Polypropylene film

Abstract

This polypropylene film satisfies the following expressions 1 and 2, where A direction is the main orientation axis direction, B direction is a direction perpendicular to the main orientation, E'A (GPa) and E'B (GPa) are the values of storage elastic modulus at 160˚C in dynamic viscoelasticity measurement in the A direction and the B direction, respectively, and PA (MPa) and PB (MPa) are the values of shrinkage stress at 160˚C in TMA measurements in the A direction and the B direction, respectively. Expression 1: 0.30≤E'A+E'B≤2.00. Expression 2: -1.0≤PA+PB≤5.0.　The present invention addresses the problem of providing a polypropylene film which can be suitably used as a release film even in a high-temperature environment in which conventional polypropylene films cannot be used as release films.

Description

Polypropylene film

[0001] The present invention relates to a polypropylene film that has both low shrinkage at high temperatures and high rigidity and is excellent in heat resistance.

[0002] Polypropylene films are excellent in transparency and electrical properties, and are therefore used in a variety of applications, including packaging, tapes, cable wrapping, capacitors, and other electrical applications. In addition, polypropylene films are excellent in mechanical properties and releasability, and are therefore particularly suitable for use as release films and processing films for various components, such as plastic products, building materials, and optical components.

[0003] Release films are used as supports for coated materials and melt-molding, spacers for press molding, etc. The required properties of release films are set appropriately depending on the intended use, but as temperatures during heating processes and press molding tend to rise year by year due to higher performance materials and improved productivity, heat resistance in particular is becoming more important.

[0004] In the past, polyethylene terephthalate (PET) films, which have excellent heat resistance, have sometimes been used in temperature ranges above 150°C, but it was difficult to achieve both this and release properties, and the required characteristics could not be met. On the other hand, although conventional polypropylene films have high release properties, they begin to significantly shrink at around 120 to 130°C and begin to melt at around 160°C, near their melting point, significantly reducing film rigidity. This can cause problems, such as impairing the quality of mating components made of thermoplastic resin compositions or thermosetting resin compositions that require drying or molding at high temperatures. For this reason, it has been extremely difficult to use polypropylene films as release films at high temperatures above 150°C, especially above 160°C.

[0005] Important heat-resistant properties of polypropylene films include heat shrinkage and rigidity at high temperatures. To improve heat shrinkage, i.e., to reduce heat shrinkage stress, a common method is to reduce the molecular weight of the polypropylene raw material and relax the orientation and residual strain generated by stretching through relaxation treatment or heat setting. However, this method tends to reduce the rigidity of the polypropylene film because it reduces structures that contribute to mechanical strength, such as elastic modulus. On the other hand, methods for increasing rigidity include increasing the molecular weight of the polypropylene raw material and increasing the molecular orientation and tension of the amorphous portion through low-temperature stretching or high-magnification stretching, thereby increasing the elastic modulus from room temperature. However, this method tends to increase the heat shrinkage stress because it increases structures that are easily relaxed at high temperatures. Thus, with conventional techniques, it has been extremely difficult to achieve both high-temperature heat shrinkage and rigidity in polypropylene films.

[0006] Under the above circumstances, as an example of a conventional means for improving heat resistance, for example, Patent Document 1 describes an example in which the molecular weight of the polypropylene raw material is lowered to reduce the heat shrinkage rate. Also, Patent Document 2 describes an example in which the heat shrinkage rate is lowered by increasing the heat treatment temperature in the relaxation treatment to relax the molecular orientation. Furthermore, Patent Document 3 describes an example in which the rigidity of the film at high temperatures is increased by multistage widthwise stretching including low-temperature stretching at 150°C or less.

[0007] Japanese Patent Application Laid-Open No. 2014-051657 International Publication No. 2020 / 196602 Japanese Patent Application Laid-Open No. 2021-178974

[0008] However, the methods described in Patent Documents 1 and 2 have problems in that the resulting polypropylene film has low rigidity and low stretching stability at high temperatures. Furthermore, the method described in Patent Document 3 has problems in that the resulting polypropylene film has high heat shrinkage stress at high temperatures, making it difficult to achieve both heat shrinkage properties and rigidity at high temperatures. In other words, the polypropylene films obtained by these methods are difficult to use as release films in high-temperature environments.

[0009] Therefore, an object of the present invention is to solve the above-mentioned problems, that is, to provide a polypropylene film that can be suitably used as a release film even in high-temperature environments, where conventional polypropylene films have not been able to be used as release films.

[0010] In order to solve the above-mentioned problems, the polypropylene film of the present invention has the following constitution: That is, the polypropylene film of the present invention has a main orientation axis direction as A-direction, a direction perpendicular to the main orientation as B-direction, and storage moduli at 160°C in the A-direction and the B-direction in dynamic viscoelasticity measurement as E' Ａ (GPa), E' Ｂ (GPa), and the 160°C shrinkage stress in the A direction and the B direction measured by TMA is P Ａ (MPa), P Ｂ The polypropylene film satisfies the following formulas 1 and 2 when the modulus of elasticity is expressed as 0.30≦E′ (MPa). Ａ +E' Ｂ ≦2.00 Formula 2: -1.0≦P Ａ +P Ｂ ≦5.0

[0011] According to the present invention, it is possible to provide a polypropylene film that can be suitably used as a release film even in high-temperature environments where conventional polypropylene films have been unable to be used as release films.

[0012] FIG. 2 is a schematic diagram illustrating a pressurization method used in evaluating heat resistance characteristics.

[0013] In the polypropylene film of the present invention, the main orientation axis direction is A direction, the direction perpendicular to the main orientation is B direction, and the storage moduli at 160° C. in the A direction and the B direction in dynamic viscoelasticity measurement are E' Ａ (GPa), E' Ｂ (GPa), and the 160°C shrinkage stress in the A direction and the B direction measured by TMA is P Ａ (MPa), P Ｂ (MPa), the polypropylene film of the present invention satisfies the following formulas 1 and 2. The polypropylene film of the present invention will be described in detail below. Formula 1: 0.30≦E′ Ａ +E' Ｂ≦2.00 Formula 2: -1.0≦P Ａ +P Ｂ ≦5.0.

[0014] In the present invention, when a numerical range is expressed with "to", the numerical range includes both ends of the range, and when a unit is written only after the numerical range, the unit is the same throughout the entire numerical range.

[0015] From the viewpoint of maintaining film rigidity at high temperatures, the polypropylene film of the present invention is formed such that the main orientation axis direction is A-direction, the direction perpendicular to the main orientation direction is B-direction, and the storage moduli at 160° C. in the A-direction and B-direction in dynamic viscoelasticity measurement are E' Ａ (GPa), E' Ｂ (GPa), 0.30≦E′ Ａ +E' Ｂ It is important that E' satisfies the above requirement. Ａ +E' Ｂ The lower limit of E' is preferably 0.40, more preferably 0.50, even more preferably 0.60, and particularly preferably 0.70. Ａ +E' Ｂ If E' is less than 0.30, when the polypropylene film is attached to a counter member and treated in a molding press or a heating oven at high temperatures, the polypropylene film cannot withstand the heat and undergoes compression or elongation deformation, which induces excessive sinking or sticking to the counter member. Therefore, there is a concern that the counter member may be damaged or deformed when the polypropylene film is peeled off from the counter member. Ａ +E' Ｂ The upper limit of is 2.00 in view of the thermal properties of polypropylene, and is preferably 1.50 in view of compatibility with the heat shrinkage stress.

[0016] The main orientation axis direction (A direction) of the polypropylene film of the present invention refers to the direction that shows the highest storage modulus at 30°C when dynamic viscoelasticity measurements are performed in each of the directions that form angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° with respect to the longitudinal direction, where the longitudinal direction is defined as 0°. On the other hand, in the case of a film in which it is unclear from the appearance which direction corresponds to the longitudinal direction, for example, lines are drawn at 15° intervals based on an arbitrary straight line on the film plane, slit-shaped film pieces are sampled parallel to each line, and the storage modulus at 30°C is determined by dynamic viscoelasticity measurement, and the direction that gives the highest storage modulus is regarded as the main orientation axis direction. Here, the longitudinal direction refers to the direction in which the film runs during the production process (corresponding to the winding direction in the case of a film roll), and the direction perpendicular to this in the film plane is referred to as the width direction. The direction perpendicular to the main orientation (direction B) in the polypropylene film of the present invention refers to a direction perpendicular to the main orientation axis direction in the film plane. Ａ and E' Ｂ The details of the method for measuring the storage modulus by dynamic viscoelasticity measurement including the above will be described later.

[0017] From the viewpoint of film shrinkage properties at high temperatures, the polypropylene film of the present invention has a shrinkage stress at 160°C measured by TMA in the A direction and the B direction of P Ａ (MPa), P Ｂ (MPa), -1.0≦P Ａ +P Ｂ It is important to satisfy the above condition. Ａ +P Ｂ The upper limit of P is preferably 4.0, more preferably 3.5, even more preferably 3.0, particularly preferably 2.0, and most preferably 1.0. Ａ +P ＢIf the value exceeds 5.0, the polypropylene film will undergo thermal shrinkage when it is placed on a mating member or attached to the mating member and then processed in a molding press or a heating oven at high temperatures. As a result, the polypropylene film is prone to wrinkles and curls, and there is a risk that the deformation of the film, such as wrinkles, may be transferred to the mating member to which it is attached. Ａ +P Ｂ The lower limit of is -1.0 from the viewpoint of film formability, and 0.0 is preferable in consideration of compatibility with the rigidity of the film at high temperatures. The method for measuring the 160°C shrinkage stress in the TMA measurement will be described later in detail.

[0018] E' Ａ +E' Ｂ and P Ａ +P Ｂ To achieve both values ​​within the above ranges, a method can be used in which the raw material composition of the polypropylene film is within the ranges described below, and the film-forming conditions are within the ranges described below. In particular, in order to appropriately control high-melting-point crystal formation and amorphous relaxation under high-temperature film-forming conditions, it is effective to use a polypropylene composition as a raw material that has a high melting point, a fast crystallization rate, and an appropriate range of angular frequency ω (details described below), which indicates relaxation characteristics. In terms of processing, it is also effective to set the preheating and stretching temperatures for longitudinal and transverse stretching within the ranges described below, and to further introduce relaxation steps after longitudinal and transverse stretching, and to treat the film at temperatures and total area relaxation rates within the ranges described below. These methods can also be used in combination as appropriate. By adopting the raw material composition and process conditions described above, it is possible to perform stretching and relaxation treatments under high-temperature conditions while maintaining the film-forming properties of the film, promoting the relaxation of tense amorphous chains, which are a cause of heat shrinkage stress, and forming crystals with extremely high melting points that have not previously been expected for polypropylene films. As a result, both rigidity and heat shrinkage stress can be achieved even at high temperatures of 160°C or higher, and the resulting polypropylene film can be used in such high-temperature environments.

[0019] The polypropylene film of the present invention is Ａ +P Ｂ ) / (E' Ａ +E' Ｂ) is preferably 0.001 or more and 7.500 or less. Ａ +P Ｂ ) / (E' Ａ +E' Ｂ ) is an index showing the balance between the elastic modulus and the thermal shrinkage stress at high temperatures, which have traditionally been in a trade-off relationship, and when this is in the above range, it is possible to reduce compression and elongation deformation in a high-temperature environment. Ａ +P Ｂ ) / (E' Ａ +E' Ｂ The upper limit of (P) is more preferably 5,000, even more preferably 2,000, and particularly preferably 1,000. Ａ +P Ｂ ) / (E' Ａ +E' Ｂ When (P) is 7,500 or less, the elastic modulus becomes relatively higher than the heat shrinkage stress, and when the polypropylene film is attached to a mating member in a molding press or a heating oven at high temperature, the heat shrinkage of the polypropylene film is suppressed, and deterioration in the quality of the attached mating member can be reduced. Ａ +P Ｂ ) / (E' Ａ +E' Ｂ The lower limit of ) is preferably 0.001, more preferably 0.0100, and even more preferably 0.500, from the viewpoint of maintaining the rigidity of the film at high temperatures.

[0020] (P Ａ +P Ｂ ) / (E' Ａ +E' Ｂ In order to achieve the above range, it is effective to set the raw material composition of the polypropylene film within the range described below and to set the film-forming conditions within the range described below. In particular, from the viewpoint of raw materials, it is effective to set the angular frequency ω (described in detail below), which indicates relaxation characteristics, within a more appropriate range in order to further promote the formation of high-melting-point crystals as well as amorphous relaxation, and to configure the polypropylene film with a high proportion of X layers (described in detail below), which contain a large amount of resin with high heat resistance. Furthermore, from the viewpoint of process, it is effective to set the longitudinal stretching relaxation ratio to 0.1% or more, preferably 1.0% or more, in order to promote the formation of high-melting-point crystals while promoting amorphous relaxation.

[0021] From the viewpoint of suppressing thermal shrinkage in a high-temperature environment, the polypropylene film of the present invention preferably has a shrinkage onset temperature measured by TMA in both the A and B directions of 140°C or higher and 170°C or lower (hereinafter, the "shrinkage onset temperature measured by TMA" may be referred to as the "TMA shrinkage stress onset temperature"). The lower limit of the TMA shrinkage stress onset temperature in both the A and B directions is more preferably 145°C, and even more preferably 150°C. By having a TMA shrinkage stress onset temperature of 140°C or higher in both the A and B directions, it becomes easier to keep the heat shrinkage rate of the polypropylene film low in all directions even in high-temperature regions where conventional polypropylene films are difficult to use, and as a result, dimensional stability is improved. The upper limit of the TMA shrinkage stress onset temperature is substantially 170°C. The method for measuring the TMA shrinkage stress onset temperature will be described in detail later.

[0022] To achieve the TMA shrinkage stress onset temperature within the above range, it is effective to set the raw material composition of the polypropylene film within the range described below and to set the film-forming conditions within the range described below. In particular, in terms of raw materials, in order to promote relaxation at higher temperatures, it is effective to use a polypropylene resin or composition whose lower limit of the angular frequency ω (details described below), which indicates the relaxation characteristics, is 15 rad / s or more (preferably 19 rad / s or more). Furthermore, in terms of processing, in order to eliminate the strain caused by longitudinal stretching and transverse stretching by relaxation treatment at higher temperatures, it is effective to set the relaxation temperatures after each of the longitudinal stretching and transverse stretching within the range described below. These methods may also be combined as appropriate.

[0023] The polypropylene film of the present invention preferably has a heat of fusion ratio H of 175°C to 200°C relative to the total heat of fusion in the first run of DSC measurement at a heating rate of 20°C / min of 10%≦H≦50% (hereinafter, "the heat of fusion ratio H of 175°C to 200°C in the first run of DSC measurement at a heating rate of 20°C / min" may be referred to as "heat of fusion ratio H"). This heat of fusion ratio H is an index showing the content of crystals that melt at 175°C or higher, which are present in extremely low proportions in conventional polypropylene films, and a high heat of fusion ratio H means that the polypropylene film has excellent heat resistance. From the above viewpoint, the lower limit of the heat of fusion ratio H is more preferably 15%, even more preferably 20%, and particularly preferably 25%.

[0024] When the heat of fusion ratio H of a polypropylene film is 10% or more, many crystals remain unmelted even in a high-temperature environment of 160°C or higher, which conventional polypropylene films cannot withstand, and high heat resistance is easily achieved. The upper limit of the heat of fusion ratio H is preferably substantially 50%, and more preferably 40% in consideration of compatibility with other properties. The method for measuring the heat of fusion ratio H will be described in detail later.

[0025] To achieve the above-mentioned range of heat of fusion ratio H, it is effective to set the raw material composition of the film within the range described below and the film-forming conditions within the range described below. In particular, to promote the formation of high-melting-point crystals under high-temperature film-forming conditions, it is effective to use a polypropylene resin or composition having a melting point of 166.0°C or higher, a half-crystallization time of 100 seconds or less, and an angular frequency ω (details described below), which is a relaxation characteristic observed with a rheometer, of 50 rad / s or less. In terms of process, it is effective to lower the casting temperature to suppress the formation of low-melting-point β-crystals in the unstretched film during the casting process, and to set the preheating and stretching temperatures for longitudinal and transverse stretching within the ranges described below. Furthermore, in order to rearrange the crystals partially broken down by stretching in the relaxation process and promote the formation of high-melting-point crystals, it is effective to introduce relaxation steps after longitudinal and transverse stretching, and to treat after each stretching at a temperature and relaxation rate within the ranges described below. These methods can also be used in combination as appropriate.

[0026] From the viewpoint of releasability from a mating member when used as a release film, the polypropylene film of the present invention preferably has a root-mean-square slope Sdq of 0.005 or more and 1.000 or less on at least one side (hereinafter, "root-mean-square slope Sdq" may be referred to as "Sdq"). Here, "at least one side" means one side or both sides. Sdq is one of the surface parameters that indicates the slope of the uneven structure of the film surface, and exhibits a high value when the surface contains a steep uneven structure. The lower limit of Sdq is preferably 0.005, more preferably 0.007, and even more preferably 0.015. The upper limit of Sdq is not particularly limited, but is substantially 1.000, preferably 0.100, from the viewpoint of film formability. When Sdq is 0.005 or more, the polypropylene film has a steep uneven structure on the surface, which makes it difficult for the films to adhere to each other when used as a release film, and tends to improve fusion resistance at high temperatures. Sdq can be measured by a known non-contact surface / layer cross-sectional shape measurement system (for example, the "VertScan" (registered trademark) series manufactured by Ryoka Systems Co., Ltd.), the details of which will be described later.

[0027] To achieve the above range of Sdq, it is effective to set the raw materials and film-forming conditions to the ranges described below. In particular, in terms of raw materials, in order to form steep protrusions in combination with stretching, it is effective to add a resin or additive that is incompatible with polypropylene to the surface layer (the film itself in the case of a single-layer structure), or to add branched polypropylene or the like to an extent that does not deteriorate the relaxation properties. In terms of processing, it is effective to increase the preheating temperature in the longitudinal stretching step to coarsen the surface unevenness structure derived from polypropylene. These methods can be used in combination as appropriate.

[0028] From the viewpoint of heat resistance, the polypropylene film of the present invention has a melting point Tm obtained in the second run of DSC measurement at a temperature rise rate of 20°C / min. ２ It is preferable that the melting point Tm obtained in the second run of DSC measurement at a temperature rise rate of 20°C / min is 164.0°C or higher and 170.0°C or lower (hereinafter referred to as "the melting point Tm obtained in the second run of DSC measurement at a temperature rise rate of 20°C / min"). ２ " to "Tm ２ From the above viewpoint, the melting point Tm ２The lower limit of the melting point Tm is more preferably 165.0°C, and even more preferably 166.0°C. ２ Considering the characteristics of polypropylene, the upper limit of Tm is 170.0°C. ２ The method for measuring this will be described in detail later.

[0029] Melting point Tm ２ is an index showing the melting point of the raw material of the entire polypropylene film, and if this is within the above range, film formation under higher temperature conditions becomes possible. Therefore, it is easy to improve the heat shrinkage characteristics and is also advantageous in terms of the formation of high melting point crystals, and as a result, it is easy to improve the heat resistance of the polypropylene film. ２ In order to achieve the above range, it is effective to set the raw material composition of the polypropylene film within the range described below, in particular to use a high-melting point raw material and minimize the amount of mixtures other than the high-melting point raw material, or to increase the proportion of the X layer described below. These methods may be used in combination as appropriate.

[0030] From the viewpoint of improving heat resistance, the polypropylene film of the present invention preferably has an angular frequency ω of 10 rad / s or more and 70 rad / s or less, at which the storage viscoelastic modulus G' and loss viscoelastic modulus G'' obtained by melt viscoelasticity measurement at 200°C give G' = G'' (hereinafter, "the angular frequency ω at which the storage viscoelastic modulus G' and loss viscoelastic modulus G'' obtained by melt viscoelasticity measurement at 200°C give G' = G''). The angular frequency ω is an index showing the relaxation properties of the polymer in the polypropylene film; a lower value indicates lower relaxation properties, and a higher value indicates higher relaxation properties. From the above viewpoint, the lower limit of the angular frequency ω is more preferably 15 rad / s, and even more preferably 20 rad / s. The upper limit of the angular frequency ω is more preferably 60 rad / s, even more preferably 50 rad / s, and particularly preferably 40 rad / s. When the angular frequency ω is within the above range, the polypropylene film has appropriate relaxation characteristics, and is excellent in both achieving a high crystalline melting point and amorphous relaxation during film formation, and is likely to exhibit excellent heat resistance. The angular frequency ω can be measured using a rotational rheometer, and the details of the measurement method will be described later.

[0031] To achieve the angular frequency ω in the above range, it is effective to set the raw material composition of the polypropylene film within the range described below and to set the film-forming conditions within the range described below. In particular, it is effective to use a resin having an angular frequency ω within the range described below and to reduce the amount of branched polypropylene added, which deteriorates the relaxation characteristics.

[0032] The thickness of the polypropylene film of the present invention is not particularly limited and is adjusted appropriately depending on the application, but is preferably 0.5 μm to 100 μm from the viewpoint of handleability. To make the most of these characteristics, the thickness of the polypropylene film is more preferably 1 μm to 40 μm, even more preferably 1 μm to 30 μm, and particularly preferably 6 μm to 30 μm. The thickness of the polypropylene film can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film-forming speed, the stretching ratio, etc., within a range that does not deteriorate other physical properties. The thickness of the polypropylene film can be measured using a known micro thickness meter, the details of which will be described later.

[0033] In the polypropylene film of the present invention, in a molecular weight distribution curve measured by gel permeation chromatography, the proportion of components having a logarithmic molecular weight Log(M) of 5.0 or less is preferably 39.0% by mass or less, more preferably 37.0% by mass or less, even more preferably 36.0% by mass or less, and particularly preferably less than 35.0% by mass. The lower limit of the proportion of components having a logarithmic molecular weight Log(M) of 5.0 or less is preferably 30.0% by mass or more, more preferably 33.0% by mass or more.

[0034] In the polypropylene film of the present invention, in a molecular weight distribution curve measured by gel permeation chromatography, the proportion of components having a logarithmic molecular weight Log(M) of 6.0 or more is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, and even more preferably 6.0% by mass or less. The lower limit of the proportion of components having a logarithmic molecular weight Log(M) of 6.0 or more is preferably 3.0% by mass or more, and more preferably 4.0% by mass or more.

[0035] When the ratio of components with a logarithmic molecular weight Log(M) of 5.0 or less to components with a logarithmic molecular weight Log(M) of 6.0 or more is within the above range, the polypropylene film of the present invention has appropriate relaxation characteristics, is excellent in achieving both a high crystalline melting point and amorphous relaxation during film formation, and is likely to exhibit excellent heat resistance. To achieve the ratio of components with a logarithmic molecular weight Log(M) of 5.0 or less to components with a logarithmic molecular weight Log(M) of 6.0 or more within the above range, it is effective to set the raw material composition of the polypropylene film within the range described below and the film formation conditions within the range described below. In particular, it is effective to use a polypropylene resin or polypropylene resin composition having an angular frequency ω of 15 rad / s to 70 rad / s as the raw material, or to adjust the kneading temperature during pre-mixing and film formation to appropriately control the molecular weight. These methods can be used in combination as appropriate.

[0036] Next, raw materials that can be used in the production of the polypropylene film of the present invention will be described, but are not necessarily limited to these.

[0037] In the polypropylene film of the present invention, when a layer composed of polypropylene composition X described below is defined as the X layer, the X layer preferably accounts for 90% to 100% of the entire polypropylene film in terms of thickness. The lower limit of the proportion of the X layer in the polypropylene film of the present invention is preferably 90% in terms of thickness, more preferably 92%, even more preferably 95%, and particularly preferably 98%. Note that the "thickness basis" means that the ratio is calculated with the entire thickness of the polypropylene film as 100%. When the proportion of the X layer is within the above range, the proportion of high-melting-point crystals in the polypropylene film increases, making it easier to maintain the rigidity of the film even at high temperatures where conventional polypropylene films cannot be used. Furthermore, the polypropylene film of the present invention preferably contains the X layer at an appropriate thickness ratio, but the layer structure may be a single layer or a laminate structure having multiple layers, such as two-type three-layer or three-type three-layer.

[0038] Polypropylene composition X is a resin composition that contains 95% by mass or more and 100% by mass or less of polypropylene resin when the entire composition is taken as 100% by mass, and has a melting point of 166.0°C or more and 170.0°C or less, a half-crystallization time of 5 seconds or more and 200 seconds or less, and an angular frequency ω described below of 10 rad / s or more and 70 rad / s or less. Note that when multiple components corresponding to polypropylene resin are contained, the composition is considered to fall under polypropylene composition X as long as the total amount of these components exceeds 95% by mass and the melting point, half-crystallization time, and angular frequency ω are within the above ranges. Furthermore, polypropylene resin refers to a resin that contains more than 50 mol% but not more than 100 mol% of propylene units when all structural units constituting the molecular chain of the resin are taken as 100 mol%.

[0039] The melting point of polypropylene composition X is 166.0°C or higher and 170.0°C or lower. The lower limit of the melting point of polypropylene composition X is preferably 166.5°C, more preferably 167.0°C, and even more preferably 167.5°C. When the melting point of polypropylene composition X is 166.0°C or higher, high-melting-point crystals are likely to be formed when the polypropylene composition X is formed into a film at a high temperature, improving heat resistance such as film rigidity in the high-temperature range. The melting point of polypropylene composition X can be measured by DSC, the details of which will be described later.

[0040] Furthermore, the polypropylene composition X has a crystallization half time, which indicates the crystallization rate obtained by DSC isothermal crystallization measurement described below, of 5 seconds or more and 200 seconds or less. The upper limit of the crystallization half time of the polypropylene resin X is preferably 100 seconds, more preferably 50 seconds, and even more preferably 30 seconds. When the crystallization half time is within the above range, recrystallization is likely to occur even during film formation, and high-melting-point crystals are likely to be formed. In order to keep the crystallization half time of the polypropylene composition X within the above range, it is effective to appropriately adjust the stereoregularity and molecular weight distribution of the polypropylene resin constituting the polypropylene composition X, or to add a branched polypropylene that exhibits a crystal nucleating agent effect.

[0041] Furthermore, polypropylene composition X has an angular frequency ω of 10 rad / s or more and 70 rad / s or less, at which G'=G'', in the storage viscoelastic modulus G' and loss viscoelastic modulus G'', obtained by melt viscoelasticity measurement at 200°C (hereinafter, "the angular frequency ω at which G'=G'', in the storage viscoelastic modulus G' and loss viscoelastic modulus G'', obtained by melt viscoelasticity measurement at 200°C" may be referred to as "angular frequency ω"). The angular frequency ω is the angular frequency at which the storage viscoelastic modulus G' and loss viscoelastic modulus G'' of molten polypropylene coincide, and is an index of the relaxation properties of polypropylene.

[0042] When the angular frequency ω is small, the relaxation characteristics are low (relaxation is slow) due to entanglement of molecular chains, etc., but the entanglement of molecular chains is easily maintained even at high temperatures, which is advantageous for increasing the melting point of the crystal. On the other hand, when the angular frequency ω is large, the entanglement of molecular chains is low, the relaxation characteristics are high (relaxation is fast), and the residual strain is efficiently reduced in the Relax step, and the amorphous portion is easily relaxed. The lower limit of the angular frequency ω of polypropylene composition X is preferably 15 rad / s, more preferably 20 rad / s. The upper limit of the angular frequency ω is preferably 60 rad / s, more preferably 50 rad / s or less, and even more preferably 40 rad / s. When the angular frequency ω is within the above range, it is easy to achieve both a high crystalline melting point and amorphous relaxation of polypropylene composition X, and it is possible to further improve the heat resistance of the resulting polypropylene film.

[0043] In order to set the angular frequency ω of polypropylene composition X within the above range, it is effective to adjust the molecular weight distribution of the polypropylene resin constituting polypropylene composition X to an appropriate range, and also to adjust the molecular weight distribution of the polypropylene resin by the pre-mixing conditions or to adjust the amount of branched polypropylene resin added. These methods can be combined as appropriate.

[0044] Polypropylene composition X may be composed solely of a homopolypropylene resin, but as described below, other resin components may be mixed therein by pre-kneading or the like to the extent that the properties are not deteriorated. When other resin components are added to polypropylene composition X, the amount added is preferably 1.2% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less, based on 100% by mass of the total resin of polypropylene composition X. Here, homopolypropylene resin refers to a polypropylene resin in which the amount of propylene units is 99.9 mol% or more and 100 mol% or less, when all structural units constituting the molecular chain of the resin are taken as 100 mol%.

[0045] Examples of other resin components that can be added to polypropylene composition X include polyolefin resins (resins that are not polypropylene resins and contain 50 mol % to 100 mol % of olefin units when all structural units constituting the molecular chain of the resin are taken as 100 mol %), polymer particles such as acrylic that are completely incompatible with polypropylene, etc. For example, by adding a resin component that is completely incompatible with polypropylene resins to polypropylene composition X that constitutes the outermost layer (the polypropylene film itself when the polypropylene film has a single-layer structure), it is possible to form steep protrusions on the surface when the film is made, and as a result, it is possible to improve the fusion resistance of the polypropylene film at high temperatures.

[0046] The polypropylene resin used in polypropylene composition X can be preferably selected from those that satisfy the above-mentioned conditions for polypropylene composition X, and commercially available polypropylene resins include, for example, F-704NP and F133A, which are polypropylene resins manufactured by Prime Polymer Co., Ltd., HC310BF, which is a polypropylene resin manufactured by Borealis, and FY6H, which is a polypropylene resin manufactured by Japan Polypropylene Corporation. Furthermore, commercially available branched polypropylenes that can be contained in polypropylene composition X include, for example, "Daploy" (trademark) WB130HMS, WB135HMS, and WB140HMS, which are manufactured by Borealis, and "WAYMAX" (registered trademark) MFX8, MFX6, and MFX3, which are manufactured by Japan Polypropylene Corporation.

[0047] The entire resin including the polypropylene composition X used in the polypropylene film of the present invention may contain various additives, such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a slipping agent, an antistatic agent, an antiblocking agent, a filler, a viscosity modifier, a color inhibitor, etc., within the scope of not impairing the object of the present invention.

[0048] Among these, the selection of the type and amount of antioxidant is important from the viewpoint of antioxidant bleed-out. That is, such antioxidants are preferably sterically hindered phenol-based antioxidants, with at least one of them being a high molecular weight type having a molecular weight of 500 or more. Specific examples include various antioxidants, but it is preferable to use, alone or in combination, 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4), 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox" (registered trademark) 1330: molecular weight 775.2), tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox" (registered trademark) 1010: molecular weight 1177.7), etc.

[0049] In particular, phosphorus-based antioxidants may be prone to bleed-out onto the surface of a polypropylene film. Such bleed-out can lead to various problems. For example, when a resin film is formed on the surface of a polypropylene film, curing the uncured or semi-cured resin film may inhibit curing. Furthermore, when an electrolyte membrane or a metal membrane is formed on the surface of a polypropylene film, the properties of the electrolyte membrane and the quality of the metal layer may be reduced. From the above viewpoints, the content of the phosphorus-based antioxidant in the polypropylene film is preferably 0.01 parts by mass or less, more preferably 0.005 parts by mass or less, and even more preferably 0.001 parts by mass or less, per 100 parts by mass of the total polypropylene resin. From the above viewpoints, it is preferable that no phosphorus-based antioxidant is contained in the polypropylene film, and the lower limit of the content is 0.000 parts by mass. Examples of phosphorus-based antioxidants include tris(2,4-di-t-butylphenyl)phosphite (e.g., "Irgafos" (registered trademark) 168 manufactured by BASF, molecular weight 647).

[0050] The total content of these antioxidants is preferably in the range of 0.03 to 1.0 parts by mass relative to 100 parts by mass of the total amount of polypropylene resin. If the amount of antioxidant is too small, the polymer may deteriorate during the extrusion process, causing the film to discolor, or the film may have poor long-term heat resistance. If the amount of antioxidant is too large, the transparency may decrease due to bleed-out of the antioxidant. A more preferred content is 0.05 to 0.9 parts by mass, and particularly preferably 0.1 to 0.8 parts by mass.

[0051] Furthermore, a crystal nucleating agent can be added to the polypropylene raw material (including polypropylene composition X) used for the polypropylene film of the present invention, provided that it does not contradict the object of the present invention. Examples include α crystal nucleating agents (dibenzylidene sorbitols, sodium benzoate, etc.), β crystal nucleating agents (potassium 1,2-hydroxystearate, magnesium benzoate, amide compounds such as N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide, quinacridone compounds, etc.). However, since excessive addition of the above-mentioned other nucleating agents can cause a decrease in stretchability or a decrease in transparency and strength due to void formation, the amount added is usually 0.5 parts by mass or less, preferably 0.1 parts by mass or less, and more preferably 0.05 parts by mass or less, based on 100 parts by mass of the total raw material.

[0052] The polypropylene film of the present invention is preferably a biaxially stretched film. As the biaxial stretching method, any of an inflation simultaneous biaxial stretching method, a stenter simultaneous biaxial stretching method, and a stenter sequential biaxial stretching method may be used, but among them, it is preferable to adopt a stenter sequential biaxial stretching method in terms of film formation stability, thickness uniformity, and control of film rigidity and dimensional stability.

[0053] Next, one embodiment of the method for producing a polypropylene film of the present invention will be described as an example, but the present invention is not necessarily limited to this.

[0054] First, 99.0 to 99.9 parts by mass of homopolypropylene resin and 0.1 to 1.0 part by mass of branched polypropylene resin (for example, homopolypropylene resin:branched polypropylene resin=99.7:0.3 (mass ratio)) are dry-blended, and the mixture is charged into a twin-screw extruder set at 240 to 280°C, melt-kneaded, and then cooled to obtain pellets of polypropylene composition X for the base layer (A layer). Also, 99.0 to 99.9 parts by mass of homopolypropylene resin and 0.1 to 1.0 part by mass of acrylic particles (for example, homopolypropylene resin:acrylic particles=99.8:0.2 (mass ratio)) are dry-blended, and the mixture is charged into a twin-screw extruder set at 240 to 280°C, melt-kneaded, and then cooled to obtain pellets of polypropylene composition X for the surface layer (B layer).

[0055] Pellets of polypropylene composition X obtained by the above procedure are fed into single-screw extruders for the base layer (A layer) and the surface layer (B layer), respectively, and melt-extruded at 200 to 290°C, more preferably 240 to 280°C, and even more preferably 260 to 280°C. After removing foreign matter and modified polymers using a filter installed midway through the polymer tube, the resulting mixture is laminated in a layer structure of surface layer (B layer) / base layer (A layer) / surface layer (B layer) using a multi-manifold composite T-die, and then extruded onto a casting drum and cooled and solidified to obtain a laminated unstretched sheet having a layer structure of surface layer (B layer) / base layer (A layer) / surface layer (B layer). In this case, the proportion of layer A in the thickness is preferably 90% to 100%, with the lower limit being more preferably 92%, even more preferably 95%, and particularly preferably 98%.

[0056] The surface temperature of the casting drum is preferably 20 to 80°C, more preferably 25 to 60°C, and even more preferably 30 to 60°C. A casting temperature within the above range can suppress the formation of β-crystals, which have a low melting point among crystals, and is likely to favorably increase the proportion of high-melting-point crystals in the film. The method of adhesion to the casting drum may be any of electrostatic application, adhesion methods utilizing the surface tension of water, air knife methods, press roll methods, and underwater casting methods, but the air knife method is preferred because it allows for easy control of surface roughness. When using the air knife method, the air temperature of the air knife is preferably 20 to 100°C, and the blown air speed is preferably 130 to 150 m / s. Furthermore, in order to prevent vibration of the laminated unstretched sheet, it is also preferable to appropriately adjust the position of the air knife so that air flows downstream of the film production.

[0057] The obtained laminated unstretched sheet is introduced into the longitudinal stretching process (stretching in the longitudinal direction). In the longitudinal stretching process, the laminated unstretched sheet is preheated before stretching using metal rolls heated to 150°C or higher and 160°C or lower, preferably 152°C or higher and 158°C or lower, and more preferably 154°C or higher and 158°C or lower. When the preheating temperature is within the above range, the laminated unstretched sheet proceeds to the longitudinal stretching process in a softened state, allowing stretching without applying excessive stress in the longitudinal stretching process, thereby easily reducing heat shrinkage stress. In addition, it is also possible to reduce the low-melting point β crystals contained in the laminated unstretched sheet, which is likely to favorably act to increase the proportion of high-melting point crystals in the film. In addition, before the above preheating, the unstretched laminated sheet may be preheated by contacting it with multiple metal rolls maintained at 50°C or higher and 145°C or lower.

[0058] Then, immediately after preheating, the film is stretched between rolls with a peripheral speed difference at a ratio of 4.0 to 8.0 in the longitudinal direction to obtain a longitudinally uniaxially stretched film. The stretching ratio is preferably 4.0 to 7.0, more preferably 4.3 to 6.0. The stretching temperature is greater than 150°C and less than 160°C, preferably 152 to 158°C, more preferably 154 to 158°C. When the stretching temperature is within the above range, it is possible to pull molecular chains from the softened crystals while suppressing excessive residual strain, and, together with the subsequent relaxation process, the crystal melting point is increased. Therefore, the heat resistance of the resulting polypropylene film, as indicated by the storage modulus obtained by dynamic viscoelasticity measurement, is likely to be improved.

[0059] At the end of the longitudinal stretching process, the longitudinally uniaxially stretched film is contacted with metal rolls with a peripheral speed difference and maintained at 140 to 160°C, and relaxed in the longitudinal direction at a relaxation rate of more than 0% but not exceeding 10%, followed by cooling to room temperature. The relaxation temperature is preferably 145 to 160°C, more preferably 150 to 160°C, and even more preferably 154 to 160°C. The relaxation temperature is preferably between the stretching temperature −10°C and the stretching temperature +5°C, more preferably between the stretching temperature −5°C and the stretching temperature +5°C, and even more preferably between the stretching temperature −5°C and the stretching temperature. A relaxation temperature within the above range promotes rearrangement of molecular chains extracted from crystals by longitudinal stretching, enabling the formation of crystals with a thicker lamellar thickness and a higher melting point. The relaxation rate during the longitudinal stretching process is preferably 0.1 to 10%, more preferably 1.0 to 10%, even more preferably 3.0 to 10%, and particularly preferably 5.0 to 10%. By keeping the relaxation ratio within the above range during the longitudinal stretching process, tension in the molecular chains is easily relieved. As a result, amorphous relaxation is promoted, shrinkage stress is reduced, and the mobility of the molecular chains is within a moderate range, which also facilitates rearrangement of the molecular chains. As a result, the dimensional stability of the polypropylene film is improved.

[0060] The longitudinally uniaxially stretched film is then introduced into a tenter, where both widthwise ends are held with clips and preheated, followed by transverse stretching in the widthwise direction at a ratio of 7.0 to 13, preferably 9.6 to 13 (transverse stretching step). By adopting such a stretching ratio, the resulting polypropylene film has improved resistance to high-temperature crimping. Furthermore, the temperature in the preheating step before stretching is preferably 170°C or higher and 190°C or lower, more preferably 173°C or higher and 185°C or lower, even more preferably 175°C or higher and 185°C or lower, and particularly preferably 177°C or higher and 185°C or lower. When the preheating temperature is within the above range, the crystals formed in the longitudinal stretching step can be softened and the film can be stretched in the transverse stretching step without applying excessive stress, which tends to reduce heat shrinkage stress.

[0061] The stretching temperature in the transverse stretching step after the preheating step is preferably above 170°C and not higher than 180°C, more preferably from 173°C to 180°C, and even more preferably from 175°C to 180°C. When the transverse stretching temperature is within the above range, it becomes possible to pull out molecular chains from the crystals softened by preheating while suppressing excessive residual strain. Therefore, together with the subsequent relaxation step, the crystal melting point is promoted, and the heat resistance indicated by the storage modulus obtained by dynamic viscoelasticity measurement of the polypropylene film is likely to improve.

[0062] In the subsequent relaxation step after transverse stretching, the film is relaxed in the width direction while being held with moderate tension by clips, preferably at a relaxation rate of 10% to 20%, more preferably 11% to 18%, and even more preferably 12% to 15%. A relaxation rate within the above range after transverse stretching facilitates the release of tension in the molecular chains. This promotes amorphous relaxation, reduces shrinkage stress, and provides a moderate range of molecular chain mobility, facilitating molecular chain rearrangement. The heat setting temperature during this step is preferably 168°C to 190°C, more preferably 170°C to 190°C, even more preferably 173°C to 185°C, and particularly preferably 175°C to 185°C, and is preferably equal to or higher than the stretching temperature in the immediately preceding stretching step, and more preferably 2°C higher than the stretching temperature in the immediately preceding stretching step. If the relaxation temperature is within the above range, the rearrangement of molecular chains pulled out from the crystals by transverse stretching is promoted, making it possible to form crystals with a thicker lamellar thickness and a higher melting point.

[0063] Furthermore, the polypropylene film of the present invention includes a relaxation step in the longitudinal stretching step and the transverse stretching step, and the total area relaxation rate (%) calculated from the respective stretch ratios and relaxation rates in the longitudinal stretching step and the transverse stretching step is preferably 10.0% to 30.0%, more preferably 13.0% to 25.0%, and even more preferably 15.0% to 20.0%. The total area relaxation rate (%) is calculated using the following formula, and within the above range, amorphous relaxation is likely to proceed, and the shrinkage stress of the entire polypropylene film is likely to be reduced. Total area relaxation rate (%) = [1 - (1 - relaxation rate in the longitudinal stretching step / 100) x (1 - relaxation rate in the transverse stretching step / 100)] x 100.

[0064] The film is then cooled at 80 to 130°C while still being held taut across the width with clips, and then led to the outside of the tenter. The clips on the film ends are released, and the film edges are slit in the winding process, and the film product roll is wound up.

[0065] The polypropylene film of the present invention obtained as described above can be used for various purposes such as packaging films, surface protection films, processing films, battery films, sanitary products, agricultural products, construction products, and medical products. In particular, since it has excellent heat resistance, it can be preferably used as processing films that require high-temperature treatment such as drying coating materials and molding thermosetting resins, release films, current collector substrate films for secondary batteries, and packaging films for retort pouches, and is particularly preferably used as release films for use in high-temperature regions.

[0066] In the present invention, a release film refers to a film that has the function of being attached to an object such as a molded body or a film to protect the object from scratches, contamination, etc. during processing or transportation, and can be easily peeled off and discarded when used as a final product. Also, a process film refers to a film used in the manufacturing process of an object such as a molded body or a film, and examples include a film that is attached to an object during the manufacturing process to protect it from scratches, contamination, etc., and a film that functions as a support when it is difficult to form a film from the object itself because it is thin or fragile.

[0067] The laminate of the present invention will be described below.

[0068] The polypropylene film of the present invention has excellent heat resistance and releasability, and therefore can be preferably used when forming a laminate with a metal film by subjecting the polypropylene film of the present invention to vapor deposition or sputtering. That is, one embodiment of the laminate of the present invention is one in which a metal film or an electrolyte membrane is in contact with at least one surface of the polypropylene film.

[0069] In vapor deposition and sputtering processes, polyethylene terephthalate (PET) films have often been used due to their excellent heat resistance and rigidity. However, PET has high hydrophilicity due to the presence of ester bonds, and PET films contain trace amounts of moisture. Such trace amounts of moisture can have adverse effects during vapor deposition and sputtering, particularly when vapor-depositing metals belonging to Group 1 or 2 of the periodic table, or compounds containing these metals, which are susceptible to moisture. Given this background, the laminate of the present invention preferably contains a metal belonging to Group 1 or 2 of the periodic table, since it can be used to obtain a laminate even when the presence of trace amounts of moisture makes it difficult to use PET films. Here, metals belonging to Group 1 or 2 refer to lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium. The metal film may contain one or more of these metal components, and in the latter case, the combination of components may be arbitrary.

[0070] Furthermore, in a high-temperature environment, moisture in the film volatilizes as outgassing, and this effect is particularly pronounced under high-vacuum conditions such as in a metal vapor deposition process. Outgassing from the film can deteriorate the degree of vacuum in the system, potentially reducing the quality of the metal film formed by vapor deposition and the yield of the vapor deposition process. From this perspective, the polypropylene film of the present invention, which has a lower moisture content than PET film, can be suitably used in applications where a metal film is formed, and the laminate of the present invention can maintain good metal film quality.

[0071] Furthermore, electrolyte membranes used in fuel cells, semi-solid batteries, all-solid batteries, and the like are usually produced in an environment where temperature and humidity are strictly controlled. In particular, sulfide-type electrolyte membranes react with moisture to generate hydrogen sulfide, so the processing film used in their production is also required to have an extremely low moisture content. Therefore, the polypropylene film of the present invention is preferably used as the processing film in the production of such electrolyte membranes. That is, a preferred embodiment of the laminate of the present invention includes one in which an electrolyte membrane is in contact with at least one surface of a polypropylene film, and it is particularly preferred that the electrolyte membrane is for a fuel cell, a semi-solid battery, or an all-solid battery.

[0072] From the above viewpoints, the upper limit of the moisture content of the polypropylene film of the present invention is preferably 2000 ppm, more preferably 1000 ppm, still more preferably 500 ppm, particularly preferably 200 ppm, and most preferably 100 ppm. The lower limit of the moisture content is not particularly limited, but is substantially 1 ppm. The moisture content of the polypropylene film can be measured by the Karl Fischer method, the details of which will be described later.

[0073] In order to set the moisture content of the polypropylene film of the present invention within the above range, it is preferable to minimize the content of hydrophilic resins in the polypropylene film and to limit the amount of additives to the minimum necessary. Specifically, assuming that the total amount of all constituent components of the polypropylene film of the present invention is 100% by mass, the lower limit of the content of polyolefin resins such as polypropylene resins is preferably 90% by mass, more preferably 95% by mass, and even more preferably 97% by mass. The upper limit of the content of these resins is substantially 100% by mass.

[0074] From the above viewpoints, the content of the antioxidant is preferably 0.03 to 1.0 part by mass, more preferably 0.05 to 0.9 parts by mass, and even more preferably 0.1 to 0.8 parts by mass, relative to 100 parts by mass of the total polypropylene resin of the polypropylene film of the present invention. In particular, since phosphorus-based antioxidants that bleed out onto the surface may degrade the properties and quality of the metal film formed on the surface, it is preferable to control their content. More specifically, when the total components of the polypropylene film of the present invention are taken as 100 parts by mass, the content of the phosphorus-based antioxidant is preferably 0.01 part by mass or less, more preferably 0.005 parts by mass ppm or less, and even more preferably 0.001 part by mass. There is no particular lower limit for the content of the phosphorus-based antioxidant, and theoretically it is 0.000 parts by mass (equivalent to no phosphorus-based antioxidant). It should be noted that the content of antioxidants, including phosphorus-based antioxidants, is preferably the same even when the film formed on the surface is not a metal film, from the viewpoints of properties, quality, and reducing inhibition of effects.

[0075] In order to reduce defects caused by bleed-out in the polypropylene film of the present invention, the total content of additives other than the antioxidant (for example, antistatic agents, viscosity modifiers, color inhibitors, slip agents, etc.) is preferably 0 to 0.05 parts by mass or less.

[0076] The antioxidant preferably used in the polypropylene film of the present invention is a sterically hindered phenolic antioxidant, and at least one of these antioxidants is preferably a high molecular weight type having a molecular weight of at least 500. Specific examples include various antioxidants, but it is preferable to use 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) in combination with 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox" (registered trademark) 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox" (registered trademark) 1010: molecular weight 1177.7).

[0077] As described above, the polypropylene film of the present invention has an extremely low moisture content and generates very little outgassing, and is superior in smoothness and handling to existing olefin-based films. Therefore, it is preferably used when forming transparent conductive films that require stricter vacuum conditions or high quality. That is, a preferred embodiment of the laminate of the present invention includes a laminate in which a transparent conductive film is in contact with at least one surface of the polypropylene film of the present invention. Here, the transparent conductive film refers to a thin film formed from a material that is conductive and transmits visible light. Specific examples include indium-tin composite oxide (ITO), zinc oxide (ZnO), and palladium films.

[0078] Next, the current collector of the present invention will be described. The current collector of the present invention is formed using the polypropylene film of the present invention. The polypropylene film of the present invention is preferably used as a current collector due to its excellent heat resistance. The current collector is a foil-like laminate used as an electrode for a storage battery such as a lithium-ion battery. Metal foil is typically used as a current collector, but laminates in which a metal film is laminated on a resin film substrate are also used for the purpose of improving safety and reducing weight. This metal film is laminated by processes such as vapor deposition, sputtering, plating, and electroless plating. Furthermore, to increase the energy density of the battery, the film substrate of the current collector is required to have a small thickness. However, as the film becomes thinner, its stiffness decreases, significantly reducing its handleability during processing. In particular, the process of laminating the metal film requires good handleability because it is subjected to high heat such as radiant heat during processing and also to tension in the conveying direction. The polypropylene film of the present invention can be thinned and has good handleability, making it suitable for use as a current collector.

[0079] Next, the storage battery of the present invention will be described. The storage battery of the present invention uses the polypropylene film of the present invention. The polypropylene film of the present invention has excellent heat resistance and is therefore preferably used as a current collector, and is generally used in storage batteries in which the current collector serves as an electrode. A storage battery is a device that stores electrical energy and converts it back into electrical energy when needed. Specific examples include lead-acid batteries, nickel-metal hydride batteries, lithium-ion batteries, NAS batteries, and redox flow batteries.

[0080] The present invention will be described in detail below with reference to examples. The properties were measured and evaluated by the following methods.

[0081] (1) Film Thickness: Measured using a micro thickness meter (manufactured by Anritsu Corporation). The film was sampled in a 10 cm square, and measurements were taken at five random points to calculate the average value.

[0082] (2) E' Ａ +E' Ｂ (Storage Modulus) A rectangular test piece (5 mm wide x 20 mm long) cut from a polypropylene film with the measurement direction as the long side was attached to the chuck of the device in a 23 ° C. atmosphere, cooled to -100 ° C., and E' was measured from -100 ° C. to 180 ° C. after the start of heating. A viscoelasticity-temperature curve was drawn using a dynamic viscoelasticity method, and E' at 30 ° C. was calculated. Next, when the longitudinal direction of the polypropylene film was set to 0 ° C., dynamic viscoelasticity was similarly measured for each direction forming an angle of 0 ° C., 15 ° C., 30 ° C., 45 ° C., 60 ° C., 75 ° C., 90 ° C., 105 ° C., 120 ° C., 135 ° C., 150 ° C., and 165 ° C. with respect to the longitudinal direction, and E' at 30 ° C. was calculated. The direction showing the highest storage modulus was designated as direction A, and the direction perpendicular to direction A was designated as direction B. Then, the storage modulus at 160 ° C. was read for direction A and direction B, and E' was calculated for each direction. Ａ , E' Ｂ The test was carried out with n = 3, and the average value of the obtained values ​​was taken as the storage modulus of the polypropylene film in the measurement direction. Ａ '+E Ｂ ' is the obtained E Ａ ' and E ＢThe measurement was performed using the following equipment and conditions: <Measurement equipment and conditions> Equipment: EXSTAR DMS6100 (Seiko Instruments Inc.) Geometry: Tension Distance between chucks: 20 mm Frequency: 10 Hz Strain: 0.1 to 0.2% Temperature range: -100 to 200°C Heating rate: 5°C / min Measurement atmosphere: Nitrogen.

[0083] (3) P Ａ +P Ｂ , shrinkage starting temperature Using a TMA (manufactured by SII Nanotechnology Co., Ltd. / Model TMA / SS6100), heat shrinkage stress curves in the measurement directions (A direction and B direction) were obtained under the following conditions: (a) Sample: Width 4 mm x Length 20 mm (b) Initial load: 0.0 mN (c) Temperature program: Temperature increased from 30°C to 200°C at a heating rate of 10°C / min (d) Preparation of heat shrinkage stress curve: The load (N) at each observed temperature was divided by the cross-sectional area of ​​the polypropylene film (thickness x sample width) to calculate the shrinkage stress (MPa) at each temperature, and a temperature-shrinkage stress curve (heat shrinkage stress curve) was prepared.

[0084] <P Ａ +P Ｂ The shrinkage stress (MPa) at 160°C was read from the shrinkage stress curve. Measurements were carried out three times in each direction, and the average was calculated. The value in the A direction was used as the P value. Ａ , the value in the B direction is P Ｂ With P Ａ and P Ｂ The sum of Ａ +P Ｂ It was decided.

[0085] <Shrinkage Starting Temperature> The temperature at which the shrinkage stress first reached 0.2 MPa during the temperature rise process was read from the shrinkage stress curve. Measurements were carried out three times in each direction, and the average was calculated.

[0086] (4) Percentage H of Heat of Fusion from 175°C to 200°C Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), each layer of 3 mg of polypropylene film was heated from 25°C to 250°C at 20°C / min in a nitrogen atmosphere to obtain a melting curve. For the obtained melting curve during melting, a linear baseline was set in the range of 60°C to 200°C, and the heat of fusion was calculated from the area enclosed by the linear baseline and the melting curve, and this was converted to a value per sample mass to calculate the total heat of fusion (J / g). In addition, the heat was calculated from the area enclosed by the linear baseline and the melting curve at temperatures above 175°C, and this was converted to a value per sample mass to obtain the heat of fusion above 175°C (J / g). The obtained total heat of fusion and the heat of fusion at 175°C or above were applied to the following formula to determine the crystalline melting ratio H (%) at 175°C or above: Crystalline melting ratio H (%) at 175°C or above = Heat of fusion at 175°C or above × 100 / total heat of fusion.

[0087] (5) Root-mean-square slope Sdq Measurements were performed using a Ryoka Systems "VertScan" (registered trademark) 2.0 R5300GL-Lite-AC, and the surface shape was determined by surface correction of the photographed image using a polynomial fourth-order approximation using the attached analysis software. The measurement conditions were as follows. Measurements were performed on both sides of the film, n = 3 (number of measurements = 3), and the average value of each side was calculated and used as the Sdq of each side. Manufacturer: Ryoka Systems Co., Ltd. Device name: "VertScan" (registered trademark) 2.0 R5300GL-Lite-AC Measurement conditions: CCD camera SONY HR-57 1 / 2 inch Objective lens: 10x Intermediate lens: 0.5x Wavelength filter: 530 nm white Measurement mode: Wave Measurement software: VS-Measure Version 5.5.1 Analysis software: VS-Viewer Version 5.5.1 Measurement area: 561.097 μm x 561.473 μm.

[0088] (6) Melting point of raw material and Tm of polypropylene film ２5 mg of the raw material was placed in an aluminum pan as a sample and measured under a nitrogen atmosphere using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments). First, the temperature was raised from 30°C to 260°C at 20°C / min, and then held at 260°C for 5 minutes. Then, the temperature was lowered from 260°C to 30°C at 20°C / min, and then the temperature was raised again from 30°C to 260°C at 20°C / min. The maximum peak temperature in the temperature range of 30°C to 180°C was taken as the melting point of the raw material. Similarly, measurements were also performed on polypropylene film, and the maximum peak temperature in the temperature range of 30°C to 180°C was taken as the Tm of the polypropylene film. ２ (℃).

[0089] (7) Crystallization Half Time Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments, Inc.), 3 mg of polypropylene film was heated in a nitrogen atmosphere from 25°C to 250°C at a rate of 20°C / min and held for 5 minutes. The temperature was then lowered from 250°C to 130°C at a rate of 20°C / min and held at 130°C for 30 minutes. The time when the sample temperature reached 130°C was defined as 0 seconds, and the elapsed time from the first peak appearing in the endothermic curve obtained during isothermal holding at 130°C was defined as the crystallization half time (seconds).

[0090] (8) Angular frequency ω Measurements were performed using a rotational rheometer (MCR302 manufactured by Anton Paar Japan) equipped with a 25 mm diameter cone plate. The raw material was left to stand on a plate heated to 200 °C under a nitrogen atmosphere for 10 minutes. In addition, when the sample was a polypropylene film, it was pre-laminated and melted in a press heated to 200 °C, cooled to form a sheet, and then placed on the plate in the same manner as the raw material. After confirming that the sample had melted on the plate, the gap between the upper and lower plates was narrowed to the measurement setting (0.25 mm) and left to stand for 5 minutes under a nitrogen atmosphere until it stabilized at 200 °C. Then, while maintaining the temperature at 200 °C, the angular frequency was changed from low to high angular frequency from 0.5 rad / s to 500 rad / s at 5% strain, and viscoelasticity measurements were performed. From the obtained curves of angular frequency, storage modulus G', and loss modulus G'', the angular frequency at which G'=G" was determined as the angular frequency ω (rad / s) of the raw material and the polypropylene film.

[0091] (9) Ratio of Components with Logarithmic Molecular Weight Log(M) = 5.0 or Less and Components with Log(M) = 6.0 or More 1,2,4-Trichlorobenzene was used as a solvent and stirred at 165°C for 30 minutes to dissolve a polypropylene film. The solution was then filtered using a 0.5 µm filter, and the molecular weight distribution of the filtrate was measured by gel permeation chromatography (GPC), with the measurement results calculated in terms of polystyrene. The molecular weight was then converted to that of polypropylene using a Q-factor, and the ratio of components with logarithmic molecular weight Log(M) = 5.0 or less and components with Log(M) = 6.0 or more was determined from the integral curve of the resulting molecular weight distribution. The measurement by gel permeation chromatography (GPC) was performed using the following equipment and conditions. <Apparatus and measurement conditions> Apparatus: Agilent high-temperature GPC apparatus PL-GPC220 Detector: Agilent differential refractive index detector (RI detector) Column: Agilent PL1110-6200 (20 μm MIXED-A) × 2 Flow rate: 1.0 mL / min Column temperature: 145° C. Injection volume: 0.500 mL Sample concentration: 0.1 mass % Standard sample: Tosoh monodisperse polystyrene, Tokyo Chemical Industry Co., Ltd. dibenzyl.

[0092] (10) Heat Resistance Evaluation Cardboard (product number C-55, manufactured by Daio Paper Co., Ltd.) was cut into 10 cm squares, and then 15 cm square pieces of polypropylene or PET film were placed on both sides of the cardboard along with 20 cm square SUS plates, as shown in Figure 1. The plates were heated and pressed using a heating press at a pressure of 1.5 MPa at temperatures of 160°C, 165°C, and 170°C for 15 minutes each, then removed from the press and cooled to room temperature. The biaxially oriented polyolefin or PET film that protruded from the cardboard was then peeled away from the polypropylene or PET film, and the cardboard was then peeled away from the polypropylene or PET film. Note that symbols 1 to 4 in Figure 1 represent the SUS plate, polypropylene film or PET film, cardboard, and pressure direction, respectively. The condition of the cardboard and polypropylene film treated at each temperature was visually evaluated according to the following criteria. Evaluation was initially performed at a heating temperature of 160°C for each evaluation item, and only evaluation items that passed were evaluated at a heating temperature of 165°C. Further, only those items that passed the evaluation at 165°C were evaluated at a heating temperature of 170°C. (Crack Resistance) A case in which the polypropylene film or PET film was completely peeled from the cardboard was judged to be a pass, and a case in which the peeling was incomplete or a case in which the cardboard and a portion of the polypropylene film or PET film remained on the other side after peeling was judged to be a fail. Evaluation was based on the following criteria. (Dimensional Stability) A case in which no folds or wrinkles were observed in the cardboard was judged to be a pass, and a case in which at least one of folds or wrinkles was observed was judged to be a fail. Evaluation was based on the following criteria. (Fusing Resistance) A case in which the polypropylene films or the PET films outside the pressure-applied surface after the pressure treatment were not fused to each other was judged to be a pass, and a case in which even a portion of the films was fused to each other was judged to be a fail. Evaluation was based on the following criteria (if fused, the fused portion was removed and then peeled from the cardboard, and the above evaluation was performed). <Evaluation Criteria (Common to Cracking Resistance, Dimensional Stability, and Fusion Resistance)> Cracking resistance, dimensional stability, and fusion resistance were evaluated based on the following criteria, and if each characteristic was A to C, it was judged to have heat resistance. A: Passed at 160°C, 165°C, and 170°C. B: Passed at 160°C and 165°C, but failed at 170°C. C: Passed at 160°C, but failed at 165°C. D: Failed at 160°C.

[0093] (11) Yield evaluation during metal film formation: Using a vacuum deposition device, the pressure was reduced from atmospheric pressure to 1 × 10 －５ The pressure was reduced to 100 kJ, and a magnesium vapor deposition film with a thickness of 200 angstroms was formed on one side of a polypropylene film or a PET film by vacuum deposition using magnesium as a vapor deposition source. －５ The time required for the pressure to be reduced to a full pressure was measured, and the unevenness of the metal film surface was visually observed to evaluate the yield according to the following criteria. The evaluation criteria were A as pass and B as fail. A: 1×10 －５ The time required for reducing the pressure to a full pressure was 50 minutes or less, and no irregularities were observed on the surface of the metal film. B: The pressure was reduced from atmospheric pressure to 1×10 －５ The time required to reduce the pressure to the full pressure was longer than 50 minutes, or irregularities were observed on the surface of the metal film.

[0094] (12) Moisture Content A polypropylene film or PET film sample was left for 4 hours or more in a room conditioned at 23° C. and a relative humidity of 20%, and then immersed for 24 hours in distilled water at 23° C. Thereafter, the moisture on the surface of the sample was wiped off, and the moisture in the sample was dried and evaporated at a temperature of 150° C. using a trace moisture meter (manufactured by Mitsubishi Chemical Corporation, CA-20 model), and the moisture amount was then quantified by the Karl Fischer method to calculate the moisture content.

[0095] (Polypropylene Resin, etc.) The raw materials and their properties used in the polypropylene films of the Examples and Comparative Examples are shown in Tables 1 to 3 below. These property values ​​are values ​​evaluated in the form of resin pellets. Eight types of polypropylene raw materials (PP1 to PP8) were prepared. All of PP1 to PP8 contained 1,000 ppm to 5,000 ppm of BASF's "Irganox" (registered trademark) 1010 as an antioxidant, with only PP8 containing 3,000 ppm of BASF's "Irgafos" (registered trademark) 168. Seven types of polypropylene resin pellets (PP9 to PP15) were also prepared by pre-kneading the compositions shown in Table 3 (kneading was performed by dry blending the materials, feeding them into a twin-screw extruder, kneading at 260°C, and cooling). Homopolypropylene resin 1 (PP1): manufactured by Prime Polymer Co., Ltd. Homopolypropylene resin 2 (PP2): manufactured by Prime Polymer Co., Ltd. Homopolypropylene resin 3 (PP3): manufactured by Prime Polymer Co., Ltd. Branched-chain polypropylene resin 4 (PP4): manufactured by Borealis Co., Ltd. Homopolypropylene resin 5 (PP5): manufactured by Prime Polymer Co., Ltd. Homopolypropylene resin 6 (PP6): manufactured by Sumitomo Chemical Co., Ltd. Homopolypropylene resin 7 (PP7): manufactured by Japan Polypropylene Co., Ltd. Homopolypropylene resin 8 (PP8): manufactured by Prime Polymer Co., Ltd.

[0096]

[0097] Acrylic particles 1 (particles 1): Acrylic beads "Eposter" (registered trademark) MA1002 manufactured by Nippon Shokubai Co., Ltd.

[0098]

[0099] Polypropylene resin 9 (PP9): Mixed polypropylene resin pellets obtained by mixing PP1 and PP4 in the mass ratio shown in Table 3. Polypropylene resin 10 (PP10): Mixed polypropylene resin pellets obtained by mixing PP2 and PP4 in the mass ratio shown in Table 3. Polypropylene resin 11 (PP11): Mixed polypropylene resin pellets obtained by mixing PP3 and PP8 in the mass ratio shown in Table 3. Polypropylene resin 12 (PP12): Mixed polypropylene resin pellets obtained by mixing PP5 and particle 1 in the mass ratio shown in Table 3. Polypropylene resin 13 (PP13): Mixed polypropylene resin pellets obtained by mixing PP3 and PP4 in the mass ratio shown in Table 3. Polypropylene resin 14 (PP14): Mixed polypropylene resin pellets obtained by mixing PP5 and PP4 in the mass ratio shown in Table 3. Polypropylene resin 15 (PP15): Mixed polypropylene resin pellets obtained by mixing PP9 and particle 1 in the mass ratio shown in Table 3.

[0100]

[0101] Example 1 Polypropylene resin 9 was fed into a single-screw extruder for the base layer (A layer), and polypropylene resin 15 was fed into a single-screw extruder for the surface layer (B layer). The resin mixture for each layer was melt-extruded at 260 ° C., and after removing foreign matter with a 20 μm cut sintered filter, the surface layer (B layer) / base layer (A layer) / surface layer (B layer) was laminated in a feed block type B / A / B composite T-die so that the thickness ratio was 1 / 28 / 1, and the resulting molten laminate was molded into a sheet using a T-die. Then, the molten sheet-like material was ejected from the T-die onto a casting drum whose surface temperature was controlled to 30 ° C., and compressed air at 25 ° C. was sprayed using an air knife at an air speed of 140 m / s to adhere the molten sheet-like material to the casting drum, obtaining an unstretched sheet. The unstretched sheet was then preheated to 156°C using ceramic rolls, stretched 4.3 times in the longitudinal direction between rolls at 156°C with a peripheral speed difference, and then further relaxed 5.6% in the longitudinal direction between rolls at 155°C with a peripheral speed difference to obtain a uniaxially stretched film. The uniaxially stretched film was then introduced into a tenter-type stretching machine with both widthwise ends held by clips, preheated at 180°C for 10 seconds, stretched 9.8 times in the widthwise direction at 176°C, and heat-set at 178°C while providing 13% relaxation in the widthwise direction. After a cooling step at 100°C, the film was introduced to the outside of the tenter-type stretching machine, the clips at both widthwise ends were released, and the film was wound around a core to obtain a 30 μm thick polypropylene film. The physical properties and evaluation results of the resulting polypropylene film are shown in Table 4.

[0102] (Examples 2 to 5, Comparative Examples 1 to 5) Polypropylene films were obtained in the same manner as in Example 1, except that the raw material composition of each layer and the film-forming conditions were as shown in Table 4. The thickness was adjusted by adjusting the discharge rate during extrusion and the speed of the casting drum. The physical properties and evaluation results of the obtained polypropylene films are shown in Table 4. Note that in Examples 2 to 4 and Comparative Examples 1 and 3 to 5, which have a single-layer structure, the same resin or resin composition was fed into two single-screw extruders. (Comparative Example 6) A PET film "Lumirror" (registered trademark) S10 (manufactured by Toray Industries, Inc.) was used instead of a polypropylene film, and heat resistance evaluation and yield evaluation during metal film formation were performed, and the moisture content was measured. The evaluation results are shown in Table 4.

[0103]

[0104] The polypropylene films of Examples 2 to 4 and Comparative Examples 1 and 3 to 5 were single-layer polypropylene films produced by feeding the same resin or resin composition into two single-screw extruders, so the resin type in the table is listed only for Layer A. Furthermore, in Comparative Examples 1 and 3, the Sdq values ​​were the same on both sides, so there was no distinction between the high-value and low-value sides, but the values ​​for both sides are listed in the table. Note that moisture content and yield during metal film production were evaluated only for Example 1 and Comparative Examples 3 and 6.

[0105] As described above, the polypropylene film of the present invention can be used in various applications such as packaging films, release films, processing films, sanitary products, agricultural products, construction products, medical products, current collectors, storage batteries, etc. In particular, because of its excellent heat resistance, it can be preferably used as release films and processing films to be used at high temperatures, where conventional polypropylene films have been difficult to use.

[0106] 1: SUS plate 2: Polypropylene film 3: Cardboard 4: Pressure direction

Claims

1. The main orientation axis direction is the A direction, the direction perpendicular to the main orientation is the B direction, and the 160° C. storage moduli in the A direction and the B direction in the dynamic viscoelasticity measurement are E′. Ａ (GPa), E' Ｂ (GPa), and the 160° C. shrinkage stress in the A direction and the B direction measured by TMA is P Ａ (MPa), P Ｂ A polypropylene film satisfying the following formulas 1 and 2 when expressed as (MPa). Formula 1: 0.30 ≦ E' Ａ +E' Ｂ ≦2.00 Formula 2: -1.0≦P Ａ +P Ｂ ≦5.0

2. (P Ａ +P Ｂ ) / (E' Ａ + E' Ｂ 2. The polypropylene film according to claim 1, wherein the polypropylene film has a refractive index of 0.001 or more and 7.500 or less.

3. The polypropylene film according to claim 1 or 2, wherein the shrinkage initiation temperatures in the A direction and the B direction measured by TMA are both 140° C. or higher and 170° C. or lower.

4. 3. The polypropylene film according to claim 1 or 2, wherein the ratio H of the heat of fusion at 175° C. or more and 200° C. or less to the total heat of fusion in the first run of DSC measurement at a heating rate of 20° C. / min is 10%≦H≦50%.

5. 3. The polypropylene film according to claim 1, wherein at least one surface of the film has a root-mean-square slope Sdq of 0.005 or more and 1.000 or less.

6. Melting point (Tm) obtained in the second run of DSC measurement at a heating rate of 20° C. / min ２ The polypropylene film according to claim 1 or 2, wherein the melting point is 164.0°C or more and 170.0°C or less.

7. 3. The polypropylene film according to claim 1, wherein the angular frequency ω at which G'=G'' in the storage viscoelastic modulus G' and loss viscoelastic modulus G'' obtained by melt viscoelasticity measurement at 200°C is 10 rad / s or more and 70 rad / s or less.

8. 3. The polypropylene film according to claim 1, wherein in a molecular weight distribution curve measured by gel permeation chromatography, the proportion of components having a logarithmic molecular weight Log(M) of 5.0 or less is 39.0 mass% or less, and the proportion of components having a logarithmic molecular weight Log(M) of 6.0 or more is 10.0 mass% or less.

9. The polypropylene film according to claim 1 or 2, which is a release film.

10. 3. The polypropylene film according to claim 1 or 2, which is a processing film.

11. A laminate comprising the polypropylene film according to claim 1 or 2 and a metal film in contact with at least one surface of the polypropylene film.

12. 12. The laminate of claim 11, wherein the metal film comprises a metal from Group 1 or 2 of the periodic table.

13. A laminate comprising the polypropylene film according to claim 1 or 2 and a transparent conductive film in contact with at least one surface of the polypropylene film.

14. A laminate comprising the polypropylene film according to claim 1 or 2 and an electrolyte membrane in contact with at least one surface of the polypropylene film.

15. The laminate according to claim 14, wherein the electrolyte membrane is for a fuel cell, a semi-solid battery, or an all-solid battery.

16. A current collector comprising the polypropylene film according to claim 1 or 2.

17. A storage battery comprising the polypropylene film according to claim 1 or 2.