JP7047428B2 - Biaxially oriented polypropylene film - Google Patents

Description

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

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

The required characteristics for the release film are appropriately set according to the intended use, but due to the recent miniaturization and higher accuracy of equipment, the products to be protected may also be required to be thin and of high quality. If the polypropylene film has poor quality such as flatness, for example, when it is used as a release film for an optical member, the surface unevenness of the film may be transferred to the optical member and affect the visibility of the product. ..

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

Japanese Patent Application Laid-Open No. 2002-40667 International Publication No. 2015/129851 Japanese Unexamined Patent Publication No. 2014-101471

In the biaxially oriented polypropylene film, even when the surface roughness is small, minute waviness may occur in the film, which may be transferred, and the surface of the optical member may be roughened like a citron skin. Patent Documents 1 to 3 It was difficult to suppress the occurrence of minute swells and improve the quality by the method disclosed in. An object of the present invention is to solve the above-mentioned problems. That is, it is an object of the present invention to provide a polypropylene film having excellent surface smoothness and quality, and excellent 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. It is characterized by being 3 to 2%.

The biaxially oriented polypropylene film of the present invention is excellent in surface smoothness and transparency, and is excellent in quality and handleability. Therefore, 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. If Wa exceeds 45 nm, the uneven shape may be transferred to the surface of the product when the biaxially oriented polypropylene film of the present invention is peeled off after being bonded to a product of another material as a protective film or cover film. be. From the viewpoint of suppressing the shape of unevenness, the smaller the Wa, the more preferable, but the lower limit is substantially about 5 nm. Further, 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, the back surface also comes into contact with the product, so that the waviness value Wa on both sides is 45 nm or less. It is preferable, more preferably both sides are 35 nm or less, and further preferably both sides are 30 nm or less. In order to set Wa in the above range, the raw material composition of the film shall be in the range described later, and the film forming conditions shall be in the range described later, and in particular, the heat fixing, relaxation conditions, and winding conditions after biaxial stretching shall be described later. Is effective.

The biaxially oriented polypropylene film of the present invention has a heat shrinkage rate 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%, further 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%, the film may be deformed and peeled off, for example, when it is bonded to another material as a protective film or cover film and then passed through a drying process in which heat is applied. , Wrinkles may occur. Further, when the film is bonded to the adherend and wound into a roll and stored, if the environmental temperature rises, wrinkles or the like may occur on the roll due to the dimensional change of the film, and the Wa may increase. On the other hand, even if the heat shrinkage rate in the MD direction is less than 0.3%, Wa may increase. The reason for this is considered as follows. When the film is wound into a roll in the film forming process, a small amount of air is caught between the films that are normally wound and wound. The size of the biaxially oriented polypropylene film changes due to the relaxation of the molecular chain of the polymer immediately after film formation. By being fixed, it becomes possible to obtain a film having a small Wa. When the heat shrinkage rate in the MD direction is less than 0.3%, the roll tightness immediately after film formation is small, and the film is stored in a surplus state, and as a result, Wa may increase. In order to keep the heat shrinkage 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 the heat fixing and relaxation conditions after biaxial stretching are set to the range described later. Is effective. Here, the heat shrinkage rate is defined by cutting out five samples with a width of 10 mm and a length of 200 mm (measurement direction) in the width direction of the film, marking them at positions 25 mm from both ends as marked lines, and using a universal projector. The distance between the marked lines is measured to set the test length (l ₀ ), then the test piece is sandwiched between papers, heated in an oven kept at 85 ° C with no 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 calculated by the following formula, and the average value of 5 pieces was taken as the heat shrinkage rate.

Heat shrinkage rate = {(l ₀ − l ₁ ) / l ₀ } × 100 (%)
In the present application, the direction parallel to the film forming direction of the film is referred to as the film forming direction, the longitudinal direction, or the MD direction, and the direction orthogonal to the film forming direction in the film surface is referred to as the width direction or the TD direction.

The biaxially oriented polypropylene film of the present invention preferably has a coefficient of static friction μs between one surface of the film and the other surface of 0.55 or less. 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 it is wound, so that Wa may increase. Further, during the film forming process, the film surface may be scraped due to a slight speed difference between the transport roll and the film to generate PP powder, or the amount of PP powder generated may increase. From the viewpoint of suppressing PP powder, the smaller the coefficient of static friction μs is, the more preferable it is, but substantially 0.2 is the lower limit. In order to set the static friction coefficient μs in the above range, the raw material composition of the film and the laminated structure of the film are set to the range described later, and in particular, the raw material composition of at least one surface layer (surface layer (I)) of the laminated structure will be described later. It is preferable that the range is within the range of the above.

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. If the haze exceeds 1%, the surface roughness of the film surface is large, and the surface shape may be transferred to the adherend. Further, when used as a protective film for a product requiring high quality such as a display member or a base film for manufacturing, it may not be possible to detect defects in a state of being bonded to the product. The lower the haze, the more preferable it is from the viewpoint of transparency, but the lower limit is practically about 0.05%. In order to set the haze in the above range, the raw material composition of the film and the laminated structure of the film are set to the range described later to prevent deterioration of transparency due to particles and the like, and the casting conditions and the longitudinal stretching conditions at the time of film formation are described later. It is preferable to keep the range within the range to reduce β crystals of the cast sheet.

The biaxially oriented polypropylene film of the present invention preferably has 20 fisheyes / m ² or less. The number of fish eyes is more preferably 10 / m ² or less, still more preferably 5 / m ² or less. If the number of fish eyes exceeds 20 / m ² , the yield may decrease when used as a protective film for products requiring high quality such as display members or as a base film for manufacturing. In order to keep the number of fish eyes in the above range, the composition and adjustment method of the raw material and the laminated 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. Further, it is effective to set the conditions at the time of film formation within the range described later, remove foreign substances by filtration until the raw materials are melted and formed into a sheet, and reduce the retention portion of the resin.

The thickness of the biaxially oriented polypropylene film of the present invention is appropriately adjusted depending on the intended use 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 be 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 an appropriate strength (Young's modulus) and maintain handleability even if 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, further preferably 5 μm or more and 30 μm or less, and most preferably 5 μm or more and 25 μm or less. The thickness can be adjusted by adjusting the screw rotation speed 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.

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

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 application means that the ratio of the specific component to all the components is 50% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more. It is more preferably 96% by mass or more, further preferably 97% by mass or more, still more preferably 98% by mass or more.

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) for the biaxially oriented polypropylene film of the present invention. As the polypropylene raw material A, it is preferable to use a polypropylene raw material having high crystallinity in order to reduce the heat shrinkage rate, and as the polypropylene raw material B, a polypropylene raw material having low crystallinity is used in order to reduce the tensile elastic modulus of the film. Is preferable.

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

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

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

Further, as the polypropylene raw material A , the melt flow rate (MFR) is 1 to 10 g / 10 minutes (230 ° C., 21.18 N load ). The one in the range of 2 to 5 g / 10 minutes (230 ° C., 21.18 N load) is preferable , from the viewpoint of film forming property. 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 may contain a copolymerization component due to other unsaturated hydrocarbons as long as the object of the present invention is not impaired, and propylene is not a single material. The coalescence may be blended. Examples of the monomer components constituting such copolymerization components and blends include ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene. 1,1-Hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2- Norbornene and the like can be mentioned. From the viewpoint of improving the elastic modulus in the thickness direction, the copolymerization amount or the blend amount is preferably less than 1 mol% in the copolymerization amount and less than 10% by mass in the blend amount.

Subsequently, the polypropylene raw material B will be described.

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

As the amorphous polypropylene preferably used as the polypropylene raw material B, it is preferable that the main component is a polypropylene polymer having an atactic stereoregularity, and specifically, a homopolymer or a copolymer with an α-olefin is used. Can be mentioned. In particular, the latter, that is, an amorphous polypropylene-α-olefin copolymer is preferable.

The amorphous polypropylene can be produced as a by-product of isotactic polypropylene during homopolypropylene polymerization. Since the glass transition temperature is lower than that of general polypropylene, it can be extracted as a boiling n-heptane (or xylene) soluble component of homopolypropylene. Alternatively, it can be independently polymerized with crystalline polypropylene by changing the catalyst and polymerization conditions. The amorphous polypropylene preferably used in the present invention can be used without particular limitation as long as it is produced by a conventionally known production method. As the amorphous polypropylene having the above characteristics, a commercially available product such as "Tough Selene" (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, the α-olefin may be, for example, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene. , 4-Methyl-1-pentene, propylene-ethylene-1-butene and the like are desirable.

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

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

The biaxially oriented polypropylene film of the present invention preferably contains an ethylene component of 10% by mass or less in the polymer constituting the film. It is more preferably 5% by mass or less, still more preferably 3% by mass or less. The higher the content of ethylene component, the lower the crystallinity and the easier it is to improve flexibility and transparency. However, if the content of ethylene component exceeds 10% by mass, the heat resistance will decrease and fish eyes will occur. It may be more likely to occur.

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

The polypropylene raw material of the present invention contains various additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a slip agent, an antistatic agent, an antiblocking agent, a filler and a viscosity, as long as the object of the present invention is not impaired. It can also contain an adjusting agent, an anticoloring agent and the like.

Among these, the selection of the type and amount of antioxidant is important from the viewpoint of long-term stability. That is, the antioxidant is preferably a phenolic agent having steric hindrance, and at least one of them is a high molecular weight type having a molecular weight of 500 or more. Specific examples thereof include various examples, such as 1,3,5-trimethyl-2,4,6-with 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4). Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (eg, BASF's "Irganox"® 1330: molecular weight 775.2) or tetrakis [methylene-3 (3,5-di-) t-Butyl-4-hydroxyphenyl) propionate] methane (for example, "Irganox" 1010 manufactured by BASF: molecular weight 1177.7) or the like is preferably used in combination. The total content of these antioxidants is preferably in the range of 0.03 to 1.0% by mass with respect to the total amount of polypropylene. If the amount of the antioxidant is too small, the polymer may deteriorate in the extrusion process, the film may be colored, or the long-term heat resistance may be inferior. If there are too many antioxidants, the bleed-out of these antioxidants may reduce transparency. 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 within a range not contrary to the object of the present invention. Examples of the crystal nucleating agent include α-crystal nucleating agents (dibenzylidene sorbitols, sodium benzoate, etc.) and β-crystal nucleating agents (potassium 1,2-hydroxystearate, magnesium benzoate, N, N'-dicyclohexyl-2,6. -Amid compounds such as naphthalenedicarboxamide, quinacridone compounds, etc.) are exemplified. However, since excessive addition of the above-mentioned other type of nucleating agent may cause a decrease in stretchability and a decrease in transparency and strength due to void formation, etc., the addition amount is usually 0.5% by mass or less, preferably 0.1. It is preferably mass% or less, more preferably 0.05 mass% or less.

The biaxially oriented polypropylene film of the present invention is obtained by biaxially stretching using the above-mentioned raw materials. As a method of biaxial stretching, any of the inflation simultaneous biaxial stretching method, the stenter simultaneous biaxial stretching method, and the stenter sequential biaxial stretching method can be obtained. Among them, the film forming stability, the thickness uniformity, and the film It is preferable to adopt the stenter sequential biaxial stretching method in terms 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 laminated structure of at least two layers from the viewpoint of achieving both transparency and slipperiness .

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

Further, in the biaxially oriented polypropylene film of the present invention, it is preferable that at least one layer (base layer (II)) other than the surface layer (I) contains polypropylene raw material B from the viewpoint of improving transparency in the laminated structure. , The mixing ratio of the polypropylene raw material A and the polypropylene raw material B is preferably 0: 100 to 95: 5 (mass ratio; the same applies hereinafter). It is more preferably 0: 100 to 90:10, and even 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 thickness d of the surface layer (I) is preferably 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 it is less than 0.1 μm, the stacking accuracy becomes unstable and the thickness unevenness of the surface layer (I) may become large. The thickness d of the surface layer (I) can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film forming speed, the stretching ratio, and the like within a range that does not deteriorate other physical properties. When the surface layers (I) are provided on both surfaces of the film, it is preferable that the above range is satisfied for each layer.

In the biaxially oriented polypropylene film of the present invention, the ratio of the surface layer (I) to the total thickness of the film is preferably 1 to 15%. It is 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 stacking accuracy becomes unstable and the thickness unevenness of the surface layer (I) may become large. The thickness d of the surface layer (I) can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film forming speed, the stretching ratio, and the like within a range that does not deteriorate other physical properties. When the surface layers (I) are provided on both surfaces of the film, it is preferable that the above range is satisfied for each layer.

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

The slippery particles are not particularly limited as long as they do not impair the effects of the present invention, and for example, inorganic particles and organic particles can be used. Inorganic particles include silica, titanium oxide, aluminum oxide, zirconium oxide, calcium carbonate, carbon black, zeolite particles, etc. Organic particles include acrylic resin particles, styrene resin particles, polyester resin particles, polyurethane resin particles. , Polycarbonate resin particles, polyamide resin particles, silicone resin particles, fluorine resin particles, copolymer resin particles of two or more kinds of monomers used for synthesizing the above resin, and the like. However, since polypropylene resin has a low surface energy, when particles are added and stretched, the particle interface may peel off during stretching to generate voids, which may increase haze and reduce transparency. From the viewpoint of improving transparency, it is preferable to use the above-mentioned inorganic particles or organic particles having a silane coupling treatment on the surface, and silica particles having a silane coupling treatment are particularly preferable.

The average particle size of the slippery 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 and the transparency may decrease. When the average particle size is 1.0 μm or more, voids are likely to be generated at the particle interface during stretching, and the transparency may be lowered. In addition, the particles added to the surface layer may fall off during film formation, resulting in an increase in surface roughness or an increase in haze. The average particle size is more preferably 0.15 μm or more and less than 0.9 μm, and further preferably 0.15 μm or more and less than 0.8 μm. Further, from the viewpoint of improving handleability, two or more kinds of particles having different average particle diameters may be used in combination.

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

The content of the slippery particles in the raw material of the layer containing the slippery particles is preferably 0.01% by mass or more and less than 1.0% by mass. If the content is less than 0.01% by mass, the effect of reducing the friction coefficient may not be obtained. If the content is 1.0% by mass or more, 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 further 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 containing 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 protrusions on the film surface and improve the slipperiness. In such a case, it is preferable that the film is composed of at least two layers of the surface layer (I) and the base layer (II), and the surface layer (I) contains a resin having a melting point of 180 ° C. or higher. When a melting point of 180 ° C. or higher is present in the surface layer (I), it is melted and dispersed in polypropylene in the melt extrusion step described later, and is not deformed in the stretching step, and the above-mentioned protrusions can be formed. In order to make the protrusions to be formed fine as described above, it is necessary to finely disperse them in polypropylene in the melt extrusion step, and it is important that they have a high affinity with polypropylene. From this point of view, the resin having a melting point of 180 ° C. or higher is preferably an olefin resin, but among the olefin resins, the olefin resin containing 4-methylpentene-1 unit may be the main component. preferable. Since the resin containing 4-methylpentene-1 unit has a higher affinity with the polypropylene resin as compared with the non-olefin resin, the dispersibility can be enhanced. Examples of the olefin resin containing 4-methylpentene-1 unit include "TPX" (registered trademark) DX310, "TPX" DX231, and "TPX" MX004 manufactured by Mitsui Chemicals, Inc.

In the biaxially oriented polypropylene film of the present invention, the content of the olefin resin containing 4-methylpentene-1 unit in the resin composition of the surface layer (I) is 0.1 to 5% by mass. Is preferable, 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 unit is more than 5% by mass, the protrusions may form a long mountain range in the longitudinal direction, and when used as a base film or cover film, There are drawbacks such as air biting when winding is difficult, 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. It may be more likely to occur. When the content is less than 0.1% by mass, the frequency of the formed protrusions becomes too low, which does not contribute to the improvement of slipperiness and may reduce the winding property.

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

The raw material used for the surface layer of the biaxially oriented polypropylene film of the present invention is a blend of a refractory resin and a polypropylene resin, and a method of kneading in advance with a biaxial extruder to form chips is preferable. The kneading temperature at this time is preferably higher than the melting point of the refractory resin from the viewpoint of dispersion uniformity, more preferably 10 ° C. or higher, still more preferably 20 ° C. or higher. When the kneading temperature is lower than the melting point of the high melting point resin, the dispersibility may decrease and the protrusions may become coarse. The upper limit of the kneading temperature is not particularly determined, but if it is too high, thermal decomposition of the polypropylene resin may occur, and the upper limit is 280 ° C.

In the biaxially oriented polypropylene film of the present invention, it is preferable that the extrusion temperature at the time of melt extrusion is equal to or lower than the melting point of the refractory resin. It is more preferably 10 ° C. or lower, and even more preferably 20 ° C. or lower. When melt-extruded at a temperature equal to or higher than the melting point of the refractory resin, the refractory resin uniformly and finely dispersed in the polypropylene resin may be melted and fused and coarsened, or stretched for a long time due to shear flow during extrusion. As a result, the protrusions 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 filter pressure may increase during extrusion or unmelted polypropylene resin may be generated, and the lower limit is 200 ° C.

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

Next, the method for producing a biaxially oriented polypropylene film of the present invention will be described by way of example, but 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, more preferably 240 to 280 ° C, and even more preferably 250 to 280 ° C. A master raw material, 20 parts by mass and a polypropylene raw material A, 80 parts by mass are dry-blended and supplied to a single-screw extruder for the A layer (surface layer (I)), and the polypropylene raw material A, 60 parts by mass and the polypropylene raw material B, 40 are supplied. The mass portion is supplied to a single-screw extruder for the B layer (base layer (II)), and melt extrusion is performed at 200 to 260 ° C. Then, after removing foreign substances and modified polymers with a filter installed in the middle of the polymer tube, they are 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 a layer / B layer / A layer is obtained. At this time, the laminated thickness ratio is preferably 1/8/1 to 1/50/1. Further, it is preferable that the surface temperature of the casting drum is 10 to 40 ° C. from the viewpoint of transparency. Further, a two-layer laminated structure of A layer / B layer may be used.

At this time, it is preferable to set the lip temperature of the base to a low temperature of 20 to 40 ° C. from the melt extrusion temperature, and more preferably 30 to 40 ° C. By lowering the lip temperature, the shear stress of the molten polymer in contact with the inner wall of the base increases, the orientation of the film surface layer becomes particularly high, and when the film roll is wound, the film surface is less likely to be deformed, which is effective in reducing Wa. I found that.

As the adhesion method 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, the underwater casting method, etc. may be used, but the flatness is high. The air knife method, which is good and can control the surface roughness, is preferable. The air temperature of the air knife is 0 to 50 ° C., preferably 0 to 30 ° C., and the blowing air speed is preferably 130 to 150 m / s. Further, it is preferable to appropriately adjust the position of the air knife so that air flows to the downstream side of the film formation so as not to cause vibration of the film.

Further, by further forcibly cooling the non-casting drum surface of the film after the film is brought into close contact with the casting drum, β crystal formation on the non-casting drum surface can be suppressed, and the smoothness and transparency of the film are improved. be able to. The non-casting drum surface may be cooled by any of air cooling, press roll method, underwater casting method, etc., but the equipment is simple, the surface roughness can be easily controlled, and the smoothness is high. Air cooling with good air is preferred.

The obtained unstretched sheet is introduced into the longitudinal stretching step. In the longitudinal stretching step, first, the unstretched sheet is brought into contact with a plurality of metal rolls kept at 120 ° C. or higher and lower than 150 ° C. to preheat and raise the temperature to the stretching temperature. After stretching 3 to 8 times, cool to room temperature. If the stretching temperature is 150 ° C. or higher, the surface of the film may be roughened and the transparency may be lowered. If the draw ratio is less than 3 times, the surface of the film may be roughened and the transparency may be lowered. Further, at this time, among the two pairs of nip rolls provided with the peripheral speed difference, the temperature of the roll having a high speed on the downstream side is preferably 10 ° C. or more lower than the temperature of the roll on the upstream side. 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 the Wa becomes large, and when used as a base film or a cover film, the surface of the product becomes uneven. It may be transferred. From the above viewpoint, the temperature of the roll on the upstream side is preferably 120 ° C. or higher and lower than 150 ° C., and the temperature of the roll on the downstream side is more preferably 30 ° C. or higher and lower than 100 ° C.

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

In the subsequent heat treatment and relaxation treatment steps, while tensioning the width direction with a clip and giving relaxation at a relaxation rate of 2 to 20% in the width direction, heat fixing at a temperature of 100 ° C or higher and lower than 160 ° C is performed, and the width direction is fixed with a clip. Is guided to the outside of the tenter through a cooling step at 80 to 100 ° C. while being tensely gripped, the clip at the end of the film is released, the film edge is slit in the winder step, and the wide film roll is wound up. The take-up tension at this time is preferably 10 to 100 N / m. If the tension is less than 10 N / m, the film may be unwound, and if it exceeds 100 N / m, the biaxially oriented polypropylene film may be rolled tight due to dimensional shrinkage immediately after film formation, and the flatness may be deteriorated.

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

The biaxially oriented polypropylene film obtained as described above can be used for various purposes such as packaging films, surface protective films, process films, sanitary products, agricultural products, building products, medical products, etc., but especially on the surface. 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 resist as an example. The PET film subjected to the silicone mold release treatment is unwound as a process film, and a resist coating liquid is applied onto the film. After the coating liquid is dried at a predetermined temperature, the biaxially oriented polypropylene film of the present invention is bonded as a resist cover film, and the PET film, the resist layer, and the laminated body of the biaxially oriented polypropylene film are wound up to obtain a product. .. Since the surface of the biaxially oriented polypropylene film of the present invention is smooth, there is little uneven transfer to the resist surface, and the biaxially oriented polypropylene film can be preferably used in applications requiring a high-definition exposure pattern.

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 film formation of an optical film as an example. The biaxially oriented polypropylene film of the present invention is unwound from a coater, coated with a solution of an optical member and dried at 80 to 100 ° C., and then the optical film is peeled off from the process film to completely remove the solvent. Further dry to obtain an optical film. Since the surface of the biaxially oriented polypropylene film of the present invention is smooth, surface unevenness transfer to the optical film is small, and the biaxially oriented polypropylene film can be preferably used as a protective film for a high-quality optical film.

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

The pressure-sensitive adhesive used for the pressure-sensitive 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, examples of the rubber-based pressure-sensitive adhesive include a butadiene-styrene copolymer system, a butadiene-acrylonitrile copolymer system, and an isobutylene-isoprene copolymer system. Examples of the vinyl polymerization type pressure-sensitive adhesive include an acrylic type, a styrene type, a vinyl acetate-ethylene copolymer system, and a vinyl chloride-vinyl acetate copolymer system. Moreover, as a condensation polymerization type pressure-sensitive adhesive, a polyester type can be mentioned. Further, examples of the thermosetting resin-based adhesive include an epoxy resin-based adhesive and a urethane resin-based adhesive.

Among these, an acrylic pressure-sensitive adhesive is preferably used in consideration of excellent transparency, weather resistance, heat resistance, moisture heat resistance, substrate adhesion, and the like. Specific examples of such an acrylic pressure-sensitive adhesive 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 Kagaku Co., Ltd. , SK Dyne 1852 and the like are preferred examples.

Further, it is preferable to use a curing agent together with the acrylic pressure-sensitive adhesive. Specific examples of the curing agent include toluene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylene diisocyanate, and diphenylmethane-4 in the case of isocyanate. -4'-diisocyanate, diphenylmethane-2-4'-diisocyanate, 3-methyldiphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4-4'-diisocyanate, disiquiurohexylmethane-2-4'-diisocyanate , Lysine isocyanate and the like. The mixing ratio of the curing agent is 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the pressure-sensitive adhesive. If it is less than 0.1 part by mass, the pressure-sensitive adhesive layer may not be sufficiently cured in the drying oven, resulting in lining up. If it exceeds 10 parts by mass, the excess curing agent may be transferred to the substrate or gasified at a high temperature to cause contamination.

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

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, 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, the adhesive layer may be lined off. “Betrayal” means that the pressure-sensitive adhesive layer solution is applied to one side of the base film, then dried and cured in a drying furnace, and the pressure-sensitive adhesive film of the present invention is wound into a roll without using a release film. Later, when the adhesive film is unwound during use, a part of the adhesive layer is transferred to the back surface of the base film. If the thickness d of the pressure-sensitive adhesive layer exceeds 1.0 μm, the pressure-sensitive adhesive layer may not be sufficiently dried in a drying oven, resulting in betrayal. Further, if the thickness of the adhesive layer is thick, when the film of the present invention is attached to a product and used in a process requiring decompression such as vapor deposition or sputtering, the volatile components from the adhesive layer hinder the decrease in the degree of decompression. There is. A known technique can be used as a method for setting the thickness of the adhesive layer within the above range, and it can be controlled by adjusting the solid content concentration of the solution of the adhesive layer and adjusting the coating thickness in various coating methods. If the thickness of the adhesive layer is too thin, stable coating may be difficult, or the adhesive strength may be too low to adhere to the adherend. Therefore, 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 being bonded to a glass plate. The peeling force is more preferably 0.5 N / 25 mm or less, further preferably 0.2 N / 25 mm or less, still more preferably 0.05 N / 25 mm or less. If the peeling force exceeds 1 N / 25 mm, the slipperiness between the back surface of the base film and the surface of the adhesive layer deteriorates, which may make winding difficult or betrayal. In order to set the peeling force in the above range, the composition and thickness of the adhesive layer are set in the range described later, and the raw material composition and film forming conditions of the film are set in the range described later, and the surface roughness of the base film is controlled. Is effective. If the peeling force is less than 0.01 N / 25 mm, the adhesive film may be peeled off during transportation after being bonded to the adherend, so the lower limit is about 0.01 N / 25 mm.

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

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

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

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

After applying the coating material for the pressure-sensitive adhesive layer to the base film, the film is guided to a drying furnace and the solvent in the coating material is removed to obtain a pressure-sensitive adhesive film. The drying temperature here is appropriately set depending on the heat resistance of the base film and the boiling point of the solvent, but is preferably 60 to 170 ° C. If the temperature is lower than 60 ° C., the pressure-sensitive adhesive layer may not be sufficiently cured and betrayed may occur. If the temperature exceeds 170 ° C., the base film may be deformed and the flatness may be deteriorated. The drying time is preferably 15 to 60 seconds. If it is less than 15 seconds, the adhesive layer may not be sufficiently cured and betrayed may occur. If it exceeds 60 seconds, the productivity is lowered, which is not preferable.

The adhesive film after drying can be wound with a winder without using a release film or the like to obtain an adhesive film roll. The pressure-sensitive adhesive film of the present invention has the above-mentioned structure, so that the pressure-sensitive adhesive layer is sufficiently cured and the slipperiness between the back surface of the base film and the surface of the pressure-sensitive adhesive layer is good. Even if it is taken, there is no problem such as line-up or wrinkles during winding, and a high-quality adhesive film roll can be obtained. However, if necessary, it may be wound using a release film.

The adhesive film obtained as described above can be used for various purposes such as packaging films, surface protective films, process films, sanitary products, agricultural products, construction products, medical products, etc., but especially for surface smoothness. Since it is excellent, it can be preferably used as a surface protective film or 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, an adhesive is applied to one side thereof, and the film is dried at 80 to 100 ° C. to obtain an adhesive film. After that, the adhesive film can be bonded and used in the film forming process and the inspection process of the optical member. Since the surface of the biaxially oriented polypropylene film of the present invention is smooth, there is little surface unevenness transfer to the optical member, and the biaxially oriented polypropylene film can be preferably used as a release film for a member of a high-definition image display element.

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

Hereinafter, the present invention will be described in detail with reference to Examples. The characteristics were measured and evaluated by the following methods.

(1) Film thickness Measured using a microthickness meter (manufactured by Anritsu). The film was sampled in a 10 cm square, and 5 points were arbitrarily measured to obtain an average value.

(2) Waviness value (Wa)
The measurement was performed using Ryoka System Co., Ltd. VertScan 2.0 R5300GL-Lite-AC, and the surface shape was obtained by surface-correcting the photographed screen by polynomial quaternary approximation using the attached analysis software. The measurement conditions are as follows. The measurement was carried out at n = 3 on both sides of the film according to the method specified in JIS B0601 (2001), and the average value was adopted as Wa on 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 minute intermediate lens 0.5x
Wavelength filter 530nm white
Measurement mode: Wave
Measurement software: VS-Measure Version 5.5.1
Analysis software: VS-Viewer Version 5.5.1
Measurement area: 1.252 x 0.939 mm ² .

(3) Heat shrinkage rate in the MD direction Five samples with a width of 10 mm and a length of 200 mm (measurement direction) are cut out in each of the width directions of the film, and marked as marked lines at positions 25 mm from both ends for universal use. Measure the distance between the marked lines with a projector and use it as the test length (l ₀ ). Next, the test piece is sandwiched between papers, heated in an oven kept at 85 ° C. with no load, taken out after heating for 60 minutes, cooled at room temperature, and then the dimensions (l ₁ ) are measured with a universal projector and described below. It was calculated by the formula, and the average value of 5 pieces was taken as the heat shrinkage rate.

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

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

(5) Static friction coefficient μs
Using a friction measuring instrument manufactured by Toyo Tester Industries, measure the initial rising resistance value when one side of the film and the other side are overlapped so as to be in contact with each other and the MD directions are rubbed against each other according to ASTM D1894. The maximum value was set to the static friction coefficient μs. However, if the initial rise was large and exceeded the upper limit of the measured value (5.0), measurement was not possible. The sample was a rectangle with a width of 80 mm and a length of 200 mm, and 5 sets (10 sheets) were cut out. The measurement was performed 5 times, and the average value was calculated.

(6) Evaluation of transfer to an adherend An adhesive film and "Zeonoa film" (registered trademark) manufactured by Nippon Zeon Corporation with a thickness of 40 μm were sample-ringed into a square with a width of 100 mm and a length of 100 mm, and the back surface of the adhesive film and "Zeonoa" were sampled. The films were stacked so as to be in contact with each other, sandwiched between two acrylic plates (width 100 mm, length 100 mm), a load of 3 kg was applied, and the film was allowed to stand for 24 hours in an atmosphere of 23 ° C. After 24 hours, the surface of the "Zeonoa 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: Transfer of weak yuzu skin or transfer of weak unevenness is confirmed C: Transfer of weak yuzu skin and transfer of weak unevenness are confirmed D: Strong yuzu skin transfer and / or strong uneven transfer is confirmed.

(7) Evaluation of transfer to the adherend after heating An adhesive film and "Zeonoa film" (registered trademark) manufactured by Nippon Zeon Corporation with a thickness of 40 μm are sample-ringed into a square with a width of 100 mm and a length of 100 mm, and the back surface of the adhesive film is formed. And "Zeonoa film" are stacked so that they 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 the film is heated in an oven heated to 85 ° C for 1 hour. bottom. Then, it was taken out from the oven, the weight was removed, and after standing for 24 hours, the surface of the "Zeonoa 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: Transfer of weak yuzu skin or transfer of weak unevenness is confirmed C: Transfer of weak yuzu skin and transfer of weak unevenness are confirmed D: Strong yuzu skin transfer and / or strong uneven transfer is confirmed.

(Example 1)
Crystalline polypropylene (manufactured by Prime Polymer Co., Ltd., TF850H, MFR: 2.9 g / 10 minutes, 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, it was discharged to a casting drum whose surface temperature was controlled to 30 ° C. and brought into close contact with the casting drum with an air knife. Then, the uncooled drum surface of the sheet on the casting drum was cooled by injecting compressed air at a temperature of 30 ° C. and a pressure of 0.3 MPa to obtain an unstretched sheet. Subsequently, the sheet was preheated to 145 ° C. using a ceramic roll, and the film was stretched 4.2 times in the longitudinal direction between the rolls provided with a peripheral speed difference. At this time, among the rolls provided with the peripheral speed difference, the temperature of the roll on the upstream side was 143 ° C, and the temperature of the roll having a high speed on the downstream side was 70 ° C. Next, the end was gripped with a clip and introduced into a tenter type stretching machine, preheated at 170 ° C for 3 seconds, stretched 8.0 times at 165 ° C, and at 150 ° C while giving 10% relaxation in the width direction. The heat treatment was performed, and then the film was guided to the outside of the tenter through a cooling step of 100 ° C., the clip at the end of the film was released, and the film having a width of 800 mm was wound around the core. The take-up tension at this time was 50 N / m. After storage in an atmosphere of 25 ° C. for 48 hours, 100 mm at each end was slit to a width of 600 mm, and the film was wound around a core at 100 N / m to obtain a biaxially oriented polypropylene film having a thickness of 24 μm. Table 1 shows the physical characteristics of the obtained film and the evaluation results. However, the contact surface with the casting drum is the A surface, and the opposite surface is the B surface.

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

As a polypropylene raw material for the surface 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 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, the polypropylene is laminated with a feed block type A / B / A composite T-die at a thickness ratio of 1/22/1, discharged to a casting drum whose surface temperature is controlled to 25 ° C., and cast drum with an air knife. It was brought into close contact with. Then, the uncooled drum surface of the sheet on the casting drum was cooled by injecting compressed air at a temperature of 30 ° C. and a pressure of 0.3 MPa to obtain an unstretched sheet. In the following, a biaxially oriented polypropylene film having a thickness of 24 μm was obtained by the same method as in Example 1. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

(Example 3)
In Example 2, as a polypropylene raw material for the core layer (B), 90 parts by mass of a polypropylene resin FSX20L8 (MFR = 2.0 g / 10 min, isotactic index (II) = 96%) manufactured by Sumitomo Chemical Co., Ltd. and Idemitsu Kosan Co., Ltd. 10 parts by mass of "El Modu" (registered trademark) S901 (MFR 50 g / 10 min, mesopentad fraction 50%) is dry-blended and supplied to a single-screw melt extruder for layer B. 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 characteristics of the obtained film and the evaluation results.

(Example 4)
In Example 2, the temperature of the roll on the downstream side of the rolls provided with the peripheral speed difference of the longitudinal stretching was set to 125 ° C., and further relaxed by 5% in the MD direction with the following rolls, and the other rolls were relaxed. A biaxially oriented polypropylene film having a thickness of 24 μm was obtained by the same method as in Example 2. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

(Example 5)
In Example 2, the thickness ratio at the time of lamination was set to 1/38/1, and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained by the same method as in Example 3 except that. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

(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 the same method as in Example 3 was used to obtain a biaxially oriented polypropylene film having a thickness of 24 μm. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

(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) are dry-blended as the polypropylene raw material for the surface layer (A) to melt the single shaft for the A layer. As a polypropylene raw material for the core layer (B) supplied to the extruder, 80 parts by mass of Sumitomo Chemical polypropylene resin FSX20L8 and 20 parts by mass of Idemitsu Kosan Co., Ltd. "El Modu" S901 are dry-blended to form B layer. It is supplied to a single-screw melt extruder for use, melt-extruded at a melt temperature of 210 ° C and a lip temperature of 200 ° C, and a film having a width of 800 mm is wound around a core and then stored in an atmosphere of 40 ° C for 60 hours. Later, slitting was performed to obtain a biaxially oriented polypropylene film. A biaxially oriented polypropylene film having a thickness of 22 μm was obtained by the same method as in Example 2 except for the above. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

(Comparative Example 1)
In Example 2, a winding tension when winding a film having a width of 800 mm on a core was set to 120 N / m, and a biaxially oriented polypropylene film having a thickness of 24 μm was obtained by the same method as in Example 2 except that. The swell value Wa increased, and transfer of yuzu skin was confirmed. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

(Comparative Example 2)
In Example 1, the temperature of the roll on the downstream side of the rolls provided with the peripheral speed difference of longitudinal stretching was set to 140 ° C., and further relaxed by 10% in the MD direction with the following rolls, and other than that. A biaxially oriented polypropylene film having a thickness of 24 μm was obtained by the same method as in Example 1. The heat yield in the MD direction was small, the waviness value Wa was large, and the transfer of yuzu skin was confirmed. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

(Comparative Example 3)
In Example 1, among the rolls provided with the peripheral speed difference of longitudinal stretching, the temperature of the roll on the upstream side 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. Obtained a biaxially oriented polypropylene film having a thickness of 24 μm in the same manner as in Example 1. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

(Comparative Example 4)
In Example 1, the lip temperature at the time of melt extrusion was set to 240 ° C., the temperature of the roll on the downstream side of the rolls provided with the peripheral speed difference of longitudinal stretching was set to 138 ° C., and the other methods were the same as in Example 1. A biaxially oriented polypropylene film having a thickness of 24 μm was obtained. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

(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 the same method as in Example 3 was used to obtain a biaxially oriented polypropylene film having a thickness of 24 μm. rice field. Table 1 shows the physical characteristics of the obtained film and the evaluation results.

Claims (9)

A biaxially oriented polypropylene film having a laminated structure of at least two layers, the surface layer 1 layer (surface layer (I)) on at least one side of the laminated structure contains 96% by mass or more of the polypropylene raw material A, and the polypropylene raw material A is contained. The cold xylene soluble part (CXS) is 4% by mass or less, the mesopentad fraction is 0.95 or more, and the melt flow rate (MFR) is 1 to 10 g / 10 minutes (230 ° C., 21.18N). Load)
Biaxially oriented polypropylene having a waviness value Wa of at least one side of 45 nm or less, a heat shrinkage rate in the MD direction after 60 minutes at 85 ° C. of 0.3 to 2%, and a static friction coefficient μs of 0.55 or less. the film. The biaxially oriented polypropylene film according to claim 1 , wherein the haze is 1% or less. A release film using the biaxially oriented polypropylene film according to claim 1 or 2 . A process film for solution film formation using the biaxially oriented polypropylene film according to claim 1 or 2 . An adhesive film provided with an adhesive layer on the biaxially oriented polypropylene film according to claim 1 or 2 . A biaxially oriented polypropylene film having a laminated structure of at least two layers, the surface layer 1 layer (surface layer (I)) on at least one side of the laminated structure contains 96% by mass or more of the polypropylene raw material A, and the polypropylene raw material A is contained. The cold xylene soluble part (CXS) is 4% by mass or less, the mesopentad fraction is 0.95 or more, and the melt flow rate (MFR) is 1 to 10 g / 10 minutes (230 ° C., 21.18N). Load)
A biaxially oriented polypropylene film having a waviness value Wa of at least one side of 45 nm or less, a heat shrinkage rate of 0.3 to 2% in the MD direction after 60 minutes at 85 ° C., and a haze of 1% or less. A biaxially oriented polypropylene film having a laminated structure of at least two layers, the surface layer 1 layer (surface layer (I)) on at least one side of the laminated structure contains 96% by mass or more of the polypropylene raw material A, and the polypropylene raw material A is contained. The cold xylene soluble part (CXS) is 4% by mass or less, the mesopentad fraction is 0.95 or more, and the melt flow rate (MFR) is 1 to 10 g / 10 minutes (230 ° C., 21.18N). Load)
A release film using a biaxially oriented polypropylene film having a waviness value Wa of at least one side of 45 nm or less and a heat shrinkage rate of 0.3 to 2% in the MD direction after 60 minutes at 85 ° C. A biaxially oriented polypropylene film having a laminated structure of at least two layers, the surface layer 1 layer (surface layer (I)) on at least one side of the laminated structure contains 96% by mass or more of the polypropylene raw material A, and the polypropylene raw material A is contained. The cold xylene soluble part (CXS) is 4% by mass or less, the mesopentad fraction is 0.95 or more, and the melt flow rate (MFR) is 1 to 10 g / 10 minutes (230 ° C., 21.18N). Load)
A process film for solution film formation using a biaxially oriented polypropylene film having a waviness value Wa of at least one side of 45 nm or less and a heat shrinkage rate of 0.3 to 2% in the MD direction after 60 minutes at 85 ° C. A biaxially oriented polypropylene film having a laminated structure of at least two layers, the surface layer 1 layer (surface layer (I)) on at least one side of the laminated structure contains 96% by mass or more of the polypropylene raw material A, and the polypropylene raw material A is contained. The cold xylene soluble part (CXS) is 4% by mass or less, the mesopentad fraction is 0.95 or more, and the melt flow rate (MFR) is 1 to 10 g / 10 minutes (230 ° C., 21.18N). Load)
A pressure-sensitive adhesive film provided with an adhesive layer on a biaxially oriented polypropylene film having a waviness value Wa of at least one side of 45 nm or less and a heat shrinkage rate of 0.3 to 2% in the MD direction after 60 minutes at 85 ° C.