Stretched film, metal-laminated film, and capacitor

Abstract

To provide a film capable of maintaining dielectric breakdown strength at high temperatures, achieving high dielectric breakdown strength at high temperatures, and exhibiting high volume resistivity in high-temperature environments.SOLUTION: A stretched film has at least an A layer, wherein (1) the A layer contains 55 mass% or more and 99 mass% or less of a polypropylene resin based on 100 mass%, (2) in temperature dispersion data at a frequency of 1 Hz in a dynamic viscoelasticity measurement in a film machine direction (MD), the film has a dispersion peak of a loss tangent (tanδ) in a temperature range of 145°C or higher, and (3) the film is stretched in at least one direction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a stretched film, a metal laminated film, and a capacitor. [Background technology]

[0002] Capacitors using resin films have conventionally been used in electronic devices, electrical devices, etc., as, for example, high-voltage capacitors, filter capacitors and smoothing capacitors for various switching power supplies, converters, inverters, etc. Resin film capacitors are also used in inverters and converters that control drive motors for electric vehicles, hybrid vehicles, etc., for which demand has been increasing in recent years.

[0003] Capacitors, especially automotive capacitors, are increasingly being used in high-temperature environments. For example, in devices (inverters, converters, etc.) that control automobile drive motors, the use of highly heat-resistant semiconductors (silicon carbide semiconductors, etc.) has recently increased. As a result, the capacitors used in these devices are also required to have higher heat resistance. In addition, in recent years, the miniaturization and increased capacity of capacitors have led to a demand for thinner film thickness. For this reason, the films used in capacitors are required to have high voltage resistance and high insulation properties in high-temperature environments.

[0004] As one of the resin films with high heat resistance, a resin film containing syndiotactic polystyrene has been proposed (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-111592 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 discloses a film containing a syndiotactic polystyrene resin and a polyphenylene ether resin, which have excellent heat resistance, and exhibits a dielectric breakdown voltage and suitability for winding elements. However, the film described in Patent Document 1 does not have sufficient dielectric breakdown strength at high temperatures, is poor in safety, and is prone to short circuits, so there is room for further study.

[0007] Furthermore, as mentioned above, capacitors are increasingly being used in high-temperature environments, and therefore films used in capacitors are required to have high dielectric breakdown strength at room temperature (23°C) and also to suppress the decrease in dielectric breakdown strength in high-temperature environments such as 135°C.

[0008] Furthermore, films used in capacitors that are used in high-temperature environments are also required to exhibit high volume resistivity in high-temperature environments.

[0009] In view of the above circumstances, an object of the present invention is to provide a film that suppresses a decrease in dielectric breakdown strength at high temperatures, can exhibit high dielectric breakdown strength at high temperatures, and can also exhibit high volume resistivity in a high-temperature environment. [Means for solving the problem]

[0010] As a result of extensive research into achieving the above-mentioned object, the inventors have found that the above-mentioned object can be achieved by a stretched film that is composed of a specific resin composition, that has a dispersion peak of loss tangent (tan δ) in a temperature range of 145°C or higher in temperature dispersion data in the machine direction (MD) of the film in dynamic viscoelasticity measurement at a frequency of 1 Hz, and that is stretched in at least one direction, and that has led to the completion of the present invention.

[0011] That is, the present invention relates to the following stretched film, metal layer-integrated film, and capacitor. 1. A stretched film having at least layer A, (1) The layer A contains 55% by mass or more and 99% by mass or less of a polypropylene-based resin, based on 100% by mass, (2) In dynamic viscoelasticity measurement, the temperature dispersion data in the film machine direction (MD) at a frequency of 1 Hz shows a dispersion peak of the loss tangent (tanδ) in the temperature range of 145°C or higher, (3) stretched in at least one direction; A stretched film characterized by: 2. The stretched film according to Item 1, wherein the layer A contains, based on 100% by mass, 55% by mass to 99% by mass of isotactic polypropylene resin and 1% by mass to 45% by mass of hydrogenated polystyrene. 3. The stretched film according to Item 2, wherein the hydrogenated polystyrene has an atactic stereoregularity and a hydrogenation rate of 95% or more. 4. The stretched film according to any one of items 1 to 3, wherein in dynamic viscoelasticity measurement, in temperature dispersion data in the machine direction (MD) of the film at a frequency of 1 Hz, the loss tangent (tanδ) at 100°C is 0.1 or less and has substantially no peak. 5. The stretched film according to any one of items 1 to 4, wherein in dynamic viscoelasticity measurement, in temperature dispersion data in the machine direction (MD) of the film at a frequency of 1 Hz, the ratio E'(135) / E'(25) of the storage modulus E'(135) at 135°C to the storage modulus E'(25) at 25°C is 0.19 or more. 6. The stretched film according to any one of items 1 to 5, wherein the stretched film has a thickness of 1.8 μm or more and 10 μm or less and a total light transmittance of 80% or more. 7. The stretched film according to any one of items 1 to 6, which is a single-layer film. 8. The stretched film according to any one of items 1 to 7, which is a biaxially stretched film. 9. The stretched film according to any one of items 1 to 8, which is for a capacitor. 10. A metal laminated film comprising the stretched film according to any one of items 1 to 9 and a metal layer laminated on one or both sides of the stretched film. 11. A capacitor comprising the film according to item 1. 12. A capacitor comprising the metal laminated film according to item 10. [Effects of the Invention]

[0012] The film of the present invention is inhibited from decreasing in dielectric breakdown strength at high temperatures, and can exhibit high dielectric breakdown strength at high temperatures and high volume resistivity in a high-temperature environment. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the measurement results of the logarithm of storage modulus (logE′) and loss tangent (tan δ) in Example 2 and Comparative Example 1. [Figure 2] 10 is a diagram showing the relationship between the rate of change in capacitance and elapsed time in Example 2 and Comparative Example 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below.

[0015] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. Furthermore, in this specification, a numerical value connected with "to" means a numerical range that includes the numbers before and after "to" as the upper and lower limits.

[0016] In this specification, the expressions "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0017] 1. Stretched film The present invention relates to a stretched film having at least Layer A, wherein (1) Layer A contains 55% by mass or more and 99% by mass or less of a polypropylene-based resin, based on 100% by mass; (2) in temperature dispersion data in the machine direction (MD) of the film obtained by dynamic viscoelasticity measurement at a frequency of 1 Hz, the film has a dispersion peak of loss tangent (tan δ) in a temperature range of 145°C or more; and (3) the film is stretched in at least one direction (sometimes referred to simply as a "stretched film" or "stretched film of the present invention" in this specification).

[0018] The action of the present invention will be explained using the drawings. Figure 1 shows the logarithm of the storage modulus logE' and the loss tangent (tanδ) of a stretched film of the present invention (Example 2 described later) and a stretched film (Comparative Example 1 described later) that does not have a dispersion peak of the loss tangent (tanδ) in a temperature range of 145°C or higher in temperature dispersion data at a frequency of 1 Hz in the machine direction (MD) of the film in dynamic viscoelasticity measurement.

[0019] In the stretched film of the present invention (Example 2), as a result of measuring the dynamic viscoelasticity in the MD direction of the film, a clear peak of tan δ was observed in the temperature range of 145° C. or higher. On the other hand, in Comparative Example 1, in which no hydrogenated polystyrene was added, although there was a gentle slope in the temperature range of 145° C. or higher, no peak was present.

[0020] In Example 2 of Figure 1, the tan δ peak corresponds to the glass transition temperature (Tg) of the added hydrogenated polystyrene, and as the amount of hydrogenated polystyrene added increases, this peak becomes clearer. At the same time, the gradual increase in tan δ around 100°C shown by polypropylene (100% polypropylene) (which is thought to correspond to the lattice relaxation of general polypropylene) decreases with the addition of hydrogenated polystyrene.

[0021] The above results indicate that polypropylene and hydrogenated polystyrene have a phase-separated structure when mixed. It is believed that polypropylene and hydrogenated polystyrene form a sea-island structure, with the polypropylene as the sea and the hydrogenated polystyrene as the islands. When a film containing polypropylene and hydrogenated polystyrene is stretched, the hydrogenated polystyrene in the phase-separated island phase interpenetrates the oriented polypropylene sea phase. This suppresses the relaxation motion (molecular chain motion) of polypropylene that occurs at high temperatures, thereby suppressing the decrease in dielectric breakdown strength at high temperatures. The resulting stretched film exhibits high dielectric breakdown strength at high temperatures and high volume resistivity in high-temperature environments.

[0022] Furthermore, in Example 2 in Figure 1, a high Tg is maintained (main dispersion peak at 150°C), the loss tangent (tan δ) at 100°C is low, the lattice relaxation motion of polypropylene is contained, the temperature dependence of the storage modulus is small and there is little increase or decrease with temperature, and the film is not cloudy, which indicates that the phase separation structure is not a fragile (brittle) phase separation structure.

[0023] As described above, the stretched film of the present invention has the following configuration: (1) Layer A contains 55% to 99% by mass of polypropylene-based resin out of 100% by mass; (2) in temperature dispersion data in the machine direction (MD) of the film at a frequency of 1 Hz in dynamic viscoelasticity measurement, the loss tangent (tan δ) has a dispersion peak in the temperature range of 145°C or higher; and (3) is stretched in at least one direction. By forming a "phase separation structure," the relaxation motion (molecular chain motion) of polypropylene that occurs at high temperatures can be suppressed, and therefore the decrease in dielectric breakdown strength at high temperatures is suppressed, and the film can exhibit high dielectric breakdown strength at high temperatures and high volume resistivity in a high-temperature environment.

[0024] Therefore, as shown in Figure 2, a capacitor using the stretched film of the present invention as a dielectric can maintain its insulation and capacitance for more than 500 hours without short-circuiting even when a voltage of 200 Vdc / μm is continuously applied at a high temperature of 135°C or higher.

[0025] Each component of the stretched film of the present invention will be described in detail below.

[0026] 1-1. Polypropylene resin The layer A of the film of the present invention contains 55% by mass or more and 99% by mass or less of a polypropylene resin, with the mass of the layer A being 100% by mass.

[0027] Examples of the polypropylene-based resin include propylene homopolymers such as isotactic polypropylene and syndiotactic polypropylene; copolymers of propylene with other olefins (e.g., ethylene, 1-butene, etc.) (the copolymer may be a random copolymer or a block copolymer having at least two polymer blocks); long-chain branched polypropylene; and polypropylene-based resins produced from plant-derived raw materials. Among these, isotactic polypropylene is preferably used from the viewpoint of improving the rigidity, electrical insulation, and stretchability of the stretched film of the present invention.

[0028] When the polypropylene resin is a copolymer of propylene and another olefin, the propylene content in the copolymer is 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more, where the mass of the polypropylene resin is 100% by mass. Note that the polypropylene resin does not include a polypropylene resin having an alicyclic structure in a side chain.

[0029] The polypropylene resin contained in the layer A may be one type or two or more types.

[0030] The content of the polypropylene resin in Layer A may be from 55% to 99% by mass, more preferably from 60% to 90% by mass, and even more preferably from 65% to 85% by mass. In this case, the rigidity, electrical insulation, and stretchability of the stretched film of the present invention are improved. Note that, when the film of the present invention is a multilayer film having other layers in addition to Layer A (for example, a skin layer, as described below), the effect of improving stretchability also includes the case where the entire multilayer film is stretched (the same applies hereinafter).

[0031] The melt mass flow rate (MFR) of the polypropylene resin contained in Layer A, measured at 230°C under a weight of 2.16 kg, is preferably 0.5 g / 10 min to 6 g / 10 min, more preferably 1 g / 10 min to 5 g / 10 min, and even more preferably 1.5 g / 10 min to 4 g / 10 min, inclusive. In this case, appropriate resin fluidity is obtained during stretching of the stretched film, improving stretchability.

[0032] The melting point of the polypropylene resin contained in Layer A is preferably 155°C or higher. In this case, electrical insulation and stretchability at high temperatures are improved. The melting point is more preferably 160°C or higher and 180°C or lower, and even more preferably 161°C or higher and 170°C or lower.

[0033] The polypropylene resin contained in Layer A preferably has a mesopentad fraction of 95 mol% or more and 99.9 mol% or less. When the mesopentad fraction is 95 mol% or more, the rigidity and electrical insulation of the stretched film of the present invention are likely to be improved, and when the mesopentad fraction is 99.9 mol% or less, the stretchability is likely to be improved. The mesopentad fraction of the polypropylene resin is more preferably 96 mol% or more and 99.5 mol% or less, even more preferably 97 mol% or more and 99.2 mol% or less, and particularly preferably 98 mol% or more and 99 mol% or less.

[0034] The heptane insoluble content (HI) of the polypropylene resin contained in Layer A is preferably 94% by mass or more and 99.9% by mass or less. When it is 94% by mass or more, the rigidity and electrical insulation of the stretched film tend to be improved, and when it is 99.9% by mass or less, the stretchability tends to be improved. The heptane insoluble content of the polypropylene resin is more preferably 96% by mass or more and 99.5% by mass or less, even more preferably 97% by mass or more and 99.2% by mass or less, and particularly preferably 98% by mass or more and 99% by mass or less.

[0035] The number average molecular weight (Mn) of the polypropylene resin contained in Layer A is preferably from 30,000 to 70,000, and more preferably from 35,000 to 65,000. When Layer A contains a polypropylene resin with such a number average molecular weight (Mn), the rigidity, electrical insulation, and stretchability of the stretched film of the present invention are likely to be improved.

[0036] The weight average molecular weight (Mw) of the polypropylene resin contained in Layer A is preferably from 250,000 to 500,000, and more preferably from 300,000 to 450,000. When Layer A contains a polypropylene resin with such a weight average molecular weight (Mw), the rigidity, electrical insulation properties, and stretchability of the stretched film of the present invention are likely to be improved.

[0037] The polypropylene resin contained in Layer A preferably has a molecular weight distribution (Mw / Mn), calculated as the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), of 3 to 12, more preferably 5 to 10, and even more preferably 6 to 9.5. When Layer A contains a polypropylene resin with such a molecular weight distribution (Mw / Mn), the rigidity, electrical insulation, and stretchability of the stretched film of the present invention are likely to be improved.

[0038] The z-average molecular weight (Mz) of the polypropylene resin contained in Layer A is preferably from 700,000 to 3,000,000, and more preferably from 1,000,000 to 2,500,000. When Layer A contains a polypropylene resin with such a z-average molecular weight (Mz), the rigidity, electrical insulation properties, and stretchability of the stretched film of the present invention are likely to be improved.

[0039] The polypropylene resin contained in Layer A preferably has a molecular weight distribution (Mz / Mw) calculated as the ratio of the z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of 2 or more and 7 or less, more preferably 2.5 or more and 6 or less, and even more preferably 3 or more and 5 or less. When Layer A contains a polypropylene resin with such a molecular weight distribution (Mz / Mw), the rigidity, electrical insulation properties, and stretchability of the stretched film of the present invention are likely to be improved.

[0040] Polypropylene-based resins can be produced using conventionally known methods. Examples of polymerization methods include gas-phase polymerization, bulk polymerization, and slurry polymerization. Polymerization may be single-stage polymerization using one polymerization reactor or multi-stage polymerization using two or more polymerization reactors. Furthermore, polymerization may be carried out by adding hydrogen or a comonomer to the reactor as a molecular weight modifier. Conventional Ziegler-Natta catalysts or metallocene catalysts can be used as polymerization catalysts, and the polymerization catalyst may contain a cocatalyst component or a donor. The mesopentad fraction, melt mass flow rate, molecular weight, and molecular weight distribution of the polypropylene-based resin can be controlled by appropriately adjusting the polymerization catalyst and other polymerization conditions.

[0041] 1-2.Hydrogenated polystyrene Layer A of the film of the present invention preferably contains hydrogenated polystyrene in an amount of 1% by mass to 45% by mass, with the mass of Layer A being 100%. The hydrogenated polystyrene contained in Layer A may be one type or two or more types.

[0042] The content of hydrogenated polystyrene in Layer A is preferably from 1 to 45% by mass, more preferably from 2 to 40% by mass, even more preferably from 2 to 35% by mass, and particularly preferably from 5 to 20% by mass, which improves the rigidity, electrical insulation, and stretchability of the stretched film of the present invention.

[0043] The hydrogenation rate of the hydrogenated polystyrene contained in Layer A is preferably 50% or more, more preferably 80% or more, even more preferably 85% or more, particularly preferably 90% or more, and even more particularly preferably 95% or more. The hydrogenation rate may be 100%. By setting the hydrogenation rate within the above range, stretchability tends to be improved, which is preferable.

[0044] The hydrogenated polystyrene is not particularly limited, but it is preferable to use a polymer having an alicyclic structure in the side chain.

[0045] Here, the alicyclic structure includes one or more saturated and / or unsaturated carbon ring structures that do not have aromaticity. The number of carbon ring structures may be two or more. The carbon ring structure may have a branched aliphatic hydrocarbon structure. The carbon ring structure is bonded directly or via a hydrocarbon chain to the hydrocarbon chain of the polymer main chain.

[0046] Examples of the carbon ring structure include monocyclic structures such as cycloalkane structures such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, and cyclododecane, and cycloalkene structures such as cyclopropene, cyclobutene, cyclopropene, cyclohexene, cycloheptene, and cyclooctene. Examples of bicyclic structures include bicyclic alkane structures such as bicycloundecane, and bicyclic alkene structures such as norbornene and norbornadiene, which can be suitably used. Of these, a carbon ring structure having 4 to 8 carbon atoms is preferred from the viewpoint of stretchability, a monocyclic carbon ring structure having 4 to 8 carbon atoms is more preferred, a carbon ring structure that is a monocyclic cycloalkane structure having 4 to 8 carbon atoms is even more preferred, and a cyclohexane structure is particularly preferred.

[0047] The polymer main chain is mainly composed of aliphatic hydrocarbons. The polymer main chain may contain cyclic hydrocarbon structures and / or aromatic hydrocarbon structures as structural units, but preferably does not contain these. The aliphatic hydrocarbons in the polymer main chain may have branches of aliphatic hydrocarbon structures and / or aromatic hydrocarbon structures.

[0048] The polymer having an alicyclic structure in the side chain may be a homopolymer having a structure having an alicyclic structure in the side chain as a structural unit. For example, it may be polyvinylcycloolefin obtained by homopolymerizing vinylcycloolefin. Examples of polyvinylcycloolefin include polyvinylcyclopropane, polyvinylcyclobutane, polyvinylcyclopentane, polyvinylcyclohexane, polyvinylcycloheptane, polyvinylcyclooctane, polyvinylcyclononane, polyvinylcyclodecane, polyvinylcycloundecane, and polyvinylcyclododecane. Homopolymers are preferred because they tend to have high rigidity and electrical insulation properties in high-temperature environments. Among these, polyvinylcyclopentane, polyvinylcyclohexane, and polyvinylcycloheptane are preferred, with polyvinylcyclohexane being most preferred.

[0049] (Method of producing polymer having alicyclic structure in the side chain) The method for producing the polymer having an alicyclic structure in the side chain is not particularly limited, and the polymer can be produced using a known method such as a radical polymerization method, an ionic polymerization method (anionic polymerization method, coordination anionic polymerization method, etc.), or a polymerization method such as bulk polymerization, solution polymerization, or suspension polymerization.

[0050] Specifically, a polymer having an alicyclic structure in a side chain can be produced by carrying out a polymerization reaction using a known initiator such as an alkyllithium compound or a dilithium compound to sequentially polymerize a monomer having an alicyclic structure (e.g., vinylcycloolefin, etc.); or a method in which a monomer having an alicyclic structure is sequentially polymerized and then a coupling agent is added to perform coupling.

[0051] Furthermore, a polymer having an alicyclic structure in the side chain can be produced by polymerizing a monomer having an aromatic ring structure (e.g., styrene) by a known method, followed by a hydrogenation reaction. The hydrogenation reaction can be carried out, for example, by the method described later in the "Method for producing a hydrogenated block copolymer."

[0052] When produced by hydrogenation reaction, the hydrogenation rate of the aromatic ring structure is preferably 50 mol% or more, more preferably 80 mol% or more, even more preferably 85 mol% or more, particularly preferably 90 mol% or more, and even more particularly preferably 95 mol% or more. The hydrogenation rate may be 100 mol%. By setting the hydrogenation rate within the above range, stretchability tends to be improved, which is preferable.

[0053] The polymer having an alicyclic structure in the side chain may be a copolymer having a structural unit having an alicyclic structure in the side chain and one or more other structural units. The copolymer may be a random copolymer or a block copolymer having at least two polymer blocks. From the viewpoint of stretchability, copolymers are preferred, and block copolymers are more preferred.

[0054] Examples of other structural units include ethylene, propylene, butene, pentene, hexene, heptene, and octene, and may or may not have a side chain. Furthermore, the polymer may contain both structural units with and without a side chain. Examples of structural units with a side chain include propylene, 1-butene, 1-pentene, 1-hexene, and 4-methyl-1-pentene. The other structural units may be unsaturated hydrocarbons, but saturated hydrocarbons are preferred from the viewpoint of electrical insulation.

[0055] Here, when a polymer having an alicyclic structure in a side chain (hereinafter also referred to as simply "polymer" or "the polymer") contains, for example, propylene as another structural unit, the propylene content in the polymer is less than 50% by mass, preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 2% by mass or less, based on 100% by mass of the polymer.

[0056] A polymer having an alicyclic structure in a side chain can be obtained, for example, by polymerizing a monomer having each structural unit by a known method. Alternatively, the polymer can be obtained by hydrogenating a polymer having an aromatic ring structure in a side chain. Hydrogenating a polymer having an aromatic ring structure in a side chain is preferred because it is easy to industrially obtain a polymer having an alicyclic structure in a side chain at low cost.

[0057] When a polymer having an aromatic ring structure in a side chain is hydrogenated, the polymer having an aromatic ring structure in a side chain may be a homopolymer or a copolymer. In the case of a copolymer, a block copolymer having at least a vinyl aromatic polymer block and a conjugated diene polymer block is preferred. By hydrogenating this, a hydrogenated block copolymer having at least a hydrogenated vinyl aromatic polymer block and a hydrogenated conjugated diene polymer block is obtained.

[0058] Hereinafter, a hydrogenated block copolymer having at least a hydrogenated vinyl aromatic polymer block and a hydrogenated conjugated diene polymer block will be described as one preferred embodiment.

[0059] (hydrogenated vinyl aromatic polymer block) The hydrogenated vinyl aromatic polymer block contains structural units derived from a vinyl aromatic compound and hydrogenated therefrom. The hydrogenated vinyl aromatic polymer block contains structural units derived from a vinyl aromatic compound in an amount of 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass. By making the structural units derived from a vinyl aromatic compound 50% by mass or more, rigidity and electrical insulation properties in high-temperature environments are likely to be improved.

[0060] Examples of vinyl aromatic compounds include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, vinyltoluene, 1-vinylnaphthalene, 2-vinylnaphthalene, etc. The vinyl aromatic compound is preferably selected from styrene and α-methylstyrene, more preferably styrene.

[0061] The hydrogenated vinyl aromatic polymer block may be composed of only one type of the above vinyl aromatic compound, or may be composed of two or more types.

[0062] The hydrogenated vinyl aromatic polymer block may contain other structural units besides those derived from vinyl aromatic compounds, such as those derived from isoprene, butadiene, 2,3-dimethylbutadiene, 1,3-pentadiene, and 1,3-hexadiene.

[0063] The content of the hydrogenated vinyl aromatic polymer block is preferably 50% by mass or more but less than 100% by mass, based on 100% by mass of the total of the hydrogenated vinyl aromatic polymer block and the hydrogenated conjugated diene polymer block. By making it 50% by mass or more, rigidity and electrical insulation at high temperatures tend to be improved. It is more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more.

[0064] (Hydrogenated conjugated diene polymer block) The hydrogenated conjugated diene polymer block contains structural units derived from a conjugated diene and hydrogenated from the conjugated diene, and the hydrogenated conjugated diene polymer block contains 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass of structural units derived from the conjugated diene.

[0065] Examples of conjugated dienes include butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-butadiene, 1,3-pentadiene, 1,3-hexadiene, etc. The conjugated diene is preferably selected from butadiene and isoprene, and more preferably butadiene.

[0066] The hydrogenated conjugated diene polymer block may contain a structural unit derived from a conjugated diene having no side chain. Examples of the conjugated diene having no side chain include butadiene, 1,3-pentadiene, and 1,3-hexadiene. The preferred conjugated diene having no side chain is butadiene.

[0067] In the hydrogenated conjugated diene polymer block, the bonding form of the conjugated diene, i.e., the microstructure, is not particularly limited. For example, in the case of butadiene, bonding forms of 1,2-bonds and 1,4-bonds can be used. In addition, in the case of isoprene, bonding forms of 1,2-bonds, 3,4-bonds and 1,4-bonds can be used. Only one type of these bonding forms may be present, or two or more types may be present. When two or more types of bonding forms are present, the ratio of the bonding forms is not particularly limited.

[0068] The hydrogenated conjugated diene polymer block may contain other structural units besides those derived from conjugated dienes, such as structural units derived from styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, vinyltoluene, 1-vinylnaphthalene, and 2-vinylnaphthalene.

[0069] The content of the hydrogenated conjugated diene polymer block is preferably more than 0% by mass (e.g., 1% by mass or more) and 50% by mass or less, based on 100% by mass of the total of the hydrogenated vinyl aromatic polymer block and the hydrogenated conjugated diene polymer block. By setting it to 50% by mass or less, rigidity and electrical insulation at high temperatures tend to be improved, which is preferable. It is more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less.

[0070] (hydrogenation rate) In the hydrogenated vinyl aromatic polymer block according to this embodiment, the hydrogenation rate of the aromatic rings of the hydrogenated vinyl aromatic polymer block is preferably 50 mol% or more, more preferably 80 mol% or more, even more preferably 85 mol% or more, particularly preferably 90 mol% or more, and even more particularly preferably 95 mol% or more. The hydrogenation rate may be 100 mol%. The hydrogenation rate of the carbon-carbon double bonds derived from the conjugated diene of the hydrogenated conjugated diene polymer block is preferably 90 mol% or more, more preferably 95 mol% or more. The hydrogenation rate may be 100 mol%.

[0071] By setting the hydrogenation rate of the aromatic ring of the hydrogenated vinyl aromatic polymer block and / or the hydrogenation rate of the carbon-carbon double bond derived from the conjugated diene of the hydrogenated conjugated diene polymer block within the above-mentioned ranges, stretchability tends to be improved, which is preferable.

[0072] (Bonding pattern of hydrogenated block copolymer) The bonding mode of the polymer blocks in the hydrogenated block copolymer may be any of linear, branched and radial, or a combination thereof.

[0073] For example, if the hydrogenated vinyl aromatic polymer block is represented by "X" and the hydrogenated conjugated diene polymer block is represented by "Y", examples of the bonding pattern include a diblock copolymer (XY), a triblock copolymer (XYX), a tetrablock copolymer (XYXY), a pentablock copolymer (XYXYX or YXYXY), etc. From the viewpoint of ease of production, the bonding pattern is preferably a diblock copolymer, a triblock copolymer, or a tetrablock copolymer.

[0074] Specific examples of hydrogenated block copolymers include hydrogenated block copolymers of styrene-isoprene diblock copolymer (SI), styrene-butadiene diblock copolymer (SB), styrene-isoprene-styrene triblock copolymer (SIS), styrene-butadiene / isoprene-styrene triblock copolymer (SB / IS), styrene-butadiene-styrene triblock copolymer (SBS), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-ethylene-propylene-styrene copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS), styrene-butylene-butadiene-styrene copolymer (SBBS), etc. Among these, hydrogenated block copolymers of styrene-butadiene diblock copolymer (SB) are particularly preferred.

[0075] (Method of producing hydrogenated block copolymer) The method for producing the hydrogenated block copolymer is not particularly limited, and known methods such as anionic polymerization can be used.

[0076] Specifically, the hydrogenated block copolymer can be produced by carrying out a polymerization reaction using, for example, a method of sequentially polymerizing a vinyl aromatic compound and a conjugated diene using an alkyllithium compound as an initiator; a method of sequentially polymerizing a vinyl aromatic compound and a conjugated diene using an alkyllithium compound as an initiator, followed by coupling by adding a coupling agent; or a method of sequentially polymerizing a conjugated diene and then a vinyl aromatic compound using a dilithium compound as an initiator, followed by carrying out a hydrogenation reaction.

[0077] Examples of the alkyllithium compound include methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, and pentyllithium.

[0078] Examples of coupling agents include divinylbenzene; polyfunctional epoxy compounds such as epoxidized 1,2-polybutadiene, epoxidized soybean oil, and 1,3-bis(N,N-glycidylaminomethyl)cyclohexane; halogen compounds such as dimethyldichlorosilane, dimethyldibromosilane, trichlorosilane, methyltrichlorosilane, tetrachlorosilane, and tetrachlorotin; ester compounds such as methyl benzoate, ethyl benzoate, phenyl benzoate, diethyl oxalate, diethyl malonate, diethyl adipate, dioctyl adipate, dimethyl phthalate, diethyl phthalate, dimethyl isophthalate, and dimethyl terephthalate; carbonate ester compounds such as dimethyl carbonate, diethyl carbonate, and diphenyl carbonate; and alkoxysilane compounds such as dimethyldimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, bis(trimethoxysilyl)hexane, and bis(triethoxysilyl)ethane.

[0079] Examples of dilithium compounds include naphthalenedilithium and dilithiohexylbenzene.

[0080] The polymerization reaction is preferably carried out in the presence of a solvent. The solvent is not particularly limited as long as it is inert to the initiator and does not adversely affect the reaction, and examples thereof include saturated aliphatic hydrocarbons such as hexane, cyclohexane, heptane, octane, and decane; and aromatic hydrocarbons such as toluene, benzene, and xylene. Furthermore, the temperature of the polymerization reaction is preferably 0 to 100°C, more preferably 30 to 90°C, even more preferably 40 to 80°C, and particularly preferably 50 to 80°C, from the viewpoint of controlling the microstructure. The time of the polymerization reaction is preferably 0.5 to 50 hours, from the viewpoint of controlling the microstructure.

[0081] A Lewis base may also be used as a co-catalyst during the polymerization reaction. Examples of Lewis bases include ethers such as dimethyl ether, diethyl ether, and tetrahydrofuran; glycol ethers such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether; and amines such as triethylamine, N,N,N',N'-tetramethylethylenediamine, and N-methylmorpholine. These Lewis bases may be used alone or in combination of two or more.

[0082] The hydrogenation reaction may be carried out immediately after the polymerization reaction, or may be carried out after the block copolymer has been isolated after the polymerization reaction.

[0083] When the block copolymer is temporarily isolated after the polymerization reaction, the block copolymer can be isolated by pouring the polymerization reaction solution obtained after the polymerization reaction into a poor solvent for the block copolymer, such as methanol, to solidify the block copolymer, or by pouring the polymerization reaction solution together with steam into hot water to remove the solvent by azeotropy (steam stripping), followed by drying.

[0084] The hydrogenation reaction of the block copolymer can be carried out, for example, in the presence of a hydrogenation catalyst at a reaction temperature of 20 to 200° C. and a hydrogen pressure of 0.1 to 20 MPa for 0.1 to 100 hours.

[0085] Examples of hydrogenation catalysts include Raney nickel; heterogeneous catalysts in which a metal such as platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), or nickel (Ni) is supported on a carrier such as carbon, alumina, or diatomaceous earth; Ziegler catalysts consisting of a combination of a transition metal compound (nickel octylate, nickel naphthenate, nickel acetylacetonate, cobalt octylate, cobalt naphthenate, or cobalt acetylacetonate) with an organoaluminum compound such as triethylaluminum or triisobutylaluminum, or an organolithium compound; and metallocene catalysts consisting of a combination of a bis(cyclopentadienyl) compound of a transition metal such as titanium, zirconium, or hafnium with an organometallic compound such as lithium, sodium, potassium, aluminum, zinc, or magnesium.

[0086] When the hydrogenation reaction is carried out subsequent to the polymerization reaction, the hydrogenated block copolymer can be isolated by pouring the hydrogenation reaction solution into a poor solvent for the hydrogenated block copolymer, such as methanol, to coagulate it, or by pouring the hydrogenation reaction solution into hot water together with steam to remove the solvent by azeotropy (steam stripping), followed by drying.

[0087] The glass transition temperature (Tg) of the polymer having an alicyclic structure in its side chain contained in Layer A is preferably 100°C or higher and 180°C or lower. A glass transition temperature of 100°C or higher tends to increase rigidity and electrical insulation at high temperatures, while a glass transition temperature of 180°C or lower can improve stretchability. The glass transition temperature is more preferably 120°C or higher and 165°C or lower, more preferably 130°C or higher and 160°C or lower, and particularly preferably 140°C or higher and 155°C or lower.

[0088] The Vicat softening point (1 kg, 50°C / hr) of the polymer having an alicyclic structure in its side chain contained in Layer A is preferably 100°C or higher and 170°C or lower. By setting the Vicat softening point to 100°C or higher, rigidity and electrical insulation at high temperatures tend to be increased, and by setting it to 170°C or lower, stretchability can be improved. The Vicat softening point is more preferably 120°C or higher and 165°C or lower, more preferably 130°C or higher and 160°C or lower, and particularly preferably 140°C or higher and 155°C or lower.

[0089] The glass transition temperature (Tg) and Vicat softening point of the polymer having an alicyclic structure in its side chain contained in Layer A can be adjusted by the type of structural unit having the above-mentioned alicyclic structure in its side chain, or the types and ratios of one or more other structural units.

[0090] The weight-average molecular weight (Mw) of the polymer having an alicyclic structure in its side chain contained in Layer A is not particularly limited, but is preferably from 50,000 to 400,000. When Layer A contains a polymer having an alicyclic structure with such a weight-average molecular weight (Mw), the rigidity, electrical insulation, and stretchability of the film of the present invention are likely to be improved.

[0091] The melt mass flow rate (MFR) of the polymer having an alicyclic structure in its side chain contained in Layer A, measured at 260°C under a load of 2.16 kg, is preferably 1 g / 10 min to 40 g / 10 min, more preferably 2 g / 10 min to 20 g / 10 min, and even more preferably 3 g / 10 min to 15 g / 10 min, inclusive. In this case, appropriate resin fluidity is obtained during stretching of the film, and stretchability is easily improved.

[0092] The polymer having an alicyclic structure in the side chain contained in Layer A may be produced by the method described above, or a commercially available product such as ViviOn (registered trademark) (manufactured by USI Corporation) may be used.

[0093] (Atactic polystyrene resin) The hydrogenated polystyrene contained in the layer A may be an atactic polystyrene resin having an atactic stereoregularity.

[0094] The atactic polystyrene resin is not particularly limited as long as it is an amorphous resin having a main chain of polystyrene with an atactic structure. As the atactic polystyrene resin, it is preferable that 90% or more, more preferably 95% or more of the structural units constituting the main chain are styrene and / or styrene having a substituent on the aromatic ring.

[0095] The atactic structure means that the phenyl groups or substituted phenyl groups, which are side chains of the main chain formed by carbon-carbon bonds, have a random three-dimensional structure. Tacticity is usually measured by nuclear magnetic resonance spectroscopy using carbon isotopes ( 13 The syndiotacticity of atactic polystyrene resins is quantified by C-NMR (C-NMR method) and can be expressed as the proportion of consecutive structural units present, for example, a dyad when two units are present, a triad when three units are present, and a pentad when five units are present. Atactic polystyrene resins are, for example, racemic dyads and have a syndiotacticity of less than 75%, preferably 65% ​​or less. Atactic polystyrene resins are, for example, racemic pentads and have a syndiotacticity of less than 30%, preferably 25% or less.

[0096] Specific examples of atactic polystyrene resins include polystyrene, poly(alkylstyrene), poly(halogenated styrene), poly(halogenated alkylstyrene), poly(alkoxystyrene), and mixtures thereof, as well as copolymers containing these as main components.

[0097] Examples of poly(alkylstyrenes) include poly(methylstyrene), poly(ethylstyrene), poly(isopropylstyrene), poly(tertiarybutylstyrene), poly(phenylstyrene), poly(vinylstyrene), poly(vinylnaphthalene), etc. Examples of poly(halogenated styrenes) include poly(chlorostyrene), poly(bromostyrene), poly(fluorostyrene), etc. Examples of poly(halogenated alkylstyrenes) include poly(chloromethylstyrene), etc. Examples of poly(alkoxystyrenes) include poly(methoxystyrene), poly(ethoxystyrene), etc.

[0098] Among these, particularly preferred atactic polystyrene resins include polystyrene, poly(p-methylstyrene), poly(m-methylstyrene), poly(p-tertiarybutylstyrene), poly(p-chlorostyrene), poly(m-chlorostyrene), poly(p-fluorostyrene), hydrogenated polystyrene, and styrene-alkylstyrene copolymers such as a copolymer of styrene and p-methylstyrene.

[0099] Atactic polystyrene resins are commercially available or can be produced by known methods. As commercially available atactic polystyrene resins, resins generally known as general-purpose polystyrene (GPPS) can be suitably used, and are available, for example, as "PSJ-Polystyrene GPPS" (HF77, 679, SGP10, etc.) manufactured by PS Japan Co., Ltd.

[0100] The atactic polystyrene resins can be used alone or in combination of two or more.

[0101] 1-3.A layer The present invention has Layer A containing 55% by mass to 99% by mass of a polypropylene resin, and preferably 1% by mass to 45% by mass of hydrogenated polystyrene, where the mass of Layer A is 100% by mass.

[0102] Layer A may further contain other resins for the purposes of adjusting the low-temperature impact resistance of the stretched film, adjusting the surface roughness, and adjusting various physical properties such as rigidity, strength, and elongation, as well as adjusting the mixability of the polypropylene-based resin and the polymer having an alicyclic structure in the side chain, and stretchability.

[0103] The amount of the other resin added is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on 100% by mass of Layer A. The other resin is not particularly limited, and conventionally known resins suitable for stretched film applications can be used appropriately in the present invention. Examples include polyolefin resins such as polyethylene, poly(1-butene), polyisobutene, poly(1-pentene), and poly(4-methyl-1-pentene), and copolymer resins thereof, as well as copolymers of α-olefins such as ethylene-propylene copolymer, propylene-butene copolymer, ethylene-butene copolymer, and ethylene-(4-methyl-1-pentene) copolymer. Other examples include polystyrene resins, elastomers, polyvinyl resins, polyester resins, polyurethane resins, nylon resins, and copolymers thereof.

[0104] Here, when the other resin is a copolymer containing propylene, the propylene content is less than 50% by mass (for example, 40% by mass or less), preferably 20% by mass or less, and more preferably 10% by mass or less, based on 100% by mass of the other resin.

[0105] As the other resin, commercially available products may be used, for example, Tafmer (registered trademark) (manufactured by Mitsui Chemicals, Inc.) as a copolymer of α-olefins, which can be suitably used for the above-mentioned purpose.

[0106] Layer A may further contain particles such as inorganic particles and organic particles, either alone or in combination of two or more types. However, in the stretched film of the present invention, Layer A preferably does not contain particles. Therefore, the upper limit of the particle content in Layer A, based on 100% by mass of Layer A, is preferably 1% by mass or less, 0.5% by mass or less, 0.3% by mass or less, 0.1% by mass or less, 0.05% by mass or less, or 0.01% by mass or less. In addition, the lower limit of the particle content in Layer A is not particularly limited and may be 0.005% by mass or more or may be 0% by mass or more.

[0107] Layer A may further contain an antioxidant. Antioxidants are primarily used for the following two purposes. One purpose is to suppress thermal and oxidative degradation of the resin in a film-forming extruder and / or melt kneader, and the other purpose is to suppress the deterioration of physical properties such as strength due to degradation over long-term use of the stretched film. An example of the latter purpose is to contribute to suppressing degradation over long-term use and maintaining the electrical properties of the capacitor when used in a capacitor. An antioxidant that primarily contributes to the former purpose is also called a "primary agent," and an antioxidant that primarily contributes to the latter purpose is also called a "secondary agent." Two or more types of antioxidants may be used for these two purposes, or one type of antioxidant may be used for both purposes.

[0108] An example of a primary antioxidant is 2,6-di-tertiary-butyl-para-cresol (common name: BHT). This antioxidant is mostly oxidized, decomposed, or evaporated in the extruder, and almost none remains after the stretched film is formed. Therefore, if Layer A contains BHT after stretching, the content is usually less than 100 ppm by mass, with the mass of Layer A being 100%.

[0109] Examples of the secondary agent include hindered phenol-based antioxidants having a carbonyl group. Among the hindered phenol-based antioxidants, examples of the hindered phenol-based antioxidants 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-thiazolinone-4-hydroxyphenylpropionate, and the like. Examples include N,N'-hexamethylenebis(3,5-ditertiary-butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1035), octadecyl-3-(3,5-ditertiary-butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1076), and N,N'-hexamethylenebis(3,5-ditertiary-butyl-4-hydroxyhydrocinnamamide) (trade name: Irganox 1098). Pentaerythritol tetrakis(3-(3,5-ditertiary-butyl-4-hydroxyphenyl)propionate) is particularly preferred due to its excellent heat resistance. (Here, all Irganox® trade names are manufactured by BASF Japan Ltd.)

[0110] When Layer A contains one or more hindered phenol-based antioxidants, the total content thereof is preferably from 1,000 to 7,000 ppm by mass, and more preferably from 2,000 to 6,000 ppm by mass, based on 100% by mass of Layer A, from the viewpoint of achieving optimal effects. Note that the hindered phenol-based antioxidant is partially oxidized and decomposed during the extrusion process or the like during stretched film formation, and the remaining amount in the stretched film is generally 60 to 80% by mass of the aforementioned content.

[0111] Layer A may further contain additives. Examples of additives include nucleating agents, chlorine absorbers, lubricants, plasticizers, flame retardants, and colorants. The content of the additives in Layer A is, for example, 0% by mass to 10% by mass, 0% by mass to 5% by mass, 0% by mass to 1% by mass, 0% by mass to 0.5% by mass, or 0% by mass to 0.1% by mass. The substantial lower limit is about 0.01% by mass.

[0112] The thickness of Layer A is not particularly limited. The preferred thickness depends on the application, but for example, for packaging applications, separator applications, etc., a thickness of 5 μm to 80 μm, or 10 μm to 50 μm, is suitably used. For capacitor applications, a thinner thickness is preferred from the viewpoint of reducing the volume of the capacitor and increasing the capacitance. From this viewpoint, the thickness is preferably 10 μm or less, more preferably 9.5 μm or less, even more preferably 9 μm or less, even more preferably 8.5 μm or less, and particularly preferably 8 μm or less. Furthermore, from the viewpoint of stretchability and the metal vapor deposition process, the thickness after stretching is, for example, 1 μm or more, preferably 1.5 μm or more, more preferably 2 μm or more, and even more preferably 2.3 μm or more.

[0113] 1-4. Stretched film The stretched film of the present invention has at least Layer A, and (1) Layer A contains 55% by mass to 99% by mass of a polypropylene-based resin, based on 100% by mass, (2) in dynamic viscoelasticity measurement, temperature dispersion data in the machine direction (MD) of the film at a frequency of 1 Hz shows a dispersion peak of loss tangent (tan δ) in a temperature range of 145°C or higher, and (3) is stretched in at least one direction. The stretched film of the present invention will be described below.

[0114] The stretched film of the present invention has a dispersion peak of loss tangent (tan δ) in the temperature range of 145° C. or higher in temperature dispersion data at a frequency of 1 Hz in the machine direction (MD) of the film in dynamic viscoelasticity measurement.

[0115] "Having a dispersion peak of loss tangent (tanδ)" means having a maximum point in the graph of the temperature dispersion data, as shown in Example 2 in Figure 1. In the stretched film of the present invention, the maximum point exists in a temperature range of 145°C or higher. It is preferable that the stretched film of the present invention has a clear dispersion peak. In this specification, "clear peak" means that the curve in the graph has a maximum point and is convex upward, and refers to a curve that is drawn when the value increases and then immediately decreases.

[0116] The temperature at which the loss tangent (tan δ) exhibits a dispersion peak in the MD direction (the temperature at which the main dispersion peak value (MD) is exhibited) is 145°C or higher, preferably 148°C or higher, more preferably 150°C or higher, and even more preferably 151°C or higher. The upper limit of the temperature at which the loss tangent (tan δ) exhibits a dispersion peak in the MD direction is preferably 160°C or lower, more preferably 155°C or lower, and even more preferably 153°C or lower. When the film has a dispersion peak within the above range, this indicates that Layer A contains hydrogenated polystyrene, and the stretched film of the present invention is able to further suppress the decrease in dielectric breakdown strength at high temperatures, exhibit higher dielectric breakdown strength at high temperatures, and exhibit higher volume resistivity in a high-temperature environment.

[0117] The peak value of the loss tangent (tan δ) in the MD direction (main dispersion peak value (MD)) is preferably 0.1 or more, more preferably 0.13 or more, even more preferably 0.15 or more, particularly preferably 0.18 or more, more particularly preferably 0.19 or more, and more particularly preferably 0.20 or more. The upper limit of the peak value of the loss tangent (tan δ) in the MD direction is not particularly limited and may be 0.35, 0.32, 0.30, 0.27, etc. The fact that the lower limit of the peak value of the loss tangent (tan δ) in the MD direction is within the above range indicates that Layer A contains a sufficient amount of hydrogenated polystyrene and forms a so-called "phase-separated structure." This structure formation can further suppress the relaxation motion (molecular chain motion) of polypropylene that occurs at high temperatures, thereby further suppressing the decrease in dielectric breakdown strength at high temperatures, allowing the film to exhibit higher dielectric breakdown strength at high temperatures and higher volume resistivity in high-temperature environments.

[0118] In the stretched film of the present invention, the loss tangent (tan δ) at 100°C in the temperature dispersion data in the machine direction (MD) of the film at a frequency of 1 Hz in dynamic viscoelasticity measurement is preferably 0.1 or less, more preferably 0.09 or less, and even more preferably 0.08 or less. The upper limit of the loss tangent (tan δ) at 100°C within the above range means that a large number of β crystals are generated on the surface of the stretched film, forming a phase-separated structure and suppressing the relaxation motion (molecular chain motion) of polypropylene that occurs at high temperatures. This further suppresses the decrease in dielectric breakdown strength at high temperatures, resulting in a stretched film that can exhibit higher dielectric breakdown strength at high temperatures and higher volume resistivity in high-temperature environments. The lower limit of the loss tangent (tan δ) at 100°C is not particularly limited and may be 0.01, 0.03, 0.05, etc.

[0119] It is preferable that the loss tangent (tan δ) does not substantially have a peak near 100° C. (80 to 140° C., preferably 90 to 135° C., more preferably 95 to 130° C.) The peak is due to the relaxation motion (molecular chain motion) of polypropylene.

[0120] In dynamic viscoelasticity measurement, in temperature dispersion data in the film machine direction (MD) at a frequency of 1 Hz, the logarithm (logE') of the storage modulus E'(135) at 135°C is preferably 8 to 10, more preferably 8.3 to 9.8, even more preferably 8.5 to 9.5, and particularly preferably 8.7 to 9.3.

[0121] In dynamic viscoelasticity measurement, in temperature dispersion data in the film machine direction (MD) at a frequency of 1 Hz, the logarithm (logE') of the storage modulus E'(25) at 25°C is preferably 8 to 10.5, more preferably 8.3 to 10, even more preferably 8.5 to 9.8, and particularly preferably 8.7 to 9.5.

[0122] In dynamic viscoelasticity measurements, the temperature dispersion data in the machine direction (MD) of the film at a frequency of 1 Hz shows that the ratio E'(135) / E'(25), between the storage modulus E'(135) at 135°C and the storage modulus E'(25) at 25°C, is preferably 0.19 or greater, more preferably 0.20 or greater. The fact that the lower limit of E'(135) / E'(25) is within the above range indicates that a so-called "phase-separated structure" of hydrogenated polystyrene is formed. This structure formation can further suppress the relaxation motion (molecular chain motion) of polypropylene that occurs at high temperatures, thereby further suppressing the decrease in dielectric breakdown strength at high temperatures, allowing the film to exhibit both higher dielectric breakdown strength at high temperatures and higher volume resistivity in high-temperature environments. The upper limit of E'(135) / E'(25) may be 0.50 or less, 0.40 or less, 0.35 or less, 0.30 or less, 0.25 or less, 0.23 or less, 0.22 or less, 0.215 or less, 0.21 or less, 0.205 or less, or the like.

[0123] The loss tangent (tan δ) and dynamic viscoelasticity (storage modulus (E')) are measured by the following measurement methods, and the temperature dispersion data of the stretched film, the main dispersion peak of the loss tangent (tan δ), the loss tangent (tan δ) value at 100°C, and the storage modulus (E') at 25°C and 135°C can be determined from the measurement results obtained by the following measurement methods.

[0124] Measurement method for dynamic viscoelasticity (storage modulus (E')) and loss tangent (tanδ) The dynamic viscoelasticity measuring device used is a "Viscoelasticity Measuring Device (Model: DMS6100)" manufactured by Seiko Instruments Inc. As a measurement sample, the stretched film is cut into a strip of 40 mm lengthwise and 8 mm widthwise, with the film machine direction (MD) as the long axis, and the temperature dependency of the dynamic viscoelasticity of the film (temperature dispersion data) is measured under the measurement conditions shown below in accordance with JIS-K7244 (1999 edition). Test mode: Tensile mode Chuck distance: 20mm Vibration frequency: 1Hz Distortion amplitude: 10μm Minimum tension: 100mN Tension Gain: 1.2 Initial force amplitude: 100mN Temperature range: -60 to 150°C Heating rate: 2℃ / min Measurement atmosphere: In air Measurement thickness: 7.0 μm

[0125] The stretched film of the present invention is a stretched film stretched in at least one direction, but it is also preferably a biaxially stretched film (hereinafter sometimes referred to as a "biaxially stretched film" or "biaxially stretched film of the present invention").

[0126] The stretched film of the present invention may be a single-layer film consisting of Layer A, or may be a multilayer film obtained by laminating multiple layers and / or films using a conventionally known lamination method, such as coextrusion, lamination, heat sealing, coating, etc., either alone or in combination. The lamination may be carried out before or after stretching Layer A.

[0127] The multilayer film can have, for example, a three-layer structure (layer b / layer a / layer b) consisting of a surface layer (skin layer: layer b) and a core layer (layer a); a three-layer structure (layer b / layer a / layer c) in which one surface layer is further added with another layer (layer c); a four-layer structure (layer b / layer a / layer a / layer c) in which there are two core layers; a four-layer structure (layer b / layer a / layer a' / layer c) in which one core layer is replaced with the other core layer (layer a'); a so-called super multilayer film including a two-layer or more structure in which two or more layers of layer a are laminated, or a laminate structure in which ten or more layers of layer a are laminated. Each layer may be made of a different resin or the same resin.

[0128] The Layer A of the present invention can be used as any of Layer a, Layer a', Layer b, Layer c, Layer d, etc. For example, when used as a surface layer, it tends to have excellent stretchability, and when used as a core layer, it tends to have excellent rigidity and insulation properties at high temperatures.

[0129] In order to facilitate the realization of the effects of the present invention, the thickness ratio of layer A to the stretched film of the present invention is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more, relative to 100% of the stretched film thickness.

[0130] When the layer A of the present invention is used as a core layer, a preferred surface layer to be laminated is a layer containing a polypropylene resin as a main component and a pigment. The polypropylene resin and pigment may be the same as those for the layer A.

[0131] The preferred layer configuration depends on the application, but for example, in applications such as packaging and separators, two or more layers are preferred from the viewpoint of functional separation between the core layer and the skin layer. In applications such as capacitors, a single layer is preferred from the viewpoint of reducing the thickness, and two or more layers are preferred from the viewpoint of electrical insulation.

[0132] Specific examples of coextrusion methods include pre-die lamination, in which molten resins are brought into contact in a feed block before the die, in-die lamination, in which they are brought into contact along a path inside the die, and out-of-die lamination, in which they are discharged from multiple concentric lips and brought into contact, etc. For example, in-die lamination can be performed using a multi-layer die such as a three-layer multi-manifold die.

[0133] The thickness of the stretched film of the present invention is not particularly limited. The preferred thickness depends on the application; for example, for packaging applications, separator applications, etc., a thickness of 5 μm to 80 μm, or 10 μm to 50 μm, is preferred. For capacitor applications, a thinner thickness is preferred from the viewpoint of reducing the volume of the capacitor and increasing the capacitance. From this viewpoint, the thickness is preferably 10 μm or less, more preferably 9 μm or less, even more preferably 8 μm or less, even more preferably 6 μm or less, particularly preferably 5 μm or less, especially more preferably 4 μm or less, and particularly preferably 3 μm or less. Furthermore, from the viewpoint of stretchability and the metal vapor deposition process, the thickness after stretching is, for example, 1 μm or more, preferably 1.5 μm or more, more preferably 1.8 μm or more, even more preferably 2 μm or more, and even more preferably 2.2 μm or more.

[0134] The film thickness of the stretched film of the present invention is measured using an outside micrometer (high-precision digimatic micrometer MDH-25MB manufactured by Mitutoyo Corporation) in accordance with JIS K 7130:1999 Method A.

[0135] The stretched film of the present invention has high dielectric breakdown strength at room temperature and at high temperatures, which are measured at room temperature (23°C), 120°C, and 135°C according to the method described in the Examples below.

[0136] The stretched film of the present invention preferably has a dielectric breakdown strength of 450 V in a 23°C environment. DC / μm or more, preferably 470V DC / μm or more, more preferably 490V DC / μm or more, particularly preferably 500V DC / μm or more, more particularly preferably 510V DC The upper limit of the dielectric breakdown strength at the above temperature is not particularly limited, and is, for example, 700V DC / μm or less, 650V DC / μm or less, 620 DC / μm or less.

[0137] The stretched film of the present invention preferably has a dielectric breakdown strength of 490 V in a 120°C environment. DC / μm or more, preferably 500V DC / μm or more, more preferably 530V DC The upper limit of the dielectric breakdown strength at the above temperature is not particularly limited, and is, for example, 640 V DC / μm or less, 620V DC / μm or less, 600V DC / μm or less, 580V DC / μm or less.

[0138] The stretched film of the present invention preferably has a dielectric breakdown strength of 480 V in a 135°C environment. DC / μm or more, preferably 500V DC / μm or more, more preferably 520V DC The upper limit of the dielectric breakdown strength at the above temperature is not particularly limited, and is, for example, 620V DC / μm or less, 600V DC / μm or less, 580V DC / μm or less, 560V DC / μm or less.

[0139] The stretched film of the present invention is preferred because it exhibits little change in dielectric breakdown strength with increasing temperature. The dielectric breakdown strength ratio, which is the ratio of the dielectric breakdown strength in a 135°C environment to the dielectric breakdown strength in a 23°C environment (dielectric breakdown strength in a 135°C environment / dielectric breakdown strength in a 23°C environment), is preferably 0.7% or more, more preferably 0.75 or more, even more preferably 0.80% or more, and particularly preferably 0.85 or more. The upper limit is not particularly limited and may be, for example, 1.0, 0.99, 0.98, or 0.95. Note that the load related to dielectric breakdown strength differs significantly between a 23°C environment and a 135°C environment. Therefore, general polypropylene films are not preferred because they have a small dielectric breakdown ratio and the temperature stability of the electrical properties of capacitors using them is reduced. The stretched film of the present invention is preferred because it exhibits little change in dielectric breakdown strength from a 23°C environment to a 135°C environment, improving the temperature stability of the electrical properties of capacitors using it.

[0140] The uses of the stretched film of the present invention are not particularly limited. The stretched film of the present invention can be used, for example, as a packaging film or separator with excellent heat resistance, taking advantage of its heat resistance. The stretched film of the present invention can also be suitably used as a film for capacitors. In particular, it can be extremely suitably used in capacitors that are used in high-temperature environments of 135°C or higher, and that are small in size and have a high capacity (for example, 5 μF or more, preferably 10 μF or more, and more preferably 20 μF or more).

[0141] 1-5. Stretched film manufacturing method If the raw material for the stretched film of the present invention (containing at least the polypropylene resin described above and hydrogenated polystyrene, which is added as needed) has a high moisture content, it is dried before use. The drying conditions are not particularly limited, but are, for example, 70 to 150°C, preferably 80 to 130°C. The drying time can be adjusted appropriately depending on the drying temperature, and is, for example, 2 to 30 hours, preferably 3 to 20 hours. If the moisture content is low, the drying step can be omitted.

[0142] The raw materials may be individually fed into the film-forming extruder and mixed inside the film-forming extruder, or may be mixed before being fed into the film-forming extruder and then fed into the film-forming extruder as a raw material mixture.

[0143] The mixing method for preparing the raw material mixture is not particularly limited, but examples include a method in which a plurality of types of resin blocks (pellets, etc.) are dry-blended using a mixer or the like.

[0144] As a mixing method, melt kneading (melt blending) may be used. Melt kneading is preferred because if the resins can be kneaded uniformly, the rigidity, electrical insulation properties, stretchability, etc. of the stretched film are likely to be improved.

[0145] As a method of melt kneading, a single-screw type, twin-screw type, or multi-screw type melt kneader having more than one screw can be used. Twin-screw melt kneaders are particularly suitable because they are highly effective in improving the rigidity, electrical insulation, stretchability, etc. of the stretched film. In the case of twin-screw types, either co-rotating or counter-rotating kneading types can be used, but co-rotating types are preferred from the viewpoint of suppressing resin degradation. The screw diameter-to-length ratio (L / D) of the melt kneader is preferably 20 or more, more preferably 25 or more, and even more preferably 28 or more. By setting the L / D to 20 or more, the resins are thoroughly mixed, improving the rigidity, electrical insulation, and stretchability of the stretched film. There is no upper limit to L / D, but from the viewpoint of suppressing resin degradation, it is 80 or less, preferably 50 or less.

[0146] The temperature during melt kneading is preferably 200° C. to 300° C., more preferably 220° C. to 280° C., in order to balance suppression of resin deterioration and kneadability. During melt kneading, it is preferable to purge the kneader with an inert gas such as nitrogen in order to suppress resin deterioration.

[0147] The raw materials and / or raw material mixture for producing the stretched film of the present invention are supplied to a film-forming extruder and extruded. The extrusion method is not particularly limited, and any known extrusion method can be used. For example, the solid raw materials or resin composition of the present invention supplied to the film-forming extruder are mixed in a heated, molten state by a screw, filtered through a filter, extruded into a film form through a die such as a single-layer T-die, and solidified by contact with a cooling roll set at a predetermined surface temperature to form an unstretched film.

[0148] Examples of film-forming extruders include single-screw types, twin-screw types, and multi-screw types with three or more screws. In the case of twin or more screws, the screw rotation type may be, for example, co-rotating or counter-rotating. The melt temperature is preferably 200 to 300°C, preferably 230 to 280°C, and more preferably 240 to 275°C. This allows the resin to be appropriately kneaded, which tends to improve the rigidity, electrical insulation, stretchability, etc. of the film. To suppress deterioration of the resin during melt extrusion, it is preferable to purge the extruder with an inert gas such as nitrogen.

[0149] The filtration accuracy of the filter used to filter the molten resin is not particularly limited, but is, for example, 2 to 30 μm, preferably 5 to 25 μm, and more preferably 10 to 25 μm.

[0150] The temperature of the die is not particularly limited, but is preferably 200 to 300°C, more preferably 210 to 280°C, more preferably 215 to 270°C, and even more preferably 220 to 260°C.

[0151] The method of contacting the molten resin extruded from the die with a chill roll to solidify it is not particularly limited, and examples include air knife, electrostatic pinning, elastic roll nip, metal roll nip, elastic metal roll nip, etc. The surface temperature of the chill roll is, for example, 30 to 130°C, preferably 35 to 120°C, and more preferably 40 to 110°C.

[0152] The draft ratio when the molten resin extruded from the die is brought into contact with the cooling roll is preferably 1 to 20, more preferably 1.1 to 16, more preferably 1.2 to 10, and even more preferably 1.3 to 8. By setting the draft ratio within this range, the longitudinal orientation of the film can be set to an appropriate range, and the stretchability can be improved. The draft ratio is determined based on the density d (g / cm) of the molten resin. 3 ), width W (cm) of the die lip outlet, average slit gap t (cm) of the die lip outlet, resin discharge rate Q (g / min), and peripheral speed V (cm / min) of the cooling and forming roll, are used to calculate the cooling and forming rate using the following formula. Draft ratio = dVWt / Q

[0153] The thickness of the unstretched film is not particularly limited, but is, for example, 20 to 300 μm.

[0154] The film of the present invention is a stretched film stretched in at least one direction. The method for stretching the unstretched film is not particularly limited, and known stretching methods can be used. Examples include a method in which the unstretched film of the present invention is heated with a heated roll and stretched in the longitudinal direction (machine direction, MD) (longitudinal uniaxial roll stretching method); a method in which the unstretched film of the present invention is stretched in the transverse direction (width direction, TD) in an oven (commonly called a tenter) at a predetermined temperature (transverse uniaxial stretching method); a method in which longitudinal uniaxial roll stretching is followed by transverse uniaxial stretching (sequential biaxial stretching method); a method in which longitudinal uniaxial roll stretching is followed by transverse uniaxial stretching and then longitudinal uniaxial (roll or tenter method) stretching (multistage sequential biaxial stretching method); a method in which the unstretched film of the present invention is sequentially longitudinally stretched and transversely stretched in a tenter at a predetermined temperature (tenter method sequential biaxial stretching method); and a method in which the unstretched film of the present invention is simultaneously longitudinally stretched and transversely stretched in a tenter (simultaneous biaxial stretching method). As a method for stretching the unstretched film of the present invention, a method of longitudinal uniaxial roll stretching followed by transverse uniaxial stretching (sequential biaxial stretching method) is preferred, as it provides excellent rigidity, electrical insulation, stretchability, etc. of the stretched film.

[0155] In the longitudinal uniaxial roll stretching method, a plurality of heating rolls may be used. The stretching point may be one or two or more. When there is one stretching point, the temperature of the roll immediately before the stretching point (roll before stretching) (T MD-延伸前 ), and if there are two or more stretching points, the surface temperature of the roll before stretching at the point where the stretching ratio is maximum (T MD-延伸前 ) is preferably 125°C or higher and 175°C or lower, more preferably 130°C or higher and 170°C or lower, even more preferably 135°C or higher and 168°C or lower, and particularly preferably 140°C or higher and 166°C or lower. In addition, when there is one stretching point, the temperature of the roll (post-stretching roll) immediately after the stretching point (T MD-延伸後 ), and if there are two or more stretching points, the surface temperature of the roll after stretching at the point where the stretching ratio is maximum (T MD-延伸後 ) is preferably 80°C or higher and 140°C or lower, more preferably 90°C or higher and 130°C or lower, even more preferably 100°C or higher and 120°C or lower, and particularly preferably 105°C or higher and 115°C or lower.

[0156] The stretching ratio in the machine direction (the product of the stretching ratios when there are two or more stretching points) is preferably 1.5 to 5.0, more preferably 2.0 to 4.6, and even more preferably 2.2 to 4.2. By setting the temperature and stretching ratio within these ranges, orientation in the machine direction is suppressed within an appropriate range, and a stretched film excellent in rigidity, electrical insulation, stretchability, etc. can be easily obtained.

[0157] The tenter to be used preferably has three or more temperature zones, and more preferably five or more temperature zones, so that heating, stretching, and the later-described heating treatment, relaxation treatment, cooling treatment, etc. can be performed at different temperatures.

[0158] When longitudinal stretching is performed in a tenter, the oven temperature during stretching (T MD) is preferably 125° C. or higher and 175° C. or lower, more preferably 130° C. or higher and 170° C. or lower, even more preferably 135° C. or higher and 168° C. or lower, and particularly preferably 140° C. or higher and 166° C. or lower. The draw ratio in the machine direction is preferably 1.5 times or higher and 5.0 times or lower, more preferably 2.0 times or higher and 4.6 times or lower, and even more preferably 2.2 times or higher and 4.2 times or lower.

[0159] When transverse stretching is performed in a tenter, the oven temperature during stretching (T TD ) is preferably 140°C or higher and 175°C or lower, more preferably 145°C or higher and 170°C or lower, even more preferably 150°C or higher and 168°C or lower, and particularly preferably 155°C or higher and 166°C or lower. The stretching ratio in the transverse direction is preferably 5.0 times or higher and 11.0 times or lower, more preferably 6.0 times or higher and 10.0 times or lower, and even more preferably 7.0 times or higher and 9.5 times or lower. By setting the temperature and stretching ratio within these ranges, orientation in the transverse direction is suppressed within an appropriate range, making it easy to obtain a stretched film that is excellent in rigidity, electrical insulation, stretchability, etc.

[0160] The above-mentioned stretching temperature (T MD , T MD-延伸前 , and T TD When hydrogenated polystyrene is contained in the layer A of the present invention, it is more preferable that T be adjusted according to the glass transition temperature (Tg) of the hydrogenated polystyrene. MD , and T MD-延伸前 is preferably Tg-10°C or more and Tg+25°C or less, more preferably Tg-5°C or more and Tg+20°C or less, and even more preferably Tg or more and Tg+16°C or less. TD is preferably Tg or higher and Tg+30° C. or lower, more preferably Tg+5° C. or higher and Tg+28° C. or lower, and even more preferably Tg+10° C. or higher and Tg+25° C. or lower. By setting the temperature within this range, the orientation of the stretched film is suppressed within an appropriate range, and a stretched film excellent in rigidity, electrical insulation, stretchability, etc. can be easily obtained.

[0161] In addition, the aforementioned stretching temperature (T MD , T MD-延伸前 , and T TDIf the temperature is below the aforementioned range, if the kneading properties during resin blending or extrusion are poor, or if the draft ratio during extrusion molding is inappropriate, pores may form in Layer A during stretching. If many pores form, the rigidity, electrical insulation, and stretchability of the stretched film tend to decrease.

[0162] Since the total light transmittance of the stretched film is likely to decrease when many pores are formed, the total light transmittance of the stretched film of the present invention is preferably 80% or more, more preferably 85% or more, even more preferably 88% or more, and particularly preferably 90% or more. From the viewpoint of the electrical characteristics (safety) of the capacitor, the total light transmittance is preferably 99% or less, more preferably 98% or less, even more preferably 97% or less, and particularly preferably 96% or less.

[0163] The product of the longitudinal stretching ratio and the transverse stretching ratio of the stretched film (when a relaxation treatment described below is performed, the product is calculated using the longitudinal stretching ratio and the transverse stretching ratio before relaxation) is preferably 15 to 48, more preferably 17 to 42, even more preferably 19 to 38, particularly preferably 21 to less than 35, and more particularly preferably 22 to 34. By setting the temperature and stretching ratio within these ranges, a stretched film excellent in rigidity, electrical insulation, stretchability, etc. can be easily obtained.

[0164] Stretched films with an area ratio of 12% or less and unstretched films (with an area ratio of 1%) tend to have reduced rigidity and electrical insulation. Furthermore, if the area ratio at which a film can be stretched without breaking is 12% or less, the film's stretchability is not very good.

[0165] The stretched film of the present invention may be subjected to a relaxation treatment (a treatment of reducing the stretch ratio after stretching, for example, by up to 20% of the stretch ratio), a heating treatment, or a cooling treatment, as necessary. These treatments may be performed independently or in combination, for example, by performing the relaxation treatment and the heating treatment simultaneously, or by performing the relaxation treatment and the cooling treatment simultaneously. By appropriately performing the relaxation treatment, the heating treatment, and the cooling treatment, the flatness of the stretched film, the dimensional stability against temperature changes, the passability through the vapor deposition process, etc. can be improved.

[0166] The relaxation in the transverse direction is preferably 3% to 20% of the maximum stretching ratio in the transverse direction, more preferably 5% to 16%, and even more preferably 6.5% to 14%.

[0167] The heat treatment temperature is preferably 130° C. to 180° C., more preferably 140° C. to 175° C., and even more preferably 145° C. to 170° C. The heat treatment time is preferably 1 second to 20 seconds, and more preferably 2 seconds to 15 seconds.

[0168] The stretched film of the present invention may be subjected to corona treatment, static electricity removal treatment, heating treatment, etc. Appropriately performing corona treatment, static electricity removal treatment, heating treatment, etc. can improve the passability through the deposition process. The heating treatment temperature is preferably 20°C or higher and 80°C or lower, more preferably 25°C or higher and 60°C or lower, and even more preferably 30°C or higher and 55°C or lower. The heating treatment time is preferably 3 hours or higher and 50 hours or lower, and more preferably 6 hours or higher and 30 hours or lower.

[0169] 2. Metal laminated film In one aspect, the present invention relates to a metal laminated film (sometimes referred to herein as "the metal laminated film of the present invention") having the stretched film of the present invention and a metal layer laminated on one or both sides of the stretched film. This will be described below.

[0170] The stretched film of the present invention may have a metal layer on one or both sides thereof, for example, to adjust the permeability of gases such as oxygen and water vapor when used as a packaging film, or as an electrode when used as a capacitor.

[0171] Examples of methods for laminating a metal layer on the surface of the stretched film of the present invention include vacuum plating such as metal vapor deposition and sputtering, coating and drying of a metal-containing paste, and pressure bonding of a metal foil or metal powder. Among these, from the viewpoints of productivity and economy, vacuum vapor deposition and sputtering are more preferred, and vacuum vapor deposition is even more preferred. Examples of vacuum vapor deposition methods include the crucible method and the wire method, but the method is not particularly limited and the most suitable method can be selected as appropriate.

[0172] The metal used in the metal layer may be, for example, a single metal such as zinc, lead, silver, chromium, aluminum, copper, or nickel, a mixture of two or more of these metals, or an alloy of these metals. However, taking into consideration the environment, economy, and performance, one or more of zinc and aluminum are preferred.

[0173] The film resistance of the metal layer is preferably about 0.5 to 10 Ω / □ from the viewpoint of permeability to gases such as oxygen and water vapor, and about 1 to 60 Ω / □ from the viewpoint of the electrical properties of the capacitor. From the viewpoint of the electrical properties of the capacitor, in order to exhibit self-healing properties, the film resistance is more preferably 5 Ω / □ or more, and even more preferably 10 Ω / □ or more, and from the viewpoint of safety as a capacitor, the film resistance is more preferably 50 Ω / □ or less, and even more preferably 30 Ω / □ or less.

[0174] In this specification, "Ω / □" is a unit that is also expressed as "Ω / square."

[0175] When forming an electrode (metal vapor deposition film) by vacuum deposition, the film resistance can be measured during deposition, for example, by a non-contact eddy current method or light transmittance 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 adjust the evaporation amount.

[0176] When the film is used in capacitors, when a metal vapor deposition film is formed on one side of the film, an insulating margin (vertical margin) of a certain width where no metal is laminated is formed so that it will become an insulating part when the film is rolled up to make a capacitor.

[0177] Furthermore, it is preferable to form a heavy edge portion to strengthen the bond between the metal layer of the metal layer-integrated film and the metallikon electrode. The film resistance of the heavy edge portion is usually about 1 to 8 Ω / □, preferably about 1 to 5 Ω / □. The thickness of the metal film in the heavy edge portion is not particularly limited, but is preferably 1 to 200 nm.

[0178] In capacitor applications, there are no particular limitations on the deposition pattern (fuse pattern) of the metal deposition film to be formed, but from the viewpoint of improving the safety and other properties of the capacitor, it is preferable to form fuses by pattern deposition such as a fishnet pattern, a T-margin pattern, etc. Forming a metal deposition film with a deposition pattern including a fuse on at least one surface of the stretched film of the present invention is preferable because it improves the safety of the resulting capacitor and is effective in preventing breakdown and short circuits of the capacitor.

[0179] As a method for forming the fuse and the insulating margin, any known method can be used without any restrictions, such as a tape method in which masking is performed with tape during vapor deposition, or an oil method in which masking is performed by applying oil.

[0180] A protective agent may be applied to the metal laminated film of the present invention for the purposes of physical protection of the metal layer, prevention of moisture absorption, prevention of oxidation, etc. As the protective agent, silicone oil, fluorine oil, etc. can be preferably used. The protective agent may be provided as a layer on the metal layer, or may be impregnated into the metal layer.

[0181] The metal laminated film of the present invention can be processed into the capacitor of the present invention described below. The metal laminated film of the present invention can also be used for packaging purposes, for example, as a barrier film against oxygen and other gases.

[0182] 3. Capacitor In one aspect, the present invention relates to a capacitor (film capacitor) (sometimes referred to as "the capacitor of the present invention" in this specification) comprising the film of the present invention or the metal laminated film of the present invention. This will be described below.

[0183] In such capacitors, the stretched film of the present invention can be used as a dielectric film for a capacitor by, for example, (i) using the above-mentioned metal laminated film, (ii) laminating the stretched film of the present invention not provided with electrodes with a dielectric having metallized surfaces (the dielectric can be, for example, the stretched film of the present invention or another plastic film), or (iii) laminating the stretched film of the present invention not provided with electrodes with another conductor (for example, a metal foil).

[0184] In the process of producing a capacitor, a film is wound. For example, two pairs of the metal laminated film of the present invention are overlapped and wound so that the metal layers of the metal laminated film of the present invention and the stretched film of the present invention are alternately stacked, and further so that the insulating margins are on opposite sides. In this case, it is preferable to stack the two pairs of the metal laminated film of the present invention with a 1 to 2 mm offset. The winding machine used is not particularly limited, and for example, an automatic winding machine 3KAW-N2 manufactured by Kaito Seisakusho Co., Ltd. can be used.

[0185] The winding process of the stretched film is not limited to the above method, and other methods may be used, for example, a double-sided vapor-deposited stretched film of the present invention (in which case the heavy edges are positioned at the opposite ends of the front and back surfaces) and an undeposited film of the present invention (2 to 3 mm narrower than the double-sided vapor-deposited film of the present invention) may be alternately laminated and wound.

[0186] When producing a flat capacitor, the resulting roll is usually pressed after winding. Pressing promotes tightening of the capacitor and element formation. From the viewpoint of controlling and stabilizing the interlayer gap, the optimum pressure to be applied varies depending on the thickness of the stretched film of the present invention, but is generally 2 to 20 kg / cm. 2 is.

[0187] Next, metal is sprayed onto both end surfaces of the wound body to provide metallikon electrodes, thereby producing a capacitor.

[0188] The capacitor is further subjected to a predetermined heat treatment. That is, the present invention includes a step of subjecting the capacitor to heat treatment (hereinafter, sometimes referred to as "thermal aging"). The heat treatment temperature is not particularly limited, but is, for example, 80 to 190°C. The method for subjecting the capacitor to heat treatment may be appropriately selected from known methods, including, for example, a method using a thermostatic bath in a vacuum atmosphere or a method using high-frequency induction heating. The heat treatment time is preferably 1 hour or more, and more preferably 5 hours or more, from the viewpoint of obtaining mechanical and thermal stability, but is more preferably 20 hours or less, from the viewpoint of preventing molding defects such as heat wrinkles and molding.

[0189] The heat treatment provides the effect of thermal aging. Specifically, the gaps between the films constituting the capacitor based on the stretched film of the present invention are reduced, corona discharge is suppressed, and the internal structure of the stretched film of the present invention is changed, promoting crystallization. As a result, it is believed that the electrical insulation properties are improved. If the heat treatment temperature is lower than the predetermined temperature, the above-mentioned effect of thermal aging cannot be fully obtained. On the other hand, if the heat treatment temperature is higher than the predetermined temperature, the stretched film of the present invention may undergo thermal decomposition, oxidative degradation, etc.

[0190] Lead wires or bus bars are usually welded to the metallikon electrodes of the heat-aged capacitor. To impart weather resistance, particularly to prevent humidity degradation, the capacitor is preferably encapsulated in a case and potted with epoxy resin.

[0191] The capacitor of the present invention using the stretched film of the present invention can be suitably used in high-temperature environments, and can be made into a small-sized capacitor with a high capacity (for example, 5 μF or more, preferably 10 μF or more, and more preferably 20 μF or more). Therefore, the capacitor of the present invention can be used as a high-voltage capacitor used in electronic devices, electrical devices, etc.; various switching power supplies; filter capacitors, smoothing capacitors for converters, inverters, etc. Furthermore, the capacitor of the present invention can be suitably used as an inverter capacitor, converter capacitor, etc. for controlling the drive motor of electric vehicles, hybrid vehicles, etc., which have seen increasing demand in recent years. [Example]

[0192] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0193] (1)Measurement method The various measurement methods are as follows.

[0194] (1-1) Number average molecular weight (Mn), weight average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mw) of polypropylene resin The number average molecular weight (Mn), weight average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mw) of each resin were measured using GPC (gel permeation chromatography) under the following conditions.

[0195] Specifically, a Tosoh Corporation HLC-8121GPC-HT model high-temperature GPC system with a built-in differential refractometer (RI) was used. Three Tosoh Corporation TSKgel GMHHR-H(20)HT columns were connected together. Measurements were performed at a column temperature of 140°C using trichlorobenzene as the eluent at a flow rate of 1.0 ml / min. A calibration curve for the molecular weight M was created using standard polystyrene manufactured by Tosoh Corporation, and the measured values ​​were converted to polypropylene molecular weights using the Q-factor to obtain the number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz). The molecular weight distribution (Mw / Mn) was obtained using the Mw and Mn values. The molecular weight distribution (Mz / Mw) was also obtained using the Mz and Mw values.

[0196] (1-2) Mesopentad fraction of polypropylene resin The polypropylene resin was dissolved in a solvent, and the measurement was carried out using a high-temperature Fourier transform nuclear magnetic resonance spectrometer (high-temperature FT-NMR) under the following conditions. High-temperature nuclear magnetic resonance (NMR) spectrometer: JEOL Ltd., high-temperature Fourier transform nuclear magnetic resonance spectrometer (high-temperature FT-NMR), JNM-ECP500 Observed nucleus: 13C (125MHz) Measurement temperature: 135℃ Solvent: ortho-dichlorobenzene (ODCB: a mixed solvent of ODCB and deuterated ODCB (mixing ratio = 4 / 1)) Measurement mode: Single pulse proton broadband decoupling Pulse width: 9.1 μsec (45° pulse) Pulse interval: 5.5 seconds Accumulation count: 4,500 times Shift standard: CH3 (mmmm) = 21.7 ppm The pentad fraction, which indicates the degree of stereoregularity, was calculated as a percentage (%) from the integrated intensity of each signal derived from a combination of five pentads (pentads) consisting of meso (m) pentads arranged in the same direction and racemo (r) pentads arranged in the opposite direction (e.g., mmmm and mrrm). The assignment of each signal derived from mmmm, mrrm, etc. was based on the spectral descriptions in, for example, T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988).

[0197] (1-3) Heptane insolubles (HI) of polypropylene resins Polypropylene resin was press-molded to a size of 10 mm x 35 mm x 0.3 mm to prepare a measurement sample weighing 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.

[0198] (1-4) Melt mass flow rate of resin The melt flow rate (MFR) of each resin in the form of raw resin pellets was measured using a Toyo Seiki melt indexer in accordance with JIS K 7210-1:2014. Specifically, 4 g of raw material was placed in a cylinder heated to the test temperature (230°C for polypropylene resins, 260°C for polymers with alicyclic structures in the side chain and polymers with alicyclic structures in the main chain) and preheated for 3.5 minutes under a load of 2.16 kg. The weight of the raw resin extruded through the bottom hole over 30 seconds was then measured, and the MFR (g / 10 min) was calculated. The above measurement was repeated three times, and the average value was used as the measured MFR.

[0199] (1-5) Melting point and glass transition temperature of resin The calculations were performed using a Perkin-Elmer Diamond DSC (power compensation type). Five mg of each resin was weighed, placed in an aluminum sample holder, and placed in the DSC instrument. Under a nitrogen flow, the resin was heated from 30°C to 230°C at a rate of 20°C / min, held at 230°C for 5 minutes, cooled to 30°C at 20°C / min, and held at 30°C for 5 minutes. The melting point and glass transition temperature were then determined from the DSC curve obtained while the temperature was again raised to 230°C at 20°C / min. Specifically, the melting peak (the largest melting peak in the case of multiple melting peaks) as defined in JIS-K7121, 9.1(1), was used as the melting point, and the midpoint glass transition temperature as defined in JIS-K7121, 9.3(1), was used as the glass transition temperature.

[0200] (2) Preparation of resin composition and stretched film (2-1)Resin used etc. [Polypropylene resin] Raw material A: Isotactic polypropylene resin manufactured by Prime Polymer Co., Ltd. Prime Polypro (registered trademark) MFR: 3.5g / 10min (measurement temperature 230℃) Melting point: 164℃ Mesopentad fraction: 98.6mol% Heptane insolubles: 98.1% by mass Number average molecular weight (Mn): 49000 Weight average molecular weight (Mw): 390000 z average molecular weight (Mz): 1520000 Molecular weight distribution (Mw / Mn): 8.0 Molecular weight distribution (Mz / Mw): 3.9

[0201] Material B: Polymer with alicyclic structures in the side chain (hydrogenated polystyrene) manufactured by USI Corporation ViviOn® 0645 Glass transition temperature: 146℃ MFR: 5.5g / 10min (measurement temperature 260℃) Hydrogenation rate of 99% or more Hydrogenated polystyrene with cyclohexane structures in the side chains

[0202] (2-2) Method for producing stretched film [Preparation of unstretched film] Raw materials A and B were weighed so that the mass percentages of each raw material were as shown in Table 1, and dry-blended using a tumbler. The resulting raw material mixture was fed into an extruder, melted at a resin temperature of 260°C, and extruded using a T-die. The molten resin was solidified by contact with a mirror-finished metal roll (cooling roll) with an air knife at a surface temperature of 90°C and formed into a film, yielding an unstretched cast raw sheet with a thickness of approximately 170 μm.

[0203] [Preparation of stretched film] Next, the unstretched cast raw sheet was stretched 3.5 times in the machine direction at 150°C using a Bruckner KARO IV Lab Stretcher, and then immediately stretched 7 times in the transverse direction to obtain a 7μm thick biaxially oriented polypropylene film.In Comparative Example 1 (100% polypropylene resin), an approximately 320μm unstretched cast raw sheet was stretched 5 times in the MD and 9 times in the TD to obtain a 7μm thick biaxially oriented polypropylene film.

[0204] (3) Evaluation method for stretched film properties The stretched films of the Examples and Comparative Examples were evaluated as follows.

[0205] (3-1) Measurement of total light transmittance The total light transmittance of the stretched films obtained in the examples and comparative examples was measured using a haze meter NDH-5000 manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS-K7361.

[0206] (3-2) Measurement of dynamic viscoelasticity (storage modulus (E')) and loss tangent (tanδ) The dynamic viscoelasticity measuring device used was a "Viscoelasticity Measuring Device (Model: DMS6100)" manufactured by Seiko Instruments Inc. As measurement samples, stretched films were cut into strips measuring 40 mm in the machine direction and 8 mm in the transverse direction, with the machine direction (MD) of the film as the long axis, and the temperature dependence of the dynamic viscoelasticity of the films (temperature dispersion data) was measured under the measurement conditions shown below in accordance with JIS-K7244 (1999 edition). Test mode: Tensile mode Chuck distance: 20mm Vibration frequency: 1Hz Distortion amplitude: 10μm Minimum tension: 100mN Tension Gain: 1.2 Initial force amplitude: 100mN Temperature range: -60 to 150°C Heating rate: 2℃ / min Measurement atmosphere: In air Measurement thickness: 7.0 μm

[0207] From the results of the above measurement methods, the temperature dispersion data of the stretched film, the main dispersion peak of the loss tangent (tan δ), the loss tangent (tan δ) value at 100°C, and the storage modulus (E') at 25°C and 135°C were determined. The measurement results of the logarithm of the storage modulus (logE') and the temperature dependence of the loss tangent (tan δ) for Example 2 and Comparative Example 1 are shown in Figure 1.

[0208] (3-3) Evaluation of dielectric breakdown strength The dielectric breakdown strength at high temperatures of the stretched films obtained in the examples and comparative examples was evaluated as follows. That is, a measuring device was prepared in accordance with 17.2.2 (plate electrode method) of JIS C2151:2006. However, instead of the elastic material described in 17.2.2 of JIS C2151:2006, a conductive rubber (E12S10 manufactured by Seiwa Electric Co., Ltd.) was used as the lower electrode, and aluminum foil was not wrapped around the electrode.

[0209] The measurement environment was a forced circulation oven at room temperature (23°C), 120°C, or 135°C, and the electrodes and films were used after 30 minutes of temperature adjustment in the oven. The voltage was increased from 0 V at a rate of 100 V / sec, and the voltage when the current value exceeded 5 mA was taken as the breakdown voltage. The breakdown voltage was measured 20 times, and each breakdown voltage value V DC Divide by the thickness (μm) of the stretched film, and the average of 16 points excluding the top 2 and bottom 2 points of the 20 calculation results is calculated as the dielectric breakdown strength (V DC / μm).

[0210] (3-4) Measurement of volume resistivity (ρV) The volume resistivity (ρV) of the stretched films obtained in the examples and comparative examples was measured in accordance with JIS C2139-3-1:2018 under conditions of a 135°C environment and a 1000V load. Specifically, a volume resistivity measuring jig (hereinafter also referred to as "jig") was first placed in a thermostatic chamber in a 135°C environment. The jig had the following configuration. A DC power supply and a DC ammeter were also connected to the jig.

[0211] <Volume resistivity measurement jig> Main electrode (50mm diameter) Counter electrode (diameter 85 mm) An annular guard electrode (outer diameter 80 mm, inner diameter 70 mm) surrounds the main electrode. Each electrode was made of gold-plated copper, and conductive rubber was attached to the surface that came into contact with the sample. The conductive rubber used was EC-60BL (W300) manufactured by Shin-Etsu Silicone Co., Ltd., and the glossy side of the conductive rubber was attached so that it was in contact with the gold-plated copper.

[0212] Next, the stretched film (hereinafter also referred to as "sample") was set in a jig in a thermostatic chamber. Specifically, the main electrode and the guard electrode were attached to one side of the sample, and the counter electrode was attached to the other side, and the sample and each electrode were attached to each other under a load of 5 kgf. Then, the sample was left to stand for 30 minutes.

[0213] Next, a voltage of 1000 V was applied to the sample using a DC power supply. The current value was read one minute after the voltage application, and the volume resistivity was calculated using the following formula. The voltage was applied using a Keithley 2290-10 (DC power supply), and the current value was measured using a Keithley 2635B (DC ammeter). Volume resistivity = [(effective electrode area) × (applied voltage)] / [(sample thickness) × (current value)] Here, the effective electrode area was calculated by the following formula. (Effective electrode area) = Pi × [[[(main electrode diameter) + (guard electrode inner diameter)] / 2] / 2]2 This was repeated three times, and the arithmetic mean value calculated to one significant digit was taken as the volume resistivity (Ω·cm).

[0214] The results are shown in Table 1.

[0215] [Table 1]

[0216] (4) Fabrication of metal layer integrated film and capacitor Using the biaxially stretched films of the examples and comparative examples, metal layer-integrated films and capacitors were fabricated using the following method. Specifically, a special vapor deposition pattern margin and an insulating margin were formed on the biaxially stretched film to provide film capacitor safety, and aluminum was vapor-deposited on the biaxially stretched film to achieve a surface resistivity of 20 Ω / □. The metal layer-integrated film was then slit into a 30 mm width, and two sheets of the metal layer-integrated film were combined and wound using a Kaito Seisakusho automatic winder, Model 3KAW-N2-60 / 83, with the number of turns set to achieve an element capacitance of 20 μF. The wound element was then flattened by pressing, and zinc metal was sprayed onto the element end surfaces while the pressing load was still applied to form electrode leads. The element was then heat-cured at 120°C for 15 hours. After heat curing, leads were soldered to the element end surfaces and sealed with epoxy resin to obtain a flat film capacitor.

[0217] (5) Measurement and evaluation of the physical properties and characteristics of capacitors (5-1) Evaluation of voltage resistance [Voltage resistance at 135℃] The capacitor obtained above was preheated at 135°C for 1 hour, and then the capacitance was measured (initial capacitance) using a Hioki E.E. Corporation LCR HiTester 3522-50. Next, a voltage of 180 Vdc / μm was continuously applied to the capacitor in a thermostatic chamber at 135°C. The capacitance of the capacitor after voltage application was measured in the same manner. Measurements were taken at 24 hours, 100 hours, 200 hours, 300 hours, 400 hours, and 500 hours after application of the DC voltage. The rate of change in capacitance before and after the test was calculated using the following formula. (Capacitance change rate) = [(Capacitance after voltage application) - (Initial capacitance)] / (Initial capacitance) x 100 (%)

[0218] The results are shown in Figure 2.

[0219] (6) Discussion of the results 1, in the stretched film of the present invention (Example 2), a clear tan δ peak is observed in the temperature range of 145°C or higher as a result of measuring the dynamic viscoelasticity in the MD direction of the film. Furthermore, as shown in Table 1, clear tan δ peaks are also observed in the temperature range of 145°C or higher in Examples 1, 3, and 4. On the other hand, in Comparative Example 1, in which no hydrogenated polystyrene is added, although there is a gentle slope in the temperature range of 145°C or higher, no peak is present.

[0220] 1, in Examples 1 to 4, the tan δ peak corresponds to the glass transition temperature (Tg) of the added hydrogenated polystyrene, and as the amount of hydrogenated polystyrene increases, this peak becomes clearer. At the same time, the gradual increase in tan δ around 100°C exhibited by polypropylene (100% polypropylene) (which is thought to correspond to the lattice relaxation of general polypropylene) decreases with the addition of hydrogenated polystyrene.

[0221] The above results indicate that polypropylene and hydrogenated polystyrene form a phase-separated structure when mixed. Polypropylene and hydrogenated polystyrene are thought to form a sea-island structure with polypropylene as the sea and hydrogenated polystyrene as the islands.

[0222] Furthermore, from FIG. 1, it can be seen that in Example 2, a high Tg is maintained (main dispersion peak at 150°C), the loss tangent (tan δ) at 100°C is low, the lattice relaxation motion of polypropylene is contained, the temperature dependence of the storage modulus is small, with little increase or decrease with temperature, and the film is not cloudy, and therefore the phase separation structure is not a fragile (brittle) one.

[0223] From the above, the stretched film of the present invention has the following configuration: (1) Layer A contains 55% to 99% by mass of polypropylene-based resin out of 100% by mass; (2) in temperature dispersion data in the machine direction (MD) of the film in dynamic viscoelasticity measurement, the loss tangent (tan δ) has a dispersion peak in the temperature range of 145°C or higher at a frequency of 1 Hz; and (3) is stretched in at least one direction. By forming a "phase separation structure," it is possible to suppress the relaxation motion (molecular chain motion) of polypropylene that occurs at high temperatures, and therefore it is thought that the decrease in dielectric breakdown strength at high temperatures is suppressed, and the film can exhibit high dielectric breakdown strength at high temperatures and high volume resistivity in a high-temperature environment.

[0224] Therefore, as shown in Figure 2, it is believed that a capacitor using the stretched film of the present invention as a dielectric will not short-circuit even when a voltage of 200 Vdc / μm is continuously applied at a high temperature of 135°C or higher, and will be able to maintain its insulation and capacitance for more than 500 hours.

Claims

1. A stretched film having at least Layer A, (1) The layer A contains 55% by mass or more and 99% by mass or less of a polypropylene-based resin, based on 100% by mass, (2) In dynamic viscoelasticity measurement, the temperature dispersion data in the film machine direction (MD) at a frequency of 1 Hz shows a dispersion peak of loss tangent (tanδ) in a temperature range of 145°C or higher, (3) stretched in at least one direction; A stretched film characterized by:

2. 2. The stretched film according to claim 1, wherein the layer A contains, based on 100% by mass, 55% by mass to 99% by mass of an isotactic polypropylene resin and 1% by mass to 45% by mass of a hydrogenated polystyrene.

3. 3. The stretched film according to claim 2, wherein the hydrogenated polystyrene has an atactic stereoregularity and a hydrogenation rate of 95% or more.

4. 2. The stretched film according to claim 1, wherein, in dynamic viscoelasticity measurement, temperature dispersion data in the machine direction (MD) of the film at a frequency of 1 Hz shows a loss tangent (tanδ) at 100°C of 0.1 or less and has substantially no peak.

5. 2. The stretched film according to claim 1, wherein, in temperature dispersion data in a dynamic viscoelastic measurement in the machine direction (MD) of the film at a frequency of 1 Hz, the ratio E'(135) / E'(25) of the storage modulus E'(135) at 135°C to the storage modulus E'(25) at 25°C is 0.19 or more.

6. 2. The stretched film according to claim 1, wherein the stretched film has a thickness of 1.8 μm or more and 10 μm or less and a total light transmittance of 80% or more.

7. 10. The stretched film of claim 1, which is a monolayer film.

8. 10. The stretched film of claim 1, which is a biaxially stretched film.

9. The stretched film according to claim 1, which is used for a capacitor.

10. A metal laminated film comprising the stretched film according to any one of claims 1 to 9 and a metal layer laminated on one or both sides of the stretched film.

11. A capacitor comprising the film of claim 1.

12. A capacitor comprising the metal laminate film of claim 10.

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