Biaxially oriented polypropylene film, and mold release film

Abstract

To provide a polypropylene film which can be suitably used as a mold release film even under a high temperature environment in which a polypropylene film is conventionally unable to be used as the mold release film.SOLUTION: When a surface with an actual volume Vmp of mountain portions is 0.0015 mL / m2 or more and 0.0050 mL / m2 or less, a void volume Vvv of valley portions is 0.0050 mL / m2 or more and 0.0100 mL / m2 or less, and density of peaks Spd is 20 / mm2 or more and 120 / mm2 or less is expressed as an A surface, provided is a biaxially oriented polypropylene film with both surfaces being the A surface.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented polypropylene film having excellent releasability and heat resistance, and a release film using the same. [Background technology]

[0002] Polypropylene films are excellent in various properties such as transparency, mechanical properties, electrical properties, etc., and are therefore used in a variety of applications such as packaging applications, release applications, tape applications, cable wrapping, capacitors, and other electrical applications. In particular, because of their excellent surface peeling properties and mechanical properties, they are suitably used as release films and process films for protecting various components such as plastic products, building materials, and optical components.

[0003] The uses of release films include supports for coatings and melt-forming, spacers for press molding, etc. The required properties of release films are set appropriately depending on the application, but since the temperatures during heating and press molding are increasing year by year with the improvement of material performance and productivity, it is becoming important to have both releasability and heat resistance.

[0004] In the past, polyethylene terephthalate (PET) films with excellent heat resistance were sometimes used in the temperature range above 150°C, but they had poor releasability and could not satisfy the required characteristics. On the other hand, conventional polypropylene films have high releasability, but they begin to significantly shrink from 120°C to 130°C, and at 160°C near the melting point, they begin to melt and fuse, significantly reducing their releasability, which causes a problem of impairing the quality of mating members made of thermoplastic resin compositions or thermosetting resin compositions that require drying or molding at high temperatures. Therefore, it was very difficult to use polypropylene films as release films at high temperatures of 150°C or higher, especially at high temperatures of 160°C or higher.

[0005] Under the above circumstances, as an example of a conventional means for improving releasability, i.e., for making the surface dense and rough, for example, Patent Document 1 describes a method of forming fine protrusions by adding a branched polypropylene resin. On the other hand, as an example of a conventional means for improving heat resistance, for example, Patent Document 2 describes a method of lowering the heat shrinkage rate by lowering the molecular weight of the polypropylene raw material. In addition, Patent Document 3 describes a method of lowering the heat shrinkage rate by increasing the heat treatment temperature in the relaxation treatment to relax the molecular orientation. As an example of a means for achieving both releasability and heat resistance, for example, Patent Document 4 describes a method of applying a silicone resin to a polypropylene film using a highly crystalline polypropylene resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-172973 A [Patent Document 2] JP 2014-051657 A [Patent Document 3] International Publication No. 2020 / 196602 [Patent Document 4] JP 2023-95426 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the method described in the above-mentioned Patent Document 1 has a problem in that the polypropylene film obtained has a large shrinkage at high temperatures. In addition, the methods described in Patent Documents 2 and 3 have a problem in that the polypropylene film obtained has low rigidity and low stretching stability. The silicone resin laminated release film obtained by the method described in Patent Document 4 has a problem in that the low molecular weight silicone resin is transferred to a mating member, causing adverse effects.

[0008] The object of the present invention is to solve the above problems, that is, to provide a biaxially oriented polypropylene film that exhibits excellent releasability even in a high-temperature environment, where it has been impossible to use a conventional polypropylene film as a release film, and that can be suitably used as a release film. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the biaxially oriented polypropylene film of the present invention has the following configuration. That is, the biaxially oriented polypropylene film of the present invention has a peak actual volume Vmp of 0.0015 ml / m 2 More than 0.0050ml / m 2 The void volume Vvv of the valley is 0.0050 ml / m or less. 2 More than 0.0100ml / m 2 and the peak density (Spd) is 20 / mm 2 More than 120 / mm 2 The biaxially oriented polypropylene film is characterized in that, when the surface described below is designated as side A, both surfaces are the above-described side A. (1) The actual volume of the peak Vmp is 0.0015 ml / m 2 More than 0.0050ml / m 2 The void volume Vvv of the valley is 0.0050 ml / m or less. 2 More than 0.0100ml / m 2 and the peak density (Spd) is 20 / mm 2 More than 120 / mm 2 A biaxially oriented polypropylene film, characterized in that both surfaces are side A, with the following surface being side A: (2) A biaxially oriented polypropylene film according to (1), characterized in that the height S5p of the five-point peak region on both sides is 30 nm or more and 700 nm or less, and the breaking strength in the direction perpendicular to the main orientation is 100 MPa or more and 200 MPa or less. (3) A biaxially oriented polypropylene film according to (1) or (2), characterized in that the onset temperature of the heat shrinkage stress in the direction perpendicular to the main orientation is 140°C or higher and 160°C or lower, and the heat shrinkage stress value at 160°C in the direction perpendicular to the main orientation is 0.5 MPa or higher and 1.0 MPa or lower. (4) A biaxially oriented polypropylene film according to any one of (1) to (3), characterized in that the onset temperature of the heat shrinkage stress in the main orientation direction is 150°C or higher and 170°C or lower, and the heat shrinkage stress value at 160°C in the main orientation direction is 1.0 MPa or higher and 3.0 MPa or lower. (5) The biaxially oriented polypropylene film according to claim 1 or 2, having a laminated structure of at least two layers. (6) A release film comprising the biaxially oriented polypropylene film according to any one of (1) to (5) and having a laminated structure of at least two layers. Effect of the Invention

[0010] The present invention makes it possible to provide a biaxially oriented polypropylene film that exhibits excellent releasability even in high-temperature environments, where it was impossible to use conventional polypropylene films as release films, and that can be suitably used as a release film. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram illustrating a method for evaluating high-temperature releasability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The biaxially oriented polypropylene film of the present invention has a peak volume Vmp of 0.0015 ml / m 2 More than 0.0050ml / m 2 The void volume Vvv of the valley is 0.0050 ml / m or less. 2 More than 0.0100ml / m 2 and the peak density (Spd) is 20 / mm 2 More than 120 / mm 2The biaxially oriented polypropylene film of the present invention is characterized in that, when the surface described below is designated as surface A, both surfaces are the above surface A. Hereinafter, the biaxially oriented polypropylene film of the present invention will be specifically described.

[0013] A polypropylene film refers to a sheet-shaped molded product whose main component is polypropylene resin. The main component refers to a component that is contained in an amount of more than 50% by mass and not more than 100% by mass when the total components of the object (here, the film) are taken as 100% by mass, and the main component can be interpreted in the same manner hereinafter. In addition, when a plurality of components corresponding to polypropylene resin are contained, if the total amount is more than 50% by mass, polypropylene resin is considered to be the main component. In addition, in the biaxially oriented polypropylene film of the present invention, the content of polypropylene resin is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 96% by mass or more, particularly preferably 97% by mass or more, and most preferably 98% by mass or more of the total components of the film.

[0014] Polypropylene resin refers to a resin whose main structural unit is a propylene unit, and a main structural unit refers to a structural unit that is contained in an amount of more than 50 mass% to 100 mass% or less when all structural units are taken as 100 mass% (this definition can be interpreted similarly for other olefin resins, except that the propylene unit is replaced by another olefin unit).

[0015] Biaxial orientation means that the molecules are oriented in two perpendicular directions, and can be achieved by stretching an unstretched polypropylene sheet in two perpendicular directions (usually the longitudinal direction and the width direction). The longitudinal direction refers to the direction in which the polypropylene film runs during the manufacturing process (corresponding to the winding direction in the case of a film roll), and the width direction refers to the direction perpendicular to the longitudinal direction within the film plane. By using a biaxially oriented polypropylene film, the release properties and quality, as well as the heat shrinkage properties described below, are particularly improved.

[0016] In addition, from the viewpoint of multifunctionalization, the biaxially oriented polypropylene film of the present invention preferably has a laminated structure of at least two layers, and more preferably has a laminated structure of at least two layers including a plurality of layers mainly composed of polypropylene resin. The laminated structure means that two or more layers having different compositions are laminated in the thickness direction (direction perpendicular to the film surface), and the different compositions means that the components constituting each layer differ by 1.0% by mass or more and 100% by mass or less. By adopting such an embodiment, for example, a laminated structure of a layer that plays a role in enhancing heat resistance and a layer that plays a role in enhancing releasability is formed, and the biaxially oriented polypropylene film can achieve both releasability and heat resistance. In addition, the "laminated structure of at least two layers" means a state in which at least two or more layers having different compositions are laminated in total to form two or more layers. Specific examples of such an embodiment include a two-type two-layer structure of base layer (A) / surface layer (B), a two-type three-layer structure of surface layer (B) / base layer (A) / surface layer (B), and the like.

[0017] From the viewpoint of releasability, the biaxially oriented polypropylene film of the present invention has a peak actual volume Vmp of 0.0015 ml / m 2 More than 0.0050ml / m 2 The void volume Vvv of the valley is 0.0050 ml / m or less. 2 More than 0.0100ml / m 2 and the peak density (Spd) is 20 / mm 2 More than 120 / mm 2 It is important that both surfaces are surfaces A when the surface described below is designated as surface A. In the following, the "real volume of the peaks Vmp," "void volume of the valleys Vvv," and "peak density Spd" may be simply referred to as "Vmp," "Vvv," and "Spd."

[0018] From the above viewpoints, the preferred ranges of Vmp, Vvv, and Spd on the A side of the biaxially oriented polypropylene film of the present invention are as follows: Vmp on the A side is 0.0023 ml / m 2 More than 0.0040ml / m 2 Less than 0.0024 ml / m is preferable. 2 More than 0.0040ml / m 2More preferably, Vvv on side A is 0.0060 ml / m 2 More than 0.0075ml / m 2 The preferred value of Spd on the A side is 30 / mm 2 More than 100 / mm 2 It is preferable that the Vmp, Vvv, and Spd of the biaxially oriented polypropylene film of the present invention is equal to or different from each other if both sides are sides A, but it is more preferable that at least one of these indices is within the above-mentioned preferred range on both sides. Most preferably, all of these indices are within the above-mentioned preferred range on both sides.

[0019] The peak material volume (Vmp) is a type of functional (volume) parameter defined in ISO25178 (2021), and indicates the volume of the material part per unit area (the protruding part of the film corresponding to the surface area ratio of 0% to 10%) calculated from the bearing curve of the height data (the frequency at a certain height is accumulated from the high side, and the total number of all height data is expressed as a percentage with 100% being the total. The surface area ratio at a certain height C is given by Smr(C)). When Vmp is 0.0050ml / m 2 If the surface roughness exceeds 0.015 ml / m, the number of large peaks will increase, and when the film is used as a release film, when the mating part that will become the product comes into contact with the surface, transfer marks may be generated on the mating part, which may impair the quality. 2 If the thickness falls below this value, the surface approaches a flat surface, and there is a possibility that a peeling mark will be left on the counter member when the surface is peeled off from the counter member.

[0020] The valley void volume (Vvv) is a type of functional (volume) parameter defined in ISO25178 (2021), and indicates the volume of the space per unit area (the concave portion of the film corresponding to the area load ratio of 80% to 100%) calculated from the bearing curve of the height data with an area load ratio of 80% to 100%. 2If the Vvv exceeds 0.0050 ml / m, the surface will have many large valleys, and when the film is used as a release film, when the mating part that will become the product comes into contact with the surface, transfer marks may be generated on the mating part, damaging the quality. 2 If the thickness falls below this value, the surface approaches a flat surface, and there is a possibility that a peeling mark will be left on the counter member when the surface is peeled off from the counter member.

[0021] Peak density (Spd) is a parameter that expresses surface roughness defined in ISO25178 (2021) and represents the number of peaks per unit area. 2 If the surface density exceeds 20 / mm, the surface will have many sharp protrusions, and when the film is used as a release film and the mating part that will become the product comes into contact with the surface, the protrusions may be transferred to the mating part, causing dents and impairing the quality. 2 If the thickness falls below this value, the surface will be smooth and peeling marks may be left on the mating member.

[0022] Vmp, Vvv, and Spd can be measured using a known layer cross-sectional shape measuring device, and an example of the measuring device that can be used is the non-contact surface / layer cross-sectional shape measuring system "VertScan" (registered trademark) 2.0 manufactured by Ryoka Systems Co., Ltd. A specific method for measuring Vmp, Vvv, and Spd using this device will be described later.

[0023] In order to set Vmp, Vvv, and Spd to the above ranges, it is effective to set the raw material composition and film-forming conditions to the ranges described later. In particular, in terms of raw materials, in order to form a moderately rough surface with uniform protrusions, it is effective to make a biaxially oriented polypropylene film have a laminated structure of two or more layers, add a resin or additive that is incompatible with polypropylene to the surface layer (B) as an antiblocking agent in the range described later, or add a branched polypropylene resin to the base layer (A) in the range described later. In terms of process, it is effective to cool the unstretched sheet using a water bath with a water temperature of 20°C to 70°C in order to form more uniform fine protrusions on both sides by cooling both sides evenly. By performing water cooling in a water bath, it is possible to suppress the inter-face difference of the surface protrusions. In terms of process, it is also effective to set the transverse stretching ratio to the range described later. The amount of surface protrusions can be controlled by setting the transverse stretching ratio and the Relax ratio after transverse stretching to the range described later. It is possible to combine these methods appropriately.

[0024] From the viewpoint of releasability, the biaxially oriented polypropylene film of the present invention preferably has a five-point peak region height S5p of 30 nm or more and 700 nm or less on both sides. Hereinafter, the "five-point peak region height S5p" may be simply referred to as "S5p". From the above viewpoint, it is more preferable that S5p is 200 nm or more and 650 nm or less on at least one side, and even more preferable that S5p is 200 nm or more and 650 nm or less on both sides.

[0025] The 5-point peak height (S5p) is a parameter that represents surface roughness defined in ISO25178 (2021), and represents the average peak height from the highest peak to the fifth highest peak in the defined region. If S5p is 700 nm or less, there will be fewer sharp protrusions on the surface, so when the biaxially oriented polypropylene film is used as a release film and the mating component that will become the product comes into contact with the surface, the dents transferred to the mating component are reduced, and the appearance of the mating component is maintained in good condition. On the other hand, if S5p is 30 nm or more, the smoothness of the surface is suppressed, making it easier to peel off from the mating component.

[0026] S5p can be measured using a known layer cross-sectional shape measuring device, and as the measuring device, for example, a non-contact surface / layer cross-sectional shape measuring system "VertScan" (registered trademark) 2.0 manufactured by Ryoka Systems Co., Ltd. A specific method for measuring S5p using this device will be described later.

[0027] In order to set S5p to a value within the above range, it is effective to set the raw material composition and film-forming conditions to the ranges described below. In particular, in terms of raw materials, in order to form protrusions distributed with a uniform height, it is effective to form a biaxially oriented polypropylene film in a laminated structure of two or more layers and add an antiblocking agent to the surface layer (B) in the amount range described below. In terms of process, in order to control the amount of β crystal formation that is the source of the formation of craters that become sharp irregularities, it is effective to set the surface temperature of the casting drum to 20°C or more and 80°C or less. Note that these methods can be combined as appropriate.

[0028] From the viewpoint of handling, the biaxially oriented polypropylene film of the present invention preferably has a breaking strength in the direction perpendicular to the main orientation of 100 MPa or more and 200 MPa or less. From the above viewpoint, the breaking strength in the direction perpendicular to the main orientation is more preferably 130 MPa or more and 180 MPa or less.

[0029] The breaking strength in the direction perpendicular to the main orientation is one of the indicators of the rigidity of the film. If the breaking strength in the direction perpendicular to the main orientation is 200 MPa or less, the rigidity of the film is suppressed, so that the transportability is maintained good. On the other hand, if the breaking strength in the direction perpendicular to the main orientation is 100 MPa or more, the stiffness of the biaxially oriented polypropylene film is sufficient, and the handling property is improved. The details of the method for measuring the breaking strength in the direction perpendicular to the main orientation will be described later.

[0030] The main orientation direction in the biaxially oriented polypropylene film of the present invention refers to the direction that shows the highest storage modulus at 30°C when dynamic viscoelasticity measurement is performed in each direction that forms an angle of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° with respect to the longitudinal direction, with the longitudinal direction being taken as 0°, in the plane of the film. In many cases, the direction with the largest stretching ratio is the main orientation direction for biaxially oriented polypropylene films. In the case of a film in which 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 surface, and slit-shaped film pieces are sampled parallel to each line, and the storage modulus at 30°C is measured by dynamic viscoelasticity measurement, and the direction that gives the maximum storage modulus is regarded as the main orientation direction. The direction perpendicular to the main orientation in the biaxially oriented polypropylene film of the present invention means a direction perpendicular to the main orientation direction in the film plane. The method for measuring the storage modulus by dynamic viscoelasticity measurement will be described later in detail.

[0031] In order to set the breaking strength in the direction perpendicular to the main orientation to the above range, it is effective to set the raw material composition and film-forming conditions to the ranges described later. In particular, in terms of raw materials, since the strength can be increased by increasing the crystallinity, it is effective to use a resin with a high mesopentad fraction for the base layer (A) after forming a biaxially oriented polypropylene film into a laminated structure of two or more layers. In terms of process, in order to achieve stable film formation and uniform stretching, it is effective to set the film thickness to the range described later, the longitudinal stretching preheating temperature to the range described later, and the longitudinal stretching ratio to the range described later. Note that these methods can be appropriately combined. Details of the method for measuring the thickness of the biaxially oriented polypropylene film and the mesopentad fraction of the raw material will be described later.

[0032] From the viewpoint of suppressing heat shrinkage in a high-temperature environment, the biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage stress rise temperature in the direction perpendicular to the main orientation of 140° C. or more and 160° C. or less, and a heat shrinkage stress value at 160° C. in the direction perpendicular to the main orientation of 0.5 MPa or more and 1.0 MPa or less. From the above viewpoint, it is more preferable that the heat shrinkage stress rise temperature in the direction perpendicular to the main orientation of 145° C. or more and 155° C. or less, and the heat shrinkage stress value at 160° C. in the direction perpendicular to the main orientation of 0.5 MPa or more and 0.8 MPa or less. By having a heat shrinkage stress rise temperature in the direction perpendicular to the main orientation of 140° C. or more and a heat shrinkage stress value at 160° C. in the direction perpendicular to the main orientation of 1.0 MPa or less, the heat shrinkage rate in the direction perpendicular to the main orientation of the biaxially oriented polypropylene film can be kept low even in a high temperature region where it is difficult to use a conventional polypropylene film, and the film can be peeled off without impairing the quality of the mating member to be bonded. The upper limit of the heat shrinkage stress rise temperature in the direction perpendicular to the main orientation of the film is substantially 160° C. from the viewpoint of feasibility. The lower limit of the heat shrinkage stress value at 160° C. in the direction perpendicular to the main orientation is practically 0.5 MPa from the viewpoint of feasibility. The details of the heat shrinkage stress rise temperature and the method of measuring the heat shrinkage stress value will be described later.

[0033] In order to set the heat shrinkage stress rise temperature in the direction perpendicular to the main orientation and the heat shrinkage stress value at 160 ° C. in the direction perpendicular to the main orientation within the above range, it is effective to set the raw material composition and film formation conditions to the ranges described later. In particular, in terms of raw materials, in order to promote relaxation at higher temperatures, it is effective to use a polypropylene resin whose melting point and melt flow rate (hereinafter referred to as MFR) are in the ranges described later (in the case of a laminated structure having a base layer (A) and a surface layer (B), it is preferable to use such a polypropylene resin for the base layer (A). In terms of process, in order to eliminate the strain caused by longitudinal stretching by a relaxation treatment at a higher temperature, it is effective to set the Relax temperature after longitudinal stretching to the range described later. Note that these methods may be appropriately combined. The MFR of polypropylene resin can be measured under conditions of 230 ° C. and 2.16 kg in accordance with JIS K 7210-1 (2014).

[0034] From the viewpoint of suppressing heat shrinkage in a high-temperature environment, the biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage stress onset temperature in the main orientation direction of 150°C to 170°C and a heat shrinkage stress value in the main orientation direction at 160°C of 1.0 MPa to 3.0 MPa. From the viewpoint above, it is more preferable that the heat shrinkage stress onset temperature in the main orientation direction is 150°C to 160°C and a heat shrinkage stress value in the direction perpendicular to the main orientation at 160°C of 1.0 MPa to 2.3 MPa. Even more preferably, the heat shrinkage stress onset temperature in the main orientation direction is 154°C to 160°C and a heat shrinkage stress value in the direction perpendicular to the main orientation at 160°C of 1.0 MPa to 2.1 MPa. By having a heat shrinkage stress rise temperature in the direction perpendicular to the main orientation of 150°C or higher and a heat shrinkage stress value in the direction perpendicular to the main orientation of 3.0MPa or lower at 160°C, it becomes easier to keep the heat shrinkage rate in the main orientation of the biaxially oriented polypropylene film low even in high temperature regions where it is difficult to use conventional polypropylene films, and the film can be peeled off without impairing the quality of the mating member to be laminated. From the viewpoint of feasibility, the upper limit of the heat shrinkage stress rise temperature in the main orientation is substantially 170°C, and the lower limit of the heat shrinkage stress value in the main orientation at 160°C is substantially 1.0MPa.

[0035] In order to set the heat shrinkage stress rise temperature in the main orientation direction and the heat shrinkage stress value at 160°C in the main orientation direction within the above ranges, it is effective to set the raw material composition and film-forming conditions within the ranges described below. In particular, in terms of raw materials, it is effective to use a polypropylene resin whose melting point and MFR are within the ranges described below in order to promote relaxation at higher temperatures. In terms of process, it is effective to set the transverse stretch ratio within the ranges described below and the Relax temperature and Relax rate after transverse stretching within the ranges described below in order to suppress the distortion caused by transverse stretching and to eliminate the distortion by relaxation treatment at higher temperatures. These methods may be combined as appropriate.

[0036] The thickness of the biaxially oriented polypropylene film of the present invention is adjusted appropriately depending on the application and is not particularly limited, but is preferably 5.0 μm or more and 70.0 μm or less from the viewpoint of handleability. When the thickness is 5.0 μm or more, handling is good, and when it is 70.0 μm or less, the decrease in productivity due to an increase in the amount of resin is suppressed. Even if the thickness is reduced, the biaxially oriented polypropylene film of the present invention can maintain a moderate strength (breaking strength) and handleability. In order to make the most of such characteristics, the thickness of the biaxially oriented polypropylene film is more preferably 5.0 μm or more and 60.0 μm or less, even more preferably 15.0 μm or more and 50.0 μm or less, and particularly preferably more than 20.0 μm and less than 50.0 μm.

[0037] Next, the raw materials for the biaxially oriented polypropylene film of the present invention will be described, but the raw materials for the biaxially oriented polypropylene film of the present invention are not necessarily limited to those mentioned above.

[0038] The biaxially oriented polypropylene film of the present invention may contain a resin other than polypropylene resin as long as the effect of the present invention is not impaired. Examples of resins other than polypropylene resin that can be contained in the biaxially oriented polypropylene film of the present invention include polyolefins having ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene, etc. as main structural units (among which, polyethylene and polymethylpentene are preferred), and polyesters such as polyethylene terephthalate and polybutylene terephthalate, but are not limited to the above examples. These may be added to the polypropylene resin alone or in combination of two or more at any ratio, and may be homopolymers or copolymers. From the viewpoints of dielectric breakdown resistance and dimensional stability, the content of these resins is preferably less than 10% by mass when all components constituting the biaxially oriented polypropylene film are taken as 100% by mass.

[0039] In addition, the biaxially oriented polypropylene film of the present invention may contain various additives other than the above resins, such as crystal nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and color inhibitors, within the scope of the present invention. These components may be used in combination of two or more types, as long as the effects of the present invention are not impaired.

[0040] Selection of the antioxidant and adjustment of the amount of the antioxidant are important from the viewpoint of the bleed-out of the antioxidant. As the antioxidant, a phenolic one having steric hindrance is preferable, and when a plurality of antioxidants are used in combination, it is preferable that at least one of them is a high molecular weight type having a molecular weight of 500 or more. Specific examples of the antioxidant that can be used in the biaxially oriented polypropylene film of the present invention include various ones, and 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 (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), etc.

[0041] The total content of these antioxidants is preferably in the range of 0.03% by mass or more and 1.00% by mass or less, when the entire raw material for obtaining the biaxially oriented polypropylene film is taken as 100% by mass, from the viewpoint of reducing coloring due to deterioration of the polymer and reduction in transparency due to bleed-out of the antioxidant. By using 0.03% by mass or more of the antioxidant, coloring of the film caused by deterioration of the polymer in the extrusion process and reduction in long-term heat resistance can be reduced. On the other hand, by using 1.00% by mass or less of the antioxidant, reduction in transparency caused by bleed-out of the antioxidant can be suppressed. From the above viewpoint, the content of the antioxidant is more preferably 0.05% by mass or more and 0.90% by mass or less, and even more preferably 0.10% by mass or more and 0.80% by mass or less. In addition, when the biaxially oriented polypropylene film has a laminated structure, these antioxidants may be added to any layer or to multiple layers.

[0042] The biaxially oriented polypropylene film of the present invention may contain copolymerization components of other unsaturated hydrocarbons within the range that does not impair the object of the present invention. Examples of copolymerization components include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and 5-methyl-2-norbornene. From the viewpoint of dimensional stability, it is preferable that the copolymerization amount is less than 1% by mass when the total constituent units are taken as 100% by mass.

[0043] When the biaxially oriented polypropylene film of the present invention has a laminated structure having a base layer (A) and a surface layer (B), the main components of the base layer (A) and the surface layer (B) are preferably polypropylene resins. Hereinafter, the polypropylene resin that is the main component of the base layer (A) of the biaxially oriented polypropylene film may be referred to as polypropylene resin I, and the polypropylene resin that is the main component of the surface layer (B) may be referred to as polypropylene resin II. The base layer (A) preferably accounts for 85.0% to 98.0% of the entire biaxially oriented polypropylene film based on thickness, more preferably 90.0% to 98.0%, and even more preferably 92.0% to 96.0%. The thickness basis means that the thickness ratio is calculated with the total thickness of the biaxially oriented polypropylene film as 100%. When the ratio of the base layer (A) is within the above range, the proportion of a high-melting polypropylene composition in the biaxially oriented polypropylene film is high, and the shape of the film is easily maintained even at high temperatures at which conventional polypropylene cannot be used.

[0044] From the viewpoint of film-forming property and film strength, the MFR of the polypropylene resin I is preferably 3.0 g / 10 min or more and 8.0 g / 10 min or less from the viewpoint of film-forming stability when measured under conditions of 230 ° C. and 2.16 kg according to JIS K 7210 (2014). In order to set the melt flow rate (MFR) of the polypropylene resin I to the above value, a method of controlling the average molecular weight and molecular weight distribution is adopted. When the MFR of the polypropylene resin I, which is the main component, is 3.0 g / 10 min or more, the film-forming property is stable. On the other hand, when the MFR of the polypropylene resin I is 8.0 g / 10 min or less, the heat shrinkage stress value at 160 ° C. when made into a biaxially oriented polypropylene film can be kept low.

[0045] From the viewpoint of strength, heat resistance, and film formation stability, the mesopentad fraction of polypropylene resin I is preferably 0.90 or more, more preferably 0.96 or more. The mesopentad fraction is an index showing the stereoregularity of the crystalline phase of polypropylene resin measured by nuclear magnetic resonance (NMR), and the higher the value, the higher the crystallinity and the higher the dimensional stability at high temperatures, which is preferable. There is no particular upper limit for the mesopentad fraction. In order to obtain a resin with such high stereoregularity, a method of washing the obtained resin powder with a solvent such as n-heptane, a method of appropriately selecting a catalyst and / or cocatalyst, and a method of appropriately selecting a composition are preferably adopted.

[0046] From the viewpoint of heat resistance and dimensional stability at high temperatures, the melting point of polypropylene resin I is preferably 160°C or more and 170°C or less, more preferably 165°C or more and 170°C or less. If the melting point of polypropylene resin I is less than 160°C, high melting point crystals are unlikely to form when the film is formed, and there is a concern that heat resistance such as film rigidity in the high temperature range may be poor. In addition, the upper limit of the melting point is 170°C, taking into account the characteristics of polypropylene resin.

[0047] From the viewpoint of releasability, the base layer (A) mainly composed of polypropylene resin I preferably contains a branched polypropylene resin within a range that does not deteriorate the properties. When the base layer (A) contains a branched polypropylene resin, the content is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, and even more preferably 7.0% by mass or less, when the entire base layer (A) is taken as 100% by mass. By making the amount of branched polypropylene resin in the base layer (A) 10.0% by mass or less, an increase in the heat shrinkage stress value at 160°C can be suppressed. When the base layer (A) contains a branched polypropylene resin, it is preferable to mix the branched polypropylene resin in the above-mentioned preferable amount by pre-mixing or the like.

[0048] Next, the polypropylene resin II that can be suitably used as the main component of the surface layer (B) of the biaxially oriented polypropylene film of the present invention will be described.

[0049] From the viewpoint of film-forming property and film strength, the MFR of the polypropylene resin II is preferably 1.0 g / 10 min or more and 10.0 g / 10 min or less, and more preferably 2.0 g / 10 min or more and 7.0 g / 10 min or less, from the viewpoint of film-forming stability, when measured under conditions of 230 ° C. and 2.16 kg according to JIS K 7210 (2014). In order to make the melt flow rate (MFR) of the polypropylene resin II the above value, a method of controlling the average molecular weight and molecular weight distribution is adopted. When the MFR of the polypropylene resin II, which is the main component, is 1.0 g / 10 min or more, the film-forming property is stable. On the other hand, when the MFR of the polypropylene resin II is 10.0 g / 10 min or less, the heat shrinkage rate when made into a biaxially oriented polypropylene film can be kept low.

[0050] From the viewpoint of heat resistance and dimensional stability at high temperatures, the melting point of polypropylene resin II is preferably 150° C. or more and 170° C. or less, more preferably 155° C. or more and 170° C. or less. When the melting point of polypropylene resin II is 150° C. or more, high melting point crystals are easily formed during film formation, improving heat resistance such as film rigidity in high temperature regions. In addition, the upper limit of the melting point is 170° C. in consideration of the characteristics of polypropylene resins.

[0051] The surface layer (B) mainly composed of polypropylene resin II preferably contains an antiblocking agent within a range that does not deteriorate the properties. When the surface layer (B) contains an antiblocking agent, the content is preferably 1.2 mass% or less, more preferably 1.0 mass% or less, and even more preferably 0.5 mass% or less, when the entire surface layer (B) is taken as 100 mass%. By making the content of the antiblocking agent in the surface layer (B) 1.2 mass% or less, it is possible to suppress a decrease in transparency and strength due to a decrease in stretchability and void formation. When an antiblocking agent is contained in the surface layer (B), it is preferable to mix the above-mentioned preferred amount of the antiblocking agent by pre-kneading or the like.

[0052] Examples of anti-blocking agents that can be added to the surface layer (B) include polymer particles such as acrylic that are completely incompatible with polypropylene resin II. By adding a component that is completely incompatible with polypropylene resin II to polypropylene resin II, uniform protrusions can be formed on the surface when the biaxially oriented polypropylene film is made, and the fusion resistance of the biaxially oriented polypropylene film at high temperatures can be improved. In addition, when branched PP is added to the surface layer (B), the number of protrusions increases, and there is a possibility that dents will occur when the protrusions are transferred to the opposing member, causing a loss of quality.

[0053] The polypropylene resin that can be used as polypropylene resin I and polypropylene resin II is not particularly limited as long as it satisfies the above-mentioned conditions, and examples of commercially available polypropylene resins include "Prime Polypro" (registered trademark) F-704NP and F133A manufactured by Prime Polymer Co., Ltd., "Borclean" (trademark) HC310BF manufactured by Borealis, and "Novatec" (registered trademark) FY6H manufactured by Japan Polypropylene Corporation. In addition, examples of commercially available branched polypropylenes that can be added to polypropylene resin I and polypropylene resin II include "Daploy" (trademark) WB135HMS and WB140HMS manufactured by Borealis, and "WAYMAX" (registered trademark) MFX8, MFX6, and MFX3 manufactured by Japan Polypropylene Corporation.

[0054] Next, one embodiment of the method for producing a biaxially oriented polypropylene film of the present invention will be described as an example, but the present invention is not necessarily limited thereto.

[0055] First, 90.0 parts by mass or more and 99.9 parts by mass or less of homopolypropylene resin and 0.1 parts by mass or more and 10.0 parts by mass or less of branched chain polypropylene resin are dry-blended, and then fed into a twin-screw extruder set at 240°C to 280°C, melt-kneaded, and then cooled to obtain pellets of a polypropylene composition for the base layer (A). Also, 99.5 parts by mass or more and 99.9 parts by mass or less of homopolypropylene resin and 0.1 parts by mass or more and 0.5 parts by mass or less of acrylic particles are dry-blended, and then fed into a twin-screw extruder set at 240°C to 280°C, melt-kneaded, and then cooled to obtain pellets of a polypropylene composition for the surface layer (B). The pellets of each polypropylene composition obtained by the above-mentioned procedure are fed into single-screw extruders for the base layer (A) and the surface layer (B), respectively, and melt-extruded at 200°C to 290°C, more preferably 220°C to 280°C, and even more preferably 240°C to 260°C. Then, after removing foreign matter and modified polymers using a filter installed midway through the polymer pipe, the mixture is laminated in a layer structure of surface layer (B) / base layer (A) / surface layer (B) using a multi-manifold type composite T-die, extruded onto a casting drum and cooled to solidify, and further cooled through a water tank to obtain a laminated unstretched sheet having a layer structure of surface layer (B) / base layer (A) / surface layer (B).

[0056] In addition, the surface temperature of the casting drum is preferably 20°C or more and 80°C or less, and the water temperature of the water tank is preferably 20°C or more and 70°C or less, more preferably the surface temperature of the casting drum is 25°C or more and 60°C or less, and the water temperature of the water tank is 30°C or more and 60°C or less, and even more preferably the surface temperature of the casting drum is 30°C or more and 50°C or less, and the water temperature of the water tank is 40°C or more and 50°C or less. When the surface temperature of the casting drum and the water temperature of the water tank are within the above ranges, the formation of β crystals, which have a low melting point among crystals, can be suppressed, and the proportion of high melting point crystals in the film is easily increased, making it easy to adjust Vmp and Vvv to a suitable range. As a method for adhering to the casting drum, any method from among electrostatic application method, adhesion method using the surface tension of water, air knife method, press roll method, underwater casting method, etc. may be used, but the air knife method, which is easy to control the surface roughness, is preferred. When the air knife method is used, the air temperature of the air knife is preferably 20° C. to 100° C., and the blowing air speed is preferably 30 m / s to 50 m / s. In order to prevent the laminated unstretched sheet from vibrating, it is also preferable to appropriately adjust the position of the air knife so that air flows downstream of the film formation.

[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 by passing through a hot air oven heated to 145°C to 165°C, preferably 150°C to 160°C, more preferably 153°C to 157°C, before stretching. If the preheating temperature is within the above range, the laminated unstretched sheet advances to the longitudinal stretching process in a softened state, and stretching is possible without applying more stress than necessary in the longitudinal stretching process, so that the heat shrinkage stress is easily reduced. In addition, it is also possible to reduce the low-melting point β crystals contained in the laminated unstretched sheet, which is also likely to act favorably on increasing the proportion of high-melting point crystals in the film.

[0058] Then, the film is stretched between rolls with a peripheral speed difference immediately after preheating at 4.0 times or more and 8.0 times or less in the longitudinal direction to obtain a uniaxially stretched film. The stretching ratio is preferably 4.0 times or more and 7.0 times or less, more preferably 4.2 times or more and 6.0 times or less, and even more preferably 4.2 times or more and 5.6 times or less. The stretching temperature is 140 ° C. or more and 170 ° C. or less, preferably 145 ° C. or more and 165 ° C. or less, more preferably 150 ° C. or more and 160 ° C. or less. When the stretching temperature is within the above range, it is possible to pull out molecular chains from the softened crystals while suppressing the remaining of excessive strain, and the crystal high melting point is promoted together with the subsequent Relax process. Therefore, the heat resistance indicated by the storage modulus obtained by dynamic viscoelasticity measurement of the obtained biaxially oriented polypropylene film is easily improved.

[0059] At the end of the longitudinal stretching process, the longitudinal uniaxially stretched film is contacted with a metal roll having a peripheral speed difference and kept at 121°C to 160°C to relax in the longitudinal direction at a relaxation rate of 1.0% to 10.0%, and then cooled to room temperature. The relaxation temperature is preferably 120°C to 160°C, more preferably 125°C to 155°C, and even more preferably 130°C to 150°C. If the relaxation temperature is within the above range, it is possible to promote the rearrangement of molecular chains drawn out from the crystals by longitudinal stretching and form high-melting crystals with a thicker lamellar thickness, so that it is easy to adjust the start-up temperature of the heat shrinkage stress in the direction perpendicular to the main orientation and the heat shrinkage stress value at 160°C in the direction perpendicular to the main orientation to a suitable range. In addition, the relaxation rate in the longitudinal stretching process is preferably 1.0% to 10.0%, more preferably 2.0% to 10.0%, and even more preferably 3.5% to 7.5%. By setting the Relax ratio in the longitudinal stretching step within the above range, the tension of 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 in a suitable range, which facilitates rearrangement of the molecular chains. This makes it easy to adjust the onset temperature of the heat shrinkage stress in the direction perpendicular to the main orientation and the heat shrinkage stress value at 160°C in the direction perpendicular to the main orientation to suitable ranges.

[0060] The longitudinally uniaxially stretched film is then introduced into a tenter, and after preheating by holding both ends in the width direction with clips, the film is transversely stretched 7.0 times or more and 13.0 times or less in the width direction (transverse stretching step). By setting the stretching ratio within the above range, excessive distortion in the main orientation direction can be suppressed, and it becomes easy to adjust the heat shrinkage stress rise temperature in the main orientation direction and the heat shrinkage stress value at 160 ° C. in the main orientation direction to a suitable range. The temperature in the preheating step before stretching is preferably 160 ° C. or more and 180 ° C. or less, more preferably 165 ° C. or more and 175 ° C. or less, even more preferably 167 ° C. or more and 173 ° C. or less, and particularly preferably 168 ° C. or more and 172 ° C. or less. When the preheating temperature is within the above range, the crystals formed in the longitudinal stretching step can be softened and proceeded to the transverse stretching step, and stretching is possible without applying more stress than necessary in the transverse stretching step, and the heat shrinkage stress is easily reduced.

[0061] The stretching temperature in the transverse stretching step after the preheating step is preferably 155°C to 180°C, more preferably 158°C to 175°C, and even more preferably 160°C to 170°C. When the transverse stretching temperature is within the above range, it is possible to draw molecular chains from the crystals softened by preheating while suppressing the remaining of excessive strain. Therefore, together with the subsequent Relax step, the crystal melting point is promoted, and the heat resistance indicated by the storage modulus obtained by dynamic viscoelasticity measurement of the biaxially oriented polypropylene film is easily improved.

[0062] In the subsequent Relax process after transverse stretching, the film is relaxed in the transverse direction with clips holding the film with moderate tension at a Relax ratio of preferably 8.0% to 20.0%, more preferably 10.0% to 18.0%, and even more preferably 11.0% to 15.0%. When the Relax ratio after transverse stretching is within the above range, tension in the molecular chains is easily relieved. This promotes amorphous relaxation and reduces the shrinkage stress, and the mobility of the molecular chains is in a moderate range, which also facilitates rearrangement of the molecular chains. This makes it easy to adjust the onset temperature of the heat shrinkage stress in the main orientation direction and the heat shrinkage stress value at 160°C in the main orientation direction to suitable ranges.

[0063] The Relax temperature at this time is preferably 145° C. to 165° C., more preferably 150° C. to 163° C., and even more preferably 155° C. to 160° C. If the Relax temperature is within the above range, it is possible to promote rearrangement of molecular chains pulled out from the crystals by transverse stretching, and form crystals with a higher melting point and a thicker lamellar thickness. Therefore, it becomes easy to adjust the rise temperature of the heat shrinkage stress in the main orientation direction and the heat shrinkage stress value at 160° C. in the main orientation direction to a suitable range.

[0064] The biaxially oriented polypropylene film of the present invention includes a Relax step in the longitudinal and transverse stretching steps, and the total area Relax rate (%) calculated from the stretch ratios and Relax rates in the longitudinal and transverse stretching steps is preferably 10.0% to 30.0%, more preferably 13.0% to 25.0%, and even more preferably 16.0% to 20.0%. The total area Relax rate (%) is calculated by the following formula, and when it is within the above range, amorphous relaxation is likely to proceed, and the shrinkage stress of the biaxially oriented polypropylene film as a whole is likely to be reduced. Total area Relax rate (%)=[1-(1-longitudinal stretching process Relax rate / 100)×(1-transverse stretching process Relax rate / 100)]×100.

[0065] The film is then cooled to between 80°C and 130°C while still being held taut in the width direction with clips, and then led to the outside of the tenter. The clips on both ends in the width direction are released, and the film edges are slit in the winder process, and the biaxially oriented polypropylene film product roll is wound up.

[0066] The biaxially oriented polypropylene film 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 a processing film that requires high-temperature processing such as drying coating materials and molding thermosetting resins, a release film, a base film for current collectors for secondary batteries, or a packaging film for retort pouches, and is particularly preferably used as a release film for use in high-temperature regions.

[0067] In addition, when the biaxially oriented polypropylene film of the present invention is used as a release film, it is preferable that the film has a laminated structure of at least two layers from the viewpoint of achieving both strength and releasability. By adopting such an embodiment, for example, a layer that plays a role in enhancing heat resistance and a layer that plays a role in enhancing releasability can be provided, and both properties can be achieved at the same time. That is, the release film of the present invention is made of the biaxially oriented polypropylene film of the present invention and has a laminated structure of at least two layers. EXAMPLES

[0068] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the embodiments shown in the following examples. The properties were measured and evaluated by the following methods.

[0069] [Evaluation method for each characteristic] (1) Film thickness Five biaxially oriented polypropylene films were stacked to prepare a measurement sample, and the thickness of the measurement sample was measured using an electronic micrometer (TT80 manufactured by TESA). The obtained value was then divided by 5 to calculate the thickness per biaxially oriented polypropylene film. The same measurement was then performed at a position shifted by 50 mm in the width direction as the measurement point, and the same measurement was repeated five times in total. From the obtained measurement results, the maximum, minimum, and average values ​​of the thickness per biaxially oriented polypropylene film were obtained, and the average value was taken as the film thickness (μm) of the biaxially oriented polypropylene film.

[0070] (2) Peak volume (Vmp), valley volume (Vvv), peak density (Spd), 5-point peak area height (S5p) Measurements were performed using the non-contact surface / layer cross-sectional shape measuring system "VertScan" (registered trademark) 2.0 (model: R3300GL-Lite-AC) manufactured by Ryoka Systems Co., Ltd., under the following procedures and conditions. First, the biaxially oriented polypropylene film was unwound from the film roll, and measurement samples were taken so that 10 measurement points were determined at random on a straight line passing through the center in the width direction and parallel to the longitudinal direction, and Vmp, Vvv, Spd, and S5p were measured at the 10 points. The average values ​​of the obtained measurements were calculated and were defined as Vmp, Vvv, Spd, and S5p of the biaxially oriented polypropylene film, respectively. Thereafter, the measurement surface was changed and the same measurement was performed. Note that in one measurement, one visual field (visual field area: vertical 939 μm × horizontal 1,252 μm = 1,175,628 μm 2 ) measurements were carried out.

[0071] A. Measurement conditions CCD camera: SONY HR-57 1 / 2 Objective lens: 10X Lens tube: 0.5X BODY Wavelength filter: 530 white Measurement mode: Wave Field of view size: 640 x 480 Scan range: (start) 5μm, (stop) -5μm.

[0072] B. How to fix the measurement sample A dedicated sample holder was used to fix the measurement sample in place. The sample holder is made of two removable metal plates with a circular hole in the center, and the measurement sample is sandwiched and fixed between them without any wrinkles, and measurements are taken of the sample located in the circular hole.

[0073] C. Analysis method The data obtained by the above measurements was analyzed using the image analysis software VS-Viewer of "VertScan" (registered trademark) 2.0. First, noise was removed using a median filter (5 × 5), and undulation components were removed using a Gaussian filter with a cutoff value of 250 μm. Next, Vmp, Vvv, Spd, and S5p defined in ISO25178 (2021) were measured using the "ISOPara" function. In the "ISOPara" function, the S-Filter was set to 6.0 μm.

[0074] (3) Heat shrinkage stress rise temperature, heat shrinkage stress value at 160℃ The rate of change of the sample at each temperature was measured by the TMA (Thermo Mechanical Analysis) method, and a curve (TMA curve) was drawn by plotting the temperature on the horizontal axis and the change in the length of the sample on the vertical axis. In the TMA curve, the temperature at which the shrinkage stress first reached 0.2 MPa during the heating process was read as the heat shrinkage stress rise temperature, and the heat shrinkage stress was measured at each temperature thereafter. The measurement device and measurement conditions were as follows, and the measurement directions were the main orientation direction and the direction perpendicular to the main orientation. The main orientation direction and the direction perpendicular to the main orientation were determined by measuring the storage modulus using the dynamic viscoelasticity method described later. <Measurement equipment and conditions> Stress loading device: "TMA / SS 6100" manufactured by Seiko Instruments Inc. Data processing device: "EXSTAR 6000" manufactured by Seiko Instruments Inc. Measurement mode: Constant temperature rise of 10℃ / min Device placement atmosphere: Room temperature air Sample: 15mm x 2mm rectangle (measurement direction is 15mm).

[0075] (4) Storage modulus A rectangular test piece (5 mm wide x 20 mm long) cut from a biaxially oriented 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 the storage modulus was measured from -100 ° C. to 180 ° C. after the start of heating. Furthermore, a viscoelasticity-temperature curve was drawn by a dynamic viscoelasticity method, and the storage modulus at 30 ° C. was calculated. Next, when the longitudinal direction of the biaxially oriented polypropylene film was set to 0 °, dynamic viscoelasticity was similarly measured for each direction forming an angle of 0 °, 15 °, 30 °, 45 °, 60 °, 75 °, 90 °, 105 °, 120 °, 135 °, 150 °, and 165 ° with respect to the longitudinal direction, and the storage modulus of each direction at 30 ° C. was calculated, and the direction showing the highest storage modulus was set to the main orientation direction, and the direction perpendicular to this in the film plane was set to the direction perpendicular to the main orientation direction (main orientation perpendicular direction). The measuring apparatus and conditions are as follows. <Measurement equipment and conditions> Equipment: EXSTAR DMS6100 (Seiko Instruments Inc.) Geometry: Tensile Chuck distance: 20mm Frequency: 10Hz Distortion: 0.1~0.2% Temperature range: -100~180℃ Heating rate: 5℃ / min Measurement atmosphere: Nitrogen.

[0076] (5) Mesopentad fraction of raw material (mmmm) A polypropylene resin sample is dissolved in a solvent. 13 The mesopentad fraction (mmmm) was measured and calculated using C-NMR (Reference: New Edition Polymer Analysis Handbook, edited by the Japan Society for Analytical Chemistry and the Polymer Analysis Research Forum, 1995, pp. 609-611). The measurement equipment and conditions are as follows:

[0077] A. Measurement equipment and conditions Equipment: Bruker DRX-500 Measurement nuclei: 13 C nucleus (resonance frequency: 125.8MHz) Measured concentration: 10% by mass Solvent: Benzene / d-o-dichlorobenzene = 1:3 mass ratio mixed solution Measurement temperature: 130℃ Spin speed: 12Hz NMR sample tube: 5mm tube Pulse width: 45° (4.5μs) Pulse repetition time: 10 seconds Data points: 64K Conversion count: 10,000 times Measurement mode: complete decoupling.

[0078] B.Analysis conditions Fourier transformation was performed with LB (line broadening factor) set to 1.0, the mmmm peak was set to 21.86 ppm, and peak division was performed using WINFIT software (Bruker). At that time, peak division was performed from the peak on the high magnetic field side as follows, and automatic fitting was performed using the attached software. After that, the peak division was optimized, and the total mmmm peak fraction was calculated. The above measurement was performed five times, and the average value was taken as the mesopentad fraction (mmmm) of the measured sample. (peak division) (a)mrrm (b)(c) rrrm (split into two peaks) (d)rrrr (e)mrmr (f)mrmm+rmrr (g)mmrr (h)rmmr (i) mmmr (j)mmmm.

[0079] (6) Melt flow rate (MFR) Measurements were performed at 230°C and 2.16 kg in accordance with JIS K 7210-1 (2014).

[0080] (7) Breaking strength A rectangular biaxially oriented polypropylene film (10 mm x 150 mm size) cut out with the main orientation orthogonal direction specified by the method described in "(4) Storage modulus" as the long side direction (measurement direction) was used as the measurement sample. Next, the measurement sample was set in a tensile tester (Orientec "Tensilon" (registered trademark) UCT-100) with an initial chuck distance of 20 mm, and a tensile test was performed at a tensile speed of 300 mm / min in a room temperature environment. At this time, the position of the long side direction of the sample was adjusted so that the center of the measurement sample was near the center between the chucks. The load applied to the measurement sample at the time of break was read in real time, and the value divided by the cross-sectional area of ​​the sample before the test (film thickness x width (10 mm)) was calculated as the breaking strength. Measurements were performed three times for each sample, and the average value was used.

[0081] (8) Melting point of raw materials 5 mg of the raw material was collected as a sample in an aluminum pan 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 of the melting curve observed when the temperature was raised was taken as the melting point of the raw material.

[0082] (9) Evaluation of high temperature release properties After cutting cardboard (product number C-55, manufactured by Daio Paper Co., Ltd.) into 10 cm squares, biaxially oriented polypropylene films cut into 15 cm squares were placed on both sides of the cardboard together with 20 cm square SUS plates as shown in Figure 1. The obtained laminate was heated and pressed for 15 minutes at a pressure of 1.5 MPa and temperatures of 160°C and 165°C using a heating press, removed from the press, and cooled to room temperature. The polypropylene film was then peeled off. Note that the symbols 1 to 4 in Figure 1 indicate the SUS plate, polypropylene film, cardboard, and pressure direction, respectively. The state of the cardboard and biaxially oriented polypropylene film treated at each temperature was visually evaluated from the following perspectives. Evaluation was first 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. (Crimp resistance) A test was evaluated as passing if the polypropylene film was completely peeled off from the cardboard, and failing if the peeling was incomplete or if part of the cardboard or polypropylene film remained on the other side after peeling, and was evaluated according to the following criteria. (Dimensional stability) The cardboard was rated as passed when no folds or wrinkles were observed, and was rated as failed when at least either folds or wrinkles were observed, and was evaluated according to the following criteria. (Transferability) The cardboard was irradiated with light from a fluorescent lamp, and the case where no transfer mark was observed was judged as pass, and the case where a transfer mark was observed was judged as fail. Evaluation was performed according to the following criteria. (Easy peeling) When the polypropylene film was peeled off from the cardboard in the direction perpendicular to the main orientation, if the polypropylene film was not torn, it was judged as pass, and if it was torn, it was judged as fail. Evaluation was performed according to the following criteria. <Evaluation criteria (common to pressure bonding resistance, dimensional stability, transferability, and peelability)> The compression resistance, dimensional stability, and fusion resistance were evaluated according to the following criteria. If each characteristic was ◯ or Δ, it was judged to have high temperature releasability, and if any was ×, it was judged to have no high temperature releasability. Good: Passed at 160℃ and 165℃. △: Passed at 160°C, but failed at 165°C. ×: Failed at 160°C.

[0083] [Raw materials] The following raw materials were used to manufacture the biaxially oriented polypropylene films of the Examples and Comparative Examples. The antioxidants listed below were already mixed into the polypropylene resin, so the content was not finely adjusted in the Examples and Comparative Examples. The antioxidants contained in each resin were in trace amounts (less than 1.0 mass% of all components), and considering the volatile content when made into a film, the amount of antioxidant would be even smaller, so they will not be listed in the manufacturing methods of the Examples and Comparative Examples and Table 1 described below. In the table, the biaxially oriented polypropylene film of Comparative Example 6 has a single layer structure, so there is no surface layer (B), and the composition of the biaxially oriented polypropylene film itself is listed as the base layer (A).

[0084] (1) Antioxidants Antioxidant 1: "Irganox" (registered trademark) 1010 manufactured by BASF Japan Ltd. Antioxidant 2: 2,6-di-t-butyl-p-cresol (BHT) manufactured by ADEKA Corporation.

[0085] (2) Resin Polypropylene resin 1 (homopolypropylene resin / homoPP1): Manufactured by Prime Polymer Co., Ltd., a highly stereoregular homopolypropylene resin having an MFR of 4.1 / 10 minutes, a melting point of 166°C, and a mesopentad fraction of 0.98, mixed with 0.5% by mass of antioxidant 1 and 0.3% by mass of antioxidant 2. Polypropylene resin 2 (homopolypropylene resin / homoPP2): manufactured by Prime Polymer Co., Ltd., a homopolypropylene resin having an MFR of 2.9 g / 10 min, a melting point of 163°C, and a mesopentad fraction of 0.94, mixed with 0.5 mass% of antioxidant 1 and 0.3 mass% of antioxidant 2. Polypropylene resin 3 (polypropylene resin / PP3): Manufactured by Sumitomo Chemical Co., Ltd., polypropylene resin with MFR of 4.0g / 10min and melting point of 158℃ (homopolypropylene resin mixed with ethylene-propylene copolymer so that the ethylene unit content is 0.5% by mass) mixed with 0.3% by mass of acrylic bead particles with an average particle size of 2μm measured by the electrical detection zone method. Note that the mesopentad fraction cannot be measured. Branched chain polypropylene resin 1: (Branched chain polypropylene resin / Branched PP1) "WAYMAX" (registered trademark) (MFX3) manufactured by Japan Polypropylene Corporation. A branched chain polypropylene resin having an MFR of 9.0 g / 10 min.

[0086] Example 1 First, 95.0 parts by mass of polypropylene resin 1 and 5.0 parts by mass of branched polypropylene resin were dry-blended and fed into a twin-screw extruder set at 260 ° C., melt-kneaded, and cooled to obtain pellets of a polypropylene composition for the base layer (A). The pellets of polypropylene resin obtained by the above procedure were fed into a single-screw extruder for the base layer (A), and polypropylene resin 3 was fed into a single-screw extruder for the surface layer (B). Thereafter, the resin or resin mixture for each layer was melt-extruded at 260 ° C., and after removing foreign matter with a 30 μm cut sintered filter, the layers were laminated in a feed block type B / A / B composite T-die so that the thickness ratio of the surface layer (B) / base layer (A) / surface layer (B) was 1 / 28 / 1, and the obtained molten laminate was molded into a sheet shape with a T-die. Then, the molten sheet-like material was discharged from the T-die onto a casting drum whose surface temperature was controlled at 45°C, and compressed air at 30°C was sprayed by an air knife at an air speed of 40m / s to adhere the molten sheet-like material to the casting drum, thereby obtaining a laminated unstretched sheet. The laminated unstretched sheet was then passed through a water bath at a water temperature of 45°C, and then preheated to 155°C by passing through a hot air oven, and stretched at a ratio of 4.3 times in the longitudinal direction between rolls at 155°C with a peripheral speed difference, and then relaxed by 6.1% in the longitudinal direction with rolls at 140°C with a peripheral speed difference to obtain a uniaxially stretched film. Next, the uniaxially stretched film was introduced into a tenter-type stretching machine by holding both ends in the width direction with clips, and after preheating at 170°C for 7 seconds, it was stretched at 8.8 times in the width direction at 163°C, and relaxed by 11.3% in the width direction at 157°C. After that, after a cooling process at 100°C, the film was introduced to the outside of a tenter-type stretching machine, the clips at both ends in the width direction were released, and the film was wound up on a core to obtain a biaxially oriented polypropylene film with a thickness of 30 μm. The physical properties and evaluation results of the obtained biaxially oriented polypropylene film are shown in Table 1.

[0087] (Examples 2 to 7, Comparative Examples 1 to 8) A biaxially oriented polypropylene film was 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 1. The physical properties and evaluation results of the obtained biaxially oriented polypropylene film are shown in Table 1. The thickness was adjusted by controlling the resin discharge amount by the rotation speed of the extruder, and by controlling the peripheral speed of the casting drum, the longitudinal stretching ratio, and the transverse stretching ratio. In Comparative Examples 2 and 6, unlike Example 1, the laminated unstretched sheet was cooled only by a metal roll. Since Comparative Examples 6 and 8 have a single-layer structure, lamination was not performed with a composite T-die, but a normal T-die was used.

[0088] [Table 1]

[0089] In the table, the high value side is the side that was in contact with the casting drum. The high value side was used for the evaluation of high temperature releasability. [Industrial Applicability]

[0090] The biaxially oriented polypropylene film of the present invention can be used for various applications such as packaging films, release films, processing films, sanitary products, agricultural products, construction products, medical products, etc. In particular, since it exhibits excellent releasability even in high-temperature environments, it can be preferably used as a release film or processing film to be used at high temperatures where conventional polypropylene films are difficult to use. [Explanation of symbols]

[0091] 1:SUS board 2: Polypropylene film 3: Cardboard 4: Pressure direction

Claims

1. The actual volume Vmp of the peak is 0.0015 ml / m ２ 0.0050ml / m or more ２ The void volume Vvv of the valley portion is 0.0050 ml / m or less. ２ 0.0100ml / m or more ２ and the peak density Spd is 20 / mm ２ 120 / mm or more ２ A biaxially oriented polypropylene film, characterized in that both surfaces of the film are the A-sides, where the A-side is one of the surfaces below.

2. 2. The biaxially oriented polypropylene film according to claim 1, characterized in that the height S5p of the five-point peak region on both sides is 30 nm or more and 700 nm or less, and the breaking strength in the direction perpendicular to the main orientation is 100 MPa or more and 200 MPa or less.

3. 3. The biaxially oriented polypropylene film according to claim 1, characterized in that the onset temperature of the heat shrinkage stress in the direction perpendicular to the main orientation is 140°C or higher and 160°C or lower, and the heat shrinkage stress value at 160°C in the direction perpendicular to the main orientation is 0.5 MPa or higher and 1.0 MPa or lower.

4. 3. The biaxially oriented polypropylene film according to claim 1 or 2, characterized in that the onset temperature of the heat shrinkage stress in the main orientation direction is 150°C or higher and 170°C or lower, and the heat shrinkage stress value at 160°C in the main orientation direction is 1.0 MPa or higher and 3.0 MPa or lower.

5. The biaxially oriented polypropylene film according to claim 1 or 2, having a laminated structure of at least two layers.

6. A release film comprising the biaxially oriented polypropylene film according to claim 1 or 2 and having a laminated structure of at least two layers.

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