JP2022140476A - polyolefin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film which is excellent in transparency, slipperiness and heat resistance.

SOLUTION: A polyolefin film has a crystallization temperature Tc0 determined by measuring a film by DSC and using an extrapolation point method of 110°C or higher and in-plane retardation of 400 nm or less, a coefficient μd of dynamic friction after surface layers (I) have been heated at 130°C for 10 minutes of 0.7 or less, breaking elongation at 130°C in a direction orthogonal to a film main orientation direction of 100% or more, contains a polypropylene resin as a main component, and has at least surface layers (I) and a base layer (II).

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a polyolefin film that is excellent in transparency, lubricity and heat resistance and that can be suitably used as a film for industrial materials.

Polyolefin films are excellent in transparency, mechanical properties, electrical properties, etc., and are used in various applications such as packaging, mold 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.

When used as a protective film or a cover film, the presence or absence of defects in the adherend may be checked while it is attached to the adherend. At that time, if the transparency of the protective film or cover film is low, it may be difficult to confirm the defect of the adherend. In particular, when used as a protective film for a retardation plate, not only transparency but also low retardation properties are required, and in recent years, the required level has been increasing more and more.

In general, when it is intended to increase the transparency, the film surface is also smoothed, so the slipperiness is impaired, and the flatness may be deteriorated, for example, wrinkles are likely to occur during process transportation. Moreover, when it is going to raise transparency, the method of reducing the crystallinity of polyolefin resin is used. However, if the crystallinity is lowered, when the film is exposed to a high-temperature environment, the low-melting-point portion of the film surface may partially melt, increasing the dynamic friction coefficient and further impairing the lubricity. Thus, conventionally, it has been difficult to achieve both smoothness and slipperiness.

From the above, a film for industrial materials that satisfies the required properties is required to have transparency, lubricity, and heat resistance.

As a film having a reduced in-plane retardation, for example, Patent Document 1 describes an example in which the retardation is reduced by adding a low melting point polypropylene resin to the inner layer of the film. In addition, as a film with improved lubricity, for example, Patent Document 2 describes an example in which the cast temperature is raised, a large amount of β crystals are formed, and the surface is roughened to make the film easier to lubricate. Further, Patent Document 3 describes a film in which retardation is reduced by using a cyclic olefin resin.

WO2015/129851 Japanese Patent Application Laid-Open No. 2001-247693 JP 2018-126909 A

However, the method described in Patent Document 1 described above has the problem that the film surface is smooth and the slipperiness is low, especially after high-temperature heating, the slipperiness is low and the flatness is insufficient. Further, in the method described in Patent Document 2, the surface roughness is high and the in-plane retardation of the film is insufficient. Moreover, the method described in Patent Document 3 has problems that the film itself is fragile, that handling is insufficient, and that the cost is high.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems. That is, the object is to provide a polyolefin film excellent in transparency, lubricity and heat resistance.

In order to solve the above-mentioned problems and achieve the object, the polyolefin film of the present invention has a crystallization temperature Tc ₀ of 110 ° C. or higher measured by DSC and obtained by extrapolation point method, and the surface of the film The internal retardation is 400 nm or less, the dynamic friction coefficient μd after heating at 130 ° C. for 10 minutes is 0.7 or less, the main component is a polypropylene resin, and at least
It is characterized by having a surface layer (I) and a base layer (II).

INDUSTRIAL APPLICABILITY The polyolefin film of the present invention is excellent in transparency, heat resistance, and lubricity, and thus can be widely and suitably used as a film for industrial materials.

It is an example of a graph showing the crystallization temperature _Tc0 of a polyolefin film.

In the polyolefin film of the present invention, the film is measured by DSC, the crystallization temperature _Tc0 obtained by the extrapolation point method is 110 ° C. or more, the in-plane retardation of the film is 400 nm or less, and the film is heated at 130 ° C. for 10 minutes. The subsequent dynamic friction coefficient μd is 0.7 or less. A polyolefin film is a film containing more than 50% by mass and 100% by mass or less of a polyolefin resin when all components constituting the film are taken as 100% by mass. A polyolefin resin is a resin in which olefin units account for more than 50 mol % and not more than 100 mol % of all structural units constituting the resin.

The polyolefin film of the present invention has a crystallization temperature _Tc0 of 110° C. or higher, preferably 115° C. or higher, more preferably 118° C. or higher, more preferably 118° C. or higher, which is obtained by measuring the film with DSC and obtaining it by extrapolation point method. is above 123°C. If Tc ₀ is less than 110° C., for example, coarse spherulites are formed during casting, resulting in a large in-plane retardation. may occur. In order to make Tc ₀ equal to or higher than 110° C., for example, the raw material composition of the polyolefin film is set within the range described later, and in particular, it is preferable to add a raw material having a nucleating agent action, and among these, it is preferable to add a branched chain polypropylene raw material. preferable. It is also effective to adjust the amounts of the high-molecular-weight components and the low-molecular-weight components of the polypropylene resin used for the polyolefin film within a specific range. Although the upper limit of the crystallization temperature _Tc0 is not particularly limited, it is substantially about 135°C. DSC means differential scanning calorimeter.

In the polyolefin film of the present invention, the in-plane retardation of the film is 400 nm or less, preferably 300 nm or less, more preferably 200 nm or less, and even more preferably 100 nm or less. If the in-plane retardation is greater than 400 nm, for example, when the film is used as a retardation protective film, problems may occur when inspecting the retardation properties in a state where the film is attached to an adherend. In order to make the in-plane retardation 400 nm or less, for example, the raw material composition of the polyolefin film is set to the range described later, and the film forming conditions are set to the range described later. By reducing the size of the spherulites, by lowering the extrusion temperature and the temperature of the cast drum to increase the cooling during casting, by raising the preheating temperature during longitudinal/transverse stretching and stretching at a low temperature, uniform stretching can be achieved. It is effective to Although the lower limit of the in-plane retardation is not particularly limited, it is substantially about 30 nm.

In the polyolefin film of the present invention, the dynamic friction coefficient μd in the direction orthogonal to the main orientation direction (hereinafter sometimes referred to as the main orientation orthogonal direction) after heat treatment at 130° C. for 10 minutes is 0.7 or less. It is more preferably 0.6 or less, still more preferably 0.5 or less. The main orientation direction in the present invention is each direction forming an angle of 0° to 175° in increments of 5° with respect to an arbitrary direction in the plane of the film, when an arbitrary direction is 0°. The direction showing the highest value when Young's modulus is measured in In the polyolefin film of the present invention, the direction parallel to the film forming direction of the polyolefin 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 plane is the width direction or TD. called direction.

When using the polyolefin film of the present invention as a protective film, it may go through various high temperature processes. For example, when used as a release film for thermosetting resin, it may be thermally cured in a temperature range of about 120 to 150° C. after bonding to the thermosetting resin. When used as a capacitor film, radiant heat of 130 to 150° C. may be applied during metal sputtering. A well-known technique is to reduce the crystallinity of the polyolefin film when smoothing the polyolefin film. It may grow. When μd is 0.7 or less after heating at 130° C. for 10 minutes, for example, when used as a release film or a capacitor film, wrinkles are formed on the conveying roll by passing through a high temperature process, It is possible to reduce winding misalignment when winding together with the adherend.

In order to set the μd after heating at 130° C. for 10 minutes to 0.7 or less, for example, the raw material composition of the polyolefin film is set to the range described later, and the film forming conditions are set to the range described later, particularly preheating during longitudinal/transverse stretching. It is effective to raise the temperature, stretch the film at a low temperature at a high magnification, and perform the heat treatment and relaxation after the biaxial stretching within the range described later. Although the lower limit of μd after heating at 130° C. for 10 minutes is not particularly limited, it is substantially about 0.1.

The polyolefin film of the present invention preferably has a breaking elongation at 130° C. in the direction perpendicular to the main orientation of the film of 100% or more. More preferably 110% or more, still more preferably 120% or more. When the elongation at break at 130° C. is 100% or more, the breakage of the polyolefin film can be reduced in the above-described transportation process where high-temperature heat is applied, for example.

In order to achieve a breaking elongation of 100% or more at 130° C., for example, the raw material composition of the film is set within the range described later. It is effective to stretch the film at a low temperature and at a high magnification uniformly. Although the upper limit of the breaking elongation at 130°C is not particularly limited, it is substantially about 300%.

The polyolefin film of the present invention preferably has an internal haze (hereinafter sometimes simply referred to as haze) of 1.0% or less after heating at 130° C. for 10 minutes. It is more preferably 0.6% or less, still more preferably 0.3% or less. When the haze after heating at 130° C. for 10 minutes is 1.0% or less, for example, when used as a protective film, the transparency of the protective film is maintained even after passing through the above-described transportation process where high temperature heat is applied. It is possible to reduce defects that occur when inspecting with a defect inspection machine in the state of being bonded to the adherend.

In general, means for reducing the crystallinity of polyolefin resins may be used to reduce haze. For this reason, a polyolefin resin with low stereoregularity may be used, or a copolymer with a low melting point may be added. However, when such a low-melting resin is used, the mobility of the amorphous portion in the polyolefin film increases, and when heat is applied at a high temperature of 130° C. or higher, additives such as antioxidants in the polyolefin degrade the film. May bleed out to surface and impair transparency.

Based on the above points, in order to make the haze after heating at 130 ° C. 1.0% or less, for example, the raw material composition of the film is set to the range described later, and the film forming conditions are set to the range described later. Using a raw material with a high temperature to reduce the size of spherulites formed during casting, lowering the extrusion temperature and the temperature of the cast drum to increase cooling during casting, raising the preheating temperature during longitudinal/transverse stretching, and stretching It is effective to stretch uniformly by performing at a low temperature. It is also effective to use a raw material with high stereoregularity and low cold xylene solubles (hereinafter referred to as CXS) to improve crystallinity, and to perform heat treatment and relaxation after longitudinal and transverse stretching. Although the lower limit of haze after heating at 130° C. for 10 minutes is not particularly limited, it is substantially about 0.05%.

In the polyolefin film of the present invention, it is preferable that the unevenness of the orientation angle within a 10 cm square film is 3.0° or less. It is more preferably 2.5° or less, still more preferably 2.0° or less. When the unevenness of the orientation angle is less than or equal to 3.0°, it is possible to reduce problems that occur when the orientation angle is inspected in a state of being bonded to an adherend, for example.

In order to make the unevenness of the orientation angle 3.0° or less, for example, the raw material composition of the film is set to the range described later, and the film forming conditions are set to the range described later. / It is effective to increase the preheating temperature during lateral stretching, and to stretch the film uniformly at a high magnification at a low temperature. Although the lower limit of the unevenness of the orientation angle is not particularly limited, it is substantially about 0.1%.

Although the thickness of the polyolefin film of the present invention is appropriately adjusted depending on the application and is not particularly limited, it is preferably 0.5 μm or more and 100 μm or less from the viewpoint of handling. The upper limit of the thickness when used as a release film is more preferably 60 μm, still more preferably 30 μm, and most preferably 16 μm. The lower limit is more preferably 4 μm, still more preferably 8 μm, and most preferably 11 μm. Further, the upper limit of the thickness when used as a capacitor film is more preferably 15 μm, still more preferably 8 μm, and most preferably 3 μm. The lower limit is more preferably 0.9 μm, still more preferably 1.5 μm. 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 impair other physical properties.

Next, resins and the like suitable for producing the polyolefin film of the present invention will be described, but resins and the like constituting the polyolefin film of the present invention are not necessarily limited to these.

From the viewpoint of transparency and heat resistance, the polyolefin film of the present invention preferably contains a polypropylene resin as a main component. In the present invention, the "main component" means that the proportion of a specific component in all components is 50% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and still more preferably is 95% by mass or more and 100% by mass or less, more preferably 96% by mass or more and 100% by mass or less, particularly preferably 97% by mass or more and 100% by mass or less, and most preferably 98% by mass or more and 100% by mass or less. The polyolefin film of the present invention may contain only one kind of polypropylene resin, but preferably contains two or more kinds of polypropylene resins. When two or more components corresponding to polypropylene resin are contained in the film, if the total of these components is more than 50% by mass and not more than 100% by mass, it is considered to be "mainly composed of polypropylene resin". and

A polypropylene resin is a polyolefin resin containing more than 50 mol % and 100 mol % or less of propylene units when the total structural units constituting the molecular chains of the resin are taken as 100 mol %. Incidentally, the polypropylene resin may be hereinafter referred to as "polypropylene raw material".

The layer structure of the polyolefin film of the present invention is not particularly limited, and can be either a single layer structure or a laminated structure. Therefore, it is preferable to have at least the surface layer (I) and the base layer (II). When the polyolefin film has a single-layer structure, the main component of the polyolefin film itself is preferably polypropylene resin. When the polyolefin film has a laminated structure, it is preferable that the polyolefin film itself contains a polypropylene resin as a main component, and that the main component of the base layer (II), which will be described later, is a polypropylene resin.

In the polyolefin film of the present invention, the content of the cyclic olefin resin in the film is preferably less than 2.0% by mass when the entire film is taken as 100% by mass. It is more preferably less than 1.0% by mass, still more preferably less than 0.5% by mass. When the content of the cyclic olefin-based resin is less than 2.0% by mass, for example, even when a polypropylene resin and a cyclic olefin-based resin having low compatibility with each other are blended, deterioration in transparency of the polyolefin film is reduced. In addition, since the cyclic olefin resin is brittle, the content of the cyclic olefin resin is less than 2.0% by mass, so that breakage in a process in which a strong tension is applied can be reduced, thereby suppressing deterioration in handleability.

Hereinafter, the polypropylene resin (sometimes referred to as polypropylene raw material A), which is the main component of the polyolefin film of the present invention, will be described.

The lower limit of the number average molecular weight (Mn) of polypropylene raw material A is preferably 75,000, more preferably 80,000, and even more preferably 85,000, from the viewpoint of limiting the amount of low molecular weight components to a certain amount or less. The upper limit of Mn is preferably 100,000, more preferably 94,000. The lower limit of the Z+1 average molecular weight (Mz+1) is preferably 1,800,000, more preferably 2,000,000, from the viewpoint of containing a certain amount or more of high molecular weight components. The upper limit of Mz+1 is preferably 2,500,000, more preferably 2,200,000.

The melt flow rate (MFR) of polypropylene raw material A is preferably in the range of 1 g/10 minutes or more and 10 g/10 minutes or less (230° C., 21.18 N load) from the viewpoint of film formability and film strength. From the above viewpoint, the lower limit of MFR is more preferably 2 g/10 minutes. The upper limit of MFR is more preferably 8 g/10 minutes, still more preferably 5 g/10 minutes. 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. More specifically, a method of adjusting the hydrogen gas concentration during polymerization, a method of appropriately selecting a catalyst and/or co-catalyst, and a method of controlling the molecular weight and molecular weight distribution of the polypropylene raw material are preferably employed. be. The lower the molecular weight, the higher the MFR, and the more low-molecular-weight components in the molecular weight distribution, the higher the MFR.

The melting point of polypropylene raw material A is preferably 155° C. or higher, more preferably 160° C. or higher, and still more preferably 165° C. or higher. When the melting point is 155 ° C. or higher, the heat resistance of the obtained polyolefin film is high, and when used as a release film, for example, even if the film passes through a heat-applying process after bonding to an adherend, the film Elongation in the tension direction due to softening of the adherend is suppressed, and deformation of the adherend is reduced.

The polypropylene raw material A preferably has a cold xylene soluble portion (CXS) of 4% by mass or less and a mesopentad fraction of 0.90 or more. Satisfying these conditions reduces deterioration in the film forming stability and the strength, dimensional stability and heat resistance of the resulting polyolefin film.

Here, CXS refers to a polyolefin component dissolved in xylene when the sample 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 for the reason. If a large amount of such components are contained in the resin, the thermal dimensional stability of the film may be poor. Therefore, from the above viewpoint, CXS is preferably 3.5% by mass or less, more preferably 2.5% by mass or less, and still more preferably 2.0% by mass or less. The lower the CXS, the better, but the lower limit is about 0.1% by mass. CXS in such a range can be obtained by a method of increasing the catalytic activity in obtaining the resin, or a method of washing the obtained resin with a solvent or the olefin monomer itself.

The mesopentad fraction of polypropylene raw material A is preferably 0.94 or more, more preferably 0.96 or more, still more preferably 0.97 or more, and most preferably 0.98 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 preferable because it increases the dimensional stability. 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.

The polypropylene raw material A may contain other copolymerization components with unsaturated hydrocarbons within a range not impairing the object of the present invention. Examples of monomer components constituting such a copolymer component 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-norbornene, etc. mentioned.

It is preferable that the amount of the copolymer component in the polypropylene raw material A is 10 mol % or less. It is more preferably 5 mol % or less, still more preferably 3 mol % or less. The higher the content of the ethylene component, the lower the crystallinity and the easier it is to improve the transparency. may decrease and the heat shrinkage rate may deteriorate. In addition, the resin tends to deteriorate during the extrusion process, and fish eyes may easily occur in the polyolefin film. Yes.) can be included. By containing polypropylene raw material B, the low-molecular-weight component acts as a stretching aid during stretching, and may contribute to suppression of film breakage during stretching and reduction of unevenness in physical properties.

The upper limit of the number average molecular weight (Mn) of polypropylene raw material B is preferably 75,000, more preferably 70,000, and even more preferably 65,000, from the viewpoint of containing a certain amount or more of low molecular weight components. The lower limit of Mn is preferably 50,000, more preferably 55,000, even more preferably 62,000. In addition, the upper limit of the Z+1 average molecular weight (Mz+1) is preferably 2,000,000, more preferably 1,800,000 from the viewpoint of suppressing the high molecular weight component to a certain level or less. The lower limit of Mz+1 is preferably 1,100,000, more preferably 1,300,000, and still more preferably 1,550,000. The Mn and Mz+1 of the polypropylene raw material B are smaller than the Mn and Mz+1 of the polypropylene raw material A.

The melt flow rate (MFR) of polypropylene raw material B is preferably in the range of 3 g/10 minutes or more and 11 g/10 minutes or less (230° C., 21.18 N load) from the viewpoint of extrusion stability. The lower limit of the MFR of polypropylene raw material B is more preferably 3.5 g/10 minutes. The upper limit of the MFR of polypropylene raw material B is more preferably 9 g/10 minutes, and even more preferably 8 g/10 minutes. In order to set the MFR of polypropylene raw material B to the above value, a method of controlling the average molecular weight and molecular weight distribution is employed. More specifically, a method of adjusting the hydrogen gas concentration during polymerization, a method of appropriately selecting a catalyst and/or co-catalyst, and a method of controlling the molecular weight and molecular weight distribution of the polypropylene raw material B are preferably adopted. be done. The lower the molecular weight, the higher the MFR, and the more low-molecular-weight components in the molecular weight distribution, the higher the MFR.

The polyolefin film of the present invention can contain a branched chain polypropylene resin (hereinafter sometimes referred to as a branched chain polypropylene raw material) in addition to the polypropylene raw material A and the polypropylene raw material B, which are both linear. By containing the branched chain polypropylene raw material, the formation of coarse spherulites during casting is suppressed due to its nucleating effect, so that SPk and crystallite size can be reduced.

The MFR of the branched chain polypropylene raw material is preferably 0.5 g/10 min or more and 9 g/10 min or less (230° C., 21.18 N load) from the viewpoint of extrusion stability. The lower limit of the MFR of the branched-chain polypropylene raw material is more preferably 2 g/10 minutes, still more preferably 6 g/10 minutes. 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. More specifically, a method of adjusting the hydrogen gas concentration during polymerization, a method of appropriately selecting a catalyst and/or co-catalyst, and a method of controlling the molecular weight and molecular weight distribution of the polypropylene raw material are preferably employed. be. The lower the molecular weight, the higher the MFR, and the more low-molecular-weight components in the molecular weight distribution, the higher the MFR.

The melt tension of the branched chain polypropylene raw material is preferably 3 gf or more and 40 gf or less from the viewpoint of stretching uniformity. The lower limit of the melt tension is more preferably 4 gf, more preferably 6 gf. The upper limit is more preferably 30 gf, more preferably 25 gf. In order to adjust the melt tension to the above value, a method of controlling the average molecular weight, the molecular weight distribution, and the degree of branching in the polypropylene raw material is employed. In particular, when it has long-chain branches, the melt tension can be dramatically increased, and it can be adjusted to a preferable value by adjusting the molecular chain of the long-chain branches and the degree of branching.

A plurality of branched chain polypropylene raw materials, such as Ziegler-Natta catalysts and metallocene catalysts, are commercially available. A narrow distribution metallocene catalyst system is more preferred.

Various additives such as crystal nucleating agents, antioxidants, heat stabilizers, Slipping agents, antistatic agents, antiblocking agents, fillers, viscosity modifiers, anticoloring agents, etc. may also be incorporated.

Among these, selection of the type and amount of antioxidant to be added is important from the viewpoint of bleed-out of the antioxidant. 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 (eg "Irganox" (registered trademark) 1330 manufactured by BASF: molecular weight 775.2) or tetrakis[methylene-3(3,5-di- It is preferable to use t-butyl-4-hydroxyphenyl)propionate]methane (for example, "Irganox" (registered trademark) 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 parts by mass based on the total amount of polyolefin raw material. If the amount of the 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. From the above viewpoint, the content of the antioxidant is more preferably 0.05 to 0.9 parts by mass, particularly preferably 0.1 to 0.8 parts by mass.

A crystal nucleating agent can be added to the polyolefin raw materials A and B used for the polyolefin film of the present invention within a range not contrary to the object of the present invention. In addition, branched polypropylene may be contained, and branched polypropylene already has the effect of a crystal nucleating agent for α crystals or β crystals. , sodium benzoate, etc.), β crystal nucleating agents (potassium 1,2-hydroxystearate, magnesium benzoate, amide compounds such as N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide, quinacridone compounds, etc.) etc. are exemplified. However, if the other type of nucleating agent is excessively contained, it may cause deterioration of transparency and strength due to deterioration of stretchability and void formation, so the content is usually 0.5 mass based on the total amount of polyolefin raw material. part or less, preferably 0.1 mass part or less, more preferably 0.05 mass part or less.

The polyolefin film of the present invention is preferably free of organic and inorganic particles. The polypropylene resin, which can be preferably used as the main component of the polyolefin film of the present invention, has a low affinity for organic particles and inorganic particles, so the particles may fall off and contaminate the process and products. In addition, when coarse protrusions are formed by particles with high hardness, unevenness may be transferred to the resin layer of optical members. may cause quality deterioration. From the above viewpoint, the polyolefin film of the present invention preferably does not contain lubricants such as organic particles and inorganic particles.

In the polyolefin film of the present invention, the proportions of polypropylene raw material A, polypropylene raw material B, and branched chain polypropylene raw material to the total amount of resin components are preferably as follows. From the viewpoint of film surface smoothness and mechanical strength, the content of polypropylene raw material A is preferably 50% by mass or more and 99.9% by mass or less. The lower limit of the ratio of polypropylene raw material A is more preferably 60% by mass, and even more preferably 70% by mass. The upper limit is more preferably 99% by mass, more preferably 98% by mass. The ratio of polypropylene raw material B to the entire film is preferably 0.1% by mass or more and 50% by mass or less. The lower limit of the ratio of polypropylene raw material B is more preferably 0.5% by mass, and even more preferably 3% by mass. The upper limit is more preferably 30% by mass, still more preferably 20% by mass. The ratio of the branched chain polypropylene raw material to the entire film is preferably 0.1% by mass or more and 30% by mass or less. The lower limit of the ratio of the branched-chain polypropylene raw material is more preferably 0.2% by mass, still more preferably 0.5% by mass, and most preferably 1.0% by mass. The upper limit is more preferably 20% by mass, and even more preferably 10% by mass.

For the polyolefin film of the present invention, it is preferable to add polypropylene raw material B, branched chain polypropylene raw material, or both polypropylene raw material B and branched chain polypropylene raw material to polypropylene raw material A described above.

The polyolefin film of the present invention has a differential distribution value of 3% or more and 15% or less when the logarithmic molecular weight Log (M) is 4.0 in the molecular weight distribution curve measured by the gel permeation chromatography method described later. preferable. If the differential distribution value when the logarithmic molecular weight Log(M) is 4.0 is less than 3%, the low molecular weight component that acts as a lubricating component during stretching is small, and the film may easily break during stretching. If the differential distribution value is greater than 15% when the logarithmic molecular weight Log(M) is 4.0, the heat resistance of the polyolefin film may deteriorate. From the above point of view, the lower limit of the differential distribution value when the logarithmic molecular weight Log(M) is 4.0 is more preferably 4%, more preferably 5%. The upper limit of the differential distribution value when the logarithmic molecular weight Log(M) is 4.0 is more preferably 13%, more preferably 10%.

The polyolefin film of the present invention preferably has a differential distribution value of 1% or more and 15% or less when the logarithmic molecular weight Log(M) is 6.1 in the molecular weight distribution curve measured by gel permeation chromatography. If the differential distribution value when the logarithmic molecular weight Log(M) is 6.1 is less than 1%, the amount of high molecular weight components that become tie molecules during stretching may be small, resulting in poor uniformity during stretching. If the differential distribution value when the logarithmic molecular weight Log(M) is 6.1 is greater than 15%, after the polyolefin film is wound into a roll, room temperature shrinkage over time increases, and the flatness of the film roll may be impaired. There is From the above viewpoint, the lower limit of the differential distribution value when the logarithmic molecular weight Log(M) is 6.1 is more preferably 5%, more preferably 7%. The upper limit of the differential distribution value when the logarithmic molecular weight Log(M) is 6.1 is more preferably 13%, more preferably 11%.

The polyolefin film of the present invention is preferably biaxially stretched using 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, one aspect of the method for producing the polyolefin film of the present invention will be described by taking a two-kind, three-layer polypropylene film as an example, but the method for producing the polyolefin film of the present invention is not necessarily limited to this.

First, 80 parts by mass of polypropylene raw material A, 15 parts by mass of polypropylene raw material B, and 5 parts by mass of branched-chain polypropylene raw material are dry-blended to form a uniaxial base layer (II) (hereinafter, sometimes referred to as layer B). It is supplied to an extruder, and polyolefin raw material B is supplied to a single screw extruder for surface layer (I) (hereinafter sometimes referred to as A layer). Thereafter, melt extrusion is carried out at 200-280°C, more preferably 220-280°C, still more preferably 240-270°C, respectively. Then, after removing foreign substances and modified polymers with a filter installed in the middle of the polymer tube, the polymer is laminated with a multi-manifold type A layer/B layer/A layer composite T die, discharged onto a casting drum and cooled. By solidifying, a laminated unstretched sheet having a layer structure of A layer/B layer/A layer is obtained. At this time, the lamination thickness ratio is preferably in the range of 1/8/1 to 1/60/1. By setting it to the above range, the surface layer containing polypropylene raw material A is formed thinly and uniformly on the film surface, the uniformity of the height of the protrusions formed during stretching is increased, and the formation of coarse protrusions can be suppressed.

The casting drum has a surface temperature of 10 to 50°C, preferably 10 to 40°C, more preferably 15 to 30°C, still more preferably 15 to 20°C. Further, the layer structure may be a two-layer lamination structure of A layer/B layer. 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, but flatness is good. The air-knife method is preferred because it is flexible and the surface roughness can be controlled. From the viewpoint of cooling the non-cooled drum surface of the sheet on the casting drum, it is preferable to lower the air temperature of the air knife. The air temperature of the air knife is 10 to 50°C, preferably 10 to 40°C, more preferably 15 to 30°C, still more preferably 20 to 25°C, and the blowing 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, in the case of a two-kind two-layer lamination structure of A layer/B layer, it is preferable to make the A layer side the casting drum side.

The obtained unstretched sheet is introduced into a longitudinal stretching step. In the longitudinal stretching step, first, a plurality of metal rolls kept at 80 ° C. or higher and 150 ° C. or lower, preferably 80 ° C. or higher and 130 ° C. or lower, more preferably 90 ° C. or higher and 130 ° C. or lower, still more preferably 100 ° C. or higher and 130 ° C. or lower. The stretched sheet is brought into contact and preheated, and stretched 1.1 to 3.0 times, more preferably 1.3 to 2.5 times in the longitudinal direction between rolls having a peripheral speed difference, and then subsequently. , stretched in the longitudinal direction 2.0 to 5.0 times, more preferably 3.0 to 4.5 times, and cooled to room temperature. The stretching temperature in the first stage is 80° C. to 130° C., preferably 90° C. to 130° C., more preferably 100° C. to 130° C., and the stretching temperature in the second stage is 130° C. to 150° C. The temperature is preferably 140°C or higher and 150°C or lower, more preferably 145°C or higher and 150°C or lower. In the first half of the longitudinal stretching, the film is stretched at a low temperature and a high stress at a low draw ratio, and then stretched at a high temperature at once, so that the entire width is uniformly oriented in the machine direction, and a highly uniform, highly oriented uniaxially stretched film can be obtained.

If the longitudinal stretching temperature in the first stage and the longitudinal stretching temperature in the second stage are significantly different, the film shrinks in the width direction when it comes into contact with the high-temperature stretching rolls. At that time, the film shrinks unevenly, which may cause wrinkles in the machine direction. As a countermeasure, ceramic rolls were used as the drawing rolls. The film becomes slippery on the ceramic roll, and the film shrinks uniformly, so that it can be stretched without wrinkles. If the total draw ratio of the two-stage drawing is less than 3.0 times, the orientation of the film may become weak and the strength may decrease. 5.5 times or less is more preferable.

Next, the uniaxially stretched film is guided to a tenter by gripping both ends in the width direction with clips, preheated, and transversely stretched 7.0 to 13 times in the width direction. The preheating temperature is 165 to 180°C, preferably 168 to 180°C, still more preferably 170 to 180°C. The stretching temperature is 148 to 165°C, preferably 148 to 160°C, still more preferably 148 to 155°C. By setting the preheating temperature higher than the stretching temperature by 5°C or higher, preferably 8°C or higher, more preferably 10°C or higher, uniform highly oriented stretching can be performed over the entire width of the film, and the obtained polyolefin film has smoothness. preferred from

In the subsequent heat treatment and relaxation treatment steps, the width direction is tensely gripped by the clip, and the width direction is relaxed at a relaxation rate of 5 to 20%, more preferably 8 to 18%, and still more preferably 11 to 18%. 180° C. or higher, preferably 165° C. or higher and lower than 180° C., more preferably 168° C. or higher and lower than 180° C., still more preferably 170° C. or higher and lower than 180° C., and the width direction was tightly held with a clip. After a cooling process at 80 to 100° C., the film is led to the outside of the tenter, the clip at the film edge is released, the film edge is slit in the winder process, and the film product roll is wound up. The heat treatment temperature is 5° C. or higher, more preferably 8° C. or higher, more preferably 10° C. or higher than the transverse stretching temperature. be able to.

Moreover, from the viewpoint of heat resistance, it is preferable to heat the polyolefin film coming out of the tenter with a hot roll when passing through the transition. The heating temperature is preferably 70° C. or higher, more preferably 80° C. or higher, still more preferably 100° C. or higher, and particularly preferably 120° C. or higher. At a temperature of 140°C or higher, the lubricity between the hot roll and the polyolefin film may be impaired, and wrinkles may occur to deteriorate the flatness, so the upper limit is about 140°C. The heating time is preferably 0.2 seconds or longer, more preferably 0.4 seconds or longer. Although the upper limit of the heating time is not particularly limited, the upper limit is about 2.0 seconds from the viewpoint of productivity.

Polyolefin films obtained as described above can be used in various industrial applications such as packaging films, surface protection films, process films, sanitary products, agricultural products, building products, medical products, and films for capacitors. In particular, it can be preferably used as a surface protective film, a process film, a release film, and a film for capacitors because of its excellent surface smoothness. The term "surface protection film" as used herein refers to a film that is adhered to an object such as a molded article or film and has a function of preventing scratches, contamination, etc. that may occur during processing or transportation. A process film is a film that is adhered to an object such as a molded article or film to prevent scratches or stains that may occur during manufacturing or processing, and that is discarded when used as a final product. A release film has high releasability, is attached to objects such as moldings and films, prevents scratches and contamination that occur during processing and transportation, and can be easily peeled off when used as a final product. , refers to a film that has a function that can be discarded. A capacitor film is a film used in a film capacitor using a resin film as a dielectric.

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) Crystallization temperature T _c0 determined by extrapolation point method
Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), a 3 mg polyolefin film was heated from 25° C. to 250° C. at a rate of 20° C./min in a nitrogen atmosphere and held for 5 minutes. Then, the temperature was lowered from 250°C to 25°C at a rate of 10°C/min. The same procedure was repeated 5 times, and the arithmetic average value of the peak temperature of the exothermic curve obtained when the temperature was lowered each time was taken as _Tc10 . Thereafter, a polyolefin film sampled in the same manner was heated from 25° C. to 250° C. at a rate of 20° C./min and held for 5 minutes. Then, the temperature was lowered from 250°C to 25°C at a rate of 40°C/min. The same procedure was repeated 5 times, and the arithmetic average value of the peak temperature of the exothermic curve obtained when the temperature was lowered each time was taken as _Tc40 . Next, as shown in FIG. 1, plotting the cooling rate on the horizontal axis and the crystallization temperatures _{Tc10 and Tc40 obtained} at each cooling rate on the vertical axis, drawing a straight line from _Tc40 to _Tc10 , The crystallization temperature when the temperature drop rate was extrapolated to 0°C/min was defined as _Tc0 . In each measurement for measuring _{Tc10 and Tc40 ,} when a plurality of peak temperatures were observed, the temperature of the highest peak in the region of 80°C to 130°C was used as the peak temperature.

(3) Dynamic friction coefficient μd in the direction perpendicular to the main orientation after heat treatment at 130° C. for 10 minutes
A polyolefin film was cut into a width of 6.5 cm and a length of 12 cm, and the test piece was sandwiched between papers and heated in an oven maintained at 130 ° C. for 10 minutes. After cooling at room temperature, Toyo Seiki ( It was measured at 25° C. and 65% RH according to JIS K 7125 (1999) using a slip tester manufactured by Co., Ltd. In addition, the measurement was carried out in the directions perpendicular to the main orientation and by overlapping different surfaces, ie, the surface of one film and the back surface of the other film were in contact with each other. The same measurement was performed 5 times for each sample, and the average value of the obtained values was calculated as the dynamic friction coefficient (μd) of the sample. Note that the main orientation direction is the Young's modulus in each direction forming an angle of 0° to 175° in increments of 5° with respect to the arbitrary direction, when an arbitrary direction is 0° in the plane of the film. When measured, the direction showing the highest value was taken as the main orientation direction.

The Young's modulus was measured according to the following procedure. First, a rectangular sample having a length (measurement direction) of 150 mm and a width of 10 mm was cut out. Using a tensile tester (“Tensilon” (registered trademark) UCT-100 manufactured by Orientec), in an atmosphere with a room temperature of 23 ° C. and a relative humidity of 65%, the initial tension chuck distance is 50 mm, and the tensile speed is 300 mm / min. did Read the load applied to the film when the sample is stretched by 2% (when the distance between the chucks is 51 mm), and divide it by the cross-sectional area of the sample before the test (film thickness x 10 mm). The Young's modulus was defined as the slope of a straight line passing through the points used to measure the F2 value.

(4) In-plane Retardation Using an automatic birefringence meter (KOBRA-21ADH) manufactured by Oji Keisoku Co., Ltd., the in-plane retardation of the polyolefin film was measured with respect to light having a wavelength of 548.3 nm.

(5) Breaking elongation in the direction orthogonal to the main orientation of the film at 130 ° C. Five samples with a width of 10 mm and a length of 50 mm (measurement direction) were cut out from the polyolefin film so that the direction perpendicular to the main orientation was the measurement direction. A test length of 20 mm was obtained by marking the position of 15 mm from each. Next, the rectangular sample was set in a tensile tester ("Tensilon" (registered trademark) UCT-100 manufactured by Orientec) with an initial chuck distance of 20 mm, and heated in an oven heated to 130 ° C. for 1 minute. Thereafter, a tensile test was performed on the film at a tensile speed of 300 mm/min to obtain elongation (unit: %) and strength (unit: MPa) at the time when the sample broke. The measurement was performed 5 times, and the average value of the elongation at the time when the sample broke was calculated and defined as the elongation at break (%).

(6) Internal haze after heat treatment at 130°C for 10 minutes A polyolefin film was cut into a width of 3.0 cm and a length of 6.0 cm. After heating for 10 minutes, it was taken out, cooled to room temperature, and used as a sample. As a measuring device, a haze meter (HGM-2DP) manufactured by Suga Test Instruments Co., Ltd. was used. The value of the internal haze was obtained according to JIS K7136 (2000) from the measured value of haze when the sample was immersed in a quartz cell having an optical path length of 1 cm and filled with tetralin.

(7) Orientation angle spots in a 10 cm square film A polyolefin film was cut into a width of 10 cm and a length of 10 cm. A total of 21 points, 10 points other than the central portion of the film, were used as measurement points at intervals of 1 cm in the direction perpendicular to the main orientation of the film, and the orientation angle at each point was measured. The orientation angle was measured using a retardation measuring device (KOBRA-21ADH) manufactured by Oji Scientific Instruments Co., Ltd. so that the main orientation direction of the polyolefin film was at an angle of 0° as defined by this measuring device. A clockwise tilt with respect to the main orientation direction of the film was set as +, and a counterclockwise tilt was set as -.
Variation of orientation angle (%)=((maximum orientation angle−minimum orientation angle)/average orientation angle)×100.

(8) Melt Tension Using an apparatus according to JIS K 7199 (1999), measurement was performed under the following conditions.
・Equipment: Capilograph 1BPMD-i with melt tension tester (manufactured by Toyo Seiki Co., Ltd.)
・Temperature: 230°C (using a heat retaining chamber)
・Dice: L=8 (mm), D=2.095 (mm)
・Extrusion speed: 20 mm/min ・Take-up speed: 15.7 m/min ・Sample mass: 15 to 20 g.

(9) Projected peak height SPk, average roughness Sa, maximum height Sz
The measurement is performed using a scanning white interference microscope "VS1540" (manufactured by Hitachi High-Tech Science Co., Ltd., the measurement conditions and device configuration will be described later), and the captured screen is complemented (completely complemented) by the attached analysis software, and polynomial After surface correction by 4th-order approximation, the surface shape was obtained by processing with a median filter (3×3 pixels).

Starting from the intersection of the diagonal lines of the polyolefin film cut into a square of 5 cm x 5 cm, the measurement was performed at a total of 9 measurement positions determined according to the following procedure. Further, the same measurement was repeated by changing the surface. After that, SPk, Sa, and Sz at each measurement position were determined for each surface according to the above procedure, and the average values of SPk, Sa, and Sz were calculated for each surface. Among the obtained values, the smaller SPk value was adopted as the SPk value of the film.

<How to determine the measurement position>
Measurement 1: Position measurement of the starting point 2: Position measurement 3.0 mm right from the starting point 3: Position measurement 6.0 mm right from the starting point 4: Position measurement 3.0 mm below the starting point 5: 3 from the starting point Position measurement 0.0 mm below and 3.0 mm right 6: Position measurement 3.0 mm below and 6.0 mm right from the starting point 7: Position measurement 6.0 mm below the starting point 8: 6.0 mm below the starting point 3.0 mm right position measurement 9: Position 6.0 mm below and 6.0 mm right from the starting point <Measurement conditions and device configuration>
Objective lens: 10x
Lens barrel: 1x
Zoom lens: 1x
Wavelength filter: 530nm white
Measurement mode: Wave
Measurement software: VS-Measure 10.0.4.0
Analysis software: VS-Viewer 10.0.3.0
Measurement area: 561.1 μm×561.5 μm
Number of pixels: 1,024×1,024.

(10) Number Average Molecular Weight Mn, Z+1 Average Molecular Weight Mz+1, Molecular Weight Distribution Value A polyolefin film was dissolved in 1,2,4-trichlorobenzene as a solvent by stirring at 165° C. for 30 minutes. Then, it was filtered using a 0.5 μm filter, the molecular weight distribution of the filtrate was measured, and differential distribution values were read when the logarithmic molecular weight Log (M) was 4.0 and 6.1.
Also, the number average molecular weight and Z+1 average molecular weight of the sample were determined using a molecular weight calibration curve prepared using the following standard samples.
・ Apparatus: high temperature GPC apparatus (Equipment No. HT-GPC-1, Polymer Laboratories PL-220)
・ Detector: Differential refractive index detector RI
・Column: Shodex HT-G (guard column)
Shodex HT-806M (2 pieces) (φ8.0mm×30cm, manufactured by Showa Denko)
・Flow rate: 1.0 mL/min
・Column temperature: 145°C
・Injection volume: 0.200 mL
・Standard sample: monodisperse polystyrene manufactured by Tosoh, dibenzyl manufactured by Tokyo Kasei.

(11) Evaluation of transfer to adherend A polyolefin film and a 20 μm thick “Zeonor Film” (registered trademark) manufactured by Nippon Zeon Co., Ltd. were sampled in a square with a width of 100 mm and a length of 100 mm. The smaller surface and the "Zeonor film" (registered trademark) are stacked so that they are in contact, sandwiched between two acrylic plates (width 100 mm, length 100 mm), a load of 3 kg is applied, and the temperature is 23 ° C. It was allowed to stand under the atmosphere for 24 hours. After 24 hours, the surface of the "Zeonor film" (registered trademark) (the surface in contact with the polyolefin film) was visually observed and evaluated according to the following criteria. When the front and back surfaces have the same SPk value, the surface with the smaller average surface roughness Sa value was used as the bonding surface. Furthermore, when the value of Sa is the same on the front and back surfaces, the surface with the smaller maximum surface roughness Sz was used as the bonding surface.
A: Clean and equivalent to before the load was applied.
B: Weak unevenness is confirmed.
C: Strong unevenness is confirmed.

(12) Flatness of film A polyolefin film with a width of 500 mm and a length of 200 m was wound around a core, heated in an oven at 60 ° C. for 7 days, taken out, cooled to room temperature, and then wound around a core. The film is unwound by 1 m, free tension (a state in which the film hangs vertically due to its own weight), and tensions of 1 kg/m and 3 kg/m are applied evenly and uniformly over the entire width of the film. The presence or absence of a flatness defective portion was visually confirmed.
S: There is no portion with poor flatness due to free tension.
A: Areas with poor flatness were observed with free tension, and disappeared with a tension of 1 kg/m width.
B: When the tension is 1 kg/m width, a portion of poor flatness is observed, and when the tension is 3 kg/m width, it disappears.
C: Even with a tension of 3 kg/m width, the part with poor flatness does not disappear.

(Polypropylene raw material, etc.)
Polypropylene raw materials having a number average molecular weight (Mn) and a Z+1 average molecular weight (Mz+1) shown in Table 1 below were used to produce the polyolefin films of Examples and Comparative Examples. These values are values evaluated in the form of raw material resin pellets. Two types of PP raw material A and two types of PP raw material B were prepared. As the branched chain polypropylene raw material 1, the following was used.
Polypropylene raw material 1 (PP1): Polypropylene raw material 2 (PP2) manufactured by Prime Polymer Co., Ltd. Polypropylene raw material 3 (PP3) manufactured by Prime Polymer Co., Ltd. Polypropylene raw material 4 (PP4) manufactured by Sumitomo Chemical Co., Ltd.: Prime Co., Ltd. Polymer-made branched-chain polypropylene raw material 1 (branched PP1): metallocene-catalyzed branched-chain polypropylene raw material (manufactured by Japan Polypropylene Corporation, melt tension: 13 gf)
Branched chain polypropylene raw material 2 (branched PP2): metallocene catalyst-based branched chain polypropylene raw material (manufactured by Japan Polypropylene Corporation, melt tension: 5 gf)
Branched-chain polypropylene raw material 3 (branched PP3): Ziegler-Natta catalyst-based branched-chain polypropylene raw material (manufactured by Basell, melt tension: 15 gf)
Raw material for polypropylene with low stereoregularity: “L-MODU” (registered trademark) S901 manufactured by Idemitsu Kosan Co., Ltd.

Polypropylene raw material D: Polypropylene raw material 3 and 4-methyl-1-pentene polymer are supplied from a weighing hopper to a twin-screw extruder so that the ratio is 90:10 (mass ratio), melt-kneaded at 260 ° C., A melted resin composition is extruded from a die in the form of a strand, solidified by cooling in a water bath at 25° C., and cut into chips.
4-methyl-1-pentene polymer: MX004, manufactured by Mitsui Chemicals, Inc.
1-butene-based polymer: Mitsui Chemicals, Inc. “Tafmer” (registered trademark) BL3450 (MFR = 12 g/10 min (load 21.18 N, 230 ° C.), structural unit derived from 1-butene: 87 mol%) .

(Example 1)
As raw materials for surface layer (I), polypropylene raw material 3 and polypropylene raw material D were dry-blended at a ratio of 70:30 (mass ratio) and supplied to a single-screw extruder for surface layer (I). As a raw material for the base layer (II), polypropylene raw material 2, polypropylene raw material 3, and branched chain polypropylene raw material 1 were dry-blended at a ratio of 70:26:4 (mass ratio) and single-screw extruded for the inner layer (II). supplied to the machine. Each resin mixture was melt-extruded at 260° C., foreign matter was removed with a 20 μm-cut sintered filter, and surface layer (I)/base layer (II)/ The surface layer (I) was laminated so as to have a thickness ratio of 1/20/1, discharged onto a casting drum whose surface temperature was controlled at 22° C., and adhered to the casting drum with an air knife. Thereafter, compressed air at 22° C. was jetted onto the non-cooled drum surface of the sheet on the casting drum at an air speed of 140 m/s to cool the sheet, thereby obtaining an unstretched sheet. Subsequently, the unstretched sheet was preheated to 108° C. with ceramic rolls, and stretched 1.5 times in the longitudinal direction between rolls at 108° C. provided with a difference in circumferential speed as the first stage of stretching. Subsequently, as the second stage of stretching, the film was stretched 3.4 times in the longitudinal direction between rolls at 146°C. Next, the obtained uniaxially stretched film was gripped with clips at both ends in the width direction, introduced into a tenter-type stretching machine, preheated at 173° C. for 3 seconds, and then stretched at 152° C. at 9.2 times in the width direction. , heat treatment was performed at 175° C. while giving 13% relaxation in the width direction. After that, the film is led to the outside of the tenter through a cooling process at 100°C, the clips at both ends in the width direction of the film are released, the film is heated with hot rolls at 123°C for 0.5 seconds, and then wound around a core to have a thickness of 15 µm. of polyolefin film was obtained. Table 2 shows the physical properties and evaluation results of the obtained film.

(Examples 2 to 6, Comparative Examples 1 to 3)
A polyolefin film was obtained in the same manner as in Example 1 except that the raw material composition of each layer and the film forming conditions were as shown in Table 2. At this time, the thickness was adjusted by adjusting the discharge amount during extrusion and adjusting the speed of the casting drum. Table 2 shows the physical properties and evaluation results of the obtained film. Regarding the mixing of raw materials for the surface layer, in the surface layer (I) of Example 3 and Comparative Example 1, polypropylene raw material 3 and polypropylene raw material D were dry-blended at a ratio of 70:30 (mass ratio). In the surface layer (I) of , the polypropylene raw material 3 and the polypropylene raw material D were dry blended at 80:20 (mass ratio). In the surface layer (I) and the base layer (II) of other examples, each resin component was dry-blended at the ratio shown in Table 2 without using polypropylene raw material D.

As described above, the polyolefin film of the present invention can be used in various industrial applications such as packaging films, surface protection films, process films, sanitary products, agricultural products, construction products, medical products, and capacitor films. In particular, because of its excellent surface smoothness, it can be preferably used as a surface protective film, a process film, a release film, and a film for capacitors.

It is an example of a graph showing the crystallization temperature T c ₀ of a polyolefin film.

In the subsequent heat treatment and relaxation treatment steps, the width direction is tensely gripped by the clip, and the width direction is relaxed at a relaxation rate of 5 to 20%, more preferably 8 to 18%, and still more preferably 11 to 18%. 180 ° C. or higher, preferably 165° C. or higher and lower than 180° C., more preferably 168° C. or higher and lower than 180° C., still more preferably 170° C. or higher and lower than 180° C., and the width direction is held with a clip under tension. After a cooling process at 80 to 100° C., the film is led to the outside of the tenter, the clip at the film edge is released, the film edge is slit in the winder process, and the film product roll is wound up. The heat treatment temperature is 5° C. or higher, more preferably 8° C. or higher, more preferably 10° C. or higher than the transverse stretching temperature. be able to.

The present invention will be described in detail below with reference to examples. The properties were measured and evaluated by the following methods. However, Examples 2 and 4 are reference examples.

(2) Crystallization temperature T c ₀ determined by extrapolation point method
Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), a 3 mg polyolefin film was heated from 25° C. to 250° C. at a rate of 20° C./min in a nitrogen atmosphere and held for 5 minutes. Then, the temperature was lowered from 250°C to 25°C at a rate of 10°C/min. The same procedure was repeated ₅ times, and the arithmetic mean value of the peak temperature of the exothermic curve obtained when the temperature was lowered each time was taken as Tc10 . Thereafter, a polyolefin film sampled in the same manner was heated from 25° C. to 250° C. at a rate of 20° C./min and held for 5 minutes. Then, the temperature was lowered from 250°C to 25°C at a rate of 40°C/min. The same procedure was repeated 5 times, and the arithmetic average value of the peak temperature of the exothermic curve obtained when the temperature was lowered each time was taken as T c ₄₀ . Next, as shown in FIG . 1, the cooling rate is plotted _on the horizontal axis, and the crystallization temperatures Tc10 and Tc40 _obtained at each cooling rate are _{plotted on} the vertical axis. A straight line was drawn, and the crystallization temperature when extrapolated to a temperature drop rate of ₀ ° C /min was defined as Tc0. In each measurement for measuring T c ₁₀ and T c ₄₀ , when multiple peak temperatures were observed, the temperature of the highest peak in the range of 80° C. to 130° C. was used as the peak temperature.

Claims (11)

The film is measured by DSC, the crystallization temperature Tc0 obtained by the extrapolation point method is 110 ° C. or higher, the in-plane retardation of the film is 400 nm or less, and the surface layers (I) are heated at 130 ° C. for 10 minutes. The dynamic friction coefficient μd is 0.7 or less, the breaking elongation in the direction perpendicular to the main orientation of the film at 130 ° C. is 100% or more, the main component is a polypropylene resin, and at least the surface layer (I), the base layer (II ). The film is measured by DSC, the crystallization temperature Tc ₀ obtained by the extrapolation point method is 110 ° C. or more, the in-plane retardation of the film is 400 nm or less, and the surface layers (I) are heated at 130 ° C. for 10 minutes. The coefficient of dynamic friction μd is 0.7 or less, and the differential distribution value when the logarithmic molecular weight Log (M) is 4.0 in the molecular weight distribution curve measured by gel permeation chromatography is 3% or more and 15% or less A polyolefin film comprising a polypropylene resin as a main component and having at least a surface layer (I) and a base layer (II). 3. The polyolefin film according to claim 1, wherein the content of the cyclic olefin resin in the film is less than 2.0% by mass. The polyolefin film according to any one of claims 1 to 3, which has an internal haze of 1.0% or less after heating at 130°C for 10 minutes. 5. The polyolefin film according to any one of claims 1 to 4, wherein the unevenness of the orientation angle within a 10 cm square of the film is 3.0° or less. Any one of claims 1, 3 to 5, wherein the differential distribution value when the logarithmic molecular weight Log (M) is 4.0 is 3% or more and 15% or less in the molecular weight distribution curve measured by gel permeation chromatography. The polyolefin film described in . 7. The differential distribution value when the logarithmic molecular weight Log (M) is 6.1 in the molecular weight distribution curve measured by gel permeation chromatography is 1% or more and 15% or less, according to any one of claims 1 to 6. polyolefin film. A surface protection film using the polyolefin film according to any one of claims 1 to 7. A process film using the polyolefin film according to any one of claims 1 to 7. A release film using the polyolefin film according to any one of claims 1 to 7. A film capacitor using the polyolefin film according to any one of claims 1 to 7.

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