Biaxially oriented polypropylene film and release film

Abstract

The object of this invention is to provide a polypropylene film with excellent transfer resistance and handling properties. [Solution] The surface with a relatively low surface roughness Sa is designated as surface A, the surface with a high surface roughness Sa is designated as surface B, and the sharpness of the surface height distribution of surface A is designated as Sku. A , the Sa on surface B is Sa B In that case, the Sku A The value is 5.0 or more and 250 or less, and the aforementioned Sa B 100nm or larger 1.0×10 3 / Log(Sku A A biaxially oriented polypropylene film characterized by having a size of ) nm or less.

Description

[Technical Field]

[0001] The present invention relates to a polypropylene film with excellent peelability, transfer resistance, and handling properties, and to a biaxially oriented polypropylene film roll. [Background technology]

[0002] Polypropylene film is used in a wide range of applications, including packaging, release agents, tapes, cable wrapping, and electrical applications such as capacitors, due to its excellent transparency, mechanical properties, and electrical properties. In particular, its superior surface release properties and mechanical properties make it suitable for use as a release film or process film to protect various components such as plastic products, building materials, and optical components.

[0003] Normally, the required characteristics of release films are set appropriately depending on the object being protected and its application. However, with the miniaturization and increased precision of equipment in recent years, the products being protected sometimes require thin films with high quality. If the surface smoothness of a polypropylene film is poor, for example, when used as a release film for flexible materials such as polyurethane components, the surface irregularities of the polypropylene film can be transferred to the polyurethane component, affecting its appearance.

[0004] Therefore, attempts have been made to improve the transferability of polypropylene films. For example, Patent Document 1 discloses a method for achieving both release properties and film transportability by adjusting the value of Sp / Sv, which is the ratio of the peak height Sp to the valley depth Sv of the surface, to a certain range. Patent Document 2 also describes a polypropylene film having a surface shape that can prevent transfer marks from occurring on the adherend and significantly degrading its quality by adjusting the parameter Sku, which represents the sharpness of the height distribution of the surface shape. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2020 / 071291 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2024-92920 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, from the viewpoints of cost and waste reduction, further thinning of the film has been demanded. Even in the case of a polypropylene film with suppressed surface protrusions by the methods described in Patent Documents 1 and 2, there have been cases where surface unevenness transfer leads to a decrease in quality and yield. In addition, in these methods, when the surface is designed to be smooth for transfer suppression and wound into a roll, there are also handling problems such as wrinkles occurring because air cannot be retained between the films. Therefore, the problem of the present invention is to solve the above-mentioned problems. That is, the present invention aims to provide a biaxially oriented polypropylene film excellent in transfer resistance and handling properties. [Means for Solving the Problems]

[0007] In order to solve the above-mentioned problems, the biaxially oriented polypropylene film of the present invention has the following configuration. That is, the surface with a relatively low surface roughness Sa is the A surface, the surface with a high surface roughness is the B surface, and the sharpness Sku of the surface height distribution of the A surface is Sku , , ,

[0008] , the Sa of the B surface is Sa B When, the Sku A is 5.0 or more and 250 or less, and the Sa B is 100 nm or more and 1.0×10 3 / Log(Sku A ) nm or less, which is a biaxially oriented polypropylene film.

[0008] In addition, the biaxially oriented polypropylene film of the present invention can also be in the following embodiments, and can also be a biaxially oriented polypropylene film roll. (1) The surface with a relatively low surface roughness Sa is the A surface, the surface with a high surface roughness is the B surface, and the sharpness Sku of the surface height distribution of the A surface is SkuA When Sa of the B surface is Sa B and Sku A is 5.0 or more and 250 or less, and Sa B is 100 nm or more and 1.0×10 3 / Log(Sku A )nm or less, a biaxially oriented polypropylene film. (2) The biaxially oriented polypropylene film according to (1), wherein the heat shrinkage rate when treated at 150°C for 15 minutes is 0.0 to 5.0% in the direction of the largest shrinkage. (3) The biaxially oriented polypropylene film according to (1) or (2), having three layers with different raw material compositions. (4) A biaxially oriented polypropylene film roll made of the biaxially oriented polypropylene film according to any one of (1) to (3). (5) The biaxially oriented polypropylene film roll according to (4), wherein the winding hardness of the surface layer is 500 or more and 700 or less. (6) A laminate comprising the biaxially oriented polypropylene according to any one of (1) to (3) and a polyurethane layer.

Advantages of the Invention

[0009] According to the present invention, a polypropylene film and a biaxially oriented polypropylene film roll excellent in transfer resistance and handling properties and suitable for use as a release film, for example, can be provided.

Embodiments for Carrying Out the Invention

[0010] In the biaxially oriented polypropylene film of the present invention, the surface with relatively low surface roughness Sa is defined as the A surface, the surface with high surface roughness Sa is defined as the B surface, and the sharpness Sku of the surface height distribution of the A surface is defined as Sku A , when Sa of the B surface is Sa B and Sku A is 5.0 or more and 250 or less, and Sa B is 100 nm or more and 1.0×10 3 / Log(Sku A ​It is characterized by being less than or equal to ) nm. The biaxially oriented polypropylene film of the present invention will be described in detail below.

[0011] A polypropylene film refers to a sheet-like molded article whose main component is polypropylene resin. The main component refers to a component that is present in an amount greater than 50% by mass and less than or equal to 100% by mass when the total constituent components of the object (in this case, the film) are set to 100% by mass, and the same interpretation can be applied to the main component hereafter. If multiple components that correspond to polypropylene resin are present, the film is considered to have polypropylene resin as its main component if their total amount is greater than 50% by mass. In the polypropylene film of the present invention, the polypropylene resin content is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, particularly preferably 90% by mass or more, and most preferably 94% by mass or more, of the total constituent components of the film.

[0012] Polypropylene resin refers to a resin whose primary constituent unit is the propylene unit. The primary constituent unit is defined as the constituent unit that accounts for more than 50 mol% but not exceeding 100 mol% when the total constituent units are set to 100 mol%. (This definition can be similarly interpreted for other olefin resins, except that the propylene unit is replaced by other olefin units.)

[0013] The polypropylene film of the present invention is particularly important as a biaxially oriented film from the viewpoint of surface smoothness, quality, and the heat shrinkage characteristics described later. Biaxial orientation means having molecular orientation in two orthogonal directions, and can be achieved by stretching an unstretched sheet in two orthogonal directions (usually the longitudinal direction and the width direction). The longitudinal direction is the direction in which the polypropylene film travels during the manufacturing process (corresponding to the winding direction if it is in the state of a film roll), and the width direction is the direction perpendicular to the longitudinal direction within the film plane.

[0014] Furthermore, from the viewpoint of multifunctionality, the biaxially oriented polypropylene film of the present invention preferably has a laminated structure of at least two layers. Lamination means that two or more layers with different raw material compositions are stacked in the thickness direction (direction perpendicular to the film surface). More preferably, it has a structure with three layers with different raw material compositions. Specific examples of such embodiments include, for example, a three-layer laminated structure consisting of a layer responsible for improving handling, a layer responsible for enhancing release properties, and a layer containing recovered raw materials. A biaxially oriented polypropylene film of such an embodiment can achieve both handling and release properties, as well as cost reduction.

[0015] In the biaxially oriented polypropylene film of the present invention, from the viewpoint of transfer resistance and handling properties, the side with a relatively low surface roughness Sa is designated as side A, and the side with a relatively high surface roughness Sa is designated as side B, and the sharpness of the surface height distribution of side A is designated as Sku. A , Sa on side B is Sa B In that case, Sku A The value is between 5.0 and 250, Sa B 100nm or larger 1.0×10 3 / Log(Sku A It is important that the surface roughness is less than or equal to ) nm. Hereafter, surface roughness Sa and surface height distribution sharpness Sku will be simply referred to as Sa and Sku, respectively. Note that Log(Sku A ) is Log 10 (Sku A ) means.

[0016] Sa is a parameter that represents surface roughness; more specifically, a larger value indicates a rougher surface with more protrusions, while a smaller value indicates a smoother surface with fewer protrusions. Sku is a parameter that represents the sharpness of the height distribution of the surface shape; more specifically, a larger value indicates a surface with many sharp peaks and valleys, while a smaller value indicates a flatter surface.

[0017] In the biaxially oriented polypropylene film of the present invention, the Sku of side A is Sku AThe value is 5.0 or more and 250 or less, preferably 5.0 or more and 200 or less. Sku of side A A When the number exceeds 250, the A-side develops many sharp peaks and valleys. Therefore, when a biaxially oriented polypropylene film is used as a release film, if the adherend that will become the product comes into contact with the surface, transfer marks may occur on the adherend, potentially leading to a significant decrease in quality. On the other hand, Sku A When the value falls below 5.0, the surface approaches a flat surface. Therefore, when used as a release film, it becomes difficult to form a gap between the surface and the substrate (which will become the final product) when the substrate comes into contact with the surface, resulting in reduced release properties.

[0018] Furthermore, the biaxially oriented polypropylene film of the present invention has Sa on the B side. B 100nm or larger 1.0×10 3 / Log(Sku A ) nm or less, preferably 150 nm or more 1.0 × 10 3 / Log(Sku A It is less than ) nm. The Sa of the B side is Sa B is 1.0 × 10 3 / Log(Sku A If it exceeds )nm, the surface shape of side B will affect side A, causing a depression on side A. At this time, the Sku on side A A Depending on the value, the allowed Sa B The maximum value changes, Sku A When the value is large and there are many sharp peaks and valleys on the surface, the acceptable Sa B The maximum value becomes smaller, Sku A When the value of is small and the surface is flat, the acceptable Sa B The maximum value of will increase. Also, Sa B When the wavelength falls below 100nm, the handling properties of the film deteriorate, leading to film wrinkles and winding misalignment.

[0019] Sku and Sa can be measured using a known layer cross-sectional shape measuring device. For example, the non-contact surface and layer cross-sectional shape measuring system "VertScan" (registered trademark) 2.0 manufactured by Ryoka Systems Co., Ltd. can be used. The specific method for measuring Sku and Sa using this device will be described later.

[0020] SKU A , and Sa B To achieve the above range, it is effective to set the raw material composition and film-forming conditions of the biaxially oriented polypropylene film and each of its constituent layers within the range described below. It is also effective to use a laminated structure of base layer (I), surface layer (II), and surface layer (III), and adjust the lamination ratio of base layer (I), surface layer (II), and surface layer (III) to 58.6 / 0.7 / 0.7 to 57.8 / 1.1 / 1.1. One method for adjusting the laminated structure as described above is to use three extruders, adjust the discharge rate of each extruder, and laminate the three layers using a feed block type three-layer composite T-die. In terms of film-forming conditions, for example, it is also effective to perform cooling and solidification in two stages to obtain an unstretched film. More specifically, when using two cast drums, with the upstream cast drum being the first cast drum and the downstream cast drum being the second cast drum, it is effective to set the temperature of the first cast drum to 45-65°C and the temperature of the second cast drum to 35-55°C, and to set the contact time between the sheet and the first and second cast drums combined to 10-20 seconds. These methods can be combined as appropriate.

[0021] Surface layer (II) and Surface layer (III) are Sku A , and Sa BFrom the viewpoint of setting the values ​​within the above range, when the surface of surface layer (II) is designated as surface A and the surface of surface layer (III) is designated as surface B, it is preferable that surface layer (II) contains 0.1% to 1.0% by mass of another olefin resin (e.g., polyethylene) as a resin other than polypropylene, and surface layer (III) contains 25.0% to 30.0% by mass of polyethylene as a resin other than polypropylene. By setting surface layer (II) and surface layer (III) to the above composition, Sku A , and Sa B The roughness of each surface can be adjusted so that the value falls within the above range. Note that the amount of olefin resin in each layer is calculated assuming the entire layer is 100% by mass.

[0022] From the viewpoint of suitability as a release film even when processing in a high-temperature environment, the biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage rate of 0.0 to 5.0% in the direction with the greatest shrinkage rate when treated at 150°C for 15 minutes. The heat shrinkage rate can be measured by marking the biaxially oriented polypropylene film and observing the dimensional change before and after treatment at 150°C for 15 minutes. The measurement described below is performed while changing the direction to identify the direction with the greatest heat shrinkage rate, and the measured value in that direction is adopted (details of the measurement method are described below).

[0023] For example, when the biaxially oriented polypropylene film of the present invention is used as a release film, if the thermal shrinkage rate when treated at 150°C for 15 minutes is 0.0 to 5.0% in the direction of greatest shrinkage, the flatness defects due to thermal shrinkage of the biaxially oriented polypropylene film are suppressed, resulting in good processing suitability.

[0024] One method for achieving a thermal shrinkage rate of 0.0 to 5.0% in the direction of greatest shrinkage when treated at 150°C for 15 minutes is to use a laminated structure having a base layer (I), a surface layer (II), and a surface layer (III), as described later, and to use a polypropylene resin with an MFR of 1.0 g / 10 min to 5.0 g / 10 min for the base layer (I) of the biaxially oriented polypropylene film. It is also effective to use such a polypropylene resin and set the stretching temperature in the transverse stretching (stretching in the width direction) to 160°C to 170°C, the relaxation rate in the heat treatment process to 8.0% to 15.0%, and the heat treatment temperature to 150°C to 165°C. These methods can be combined as appropriate. By performing transverse stretching and heat treatment under the above conditions, stretching and heat fixing can be performed with the stress inside the biaxially oriented polypropylene film relaxed, resulting in a biaxially oriented polypropylene film with reduced thermal shrinkage.

[0025] Next, the biaxially oriented polypropylene film roll of the present invention will be described. The biaxially oriented polypropylene film roll of the present invention is made of the biaxially oriented polypropylene film of the present invention. "Made of the biaxially oriented polypropylene film of the present invention" means that the biaxially oriented polypropylene film of the present invention is wound around a core.

[0026] The biaxially oriented polypropylene film roll of the present invention preferably has a surface hardness of 500 to 700. A surface hardness of 700 or less reduces the occurrence of wrinkles due to residual stress. On the other hand, a surface hardness of 500 or more reduces winding misalignment and unevenness of the end faces of the film roll. The surface hardness can be measured using a known hardness tester (for example, FTS-ROLL Tester1 from FTS Corporation).

[0027] A method for making the surface hardness between 500 and 700 is, for example, Sa BEffective methods include setting the film thickness to 100 nm or more, winding the biaxially oriented polypropylene film with a tension of 100-300 N / m, and bringing the contact roll into contact with the winding roll when winding the film roll, with a pressure of 300-800 N / m.

[0028] The thickness of the biaxially oriented polypropylene film of the present invention is not particularly limited and can be adjusted as appropriate depending on the application, but it is preferably 5.0 μm or more and 80.0 μm or less. A thickness of 5.0 μm or more results in good handling, and a thickness of 80.0 μm or less suppresses the decrease in productivity that occurs with an increase in the amount of resin. The biaxially oriented polypropylene film of the present invention can maintain appropriate strength (Young's modulus) and good handling even when the thickness is reduced. To take advantage of these characteristics, the thickness of the biaxially oriented polypropylene film is more preferably 5.0 μm or more and 70.0 μm or less, and even more preferably 10.0 μm or more and 65.0 μm or less. The thickness of the biaxially oriented polypropylene film can be measured with a known electronic micrometer (details of the measurement method will be described later) and can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film formation speed, the stretching ratio, etc.

[0029] The biaxially oriented polypropylene film of the present invention may also contain resins other than polypropylene resin, as long as the effects of the present invention are not impaired. Examples of resins other than polypropylene resin that can be used in the biaxially oriented polypropylene film of the present invention include polyolefins (polyethylene being preferred among them) whose main constituent units are 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., and polyesters such as polyethylene terephthalate and polybutylene terephthalate, but are not limited to the examples given above. These may be added to the polypropylene resin individually, or two or more may be added in any ratio, and may be homopolymers or copolymers. Furthermore, from the viewpoint of dimensional stability, the content of these resins is preferably less than 20% by mass of the total components constituting the biaxially oriented polypropylene film.

[0030] In the biaxially oriented polypropylene film of the present invention, from the viewpoint of film-forming properties and film strength, the melt flow rate (hereinafter referred to as MFR) of the main component, polypropylene resin (sometimes called polypropylene resin A), when measured in accordance with the conditions M (230°C, 2.16 kg) of JIS K 7210 (1999), is preferably 1.0 g / 10 min or more and 5.0 g / 10 min or less, more preferably 2.0 g / 10 min or more and 5.0 g / 10 min or less, and even more preferably 2.2 g / 10 min or more and 5.0 g / 10 min or less, from the viewpoint of film-forming stability and thickness uniformity. In order to achieve the above values ​​for the melt flow rate (MFR) of the polypropylene resin, for example, methods such as controlling the average molecular weight and molecular weight distribution can be employed.

[0031] A polypropylene resin A with an MFR of 1.0 g / 10 min or higher ensures stable film formation and suppresses thickness variations. On the other hand, a polypropylene resin with an MFR of 5.0 g / 10 min or lower allows for low thermal shrinkage when used as a biaxially oriented polypropylene film.

[0032] Furthermore, in addition to the resin mentioned above, various additives such as nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and color inhibitors may be included, as long as they do not impair the objectives of the present invention. Multiple types of these components can also be used in combination, as long as they do not impair the effects of the present invention.

[0033] The selection of antioxidants and adjustment of their amounts are important from the viewpoint of reducing antioxidant bleed-out. Phenolic antioxidants with steric hindrance are preferred, and when multiple types of antioxidants are used in combination, it is preferable that at least one of them be a high molecular weight type with a molecular weight of 500 or more. Various specific examples of antioxidants that can be used in the biaxially oriented polypropylene film of the present invention can be listed, but for example, it is preferable to use 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox"® 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox"® 1010: molecular weight 1177.7) in combination with 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4).

[0034] The total content of these antioxidants is preferably in the range of 0.03% to 1.0% by mass, when the total raw materials for obtaining a biaxially oriented polypropylene film are considered as 100% by mass, from the viewpoint of reducing discoloration due to polymer degradation and a decrease in transparency due to antioxidant bleed-out. A antioxidant content of 0.03% by mass or more can reduce film discoloration and a decrease in long-term heat resistance caused by polymer degradation during the extrusion process. On the other hand, a antioxidant content of 1.0% by mass or less suppresses a decrease in transparency due to antioxidant bleed-out. From the above viewpoint, a more preferable antioxidant content is 0.05% to 0.90% by mass, and even more preferably 0.10% to 0.80% by mass. Note that when the biaxially oriented polypropylene film has a laminated structure, these antioxidants may be added to any layer or to multiple layers.

[0035] Polypropylene resin A may contain copolymer components of other unsaturated hydrocarbons to the extent that it does not impair the objectives of the present invention. Examples of copolymer 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. The copolymerization amount is preferably less than 1 mol% from the viewpoint of dimensional stability.

[0036] Next, the method for producing the biaxially oriented polypropylene film of the present invention will be specifically described using one embodiment as an example, but the method for producing the biaxially oriented polypropylene film of the present invention is not necessarily limited thereto.

[0037] First, the preferred polypropylene resin A described above is supplied to three melt extruders, and melt extrusion is performed at a temperature of 230°C to 260°C. At this time, the discharge volume of each extruder is adjusted so that the layering ratio of the base layer (I), surface layer (II), and surface layer (III) is 58.6 / 0.7 / 0.7 to 57.8 / 1.1 / 1.1. Next, after removing foreign matter and modified polymers using a filter installed in the middle of the polymer tube, the molten sheet obtained using a feed block type 3-layer composite T-die is discharged onto the first cast drum and solidified, and the resulting unstretched sheet is passed through the second cast drum to further adjust the temperature. Furthermore, in order to control the surface Sku and Sa of the first cast drum within an appropriate range, the surface temperature is preferably above 40°C and below 70°C, more preferably above 40°C and below 65°C, and even more preferably between 45°C and 65°C. The second cast drum preferably has a surface temperature of 25°C to 70°C, more preferably 30°C to 65°C, and even more preferably 35°C to 55°C, in order to control Sku and Sa within an appropriate range. As a method for adhering the molten sheet-like material to the first cast drum, methods such as electrostatic application, air knife method, nip roll method, and underwater casting method can be employed, but the air knife method is preferred from the viewpoint of reducing foreign matter and cooling efficiency.

[0038] Furthermore, it is preferable to adhere the sheet to the first and second cast drums and then cool the first and second cast drums together at the above temperature for 10 to 20 seconds. By controlling the temperature and time of the cast drums as described above, the formation of β crystals can be suppressed, resulting in the formation of smooth and broad protrusions without the formation of coarse protrusions.

[0039] Next, the obtained unstretched sheet is biaxially stretched and biaxially oriented. Specifically, the stretching conditions involve first controlling the temperature at which the unstretched sheet is stretched in the longitudinal direction. Methods for temperature control include using a temperature-controlled rotary roll or a hot air oven. The film temperature (preheating temperature and stretching temperature) during longitudinal stretching is determined by the Sku. A SaB Considering the need to control the temperature within a desirable range, as well as the need for stable film formation and reduction of stain-like defects, a temperature of 140°C to 160°C is preferable. The stretching ratio is preferably 3.5 to 6.0 times, and more preferably 4.0 to 5.0 times, in order to control the thermal shrinkage rate and elongation at break within a desirable range. A stretching ratio of 3.5 times or more allows for more uniform stretching, thereby reducing thickness variations. On the other hand, by limiting the stretching ratio to 6.0 times or less, film breakage in the longitudinal stretching process and in the subsequent transverse stretching process can be reduced.

[0040] Next, the uniaxially oriented film obtained by stretching in the longitudinal direction is cooled to a temperature between 10°C and 70°C. When the cooling temperature is 10°C or higher, curling of the film can be suppressed. On the other hand, when the cooling temperature is 70°C or lower, the promotion of thermal crystallization can be suppressed, and the thermal shrinkage stress and the shrinkage stress rise temperature can be easily controlled.

[0041] Next, the uniaxially oriented film obtained in this manner is gripped at both ends in the width direction with clips and introduced into a tenter-type stretcher, where it is stretched in the width direction. From the viewpoint of thickness unevenness and stable film formation, the preheating temperature is preferably 150°C to 185°C, more preferably 155°C to 180°C, and even more preferably 165°C to 180°C, and the stretching temperature is preferably 145°C to 180°C, more preferably 150°C to 175°C, and even more preferably 160°C to 170°C, and the film is stretched at a magnification of 7.0 to 12 times, and more preferably 8.0 to 11 times, in the width direction. The longitudinal direction is the direction in which the film travels during the manufacturing process (in the case of a film roll, this corresponds to the winding direction), and the width direction is the direction perpendicular to the longitudinal direction within the film surface.

[0042] Next, the film is heat-treated in the tenter. At this time, in order to control the thermal shrinkage rate in the width direction, the heat treatment temperature is preferably 110°C to 170°C, more preferably 120°C to 165°C, and even more preferably 150°C to 165°C. Furthermore, the heat treatment may be carried out while relaxing the film in the width direction, and in particular, setting the relaxation rate in the width direction to 5.0% to 15.0%, more preferably 7.0% to 13.0%, is preferable from the viewpoint of setting the thermal shrinkage rate in the width direction within an appropriate range and appropriately balancing dimensional stability.

[0043] The biaxially oriented polypropylene film obtained in this way can be used in a variety of applications, including packaging films, surface protection films, process films, sanitary products, agricultural products, building materials, and medical products. However, because it has excellent surface smoothness and quality, it can be preferably used as a surface protection film, process film, release film, cable wrapping, and electrical application film including capacitors, and is particularly preferably used as a release film. Here, a release film refers to a film that is peeled off from a component or product before it is used as a final product, such as a base material used to protect the surface of a component or for resin formation.

[0044] Next, the laminate of the present invention will be described. The laminate of the present invention consists of the biaxially oriented polypropylene of the present invention and a polyurethane layer. The biaxially oriented polypropylene film of the present invention has excellent transfer resistance and handling properties, and can therefore be suitably used as a release film for polyurethane. By peeling the biaxially oriented polypropylene film from the laminate of the present invention, a polyurethane film with excellent surface smoothness and quality can be obtained without transfer marks. The laminate of the present invention can be manufactured, for example, by laminating the polyurethane film and the biaxially oriented polypropylene film of the present invention under pressure, or by coating with a coating agent containing components having isocyanate groups and hydroxyl groups to form a crosslinked structure through the reaction of these functional groups. [Examples]

[0045] The present invention will be described in detail below with reference to examples. The properties of the film obtained by the manufacturing method were measured and evaluated by the following method.

[0046] [Evaluation methods for each characteristic] (1) Film thickness Five biaxially oriented polypropylene films were stacked to form a measurement sample, and the thickness of the sample was measured using an electronic micrometer (TESA TT80). Next, the obtained value was divided by 5 to calculate the thickness of each biaxially oriented polypropylene film. Furthermore, the same measurement was performed at a position shifted by 50 mm in the width direction, and the same measurement was repeated a total of five times. The obtained measured values ​​were averaged to obtain the film thickness.

[0047] (2) Average surface roughness (Sa), height distribution sharpness (Sku) Measurements were taken using the non-contact surface and layer cross-sectional shape measurement system "VertScan" (registered trademark) 2.0 (model: R3300GL-Lite-AC) manufactured by Ryoka Systems Co., Ltd., under the following procedure and conditions. First, after unwinding the biaxially oriented polypropylene film from the film roll, 10 measurement points were randomly selected on a straight line passing through the center in the width direction and parallel to the longitudinal direction to serve as measurement points. At these 10 points, the Sa and Sku were measured on one of the arbitrarily selected surfaces (the same surface was measured for all 10 samples). The average of the obtained measurement values ​​was calculated and designated as the Sa and Sku of the corresponding surface of the biaxially oriented polypropylene film. Subsequently, the same measurement was performed with a different surface. From the obtained results, surface A was identified, and the Sku was determined. A Sa B The following was identified. Note that in one measurement, one field of view (field of view area: 939 μm vertical × 1,252 μm horizontal = 1,175,628 μm) was used. 2 Measurements were taken of the following:

[0048] 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.

[0049] B. Method for fixing the measurement sample A dedicated sample holder was used to secure the measurement samples. The sample holder consisted of two detachable metal plates with a circular hole in the center. The measurement sample was placed between the plates, ensuring there were no wrinkles, and measurements were taken on the sample located within the circular hole.

[0050] C. Analysis method The data obtained from 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 (5x5), and then undulation components were removed using a Gaussian filter with a cutoff value of 250 μm. Next, Sa and Sku, as defined in ISO 25178 (2012), were measured using the "ISOPara" function. In the "ISOPara" function, the S-Filter was set to 6.0 μm.

[0051] (3) Heat shrinkage rate when treated at 150°C for 15 minutes Two lines were drawn on a biaxially oriented polypropylene film, with a width of 10 mm and a measurement length of 100 mm. The distance between these two lines was accurately measured at 23°C and designated as L01. Next, using a point approximately 50 mm midway between the two lines as the center, the angle in the direction of the measurement length was shifted 10 degrees clockwise. The distance between the two lines was accurately measured at 23°C at a position with a width of 10 mm and a measurement length of 100 mm, and designated as L02. Similarly, two lines were drawn with a 10-degree shift up to 90 degrees, and the distance between the two lines was accurately measured at 23°C up to L10. Each sample obtained in this way was left in a 100°C oven for 30 minutes under a load of 1.5g. Then, the distance between the two lines of each sample was measured again in a 23°C environment, and these were designated as L11, L12, L13...L110. The dimensional change rate at each temperature was calculated using the following formula, and the one with the largest dimensional change rate was selected (here, L01 corresponds to L11, L02 to L12, and so on up to L110). Formula: Dimensional change rate (%) = [(L01-L11) / L01] × 100.

[0052] (4) Hardness of the film roll surface The surface of a film roll, prepared by slitting and winding the film using a slitter, was measured at five equally spaced points in the width direction using an FTS-ROLL Tester1 from FTS Corporation. The average of these measurements was used to determine the film roll surface hardness. The five points were set to divide the roll equally.

[0053] (5) Indentation The film was cut to 300mm x 300mm, and the side with the relatively lower surface roughness Sa, side A, was visually inspected using reflected light and evaluated according to the following criteria. A result of ○ was considered a pass. ○: Confirmed that there are no dents. ×: One or more dents were found.

[0054] (6) Product rolled up After the product rolls were wound, they were visually inspected and evaluated according to the following criteria. A result of ○ or △ was considered a pass. ○: No wrinkles or misalignment occurred in the product rolls. △: Wrinkles were present in the product roll, but they disappeared when the film was pulled towards the user by holding both ends of the unwound film, and there was no actual damage to the processing. Furthermore, no winding misalignment occurred. ×: At least one of the following occurred during processing: wrinkles or misalignment.

[0055] (7) Peelability A biaxially oriented polypropylene film was cut to 150mm x 100mm. A polyurethane film measuring 150mm x 25mm was placed on side A, and a 4kg cylindrical metal roller was used to press it firmly into place by moving it back and forth once. The polyurethane film was peeled off side A, and the presence or absence of the polyurethane film adhering to side A was visually evaluated. A result of ○ was considered a pass. ○: No polyurethane film was found to be attached. ×: A polyurethane film was attached.

[0056] (8) Transferability Using the method described in (7), a polyurethane film was adhered to side A of a biaxially oriented polypropylene film and then peeled off. After this, the surface of the polyurethane film was visually inspected five times and evaluated according to the following criteria. A result of ○ or △ was considered a pass. ○: It was confirmed that there were no transfer marks in all 5 attempts. △: A transfer trace was confirmed in 1 out of 5 attempts. ×: Transfer marks were confirmed in 2 to 5 out of 5 attempts.

[0057] [Raw materials] The following raw materials were used to produce the biaxially oriented polypropylene films of the Examples and Comparative Examples. Note that the antioxidants listed below are already mixed into polypropylene resin I and polypropylene resin II, so no fine adjustments were made to their content in the Examples and Comparative Examples. Furthermore, the amount of antioxidant contained in each resin is trace (less than 1.0% by mass of the total components), and considering the volatile content when the film is formed, the amount of antioxidant will be even less. Therefore, the manufacturing methods and Table 1 for the Examples and Comparative Examples described below will not include this information.

[0058] (1) Resin Polypropylene resin I (homopolypropylene resin / homoPP1): A homopolypropylene resin manufactured by Sumitomo Chemical Co., Ltd., with an MFR of 2.3 g / 10 min and a melting point of 160°C. Polypropylene resin II (homopolypropylene resin / homoPP2): Manufactured by Sumitomo Chemical Co., Ltd., this is a homopropylene resin with an MFR of 4.0 g / 10 min and a melting point of 158°C, compounded with 0.5% by mass of homopolyethylene. Polypropylene resin III (homopolypropylene resin / homoPP3): Manufactured by Prime Polymer Co., Ltd., this homopolypropylene resin has an MFR of 5.3 g / 10 min and a melting point of 155°C, and is compounded with 30.0% by mass of homopolyethylene.

[0059] (Example 1) Polypropylene resin I was supplied to a single-screw extruder as the raw material for the base layer (I). Polypropylene resin II was supplied to another single-screw extruder as the raw material for the surface layer (II). Furthermore, polypropylene resin III was supplied to yet another single-screw extruder as the raw material for the surface layer (III). Subsequently, polypropylene resin I was melted at 230°C, polypropylene resin II at 250°C, and polypropylene resin III at 240°C in each single-screw extruder and extruded, and foreign matter was removed from each molten resin using a 30 μm cut sintered filter. Next, each raw material was stacked in a feed block type 3-layer composite T-die so that the thickness ratio of II / I / III was 1.0 / 58 / 1.0, and the molten sheet was discharged onto a first casting drum with a surface temperature controlled to 45°C, and the sheet was pressed against the first casting drum to form a sheet. The obtained sheet was pressed against a second casting drum with a surface temperature controlled to 40°C to obtain an unstretched sheet. At this stage, the peripheral speed of the casting drum was adjusted so that the total contact time of the film with the first and second casting drums was 13 seconds. Next, the unstretched sheet was preheated to 160°C using a conveyor roll, stretched 4.3 times in the longitudinal direction at a temperature of 143°C between rolls with a peripheral speed difference, and then cooled on a roll at 40°C. Next, the obtained uniaxially oriented film was introduced into a tenter stretcher with both ends in the width direction gripped with clips, preheated at 176°C for 3 seconds, and then stretched 8.9 times in the width direction at 165°C. After that, in the same tenter stretcher, it was heat-treated at 158°C while giving it a 9.5% slack in the width direction, and then guided to the outside of the tenter stretcher and the clips were released. Subsequently, the biaxially oriented polypropylene film with both ends in the width direction removed was wound on a winding machine to obtain a jumbo roll of biaxially oriented polypropylene film with a thickness of 60.0 μm. The jumbo roll of the obtained biaxially oriented polypropylene film was slit into even narrower widths and wound under conditions of a winding tension of 150 N / m and a contact roll surface pressure of 450 N / m to obtain a film roll of biaxially oriented polypropylene film. The physical properties of the obtained biaxially oriented polypropylene film and the evaluation results of the film roll are shown in Table 1.

[0060] (Examples 2-14, Comparative Examples 1-5) In Example 1, a roll of biaxially oriented polypropylene film was obtained using the same method as in Example 1, except that the film composition and film formation conditions were as shown in Table 1 or 2. The physical properties and evaluation results of the obtained biaxially oriented polypropylene film are shown in Table 1 or 2.

[0061] [Table 1]

[0062] [Table 2] [Industrial applicability]

[0063] As described above, the polypropylene film of the present invention has excellent transfer resistance and handling properties, making it suitable for use as a release film or process film, and is particularly suitable as a release film for polyurethane components, for example. Furthermore, since the polypropylene film of the present invention also has excellent surface smoothness, it can be suitably used as a release film or process film for components that require surface smoothness. In addition, the polypropylene film of the present invention, possessing the above characteristics, can be used in a variety of applications such as packaging films, sanitary products, agricultural products, construction products, and medical products.

Claims

1. The surface with relatively low surface roughness Sa is called surface A, the surface with high surface roughness Sa is called surface B, and the sharpness Sku of the surface height distribution of surface A is called Sku. Ａ , Sa on the B surface Sa Ｂ When that happens, the Sku Ａ The value is 5.0 or more and 250 or less, and the Sa Ｂ 1.0 × 10⁻¹⁰ nm or larger ３ / Log(Sku Ａ A biaxially oriented polypropylene film characterized by having a size of ) nm or less.

2. The biaxially oriented polypropylene film according to claim 1, wherein the heat shrinkage rate when treated at 150°C for 15 minutes is 0.0 to 5.0% in the direction of greatest shrinkage.

3. A biaxially oriented polypropylene film according to claim 1 or 2, having three layers with different raw material compositions.

4. A biaxially oriented polypropylene film roll comprising the biaxially oriented polypropylene film according to claim 1 or 2.

5. The biaxially oriented polypropylene film roll according to claim 4, wherein the winding hardness of the surface layer is 500 or more and 700 or less.

6. A laminate comprising a biaxially oriented polypropylene and a polyurethane layer as described in claim 1 or 2.

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