WO2018147335A1 - Biaxially oriented polypropylene film - Google Patents

Abstract

Provided is a biaxially oriented polypropylene film in which the modulus of elasticity of at least one surface in the thickness direction at 23°C is 2.0 GPa or more as measured by nanoindentation and the sum of the tensile modulus of elasticity in the MD direction and the TD direction at 23°C is 6.6 GPa or less. The present invention provides a polypropylene film having excellent surface smoothness, transparency, quality, and handling properties.

Description

Biaxially oriented polypropylene film

The present invention relates to a polypropylene film excellent in quality, excellent in surface smoothness, transparency and handling properties.

Polypropylene films are excellent in transparency, mechanical properties, electrical properties, etc., and are therefore used in various applications such as packaging, mold release, tape, cable wrapping and electrical applications such as capacitors. In particular, since it has excellent surface releasability and mechanical properties, it is suitably used as a release film or process film for various members such as plastic products, building materials and optical members.

The required characteristics for the release film are set as appropriate depending on the intended use, but due to the recent downsizing and higher precision of equipment, products to be protected may be required to be thin and high-grade. If the surface smoothness of the polypropylene film is poor, for example, when used as a release film for an optical member, the surface irregularities of the film may be transferred to the optical member and affect the visibility of the product. In some cases, fine polypropylene (PP) powder of several μm to several tens of μm is present on the surface of the axially oriented polypropylene film. PP powder is so small that it cannot be visually confirmed. However, in recent years, due to high precision and miniaturization of products, the irregularities of PP powder may be transferred to the product, leading to deterioration in quality and yield. I came.

PP powder is thought to be generated by scraping the film surface due to a slight speed difference between the transport roll and the film during the film forming process. Examples of suppressing such scraping are disclosed in Patent Documents 1 and 2, for example. It describes the improvement of abrasion resistance of polypropylene terephthalate film and polyester film.

JP-A-11-152351 JP-A-11-269283

Polypropylene resin has a lower hardness than other resins and is easily scratched. Therefore, it has been difficult to improve the quality by suppressing scraping by the methods disclosed in Patent Documents 1 and 2. An object of the present invention is to solve the above-described problems. That is, an object is to provide a polypropylene film that is excellent in quality, excellent in surface smoothness, and transparency handling properties.

In order to solve the above-described problems and achieve the object, the biaxially oriented polypropylene film of the present invention has an elastic modulus in the thickness direction at 23 ° C. of at least one side measured by a nanoindentation method of 2.0 GPa or more, And the sum of the tensile elasticity modulus of MD direction in 23 degreeC and TD direction is 6.6 GPa or less, It is characterized by the above-mentioned.

Since the biaxially oriented polypropylene film of the present invention is excellent in surface smoothness and transparency, and excellent in quality and handling properties, it is suitably used as an industrial film such as a base film for coating, a cover film, and a protective film. can do.

The biaxially oriented polypropylene film of the present invention has an elastic modulus in the thickness direction at 23 ° C. of at least one side measured by a nanoindentation method of 2.0 GPa or more. The elastic modulus in the thickness direction is more preferably 2.3 GPa or more, further preferably 2.5 GPa or more, and further preferably 2.7 GPa or more. If the elastic modulus in the thickness direction is less than 2.0 GPa, the film surface may be scraped and PP powder may be generated due to a slight speed difference between the transport roll and the film during the film forming process, or the generation amount may increase. is there. The higher the elastic modulus in the thickness direction, the better from the viewpoint of suppressing PP powder, but the upper limit is substantially about 5.0 GPa. In order to make the elastic modulus in the thickness direction within the above range, the raw material composition of the film and the laminated structure of the film are within the ranges described below, and the cast (melt-extruded resin sheeting process) conditions and longitudinal conditions during film formation The stretching conditions are preferably within the range described below.

The biaxially oriented polypropylene film of the present invention has a sum of tensile elastic modulus in the MD direction and TD direction at 23 ° C. of 6.6 GPa or less. The sum of the tensile elastic moduli is more preferably 3.0 to 6.6 GPa, still more preferably 3.5 to 6.4 GPa, still more preferably 4.0 to 6.2 GPa. When the sum of the tensile elastic modulus exceeds 6.6 GPa, the film surface is scraped due to a slight speed difference between the transport roll and the film in the film transport process after biaxial stretching, or PP powder is generated, or the amount generated is May increase. On the other hand, if it is too small, the stiffness of the film becomes weak and the handling property is lowered, so that it is preferably 3.0 GPa or more. In order to make the sum of the tensile elastic modulus within the above range, the raw material composition of the film and the laminated structure of the film are within the ranges described later, and the cast (melt-extruded resin sheeting process) conditions and longitudinal The stretching conditions are preferably within the range described below.

In the present application, a direction parallel to the film forming direction is referred to as a film forming direction, a longitudinal direction, or an MD direction, and a direction perpendicular to the film forming direction in the film plane is referred to as a width direction or a TD direction.

In some cases, fine PP powder of several μm to several tens of μm may exist on the surface of a conventional biaxially oriented polypropylene film. Although the PP powder is very small so that it cannot be visually confirmed, in recent years, there has been a case where the PP powder leads to a decrease in quality and yield due to high precision and miniaturization of the product. As a result of intensive studies, PP powder is generated by scraping the film surface due to a slight speed difference between the transport roll and the film during the film forming process. As a countermeasure, the sum of the elastic modulus in the thickness direction and the tensile elastic modulus is within the above range. Even if a slight speed difference between the transport roll and the film occurs, the surface of the film has a high elastic modulus in the thickness direction and a tensile elastic modulus lower than a certain value. It was found that the film was hard and the film was stretched to follow the speed of the transport roll, and it was possible to reduce rubbing and suppress PP powder.

The biaxially oriented polypropylene film of the present invention preferably has a maximum height roughness Sz of 1000 nm or less on both sides. In applications where the transportability of the film is important, the thickness is more preferably 10 to 800 nm, still more preferably 100 to 700 nm. In applications where the surface smoothness of the film is important, the thickness is more preferably 5 to 500 nm, further preferably 5 to 300 nm, and further preferably 5 to 200 nm. When the maximum height roughness Sz exceeds 1000 nm, the unevenness of the film may be transferred to the surface of the product when used as a base film or a cover film. From the viewpoint of suppressing uneven transfer to a product, the maximum height roughness Sz is preferably as small as possible. However, if it is too small, the surface of the film is too smooth, and handling properties and winding are difficult when transporting or winding the formed film. In some cases, the take-off property is lowered or PP powder is likely to be generated due to rubbing with the transport roll. In order to set Sz in the above range, the raw material composition of the film and the laminated structure of the film are set in the range described later, and the cast (melt-extruded resin sheeting process) condition and the longitudinal stretching condition in film formation are described later. It is preferable that the β crystal of the cast sheet is reduced. In the cast sheet of polypropylene, spherulites derived from α crystals and spherulites derived from β crystals are formed. The β crystal-derived spherulites differ from the α crystal-derived spherulites in stretchability, and form a coarse crater structure after stretching, which may impair the smoothness of the film.

The biaxially oriented polypropylene film of the present invention preferably has a maximum height roughness Sz1 of at least one side of 300 nm or less. More preferably, it is 5 to 250 nm, and still more preferably 5 to 200 nm. Here, among Sz, the maximum height roughness of one surface (smooth surface) is Sz1, the maximum height roughness of the other surface (rough surface) is Sz2 (where Sz1 ≦ Sz2), and the maximum of both surfaces When the height roughness values are equal, the maximum height roughness of the contact surface with the casting drum is Sz1. When the maximum height roughness Sz1 of at least one surface is 300 nm or less, when used as a base film or a cover film in applications where the surface smoothness of the film is important, the surface shape unevenness transfer to the product is suppressed. It is possible. From the viewpoint of suppressing uneven transfer to a product, the maximum height roughness Sz is preferably as small as possible. However, if it is too small, the surface of the film is too smooth, and handling properties and winding are difficult when transporting or winding the formed film. In some cases, the take-off property is lowered or PP powder is likely to be generated due to rubbing with the transport roll. In order to make Sz within the above range, the raw material composition of the film and the laminated structure of the film are within the ranges described below, and the casting conditions and longitudinal stretching conditions during film formation are within the ranges described below. Is preferably reduced.

The biaxially oriented polypropylene film of the present invention preferably has a static friction coefficient μs of 0.6 or less. More preferably, it is 0.55 or less, More preferably, it is 0.50 or less. If the static friction coefficient μs exceeds 0.6, the film surface may be scraped off due to a slight speed difference between the transport roll and the film during the film forming process, and PP powder may be generated or the generation amount may increase. From the viewpoint of PP powder suppression, the static friction coefficient μs is preferably as small as possible, but the lower limit is substantially about 0.2. In order to set the static friction coefficient μs in the above range, the raw material composition of the film and the laminated structure of the film are in the ranges described later, and in particular, at least one surface layer of the laminated structure (hereinafter referred to as surface layer (I)). It is preferable that the raw material composition is within the range described below.

The biaxially oriented polypropylene film of the present invention preferably has a haze of 1% or less. More preferably, it is 0.9% or less, More preferably, it is 0.8% or less, More preferably, it is 0.7% or less. When the haze exceeds 1%, the surface roughness of the film surface is large, and the surface shape may be transferred to the adherend. Moreover, when used as a protective film or a base film for production of a product such as a display member that requires high quality, defect detection may not be performed in a state of being bonded to the product. The haze is preferably as low as possible from the viewpoint of transparency, but the lower limit is substantially about 0.05%. In order to set the haze to the above range, the raw material composition of the film and the laminated structure of the film are set in a range described later to prevent deterioration of transparency due to particles and the like, and the casting conditions and longitudinal stretching conditions during film formation are described later. It is preferable that the β crystal of the cast sheet is reduced.

In the biaxially oriented polypropylene film of the present invention, the number of fish eyes is preferably 20 / m ² or less. The number of fish eyes is more preferably 10 / m ² or less, and still more preferably 5 / m ² or less. If the number of fish eyes exceeds 20 / m ² , the yield may decrease when used as a protective film or a base film for production of a product such as a display member that requires high quality. In order to set the number of fish eyes within the above range, the composition of the raw materials, the adjustment method, and the laminated structure of the film are within the ranges described later, and the additive components in the raw materials and heat deterioration may cause fish eyes. It is effective to reduce the amount of resin used. Moreover, it is effective to set the conditions during film formation within the range described later, and to remove foreign substances by filtration and to reduce the staying part of the resin before the raw material is melted into a sheet.

The thickness of the biaxially oriented polypropylene film of the present invention is appropriately adjusted depending on the application and is not particularly limited, but is preferably 5 μm or more and 100 μm or less. When the thickness is less than 5 μm, handling may be difficult, and when it exceeds 100 μm, the amount of resin may increase and productivity may decrease. The biaxially oriented polypropylene film of the present invention can maintain moderate strength (Young's modulus) and handleability even when the thickness is reduced. In order to make use of such characteristics, the thickness is more preferably 5 μm or more and 40 μm or less, further preferably 5 μm or more and 30 μm or less, and most preferably 5 μm or more and 25 μm or less. The thickness can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film forming speed, the stretch ratio, and the like within a range not deteriorating other physical properties.

Next, the raw material of the biaxially oriented polypropylene film of the present invention will be described, but the present invention is not necessarily limited thereto.

The biaxially oriented polypropylene film of the present invention is a film mainly composed of polypropylene. Here, the “main component” in the present application means that the proportion of the specific component in all the components is 50% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, More preferably, it is 96 mass% or more, More preferably, it is 97 mass% or more, More preferably, it is 98 mass% or more.

In the biaxially oriented polypropylene film of the present invention, it is preferable to use at least two types of polypropylene raw materials (polypropylene raw material A and polypropylene raw material B). As the polypropylene raw material A, it is preferable to use a polypropylene material having high crystallinity in order to improve the elastic modulus in the thickness direction of the film. As the polypropylene raw material B, polypropylene having low crystallinity in order to reduce the tensile elastic modulus of the film. It is preferable to use raw materials.

The polypropylene raw material A is preferably a polypropylene having a cold xylene soluble part (hereinafter CXS) of 4% by mass or less and a mesopentad fraction of 0.95 or more. If these conditions are not satisfied, the film forming stability may be inferior, or the elastic modulus in the thickness direction of the film may be lowered.

Here, the cold xylene-soluble part (CXS) refers to a polypropylene component dissolved in xylene when the film is completely dissolved in xylene and then deposited at room temperature, and has low stereoregularity. It is considered that it corresponds to a component that is difficult to crystallize due to low molecular weight. If many such components are contained in the resin, the elastic modulus in the thickness direction of the film may be inferior. Therefore, CXS is preferably 4% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. CXS is preferably as low as possible, but about 0.1% by mass is the lower limit. In order to obtain such polypropylene having CXS, methods such as a method for increasing the catalytic activity in obtaining a resin and a method for washing the obtained resin with a solvent or propylene monomer itself can be used.

From the same viewpoint, the mesopentad fraction of the polypropylene raw material A is preferably 0.93 or more, more preferably 0.97 or more. The mesopentad fraction is an index indicating the stereoregularity of the crystal phase of polypropylene measured by a nuclear magnetic resonance method (NMR method). The higher the numerical value, the higher the crystallinity, the higher the melting point, and the higher the temperature. It is preferable because it is suitable for use. The upper limit of the mesopentad fraction is not particularly specified. In order to obtain a resin having such a high stereoregularity, there are a method of washing resin powder obtained with a solvent such as n-heptane, a method of appropriately selecting a catalyst and / or a promoter, and a composition. Preferably employed.

The polypropylene raw material A more preferably has a melt flow rate (MFR) of 1 to 10 g / 10 minutes (230 ° C., 21.18 N load), particularly preferably 2 to 5 g / 10 minutes (230 ° C., 21.18 N). The range of (load) is preferable from the viewpoint of improving the film forming property and the elastic modulus in the thickness direction of the film. In order to set the MFR to the above value, a method of controlling the average molecular weight or the molecular weight distribution is employed.

The polypropylene raw material A is mainly composed of a propylene homopolymer, but may contain other unsaturated hydrocarbon copolymerization components or the like within a range not impairing the object of the present invention. The coalescence may be blended. For example, ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene as monomer components constituting such copolymer components and blends -1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2 -Norbornene and the like. From the viewpoint of improving the modulus of elasticity in the thickness direction, the copolymerization amount or blend amount is preferably less than 1 mol% in terms of copolymerization amount and less than 10 mass% in terms of blend amount.

Subsequently, the polypropylene raw material B will be described.

The polypropylene raw material B is preferably a polypropylene raw material having good compatibility with the above-mentioned polypropylene raw material A and low crystallinity in order to improve flexibility. As such a polypropylene raw material B, amorphous polypropylene, low stereoregular polypropylene, syndiotactic polypropylene, α-olefin copolymer, random copolymer, block polypropylene, etc. can be used, but excellent with a small addition amount. Therefore, amorphous polypropylene and low stereoregular polypropylene are particularly preferable.

The amorphous polypropylene preferably used as the polypropylene raw material B is preferably mainly composed of a polypropylene polymer having mainly atactic stereoregularity, specifically, a homopolymer or a copolymer with an α-olefin. Can be mentioned. In particular, the latter, that is, an amorphous polypropylene-α-olefin copolymer is preferred.

The amorphous polypropylene can be produced using a specific metallocene catalyst, or can be produced as a by-product of isotactic polypropylene during homopolypropylene polymerization. Since the glass transition temperature is lower than that of general polypropylene, it can be extracted as a boiling n-heptane (or xylene) soluble component of homopolypropylene. Alternatively, crystalline polypropylene can be polymerized independently by changing the catalyst and polymerization conditions. The amorphous polypropylene preferably used in the present invention can be used without particular limitation as long as it is produced by a conventionally known production method. Commercially available products such as “Tufselen” (registered trademark) manufactured by Sumitomo Chemical Co., Ltd. can be appropriately used as the amorphous polypropylene having the above-described characteristics.

When an amorphous polypropylene-α-olefin copolymer is used as the amorphous polypropylene in the present invention, examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 1-octene and 1-decene. 4-methyl / 1-pentene or propylene-ethylene-1-butene is preferred.

Examples of such amorphous polypropylene-α-olefin copolymers using α-olefins include propylene / ethylene copolymers, propylene / ethylene / 1-butene copolymers, and propylene-1-butene copolymers. , Propylene / ethylene / cyclic olefin copolymer, propylene / ethylene / butadiene copolymer, and the like.

The low stereoregular polypropylene preferably used as the polypropylene raw material B is preferably a propylene homopolymer produced using a metallocene catalyst as a polymerization catalyst. The melting point of the low stereoregular polypropylene is 100 ° C. or less, more preferably 60 to 90 ° C., and particularly preferably 65 to 85 ° C. The weight average molecular weight is preferably 40,000 to 200,000, and the molecular weight distribution Mw / Mn is preferably 1 to 3 (Mw: weight average molecular weight, Mn: number average molecular weight). Commercially available products such as “El Modu” (registered trademark) manufactured by Idemitsu Kosan Co., Ltd. can be appropriately used as the low stereoregular polypropylene having the above-described characteristics.

In the biaxially oriented polypropylene film of the present invention, the content of the ethylene component contained in the polymer constituting the film is preferably 10% by mass or less. More preferably, it is 5 mass% or less, More preferably, it is 3 mass% or less. The greater the ethylene component content, the lower the crystallinity, and the easier it is to improve flexibility and transparency. However, when the ethylene component content exceeds 10% by mass, the heat resistance decreases and fish eyes May be more likely to occur.

In the biaxially oriented polypropylene film of the present invention, the content of petroleum resin contained in the polymer constituting the film is preferably 5% by mass or less. More preferably, it is 3 mass% or less, More preferably, it is 1 mass% or less, and it is most preferable that petroleum resin is not included. Transparency can be improved by adding a petroleum resin, but if the content of the petroleum resin exceeds 5% by mass, the tensile elastic modulus may be too high or the raw material cost may be increased. .

In the biaxially oriented polypropylene film of the present invention, the content of the cycloolefin polymer contained in the polymer constituting the film is preferably 5% by mass or less. More preferably, it is 3 mass% or less, More preferably, it is 1 mass% or less, and it is most preferable that a cycloolefin polymer is not included. Heat resistance can be improved by adding a cycloolefin polymer. However, if the content of the cycloolefin polymer exceeds 5% by mass, the tensile elastic modulus becomes too high, and compatibility with polypropylene is increased. Transparency may decrease due to problems, haze may deteriorate, and raw material costs may increase.

In the present invention, the polypropylene raw material includes various additives, for example, a crystal nucleating agent, an antioxidant, a thermal stabilizer, a slipping agent, an antistatic agent, an antiblocking agent, a filler, within a range that does not impair the purpose of the present invention. Viscosity modifiers, anti-coloring agents, and the like can also be included.

Among these, selection of the type and amount of antioxidant is important from the viewpoint of long-term stability. That is, the antioxidant is a phenolic compound having steric hindrance, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more. Specific examples thereof include various compounds such as 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) and 1,3,5-trimethyl-2,4,6- Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (for example, “Irganox” (registered trademark) 1330: molecular weight 775.2 manufactured by BASF) or tetrakis [methylene-3 (3,5-di- t-butyl-4-hydroxyphenyl) propionate] methane (for example, “Irganox” (registered trademark) 1010: molecular weight 1177.7, manufactured by BASF) is preferably used in combination. The total content of these antioxidants is preferably in the range of 0.03 to 1.0 mass% with respect to the total amount of polypropylene. When there are too few antioxidants, a polymer may deteriorate in an extrusion process and a film may color, or it may be inferior to long-term heat resistance. When there are too many antioxidants, transparency may fall by the bleeding out of these antioxidants. A more preferable content is 0.1 to 0.9% by mass, particularly preferably 0.2 to 0.8% by mass.

In the present invention, a crystal nucleating agent can be added to the polypropylene raw material as long as it does not contradict the purpose of the present invention. Examples of the crystal nucleating agent include α crystal nucleating agents (dibenzylidene sorbitols, sodium benzoate, etc.), β crystal nucleating agents (potassium 1,2-hydroxystearate, magnesium benzoate, N, N′-dicyclohexyl-2,6). -Amide compounds such as naphthalene dicarboxamide, quinacridone compounds and the like). However, excessive addition of the above various nucleating agents may cause a decrease in stretchability, transparency and strength due to void formation, etc., so the addition amount is usually 0.5% by mass or less, preferably 0.1% by mass. % Or less, more preferably 0.05% by mass or less.

The biaxially oriented polypropylene film of the present invention is obtained by biaxially stretching using the above-described raw materials. The biaxial stretching method can be obtained by any of the inflation simultaneous biaxial stretching method, the stenter simultaneous biaxial stretching method, and the stenter sequential biaxial stretching method. Among them, the film forming stability, the thickness uniformity, In terms of controlling high rigidity and dimensional stability, it is preferable to employ a stenter sequential biaxial stretching method.

Next, the structure of the film using the above polypropylene material will be described.

The biaxially oriented polypropylene film of the present invention preferably has a laminated structure of at least two layers from the viewpoint of suppressing PP powder, and from the viewpoint of achieving both transparency and slipperiness.

In the biaxially oriented polypropylene film of the present invention, at least one surface layer (surface layer (I)) of the laminated structure preferably contains 96% by mass or more of polypropylene raw material A from the viewpoint of tensile rigidity. The content of the polypropylene raw material A in the surface layer (I) is more preferably 97% by mass or more, and still more preferably 98% by mass or more. When the content of the polypropylene raw material A in the surface layer (I) is less than 96% by mass, the elastic modulus in the thickness direction of the film is lowered, and when there are many additive components having low heat resistance, slipperiness is exhibited. May decrease.

In addition, the biaxially oriented polypropylene film of the present invention has at least one layer (hereinafter referred to as a base layer (II)) of the laminated structure, from the viewpoint of improving the flexibility by reducing the tensile modulus and the polypropylene raw material B. The content of the polypropylene raw material B in the base layer (II) is preferably 5 to 100% by mass. More preferably, it is 10 to 100% by mass, and further preferably 15 to 100%. If the content of the polypropylene raw material B in the base layer (II) is less than 5% by mass, the tensile elastic modulus of the film becomes too high and PP powder may be easily generated.

In the biaxially oriented polypropylene film of the present invention, the thickness d of the surface layer (I) is preferably 0.1 to 2.0 μm. More preferably, it is 0.2 to 1.5 μm, more preferably 0.3 to 1.0 μm, and still more preferably 0.3 to 0.8 μm. If the thickness d of the surface layer (I) exceeds 2.0 μm, the tensile elastic modulus of the film becomes too large and PP powder may be easily generated. If the thickness is less than 0.1 μm, the elastic modulus in the thickness direction of the film is insufficient, PP powder is likely to be generated, lamination accuracy becomes unstable, and thickness unevenness of the surface layer (I) may increase. The thickness d of the surface layer (I) can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film forming speed, the stretch ratio, and the like within a range not deteriorating other physical properties. In addition, when providing surface layer (I) on both surfaces of a film, it is preferable to satisfy | fill the said range about each layer.

In the biaxially oriented polypropylene film of the present invention, the ratio of the surface layer (I) to the thickness of the entire film is preferably 1 to 15%. More preferably, it is 1 to 10%, and further preferably 1 to 5%. If the ratio of the surface layer (I) exceeds 15%, the tensile elastic modulus of the film becomes too large, and PP powder may be easily generated. If it is less than 1%, the elastic modulus in the thickness direction of the film is insufficient, PP powder is likely to be generated, lamination accuracy becomes unstable, and thickness unevenness of the surface layer (I) may increase. The thickness d of the surface layer (I) can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film forming speed, the stretch ratio, and the like within a range not deteriorating other physical properties. In addition, it is preferable to provide surface layer (I) on both surfaces of a film, and in that case, it is preferable to satisfy the above range for each layer.

In the biaxially oriented polypropylene film of the present invention, it is preferable from the viewpoint of reducing the friction coefficient that the at least one surface layer contains easy-slip particles or a resin having a melting point of 180 ° C. or more, particularly the melting point. More preferably, it contains a resin at 180 ° C. or higher.

The easy-slip particles are not particularly limited as long as the effects of the present invention are not impaired. For example, inorganic particles and organic particles can be used. Inorganic particles include silica, titanium oxide, aluminum oxide, zirconium oxide, calcium carbonate, carbon black, zeolite particles, and organic particles include acrylic resin particles, styrene resin particles, polyester resin particles, and polyurethane resin particles. Polycarbonate resin particles, polyamide resin particles, silicone resin particles, fluorine resin particles, or copolymer resin particles of two or more monomers used for synthesizing the resin. However, since the polypropylene resin has low surface energy, when the particles are added and stretched, the particle interface peels off during stretching, voids are generated, haze increases, and transparency may decrease. From the viewpoint of improving transparency, it is preferable to use the above inorganic particles or organic particles having a silane coupling treatment on the surface, and particularly preferred are silica particles having a silane coupling treatment.

The average particle diameter of the easy-slip particles is preferably 0.01 μm or more and less than 1.0 μm. If the average particle size is less than 0.01 μm, the particles may aggregate to form coarse particles, which may reduce transparency. When the average particle size is 1.0 μm or more, voids are likely to be generated at the particle interface during stretching, and transparency may be lowered. In addition, particles added to the surface layer may fall off during film formation, resulting in increased surface roughness or increased haze. The average particle diameter is more preferably from 0.15 μm to less than 0.9 μm, further preferably from 0.15 μm to less than 0.8 μm, and most preferably from 0.15 μm to less than 0.3 μm. Moreover, you may use together two or more types of particle | grains from which an average particle diameter differs from a viewpoint of handling property improvement. Here, the average particle diameter was measured by a laser diffraction scattering method and calculated on the basis of weight.

The biaxially oriented polypropylene film of the present invention preferably contains easy-slip particles in the surface layer (I). At this time, the thickness of the layer containing easy-slip particles is preferably 0.2 to 2.0 μm. If it is less than 0.2 μm, the slippery particles may fall off during film formation. If it exceeds 2.0 μm, the haze may increase and the transparency may decrease. The thickness of the layer containing easy-slip particles is more preferably 0.2 to 1.6 μm, and further preferably 0.3 to 1.4 μm.

The content of the easy-slip particles in the raw material of the layer containing the easy-slip particles is preferably 0.01% by mass or more and less than 1.0% by mass. If the content is less than 0.01% by mass, the effect of reducing the friction coefficient may not be obtained. If the content is 1.0% by mass or more, haze may increase and transparency may decrease. The content is more preferably 0.05% by mass or more and less than 0.9% by mass, and further preferably 0.1% by mass or more and less than 0.8% by mass.

The biaxially oriented polypropylene film of the present invention preferably contains a resin having a melting point of 180 ° C. or higher from the viewpoint of reducing the friction coefficient. The melting point is more preferably 180 ° C. or higher and 240 ° C. or lower, and further preferably 200 ° C. or higher and 230 ° C. or lower. By containing a resin having a melting point of 180 ° C. or more in the surface layer of the film and forming a film under the conditions described later, it is possible to form fine protrusions on the film surface and improve slipperiness. In such a case, the film is composed of at least two layers of the surface layer (I) and the base layer (II), and the surface layer (I) preferably contains a resin having a melting point of 180 ° C. or higher. When a resin having a melting point of 180 ° C. or higher is present in the surface layer (I), it can be melted and dispersed in polypropylene in the later-described melt extrusion process, and the above-described protrusion can be formed without deformation in the stretching process. In order to make the protrusions to be formed as fine as described above, it is necessary that a resin having a melting point of 180 ° C. or higher is finely dispersed in polypropylene in the melt extrusion process, and the affinity with polypropylene is high. is important. From this point of view, the resin having a melting point of 180 ° C. or higher is preferably an olefin resin, but among the olefin resins, an olefin resin containing 4-methylpentene-1 unit as a main component is particularly preferable. preferable. Since the resin containing 4-methylpentene-1 unit has a higher affinity with a polypropylene resin than a non-olefin resin, dispersibility can be improved. Examples of the olefin resin containing 4-methylpentene-1 unit include “TPX” (registered trademark) DX310, “TPX” (registered trademark) DX231, “TPX” (registered trademark) manufactured by Mitsui Chemicals, Inc. An example is MX004.

In the biaxially oriented polypropylene film of the present invention, the content of the olefin resin comprising 4-methylpentene-1 unit in the resin composition of the surface layer (I) is 0.1 to 5% by mass. It is preferably 0.1 to 4% by mass, more preferably 0.1 to 3% by mass, and still more preferably 0.1 to 2.5% by mass. When the content of the olefin-based resin containing 4-methylpentene-1 unit is more than 5% by mass, the protrusions may be mountainous in the longitudinal direction, and when used as a base film or a cover film, When it is difficult to wind up, such as when unevenness is transferred to the surface of the product or when the biaxially oriented polypropylene film of the present invention is coated with an adhesive layer and used as a protective film, there are defects such as air biting May be more likely to occur. When the content is less than 0.1% by mass, the frequency of the formed protrusions becomes too low, which does not contribute to the improvement of slipperiness and the winding property may be lowered.

Although it is preferable to contain a high melting point resin in the surface layer of the biaxially oriented polypropylene film of the present invention, in order to make the projections formed on the film surface fine, blending conditions of the high melting point resin and the polypropylene resin, and It is very important to control the melt extrusion conditions during film formation.

The raw material used for the surface layer of the biaxially oriented polypropylene film of the present invention is a blend of a high melting point resin and a polypropylene resin, but a method of kneading in advance with a biaxial extruder to form a chip is preferred. In this case, the kneading temperature is preferably higher than the melting point of the high melting point resin from the viewpoint of dispersion uniformity, more preferably 10 ° C. or higher, and further preferably 20 ° C. or higher. When the kneading temperature is lower than the melting point of the high melting point resin, the dispersibility may be lowered and the protrusions may be coarse. The upper limit of the kneading temperature is not particularly defined, but if it is too high, thermal decomposition of the polypropylene resin may occur, and the upper limit is 280 ° C.

The extrusion temperature during melt extrusion of the biaxially oriented polypropylene film of the present invention is preferably not higher than the melting point of the high melting point resin. More preferably, it is 10 degrees C or less, and 20 degrees C or less is still more preferable. When melt extrusion is performed at a temperature equal to or higher than the melting point of the high-melting resin, the high-melting resin uniformly and finely dispersed in the polypropylene resin may be melted and coalesced, or may be elongated for a long time due to shear flow during extrusion. As a result, the projections on the film surface may become coarse. The lower limit of the melting temperature is not particularly defined, but if it is too low, an increase in the filtration pressure during extrusion or unmelted polypropylene resin may occur, and 200 ° C. is the lower limit.

The above-mentioned easy-sliding particles or the resin having a melting point of 180 ° C. or higher preferably contains at least one of them depending on the purpose and application, but may contain both.

Next, although the manufacturing method of the biaxially oriented polypropylene film of this invention is demonstrated, it is not necessarily limited to this.

First, 90 parts by mass of polypropylene raw material A and 10 parts by mass of 4-methyl-1-pentene polymer are put into a twin-screw extruder to produce a master raw material. The melt kneading temperature at this time is 230 to 280 ° C., more preferably 240 to 280 ° C., and further preferably 250 to 280 ° C. 20 parts by mass of the master raw material and 80 parts by mass of the polypropylene raw material A are dry blended and supplied to the single-screw extruder for layer A (surface layer (I)). Part by mass is supplied to a single-screw extruder for layer B (base layer (II)), and melt extrusion is performed at 200 to 260 ° C. Then, after removing foreign substances and modified polymer with a filter installed in the middle of the polymer tube, it is laminated with a multi-manifold type A layer / B layer / A layer composite T die and discharged onto a casting drum. A laminated unstretched sheet having a layer configuration of layer / B layer / A layer is obtained. At this time, the lamination thickness ratio is preferably 1/8/1 to 1/50/1. The surface temperature of the casting drum is preferably 10 to 40 ° C. from the viewpoint of transparency. Moreover, it does not matter as a 2 layer laminated structure of A layer / B layer.

At this time, it is preferable to set the lip temperature of the die to be 20 to 40 ° C. lower than the melt extrusion temperature, and more preferably 30 to 40 ° C. It has been found that by lowering the lip temperature, the shear stress of the molten polymer in contact with the inner wall of the die is increased, the orientation of the film surface layer is particularly increased, and the elastic modulus in the thickness direction is increased.

Any method can be used as an adhesion method to the casting drum, such as an electrostatic application method, an adhesion method using the surface tension of water, an air knife method, a press roll method, an underwater casting method, etc. In addition, an air knife method capable of controlling the surface roughness is preferable. The air temperature of the air knife is 0 to 50 ° C., preferably 0 to 30 ° C., and the blowing air speed is preferably 130 to 150 m / s. Further, it is preferable to appropriately adjust the position of the air knife so that air flows on the downstream side of the film formation so as not to cause vibration of the film.

In addition, after the film is brought into close contact with the casting drum, the non-casting drum surface of the film is further forcibly cooled to suppress the formation of β crystals on the non-casting drum surface, thereby improving the smoothness and transparency of the film. be able to. The cooling method of the non-casting drum surface may be any of air cooling, press roll method, underwater casting method, etc., but it is simple as equipment, easy to control surface roughness, and smooth. Air cooling with good air is preferable.

The obtained unstretched sheet is introduced into the longitudinal stretching step. In the longitudinal stretching step, first, an unstretched sheet is brought into contact with a plurality of metal rolls maintained at 120 ° C. or more and less than 150 ° C., preheated and heated to the stretching temperature, and 3 to 3 in the longitudinal direction between the rolls having a peripheral speed difference. After stretching 8 times, it is cooled to room temperature. At this time, the temperature of the hottest preheating roll (preheating temperature) is preferably 140 ° C. or higher, more preferably 142 ° C. or higher, and further preferably 145 ° C. or higher. By setting the temperature of the hottest preheating roll to 140 ° C. or higher, the elastic modulus in the thickness direction can be increased, which is preferable. The preheating temperature is preferably higher than the melting point of the polypropylene raw material B, more preferably 20 ° C. or higher, further preferably 40 ° C. or higher, and most preferably 60 ° C. or higher. By stretching at a temperature equal to or higher than the melting point of the polypropylene raw material B used for the inner layer, the stretching stress can be lowered and the tensile modulus of the film can be lowered. However, if it is 150 ° C. or higher, the film surface may be rough, and transparency may be lowered. On the other hand, if the draw ratio is less than 3, the surface of the film becomes rough and the transparency may be lowered. Further, at this time, it is preferable from the viewpoint of reducing the friction coefficient that the temperature of the roll having a high speed on the downstream side is 10 ° C. or more lower than the temperature of the upstream side roll among the rolls provided with the peripheral speed difference.

Next, the longitudinally uniaxially stretched film is guided to a tenter, the end of the film is gripped with a clip, and the film is horizontally stretched 7 to 13 times in the width direction at a temperature of 140 to 165 ° C. If the stretching temperature is low, the film may be broken or the transparency may be lowered. If the stretching temperature is too high, the orientation of the film is weak and the strength may be lowered. Further, when the magnification is high, the film may be broken, and when the magnification is low, the orientation of the film is weak and the strength may be lowered.

In the subsequent heat treatment and relaxation treatment process, the clip is heat-fixed at a temperature of 100 ° C. or more and less than 160 ° C. while being relaxed at a relaxation rate of 2 to 20% in the width direction while holding the tension in the width direction with the clip. The film is guided to the outside of the tenter through a cooling process at 80 to 100 ° C. while being held tightly, the clip at the end of the film is released, the film edge is slit in the winder process, and the film product roll is wound up.

The biaxially oriented polypropylene film obtained as described above can be used in various applications such as packaging films, surface protective films, process films, hygiene products, agricultural products, building products, and medical products. Since it is excellent in smoothness and quality, it can be preferably used as a process film such as a surface protective film and a process film for solution casting, and a release film. The process film for solution casting refers to a support when casting a polymer solution. It forms into a film by peeling from a process film through the solution film casted on the process film for solution casting, or a drying or washing process.

A release film refers to a film used for the purpose of preventing scratches and preventing contamination in the process of manufacturing and transferring optical films, adhesive films, semiconductors, electronic parts, and the like.

Next, an example in which the biaxially oriented polypropylene film of the present invention is used as a coating substrate for an adhesive film will be described.

The pressure-sensitive adhesive used for the pressure-sensitive adhesive layer is not particularly limited, and rubber, vinyl polymerization, condensation polymerization, thermosetting resin, silicone, and the like can be used. Among these, examples of the rubber-based pressure-sensitive adhesive include butadiene-styrene copolymer system, butadiene-acrylonitrile copolymer system, and isobutylene-isoprene copolymer system. Examples of the vinyl polymerization pressure-sensitive adhesive include acrylic, styrene, vinyl acetate-ethylene copolymer system, and vinyl chloride-vinyl acetate copolymer system. Examples of the condensation polymerization pressure-sensitive adhesive include polyester. Furthermore, examples of the thermosetting resin-based pressure-sensitive adhesive include epoxy resin-based and urethane resin-based adhesives.

Among these, acrylic adhesives are preferably used in consideration of excellent transparency, weather resistance, heat resistance, moist heat resistance, substrate adhesion, and the like. Specific examples of the acrylic adhesive include “SK Dyne” (registered trademark) 1310, 1435, SK Dyne 1811L, SK Dyne 1888, SK Dyne 2094, SK Dyne 2096, SK Dyne 2137, SK manufactured by Soken Chemical Co., Ltd. Dyne 3096, SK dyne 1852, and the like are preferable examples.

Moreover, it is preferable to use a curing agent together with the acrylic pressure-sensitive adhesive. Specific examples of the curing agent include, for example, in the case of isocyanate, toluene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylene diisocyanate, diphenylmethane-4 , 4'-diisocyanate, diphenylmethane-2-4'-diisocyanate, 3-methyldiphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4-4'-diisocyanate, dicyclohexylmethane-2-4'-diisocyanate And lysine isocyanate. The mixing ratio of the curing agent is 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the pressure-sensitive adhesive. If the amount is less than 0.1 parts by mass, curing of the pressure-sensitive adhesive layer may be insufficient in the drying furnace, and the film may be trimmed. If it exceeds 10 parts by mass, the excess curing agent may migrate to the substrate or gasify at a high temperature to cause contamination.

In addition, an antioxidant, an ultraviolet absorber, a silane coupling agent, a metal deactivator, and the like may be appropriately added to the acrylic pressure-sensitive adhesive depending on the material of the adherend (glass or functional film). .

In the pressure-sensitive adhesive film using the biaxially oriented polypropylene film of the present invention, the thickness d of the pressure-sensitive adhesive layer is preferably 1.0 μm or less. More preferably, it is 0.8 micrometer or less, More preferably, it is 0.6 micrometer or less, More preferably, it is 0.4 micrometer or less. If the thickness d of the pressure-sensitive adhesive layer exceeds 1.0 μm, the slipping property between the back surface of the base film and the surface of the pressure-sensitive adhesive layer may be deteriorated and winding may be difficult. Further, the back of the adhesive layer may occur. Backlining means that after the adhesive layer solution is applied to one side of the base film, it is dried and cured in a drying furnace, and the adhesive film of the present invention is wound into a roll without using a release film. Then, when unwinding an adhesive film at the time of use, the phenomenon which a part of adhesive layer transfers to the back surface of a base film is pointed out. When the thickness d of the pressure-sensitive adhesive layer exceeds 1.0 μm, drying of the pressure-sensitive adhesive layer in the drying furnace becomes insufficient, and there is a case where the film is clogged. In addition, when the adhesive layer is thick, the film of the present invention is bonded to a product, and when the volatile component from the adhesive layer becomes an obstacle to lowering the degree of reduced pressure, such as when used in a process that requires reduced pressure such as vapor deposition or sputtering. There is. A known technique can be used as the method for setting the thickness of the adhesive layer in the above range, and it can be controlled by adjusting the solid content concentration of the solution in the adhesive layer and adjusting the coating thickness in various coating methods. If the thickness of the adhesive layer is too thin, stable coating may be difficult, or the adhesive strength may be too low to adhere to the adherend, so about 0.1 μm is the lower limit.

The pressure-sensitive adhesive film using the biaxially oriented polypropylene film of the present invention preferably has a 180 ° C. peeling force of 1 N / 25 mm or less after being bonded to a glass plate. The peeling force is more preferably 0.5 N / 25 mm or less, further preferably 0.2 N / 25 mm or less, and still more preferably 0.05 N / 25 mm or less. If the peeling force exceeds 1 N / 25 mm, slipping between the back surface of the base film and the surface of the adhesive layer may be deteriorated, and winding may be difficult or betrayed. In order to set the peeling force within the above range, the composition and thickness of the adhesive layer are set within the ranges described below, and the raw material composition and film forming conditions of the film are set within the ranges described below, and the surface roughness of the base film is controlled. It is effective. If the peel force is less than 0.01 N / 25 mm, the adhesive film may be peeled off during transportation after being bonded to the adherend, so the lower limit is about 0.01 N / 25 mm.

Next, although the manufacturing method of an adhesion layer is demonstrated, it is not necessarily limited to this.

First, prepare a coating for the adhesive layer. The coating agent can be used by dissolving additives such as the above-mentioned adhesive and curing agent in a solvent. The solvent can be appropriately adjusted according to the drying temperature in the coater, the viscosity of the coating, and the like. Specific examples include methanol, ethanol, isopropyl alcohol, n-butanol, tert-butanol, ethylene glycol monomethyl ether, 1 At least one solvent selected from -methoxy-2-propanol, propylene glycol monomethyl ether, cyclohexanone, toluene, ethyl acetate, butyl acetate, isopropyl acetone, methyl ethyl ketone, methyl isobutyl ketone, diacetyl acetone, and acetyl acetone can be used.

The solid content concentration in the coating is appropriately selected depending on the viscosity of the coating and the thickness of the adhesive layer, but is preferably 5 to 20% by mass.

Next, the above-mentioned base film is conveyed to the coater, and the adhesive layer coating is applied. Here, the surface on which the adhesive layer is applied may be either surface of the base film, but the wettability with the coating agent may be improved in advance by pretreatment such as corona treatment on the coated surface. preferable. On the other hand, the back surface of the base film is preferably not subjected to pretreatment such as corona treatment in order to improve releasability. The coating method (coating method) is not particularly limited, and an existing coating method such as a metabar method, a doctor blade method, a gravure method, a die method, a knife method, a reverse method, or a dip method can be employed. However, as described above, the adhesive layer thickness is preferably 1.0 μm or less and a thin film, and the gravure method and the reverse method are preferable from the viewpoint of stably obtaining a thin coating layer.

After coating the adhesive for the adhesive layer on the base film, it is guided to a drying oven to remove the solvent in the coating to obtain an adhesive film. The drying temperature here is appropriately set depending on the heat resistance of the base film and the boiling point of the solvent, but is preferably 60 to 170 ° C. If the temperature is less than 60 ° C., the adhesive layer may not be sufficiently cured and may be trimmed. When it exceeds 170 degreeC, a base film may deform | transform and planarity may deteriorate. The drying time is preferably 15 to 60 seconds. If it is less than 15 seconds, curing of the pressure-sensitive adhesive layer may not proceed sufficiently, and the film may be backed up. Exceeding 60 seconds is not preferable because productivity decreases.

The pressure-sensitive adhesive film after drying can be wound with a winder without using a release film or the like to obtain a pressure-sensitive adhesive film roll. Since the adhesive film of the present invention has the above-described structure, the adhesive layer is sufficiently cured, and the sliding property between the back surface of the base film and the adhesive layer surface is good. Even if it is taken, there is no problem such as being backed out or wrinkling at the time of winding, and a high-quality adhesive film roll can be obtained. However, you may wind up using a release film as needed.

The adhesive film obtained as described above can be used in various applications such as packaging films, surface protective films, process films, sanitary products, agricultural products, building products, and medical products. Since it is excellent, it can be preferably used as a surface protective film and a process film.

An example in which the biaxially oriented polypropylene film of the present invention is used as a release film will be described taking a release film for an optical member as an example. The biaxially oriented polypropylene film of the present invention is unwound from a coater, coated with an adhesive on one side and dried at 80 to 100 ° C. to obtain an adhesive film. Then, an adhesive film can be bonded together and used in the film forming process and the inspection process of the optical member. Since the biaxially oriented polypropylene film of the present invention has a smooth surface, it can be preferably used as a release film for a member of a high-definition image display element with little surface irregularity transfer to an optical member.

An example in which the biaxially oriented polypropylene film of the present invention is used as a process film for forming a solution will be described. The biaxially oriented polypropylene film of the present invention is unwound from a coater, coated with a polymer solution and dried at 80 to 100 ° C., and then the solution film is peeled from the process film to completely remove the solvent. Until the solution is further dried. Since the biaxially oriented polypropylene film of the present invention has a smooth surface, it can be preferably used as a film of good quality with little surface irregularity transfer to a solution film.

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

(1) Film thickness It measured using the micro thickness meter (made by Anritsu). The film was sampled in a 10 cm square, arbitrarily measured at five points, and an average value was obtained.

(2) Elastic modulus (EIT) in the thickness direction measured by the nanoindentation method
For the measurement, a nanoindenter “ENT-2100” manufactured by Elionix Co., Ltd. was used, and the measurement was performed according to the method defined in ISO 14577 (2002). One drop of “Aron Alpha” (registered trademark) professional impact resistance manufactured by Toagosei Co., Ltd. is applied to the biaxially oriented polypropylene film, and the biaxially oriented polypropylene film is fixed to a dedicated sample fixing base via an instantaneous adhesive. Then, the measurement was performed using the surface layer side as the measurement surface. For the measurement, a triangular pyramid diamond indenter (Berkovich indenter) having a ridge angle of 115 ° was used. The measurement data was processed by “ENT-2100” dedicated analysis software (version 6.18), and the indentation elastic modulus EIT (GPa) was measured. The measurement was performed on each side of the film at n = 10, the average value was obtained, and the larger of the average values of the measured values on both sides was listed in the table.

Measurement mode: Load-unloading test Maximum load: 0.5 mN
Holding time when the maximum load is reached: 1 second Loading speed, unloading speed: 0.05 mN / sec.

(3) Tensile modulus of elasticity in the longitudinal (MD) direction and width (TD) direction The film was cut into a rectangle having a test direction length of 150 mm and a width direction length of 10 mm as a sample. Using a tensile tester (Orientec Tensilon AMF / RTA-100), the measurement is performed 5 times in an atmosphere of 23 ° C. and 65% RH according to the method defined in JIS K7161 (1994), and the average value is obtained. It was. However, the distance between the initial chucks was set to 50 mm, the tensile speed was set to 300 mm / min, and the point where the load passed 1 N after the start of the test was used as the origin of elongation.

(4) Maximum height roughness (Sz)
For the measurement, Ryoka System VertScan 2.0 R5300GL-Lite-AC was used, and the surface shape was obtained by correcting the surface of the photographic screen by polynomial fourth-order approximation with the attached analysis software. The measurement conditions are as follows. In the measurement, according to the method specified in ISO 25178, the maximum height roughness of both surfaces of the film was determined by n = 3, and the average value was adopted as Sz of each surface.

Manufacturer: Ryoka System Co., Ltd. Device name: VertScan 2.0 R5300GL-Lite-AC
Measurement conditions: CCD camera SONY HR-57 1/2 inch objective lens 5x
Intermediate lens 0.5x
Wavelength filter 530nm white
Measurement mode: Wave
Measurement software: VS-Measure Version5.5.1
Analysis software: VS-Viewer Version5.5.1
Measurement area: 1.252 × 0.939mm ^2.

(5) Haze of film Using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-5000), the haze value (%) at 23 ° C was measured three times according to JIS K7136 (2000). Average values were used.

(6) Coefficient of static friction μs
Using Toyo Tester Industry's friction measuring instrument, according to ASTM D1894, measure the initial rise resistance value when the MD direction is rubbed with one side and the other side of the film in contact with each other. The maximum value was defined as the coefficient of static friction μs. However, when the initial rise was large and the measurement value upper limit (5.0) was exceeded, measurement was impossible. Samples were rectangular with a width of 80 mm and a length of 200 mm, and 5 sets (10 sheets) were cut out. Measurement was performed 5 times, and an average value was obtained.

(7) Film quality evaluation In the examples, the film after longitudinal stretching was collected, and the film surface was observed on a 3 cm square film in a reflection mode and an observation magnification of 400 times using a differential interference microscope. At this time, when the LED light was applied from the side, it looked bright, and the foreign matter having the same color as the PP film was made into PP powder. The number of foreign matters having a size of 50 μm or more was counted, and evaluated according to the following criteria. The observation was carried out on the surface in contact with the casting drum. When the number of PP powders is 10 or less, there is little influence on the adherend, and it is suitably used as a release film, a solution film-forming process film, and an adhesive film.

A: The number of PP powders is 3 or less B: The number of PP powders is 4 to 10 C: The number of PP powders is 11 or more.

(8) Evaluation of transfer to adherend Biaxially oriented polypropylene film and “ZEONOR FILM” (registered trademark) made by Nippon Zeon Co., Ltd. having a thickness of 40 μm are sampled into a square having a width of 100 mm and a length of 100 mm to obtain a biaxially oriented polypropylene. The rough surface of the film and the “Zeonor film” are stacked so that they come into contact with each other, sandwiched between two acrylic plates (width 100 mm, length 100 mm), a load of 2 kg is applied, and the atmosphere is 24 ° C. under an atmosphere of 23 ° C. Let stand for hours. After 24 hours, the surface of the “ZEONOR film” (the surface on which the biaxially oriented polypropylene film was in contact) was visually observed and evaluated according to the following criteria.

A: It is clean and is equivalent to before applying a load. B: Weak unevenness is confirmed. C: Strong unevenness is confirmed.

Example 1
90 parts by mass of crystalline polypropylene (PP (a)) (manufactured by Prime Polymer Co., Ltd., TF850H, MFR: 2.9 g / 10 min, mesopentad fraction: 0.94, melting point: 164 ° C.), 4-methyl- 1-Pentene polymer (Mitsui Chemicals Co., Ltd., MX004) is fed from a measuring hopper to a twin screw extruder so that 10 parts by mass is mixed at this ratio, melt kneaded at 260 ° C., and strand It was discharged from the die in a solid shape, cooled and solidified in a water bath at 25 ° C., and cut into chips to obtain a polypropylene raw material (1) for the A layer.

20 parts by mass of the polypropylene raw material (1) and 80 parts by mass of the crystalline PP (a) as a polypropylene raw material for the surface layer (A) are dry-blended and supplied to a uniaxial melt extruder for the A layer, As polypropylene raw materials for the core layer (B), 90 parts by mass of polypropylene resin FSX20L8 (MFR = 2.0 g / 10 min, isotactic index (II) = 96%) manufactured by Sumitomo Chemical Co., Ltd. and “El Modu” manufactured by Idemitsu Kosan Co., Ltd. (L-MODU) (registered trademark) S901 (MFR 50 g / 10 min, melting point: 80 ° C.) and 10 parts by mass are dry-blended and supplied to a uniaxial melt extruder for the B layer, melting temperature 240 ° C. Then, melt extrusion is performed at a lip temperature of 200 ° C., and foreign matter is removed with a 10 μm cut sintered filter. Then, the feed block type A / B / A composite T-die is 1/28 / The laminated in a thickness ratio, discharged into a casting drum controlled surface temperature of 25 ° C., was brought into close contact with a casting drum by an air knife. Thereafter, the air on the non-cooled drum surface of the sheet on the casting drum was cooled by jetting compressed air at a temperature of 30 ° C. and a pressure of 0.3 MPa to obtain an unstretched sheet. Subsequently, the sheet was preheated to 147 ° C. using a ceramic roll, and stretched 4.0 times in the longitudinal direction of the film between rolls provided with a peripheral speed difference. At this time, among the rolls provided with the peripheral speed difference, the temperature of the upstream side roll was 145 ° C., and the temperature of the downstream side fast roll was 70 ° C. Next, the end part was introduced into a tenter type stretching machine by holding it with a clip, preheated at 170 ° C. for 3 seconds, stretched 8.0 times at 165 ° C., and relaxed by 10% in the width direction at 150 ° C. A heat treatment was performed, and then a cooling process at 100 ° C. was conducted to the outside of the tenter. A clip at the end of the film was released, and a film having a width of 800 mm was wound around the core. The winding tension at this time was 50 N / m. After storage for 48 hours in an atmosphere at 25 ° C., both ends 100 mm were slit to a width of 600 mm, wound on a core at 100 N / m, and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Example 2)
In Example 1, as a polypropylene raw material for the surface layer (A), 100 parts by mass of crystalline polypropylene (PP (a)) was supplied to a uniaxial melt extruder for the A layer, and the others were the same as in Example 1. Thus, a biaxially oriented polypropylene film having a thickness of 24 μm was obtained. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Example 3)
In Example 1, a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1 except that the thickness ratio during lamination was 1/38/1. The physical properties and evaluation results of the obtained film are shown in Table 1.

Example 4
In Example 1, a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1 except that the thickness ratio during lamination was 1/10/1. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Example 5)
In Example 1, the temperature of the casting drum was set to 35 ° C., the preheating temperature for longitudinal stretching was set to 142 ° C., and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Example 6)
In Example 1, the temperature of the casting drum was 40 ° C., the preheating temperature for longitudinal stretching was 140 ° C., and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1 except that. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Example 7)
In Example 1, 20 parts by mass of the polypropylene raw material (1) and 80 parts by mass of the crystalline PP (a) as a polypropylene raw material for the surface layer (A) were dry blended, and uniaxial melt extrusion for the A layer As a polypropylene raw material for the core layer (B), 90 parts by mass of Sumitomo Chemical polypropylene resin FSX20L8 (MFR = 2.0 g / 10 min, isotactic index (II) = 96%) and Sumitomo Chemical 8 parts by weight of “Tough Selenium” H3002 (MFR = 3.0 g / 10 min, melting point: 80 ° C.) is dry blended and supplied to a single-screw melt extruder for the B layer, melting temperature 240 ° C., lip temperature 200 Except that, melt extrusion was carried out at 0 ° C., and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as Example 1. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Comparative Example 1)
In Example 2, as a polypropylene raw material for the core layer (B), 100 parts by mass of crystalline polypropylene (PP (a)) was supplied to the single-layer melt extruder for the B layer (the same raw material for the surface layer and the core layer) Otherwise, a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 2. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Comparative Example 2)
In Example 1, 50 parts by mass of Sumitomo Chemical's polypropylene resin FSX20L8 and 50 parts by mass of “L-MODU” S901 made by Idemitsu Kosan Co., Ltd. were dry blended as the polypropylene raw material for the core layer (B). A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1 except that it was supplied to a uniaxial melt extruder for the B layer. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Comparative Example 3)
In Example 1, the thickness ratio at the time of lamination was 1/258/1, and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1 except that. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Comparative Example 4)
In Example 1, the thickness ratio at the time of lamination was set to 1 / 7.6 / 1, and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1 except that. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Comparative Example 5)
In Example 3, the lip temperature at the time of melt extrusion was 240 ° C., the preheating temperature for longitudinal stretching was 135 ° C., and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 3. The physical properties and evaluation results of the obtained film are shown in Table 1.

Claims (8)

1. The elastic modulus in the thickness direction at 23 ° C. of at least one surface measured by the nanoindentation method is 2.0 GPa or more, and the sum of the tensile elastic modulus in the MD direction and the TD direction at 23 ° C. is 6.6 GPa or less. Biaxially oriented polypropylene film.
2. The biaxially oriented polypropylene film according to claim 1, wherein the maximum height roughness Sz of the film is 1000 nm or less on both sides.
3. The biaxially oriented polypropylene film according to claim 1 or 2, wherein at least one surface has a maximum height roughness Sz1 of 300 nm or less.
4. The biaxially oriented polypropylene film according to any one of claims 1 to 3, having a static friction coefficient µs of 0.55 or less.
5. The biaxially oriented polypropylene film according to any one of claims 1 to 4, having a haze of 1% or less.
6. A release film using the biaxially oriented polypropylene film according to any one of claims 1 to 5.
7. A process film for forming a solution using the biaxially oriented polypropylene film according to any one of claims 1 to 5.
8. 6. An adhesive film comprising a biaxially oriented polypropylene film according to claim 1 provided with an adhesive layer.