JP7235151B2 - biaxially oriented polypropylene film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polypropylene film excellent in surface smoothness and transparency, and excellent in quality and handleability.

Polypropylene films are excellent in transparency, mechanical properties, electrical properties, etc., and are used in various applications such as packaging, release, tape, cable wrapping, and electrical applications such as capacitors. In particular, because of its 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 of the release film are appropriately set according to the intended use, but with the recent miniaturization and high precision of devices, there are cases where thin film and high quality are required for the products to be protected. If the quality such as flatness of the polypropylene film is poor, for example, when it is used as a release film for optical members, the surface unevenness of the film may be transferred to the optical member and affect the visibility of the product. .

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

Japanese Unexamined Patent Application Publication No. 2002-40667 WO2015/129851 JP 2014-101471 A

Even if the surface roughness of the biaxially oriented polypropylene film is small, the film may have minute undulations, which may be transferred and cause the surface of the optical member to become rough like an orange peel. It was difficult to suppress the occurrence of minute waviness and improve the quality by the method disclosed in . An object of the present invention is to solve the above problems. That is, the object is to provide a polypropylene film which is excellent in surface smoothness, quality, transparency and handleability.

In order to solve the above-mentioned 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 heat shrinkage rate of 0 in the MD direction after 60 minutes at 85 ° C. .3 to 2%.

The biaxially oriented polypropylene film of the present invention has excellent surface smoothness and transparency, and is excellent in quality and handling properties, so 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, 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 laminated with a product made of another material as a protective film or cover film, the uneven shape may be transferred to the surface of the product. be. Although Wa is preferably as small as possible from the viewpoint of suppressing unevenness, the practical lower limit is about 5 nm. In addition, when the biaxially oriented polypropylene film of the present invention is bonded to a product made of another material and then wound into a roll, etc., the back surface also comes into contact with the product, so the waviness value Wa of both surfaces should be 45 nm or less. It is preferably 35 nm or less on both sides, more preferably 30 nm or less on both sides. In order to make Wa within the above range, the raw material composition of the film is set to the range described later, the film forming conditions are set to the range described later, and in particular the heat setting, relaxation conditions, and winding conditions after biaxial stretching are set to the ranges described later. It is effective to

The biaxially oriented polypropylene film of the present invention has a heat shrinkage of 0.3 to 2% in the MD direction after 60 minutes at 85°C. The heat shrinkage rate in the MD direction is more preferably 0.3 to 1.7%, still more preferably 0.5 to 1.5%, still more preferably 0.5 to 1.2%. If the heat shrinkage rate in the MD direction exceeds 2%, for example, after bonding with other materials as a protective film or cover film, the film may be deformed and peeled off when passing through a drying process where heat is applied. , may wrinkle. In addition, when the film is adhered to the adherend, wound into a roll, and stored, if the ambient temperature rises, the roll may wrinkle due to dimensional changes of the film, increasing Wa. On the other hand, even if the heat shrinkage rate in the MD direction is less than 0.3%, Wa may become large. The reason for this is considered as follows. When the film is wound into a roll in the film forming process, the film is usually wound with a small amount of air trapped between the wound films. The dimensions of the biaxially oriented polypropylene film change due to the relaxation of the molecular chains of the polymer immediately after the film is formed. At this time, the film shrinks to some extent in the MD direction, and the roll is properly wound without excess film. , it is possible to obtain a film having a small Wa. If the heat shrinkage rate in the MD direction is less than 0.3%, the tightness of the roll immediately after film formation is small, and the film may be stored in a surplus state, resulting in an increase in Wa. In order to set the heat shrinkage ratio within the above range, the raw material composition of the film should be within the range described below, the film-forming conditions should be within the range described below, and in particular the heat setting and relaxation conditions after biaxial stretching should be within the range described below. is effective. Here, the thermal shrinkage rate is measured by cutting out 5 samples with a width of 10 mm and a length of 200 mm (measurement direction) in the width direction of the film, marking the position of 25 mm from both ends as a reference line, and using a universal projector. The distance between the marked lines is measured and used as the test length (l ₀ ), then the test piece is sandwiched between paper and placed in an oven maintained at 85°C with zero load, heated for 60 minutes, then taken out and cooled at room temperature. After that, the dimension (l ₁ ) was measured with a universal projector and obtained by the following formula.

Thermal shrinkage = {(l ₀ - l ₁ )/l ₀ } x 100 (%)
In the present application, the direction parallel to the film forming direction of the film is referred to as the film forming direction, longitudinal direction, or MD direction, and the direction orthogonal to the film forming direction within the film surface is referred to as the width direction or TD direction.

The biaxially oriented polypropylene film of the present invention preferably has a static friction coefficient μs between one surface and the other surface of the film of 0.55 or less. It is more preferably 0.53 or less, still more preferably 0.50 or less. If the coefficient of static friction μs exceeds 0.55, the film roll cannot be uniformly shrunk when the film roll is tightly wound, so that Wa may increase. Also, during the film-forming process, a slight difference in speed between the transport roll and the film may scrape the film surface to generate PP powder, or the amount of PP powder generated may increase. From the viewpoint of suppressing PP dust, the smaller the coefficient of static friction μs, the better, but the practical lower limit is about 0.2. In order to make the static friction coefficient μs within the above range, the raw material composition of the film and the laminated structure of the film are within the range described later, and in particular, the raw material composition of at least one surface layer (surface layer (I)) on at least one side of the laminated structure is described later. is preferably within the range of

The biaxially oriented polypropylene film of the present invention preferably has a haze of 1% or less. It is more preferably 0.9% or less, still more preferably 0.8% or less, still more preferably 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. In addition, when used as a protective film or a substrate film for production of products requiring high quality such as display members, it may not be possible to detect defects in a state where the film is attached to the product. Although haze is preferably as low as possible from the viewpoint of transparency, the practical lower limit is about 0.05%. In order to make the haze within the above range, the raw material composition of the film and the laminated structure of the film should be within the range described later to prevent deterioration of transparency due to particles, etc., and the casting conditions and longitudinal stretching conditions during film formation should be controlled later. It is preferable to reduce the β crystals in the cast sheet.

The number of fish eyes in the biaxially oriented polypropylene film of the present invention is preferably 20/m ² or less. The number of fish eyes is more preferably 10/m ² or less, more preferably 5/m ² or less. If the number of fisheyes exceeds 20/m ² , the yield may decrease when used as a protective film or base film for production of products requiring high quality such as display members. In order to make the number of fish eyes within the above range, the composition of the raw material, the adjustment method, and the lamination structure of the film should be within the range described later, and the additive components in the raw material and heat deterioration may cause fish eyes. It is effective to reduce the amount of resin used. In addition, it is effective to set the conditions during film formation within the range described below, remove foreign matter by filtration before melting the raw material and form a sheet, and reduce the stagnant portion of the resin.

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. If the thickness is less than 5 μm, handling may become difficult, and if 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 proper strength (Young's modulus) and handleability even when the thickness is reduced. In order to take advantage of such characteristics, the thickness is more preferably 5 μm or more and 40 μm or less, even 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 adjusting the number of extruder screw rotations, the width of the unstretched sheet, the film-forming speed, the stretching ratio, etc., within a range that does not deteriorate other physical properties.

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

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

For the biaxially oriented polypropylene film of the present invention, it is preferable to use at least two kinds of polypropylene raw materials (referred to as polypropylene raw material A and polypropylene raw material B). As polypropylene raw material A, it is preferable to use a polypropylene raw material with high crystallinity in order to reduce the thermal shrinkage rate. is preferred.

The polypropylene raw material A has a cold xylene soluble portion (hereinafter referred to as CXS) of 4% by mass or less and a mesopentad fraction of 0.95 or more. If these conditions are not met, the stability of film formation may be poor, or the thermal shrinkage may be increased.

Here, the cold xylene soluble part (CXS) refers to the polypropylene component dissolved in xylene when the film is completely dissolved in xylene and then precipitated at room temperature. It is considered that it corresponds to a component that is difficult to crystallize because of its low molecular weight. If the resin contains a large amount of such components, the heat 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. The lower the CXS, the better, but the lower limit is about 0.1% by mass. In order to obtain a polypropylene having such CXS, methods such as a method of increasing the catalytic activity when obtaining a resin, a method of washing the obtained resin with a solvent or the propylene monomer itself, and the like can be used.

From the same point of view, the mesopentad fraction of polypropylene raw material A is preferably 0.93 or more, more preferably 0.97 or more. The mesopentad fraction is an index showing the stereoregularity of the crystalline phase of polypropylene measured by nuclear magnetic resonance (NMR). It is preferred because it is suitable for use. The upper limit of the mesopentad fraction is not particularly specified. In order to obtain a resin with such high stereoregularity, there are methods such as washing resin powder obtained with a solvent such as n-heptane, selecting a catalyst and/or co-catalyst, and appropriately selecting a composition. preferably employed.

Further, the polypropylene raw material A has a melt flow rate (MFR) of 1 to 10 g/10 minutes (230° C., 21.18 N load). From the standpoint of film-forming properties, it is preferably in the range of 2 to 5 g/10 minutes (230° C., 21.18 N load). In order to set the MFR to the above value, a method of controlling the average molecular weight and the molecular weight distribution is adopted.

The polypropylene raw material A is mainly composed of a homopolymer of propylene, but it may contain a copolymer component of other unsaturated hydrocarbons within a range that does not impair the object of the present invention. Coalescing may be blended. Examples of monomer components constituting such copolymer components and blends include ethylene, propylene (in the case of copolymerized blends), 1-butene, 1-pentene, 3-methylpentene-1,3-methylbutene-. 1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2- and norbornene. From the viewpoint of improving the elastic modulus in the thickness direction, the copolymerization amount or blending amount is preferably less than 1 mol % in terms of copolymerization amount and less than 10% by mass in terms of blending amount.

Next, polypropylene raw material B will be described.

As the polypropylene raw material B, a polypropylene raw material with low crystallinity is preferable in order to have good compatibility with the polypropylene raw material A described above and to improve flexibility. As such polypropylene raw material B, amorphous polypropylene, low stereoregular polypropylene, syndiotactic polypropylene, α-olefin copolymer, etc. can be used, but excellent transparency can be obtained with a small amount. Amorphous polypropylene and low stereoregularity polypropylene are particularly preferred because they can be used.

As the amorphous polypropylene preferably used as the polypropylene raw material B, it is preferable that the main component is a polypropylene polymer having atactic stereoregularity, specifically, a homopolymer or a copolymer with an α-olefin. mentioned. The latter, that is, the amorphous polypropylene-α-olefin copolymer is particularly 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 boiling n-heptane (or xylene) solubles in homopolypropylene. Alternatively, crystalline polypropylene can be polymerized independently by changing the catalyst and polymerization conditions. 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. As the amorphous polypropylene having the characteristics described above, commercially available products such as "Tafselene" (registered trademark) manufactured by Sumitomo Chemical Co., Ltd. can be appropriately selected and used.

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 are 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 copolymers, and propylene/ethylene/butadiene copolymers.

The low stereoregularity polypropylene preferably used as the polypropylene raw material B is preferably a propylene homopolymer produced using a metallocene catalyst as a polymerization catalyst. The melting point of the low stereoregularity polypropylene is 100°C or less, 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). As the low stereoregularity polypropylene having the above characteristics, commercially available products such as "Elmodu" (registered trademark) manufactured by Idemitsu Kosan Co., Ltd. can be appropriately selected and used.

In the biaxially oriented polypropylene film of the present invention, the content of ethylene component contained in the polymer constituting the film is preferably 10% by mass or less. It is more preferably 5% by mass or less, still more preferably 3% by mass or less. The higher the content of the ethylene component, the lower the crystallinity and the easier it is to improve the flexibility and transparency. It may occur more easily.

In the biaxially oriented polypropylene film of the present invention, the petroleum resin content in the polymer constituting the film is preferably 5% by mass or less. It is more preferably 3% by mass or less, still more preferably 1% by mass or less, and most preferably does not contain petroleum resin. By adding a petroleum resin, the transparency can be improved, but if the content of the petroleum resin exceeds 5% by mass, the tensile modulus may become too high and the raw material cost may increase. .

Various additives such as crystal nucleating agents, antioxidants, heat stabilizers, slip agents, antistatic agents, antiblocking agents, fillers, viscosity Conditioning agents, anti-staining agents and the like may also be included.

Among these, the selection of the type and amount of antioxidant to be added is important from the viewpoint of long-term stability. That is, such antioxidants are preferably phenolic antioxidants having steric hindrance, at least one of which is of a high molecular weight type having a molecular weight of 500 or more. Various specific examples thereof include 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) and 1,3,5-trimethyl-2,4,6- Tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (for example, BASF "Irganox" (registered trademark) 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di- It is preferable to use t-butyl-4-hydroxyphenyl)propionate]methane (eg “Irganox” 1010 manufactured by BASF, molecular weight 1177.7) in combination. The total content of these antioxidants is preferably in the range of 0.03 to 1.0% by mass based on the total amount of polypropylene. If the amount of antioxidant is too small, the polymer may deteriorate during the extrusion process, resulting in coloration of the film or poor long-term heat resistance. If the amount of antioxidant is too large, transparency may be lowered due to bleeding out of these antioxidants. A 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 object of the present invention. Crystal nucleating agents include α-crystal nucleating agents (dibenzylidene sorbitols, sodium benzoate, etc.), β-crystal nucleating agents (1,2-hydroxypotassium stearate, magnesium benzoate, N,N'-dicyclohexyl-2,6 - Amide compounds such as naphthalene dicarboxamide, quinacridone compounds, etc.). However, excessive addition of the above-mentioned different nucleating agents may cause deterioration in stretchability and void formation, resulting in deterioration in transparency and strength. % by mass or less, more preferably 0.05 mass % or less.

The biaxially oriented polypropylene film of the present invention is obtained by biaxially stretching the raw materials described above. As the biaxial stretching method, it 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. It is preferable to adopt a stenter sequential biaxial stretching method from the viewpoint of controlling high rigidity and dimensional stability.

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

The biaxially oriented polypropylene film of the present invention has a laminate structure of at least two layers from the viewpoint of compatibility between transparency and slipperiness.

In the biaxially oriented polypropylene film of the present invention, at least one surface layer (surface layer (I)) on one side of the laminated structure contains polypropylene raw material A in an amount of 96% by mass or more. The content of the polypropylene raw material A in the surface layer (I) is more preferably 97% by mass or more, still more preferably 98% by mass or more. If the content of the polypropylene raw material A in the surface layer (I) is less than 96% by mass, the orientation of the film will be low and the tensile rigidity will be reduced. may decrease.

Further, 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 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 shall apply hereinafter). More preferably 0:100 to 90:10, still more preferably 0:100 to 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 surface layer (I) preferably has a thickness d of 0.1 to 2.0 μm. It is more preferably 0.2 to 1.5 μm, still more preferably 0.3 to 1.0 μm, still more preferably 0.3 to 0.8 μm. 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, lamination accuracy may become unstable, and thickness unevenness of the surface layer (I) may increase. The thickness d of the surface layer (I) can be adjusted by adjusting the number of screw revolutions of the extruder, the width of the unstretched sheet, the film forming speed, the stretching ratio, etc., within a range that does not deteriorate other physical properties. When surface layers (I) are provided on both surfaces of the film, each layer preferably satisfies the above range.

In the biaxially oriented polypropylene film of the present invention, the surface layer (I) preferably accounts for 1 to 15% of the total thickness of the film. More preferably 1 to 10%, still more preferably 1 to 5%. If the proportion 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 adjusting the number of screw revolutions of the extruder, the width of the unstretched sheet, the film forming speed, the stretching ratio, etc., within a range that does not deteriorate other physical properties. When surface layers (I) are provided on both surfaces of the film, each layer preferably satisfies the above range.

In the biaxially oriented polypropylene film of the present invention, the surface layer on at least one side of the above-described laminated structure preferably contains lubricating particles or a resin having a melting point of 180 ° C. or higher from the viewpoint of reducing the coefficient of friction, and the melting point is 180 ° C. It is more preferable to contain the above resins.

The lubricating particles are not particularly limited as long as they do not impair the effects of the present invention. For example, inorganic particles and organic particles can be used. Examples of inorganic particles include silica, titanium oxide, aluminum oxide, zirconium oxide, calcium carbonate, carbon black, and zeolite particles. Examples of organic particles include acrylic resin particles, styrene resin particles, polyester resin particles, and polyurethane resin particles. , polycarbonate-based resin particles, polyamide-based resin particles, silicone-based resin particles, fluorine-based resin particles, or copolymer resin particles of two or more monomers used for synthesizing the above resins. However, since the polypropylene resin has a low surface energy, when particles are added and the film is stretched, voids may be generated due to peeling of the particle interfaces during stretching, resulting in an increase in haze and a decrease in transparency. From the viewpoint of improving transparency, it is preferable to use the above-mentioned inorganic particles or organic particles having a silane coupling-treated surface, and silica particles having a silane coupling treatment are particularly preferred.

The average particle size of the lubricous 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, resulting in a decrease in transparency. If the average particle size is 1.0 μm or more, voids are likely to occur at the particle interface during stretching, which may reduce the transparency. In addition, the particles added to the surface layer may fall off during film formation, increasing the surface roughness or increasing the haze. The average particle size is more preferably 0.15 μm or more and less than 0.9 μm, and more preferably 0.15 μm or more and less than 0.8 μm. From the viewpoint of improving handling properties, two or more types of particles having different average particle sizes may be used in combination.

The biaxially oriented polypropylene film of the present invention preferably has a laminate structure of at least two layers, and contains slippery particles in at least one surface layer. At this time, the thickness of the layer containing the lubricous 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 the lubricous particles is more preferably 0.2 to 1.6 μm, still more preferably 0.3 to 1.4 μm.

The content of the lubricating particles in the material of the layer containing the lubricating 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 coefficient of friction may not be obtained. If the content is 1.0% by mass or more, the haze may increase and the transparency may decrease. The content is more preferably 0.05% by mass or more and less than 0.9% by mass, and still more preferably 0.1% by mass or more and less than 0.8% by mass.

From the viewpoint of reducing the coefficient of friction, the biaxially oriented polypropylene film of the present invention preferably contains a resin having a melting point of 180° C. or higher. The melting point is more preferably 180°C or higher and 240°C or lower. By incorporating a resin having a melting point of 180° C. or higher in the surface layer of the film and forming the film under the conditions described later, it is possible to form fine projections on the film surface and improve slipperiness. In such a case, it is preferable that the film is composed of at least two layers, the surface layer (I) and the base layer (II), and that the surface layer (I) contains a resin having a melting point of 180° C. or higher. When the surface layer (I) has a melting point of 180° C. or higher, it melts and disperses in the polypropylene in the melt extrusion step described later, and can form the protrusions described above without being deformed in the stretching step. In order to make the protrusions to be formed as fine as described above, it is necessary to finely disperse them in polypropylene in the melt extrusion process, and it is important that they have a high affinity with polypropylene. From this point of view, it is preferable that the resin having a melting point of 180° C. or higher is an olefin resin. preferable. A resin containing a 4-methylpentene-1 unit has a higher affinity with a polypropylene resin than a non-olefinic resin, so that dispersibility can be improved. Examples of olefinic resins containing 4-methylpentene-1 units include “TPX” (registered trademark) DX310, “TPX” DX231, “TPX” MX004 and the like manufactured by Mitsui Chemicals, Inc.

In the biaxially oriented polypropylene film of the present invention, the content of the olefin resin containing 4-methylpentene-1 units in the resin composition of the surface layer (I) is 0.1 to 5% by mass. is preferred, more preferably 0.1 to 4% by mass, still more preferably 0.1 to 3% by mass, still more preferably 0.1 to 2.5% by mass. When the content of the olefin resin containing 4-methylpentene-1 units is more than 5% by mass, the projections may form a long mountain range in the longitudinal direction, and when used as a base film or cover film, When it is difficult to take 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 entrapment. may occur more easily. When the content is less than 0.1% by mass, the frequency of the formed protrusions is too low, which may not contribute to the improvement of the slipperiness and the windability may be deteriorated.

It is preferable that at least one of the slippery particles and the resin having a melting point of 180° C. or higher is included depending on the purpose and application, but both may be included.

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. The kneading temperature at this time is preferably higher than the melting point of the high-melting resin from the viewpoint of dispersion uniformity, more preferably 10° C. or higher, and even more preferably 20° C. or higher. If the kneading temperature is lower than the melting point of the high melting point resin, the dispersibility may deteriorate and the projections may become 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, so the upper limit is 280°C.

The biaxially oriented polypropylene film of the present invention is preferably melt-extruded at a temperature not higher than the melting point of the high melting point resin. It is more preferably 10° C. or lower, and even more preferably 20° C. or lower. When melt extrusion is performed at a temperature higher than the melting point of the high melting point resin, the high melting point resin that is uniformly and finely dispersed in the polypropylene resin melts and may become coarsely fused or elongated due to shear flow during extrusion. As a result, 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, the filtration pressure may increase during extrusion or unmelted polypropylene resin may occur, so 200°C is the lower limit.

It is preferable that at least one of the slippery particles and the resin having a melting point of 180° C. or higher is included depending on the purpose and application, but both may be included.

Next, the method for producing a biaxially oriented polypropylene film of the present invention will be described as an example, but the method is not necessarily limited to this.
First, 90 parts by mass of polypropylene raw material A and 10 parts by mass of 4-methyl-1-pentene polymer are put into a twin-screw extruder to prepare a master raw material. The melt-kneading temperature at this time is 230 to 280°C, preferably 240 to 280°C, further preferably 250 to 280°C. 20 parts by mass of the master raw material and 80 parts by mass of polypropylene raw material A are dry-blended and supplied to a single screw extruder for layer A (surface layer (I)), and 60 parts by mass of polypropylene raw material A and 40 parts by mass of polypropylene raw material B. A 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 matter 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, discharged onto a casting drum, and A A laminated unstretched sheet having a layer structure of layer/B layer/A layer is obtained. At this time, the lamination thickness ratio is preferably 1/8/1 to 1/50/1. Further, the casting drum preferably has a surface temperature of 10 to 40° C. from the viewpoint of transparency. Also, a two-layer lamination structure of A layer/B layer may be employed.

At this time, the lip temperature of the die is preferably set to a temperature lower than the melt extrusion temperature by 20 to 40°C, 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 increases, and the orientation of the film surface layer is particularly enhanced. When the film roll is tightened, the film surface is less likely to deform, which is effective in reducing Wa. I found that

As a method of adhesion to the casting drum, any of the electrostatic application method, the adhesion method using the surface tension of water, the air knife method, the press roll method, and the underwater casting method may be used. The air-knife method, which is good and allows control of surface roughness, is preferred. The air temperature of the air knife is 0 to 50° C., preferably 0 to 30° C., and the blown air velocity is preferably 130 to 150 m/s. Moreover, it is preferable to appropriately adjust the position of the air knife so that the air flows downstream of the film formation so as not to cause vibration of the film.

In addition, by forcibly cooling the non-casting drum surface of the film after it is brought into close contact with the casting drum, it is possible to suppress the formation of β crystals on the non-casting drum surface and improve the smoothness and transparency of the film. be able to. The non-casting drum surface can be cooled by air cooling, the press roll method, or the underwater casting method. Air cooling with good air is preferred.

The obtained unstretched sheet is introduced into a longitudinal stretching step. In the longitudinal stretching step, first, the unstretched sheet is brought into contact with a plurality of metal rolls maintained at 120° C. or more and less than 150° C., preheated to the stretching temperature, and longitudinally between two pairs of nip rolls having a peripheral speed difference. After stretching 3 to 8 times to 20 cm, it is cooled to room temperature. If the stretching temperature is 150° C. or higher, the surface of the film may become rough and the transparency may be lowered. On the other hand, if the draw ratio is less than 3 times, the surface of the film may be rough and the transparency may be lowered. Further, at this time, it is preferable that the temperature of the downstream roll having the higher speed among the two pairs of nip rolls having a peripheral speed difference is lower than the temperature of the upstream roll by 10° C. or more. If the temperature difference is less than 10°C, the heat shrinkage rate in the MD direction after 60 minutes at 85°C becomes too small, and Wa increases, and when used as a base film or cover film, unevenness will occur on the surface of the product. It may be transcribed. 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.

Then, the longitudinally uniaxially stretched film is guided to a tenter, and the edges of the film are gripped with clips and transversely stretched 7 to 13 times in the width direction at a temperature of 140 to 165°C. If the stretching temperature is too low, the film may be ruptured or its transparency may be lowered. Also, if the magnification is high, the film may break, and if the magnification is low, the orientation of the film may be weak and the strength may decrease.

In the subsequent heat treatment and relaxation treatment steps, the film is heat-set at a temperature of 100° C. or more and less than 160° C. while being tension-held in the width direction with a clip and relaxed at a relaxation rate of 2 to 20% in the width direction, and then fixed with a clip in the width direction. While being held tightly, the film is led to the outside of the tenter through a cooling process at 80 to 100° C., the clip at the film edge is released, the film edge is slit in the winder process, and a wide film roll is wound. 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 out of alignment, and if it exceeds 100 N/m, the biaxially oriented polypropylene film may shrink due to dimensional shrinkage immediately after film formation, resulting in tight winding and poor flatness.

The resulting wide film roll is preferably aged in an atmosphere of 25-50° C. for 1-72 hours. After that, it is slit to a predetermined width depending on the application, and the product film roll is wound up. The winding tension at this time is preferably higher than the winding tension of the wide film roll, more preferably 80 to 200 N/m. Aging under the predetermined conditions described above 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 under the above tension, so that Wa is small. film can be obtained.

The biaxially oriented polypropylene film obtained as described above can be used in various applications such as packaging films, surface protective films, process films, sanitary products, agricultural products, construction 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 of using the biaxially oriented polypropylene film of the present invention as a cover film will be described by taking a cover film for a resist as an example. A PET film subjected to silicone release treatment is unwound as a process film, and a resist coating liquid is applied onto the film. After drying the coating solution at a predetermined temperature, the biaxially oriented polypropylene film of the present invention is laminated as a resist cover film, and the laminate of the PET film, the resist layer and the 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, it is less likely to transfer irregularities to the resist surface, and can be preferably used in applications that require high-definition exposure patterns.

An example of using the biaxially oriented polypropylene film of the present invention as a process film will be described by taking a process film for solution casting of an optical film as an example. The biaxially oriented polypropylene film of the present invention is unwound from the coater, the solution of the optical member is applied and dried at 80 to 100° C., and then the optical film is peeled off from the process film to completely remove the solvent. to obtain an optical film. Since the biaxially oriented polypropylene film of the present invention has a smooth surface, the transfer of surface unevenness to the optical film is small, and it can be preferably used as a protective film for a high-quality optical film.

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

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

Among these, acrylic pressure-sensitive adhesives are preferably used in consideration of excellent transparency, weather resistance, heat resistance, resistance to moist heat, adhesion to substrates, 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 suitable examples.

Moreover, it is preferable to use a hardening|curing agent together with the said acrylic adhesive. Specific examples of the curing agent include isocyanate such as toluene 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, 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 weight, preferably 0.5 to 5 parts by weight, per 100 parts by weight of the adhesive. If the amount is less than 0.1 part by mass, the adhesive layer may not be sufficiently cured in the drying oven, and backing may occur. If the amount exceeds 10 parts by mass, the excess curing agent may migrate to the substrate or gasify at high temperatures to cause contamination.

In addition, antioxidants, ultraviolet absorbers, silane coupling agents, metal deactivators, etc. may be appropriately added to the acrylic pressure-sensitive adhesive according to the material of the adherend (glass or functional film). .

In the pressure-sensitive adhesive film using the biaxially oriented polypropylene film of the present invention, the thickness d of the pressure-sensitive adhesive layer is preferably 1.0 μm or less. It is more preferably 0.8 μm or less, still more preferably 0.6 μm or less, and still more preferably 0.4 μm or less. If the thickness d of the adhesive layer exceeds 1.0 μm, the slipperiness between the back surface of the base film and the surface of the adhesive layer may deteriorate, making winding difficult. In addition, backing of the adhesive layer may occur. The backing means that after coating the solution of the adhesive layer on one side of the base film, drying and curing in a drying oven, the adhesive film of the present invention is wound into a roll without a release film interposed. Later, when the adhesive film is unwound for use, a part of the adhesive layer is transferred to the back surface of the base film. If the thickness d of the adhesive layer exceeds 1.0 µm, the adhesive layer may not be sufficiently dried in a drying oven, and backing may occur. Furthermore, if the thickness of the adhesive layer is thick, when the film of the present invention is laminated to a product and used in a process that requires reduced pressure such as vapor deposition or sputtering, volatile components from the adhesive layer may hinder the reduction in the degree of reduced pressure. There is A known technique can be used to adjust the thickness of the adhesive layer to the above range, and the thickness can be controlled by adjusting the solid content concentration of the solution of the adhesive layer and 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 the lower limit is about 0.1 μm.

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 bonding to a glass plate. The peel force is more preferably 0.5 N/25 mm or less, still more preferably 0.2 N/25 mm or less, still more preferably 0.05 N/25 mm or less. If the peel force exceeds 1 N/25 mm, the lubricity between the back surface of the base film and the surface of the pressure-sensitive adhesive layer deteriorates, which may make winding difficult or cause backing. In order to set the peel force within the above range, the composition and thickness of the adhesive layer should be within the range described below, and the raw material composition and film forming conditions of the film should be within the range described below, and the surface roughness of the base film should be controlled. is effective. If the peel force is less than 0.01 N/25 mm, the adhesive film may peel off during transport after bonding to the adherend, so the lower limit is about 0.01 N/25 mm.

Next, a method for producing the adhesive layer will be described, but the method is not necessarily limited to this.

First, prepare the coating material for the adhesive layer. The coating agent can be used by dissolving additives such as the adhesive and the curing agent described above in a solvent. The solvent can be appropriately adjusted depending on the drying temperature of the coater and the viscosity of the coating material. 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, isopropylacetone, methyl ethyl ketone, methyl isobutyl ketone, diacetylacetone, and acetylacetone can be used.

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

Next, the base film described above is transported by a coater, and the coating material for the adhesive layer is applied. Here, the surface to be coated with the adhesive layer may be either surface of the base film. 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 existing coating methods such as the metabar method, the doctor blade method, the gravure method, the die method, the knife method, the reverse method, and the dip method can be employed. However, as described above, the thickness of the adhesive layer is preferably a thin film of 1.0 μm or less, and from the viewpoint of stably obtaining a thin coating layer, the gravure method and the reverse method are preferable.

After the base film is coated with the coating agent for the adhesive layer, it is introduced into a drying oven to remove the solvent in the coating agent to obtain the adhesive film. The drying temperature here is appropriately set according to the heat resistance of the substrate film and the boiling point of the solvent, but is preferably 60 to 170°C. If the temperature is less than 60°C, the curing of the adhesive layer may not proceed sufficiently, and backing may occur. If it exceeds 170°C, the base film may be deformed and the flatness may be deteriorated. Also, the drying time is preferably 15 to 60 seconds. If the time is less than 15 seconds, the curing of the adhesive layer does not proceed sufficiently, and backing may occur. If the time exceeds 60 seconds, the productivity is lowered, which is not preferable.

The dried adhesive film can be wound up by a winding machine without using a release film or the like to obtain an adhesive film roll. The adhesive film of the present invention has the above-described structure, so that the curing of the adhesive layer proceeds sufficiently and the slipperiness between the back surface of the base film and the surface of the adhesive layer is good. It is possible to obtain a high-quality adhesive film roll without causing problems such as being backed off even when the film is removed or generating wrinkles during winding. However, if necessary, it may be wound using a release film.

The adhesive film 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, and medical products. Since it is excellent, it can be preferably used as a surface protective film and a process film.

An example of using the biaxially oriented polypropylene film of the present invention 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. After that, the pressure-sensitive adhesive film can be attached 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 device because the unevenness of the surface is less transferred to an optical member.

An example of using the biaxially oriented polypropylene film of the present invention as a process film for solution casting will be described. The biaxially oriented polypropylene film of the present invention is unwound from the coater, coated with a polymer solution and dried at 80-100° C., after which the solution cast film is peeled off from the process film to completely remove the solvent. to obtain a solution casting film. Since the biaxially oriented polypropylene film of the present invention has a smooth surface, it can be preferably used as a high-quality film with little transfer of surface unevenness to a solution-casting film.

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

(1) Film thickness Measured using a micro thickness meter (manufactured by Anritsu Corporation). The film was sampled at 10 cm square, measured at 5 random points, and the average value was obtained.

(2) Waviness value (Wa)
VertScan2.0 R5300GL-Lite-AC manufactured by Ryoka System Co., Ltd. was used for the measurement, and the surface shape was obtained by surface correction of the photographed image by polynomial fourth-order approximation using the attached analysis software. The measurement conditions are as follows. The measurement was performed on both sides of the film with n=3 in accordance with the method specified in JIS B0601 (2001), and the average value was adopted as Wa for each side.
Manufacturer: Ryoka System Co., Ltd. Device name: VertScan2.0 R5300GL-Lite-AC
Measurement conditions: CCD camera SONY HR-57 1/2 inch objective lens 5x minutes Intermediate lens 0.5x
Wavelength filter 530nm white
Measurement mode: Wave
Measurement software: VS-Measure Version5.5.1
Analysis software: VS-Viewer Version5.5.1
Measurement area: 1.252 x 0.939 ^mm2 .

(3) Heat shrinkage rate in the MD direction For each width direction of the film, cut out 5 samples with a width of 10 mm and a length of 200 mm (measurement direction), mark the position 25 mm from both ends as a reference line, The distance between the marked lines is measured with a projector and taken as the trial length (l ₀ ). Next, the test piece was sandwiched between sheets of paper and heated for 60 minutes in an oven maintained at 85°C with _zero load. It calculated|required by the formula and made the heat shrinkage rate the average value of five.

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

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

(5) Static friction coefficient μs
Using a friction measuring instrument manufactured by Toyo Tester Kogyo Co., Ltd., according to ASTM D1894, one side of the film and the other side of the film are stacked so that they are in contact with each other, and the initial rising resistance value is measured when the MD directions are rubbed. , and the maximum value was taken as the coefficient of static friction μs. However, when the initial rise was large and exceeded the upper limit (5.0) of the measured value, the measurement was considered impossible. Five sets (10 pieces) of samples were cut into rectangles having a width of 80 mm and a length of 200 mm. Measurement was performed 5 times and an average value was obtained.

(6) Evaluation of transfer to adherend An adhesive film and a 40 μm thick “Zeonor Film” (registered trademark) manufactured by Nippon Zeon Co., Ltd. were sampled into a square with a width of 100 mm and a length of 100 mm, and the back of the adhesive film and “Zeonor” It was placed between two acrylic plates (width 100 mm, length 100 mm), a load of 3 kg was applied, and the film was allowed to stand in an atmosphere of 23°C for 24 hours. After 24 hours, the surface of the "Zeonor film" (the surface in contact with the adhesive film) was visually observed and evaluated according to the following criteria.
A: Clean and equivalent to before applying load B: Either weak orange peel transfer or weak uneven transfer is confirmed C: Weak orange peel transfer and weak uneven transfer are confirmed D: A strong transfer of orange peel and/or a strong transfer of unevenness is confirmed.

(7) Transfer evaluation to adherend after heating Adhesive film and 40 μm thick “Zeonor Film” (registered trademark) manufactured by Nippon Zeon Co., Ltd. are sampled into a square with a width of 100 mm and a length of 100 mm, and the back of the adhesive film. and "Zeonor film" are in contact with each other, sandwiched between two acrylic plates (width 100 mm, length 100 mm), a load of 3 kg is applied, and heated in an oven heated to 85 ° C for 1 hour. bottom. Then, it was taken out of the oven, the weight was removed, and after standing still for 24 hours, the surface of the "Zeonor film" (the side in contact with the adhesive film) was visually observed and evaluated according to the following criteria.
A: Clean and equivalent to before applying load B: Either weak orange peel transfer or weak uneven transfer is confirmed C: Weak orange peel transfer and weak uneven transfer are confirmed D: A strong transfer of orange peel and/or a strong transfer of unevenness is confirmed.

(Example 1)
Crystalline polypropylene (manufactured by Prime Polymer Co., Ltd., TF850H, MFR: 2.9 g/10 min, mesopentad fraction: 0.94) was supplied to a single-screw melt extruder, and the melt temperature was 240°C and the lip temperature was 200°C. After removing foreign matter with a 60 μm cut sintered filter, the mixture was discharged onto a casting drum whose surface temperature was controlled at 30° C., and adhered to the casting drum with an air knife. Thereafter, compressed air having a temperature of 30° C. and a pressure of 0.3 MPa was jetted onto the non-cooled drum surface of the sheet on the casting drum to cool the sheet, thereby obtaining an unstretched sheet. Subsequently, the sheet was preheated to 145° C. using ceramic rolls, 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 the peripheral speed difference, the temperature of the upstream roll was set at 143°C, and the temperature of the downstream roll with the higher speed was set at 70°C. Next, it was introduced into a tenter-type stretching machine with its ends held by clips, preheated at 170°C for 3 seconds, stretched 8.0 times at 165°C, and stretched at 150°C while giving 10% relaxation in the width direction. After heat treatment, the film was cooled at 100° C., led to the outside of the tenter, the clips at the ends of the film were released, and the film with 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., the film was slit at 100 mm from both ends to a width of 600 mm and wound around a core at 100 N/m to obtain a biaxially oriented polypropylene film with a thickness of 24 μm. Table 1 shows the physical properties and evaluation results of the obtained film. However, the contact surface with the casting drum was A surface, and the opposite surface was B surface.

(Example 2)
Crystalline polypropylene (PP (a)) (manufactured by 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, Ltd., MX004) 10 parts by mass are supplied from a weighing hopper to a twin-screw extruder so that they are mixed at this ratio, melt-kneaded at 260 ° C., and extruded from a die in a strand shape. , 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) are dry-blended as the polypropylene raw material for the surface layer (A), and supplied to a single-screw melt extruder for the A layer, As a polypropylene raw material for the core layer (B), 100 parts by mass of the crystalline PP (a) is supplied to a single-screw melt extruder for the B layer, melt extruded at 210 ° C., and a 10 μm cut sintered filter. After removing foreign matter with a 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 an air knife is used to cast the drum. was adhered to. Thereafter, compressed air having a temperature of 30° C. and a pressure of 0.3 MPa was jetted onto the non-cooled drum surface of the sheet on the casting drum to cool the sheet, thereby obtaining an unstretched sheet. A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1. Table 1 shows the physical properties and evaluation results of the obtained film.

(Example 3)
In Example 2, as the polypropylene raw material for the core layer (B), Sumitomo Chemical's polypropylene resin FSX20L8 (MFR = 2.0 g / 10 min, isotactic index (II) = 96%) 90 parts by mass and Idemitsu Kosan Co., Ltd. 10 parts by mass of “L-MODU” (registered trademark) S901 (MFR 50 g / 10 min, mesopentad fraction 50%) was dry blended and supplied to a single-screw melt extruder for the B layer. A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 2 except for the above. Table 1 shows the physical properties and evaluation results of the obtained film.

(Example 4)
In Example 2, among the rolls provided with a difference in longitudinal stretching peripheral speed, the temperature of the downstream roll was set to 125 ° C., and further, 5% relaxation was applied in the MD direction between the following rolls. A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 2. Table 1 shows the physical properties and evaluation results of the obtained film.

(Example 5)
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 changed to 1/38/1 in Example 2. Table 1 shows the physical properties and evaluation results of the obtained film.

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

(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) were dry-blended as the polypropylene raw material for the surface layer (A), and uniaxial melting for the A layer was performed. Supplied to an extruder, as a polypropylene raw material for the core layer (B), 80 parts by mass of Sumitomo Chemical's polypropylene resin FSX20L8 and 20 parts by mass of Idemitsu Kosan Co., Ltd.'s "Elmodu" S901 are dry blended to form a B layer. and melt extruded at a melt temperature of 210°C and a lip temperature of 200°C. After winding a film with a width of 800 mm on a core, it is stored in an atmosphere of 40°C for 60 hours. After that, slitting was performed to obtain a biaxially oriented polypropylene film. A biaxially oriented polypropylene film having a thickness of 22 μm was obtained in the same manner as in Example 2 except for the above. Table 1 shows the physical properties and evaluation results of the obtained film.

(Comparative example 1)
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 was set to 120 N/m when the film having a width of 800 mm was wound around the core. The waviness value Wa increased, confirming the transfer of the orange peel. Table 1 shows the physical properties and evaluation results of the obtained film.

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

(Comparative Example 3)
In Example 1, among the rolls provided with a peripheral speed difference in longitudinal stretching, the temperature of the upstream roll was set to 125 ° C., and the relaxation in the width direction in the tenter was set to 0% in an atmosphere of 100 ° C., and other than that. A biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 1. Table 1 shows the physical properties and evaluation results of the obtained film.

(Comparative Example 4)
In Example 1, the lip temperature during melt extrusion was set to 240 ° C., and the temperature of the downstream roll among the rolls provided with a peripheral speed difference in longitudinal stretching was set to 138 ° C. Other than that, the same method as in Example 1. to obtain a biaxially oriented polypropylene film having a thickness of 24 μm. Table 1 shows the physical properties and evaluation results of the obtained film.

(Comparative Example 5)
In Example 3, the stretching ratio of longitudinal stretching was 4.8 times, the cooling temperature after biaxial stretching was 150 ° C., and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained in the same manner as in Example 3. rice field. Table 1 shows the physical properties and evaluation results of the obtained film.

Claims (6)

A biaxially oriented polypropylene film having a laminate structure of at least two layers, wherein at least one surface layer (surface layer (I)) of the laminate structure contains 96% by mass or more of polypropylene raw material A , 4-methylpentene- The polypropylene raw material A contains 0.1 to 4% by mass of an olefin resin containing 1 unit , has a cold xylene soluble part (CXS) of 4% by mass or less, and has a mesopentad fraction of 0.93 above, the melt flow rate (MFR) is 1 to 10 g/10 minutes (230 ° C., 21.18 N load),
The waviness value Wa of at least one side is 45 nm or less, and the heat shrinkage rate in the MD direction after 60 minutes at 85° C. is 0.00. 5-2 % biaxially oriented polypropylene film. 2. The biaxially oriented polypropylene film according to claim 1, having a static friction coefficient [mu]s of 0.55 or less. 3. The biaxially oriented polypropylene film according to claim 1, which has a haze of 1% or less. A release film using the biaxially oriented polypropylene film according to any one of claims 1 to 3 . A process film for solution casting using the biaxially oriented polypropylene film according to any one of claims 1 to 3 . An adhesive film comprising the biaxially oriented polypropylene film according to any one of claims 1 to 3 and an adhesive layer provided thereon .