluene), and dissolved by shaking at 140°C for 1 hour. Then, the samples were heated and filtered through a 0.5 μm sintered filter. Visual observation of the sample solutions revealed no insoluble matter. Calibration curve: A quintic approximation calibration curve was prepared using standard polystyrene from Tosoh Corporation. However, the molecular weight was converted to the molecular weight of polypropylene using the Q-factor.

[0138] From the calibration curve and SEC chromatogram obtained, the number average molecular weight (Mn) and weight average molecular weight (Mw) were obtained using the analytical software for the measuring device. The molecular weight distribution (Mw / Mn) was obtained using the Mw and Mn values.

[0139] <Measurement of various average molecular weights and molecular weight distributions of branched polypropylene resin> Using SEC-MALS (size exclusion chromatography-multi-angle light scattering detector), various average molecular weights and various molecular weight distributions were measured under the following conditions. This method involves fractionating molecules by molecular size using SEC, measuring the absolute molecular weight using MALS, and then measuring the average molecular weight. Apparatus: HLC-8321GPC / HT (with built-in differential refractometer (RI)) (manufactured by Tosoh Corporation) Light scattering detector: DAWN HELEOS (Wyatt Technology) MALS laser wavelength: 664 nm Column: TSKgel guard column H HR (30)HT(7.5mmI.D.×7.5cm)×1 + TSKgel GMH HR -H(20)HT(7.8mmI.D.×30cm)×3 (Tosoh Corporation) Eluent: 1,2,4-trichlorobenzene (Fujifilm Wako Pure Chemical Industries, Ltd., for GPC) + dibutylhydroxytoluene (0.05%) Flow rate: 1.0mL / min Injection volume: 300μL Column temperature: 140℃ System temperature: 40°C Sample concentration: 1 mg / mL Pretreatment: The samples were weighed, added with a solvent (1,2,4-trichlorobenzene with 0.1% dibutylhydroxytoluene), and dissolved by shaking at 140°C for 1 hour. Then, the samples were heated and filtered through a 0.5 μm sintered filter. Visual observation of the sample solutions revealed no insoluble matter.

[0140] Data processing was performed using analysis software Astra Ver. 5.3.4 manufactured by Wyatt Technology Co., Ltd. Analysis was performed under the following conditions. The absolute molecular weight and radius of gyration were calculated from the Zimm plot. The refractive index (1.501) of 1,2,4-trichlorobenzene at 140°C used in the calculation was determined by first approximation from the refractive index values ​​at 20°C and 135°C. The refractive index concentration increment (dn / dc) of the sample was determined based on the literature value (-0.092 mL / g). Reference: K. Lederer and I. Mingozzi, Pure and Applied Chemistry, 69(5), 993-1006(1997). In GPC-MALS, there are regions where it is difficult to evaluate the absolute molecular weight and radius of gyration for the following reasons. Therefore, these regions were excluded from the scope of absolute molecular weight calculation and radius of gyration evaluation. Low concentration (both high and low molecular weight): The sample concentration is insufficient at the base of the peak in the chromatogram, making it difficult to obtain sufficient sensitivity. Isotropic scattering (low molecular weight only): When the molecular size is less than approximately 1 / 20 of the wavelength of the incident light, the scattered light does not exhibit anisotropy, and the radius of gyration cannot be obtained based on the measurement principle.

[0141] The radius of gyration (Rw), number average molecular weight (Mn), and weight average molecular weight (Mw) were obtained from the above analysis. The molecular weight distribution (Mw / Mn) was calculated using the Mw and Mn values.

[0142] <Measurement of heptane insolubles [HI]> Polypropylene resin was press-molded to a size of 10 mm x 35 mm x 0.3 mm to prepare a measurement sample of approximately 3 g. Next, approximately 150 mL of heptane was added and Soxhlet extraction was performed for 8 hours. The heptane-insoluble content was calculated from the sample mass before and after extraction.

[0143] <Measurement of ethylene unit content> The content of ethylene units was determined using a Fourier transform nuclear magnetic resonance (FT-NMR) spectrometer under the following conditions.

[0144] Measuring instrument: Varian, high-temperature FT-NMR VNMRS-400 Observation kernel: 13 C(100.6MHz) Measurement mode: Inverse gated decoupling Shift standard: 5-unit propylene chain (mmmm) (21.86 ppm) The ethylene unit content (mol%) was calculated from the signal integral value of methylene carbon based on the head-to-tail bond dimer, with reference to, for example, "Y.-D. Zhang et al., Polym. J., Vol. 35, p. 551 (2003)".

[0145] (2) Preparation of resin composition <pp-a> Only pellets of PP-A (Table 1) were charged into an extruder from a hopper and melted to prepare a resin composition.

[0146] <pp-b> Only pellets of PP-B (Table 1) were charged into an extruder from a hopper and melted to prepare a resin composition.

[0147] <pp-c> Only pellets of PP-C (Table 1) were charged into an extruder from a hopper and melted to prepare a resin composition.

[0148] <pp-d> Only the pellets of PP-D (Table 1) were charged from the hopper into the extruder and melted to prepare a resin composition.

[0149] <PP-A / Nucleating Agent 1> PP-A (Table 1) and Nucleating Agent 1 (Table 4) were made into a masterbatch by preliminary kneading. Then, the masterbatch and PP-A were metered and mixed at a ratio such that the concentration of Nucleating Agent 1 was 2500 ppm, charged from the hopper into the extruder, and melted to prepare a resin composition.

[0150] <PP-A / Nucleating Agent 2> PP-A (Table 1) and Nucleating Agent 2 (Table 4) were made into a masterbatch by preliminary kneading. Then, the masterbatch and PP-A were metered and mixed at a ratio such that the concentration of Nucleating Agent 2 was 200 ppm, charged from the hopper into the extruder, and melted to prepare a resin composition.

[0151] <PP-A / Branched PP> PP-A (Table 1) and Branched PP (Table 3) were metered and mixed at a ratio such that the concentration of Branched PP was 3 wt%, charged from the hopper into the extruder, and melted to prepare a resin composition.

[0152] <pp-pe> Only pellets of PP-PE (Table 2) were fed into an extruder from a hopper and melted to prepare a resin composition.

[0153] <pe> Only pellets of PE (polyethylene resin) were fed into an extruder from a hopper and melted to prepare a resin composition.

[0154] (3) Measurement of crystallization temperature Each of the pellets of the resin composition obtained in the above "(2) Preparation of resin composition" was fed into an extruder from a hopper, melted, passed through a polymer filter, and extruded from a die at 260°C. The pellets were then cooled and solidified while being pressed by air pressure using an air knife onto a cooling drum whose surface temperature was adjusted to 95°C, to obtain an unstretched sheet having a thickness of 180 μm.

[0155] The crystallization temperature was measured by cutting a 5 mg sample from the unstretched sheet, sealing it in an aluminum pan, and using a power compensation differential scanning calorimeter (DSC) (Diamond DSC, manufactured by Perkin Elmer) under the following conditions.

[0156] The sample was heated in a nitrogen atmosphere at a temperature increase rate of 20°C / min, then held at 280°C for 5 minutes, and cooled at a temperature decrease rate of 20°C / min. The crystallization peak at this time was determined as the crystallization temperature.

[0157] The results are shown in Table 5.

[0158] [Table 5]

[0159] (4) Film preparation Example 1 A film consisting of a first layer (constituent resin: PP-A / nucleating agent 1), a second layer (constituent resin: PP-A), and a third layer (constituent resin: PP-A / nucleating agent 1) laminated in this order was produced as follows: PP-A / nucleating agent 1 was fed into a single-screw extruder a via a hopper, and PP-A was fed into a separate single-screw extruder b via a hopper. PP-A / nucleating agent 1 and PP-A were each melted and extruded through a polymer filter at 260°C from a multi-manifold die to form a three-layer laminate film (first layer / second layer / third layer) (the ratio of extruded resin amounts from extruder a to extruder b was 1:1). The film was then cooled and solidified by air pressure pressing the film onto a cooling drum (the surface temperature of which was adjusted to 95°C) using an air knife, yielding an unstretched sheet with a thickness of 180 μm. The unstretched sheet was then heated to 146°C while in contact with a metal roll, and stretched approximately 4.6 times in the machine direction between rolls with different peripheral speeds. The uniaxially stretched film was then clamped and introduced into a hot air oven, preheated to 170°C, and stretched approximately 10 times in the width direction at 155°C. Subsequently, heat setting was performed at 165°C while allowing approximately 10% relaxation in the width direction, continuously obtaining a laminated film with a thickness of approximately 2.8 μm (thickness ratio of first layer:second layer:third layer = 1:2:1). The edges of the resulting laminated film were trimmed, and the film was wound around a core to obtain a roll of laminated film.

[0160] The overall thickness of the resulting film was measured as follows: under an environment of 23±2°C temperature and 50±5% RH humidity, a paper thickness measuring instrument MEI-11 (measurement pressure 100 kPa, descending speed 3 mm / sec, measurement probe φ=16 mm, measuring force 20.1 N) manufactured by Citizen Seimitsu Co., Ltd. was used. The sample was cut from the roll with 10 or more sheets still stacked, and was handled so as not to wrinkle or trap air in the film during cutting. Five measurements were taken for each 10-sheet stack sample, and the thickness was calculated by dividing the average of the five measurements by 10.

[0161] <Examples 2 to 9 and Comparative Examples 1 to 7> Laminated films (Examples 1 to 9 and Comparative Examples 4 to 7) and single-layer films (Comparative Examples 1 to 3) were obtained in the same manner as in Example 1, except that the layer structure and / or constituent resins and / or film thickness and / or composition ratio of each layer were changed as shown in Tables 6 and 7.

[0162] (5) Voltage resistance measurement Using the biaxially stretched films of the examples and comparative examples, a test voltage of 550V was conducted as an index of voltage resistance. DC The cumulative breakdown density in μm was measured as follows.

[0163] As shown in Figure 1, a lower electrode 1 and an upper electrode 2 are used, and a film S (280 mm x 150 mm) for measurement is sandwiched between the two electrodes. DC The cumulative breakdown density in μm was measured.

[0164] First, a brass plate (320 mm × 250 mm), conductive rubber (280 mm × 150 mm), and aluminum foil (280 mm × 150 mm) were laminated in this order to form a laminate 10. A polypropylene sheet 11 (outer dimensions: 280 mm × 150 mm) with a rectangular cutout (100 mm × 30 mm) in the center (hereinafter, this portion will be referred to as the "window" or "window portion") was placed on the aluminum foil side of the laminate 10 to produce a lower electrode 1 including the laminate 10 and the polypropylene sheet 11. In this case, the thickness of the polypropylene sheet 11 only needed to be sufficiently thicker than the thickness of the film S to be measured, so it was set to 22 μm in this measurement. A film S for measurement was placed on the polypropylene sheet 11 side of the lower electrode 1 produced as described above. At this time, the film S for measurement was placed so as to contact the entire surface of the laminate 10 (specifically, the aluminum foil of the laminate) of the lower electrode 1 exposed through the window portion.

[0165] The upper electrode 2 was fabricated using the following procedure. First, a polypropylene film 21 (280 mm × 150 mm, fully coated) with a thickness of 6 μm and an aluminum-vapor-deposited surface 22 on one side was placed so that the vapor-deposited surface 22 was in contact with the film S placed on the lower electrode 1. One end of the polypropylene film 21 was folded back to expose the vapor-deposited surface 22 at the end of the polypropylene film 21. However, the exposed vapor-deposited surface 22 did not overlap the window in the thickness direction. Next, a cylindrical brass electrode 23 (25 mm diameter, 65 mm height) was placed on the exposed vapor-deposited surface 22, thereby fabricating the upper electrode 2 comprising the polypropylene film 21 with an aluminum-vapor-deposited surface 22 on one side and the brass electrode 23. In this way, a measuring device was assembled in which the film S was sandwiched between the upper electrode 2 and the lower electrode 1. In this measuring device, the sizes of the polypropylene film, brass plate, conductive rubber, aluminum foil, and polypropylene sheet to be measured need only be sufficiently larger than the size of the window, so the above sizes were used in this measurement.

[0166] Next, in the measuring device, the brass plate of the lower electrode 1 and the brass electrode 23 of the upper electrode 2 were electrically connected by a DC power supply. DC After applying a voltage of 450V / μm for 1 minute, the number of breakdown points in the area located within the window of the measurement film S was visually counted. When breakdown occurs in the film S, the breakdown area appears cloudy compared to areas without breakdown, so these areas were considered to be breakdown points and the number of breakdown points was counted. After this count, a voltage of 450V / μm was applied. DC After applying a voltage of 50 V / μm for 1 minute, the number of breakdown points was visually counted in the same manner. DC The number of breakdown points that occur when the voltage is increased by 1 / μm and applied for 1 minute at each voltage is counted visually. DC After all voltages were applied, the voltage was increased to 550V / μm. DC The cumulative number of breakdown points that occurred when the voltage was applied up to / μm was calculated based on the window area (100mm x 30mm = 30cm 2 ) to obtain the cumulative number of breakdown points (pieces / cm 2 The measured film S was replaced with a new film S, and the cumulative number of dielectric breakdowns (number / cm 2 ) was calculated, and the cumulative number of dielectric breakdown points (pieces / cm) obtained by measuring a total of five test films was calculated. 2 ) average value of polypropylene film 550V DC The cumulative dielectric breakdown density was calculated as the density of dielectric breakdown points per μm.

[0167] By using the lower electrode 1 and upper electrode 2 for measurement, it is possible to apply a voltage accurately to the area of ​​the film that overlaps (faces) the window, and furthermore, creeping discharge is prevented, so that the 550V of the polypropylene film can be measured with higher accuracy. DC The cumulative breakdown density in μm can be measured.

[0168] (6) Evaluation of continuous productivity The production of the biaxially stretched films of the Examples and Comparative Examples was started, and the time during which continuous film production was possible from the time when the obtained film thickness reached ±2% of the target thickness until the film broke or the like (hereinafter also referred to as "continuous film production time") was measured. The time when the thickness reached ±2% of the target thickness was confirmed by cutting the film from the center in the width direction and measuring the film thickness using a micrometer (JIS-B7502) in accordance with JIS-C2330. Based on the obtained continuous film production time, continuous productivity was evaluated according to the following evaluation criteria.

[0169] (Evaluation criteria for continuous productivity) A: Film formation was possible without stretching fracture even after 8 hours. B: A film was formed without breakage during stretching in more than 1 hour but less than 8 hours. C: The film broke during stretching within 1 hour, and film formation for more than 1 hour was impossible.

[0170] (7) Measurement and evaluation results The layer structure and constituent resins of the biaxially stretched films of the examples and comparative examples, the difference in crystallization temperature between layers (0°C for single layer films), and the voltage resistance (550V DC The measurement results of the cumulative dielectric breakdown density (cumulative dielectric breakdown point density in μm / μm) and the evaluation results of continuous productivity are shown in Tables 6 and 7.

[0171] [Table 6]

[0172] [Table 7] < / pe>

Claims

1. A polypropylene film consisting of multiple layers including a first layer and a second layer adjacent to the first layer, wherein the difference between the crystallization temperature 1 of the constituent resin 1 of the first layer and the crystallization temperature 2 of the constituent resin 2 of the second layer is 3.0°C or more.

2. The polypropylene film according to claim 1, wherein the difference is 5.0°C or more.

3. The polypropylene film according to claim 1, wherein the difference is 25.0°C or less.

4. The polypropylene film according to claim 1 , wherein the first and second constituent resins contain linear polypropylene resins.

5. The constituent resin 1 and the constituent resin 2 are different in at least one selected from the group consisting of the concentration of a nucleating agent, the concentration of a branched polypropylene resin, and the molecular weight distribution and / or heptane-insoluble content of a linear polypropylene resin; and / or the concentration ratio of propylene homopolymer to propylene copolymer is different between the constituent resin 1 and the constituent resin 2; The polypropylene film according to claim 4.

6. 2. The polypropylene film according to claim 1, comprising a third layer adjacent to the second layer, wherein the difference between the crystallization temperature 2 of the constituent resin 2 of the second layer and the crystallization temperature 3 of the constituent resin 3 of the third layer is 3.0°C or more.

7. 10. The polypropylene film of claim 1, consisting of five or fewer layers.

8. The polypropylene film according to any one of claims 1 to 7, which is a biaxially oriented polypropylene film.

9. The polypropylene film according to any one of claims 1 to 7, having a thickness of 1.4 µm or more and 6.0 µm or less.

10. The polypropylene film according to any one of claims 1 to 7, which is for use in a capacitor.

11. A metal layer-integrated polypropylene film comprising the polypropylene film according to any one of claims 1 to 7 and a metal layer laminated on one or both sides of the polypropylene film.

12. A film capacitor comprising the metal layer-integrated polypropylene film according to claim 11.

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