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

Technical Field

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

Background Art

[0002] Polypropylene films are used in various applications such as packaging, tapes, electrical applications including cable wrapping and capacitors, etc. because of their excellent transparency and electrical properties. Also, polypropylene films are particularly suitable as release films and process films for various members such as plastic products, building materials, and optical members because of their excellent mechanical properties and mold release properties.

[0003] Examples of how release films are used include as supports during coating and melt film formation, and as spacers during press molding. The required properties of release films are appropriately set according to their intended use. However, as the performance of materials improves and productivity increases, the temperature during heating processes and press molding has been increasing year by year, so heat resistance has become particularly important.

[0004] Conventionally, in temperature ranges exceeding 150°C, polyethylene terephthalate (PET) films with excellent heat resistance were sometimes used, but it was difficult to achieve both mold release properties, and there were cases where the required properties could not be satisfied. On the other hand, although conventional polypropylene films have high mold release properties, they begin to shrink significantly from around 120 - 130°C and start to melt around 160°C near the melting point, resulting in a significant decrease in film rigidity. This can impair the quality of the counterpart members made of thermoplastic resin compositions or thermosetting resin compositions that require drying or molding at high temperatures. Therefore, it has been very difficult to use polypropylene films as release films at temperatures of 150°C or higher, especially 160°C or higher.

[0005] As important properties of the heat resistance of polypropylene films, heat shrinkage properties and rigidity at high temperatures can be mentioned. As a method of increasing the heat shrinkage properties, that is, reducing the heat shrinkage stress, generally, the molecular weight of the polypropylene raw material is reduced, and a method of relaxing the orientation and residual strain expressed by stretching through relaxation treatment or heat setting is used. However, in this method, since the structure contributing to mechanical strength such as elastic modulus is reduced, the rigidity of the polypropylene film tends to decrease. On the other hand, as a method of increasing rigidity, a method of increasing the molecular weight of the polypropylene raw material, increasing the molecular orientation and the degree of tension of the amorphous part by low-temperature stretching or high-magnification stretching, and increasing the elastic modulus from room temperature has been used. However, in this method, since the structure that is likely to relax at high temperatures increases, the heat shrinkage stress tends to increase. Thus, in the conventional technology, it has been very difficult to achieve both heat shrinkage properties and rigidity at high temperatures of polypropylene films.

[0006] Among the above situations, as an example of conventional heat-resistant means, for example, Patent Document 1 describes an example of reducing the heat shrinkage rate by reducing the molecular weight of the polypropylene raw material. Further, Patent Document 2 describes an example of reducing the heat shrinkage rate by increasing the heat treatment temperature in relaxation treatment to relax the molecular orientation. Furthermore, Patent Document 3 describes an example of increasing the film rigidity at high temperatures by multi-stage stretching in the width direction including low-temperature stretching at 150°C or lower.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the methods described in Patent Documents 1 and 2 mentioned above, there is a problem that the rigidity and draw stability of the obtained polypropylene film at high temperatures are low. Further, in the method described in Patent Document 3, the heat shrinkage stress of the obtained polypropylene film at high temperatures is high, and there is a problem in achieving both heat shrinkage characteristics and rigidity at high temperatures. That is, the polypropylene films obtained by these methods are difficult to be used as release films in a high-temperature environment.

[0009] Therefore, an object of the present invention is to solve the above problems. That is, to provide a polypropylene film that can be suitably used as a release film even in a high-temperature environment where it has been impossible to use a conventional polypropylene film as a release film.

Means for Solving the Problems

[0010] In order to solve the above-described problems, the polypropylene film of the present invention has the following configuration. That is, in the polypropylene film of the present invention, 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 elastic moduli in the A direction and the B direction in the dynamic viscoelasticity measurement are E’ A (GPa) and E’ B (GPa), and the 160°C shrinkage stresses in the A direction and the B direction in the TMA measurement are P A (MPa) and P B (MPa), respectively. When the following formulas 1 and 2 are satisfied, it is a polypropylene film. Formula 1: 0.30 ≤ E’ A + E’ B ≤ 2.00 Formula 2: -1.0 ≤ P A + P B ≤ 5.0

Effects of the Invention

[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 a high-temperature environment where it has been impossible to use a conventional polypropylene film as a release film.

Brief Description of the Drawings

[0012]

Figure 1

Embodiments for Carrying Out the Invention

[0013] In the polypropylene film of the present invention, 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 elastic moduli in the A direction and the B direction in the dynamic viscoelasticity measurement are respectively E’ A (GPa), E’ B (GPa), and the 160°C shrinkage stresses in the A direction and the B direction in the TMA measurement are respectively P A (MPa), P B (MPa), when the following formulas 1 and 2 are satisfied. Hereinafter, the polypropylene film of the present invention will be described in detail. 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 represented by "~", the numerical range includes the numerical values at both ends. When the unit is described only after the numerical range, the unit is the same throughout the numerical range.

[0015] From the viewpoint of maintaining the film rigidity at high temperatures, in the polypropylene film of the present invention, 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 elastic moduli in the A direction and the B direction in the dynamic viscoelasticity measurement are respectively E’ A (GPa), E’ B (GPa), when 0.30 ≦ E’ A + E’ B ≦ 2.00 is important. From the above viewpoint, the lower limit of E’ A + E’ B is preferably 0.40, more preferably 0.50, still more preferably 0.60, and particularly preferably 0.70. E’A +E’ B When A +E’ is less than 0.30, when the adherend is adhered and processed in a molding press or a heating oven at a high temperature, the polypropylene film cannot withstand the heat and undergoes compression or elongation deformation, inducing excessive indentation or sticking to the adherend. Therefore, when peeling the polypropylene film from the adherend, there is a concern of causing damage or deformation to the adherend. Also, E’ A +E’ B The upper limit of A +E’ is 2.00 based on the thermal properties of polypropylene, and 1.50 is preferred from the viewpoint of compatibility with the thermal shrinkage stress.

[0016] In the polypropylene film of the present invention, the main orientation axis direction (A direction) means that, in the film plane, when the longitudinal direction is set to 0°, when dynamic viscoelasticity measurements are performed in the respective directions forming angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° with respect to the longitudinal direction, it is the direction showing the highest storage elastic modulus at 30°C. On the other hand, in the case of a film where it is unclear from the appearance of the film 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, and slit-shaped film pieces are sampled parallel to each line, and the storage elastic modulus at 30°C is determined by dynamic viscoelasticity measurement, and the direction giving the maximum storage elastic modulus is regarded as the main orientation axis direction. Here, the longitudinal direction means the direction in which the film travels during the manufacturing process (corresponding to the winding direction in the case of a film roll), and the direction orthogonal to this in the film plane is called the width direction. Also, the main orientation perpendicular direction (B direction) in the polypropylene film of the present invention means the direction orthogonal to the main orientation axis direction in the film plane. Note that the details of the method for measuring the storage elastic modulus by dynamic viscoelasticity measurement including E’ A and E’ B will be described later.

[0017] From the viewpoint of the film shrinkage characteristics at high temperatures, in the polypropylene film of the present invention, when the 160°C shrinkage stresses in the TMA measurements in the A direction and the B direction are respectively P A (MPa) and P B (MPa), -1.0 ≦ PA +P B It is important to satisfy ≤ 5.0. From the above perspective, P A +P B The upper limit of is preferably 4.0, more preferably 3.5, still more preferably 3.0, particularly preferably 2.0, and most preferably 1.0. P A +P B If it exceeds 5.0, when the mating member is overlapped or adhered and processed in a molding press or heating oven at high temperature, the thermal shrinkage of the polypropylene film progresses. Therefore, wrinkles and curls are likely to occur in the polypropylene film, so there is a concern that the deformed state of the film such as wrinkles will be transferred to the adhered mating member. Also, P A +P B The lower limit of is -1.0 from the perspective of film formability, and 0.0 is preferable in consideration of compatibility with the rigidity of the film at high temperature. The details of the measurement method of the shrinkage stress at 160 °C in the TMA measurement will be described later.

[0018] E’ A +E’ B and P A +P BIn order for both values to be within the above range, a method can be used in which the raw material composition of the polypropylene film is within the range described later and the film forming conditions are within the range described later. In particular, in order to appropriately control the formation of high melting point crystals and the relaxation of amorphous regions under high temperature film forming conditions, it is effective to use as a raw material a polypropylene composition having a high melting point, a fast crystallization rate, and a relaxation characteristic with an angular frequency ω (details will be described later) within an appropriate range. Also, in terms of the process, it is effective to set the preheating temperature and stretching temperature for longitudinal stretching and transverse stretching within the ranges described later, and further introduce a relaxation step after longitudinal stretching and after transverse stretching, and perform treatment at the temperature and total area Relax rate within the ranges described later. These methods can be used in combination as appropriate. By adopting the above raw material composition and process conditions, stretching and relaxation treatment under high temperature conditions can be performed while maintaining the film forming property of the film, and while promoting the relaxation of strained amorphous chains, which are the cause of thermal shrinkage stress, it is possible to form crystals having a very high melting point that has not been conventionally assumed for polypropylene films. As a result, it is possible to achieve both rigidity and thermal shrinkage stress even at a high temperature of 160 °C or higher, and the resulting polypropylene film can be used even in such a high temperature environment.

[0019] The polypropylene film of the present invention preferably has (P A +P B ) / (E’ A +E’ B ) of 0.001 or more and 7.500 or less. (P A +P B ) / (E’ A +E’ B ) is an index indicating the balance between the elastic modulus and the thermal shrinkage stress at high temperatures, which has been in a conventional trade-off relationship. By being within the above range, compression and elongation deformation under high temperature environments can be reduced. From the above viewpoints, the upper limit of (P A +P B ) / (E’ A +E’ B ) is more preferably 5.000, still more preferably 2.000, and particularly preferably 1.000. (P A +P B ) / (E‘ A +E‘ B) is 7.500 or less, the elastic modulus becomes relatively higher than the thermal shrinkage stress, and when the mating member is adhered in a molding press or a heating oven at a high temperature, the thermal shrinkage of the polypropylene film can be suppressed, and the quality deterioration of the adhered mating member can be reduced. Also, (P A +P B ) / (E’ A +E’ B ) preferably has a lower limit of 0.001, more preferably 0.0100, and even more preferably 0.500 from the viewpoint of maintaining film rigidity at high temperatures.

[0020] (P A +P B ) / (E’ A +E’ B ) is within the above range, it is effective to set the raw material composition of the polypropylene film within the range described later and the film-forming conditions within the range described later. In particular, in terms of the raw materials, in order to further promote the formation of high melting point crystals along with amorphous relaxation, it is effective to set the angular frequency ω (details will be described later) showing relaxation characteristics within a more appropriate range, or to configure the X layer (details will be described later) containing a large amount of a resin with high heat resistance at a high ratio throughout the polypropylene film. Also, in terms of the process, it is effective to set the longitudinal stretching Relax ratio to 0.1% or more, preferably 1.0% or more, to promote the formation of high melting point crystals while promoting amorphous relaxation.

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

[0022] To make the TMA shrinkage stress start temperature within the above range, it is effective to set the raw material composition of the polypropylene film within the range described later and also set the film-forming conditions within the range described later. In particular, from the raw material aspect, in order to promote relaxation at a higher temperature, it is effective to use a polypropylene resin or composition in which the lower limit of the angular frequency ω (details will be described later) showing relaxation characteristics is 15 rad / s or higher (preferably 19 rad / s or higher). Also, from the process aspect, in order to eliminate the strain generated by longitudinal stretching and transverse stretching by relaxation treatment at a higher temperature, it is effective to set the respective Relax temperatures after longitudinal stretching and transverse stretching within the range described later. These methods may be combined as appropriate.

[0023] The polypropylene film of the present invention preferably has a heat of fusion ratio H of 10% ≤ H ≤ 50% with respect to the total heat of fusion in the 1st run of DSC measurement at a heating rate of 20 °C / min (hereinafter, the "heat of fusion ratio H of 175 °C or higher and 200 °C or lower in the 1st run of DSC measurement at a heating rate of 20 °C / min" may be referred to as the "heat of fusion ratio H"). This heat of fusion ratio H is an index indicating the content ratio of crystals that melt at 175 °C or higher, which is an extremely small proportion in conventional polypropylene films. A high heat of fusion ratio H means that the polypropylene film has excellent heat resistance. From the above viewpoints, 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 the polypropylene film is 10% or more, many crystals remain without melting even in a high-temperature environment of 160 °C or higher, which cannot be tolerated by conventional polypropylene films, and it is easy to achieve high heat resistance. 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 details of the measurement method of the heat of fusion ratio H will be described later.

[0025] To make the heat of fusion ratio H within the above range, it is effective to set the raw material composition of the film within the range described later and the film-forming conditions within the range described later. In particular, in order to promote the formation of high-melting-point crystals under high-temperature film-forming conditions, a polypropylene resin or composition having a melting point of 166.0 °C or higher, a semi-crystallization time of 100 seconds or less, and a relaxation property (details will be described later) of angular frequency ω observed from a rheometer of 50 rad / s or less is used effectively. Also, on the process side, the casting temperature is lowered to suppress the formation of β-crystals, which are low-melting-point crystals, in the unstretched film during the casting process, and the preheating and stretching temperatures for longitudinal and transverse stretching are set within the ranges described later. Furthermore, in order to rearrange the partially collapsed crystals by stretching and promote the high melting point of the crystals in the relaxation process, a relaxation process is introduced after longitudinal stretching and after transverse stretching, and the films are treated at the temperatures and Relax rates within the ranges described later after each stretching. These methods can also be used in combination as appropriate.

[0026] From the perspective of peelability from the mating member when the polypropylene film of the present invention is used as a release film, it is preferable that the root mean square slope Sq is 0.005 or more and 1.000 or less on at least one surface (hereinafter, the "root mean square slope Sq" may be referred to as "Sq"). Here, at least one surface means one side or both sides. Sq is one of the surface parameters indicating the slope of the uneven structure on the film surface, and a high value is shown when the surface includes a steep uneven structure. The lower limit of Sq is preferably 0.005, more preferably 0.007, and even more preferably 0.015. The upper limit of Sq is not particularly limited, but is substantially 1.000, preferably 0.100, from the perspective of film-forming properties of the film. When Sq is 0.005 or more, the polypropylene film has a steep uneven structure on the surface, and when used as a release film, the films are less likely to adhere to each other, and the melt adhesion resistance at high temperatures is likely to be improved. Incidentally, Sq can be measured by a known non-contact surface / layer cross-sectional shape measurement system (for example, Rhodia system "VertScan" (registered trademark) series, etc.), and the details will be described later.

[0027] To make Sq within the above range, it is effective to set the raw materials and film-forming conditions within the ranges described later. In particular, on the raw material side, in order to form steep protrusions in combination with stretching, adding a resin or additive incompatible with polypropylene to the surface layer (the film itself in the case of a single-layer structure) or adding a branched-chain polypropylene or the like to the extent that the relaxation characteristics are not deteriorated is effective. On the process side, it is effective to increase the pre-stretching temperature in the longitudinal stretching process to coarsen the surface uneven structure derived from polypropylene. Incidentally, these methods can be used in combination as appropriate.

[0028] From the perspective of heat resistance and the like, the melting point Tm obtained in the 2nd run of the DSC measurement at a heating rate of 20 °C / min of the polypropylene film of the present invention 2 is preferably 164.0 °C or more and 170.0 °C or less (hereinafter, the "melting point Tm obtained in the 2nd run of the DSC measurement at a heating rate of 20 °C / min2 」 is sometimes referred to as 「Tm 2 」. From the above perspective, the melting point Tm 2 preferably has a lower limit of 165.0 °C, more preferably 166.0 °C. Also, considering the properties of polypropylene, the upper limit of the melting point Tm 2 is 170.0 °C. The details of the measurement method of Tm 2 will be described later.

[0029] The melting point Tm 2 is an index indicating the raw material melting point of the entire polypropylene film. When it is within the above range, film formation under higher temperature conditions becomes possible. Therefore, it is easier to improve the heat shrinkage characteristics and is also advantageous in terms of the formation of high melting point crystals. As a result, it is easy to enhance the heat resistance of the polypropylene film. To set the melting point Tm 2 within the above range, it is effective to set the raw material composition of the polypropylene film within the range described later. In particular, using raw materials with a high melting point and minimizing the mixture other than the high melting point raw materials, or increasing the ratio of the X layer described later. These methods may be used in combination as appropriate.

[0030] From the perspective of improving heat resistance, in the storage viscoelastic modulus G' and loss viscoelastic modulus G'' obtained by melt viscoelasticity measurement at 200°C, it is preferable that the angular frequency ω at which G' = G'' is 10 rad / s or more and 70 rad / s or less (hereinafter, "in the storage viscoelastic modulus G' and loss viscoelastic modulus G'' obtained by melt viscoelasticity measurement at 200°C, the angular frequency ω at which G' = G''" may be referred to as "angular frequency ω"). The angular frequency ω is an index indicating the relaxation characteristics of the polymer in the polypropylene film, and the lower the value, the lower the relaxation characteristics, and the higher the value, the higher the relaxation characteristics. From the above perspective, the lower limit of the angular frequency ω is more preferably 15 rad / s, and even more preferably 20 rad / s. Also, 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 will have appropriate relaxation characteristics, be excellent in achieving both high melting point crystallization and amorphous relaxation during film formation, and is likely to exhibit excellent heat resistance. The angular frequency ω can be measured with a rotational rheometer, and the details of the measurement method will be described later.

[0031] To make the angular frequency ω within the above range, it is effective to set the raw material composition of the polypropylene film within the range described later and also set the film-forming conditions within the range described later. In particular, as described later, it is effective to use a resin in which the angular frequency ω is within the range described later and to reduce the addition amount of branched-chain polypropylene, which is a factor that deteriorates the relaxation characteristics.

[0032] The thickness of the polypropylene film of the present invention is appropriately adjusted according to the application and is not particularly limited, but it is preferably 0.5 μm or more and 100 μm or less from the viewpoint of handleability. In order to take advantage of such characteristics, the thickness of the polypropylene film is more preferably 1 μm or more and 40 μm or less, still more preferably 1 μm or more and 30 μm or less, and particularly preferably 6 μm or more and 30 μm or less. 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 the range that does not reduce other physical properties. The thickness of the polypropylene film can be measured with a known micro thickness gauge, and the details will be described later.

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

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

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

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

[0037] When the layer composed of the polypropylene composition X described later is defined as the X layer in the polypropylene film of the present invention, it is preferable that the X layer occupies 90% or more and 100% or less of the entire polypropylene film based on thickness. The lower limit of the ratio of the X layer in the polypropylene film of the present invention is preferably 90% based on thickness, more preferably 92%, still more preferably 95%, and particularly preferably 98%. Note that the thickness standard means calculating the ratio with the total thickness of the polypropylene film as 100%. When the ratio of the X layer is within the above range, the ratio of high melting point crystals in the polypropylene film increases, and it is easy to maintain the rigidity of the film even at a high temperature where conventional polypropylene films cannot be used. Further, the polypropylene film of the present invention preferably contains the above X layer in an appropriate thickness ratio, and the layer structure may be a single layer or a laminated structure having a plurality of layers such as two-layer three-layer or three-layer three-layer.

[0038] When the total composition is 100% by mass, polypropylene composition X contains 95% by mass or more and 100% by mass or less of a polypropylene resin, and has a melting point of 166.0 °C or more and 170.0 °C or less, a semi-crystallization time of 5 seconds or more and 200 seconds or less, and an angular frequency ω (described later) of 10 rad / s or more and 70 rad / s or less. When there are a plurality of components corresponding to the polypropylene resin, if the total amount of these exceeds 95% by mass and the melting point, semi-crystallization time, and angular frequency ω are within the above ranges, it shall be regarded as corresponding to polypropylene composition X. The polypropylene resin refers to a resin containing more than 50 mol% and 100 mol% or less of propylene units when the total constitutional units constituting the molecular chain of the resin are 100 mol%.

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

[0040] In addition, polypropylene composition X has a semi-crystallization time indicating the crystallization rate obtained by the DSC isothermal crystallization measurement described later of 5 seconds or more and 200 seconds or less. The upper limit of the semi-crystallization time of polypropylene resin X is preferably 100 seconds, more preferably 50 seconds, and still more preferably 30 seconds. When the semi-crystallization time is within the above range, it is easy to recrystallize even during film-forming of the film, and high-melting-point crystals are likely to be formed. To make the semi-crystallization time of polypropylene composition X within the above range, it is effective to appropriately adjust the stereoregularity and molecular weight distribution of the polypropylene resin constituting polypropylene composition X or to add branched-chain polypropylene showing a crystal nucleating agent effect.

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

[0042] When this angular frequency ω is small, the relaxation characteristics are low (relaxation is slow) due to entanglement between molecular chains, etc., but entanglement between molecular chains, etc. is likely to be maintained even at high temperatures, which is advantageous for increasing the melting point of crystals. On the other hand, when the angular frequency ω is large, there is less entanglement between molecular chains, etc., the relaxation characteristics are high (relaxation is fast), the residual strain can be efficiently reduced in the Relax process, and the amorphous part is easily relaxed. The lower limit of the angular frequency ω of the polypropylene composition X is preferably 15 rad / s, more preferably 20 rad / s. Also, 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 high melting point crystallization and amorphous relaxation of the polypropylene composition X, and it is possible to further enhance the heat resistance of the obtained polypropylene film.

[0043] To make the angular frequency ω of the polypropylene composition X within the above range, it is effective to adjust the molecular weight distribution of the polypropylene resin constituting the polypropylene composition X to an appropriate range, adjust the molecular weight distribution of the polypropylene resin under the conditions of pre-kneading, or adjust the addition amount of the branched-chain polypropylene resin. These methods can be combined as appropriate.

[0044] The polypropylene composition X may be composed of only a homopolypropylene resin, but other resin components may be mixed by pre-kneading or the like as long as the properties are not deteriorated as described below. When adding other resin components to the polypropylene composition X, the addition amount 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, with respect to 100% by mass of the total resin of the polypropylene composition X. Here, the homopolypropylene resin refers to a resin in which the amount of propylene units is 99.9 mol% or more and 100 mol% or less when the total constitutional units constituting the molecular chain of the resin are 100 mol%.

[0045] Examples of other resin components that can be added to the polypropylene composition X include, for example, polyolefin resins (resins containing 50 mol% or more and 100 mol% or less of olefin units when the total constitutional units constituting the molecular chain of the resin are 100 mol%, and not being polypropylene resins), and polymer particles such as acrylics that are not completely compatible with polypropylene. For example, by adding a resin component that is not completely compatible with the polypropylene resin to the polypropylene composition X constituting the outermost layer (the polypropylene film itself in the case of a single-layer polypropylene film), sharp protrusions can be formed on the surface when made into a film, and as a result, the melt adhesion resistance of the polypropylene film at high temperatures can be improved.

[0046] The polypropylene resin used in the polypropylene composition X can preferably be selected to satisfy the conditions of the above-described polypropylene composition X. As commercially available ones, for example, F-704NP, F133A which are polypropylene resins manufactured by Prime Polymer Co., Ltd., HC310BF which is a polypropylene resin manufactured by Borealis, FY6H which is a polypropylene resin manufactured by Nippon Polypropylene Corporation, etc. can be mentioned. Further, as the branched polypropylene which can be contained in the polypropylene composition X and is commercially available, for example, “Daploy” (trademark) WB130HMS, WB135HMS, WB140HMS manufactured by Borealis, “WAYMAX” (registered trademark) MFX8, MFX6, MFX3 manufactured by Nippon Polypropylene Corporation, etc. can be mentioned.

[0047] In the whole resin containing the polypropylene composition X used in the polypropylene film of the present invention, various additives such as a nucleating agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, an antiblocking agent, a filler, a viscosity modifier, an anti-coloring agent, etc. can be contained within a range not impairing the object of the present invention.

[0048] Among these, the selection of the type and addition amount of the antioxidant is important from the viewpoint of bleed-out of the antioxidant. That is, such an antioxidant is a sterically hindered phenolic one, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more. Although various specific examples can be mentioned, for example, 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 (for example, “Irganox” (registered trademark) 1330 manufactured by BASF: molecular weight 775.2), tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (for example, “Irganox” (registered trademark) 1010 manufactured by BASF: molecular weight 1177.7), etc. are preferably used alone or in combination.

[0049] In particular, phosphorus-based antioxidants may easily bleed out to the surface of the polypropylene film. When such bleeding out occurs, it may induce various problems. For example, when forming a resin film on the surface of a polypropylene film, if a curing treatment is applied to the uncured or semi-cured resin film, the curing may be inhibited. Also, when forming an electrolyte film or a metal film on the surface of a polypropylene film, the properties of the electrolyte film or the quality of the metal layer may deteriorate. From the above viewpoints, the content of the phosphorus-based antioxidant in the polypropylene film is preferably 0.01 part by mass or less, more preferably 0.005 part by mass or less, and even more preferably 0.001 part by mass or less with respect to 100 parts by mass of the total amount of the polypropylene resin. From the above viewpoints, it is preferable that the phosphorus-based antioxidant is not contained in the polypropylene film, and the lower limit of its content is 0.000 part by mass. Examples of the phosphorus-based antioxidant include tris(2,4-di-t-butylphenyl) phosphite (for example, "Irgafos" (registered trademark) 168 manufactured by BASF: molecular weight 647), etc.

[0050] The total content of these antioxidants is preferably in the range of 0.03 to 1.0 part by mass with respect to 100 parts by mass of the total amount of the polypropylene resin. If there is too little antioxidant, the polymer may deteriorate during the extrusion process and the film may be colored, or the long-term heat resistance may be poor. If there is too much antioxidant, the transparency may decrease due to the bleeding out of these antioxidants. A more preferable content is 0.05 to 0.9 part by mass, and particularly preferably 0.1 to 0.8 part by mass.

[0051] In addition, a nucleating agent can be added to the polypropylene raw material (including polypropylene composition X) used for the polypropylene film of the present invention, as long as it does not go against the object of the present invention. Examples of α-nucleating agents include dibenzylidene sorbitols, sodium benzoate, etc., and examples of β-nucleating agents include potassium 1,2-hydroxystearate, magnesium benzoate, amide compounds such as N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide, and quinacridone compounds. However, excessive addition of the above-mentioned different types of nucleating agents may cause a decrease in stretchability or a decrease in transparency and strength due to void formation, etc. Therefore, when the total amount of the raw material is 100 parts by mass, the addition amount 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.

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

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

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

[0055] The pellets of the polypropylene composition X obtained by the above procedure are respectively supplied to single-screw extruders for the base layer (A layer) and the surface layer (B layer), and melt extrusion is performed at 200 to 290°C, more preferably 240 to 280°C, still more preferably 260 to 280°C. Then, after removing foreign substances, modified polymers, etc. with a filter installed in the middle of the polymer tube, it is laminated into a layer structure of surface layer (B layer) / base layer (A layer) / surface layer (B layer) using a multi-manifold type composite T-die, discharged 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). At this time, the ratio occupied by the A layer is preferably 90% or more and 100% or less in terms of thickness, more preferably 92%, still more preferably 95%, and particularly preferably 98%.

[0056] Also, 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. When the casting temperature is within the above range, the formation of β-crystals with a low melting point among the crystals can be suppressed, which is preferably suitable for increasing the proportion of high melting point crystals in the film. As the method of adhering to the casting drum, any of the methods such as the electrostatic printing method, the adhesion method using the surface tension of water, the air knife method, the press roll method, and the underwater casting method may be used, but the air knife method, which is easy to control the surface roughness, is preferred. When using the air knife method, the air temperature of the air knife is preferably 20 to 100°C, and the blowing air speed is preferably 130 to 150 m / s. Also, in order not to cause vibration of the laminated unstretched sheet, it is also preferable to appropriately adjust the position of the air knife so that air flows on the downstream side of the film formation.

[0057] The obtained laminated unstretched sheet is introduced into the longitudinal stretching (stretching in the longitudinal direction) process. In the longitudinal stretching process, before stretching, the laminated unstretched sheet is preheated by a metal roll 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 structure of the laminated unstretched sheet will proceed to the longitudinal stretching process in a softened state, and stretching can be performed without applying more stress than necessary in the longitudinal stretching process, so the thermal shrinkage stress is likely to be reduced. Also, it is possible to reduce the low melting point β-crystals contained in the laminated unstretched sheet, which is also preferably suitable for increasing the proportion of high melting point crystals in the film. Incidentally, before the above preheating, as preliminary preheating, the unstretched laminated sheet may be heated by contacting a plurality of metal rolls maintained at 50°C or higher and 145°C or lower.

[0058] Then, it is stretched longitudinally 4.0 times or more and 8.0 times or less between rolls with a peripheral speed difference immediately after preheating to obtain a uniaxially stretched film in the longitudinal direction. The stretching ratio is preferably 4.0 times or more and 7.0 times or less, more preferably 4.3 times or more and 6.0 times or less. The stretching temperature is above 150°C and below 160°C, preferably 152°C or more and 158°C or less, more preferably 154°C or more and 158°C or less. When the stretching temperature is within the above range, it is possible to draw out molecular chains from softened crystals while suppressing the remaining of excessive strain. Together with the subsequent relaxation process, the crystallization high melting point is promoted. Therefore, the heat resistance indicated by the storage elastic modulus obtained by the dynamic viscoelasticity measurement of the obtained polypropylene film is likely to be improved.

[0059] At the end of the longitudinal stretching process, the uniaxially stretched film in the longitudinal direction is brought into contact with a metal roll having a peripheral speed difference and maintained at 140 to 160°C, and relaxed at a Relax ratio greater than 0% and less than or equal to 10% in the longitudinal direction, and then cooled to room temperature. The relaxation temperature is preferably 145 to 160°C, more preferably 150 to 160, and even more preferably 154 to 160°C. Also, the relaxation temperature is preferably not less than the stretching temperature - 10°C and not more than the stretching temperature + 5°C, more preferably not less than the stretching temperature - 5°C and not more than the stretching temperature + 5°C, and even more preferably not less than the stretching temperature - 5°C and not more than the stretching temperature. When the relaxation temperature is within the above range, it is possible to promote the rearrangement of the molecular chains drawn out from the crystals by longitudinal stretching and form higher melting point crystals with a thicker lamellar thickness. Also, the Relax ratio in 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%. When the Relax ratio in the longitudinal stretching process is within the above range, the tension of the molecular chains is easily eliminated. As a result, in addition to promoting the amorphous relaxation and reducing the shrinkage stress, the mobility of the molecular chains is within an appropriate range, and the rearrangement of the molecular chains is also easily promoted. As a result, the dimensional stability of the polypropylene film is improved.

[0060] Next, the longitudinally uniaxially stretched film is led into a tenter, and both end portions in the width direction are gripped by clips. After preheating, it is transversely stretched 7.0 to 13 times, preferably 9.6 to 13 times, in the width direction (transverse stretching step). By adopting such a stretching ratio, the pressure adhesion resistance of the obtained polypropylene film at high temperatures is improved. Further, 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, still 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 proceed to the transverse stretching step in a softened state, and stretching can be performed without applying excessive stress in the transverse stretching step, and the thermal shrinkage stress is likely to be reduced.

[0061] Then, the stretching temperature in the transverse stretching step after the preheating step is preferably above 170°C and below 180°C, more preferably 173°C or higher and 180°C or lower, and still more preferably 175°C or higher and 180°C or lower. When the transverse stretching temperature is within the above range, it is possible to draw out molecular chains from the crystals softened by preheating while suppressing the remaining of excessive strain. Therefore, in combination with the subsequent relaxation step, the crystallization high melting point is promoted, and the heat resistance indicated by the storage elastic modulus obtained by the dynamic viscoelasticity measurement of the polypropylene film is likely to be improved.

[0062] In the subsequent Relax process after the transverse stretching, while gripping the width direction moderately tightly with clips, it is preferably relaxed at a Relax rate of 10% or more and 20% or less, more preferably 11% or more and 18% or less, still more preferably 12% or more and 15% or less in the width direction. When the Relax rate after the transverse stretching is within the above range, the tension of the molecular chains is easily eliminated. Therefore, in addition to promoting amorphous relaxation and reducing the shrinkage stress, the mobility of the molecular chains is within an appropriate range, and the rearrangement of the molecular chains is also easily promoted. And the heat setting temperature at that time is preferably 168°C or more and 190°C or less, more preferably exceeding 170°C and 190°C or less, still more preferably 173°C or more and 185°C or less, particularly preferably 175°C or more and 185°C or less, and it is preferably above the stretching temperature of the immediately preceding stretching process, and more preferably 2°C or more higher than the stretching temperature of the immediately preceding stretching process. When the relaxation temperature is within the above range, the rearrangement of the molecular chains drawn out from the crystals by the transverse stretching is promoted, and it becomes possible to form high-melting-point crystals with a thicker lamellar thickness.

[0063] Further, the polypropylene film of the present invention includes a Relax process in the longitudinal stretching process and the transverse stretching process, and the total area Relax rate (%) calculated from the stretching ratios and Relax rates of the longitudinal stretching process and the transverse stretching process is preferably 10.0% or more and 30.0% or less, more preferably 13.0% or more and 25.0% or less, still more preferably 15.0% or more and 20.0% or less. The total area Relax rate (%) is calculated by the following formula, and when it is within the above range, amorphous relaxation easily proceeds, and the shrinkage stress of the entire polypropylene film is easily reduced. Total area Relax rate (%) = [1 - (1 - Relax rate of longitudinal stretching process ÷ 100) × (1 - Relax rate of transverse stretching process ÷ 100)] × 100.

[0064] Thereafter, while gripping the width direction tightly with clips, it is guided to the outside of the tenter through a cooling process at 80 to 130°C, the clips at the film ends are released, the film edge part is 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 in various applications such as packaging films, surface protection films, process films, battery films, sanitary products, agricultural products, building products, and medical products. In particular, due to its excellent heat resistance, it is preferably used as a process film that requires high-temperature treatment in the drying of coating materials or the molding of thermosetting resins, a release film, a base film for current collectors of secondary batteries, or a packaging film for retorting. Particularly preferably, it can be used as a release film used in a high-temperature region.

[0066] In the present invention, the release film refers to a film having a function of protecting an object such as a molded body or a film from scratches and contamination during processing or transportation by attaching it to the object, and being easily peeled off and discarded when used as a final product. The process film refers to a film used in the manufacturing process of an object such as a molded body or a film. For example, it includes those that are attached to an object in the manufacturing process to protect it from scratches and contamination, or those that function as a support when it is difficult to form a film due to reasons such as the object itself being thin or brittle.

[0067] Hereinafter, the laminate of the present invention will be described.

[0068] Since the polypropylene film of the present invention is excellent in heat resistance and release properties, it can also be preferably used when vapor deposition processing or sputtering processing is performed on the polypropylene film of the present invention to form a laminate with a metal film. That is, as one aspect of the laminate of the present invention, there is mentioned one in which a metal film or an electrolyte film is in contact with at least one side of the polypropylene film.

[0069] In vapor deposition processing and sputtering processing, polyethylene terephthalate (PET) films having excellent properties in terms of heat resistance, rigidity, etc. have often been used from the viewpoint of heat resistance and rigidity. However, since PET has an ester bond, it has high hydrophilicity, and the PET film contains a small amount of moisture. Such a small amount of moisture may have an adverse effect during vapor deposition processing or sputtering processing. In particular, it becomes prominent when depositing a metal belonging to Group 1 or Group 2 of the periodic table that easily reacts with moisture or a compound containing such a metal. Against this background, in the case where it is difficult to use a PET film due to the presence of a small amount of moisture, the laminate of the present invention preferably contains a metal belonging to Group 1 or Group 2 of the periodic table in that a laminate can be suitably obtained. Here, the metals belonging to Group 1 or Group 2 refer to lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium. The metal film may contain these metal components alone or a plurality of types, and the combination of components in the latter case is arbitrary.

[0070] Also, in a high-temperature environment, the moisture in the film volatilizes as outgas, and the influence becomes particularly prominent under high-vacuum conditions such as in a metal deposition process. When outgas is generated from the film, the degree of vacuum in the system deteriorates, and the film quality of the metal film formed by vapor deposition and the yield of the vapor deposition process may decrease. From such a viewpoint, the polypropylene film of the present invention having a lower moisture content than the PET film can be suitably used for forming a metal film, and the laminate of the present invention can maintain good film quality of the metal film.

[0071] In addition, electrolyte membranes used in fuel cells, semi-solid batteries, all-solid batteries, etc. are usually manufactured in an environment where temperature and humidity are strictly controlled. In particular, sulfide-based electrolyte membranes react with moisture to generate hydrogen sulfide, so the water content of the process film used in their manufacture is also required to be extremely low. Therefore, the polypropylene film of the present invention is preferably used as the process film in the manufacture 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 side of the 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 water 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 water content is not particularly limited but is substantially 1 ppm. The water content of the polypropylene film can be measured by the Karl Fischer method, and the details will be described later.

[0073] To make the water content of the polypropylene film of the present invention within the above range, it is preferable to minimize the content of hydrophilic resin in the polypropylene film and to minimize the amount of additives. Specifically, taking the total constituent components of the polypropylene film of the present invention as 100% by mass, the lower limit of the content of polyolefin resins such as polypropylene resin is preferably 90% by mass, more preferably 95% by mass, and still more preferably 97% by mass. The upper limit of the content of these resins is substantially 100% by mass.

[0074] From the above viewpoints, with respect to 100 parts by mass of the total amount of the polypropylene resin of the polypropylene film of the present invention, the content of the antioxidant is preferably 0.03 to 1.0 part by mass, more preferably 0.05 to 0.9 part by mass, and even more preferably 0.1 to 0.8 part by mass. Among them, the phosphorus-based antioxidant that has bled out to the surface may reduce the properties and quality of the metal film formed on the surface, so it is preferable to control its content. More specifically, when the total constituent components of the polypropylene film of the present invention are 100 parts by mass, the content of the phosphorus-based antioxidant is preferably 0.01 part by mass or less, more preferably 0.005 part by mass ppm or less, and even more preferably 0.001 part by mass. There is no particular limitation on the lower limit of the content of the phosphorus-based antioxidant, and theoretically it is 0.000 part by mass (equivalent to not containing the phosphorus-based antioxidant). In addition, regarding the content of the antioxidant containing the phosphorus-based antioxidant, from the viewpoints of properties, quality, and reduction of inhibition of effects, it is preferable that the same applies even when the film formed on the surface is not a metal film.

[0075] From the viewpoint of reducing the defects due to bleeding out in the polypropylene film of the present invention, the total content of additives other than the antioxidant (for example, antistatic agent, viscosity modifier, anti-coloring agent, lubricant, etc.) is preferably 0 to 0.05 part by mass or less.

[0076] The antioxidant preferably used in the polypropylene film of the present invention is a sterically hindered phenolic one, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more. Although various specific examples can be cited, for example, 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 (for example, "Irganox" (registered trademark) 1330 manufactured by BASF: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (for example, "Irganox" (registered trademark) 1010 manufactured by BASF: molecular weight 1177.7), etc.

[0077] The polypropylene film of the present invention has an extremely low moisture content in the film and extremely little outgassing as described above, and is superior in smoothness and handleability to existing olefin-based films. Therefore, it is preferably used when forming a transparent conductive film that requires more stringent vacuum conditions and high quality. That is, as a preferred embodiment of the laminate of the present invention, there is also one in which a transparent conductive film is in contact with at least one side of the polypropylene film of the present invention. Here, the transparent conductive film refers to a thin film formed of a material that has conductivity and transmits visible light. Specific examples include indium-tin composite oxide (ITO), zinc oxide (ZnO), palladium film, and the like.

[0078] Next, the current collector of the present invention will be described. The current collector of the present invention is made using the polypropylene film of the present invention. Since the polypropylene film of the present invention is excellent in heat resistance, it is preferably used as a current collector. A current collector is a foil-like laminate used for the electrodes of a storage battery such as a lithium-ion battery. Usually, a metal foil is used as the current collector, but a laminate in which a metal film is laminated on a resin film as a base material is also used for the purpose of improving safety and reducing weight. This metal film is laminated by processes such as vapor deposition, sputtering, plating, electroless plating, and the like. Also, from the viewpoint of increasing the energy density of the battery, the film serving as the base material of the current collector is required to have a small thickness. On the other hand, when the film becomes thinner, the stiffness decreases, so the handleability during processing greatly decreases. In particular, in the process of laminating the metal film, high heat such as radiant heat is applied during processing, and tension is also applied in the conveying direction. Therefore, the film is required to have good handleability. Since the polypropylene film of the present invention can be made thinner and has good handleability, it is preferably used as a current collector.

[0079] Next, the battery of the present invention will be described. The battery of the present invention is made using the polypropylene film of the present invention. Since the polypropylene film of the present invention has excellent heat resistance, it is preferably used as a current collector and is used in a battery having a current collector as an electrode. A battery is a device that stores electrical energy and returns it to electrical energy when needed. Specific examples include lead-acid batteries, nickel-metal hydride batteries, lithium-ion batteries, NAS batteries, redox flow batteries, and the like.

Examples

[0080] Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods.

[0081] (1) Film thickness It was measured using a micro thickness gauge (manufactured by Anritsu Corporation). The film was sampled into a 10 cm square, arbitrarily measured at 5 points, and the average value was obtained.

[0082] (2) E’ A +E’ B (Storage modulus) A rectangular test piece (width 5 mm × length 20 mm) cut out from the polypropylene film with the measurement direction as the long side was attached to the device chuck part in an atmosphere of 23°C, cooled to a low temperature of -100°C, and E’ from -100°C to 180°C was measured after the start of temperature rise. A viscoelastic-temperature curve was drawn by the dynamic viscoelastic method, and E’ at 30°C was calculated. Next, when the longitudinal direction of the polypropylene film was 0°, for each direction forming angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° with respect to the longitudinal direction, the dynamic viscoelasticity was measured in the same manner, E’ in each direction at 30°C was calculated, and the direction showing the highest storage modulus was defined as the A direction, and the direction perpendicular to the A direction was defined as the B direction. Thereafter, the storage moduli at 160°C were read for the A direction and the B direction, and were designated as E’ A 、E’ B respectively. The test was conducted with n = 3, and the average value of the obtained values was taken as the storage modulus in the measurement direction of the polypropylene film. E A ’+EB ' was obtained by calculating the sum of the obtained E A ' and E B '. The measuring device and conditions are as follows. <Measuring Device and Conditions> · Device: EXSTAR DMS6100 (manufactured by Seiko Instruments Inc.) · Geometry: Tensile · Distance between chucks: 20 mm · Frequency: 10 Hz · Strain: 0.1 - 0.2% · Temperature range: -100 to 200 °C · Heating rate: 5 °C / min · Measuring atmosphere: In nitrogen.

[0083] (3) P A + P B , the shrinkage start temperature Using a TMA (manufactured by SII NanoTechnology Inc. / Model TMA / SS6100), the thermal shrinkage stress curves in the measuring directions (A direction and B direction) were obtained under the following conditions. (a) Sample: Width 4 mm × Length 20 mm (b) Initial load: 0.0 mN (c) Temperature program: Heating from 30 °C to 200 °C at a heating rate of 10 °C / min (d) Creation of the thermal shrinkage stress curve: Divide the load (N) at each observed temperature by the cross-sectional area (thickness × sample width) of the polypropylene film to calculate the shrinkage stress (MPa) at each temperature, and create a temperature-shrinkage stress curve (thermal shrinkage stress curve).

[0084] <P A + P B >] The shrinkage stress (MPa) at 160 °C was read from the above shrinkage stress curve. The measurement was performed 3 times in each direction, and the average was obtained for each. The value in the A direction was P A , and the value in the B direction was P B was taken, and the sum of P A and P B was P A + P B .

[0085] <Shrinkage start temperature> In the above shrinkage stress curve, the temperature at which the shrinkage stress first reached 0.2 MPa during the heating process was read. The measurement was performed three times in each direction, and the average value was obtained for each.

[0086] (4) Melting heat quantity ratio H at 175 °C or higher and 200 °C or lower Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), the temperature of each layer of 3 mg of polypropylene film was raised 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 melting heat quantity was calculated from the area surrounded by the linear baseline and the melting curve, and this was converted per sample mass to calculate the total melting heat quantity (J / g). Also, the heat quantity was calculated from the area surrounded by the linear baseline and the melting curve at 175 °C or higher, and this was converted per sample mass to obtain the melting heat quantity at 175 °C or higher (J / g). The obtained total melting heat quantity and the melting heat quantity at 175 °C or higher were applied to the following formula to obtain the crystal melting ratio H (%) at 175 °C or higher. Melting crystal ratio H (%) at 175 °C or higher = Melting heat quantity at 175 °C or higher × 100 ÷ Total melting heat quantity.

[0087] (5) Root mean square slope Sdq The measurement was performed using Rhodia Systems Co., Ltd.'s “VertScan” (registered trademark) 2.0 R5300GL-Lite-AC, and the surface shape was obtained by surface correction of the photographed screen by polynomial fourth-order approximation using the attached analysis software. The measurement conditions were as follows. The measurement was performed on both sides of the film, each with n = 3 (number of measurement times = 3 times), and the average value of each side was obtained to be adopted as Sdq for each side. Manufacturer: Rhodia 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: 530nm white Measurement Mode: Wave Measurement Software: VS-Measure Version5.5.1 Analysis Software: VS-Viewer Version5.5.1 Measurement Area: 561.097μm × 561.473μm.

[0088] (6) Melting Point of Raw Material and Tm of Polypropylene Film 2 5 mg of the raw material was taken as a sample into an aluminum pan and measured using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments) under a nitrogen atmosphere. First, the temperature was raised from 30°C to 260°C at 20°C / min, and then held at 260°C for 5 minutes. After that, the temperature was lowered from 260°C to 30°C at 20°C / min, and then when 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. Also, the polypropylene film was measured in the same way, and the maximum peak temperature in the temperature range of 30°C to 180°C was taken as the Tm 2 (°C).

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

[0090] (8) Angular Frequency ω Measurements were carried out using a rotational rheometer (MCR302 manufactured by Anton Paar Japan) equipped with a 25 mm diameter cone plate. The raw material was left standing on a plate heated to 200 °C for 10 minutes under a nitrogen atmosphere. When the sample was a polypropylene film, it was laminated in advance, melted with a press heated to 200 °C, cooled to form a sheet, and then left standing 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 set value during measurement (0.25 mm), and it was left standing for 5 minutes until it stabilized at 200 °C under a nitrogen atmosphere. Then, while maintaining the state at 200 °C, a viscoelasticity measurement was performed by changing from a low angular frequency of 0.5 rad / s to a high angular frequency of 500 rad / s at a strain of 5%. From the curves of the obtained angular frequency, storage modulus G', and loss modulus G'', the angular frequency ω (rad / s) at which G' = G'' was taken as the angular frequency of the raw material and the polypropylene film.

[0091] (9) Ratio of components with logarithmic molecular weight Log(M) ≤ 5.0 and components with Log(M) ≥ 6.0 Using 1,2,4-trichlorobenzene as a solvent, the polypropylene film was dissolved by stirring at 165 °C for 30 minutes. Then, it was filtered using a 0.5 μm filter, and the molecular weight distribution of the filtrate was measured by gel permeation chromatography (GPC) method, and the measurement results were obtained in terms of polystyrene conversion. Then, using the Q-factor, it was converted to the molecular weight of polypropylene, and the ratio of components with logarithmic molecular weight Log(M) ≤ 5.0 and components with Log(M) ≥ 6.0 was determined from the integral curve of the obtained molecular weight distribution. The measurement by gel permeation chromatography (GPC) method was carried out under the following apparatus and conditions. <Apparatus and measurement conditions> Apparatus: High-temperature GPC apparatus PL-GPC220 manufactured by Agilent Detector: Differential refractive index detector (RI detector) manufactured by Agilent Column: Agilent PL1110-6200 (20 μm MIXED-A) × 2 columns Flow rate: 1.0 mL / min Column temperature: 145 °C Injection volume: 0.500 mL Sample concentration: 0.1 mass% Standard sample: Monodisperse polystyrene manufactured by Tosoh Corporation, dibenzyl manufactured by Tokyo Chemical Industry Co., Ltd.

[0092] (10) Heat resistance evaluation After cutting thick paper (product number C-55 manufactured by Oji Paper Co., Ltd.) into a 10 cm square, polypropylene film or PET film cut into a 15 cm square was placed on both sides of the thick paper together with a 20 cm square SUS plate as shown in Fig. 1, and using a hot press machine, it was heated and pressed at a pressure of 1.5 MPa and temperatures of 160 °C, 165 °C, and 170 °C for 15 minutes each, removed from the pressure press machine, and cooled to room temperature. Then, after peeling off the biaxially oriented polyolefin film or PET films protruding from the thick paper, the thick paper was peeled off from the polypropylene film or PET film. In Fig. 1, reference numerals 1 to 4 indicate the SUS plate, polypropylene film or PET film, thick paper, and pressing direction in order. The states of the thick paper and polypropylene film treated at each temperature were visually evaluated from the following viewpoints. The evaluation was first carried out with the heating temperature set at 160 °C for each evaluation item, and only the evaluation items that passed proceeded to the evaluation at a heating temperature of 165 °C. Furthermore, only the items that passed the evaluation at 165 °C proceeded to the evaluation at a heating temperature of 170 °C. (Adhesion resistance) When the polypropylene film or PET film could be completely peeled off from the thick paper, it was considered a pass; when the peeling was incomplete, or when a part of the thick paper and the polypropylene film or PET film remained on the other due to peeling, it was considered a fail, and the evaluation was carried out according to the following criteria. (Dimensional stability) When no folds or wrinkles were observed on the thick paper, it was considered a pass; when at least one of a fold or a wrinkle was observed, it was considered a fail, and the evaluation was carried out according to the following criteria. (Fusion resistance) When the polypropylene films or PET films outside the pressing surface after the pressing treatment were not fused, it was considered a pass; when they were fused even partially, it was considered a fail, and the evaluation was carried out according to the following criteria (in the case of fusion, after cutting off the fused part, it was peeled off from the thick paper and the above evaluation was carried out). <Evaluation Criteria (Common for Crimp Resistance, Dimensional Stability, and Welding Resistance)> The crimp resistance, dimensional stability, and welding resistance were evaluated according to the following criteria, and if each characteristic was A to C, it was considered 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 evaporation apparatus, the pressure was reduced from atmospheric pressure to 1 × 10 -5 Torr, 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 evaporation using magnesium as the evaporation source. At that time, the time until the pressure was reduced from atmospheric pressure to 1 × 10 -5 Torr was measured, and the unevenness of the metal film surface was observed by visual confirmation, and the yield was evaluated according to the following criteria. The evaluation criteria were A for pass and B for fail. A: The time until the pressure was reduced from atmospheric pressure to 1 × 10 -5 Torr was 50 minutes or less, and no unevenness was visible on the metal film surface. B: The time until the pressure was reduced from atmospheric pressure to 1 × 10 -5 Torr was longer than 50 minutes, or unevenness was confirmed on the metal film surface.

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

[0095] (Polypropylene Resin, etc.) The raw materials used in the polypropylene films of the examples and comparative examples and their properties are shown in Tables 1 to 3 below. These property values are the values evaluated in the form of resin pellets. Eight types (PP1 to PP8) of polypropylene raw materials were prepared. Note that all of PP1 to PP8 contain "Irganox" (registered trademark) 1010 manufactured by BASF as an antioxidant in the range of 1000 ppm to 5000 ppm, and only PP8 further contains 3000 ppm of "Irgafos" (registered trademark) 168 manufactured by BASF. Also, seven types (PP9 to PP15) of polypropylene resin pellets prepared by pre-kneading with the composition shown in Table 3 were prepared (the kneading was performed by charging into a twin-screw extruder at 260 °C after dry blending 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 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 Corporation Homopolypropylene resin 8 (PP8): manufactured by Prime Polymer Co., Ltd.

[0096]

Table 1

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

[0098]

Table 2

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

[0100]

Table 3

[0101] (Example 1) The polypropylene resin 9 was supplied to a single-screw uniaxial extruder for the base layer (A layer), and the polypropylene resin 15 was supplied to a single-screw uniaxial extruder for the surface layer (B layer). The resin mixtures for each layer were melt-extruded at 260 °C. After removing foreign matters with a sintered filter with a 20-μm cut, they were laminated with a feed-block type B / A / B composite T-die so that the thickness ratio of the surface layer (B layer) / base layer (A layer) / surface layer (B layer) became 1 / 28 / 1, and the obtained melt laminate was formed into a sheet shape with the T-die. Then, the molten sheet-like material was discharged onto a casting drum whose surface temperature was controlled at 30 °C from the T-die, and compressed air at 25 °C was jetted at an air velocity of 140 m / s with an air knife to bring the molten sheet-like material into close contact with the casting drum, obtaining an unstretched sheet. Subsequently, the unstretched sheet was preheated to 156 °C with a ceramic roll and stretched longitudinally at a magnification of 4.3 times between rolls at 156 °C with a peripheral speed difference, and then further relaxed longitudinally by 5.6% with a roll at 155 °C with a peripheral speed difference to obtain a uniaxially stretched film. Next, both end portions in the width direction were gripped with clips and the uniaxially stretched film was introduced into a tenter-type stretching machine. After preheating at 180 °C for 10 seconds, it was stretched 9.8 times in the width direction at 176 °C, and heat setting was performed at 178 °C while giving a 13% relaxation in the width direction. Then, after passing through a cooling step at 100 °C, it was led outside the tenter-type stretching machine, the clips at both end portions in the width direction were released, and it was wound around a core to obtain a polypropylene film with a thickness of 30 μm. The physical properties and evaluation results of the obtained polypropylene film are shown in Table 4.

[0102] (Examples 2 to 5, Comparative Examples 1 to 5) A polypropylene film was obtained in the same manner as in Example 1 except that the raw material compositions and film-forming conditions of each layer were as shown in Table 4. At this time, the thickness was adjusted by adjusting the discharge amount during extrusion and the speed of the casting drum. The physical properties and evaluation results of the obtained polypropylene film are shown in Table 4. In Examples 2 to 4 and Comparative Examples 1, 3 to 5 having a single-layer configuration, the same resin or resin composition was charged into two single-screw extruders. (Comparative Example 6) As a substitute for the polypropylene film, the PET film "Lumirror" (registered trademark) S10 (manufactured by Toray Industries, Inc.) was used, and heat resistance characteristics evaluation and yield evaluation during metal film formation were carried out, and the moisture content was measured. The evaluation results are shown in Table 4.

[0103]

Table 4

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

Industrial Applicability

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

Explanation of Symbols

[0106] 1: SUS plate 2: Polypropylene film 3: Cardboard 4: Pressing 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 (MPa), the following formulas 1 and 2 are satisfied: The layer structure is any one selected from a single layer structure, a two-kind three-layer structure, and a three-kind three-layer structure, a resin composition X containing 95% by mass or more and 100% by mass or less of a polypropylene resin when the entire composition is taken as 100% by mass, having 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 at which G'=G'' in a storage viscoelastic modulus G' and a loss viscoelastic modulus G'' obtained by melt viscoelasticity measurement at 200° C. is 10 rad / s or more and 70 rad / s or less, and a layer composed of said polypropylene composition X is taken as an X layer, said X layer occupies 90% or more and 100% or less of the entire polypropylene film in terms of thickness, And the angular frequency ω is 10 rad / s or more and 70 rad / s or less. 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 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.

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

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

10. 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.

11. 11. The laminate of claim 10, wherein the metal film comprises a metal belonging to Group 1 or 2 of the periodic table.

12. 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.

13. 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.

14. The laminate according to claim 13, wherein the electrolyte membrane is for a fuel cell, a semi-solid battery, or an all-solid battery.

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

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

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