JP2018127620A - Biaxially oriented polypropylene film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polypropylene film having excellent surface smoothness and transparency, and having excellent quality and handleability.SOLUTION: The present invention provides a biaxially oriented polypropylene film in which: an undulation value Wa of at least one side is 45 nm or less, and a thermal shrinkage in MD direction after heating at 85°C for 60 minutes is 0.3-2%.SELECTED DRAWING: None

Description

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

  Polypropylene films are excellent in transparency, mechanical properties, electrical properties, and the like, and are therefore used in various applications such as packaging applications, mold release applications, tape applications, cable wrapping and electrical applications including 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 flatness of the polypropylene film is poor, for example, when it is 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. .

  Therefore, attempts have been made to reduce the surface roughness of the film. For example, Patent Document 1 describes a biaxially oriented polypropylene film having a small surface roughness and excellent surface smoothness. Patent Document 2 describes a polypropylene film having excellent surface smoothness and low thermal shrinkage. Patent Document 3 describes an example of improving the surface smoothness of a surface protective film using an unstretched polyethylene film.

JP 2002-40667 A International Publication No. 2015/129851 JP 2014-101471 A

  Even if the surface roughness of the biaxially oriented polypropylene film is small, fine waviness is generated in the film, which is transferred, and the surface of the optical member may be distorted into a skin shape. It has been difficult to improve the quality by suppressing the generation of minute swells by the method disclosed in the above. An object of the present invention is to solve the above-described problems. That is, an object of the present invention is to provide a polypropylene film excellent in surface smoothness and quality, and excellent in transparency and handling properties.

  In order to solve the above-described problems and achieve the object, the biaxially oriented polypropylene film of the present invention has a waviness value Wa of at least one side of 45 nm or less and a thermal shrinkage in the MD direction of 0 minutes after 85 ° C. is 0. 3 to 2%.

  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 a waviness value Wa of at least one side of 45 nm or less. Wa is more preferably 35 nm or less, and still more preferably 30 nm or less. When Wa exceeds 45 nm, when the biaxially oriented polypropylene film of the present invention is peeled off after being bonded to a product of another material as a protective film or a cover film, the uneven shape may be transferred to the surface of the product. is there. From the viewpoint of suppressing the uneven shape, Wa is preferably as small as possible, but the lower limit is substantially about 5 nm. In addition, when the biaxially oriented polypropylene film of the present invention is bonded to a product of another material and then wound up in a roll shape, the back surface is also in contact with the product, so the waviness value Wa on both sides may be 45 nm or less. More preferably, both surfaces are 35 nm or less, and more preferably, both surfaces are 30 nm or less. In order to set Wa to the above range, the raw material composition of the film is set to a range described later, and the film forming conditions are set to a range described later. In particular, the range for setting heat setting, relaxation conditions, and winding conditions after biaxial stretching are described later. Is effective.

The biaxially oriented polypropylene film of the present invention has a thermal shrinkage in the MD direction of 0.3 to 2% after 60 minutes at 85 ° C. The thermal shrinkage rate in the MD direction is more preferably 0.3 to 1.7%, further preferably 0.5 to 1.5%, and further preferably 0.5 to 1.2%. If the thermal shrinkage rate in the MD direction exceeds 2%, for example, the film may be deformed and peeled off when passing through a drying process where heat is applied after bonding with another material as a protective film or cover film. Wrinkles may enter. In addition, when the environmental temperature rises when the film is bonded to the adherend film, wound into a roll, and stored, wrinkles or the like may occur in the roll due to the dimensional change of the film, and Wa may increase. On the other hand, even if the thermal contraction rate in the MD direction is less than 0.3%, Wa may increase. The reason is considered as follows. When the film is wound into a roll in the film forming step, a slight amount of air is caught between the films that are normally wound, and the film is wound. The biaxially oriented polypropylene film changes dimensions as the polymer molecular chain relaxes immediately after film formation. At this time, the roll shrinks to some extent in the MD direction, and the roll is properly wound and tightened with no film remaining. By fixing, a film having a small Wa can be obtained. When the thermal shrinkage rate in the MD direction is less than 0.3%, the roll tightness immediately after film formation is small, and the film is stored in an excess state, and as a result, Wa may increase. In order to make the thermal shrinkage rate within the above range, the raw material composition of the film is set in the range described later, the film forming conditions are set in the range described below, and the heat setting and relaxation conditions after biaxial stretching are set in the range described below. It is effective. Here, the heat shrinkage rate refers to a film with a width of 10 mm and a length of 200 mm (measurement direction) cut out in the width direction of the film. The distance between the marked lines was measured to obtain the test length (l ₀ ), and then the test piece was sandwiched between papers and taken out after heating for 60 minutes in an oven kept at 85 ° C. with no load, and cooled at room temperature. Thereafter, the dimension (l ₁ ) was measured with a universal projector and obtained by the following formula, and the average value of the five was taken as the heat shrinkage rate.

Thermal contraction rate = {(l ₀ −l ₁ ) / l ₀ } × 100 (%)
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.

  The biaxially oriented polypropylene film of the present invention preferably has a coefficient of static friction μs between one surface of the film and the other surface of 0.55 or less. More preferably, it is 0.53 or less, More preferably, it is 0.50 or less. When the static friction coefficient μs exceeds 0.55, Wa may increase because the film roll cannot be uniformly contracted when wound. Further, during the film forming process, the film surface may be scraped due to a slight speed difference between the transport roll and the film to generate PP powder, 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, the raw material composition of at least one surface layer (surface layer (I)) of the laminated structure is described later. It is preferable to be within the range.

  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, although the raw material of the biaxially oriented polypropylene film of this invention is demonstrated, it is not necessarily limited to this.

  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 reduce the thermal shrinkage rate. As the polypropylene raw material B, a polypropylene raw material having low crystallinity is used to reduce the tensile elastic modulus of the film. Is preferred.

  The polypropylene raw material A is preferably a polypropylene having a cold xylene soluble part (hereinafter referred to as CXS) of 4% by mass or less and a mesopentad fraction of 0.95 or more. If these are not satisfied, the film-forming stability may be inferior or the heat shrinkage rate may be increased.

  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 thermal shrinkage rate may increase. 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 with high stereoregularity in this way, there are a method of washing resin powder obtained with a solvent such as n-heptane, a method of selecting a catalyst and / or promoter, and a composition as appropriate. Preferably employed.

  Further, as the polypropylene raw material A, the melt flow rate (MFR) is more preferably 1 to 10 g / 10 min (230 ° C., 21.18 N load), particularly preferably 2 to 5 g / 10 min (230 ° C., 21.18 N). The range of (load) is preferable from the viewpoint of film forming properties. 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 a copolymer component or blend. 1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2- Examples include norbornene. 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.

  Next, 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-described 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 and the like can be used, but excellent transparency can be obtained with a small addition amount. Therefore, amorphous polypropylene and low stereoregular polypropylene are particularly preferable.

  As the polypropylene raw material B, the amorphous polypropylene preferably used 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 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 desirable.

  Examples of amorphous polypropylene-α-olefin copolymers using such 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 homopolymer of propylene and 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 polypropylene raw material of the present invention, various additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a slip agent, an antistatic agent, an antiblocking agent, a filler, a viscosity are included within the range not impairing the object of the present invention. An adjusting agent, an anti-coloring agent, etc. can also be included.

  Among these, the selection of the kind of antioxidant and the amount added 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 ones. For example, 1,3,5-trimethyl-2,4,6-, together with 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4). 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” 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. The more preferable content is 0.1 to 0.9% by mass, and particularly preferably 0.2 to 0.8% by mass.

  A crystal nucleating agent can be added to the polypropylene raw material of the present invention as long as it does not contradict the purpose of the present invention. As crystal nucleating agents, 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, since excessive addition of the above-mentioned different kind of nucleating agent may cause a decrease in stretchability or a decrease in transparency and strength due to void formation, the addition amount is usually 0.5% by mass or less, preferably 0.1%. It is preferable to set it as mass% or less, More preferably, it is 0.05 mass% or less.

  The biaxially oriented polypropylene film of the present invention is obtained by biaxially stretching using the raw materials described above. 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 said polypropylene raw material is demonstrated.

  The biaxially oriented polypropylene film of the present invention preferably has a laminated structure of at least two layers 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 the polypropylene raw material A. 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 orientation of the film is lowered and the tensile rigidity is lowered. May decrease.

  In the biaxially oriented polypropylene film of the present invention, at least one layer (base layer (II)) other than the surface layer (I) in the laminated structure preferably contains the polypropylene raw material B from the viewpoint of improving transparency. The mixing ratio of the polypropylene raw material A and the polypropylene raw material B is preferably 0: 100 to 95: 5 (mass ratio; the same applies hereinafter). More preferably, it is 0: 100-90: 10, More preferably, it is 0: 100-85: 15. If the mixing ratio of the polypropylene raw material B in the base layer (II) is less than 5, the transparency may deteriorate.

  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 0.2-1.5 micrometers, More preferably, it is 0.3-1.0 micrometer, More preferably, it is 0.3-0.8 micrometer. If the thickness d of the surface layer (I) exceeds 2.0 μm, the transparency may deteriorate. If the thickness is less than 0.1 μm, the lamination accuracy becomes unstable, and the 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 1-10%, More preferably, it is 1-5%. If the ratio of the surface layer (I) exceeds 15%, the transparency may deteriorate. If it is less than 1%, the lamination accuracy becomes unstable, and the 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, it is preferable that at least one surface layer of the biaxially oriented polypropylene film contains easy-slip particles or a resin having a melting point of 180 ° C. or more from the viewpoint of reducing the friction coefficient, and the melting point is 180 ° C. More preferably, the above resin is included.

  The slippery particles are not particularly limited as long as the effects of the present invention are not impaired, and for example, inorganic particles, organic particles, and the like 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 size 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 size is more preferably 0.15 μm or more and less than 0.9 μm, and further preferably 0.15 μm or more and less than 0.8 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.

  The biaxially oriented polypropylene film of the present invention preferably has a laminate structure of at least two layers and includes easy-slip particles on at least one surface layer. 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. 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 melting point of 180 ° C. or higher is present in the surface layer (I), it is melted and dispersed in polypropylene in the later-described melt extrusion process, and the above-described protrusions 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 to finely disperse in polypropylene in the melt extrusion process, and it is important that the affinity with polypropylene is high. From this point of view, the resin having a melting point of 180 ° C. or higher is preferably an olefin resin, but among 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 higher affinity with polypropylene resin than non-olefin resin, dispersibility can be improved. Examples of the olefin resin containing 4-methylpentene-1 unit include “TPX” (registered trademark) DX310, “TPX” DX231, and “TPX” MX004 manufactured by Mitsui Chemicals, Inc.

  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. More preferably, it is 0.1-4 mass%, More preferably, it is 0.1-3 mass%, More preferably, it is 0.1-2.5 mass%. When the content of the olefin resin comprising 4-methylpentene-1 unit is more than 5% by mass, the projections may be in a mountain range that is long 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.

  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 or application, but may contain both.

  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 biaxially oriented polypropylene film of the present invention preferably has an extrusion temperature at the time of melt extrusion 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 or application, but may contain both.

  Next, although the manufacturing method of the biaxially oriented polypropylene film of this invention is demonstrated taking an aspect as an example, 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 charged into a twin screw extruder to prepare a master raw material. The melt kneading temperature in this case is 230-280 degreeC, More preferably, it is 240-280 degreeC, More preferably, it is 250-280 degreeC. 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)). The mass part 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 casting drum preferably has a surface temperature of 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 a low temperature of 20 to 40 ° C. from the melt extrusion temperature, and more preferably 30 to 40 ° C. 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 enhanced, and when the film roll is tightened, the film surface is not easily deformed and effective in reducing Wa. I found out.

  As an adhesion method to the casting drum, any method of 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. may be used. The air knife method is preferable because it is good and the surface roughness can be controlled. 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 downstream 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 for 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 process, 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 longitudinally between two pairs of nip rolls having a peripheral speed difference. The film is stretched 3 to 8 times and then cooled to room temperature. When the stretching temperature is 150 ° C. or higher, the surface of the film becomes rough, and the 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. At this time, it is preferable that the temperature of the downstream-side fast roll among the two pairs of nip rolls provided with the circumferential speed difference is lower by 10 ° C. or more than the temperature of the upstream-side roll. If the temperature difference is less than 10 ° C., the thermal shrinkage in the MD direction after 60 minutes at 85 ° C. becomes too small, Wa increases, and when used as a base film or cover film, the surface of the product is uneven. It may be transferred. From the viewpoint described above, the temperature of the upstream roll is preferably 120 ° C. or higher and lower than 150 ° C., and the temperature of the downstream roll is more preferably 30 ° C. or higher and lower than 100 ° C.

  Next, the longitudinally uniaxially stretched film is guided to a tenter, the end of the film is held with a clip, and is stretched laterally by 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-set 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 a wide film roll is wound up. The winding tension at this time is preferably 10 to 100 N / m. If the tension is less than 10 N / m, the film may be wound, and if it exceeds 100 N / m, the film may be tightened due to dimensional shrinkage of the biaxially oriented polypropylene film immediately after film formation, and the flatness may be deteriorated.

  The obtained wide film roll is preferably aged for 1 to 72 hours in an atmosphere of 25 to 50 ° C. Then, according to a use, it slits to a predetermined width and winds up a product film roll. The winding tension at this time is preferably higher than the winding tension of the wide film roll, and more preferably 80 to 200 N / m. Aging under the above-mentioned predetermined conditions promotes dimensional shrinkage of the biaxially oriented polypropylene film immediately after film formation, and after the amount of dimensional change becomes small, it is slit and wound with the above tension, thereby reducing Wa. It becomes possible to obtain a film.

  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 surface protective film, a process film, and a release film.

  An example in which the biaxially oriented polypropylene film of the present invention is used as a cover film will be described taking a resist cover film as an example. The PET film subjected to the silicone release treatment is unwound as a process film, and a resist coating solution is applied onto the film. After drying the coating liquid at a predetermined temperature, the biaxially oriented polypropylene film of the present invention is bonded as a resist cover film, and a laminate of the PET film, resist layer, and biaxially oriented polypropylene film is wound up to obtain a product. . Since the biaxially oriented polypropylene film of the present invention has a smooth surface, the uneven transfer onto the resist surface is small, and it can be preferably used in applications where a high-definition exposure pattern is required.

  An example in which the biaxially oriented polypropylene film of the present invention is used as a process film will be described with reference to a process film for solution casting of an optical film. The biaxially oriented polypropylene film of the present invention is unwound from a coater, coated with an optical member solution and dried at 80 to 100 ° C., and then the optical film is peeled off from the process film to completely remove the solvent. And further dried to obtain an optical film. Since the biaxially oriented polypropylene film of the present invention has a smooth surface, it can be used preferably as a protective film for a high-quality optical film with little surface irregularity transfer to the optical film.

  Next, the example in the case of using the biaxially oriented polypropylene film of this invention as a coating base material for adhesive films is demonstrated.

  The pressure-sensitive adhesive used for the pressure-sensitive adhesive layer is not particularly limited, and a rubber system, a vinyl polymerization system, a condensation polymerization system, a thermosetting resin system, a silicone system, or 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, vinyl chloride-vinyl acetate copolymer system, and the like. 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 transparency, weather resistance, heat resistance, moist heat resistance, substrate adhesion, and the like. Specific examples of such acrylic adhesives include SK Dyne (registered trademark) 1310, 1435, SK Dyne 1811L, SK Dyne 1888, SK Dyne 2094, SK Dyne 2096, SK Dyne 2137, and SK Dyne 3096 manufactured by Soken Chemical Co., Ltd. SK dyne 1852 and the like are preferable examples.

  Further, it is preferable to use a curing agent together with the acrylic pressure-sensitive adhesive. As specific examples of the curing agent, 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). .

  The pressure-sensitive adhesive film using the biaxially oriented polypropylene film of the present invention preferably has a thickness d of the pressure-sensitive adhesive layer of 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, a coating for the adhesive layer is prepared. 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 depending on 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 substrate film described above is conveyed to the coater, and a coating agent for the adhesive layer 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 base film with the adhesive layer coating, 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.

  An adhesive film roll can be obtained by winding the dried adhesive film with a winder without using a release film or the like. 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 by 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) Swell value (Wa)
The measurement was performed using Ryoka System VertScan 2.0 R5300GL-Lite-AC, and the surface shape was obtained by correcting the surface of the captured image with polynomial fourth-order approximation using the attached analysis software. The measurement conditions are as follows. In accordance with the method defined in JIS B0601 (2001), the measurement was performed on both sides of the film at n = 3, and the average value was adopted as Wa of each side.
Manufacturer: Ryoka System Co., Ltd. Name: VertScan2.0 R5300GL-Lite-AC
Measurement conditions: CCD camera SONY HR-57 1/2 inch objective lens 5x minute 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 × 0.939 mm ² .

(3) Thermal shrinkage in MD direction For each film width direction, cut out 5 samples with a width of 10 mm and a length of 200 mm (measurement direction), and mark them as marks at 25 mm from both ends. The distance between the marked lines is measured with a projector to obtain the test length (l ₀ ). Next, the test piece is sandwiched between papers, taken out after heating for 60 minutes in an oven kept at 85 ° C. with zero load, cooled at room temperature, and the dimension (l ₁ ) is measured with a universal projector. It calculated | required by the type | formula and made the average value of 5 the heat shrinkage rate.

Thermal contraction rate = {(l ₀ −l ₁ ) / l ₀ } × 100 (%).

(4) 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.

(5) 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.

(6) Evaluation of transfer to adherend Sample “Zeonor film” (registered trademark) made by Nippon Zeon Co., Ltd. with a thickness of 40 μm was sampled into a square with a width of 100 mm and a length of 100 mm. The film was placed in contact with each other, sandwiched between two acrylic plates (width 100 mm, length 100 mm), applied with a load of 3 kg, and allowed to stand in an atmosphere of 23 ° C. for 24 hours. After 24 hours, the surface of the “ZEONOR film” (the surface on which the adhesive 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: Either transfer of weak yuzu skin or transfer of weak unevenness is confirmed. C: Transfer of weak yuzu skin and transfer of weak unevenness are confirmed. D: Strong Yuzu skin transfer and / or strong unevenness transfer is confirmed.

(7) Evaluation of transfer to adherend after heating Sample of an adhesive film and a 40 μm thick “ZEONOR FILM” (registered trademark) made by Nippon Zeon Co., Ltd. into a square with a width of 100 mm and a length of 100 mm, and the back surface of the adhesive film And “Zeonor film” are placed in contact with each other, sandwiched between two acrylic plates (width: 100 mm, length: 100 mm), applied with a load of 3 kg, and heated in an oven heated to 85 ° C. for 1 hour. did. Thereafter, the surface was removed from the oven, the load was removed, and after standing for 24 hours, the surface of “ZEONOR film” (the surface on which the adhesive 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: Either transfer of weak yuzu skin or transfer of weak unevenness is confirmed. C: Transfer of weak yuzu skin and transfer of weak unevenness are confirmed. D: Strong Yuzu skin transfer and / or strong unevenness transfer is confirmed.

Example 1
Crystalline polypropylene (manufactured by Prime Polymer Co., Ltd., TF850H, MFR: 2.9 g / 10 min, mesopentad fraction: 0.94) is supplied to a single screw melt extruder, melting temperature 240 ° C., lip temperature 200 ° C. The mixture was melt extruded and removed with a 60 μm cut sintered filter, then discharged onto a casting drum whose surface temperature was controlled at 30 ° C., and brought into close contact with the casting drum with an air knife. Thereafter, the uncooled drum surface of the sheet on the casting drum was cooled by injecting 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 145 ° C. using a ceramic roll, and stretched 4.2 times in the longitudinal direction of the film between rolls provided with a difference in peripheral speed. At this time, among the rolls provided with a difference in peripheral speed, the temperature of the upstream-side roll was 143 ° 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. However, the contact surface with the casting drum was the A surface and the opposite surface was the B surface.

(Example 2)
Crystalline polypropylene (PP (a)) (Prime Polymer Co., Ltd., TF850H, MFR: 2.9 g / 10 min, mesopentad fraction: 0.94) 90 parts by mass, 4-methyl-1-pentene polymer (Mitsui Chemicals Co., Ltd., MX004) The raw material is supplied from the weighing hopper to the twin screw extruder so that 10 parts by mass are mixed at this ratio, melt kneaded at 260 ° C., and discharged from the die in a strand shape. Then, it was cooled and solidified in a water bath at 25 ° C. and cut into chips to obtain a polypropylene raw material (1) for layer A.

  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 a polypropylene raw material for the core layer (B), 100 parts by mass of the above crystalline PP (a) is supplied to a single-axis melt extruder for the B layer, melt extruded at 210 ° C., and a 10 μm cut sintered filter After removing the foreign matter by using the feed block type A / B / A composite T-die, it is laminated at a thickness ratio of 1/22/1, discharged to a casting drum whose surface temperature is controlled at 25 ° C., and cast by an air knife. It was made to adhere to. Thereafter, the uncooled drum surface of the sheet on the casting drum was cooled by injecting compressed air at a temperature of 30 ° C. and a pressure of 0.3 MPa to obtain an unstretched sheet. A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1 below. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Example 3)
In Example 2, as a polypropylene raw material 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 Idemitsu Kosan Co., Ltd. 10 parts by mass of “L-MODU” (registered trademark) S901 (MFR: 50 g / 10 min, mesopentad fraction: 50%) manufactured by L-MODU is supplied to a single-screw melt extruder for the B 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.

Example 4
In Example 2, among the rolls provided with the peripheral speed difference of the longitudinal stretching, the temperature of the downstream roll is set to 125 ° C., and further, 5% is relaxed in the MD direction with the subsequent roll, 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.

(Example 5)
In Example 2, a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 3 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 6)
In Example 3, the temperature of the casting drum was 45 ° C., the heat treatment after biaxial stretching was 163 ° C., and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 3 except that. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Example 7)
In Example 2, 25 parts by mass of the polypropylene raw material (1) and 75 parts by mass of the crystalline PP (a) as a polypropylene raw material for the surface layer (A) were dry-blended to melt uniaxially for the A layer. Supply to extruder and dry blend 80 parts by mass of polypropylene resin FSX20L8 made by Sumitomo Chemical and 20 parts by mass of “El Modu” S901 made by Idemitsu Kosan Co., Ltd. as a polypropylene raw material for the core layer (B). Uniaxial melt extruder, melt extrusion at a melting temperature of 210 ° C and a lip temperature of 200 ° C, and a film having a width of 800 mm is wound around a core and stored in an atmosphere at 40 ° C for 60 hours. Later, slitting was performed to obtain a biaxially oriented polypropylene film. Otherwise, a biaxially oriented polypropylene film having a thickness of 22 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 1)
In Example 2, a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 2 except that the winding tension when winding a 800 mm wide film around the core was 120 N / m. The waviness value Wa was increased, and the transfer of yuzu skin was confirmed. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Comparative Example 2)
In Example 1, among the rolls provided with the peripheral speed difference of the longitudinal stretching, the temperature of the downstream roll is set to 140 ° C., and further, 10% relaxation is applied to the subsequent roll in the MD direction. A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1. The heat gain in the MD direction was small, the waviness value Wa was large, and the transfer of the yuzu skin was confirmed. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Comparative Example 3)
In Example 1, among the rolls provided with a circumferential speed difference in longitudinal stretching, the temperature of the upstream roll is set to 125 ° C., and the relaxation in the width direction at the tenter is set to 0% in a 100 ° C. atmosphere. Obtained a biaxially oriented polypropylene film having a thickness of 24 μm in the same manner as in Example 1. The physical properties and evaluation results of the obtained film are shown in Table 1.

(Comparative Example 4)
In Example 1, the lip temperature at the time of melt extrusion is set to 240 ° C., and the temperature of the downstream side roll is set to 138 ° C. among the rolls provided with the peripheral speed difference of the longitudinal stretching. 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.

(Comparative Example 5)
In Example 3, the draw ratio of longitudinal stretching was set to 4.8 times, the cooling temperature after biaxial stretching was set to 150 ° C., and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 3 except that. It was. The physical properties and evaluation results of the obtained film are shown in Table 1.

Claims (6)

A biaxially stretched polypropylene film having a waviness value Wa of at least one side of 45 nm or less and a thermal shrinkage of 0.3 to 2% in the MD direction after 85 ° C. for 60 minutes. The biaxially oriented polypropylene film according to claim 1, wherein the static friction coefficient μs is 0.55 or less. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the haze is 1% or less. A release film using the biaxially oriented polypropylene film according to claim 1. The process film for solution film forming using the biaxially oriented polypropylene film in any one of Claims 1-3. The adhesive film which provided the adhesive layer in the biaxially oriented polypropylene film in any one of Claims 1-3.