CN110225937B

CN110225937B - Biaxially oriented polypropylene film

Info

Publication number: CN110225937B
Application number: CN201880007838.XA
Authority: CN
Inventors: 久万琢也; 冈田一马; 山中康平; 大仓正寿
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2017-02-07
Filing date: 2018-02-07
Publication date: 2022-08-30
Anticipated expiration: 2038-02-07
Also published as: WO2018147334A1; CN110225937A; KR20190111902A; JPWO2018147334A1; KR102455834B1; JP7205611B2; JP2022044604A; JP7003920B2

Abstract

A biaxially oriented polypropylene film, wherein when the maximum height roughness of one surface of the biaxially oriented polypropylene film is expressed as Sz1 and the maximum height roughness of the other surface is expressed as Sz2 (wherein Sz1 ≦ Sz2), the Sz1 is 50 to 500nm, and at least one surface has protrusions with a length of 10 [ mu ] m or less and a height of 50 to 200nm at a frequency of 5 or more protrusions in an area of 100 [ mu ] m square. Provided is a polypropylene film having excellent surface smoothness and transparency, and having excellent sliding properties, handling properties, and winding properties.

Description

Biaxially oriented polypropylene film

Technical Field

The present invention relates to a polypropylene film having excellent surface smoothness and transparency and excellent slidability, handleability, and windability, and an adhesive film roll using the polypropylene film.

Background

Polypropylene films are excellent in transparency, mechanical properties, electrical properties, and the like, and therefore are used in various applications such as packaging applications, mold release applications, tape applications, cable drum closures, and electrical applications represented by capacitors. In particular, since the film has excellent releasability and mechanical properties on the surface, it is suitable as a release film or process film for various members such as plastic products, building materials and optical members.

The properties required of a release film are appropriately set according to the use application, but in recent years, a film and high quality are sometimes required for products to be protected because of miniaturization and high precision of equipment, and if the surface smoothness of a polypropylene film is poor, for example, when the polypropylene film is used as a release film for an optical member, the surface unevenness of the film is transferred to the optical member to affect the visibility of the product. Further, if the polypropylene film has poor transparency, it may be an obstacle in the process of inspection such as defect observation after the film is bonded to a product.

On the other hand, a film having excellent surface smoothness and transparency generally has poor sliding properties, and wrinkles may be generated or workability may be reduced in a conveying step, a winding step, a post-processing step, and the like during film formation.

As means for improving the sliding property of a polypropylene film, for example, patent documents 1 to 3 describe examples in which easy-to-slide particles are used for the film surface layer.

As an example in which the slipping-prone particles are not used, patent document 4 describes an example in which a vinyl resin is added to form irregularities on the surface.

Patent documents 5 to 8 describe examples in which an olefin resin containing 4-methyl-1-pentene units is used for the film surface layer.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2007-105893

Patent document 2: japanese patent laid-open No. 2005-138386

Patent document 3: japanese patent laid-open publication No. 11-048335

Patent document 4: japanese laid-open patent publication No. 2002-

Patent document 5: japanese patent laid-open publication No. 2015-107612

Patent document 6: japanese laid-open patent publication No. 2004-114419

Patent document 7: japanese patent laid-open No. 2008-189795

Patent document 8: japanese patent laid-open publication No. 2005-280125

Disclosure of Invention

Problems to be solved by the invention

In patent documents 1 to 3, however, since polypropylene has high releasability, it has low affinity with particles, and when it is used as a release film or a process film, particles may be detached from the product in a film forming process or a post-processing process. In addition, in patent documents 1 and 2, since the haze is high and the transparency is insufficient, the haze may not be used in the step of detecting defects. Patent document 3 has excellent transparency, but the particles used have a large particle size, and thus the surface smoothness may be insufficient.

In patent document 4, the surface smoothness of the back surface is insufficient, and the shape of the back surface may be transferred to the product when the product is wound while being bonded thereto. Further, the slip property is insufficient, and when the adhesive layer is applied and used as a protective film, defects such as air entrapment may easily occur when winding is difficult.

In patent documents 5 and 6, since the addition concentration of the olefin-based resin containing 4-methyl-1-pentene units is as high as 5% or more, protrusions on the film surface become coarse, and when the film is used as a protective film by coating an adhesive layer, defects such as air entrapment may easily occur when winding is difficult, and further, since the haze of the film is also high, defect detection may not be performed. In patent documents 7 and 8, although the addition concentration of the olefin resin containing 4-methyl-1 pentene units is low, the extrusion temperature and the casting drum temperature are high, and the protrusions on the film surface become coarse, and the shape of the back surface may be transferred to the product when the film is wound up in contact with the product.

The present invention addresses the above problems. That is, a polypropylene film excellent in surface smoothness and transparency, and excellent in slidability, handleability and windability is provided.

Means for solving the problems

In order to solve the above problems and achieve the object, a biaxially oriented polypropylene film of the present invention is characterized in that when the maximum height roughness of one surface of the biaxially oriented polypropylene film is Sz1 and the maximum height roughness of the other surface is Sz2 (wherein Sz1 ≦ Sz2), Sz1 is 50 to 500nm, and protrusions having a long side of 10 μm or less and a height of 50 to 200nm are present on at least one surface at a frequency of 5 or more protrusions in an area of 100 μm square.

ADVANTAGEOUS EFFECTS OF INVENTION

The biaxially oriented polypropylene film of the present invention is excellent in surface smoothness and transparency, and is excellent in sliding property, handling property and winding property, and therefore can be suitably used as an industrial film such as a base film for coating, a cover film or a protective film.

Detailed Description

When the maximum height roughness of one surface of the biaxially oriented polypropylene film is expressed as Sz1 and the maximum height roughness of the other surface is expressed as Sz2 (wherein Sz1 ≦ Sz2), Sz1 is 50 to 500 nm. The maximum height roughness means the sum of the maximum protrusion height and the maximum depression depth. The Sz1 is more preferably 50 to 400nm, still more preferably 100 to 300nm, and yet more preferably 120 to 280 nm. If Sz1 is less than 50nm, the film surface is too smooth, and the handling and winding properties may be reduced when the film formed is conveyed or wound. When Sz1 exceeds 500nm, unevenness may be transferred to the surface of the product when the film is used as a base film or a cover film. In order to set Sz1 within the above range, it is preferable to set the raw material composition of the film and the lamination of the film within the ranges described below, and to set the casting (step of forming a sheet of melt-extruded resin) conditions and longitudinal stretching conditions during film formation of the film within the ranges described below, so as to reduce the β -crystal content of the cast sheet. In addition, it is particularly preferable to control the dispersion of the resin by setting the blending conditions of the polypropylene resin and the other resin and the conditions at the time of melt extrusion to be within the ranges described later. However, in the case where the values of the maximum height roughness of both surfaces are equal, the maximum height roughness of the contact surface with the casting drum is written as Sz 1.

The biaxially oriented polypropylene film of the present invention has protrusions having a length of 10 μm or less and a height of 50 to 200nm on at least one surface at a frequency of 5 or more protrusions in an area of 100 μm square. This makes it possible to appropriately control air retention and air discharge when winding the film, and to wind the smooth film neatly without wrinkles. In particular, when a biaxially oriented polypropylene film is coated with an adhesive layer and the film roll is wound without a release film interposed therebetween, the coefficient of friction increases, and wrinkles tend to be introduced during winding. Since the back surface of the polypropylene film is in contact with the surface of the adhesive layer, the surface shape of the back surface greatly affects the winding properties, and it has been found that the protrusion density makes it possible to reduce the contact area between the surface of the adhesive layer and the back surface, to make the winding wrinkles less likely to be introduced, and to improve the winding properties. Although coarse protrusions such as fibrils and smooth portions are present on the surface of the polypropylene film, the coarse protrusions such as fibrils may have a large major axis and contact the adhesive layer surface, which may not contribute much to improvement of the winding properties and may cause defects such as air entrapment. It was found that the windability can be improved while maintaining smoothness by making the smooth portion have a large number of minute protrusions having a specific protrusion height and a specific major diameter, which can be brought into point contact with the adhesive layer. If the height of the protrusions is less than 50nm, the protrusions may not contribute to the improvement of the slidability and the winding property. On the other hand, if the height of the protrusions exceeds 200nm, air tends to enter between the protrusions during winding, and defects tend to occur. Further, the protrusions having longer sides of more than 10 μm contribute little to improvement of winding property, and may easily cause defects such as air entrapment. From the viewpoint of improving winding properties, the frequency of protrusions is more preferably 7 or more, still more preferably 10 or more, particularly preferably 50 or more, and most preferably 100 or more. If the protrusion frequency is less than 5, the slippage may not be improved and the windability may be reduced. In order to set the state of protrusion of the film surface within the above range, it is effective to set the composition of the film raw material, the adjustment method, the film lamination configuration, the casting (the step of forming a melt-extruded resin sheet) condition at the time of film formation, and the longitudinal stretching condition within the ranges described below.

When the maximum height roughness of one surface of the biaxially oriented polypropylene film of the present invention is expressed as Sz1 and the maximum height roughness of the other surface is expressed as Sz2 (wherein Sz1 ≦ Sz2), the maximum height roughness Sz2 is preferably 100 to 1000 nm. The Sz2 is more preferably 200 to 800nm, still more preferably 300 to 700nm, and still more preferably 500 to 700 nm. If Sz2 is less than 100nm, the film surface is too smooth, and the handling and winding properties may be reduced when the film formed is conveyed or wound. When Sz2 exceeds 1000nm, unevenness may be transferred to the surface of the product when the film is used as a base film or a cover film. In order to set Sz2 in the above range, it is preferable to set the raw material composition of the film and the lamination of the film in the ranges described below, and to set the casting (step of forming a melt-extruded resin into a sheet) condition and the longitudinal stretching condition in film formation in the ranges described below, so that the β -crystal content of the cast sheet is reduced.

The biaxially oriented polypropylene film of the present invention preferably has a value of Sz2/Sz1 of 1 to 3. More preferably 1.5 or more and 3 or less. If the value of Sz2/Sz1 exceeds 3, Sz1 is too small and the film surface is too smooth, and therefore, the handling property and winding property may be deteriorated when the film formed is conveyed or wound; sz2 is too large, and when it is used as a base film or a cover film, irregularities may be transferred to the surface of the product. In order to set the value of Sz2/Sz1 in the above range, it is preferable to set the raw material composition of the film and the lamination of the film in the ranges described below, and to set the casting (step of forming a melt-extruded resin into a sheet) condition and the longitudinal stretching condition in film formation in the ranges described below, so that the β crystal of the cast sheet is reduced.

The biaxially oriented polypropylene film of the present invention preferably has 20 fish eyes/m ² The following. The number of fish eyes is more preferably 10/m ² Hereinafter, more preferably 5 pieces/m ² The following. If the number of the fish eyes exceeds 20/m ² When used as a protective film or a base film for production of a product requiring high quality such as a display member, the yield may be lowered. In order to set the number of fish eyes in the above range, it is effective to configure the composition of the raw material, the adjustment method, and the lamination of the film in the ranges described later, and to reduce the amount of the resin used, which causes the fish eyes due to the thermal degradation of the additive components in the raw material. In addition, when the film is formed under the conditions described below, it is effective to melt the raw material and remove foreign matters by filtration before the sheet formation to reduce the resin retention.

The biaxially oriented polypropylene film of the present invention preferably has a haze of 1% or less. More preferably 0.9% or less, still more preferably 0.8% or less, and still more preferably 0.7% or less. If the haze exceeds 1%, the surface roughness of the film surface is large, and the surface shape may be transferred to an adherend. In addition, when the film is used as a protective film or a base film for manufacturing of a product requiring high quality such as a display member, defect detection may not be performed in a state of being bonded to the product. From the viewpoint of transparency, the lower the haze is, the lower the limit is about 0.05%. In order to set the haze to the above range, it is preferable to configure the raw material composition of the film and the lamination of the film to the ranges described below, to prevent deterioration of transparency due to particles and the like, and to set the casting conditions and longitudinal stretching conditions at the time of film formation to the ranges described below, to reduce β -crystals in the cast sheet. In addition, regardless of the concentration of the olefin-based resin containing 4-methyl-1-pentene units added, in order to improve the transparent smoothness of the film, it is particularly preferable to quench the temperature of the casting drum after extrusion to 30 ℃ or lower, and to finely disperse the olefin-based resin containing 4-methyl-1-pentene units in the polypropylene resin, knead the same in advance by a biaxial extruder and pelletize the same.

The biaxially oriented polypropylene film of the present invention preferably has a Young's modulus E in the longitudinal direction _MD Is 1GPa or more. If the Young's modulus in the longitudinal direction E _MD When the amount is less than 1GPa, the film may be stretched and broken due to the peeling tension or peeling traces may remain on the adherend when the film is peeled from the adherend while being used as a surface protective film. Further, the film may be stretched by the transport tension at the time of bonding. E _MD More preferably 1.2GPa or more, and still more preferably 1.4GPa or more. E _MD The higher the strength, the more preferable, but the upper limit is substantially about 10 GPa. To make E _MD The value of (b) is in the above range, and it is preferable that the raw material composition of the film is in the range described below, and the film is biaxially stretched at a high magnification to obtain a base film under the film forming conditions in the range described below.

The biaxially oriented polypropylene film of the present invention is preferably characterized by Young's modulus E in the width direction _TD Is 1GPa or more. If E is _TD If the amount is less than 1GPa, wrinkles tend to be formed in the film during transport, or when the film is wound into a roll after being bonded to an adherend and stored, wrinkles or the like may occur in the roll due to dimensional changes of the film. E _TD More preferably 1.5GPa or more, still more preferably 2.0GPa or more, and still more preferably 2.5GPa or more. E _TD The higher the strength, the more preferable, but the upper limit is substantially about 10 GPa. To make E _TD The value of (b) is in the above range, and it is preferable to obtain a base film by biaxially stretching the film at a high magnification under the conditions of film formation in the ranges described below.

In the present application, a direction parallel to the film forming direction of the film is referred to as a film forming direction or a longitudinal direction or an MD direction, and a direction orthogonal to the film forming direction within the film surface is referred to as a width direction or a TD direction.

The biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage of 1.0% or less after heat treatment at 110 ℃ in the width direction. More preferably 0.8% or less, still more preferably 0.5% or less, and still more preferably 0.3% or less. If the heat shrinkage ratio in the width direction exceeds 1.0%, the film may be deformed to peel off or wrinkle, for example, after being laminated as a protective film or a cover film to another material, in a drying step in which heat is applied, or the like. When the film is laminated to a film as an adherend and wound in a roll and stored, if the ambient temperature rises, wrinkles or the like may occur in the roll due to a dimensional change of the film. The lower limit of the heat shrinkage rate is not particularly limited, but the film may expand, and the lower limit is substantially about-2.0%. In order to set the heat shrinkage ratio to the above range, it is effective to set the raw material composition of the film to the range described later, and set the film forming conditions to the range described later, particularly the heat-set and relaxation conditions after biaxial stretching to the range described later. Here, the heat shrinkage ratio is a value obtained by cutting 5 test pieces having a width of 10mm and a length of 200mm (measurement direction) in the width direction of the film, marking the test pieces with marks at positions 25mm from both ends as a reticle, and measuring the distance between the test pieces with a universal projector as a test length (l) ₀ ) Next, the test piece was sandwiched between paper, heated in an oven kept at 110 ℃ for 60 minutes under a zero load, taken out, cooled at room temperature, and measured for dimensions (l) by a universal projector ₁ ) The average of 5 bars is expressed as the thermal shrinkage ratio, which is a value obtained by the following equation.

Heat shrinkage { (l) ₀ -l ₁ )/l ₀ }×100(％)。

The thickness of the biaxially oriented polypropylene film of the present invention is not particularly limited, and is preferably 5 μm or more and 100 μm or less, though it is appropriately adjusted depending on the application. If the thickness is less than 5 μm, handling may be difficult, and if it exceeds 100 μm, the amount of resin may increase to lower productivity. The biaxially oriented polypropylene film of the present invention has excellent strength (young's modulus) even when the thickness is reduced, and therefore can maintain the handling properties. In order to achieve such characteristics, the thickness is more preferably 5 μm or more and 40 μm or less, still more 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 stretching magnification, and the like within a range not to deteriorate other physical properties.

The biaxially oriented polypropylene film of the present invention may be a single layer film or a laminate film having 2 or more layers as long as the above properties are satisfied, but is preferably a laminate structure having at least 2 layers from the viewpoint of both transparency and slidability.

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

The biaxially oriented polypropylene film of the present invention is a film containing polypropylene as a main component. Here, the "main component" in the present invention means that the ratio of the specific component in the total components is 50 mass% or more, more preferably 90 mass% or more, further preferably 95 mass% or more, further preferably 96 mass% or more, further preferably 97 mass% or more, further preferably 98 mass% or more.

The polypropylene raw material used for the biaxially oriented polypropylene film of the present invention is not particularly limited as long as it satisfies the above physical properties, and from the viewpoint of strength and heat resistance, crystalline polypropylene (hereinafter, polypropylene raw material a) is preferably used.

Preferably, the polypropylene raw material a is preferably polypropylene having a cold xylene soluble portion (hereinafter CXS) of 4% by mass or less and a meso pentad fraction of 0.90 or more. If these conditions are not satisfied, the film-forming stability is poor, the film strength is reduced, or the dimensional stability and heat resistance are greatly reduced in some cases.

The cold xylene-soluble portion (CXS) is a polypropylene component dissolved in xylene when a sample is completely dissolved in xylene and precipitated at room temperature, and is considered to correspond to a component that is difficult to crystallize due to low stereoregularity, low molecular weight, and the like. If such a component is contained in a large amount in the resin, the thermal dimensional stability of the film may be poor. Accordingly, CXS is preferably 4% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. The lower the CXS, the more preferable, but about 0.1 mass% is the lower limit. In order to obtain polypropylene having such CXS, a method of improving catalytic activity in obtaining a resin, a method of washing the obtained resin with a solvent or a propylene monomer itself, a method of using metallocene PP, or the like can be used.

From the same viewpoint, the meso pentad fraction of the polypropylene raw material a is preferably 0.90 or more, and more preferably 0.94 or more. The meso pentad fraction is an index indicating the stereoregularity of the crystal phase of polypropylene as measured by a nuclear magnetic resonance method (NMR method), and is preferably higher as the numerical value is higher, because the higher the melting point is, the higher the dimensional stability at high temperature is. The upper limit of the meso pentad fraction is not particularly specified. In order to obtain such a resin having high stereoregularity, it is preferable to employ a method of washing the obtained resin powder with a solvent such as n-heptane, a method of appropriately selecting the catalyst and/or the co-catalyst, a method of selecting the composition, and the like.

Further, as the polypropylene raw material a, a polypropylene raw material having a Melt Flow Rate (MFR) of 1 to 10g/10 min (230 ℃, 21.18N load), more preferably 2 to 5g/10 min (230 ℃, 21.18N load), is more preferable from the viewpoint of film-forming properties and film strength. In order to make the Melt Flow Rate (MFR) the above value, a method of controlling the average molecular weight, molecular weight distribution, or the like is employed.

The polypropylene material A may contain a copolymerization component of other unsaturated hydrocarbon or the like, or may be blended with non-homopolypropylene, within a range not impairing the object of the present invention. Examples of such a copolymerization component and a monomer component constituting the blend include ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 5-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene, and the like. The copolymerization amount or blending amount is preferably less than 1 mol% in terms of copolymerization amount and 10 mass% in terms of blending amount, from the viewpoint of dielectric breakdown resistance and dimensional stability.

The biaxially oriented polypropylene film of the present invention may contain a branched polypropylene H in addition to the polypropylene raw material a in view of improvement in strength and improvement in dimensional stability. The branched polypropylene H herein is a polypropylene having a chain structure of 5 or less atoms per 10,000 carbon atoms. The branched structure may be present by ¹ The proton ratio in the H-NMR spectrum was confirmed. When contained, it is preferably 0.05 to 10% by mass, more preferably 0.5 to 8% by mass, and further preferably 1 to 5% by mass. By containing the branched polypropylene H, the spherulite size generated in the cooling (casting) step of the melt-extruded resin sheet can be controlled to be small, and a polypropylene film excellent in transparency, strength and surface smoothness can be obtained.

The branched polypropylene H preferably has a Melt Flow Rate (MFR) of 1 to 20g/10 min, more preferably 1 to 10g/10 min, from the viewpoint of film-forming properties. The melt tension is preferably in the range of 1 to 30cN, more preferably in the range of 2 to 20 cN.

The biaxially oriented polypropylene film of the present invention preferably has an ethylene content of 10% by mass or less in the polypropylene polymer constituting the film. More preferably 5% by mass or less, and still more preferably 3% by mass or less. The more the content of the ethylene component is, the more the crystallinity is reduced and the more the transparency is easily improved, but if the content of the ethylene component exceeds 10 mass%, the strength is lowered and the heat resistance is lowered and the heat shrinkage ratio is deteriorated in some cases. In addition, the resin is likely to deteriorate in the extrusion process, and fish eyes are likely to occur in the film. The content of the ethylene component may be 0%, but is preferably 0.1% or more in view of lowering crystallinity and easily improving transparency.

The biaxially oriented polypropylene film of the present invention preferably contains the polypropylene polymer in an amount of 95 mass% or more of the polymers constituting the film, from the viewpoint of transparency, heat resistance and strength. More preferably 96% by mass or more, still more preferably 97% by mass or more, and still more preferably 98% by mass or more.

The biaxially oriented polypropylene film of the present invention preferably contains a resin having a melting point of 180 ℃ or higher (hereinafter, high-melting resin). The melting point is more preferably 180 ℃ or higher and 240 ℃ or lower. By incorporating a high-melting resin into the surface layer of the film and forming the film under the conditions described later, the above-mentioned projections having a length of 10 μm or less and a height of 50 to 200nm can be formed, and the sliding properties can be improved. In such a case, a film composed of at least 2 layers of the surface layer (I) and the base layer (II) is preferable, and the surface layer (I) contains a high-melting resin. If a high-melting-point resin is present in the surface layer (I), the resin is melted and dispersed in polypropylene in a melt extrusion step described later, and the protrusions can be formed without deformation in a drawing step. In order to form the fine protrusions as described above, the fine protrusions need to be finely dispersed in polypropylene in the melt extrusion step, and it is important that the affinity with polypropylene is high. From this viewpoint, the high-melting-point resin is preferably an olefin-based resin, and among the olefin-based resins, an olefin-based resin containing a 4-methyl-1-pentene unit is particularly preferably used as a main component. The resin containing 4-methyl-1-pentene units has higher affinity with a polypropylene resin than a non-olefin resin, and therefore, dispersibility can be improved. Examples of the olefin-based resin containing a 4-methyl-1 pentene unit include "TPX" (registered trademark) DX310, "TPX" (registered trademark) DX231, "TPX" (registered trademark) MX004, and the like, manufactured by mitsui chemical co.

In the biaxially oriented polypropylene film of the present invention, the content of the olefin resin containing 4-methyl-1-pentene units in the resin composition of the surface layer (I) is preferably 0.1 to 4.5% by mass, more preferably 0.1 to 4% by mass, even more preferably 0.1 to 3% by mass, and even more preferably 0.1 to 2.5% by mass. When the content of the olefin-based resin containing 4-methyl-1-pentene units is more than 5% by mass, the protrusions may have a mountain shape with a long longitudinal direction, the long sides of the protrusions may exceed 10 μm, and the height of the protrusions may exceed 200nm, and when the biaxially oriented polypropylene film of the present invention is used as a base film or a cover film, irregularities may be transferred to the surface of the product, and when the biaxially oriented polypropylene film is coated with an adhesive layer and used as a protective film, defects such as air entrapment may be easily caused when winding is difficult. When the content is less than 0.1% by mass, the frequency of the formed projections is too low, which may not contribute to improvement of the slidability and reduce the windability.

The surface layer of the biaxially oriented polypropylene film of the present invention preferably contains a high-melting resin, but in order to form fine protrusions on the film surface, it is very important to control the blending conditions of the high-melting resin and the polypropylene resin and the melt extrusion conditions in film formation.

The raw material used for the surface layer of the biaxially oriented polypropylene film of the present invention is a mixture of a high-melting resin and a polypropylene resin, but it is preferable to knead the mixture in advance by a biaxial extruder and pelletize the mixture. From the viewpoint of dispersion uniformity, the kneading temperature in this case is preferably higher than the melting point of the high-melting resin, more preferably higher by 10 ℃ or more, and still more preferably higher by 20 ℃ or more. When the kneading temperature is lower than the melting point of the high-melting resin, the dispersibility may be lowered, and the protrusions may become coarse. The upper limit of the kneading temperature is not particularly limited, and when it is too high, thermal decomposition of the polypropylene resin may occur, and 280 ℃ is the upper limit.

The biaxially oriented polypropylene film of the present invention is preferably melt-extruded at an extrusion temperature of not more than the melting point of the high-melting resin. The melting point of the high-melting resin is more preferably 10 ℃ or lower, and still more preferably 20 ℃ or lower. When melt extrusion is performed at a temperature equal to or higher than the melting point of the high-melting-point resin, the high-melting-point resin uniformly and finely dispersed in the polypropylene resin may melt to coarsen the melt, or may be elongated by shear flow during extrusion. As a result, the protrusions on the film surface were coarse, and the long side thereof was more than 10 μm in some cases. The lower limit of the melting temperature is not particularly limited, but when it is too low, the filtration pressure during extrusion may increase, or a polypropylene resin may be unmelted, and the lower limit is 200 ℃.

The polypropylene raw material used for the biaxially oriented polypropylene film of the present invention may contain various additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a slipping agent, an antistatic agent, an anti-blocking agent, a filler, a viscosity modifier, an anti-coloring agent, and the like, in a range not to impair the object of the present invention.

Among these, selection of the type and amount of the antioxidant is important from the viewpoint of bleeding of the antioxidant. That is, as such an antioxidant, a phenol-based antioxidant having steric hindrance is preferable, and at least 1 of them is a high molecular weight type antioxidant having a molecular weight of 500 or more. Specific examples thereof include various types, and preferred examples thereof include 1,3, 5-trimethyl-2, 4, 6-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) benzene (for example, "Irganox" (registered trademark) 1330: molecular weight 775.2, manufactured by BASF corporation) or tetrakis [ methylene-3 (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ] methane (for example, "Irganox" (registered trademark) 1010: molecular weight 1177.7, manufactured by BASF corporation) in combination with 2, 6-di-tert-butyl-p-cresol (BHT: molecular weight 220.4). 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 the polypropylene raw material. If the antioxidant is too small, the polymer may be deteriorated in the extrusion step to cause coloration of the film, or the long-term heat resistance may be poor. If the amount of the antioxidant is too large, the transparency may be lowered by bleeding of the antioxidant. The content is more preferably 0.05 to 0.9% by mass, and particularly preferably 0.1 to 0.8% by mass.

The polypropylene raw material used for the biaxially oriented polypropylene film of the present invention may contain a crystal nucleating agent within a range not to impair the object of the present invention. As described above, the branched polypropylene (H) itself already has the effect of the alpha-crystal or beta-crystal nucleating agent, but examples thereof include other alpha-crystal nucleating agents (dibenzylidene sorbitols, sodium benzoate, etc.), beta-crystal nucleating agents (amide-based compounds such as potassium 1, 2-hydroxystearate, magnesium benzoate, N' -dicyclohexyl-2, 6-naphthamide, quinacridone-based compounds, etc.), and the like. Among these, the addition of an excessive amount of the other nucleating agent may cause a decrease in stretchability or a decrease in transparency or strength due to void formation, and therefore the amount added is preferably usually 0.5% by mass or less, preferably 0.1% by mass or less, and more preferably 0.05% by mass or less.

The biaxially oriented polypropylene film of the present invention preferably contains no organic particles or inorganic particles. Since polypropylene has low affinity with organic particles and inorganic particles, when it is used in a biaxially stretched film, voids may be generated in the stretching step to deteriorate transparency, or particles may fall off to contaminate the process and the product, and therefore, when it is used as a protective film or a base film for production of products requiring high quality such as display members, it is preferable that a lubricant such as organic particles or inorganic particles is not contained.

The biaxially oriented polypropylene film of the present invention is obtained by biaxial stretching using the above-mentioned raw materials. The biaxial stretching method can be obtained by a simultaneous biaxial stretching method by inflation, a simultaneous biaxial stretching method by a tenter, or a sequential biaxial stretching method by a tenter, but among them, a sequential biaxial stretching method by a tenter is preferably used from the viewpoint of controlling the film forming stability, the thickness uniformity, and the high rigidity and dimensional stability of the film.

The method for producing the biaxially oriented polypropylene film of the present invention will be described below by way of example, but the present invention is not necessarily limited thereto.

First, 90 parts by mass of a polypropylene raw material A and 10 parts by mass of a 4-methyl-1-pentene polymer are fed into a twin-screw extruder, and melt-kneaded at 230 to 280 ℃, more preferably 240 to 280 ℃, and still more preferably 250 to 280 ℃ to prepare a master batch. 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 a single-screw extruder for the a layer (surface layer (I)), and the polypropylene raw material a is supplied to a single-screw extruder for the B layer (base layer (II)), and melt-extruded at 200 to 260 ℃, more preferably 200 to 230 ℃, and still more preferably 200 to 220 ℃. Further, after foreign matters, denatured polymers, and the like were removed by a filter provided in the middle of the polymer tube, the polymer tube was laminated by a multi-manifold type a layer/B layer/a layer composite T die and discharged onto a casting drum, and a laminated unstretched sheet having a layer of a layer/B layer/a layer was obtained. In this case, the ratio of the lamination thickness is preferably 1/8/1 to 1/50/1. Further, the surface temperature of the casting drum is preferably 10 to 40 ℃ from the viewpoint of transparency. Further, the laminate may be composed of 2 layers of a layer a/B.

As the method of adhesion to the casting drum, any of an electrostatic application method, an adhesion method using the surface tension of water, a doctor blade method, a roll method, an underwater casting method, and the like can be used, but the doctor blade method which has good planarity and can control the surface roughness is preferable. The air temperature of the air knife is 0-50 ℃, preferably 0-30 ℃, and the blowing air speed is preferably 130-150 m/s. In order to prevent the membrane from vibrating, it is preferable to appropriately adjust the position of the air knife so that air flows downstream of the membrane.

Further, by forcibly cooling the non-casting drum surface of the film after the film is closely adhered to the casting drum, the generation of β -crystals on the non-casting drum surface can be suppressed, and the smoothness and transparency of the film can be improved. The cooling method of the non-casting drum surface may be any of air cooling using air, a roll method, an underwater casting method, and the like, but is preferably air cooling using air which is simple in equipment, easy in surface roughness control, and excellent in smoothness.

The obtained unstretched sheet is introduced into a longitudinal stretching step. In the longitudinal stretching step, the unstretched sheet is first brought into contact with a plurality of metal rolls maintained at 120 ℃ or higher and less than 150 ℃, preferably 140 ℃ or higher and less than 150 ℃, and more preferably 144 ℃ or higher and less than 149 ℃, preheated to a stretching temperature, stretched in the longitudinal direction between rolls provided with a peripheral speed difference by a factor of 3 to 8, and then cooled to room temperature. If the preheating temperature is less than 120 ℃ and the stretching temperature is 150 ℃ or more, the orientation of the film may be weakened and the strength may be reduced. If the stretch ratio is less than 3 times, the orientation of the film may be weakened and the strength may be reduced. In this case, it is preferable that the temperature of the roll having a high speed on the downstream side is lower than the temperature of the roll on the upstream side by 10 ℃ or more in the roll having the difference in peripheral speed. When the temperature difference is less than 10 ℃, the protrusions formed on the film surface may have a mountain shape with a long length direction, and the long sides of the protrusions formed exceed 10 μm, and when the film is used as a base film or a cover film, unevenness may be transferred to the surface of the product, and when the biaxially oriented polypropylene film of the present invention is coated with an adhesive layer and used as a protective film, defects such as air entrapment may be easily caused when winding is difficult. From the above viewpoint, the temperature of the upstream roller is preferably 120 ℃ or more and less than 150 ℃, and the temperature of the downstream roller is more preferably 30 ℃ or more and less than 100 ℃.

Then, the longitudinally uniaxially stretched film is guided to a tenter, the end of the film is held by clips, and the film is stretched in the transverse direction at a temperature of 140 to 165 ℃ by 7 to 13 times. If the stretching temperature is low, the film may be broken or the transparency may be lowered, and if the stretching temperature is too high, the orientation of the film may be weak and the strength may be lowered. Further, if the magnification is high, the film may break, and if the magnification is low, the film may be weakly oriented and the strength may be reduced.

And then, in the heat treatment and relaxation treatment step, while relaxing with a relaxation rate of 2 to 20% in the width direction in a state of being gripped by a gripper in the width direction, heat-setting is performed at a temperature of 100 ℃ or higher and less than 160 ℃, the film is guided to the outside of the tenter through a cooling step of 80 to 100 ℃ in a state of being gripped by a gripper in the width direction, the gripper at the end of the film is released, the edge of the film is slit in a winding step, and a film product roll is wound.

The biaxially oriented polypropylene film obtained in the above manner can be used in various applications such as packaging films, surface protection films, process films, sanitary products, agricultural products, construction products, medical products, and the like, but is particularly excellent in surface smoothness and therefore can be preferably used as a surface protection film, a process film, and a release film.

Next, an example of using the biaxially oriented polypropylene film of the present invention as a coated substrate (substrate film) for an adhesive film will be described.

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

Among them, acrylic adhesives are preferably used in view of excellent transparency, weather resistance, heat resistance, moist heat resistance, substrate adhesion, and the like. Specific examples of such acrylic adhesives include "SK ダイン" (registered trademark) 1310, 1435, SK ダイン 1811L, SK ダイン 1888, SK ダイン 2094, SK ダイン 2096, SK ダイン 2137, SK ダイン 3096, and SK ダイン 1852, which are manufactured by seikagaku corporation.

In addition, it is preferable to use a curing agent together with the acrylic adhesive. Specific examples of the curing agent include, for example, in the case of isocyanate, tolylene diisocyanate, 2, 4-tolylene diisocyanate, 2, 6-tolylene diisocyanate, 1, 3-xylylene diisocyanate, 1, 4-xylylene diisocyanate, diphenylmethane-4-4 '-diisocyanate, diphenylmethane-2-4' -diisocyanate, 3-methyldiphenylmethane diisocyanate, 1, 6-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, per 100 parts by mass of the adhesive. If the amount is less than 0.1 part by mass, the adhesive layer may be insufficiently cured in a drying oven, resulting in occurrence of back sticking. If the amount exceeds 10 parts by mass, the excess curing agent may migrate to the substrate or vaporize at high temperature, causing contamination.

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

The adhesive film using the biaxially oriented polypropylene film of the present invention preferably has an adhesive layer thickness d of 1.0 μm or less. More preferably 0.8 μm or less, still more preferably 0.6 μm or less, and still more preferably 400nm or less. If the thickness d of the adhesive layer exceeds 1.0. mu.m, the slip between the back surface of the base film and the surface of the adhesive layer may be deteriorated, and the winding may be difficult. In addition, the adhesive layer may be back-attached. The back-to-back is a phenomenon in which the solution of the adhesive layer is applied to one surface of the base film, and then dried and cured in a drying furnace, and the adhesive film of the present invention is wound into a roll without interposing a release film therebetween, and then a part of the adhesive layer moves to the back surface of the base film when the adhesive film is unwound during use. If the thickness d of the adhesive layer exceeds 1.0. mu.m, the adhesive layer may not be sufficiently dried in the drying furnace, and back sticking may occur. The method of adjusting the thickness of the adhesive layer to the above range can be controlled by using a known technique, and by adjusting the solid content concentration of the solution of the adhesive layer and the coating thickness in various coating methods. If the thickness of the adhesive layer is too small, stable coating may be difficult, or the adhesive strength may be too low to adhere to an adherend, so that the lower limit is about 0.1 μm.

The adhesive film using the biaxially oriented polypropylene film of the present invention preferably has a 180 ° peel force of 1N/25mm or less after being bonded to a glass plate. The peeling force is more preferably 0.5N/25mm or less, still more preferably 0.2N/25mm or less, and still more preferably 0.05N/25mm or less. If the peel force exceeds 1N/25mm, the slip property between the back surface of the base film and the surface of the adhesive layer may deteriorate, and the winding may become difficult, resulting in the occurrence of back sticking. In order to set the peeling force in the above range, it is effective to set the composition and thickness of the adhesive layer in the ranges described below, and to set the raw material composition of the film and the film forming conditions in the ranges described below, and to control the surface roughness of the base film. If the peel force is less than 0.01N/25mm, the adhesive film may peel off during conveyance after the adhesive film is bonded to an adherend, and therefore the lower limit is about 0.01N/25 mm.

The following describes a method for producing an adhesive layer, but the method is not necessarily limited thereto.

First, a coating agent for an adhesive layer is prepared. The coating agent can be used by dissolving the above-mentioned additives such as the adhesive and the curing agent in a solvent. The solvent may be used by being appropriately adjusted according to the drying temperature in the coater, the viscosity of the coating agent, and the like, and specific examples thereof include at least 1 or more solvents selected from methanol, ethanol, isopropanol, n-butanol, t-butanol, ethylene glycol monomethyl ether, 1-methoxy-2-propanol, propylene glycol monomethyl ether, cyclohexanone, toluene, ethyl acetate, butyl acetate, isopropyl acetone, methyl ethyl ketone, methyl isobutyl ketone, diacetone, and acetylacetone.

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

Next, the substrate film is conveyed to a coater to apply a coating agent for an adhesive layer. Here, the surface to which the adhesive layer is applied may be any surface of the base film, but it is preferable that the surface to be coated is pretreated with corona treatment or the like in advance to improve wettability with the coating agent. On the other hand, in order to improve the releasability, it is preferable that the back surface of the base film is not subjected to a pretreatment such as corona treatment. The coating method (coating method) is not particularly limited, and conventional coating methods such as a metal bar method, a doctor blade method, a gravure method, a die method, a knife method, a reverse method, and a dipping method can be used. However, as described above, the adhesive layer is a thin film having a thickness of 1.0 μm or less, and a gravure system or a reverse system is preferable from the viewpoint of stably obtaining a coating layer of the thin film.

After the coating agent for the adhesive layer is applied to the base film, the base film is introduced into a drying furnace to remove the solvent in the coating agent, thereby obtaining an adhesive film. The drying temperature here is appropriately set according to the heat resistance of the base film and the boiling point of the solvent, but is preferably 60 to 170 ℃. If the temperature is less than 60 ℃, the adhesive layer may not be sufficiently cured to cause a back coating. If the temperature exceeds 170 ℃, the substrate film may be deformed to deteriorate planarity. In addition, the drying time is preferably 15 to 60 seconds. If the time is less than 15 seconds, the adhesive layer may not be sufficiently cured, resulting in a back-contacted portion. If it exceeds 60 seconds, productivity is lowered, so that it is not preferable.

The dried adhesive film is wound up by a winder without bonding a release film or the like to the adhesive surface thereof, to obtain an adhesive film roll. With the adhesive film of the present invention having the above-described configuration, the adhesive layer is sufficiently cured, and the slip property between the back surface of the base film and the surface of the adhesive layer is good, so that there are no problems such as back sticking and wrinkling during winding even when the adhesive film is wound without interposing a release film therebetween, and a high-quality roll of adhesive film can be obtained.

The adhesive film of the present invention obtained as described above can be used in various applications such as packaging films, surface protection films, process films, sanitary products, agricultural products, construction products, medical products, and the like, but is particularly excellent in surface smoothness and therefore can be preferably used as a surface protection film or a process film.

Examples

The present invention will be described in detail below with reference to examples. The properties were measured and evaluated by the following methods.

(1) Thickness of film

The measurement was carried out using a micro thickness meter (manufactured by アンリツ Co.). A10 cm square film was sampled, and 5-point measurement was arbitrarily carried out to obtain an average value.

(2) Thickness of adhesive layer

The film thickness was measured using a "film thickness measuring System" model F20 manufactured by フィルメトリクス K.K. A10 cm square film was sampled, and 15 spots were arbitrarily measured to obtain an average value.

(3) Maximum height roughness (Sz)

The measurement was carried out using システム VertScan2.0R5300GL-Lite-AC (Kabushiki Kaisha), and the surface shape was determined by surface correction of the captured image by polynomial 4-time fitting using attached analysis software. The measurement conditions are as follows. The measurement was performed with n being 3 for each surface of the film, and the average value was used as Sz for each surface.

The manufacturer: trapation システム, Kabushiki Kaisha

Device name: VertScan2.0R5300GL-Lite-AC

The measurement conditions were as follows: CCD camera SONY HR-571/2 inch

An objective lens: 5x

A middle 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: 1.252mm by 0.939 mm.

(4) Number of surface protrusions

The measurement was performed in 10 fields using an Atomic Force Microscope (AFM) at a changing position with respect to a film surface (rough surface) having a high value of the maximum height roughness Sz of the biaxially oriented polypropylene film. In the sample placement, the sample is placed on the piezoelectric element so that the direction perpendicular to the scanning direction of the cantilever (Y-axis direction) is the longitudinal direction of the sample film (so-called longitudinal direction, direction in which the film moves in the film manufacturing process), and the measurement is performed. The obtained images were subjected to the Roughhness Analysis of the Off-Line function to determine the height of the projections in each image, and the number of projections having a major axis of 10 μm or less and a projection height of 50 to 200nm was counted. The above operation was carried out with n being 12, and the average value (the number of projections in a square of 50 μm) was multiplied by 4 to obtain the number of projections per 100 μm square. In addition, regarding the major axis, with respect to the projection having the projection height described above, a sectional view is shown along the longitudinal direction of the projection, and the distance between 2 points where the sectional view curve intersects with the line of height 0nm as the average height line is read.

A measuring device: nanoscope (R) IIIa AFM

(manufactured by Digital Instruments Co., Ltd.)

Cantilever: silicon single crystal

Scanning mode: tapping mode

Scanning range: 50 μm

Scanning speed: 0.7978Hz

Automatic smoothing process (Flatten Auto): and 3, grade.

(5) Haze of film

The film was measured for haze value (%) at 23 ℃ 3 times using a haze meter (NDH-5000, manufactured by Nippon Denshoku industries Co., Ltd.) according to JIS K7136(2000), and the average value was used.

(6) Number of fish eyes

The film cut out into a4 plate was placed on black paper, and portions with a low degree of light transmission were visually marked under a fluorescent lamp. These portions were observed with an optical microscope, and the number of fish eyes was counted by using the portions having a maximum length of 50 μm or more as fish eyes. The A4 sample was used for evaluation in 8 copies, each 1m square.

(7) Evaluation of winding Property

An acrylic adhesive (SK ダイン (registered trademark) 1310, manufactured by seiko chemical corporation) was diluted with ethyl acetate, toluene, and Methyl Ethyl Ketone (MEK) on one surface of a film surface (smooth surface) having a low value of the maximum height roughness Sz of the biaxially oriented polypropylene film, 2.0 parts by mass of a coating agent containing a curing agent (コロネート D-90, manufactured by japanese ポリウレタン corporation) was mixed with 100 parts by mass of a solid content of the adhesive, the mixture was coated with a gravure coater, dried in an oven at 80 ℃ for 30 seconds, and an adhesive film having an adhesive layer thickness of 300nm was directly wound (without a release film interposed) at 2,000m to prepare an adhesive film roll, which was evaluated by the following criteria.

A: no wrinkles, air entrapment, etc. during winding of the film roll, and good appearance

B: small wrinkles, air entrapment were observed in the winding but were eliminated if the winding was continued

C: wrinkles and air stagnation occur, and winding is difficult.

(8) Evaluation of transfer to adherend

A square biaxially oriented polypropylene film having a width of 100mm and a length of 100mm and "ゼオノアフィルム" (registered trademark) of Japanese ゼオン K.K., having a thickness of 40 μm were sampled, and the biaxially oriented polypropylene film was sandwiched so that the rough surface thereof was in contact with "ゼオノアフィルム", and the film was held between 2 acrylic plates (having a width of 100mm and a length of 100mm), subjected to a load of 2kg, and allowed to stand at 23 ℃ for 24 hours. After 24 hours, the surface of "ゼオノアフィルム" (the surface to which the biaxially oriented polypropylene film is in contact) was visually observed and evaluated by the following criteria.

A: neat, equal to before loading

B: weak unevenness was confirmed

C: strong unevenness was confirmed.

(example 1)

Crystalline polypropylene (PP (プライムポリマー, manufactured by TOKIDA CO., LTD., TF850H, MFR: 2.9g/10 min, meso pentad fraction: 0.94)90 parts by mass and 4-methyl-1-pentene polymer (MX 004, melting point: 230 ℃ C.) 10 parts by mass were mixed at the above ratio, and supplied to a biaxial extruder from a measuring hopper, melt-kneaded at 260 ℃ to discharge the mixture in the form of strands from a die, cooled and solidified in a 25 ℃ water tank, and cut into a sheet to obtain a polypropylene raw material (1) for layer A.

20 parts by mass of the polypropylene raw material (1) as a polypropylene raw material for the surface layer (a) and 80 parts by mass of the crystalline pp (a) were dry-blended and supplied to a uniaxial melt extruder for the a layer, 100 parts by mass of the crystalline pp (a) as a polypropylene raw material for the core layer (B) was supplied to a uniaxial melt extruder for the B layer, melt-extruded at 220 ℃, and foreign matter was removed by a sintered filter with a 20 μm cut-off, and then laminated at a thickness ratio of 1/22/1 by an a/B/a composite T-die of a feedblock type, discharged to a casting drum with a surface temperature controlled to 25 ℃, and adhered to the casting drum by an air knife. Then, the non-cooled drum surface of the sheet on which the compressed air having a temperature of 30 ℃ and a pressure of 0.3MPa was blown was cooled to obtain an unstretched sheet. Subsequently, the sheet was preheated to 145 ℃ using a ceramic roll, and was stretched 4.2 times in the longitudinal direction of the film between rolls having a difference in peripheral speed. In this case, the temperature of the upstream roller is 140 ℃ and the temperature of the downstream roller having the higher speed is 70 ℃ in the rollers having the peripheral speed difference. Then, the film was held by clips at the ends and introduced into a tenter type stretching machine, preheated at 170 ℃ for 3 seconds, stretched 8.0-fold at 165 ℃, heat-treated at 150 ℃ while giving 10% relaxation in the width direction, and then subjected to a cooling step at 100 ℃ to be guided to the outside of the tenter, the clips at the ends of the film were released, and the film was wound around a core, thereby obtaining a biaxially oriented polypropylene film having a thickness of 24 μm. The physical properties and evaluation results of the obtained film are shown in table 1.

(example 2)

A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in example 1, except that 40 parts by mass of the polypropylene raw material (1) and 60 parts by mass of the crystalline pp (a) were dry-blended and supplied to the uniaxial melt extruder for the a layer in example 1. The physical properties and evaluation results of the obtained film are shown in table 1.

(example 3)

A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in example 1, except that 10 parts by mass of the polypropylene raw material (1) and 90 parts by mass of the crystalline pp (a) were dry-blended and supplied to the uniaxial melt extruder for the a layer in example 1. The physical properties and evaluation results of the obtained film are shown in table 1.

(example 4)

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 temperature of the downstream side roll was set to 125 ℃ in the roll provided with the peripheral speed difference in longitudinal stretching. The physical properties and evaluation results of the obtained film are shown in table 1.

(example 5)

A biaxially oriented polypropylene film having a thickness of 6 μm was obtained in the same manner as in example 1, except that in example 1, the screw rotation speed of the uniaxial melt extruder for the a layer and the screw rotation speed of the uniaxial melt extruder for the B layer were decreased to set the final thickness of the film to 6 μm, and the temperature of the casting drum to 20 ℃. The physical properties and evaluation results of the obtained film are shown in table 1.

(example 6)

A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in example 1, except that the temperature of the casting drum was set to 35 ℃ and the temperature of the upstream roll was set to 143 ℃ in the roll provided with the circumferential speed difference of the longitudinal stretching in example 1. The physical properties and evaluation results of the obtained film are shown in table 1.

(example 7)

A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in example 1, except that in example 1, 20 parts by mass of the polypropylene raw material (1) as the polypropylene raw material for the surface layer (a) was dry-blended with 40 parts by mass of the crystalline PP (a) and 40 parts by mass of the self-recovered PP raw material, and the blend was supplied to a uniaxial melt extruder for the a layer, and that as the polypropylene raw material for the core layer (B), 100 parts by mass of the crystalline PP (a) was supplied to a uniaxial melt extruder for the B layer, and the melt extrusion was performed at 220 ℃. The physical properties and evaluation results of the obtained film are shown in table 1. In this case, the self-recovered PP raw material means a raw material in which a loss portion generated in the production of the film of example 1 was recycled.

(example 8)

In the evaluation of the winding properties of the film of example 1, an adhesive film was collected with the thickness of the adhesive layer being 1.2 μm, and a 2,000m winding was carried out as it is (without a release film interposed) to collect an adhesive film roll. The physical properties and evaluation results of the obtained film are shown in table 1. The slip property between the back surface of the base film and the surface of the adhesive layer was poor, and wrinkles were generated.

Comparative 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 100 parts by mass of the polypropylene raw material (1) was used as the raw material supplied to the uniaxial melt extruder for the a layer in example 1. No protrusion was observed on the film surface, and the winding property evaluation was deteriorated. The physical properties and evaluation results of the obtained film are shown in table 1.

Comparative example 2

A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in example 1, except that 50 parts by mass of the polypropylene raw material (1) and 50 parts by mass of the crystalline pp (a) were dry-blended and supplied to the raw material supplied to the uniaxial melt extruder for the a layer in example 1. The protrusions on the film surface became a shape of a mountain-like shape with a thickness of more than 10 μm in the MD direction, and the winding property evaluation was deteriorated. The physical properties and evaluation results of the obtained film are shown in table 1.

Comparative example 3

A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in example 1, except that 2 parts by mass of a 4-methyl-1-pentene polymer (MX 004 manufactured by mitsui chemical) and 98 parts by mass of the crystalline pp (a) were dry-blended with the raw material supplied to the uniaxial melt extruder for the a layer in example 1. The protrusions on the film surface became a shape of a mountain-like shape with a thickness of more than 10 μm in the MD direction, and the winding property evaluation was deteriorated. The physical properties and evaluation results of the obtained film are shown in table 1.

Comparative example 4

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 temperature of the downstream roll was set to 140 ℃. The protrusions on the film surface became a shape of a mountain-like shape with a thickness of more than 10 μm in the MD direction, and the winding property evaluation was deteriorated. The physical properties and evaluation results of the obtained film are shown in table 1.

Comparative example 5

A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in example 1, except that the temperature of the casting drum was set to 45 ℃ and the temperature of the roller on the upstream side of the longitudinal stretching was set to 145 ℃. The film surface was rough and the transfer evaluation was deteriorated. The physical properties and evaluation results of the obtained film are shown in table 1.

Comparative example 6

A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in example 1, except that melt extrusion was performed at 250 ℃ in the film formation in example 1. The protrusions on the film surface became a shape of a mountain-like shape with a thickness of more than 10 μm in the MD direction, and the winding property evaluation was deteriorated. The physical properties and evaluation results of the obtained film are shown in table 1.

Comparative example 7

In example 1, 90 parts by mass of crystalline polypropylene (PP (a) (manufactured by プライムポリマー, TF850H, MFR: 2.9g/10 min, meso pentad fraction: 0.94) and 10 parts by mass of 4-methyl-1-pentene polymer (MX 004, melting point: 230 ℃ C.) were mixed at the above ratio and fed from a measuring hopper to a biaxial extruder, and melt-kneaded at 220 ℃ and discharged from a die in the form of a strand, and the mixture was cooled and solidified in a 25 ℃ water tank, and cut into a sheet to obtain a polypropylene raw material (1) for layer A. Except for this, a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in example 1. The protrusions on the film surface became a shape of a mountain-like shape with a thickness of more than 10 μm in the MD direction, and the winding property evaluation was deteriorated. The physical properties and evaluation results of the obtained film are shown in table 1.

[ Table 1]

Claims

1. A biaxially oriented polypropylene film, wherein when the maximum height roughness of one surface of the biaxially oriented polypropylene film is expressed as Sz1 and the maximum height roughness of the other surface is expressed as Sz2, Sz1 is ≦ Sz2, Sz1 is 50 to 500nm,

sz2/Sz1 is 3 or less, and at least one surface has 5 or more protrusions with a frequency of 100 μm square, wherein the protrusions have a length of 10 μm or less and a height of 50 to 200nm,

the biaxially oriented polypropylene film is a film comprising at least 2 layers of a surface layer I and a base layer II, and the content of the olefin resin containing 4-methyl-1-pentene units in the resin composition of the surface layer I is 0.1 to 4.5% by mass.

2. The biaxially oriented polypropylene film according to claim 1, wherein the maximum height roughness Sz2 is 100 to 1000 nm.

3. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the number of fish eyes is 20/m ² The following.

4. The biaxially oriented polypropylene film according to claim 1 or 2, having a haze of 1% or less.

5. The biaxially oriented polypropylene film according to claim 1 or 2, which is used as a coated substrate for adhesive films.

6. An adhesive film comprising the biaxially oriented polypropylene film according to any one of claims 1 to 5 and an adhesive layer provided on at least one surface of the film.

7. The adhesive film according to claim 6, wherein the adhesive layer has a thickness of 1.0 μm or less.

8. A film roll obtained by winding the adhesive film according to claim 6 or 7 without a release film interposed therebetween.