JP2020192813A - Polypropylene film and release film - Google Patents

Abstract

To provide a polypropylene film having excellent high-temperature heat-shrinkability, film flatness at high temperature, and quality.SOLUTION: There is provided a polypropylene film that has a heat-shrinkage of 4% or more and 30% or less after treatment at 130°C for 15 minutes in a main shrinkage direction, and a melting peak temperature of 155°C or higher when elevating the temperature from 30°C to 260°C at 20°C/minute with a differential scanning calorimeter DSC.SELECTED DRAWING: None

Description

The present invention relates to a polypropylene film having excellent flatness and quality at high temperatures in addition to high temperature heat shrinkage.

The heat-shrinkable film is used for food packaging, label packaging for the purpose of imparting design and protection of contents, and heat-shrinkable base material for functional layer coating for the purpose of controlling the orientation of the functional layer. It is used for various purposes such as. Among them, a heat-shrinkable film made of polypropylene is preferably used in these applications because it is excellent in strength and releasability. So far, high heat shrink films using α-olefin copolymers (for example, Patent Documents 1, 2 and 3) and high shrink films mainly composed of polypropylene resin having low crystallinity (for example, Patent Documents 4 and 5). Has been reported.

Japanese Unexamined Patent Publication No. 2001-294678 Japanese Unexamined Patent Publication No. 2010-064369 Japanese Unexamined Patent Publication No. 2017-074982 Japanese Unexamined Patent Publication No. 2005-324829 Japanese Unexamined Patent Publication No. 07-329177

However, when an α-olefin copolymer is used as in Patent Documents 1 to 3, fish eyes are likely to occur due to thermal deterioration and poor dispersion, which may be unsuitable for use as a label or as a release base material. Further, when a polyethylene resin or a polypropylene resin having a low melting point is mainly used as in Patent Documents 4 and 5, the film shrinks during the film forming process and during storage after winding, and wrinkles occur on the product roll. In some cases, the flatness of the film deteriorated due to high temperature.

Therefore, an object of the present invention is to solve the above-mentioned problems. That is, it is to provide a polypropylene film having excellent flatness and quality at high temperature in addition to high temperature heat shrinkage.

In order to solve the above-mentioned problems and achieve the object, the polypropylene film of the present invention has a heat shrinkage rate of 4% or more and 30% or less after treatment at 130 ° C. in the main shrinkage direction for 15 minutes, and has a differential scanning calorimetry. The main purpose is to have a melting peak temperature of 155 ° C. or higher when the temperature is raised from 30 ° C. to 260 ° C. at 20 ° C./min with a total DSC.

Although the polypropylene film of the present invention has high heat shrinkage in a specific direction in the film surface, the flatness of the film at high temperature is good, so that it is suitable for each application of the heat shrinkable film. Can be used.

In the present specification, the polypropylene film may be simply referred to as a film below.

In the present invention, the polypropylene film means a film containing 80% by mass or more and 100% by mass or less of polypropylene with respect to 100% by mass of the total mass of the film. The polypropylene in the polypropylene film is preferably 90% by mass or more and 100% by mass or less, and more preferably 95% by mass or more and 100% by mass or less. The polypropylene film of the present invention is not a microporous film, but a film having no large number of pores, and specifically, a polypropylene film having a pore ratio of 0% or more and less than 20%. The porosity of the polypropylene film is more preferably 0% or more and less than 10%, and further preferably 0% or more and less than 5%. The porosity of the film can be calculated from the specific gravity (ρ) of the film and the specific gravity (d) of the sheet obtained by hot-pressing the film at 280 ° C. and 5 MPa and then quenching with water at 25 ° C. from the following formula.
Pore ratio (%) = [(d-ρ) / d] × 100

The polypropylene film of the present invention has a heat shrinkage rate of 4% or more and 30% or less after treatment at 130 ° C. for 15 minutes in the main shrinkage direction. When the heat shrinkage rate after treatment at 130 ° C. for 15 minutes is less than 4%, for example, another product is attached or coated on the film of the present invention, and the film of the present invention is shrunk to orient the product. When used as a so-called heat-shrinkable base material for imparting, the orientation of the product after shrinkage may be insufficient. On the other hand, when the heat shrinkage rate after heat treatment at 130 ° C. for 15 minutes in the main shrinkage direction exceeds 30%, wrinkles may occur due to excessive shrinkage, flatness may deteriorate, and the appearance may be poor. Dimensional stability at ° C can be an issue. The upper limit of the heat shrinkage rate after treatment at 130 ° C. for 15 minutes in the main shrinkage direction is more preferably 25% or less, further preferably 20% or less, and the lower limit is more preferably 6% or more, still more preferably 8% or more. , Most preferably 10% or more. The heat shrinkage rate after treatment at 130 ° C. for 15 minutes in this main shrinkage direction refers to a value measured by the method described in the column of Examples. In order to reduce the heat shrinkage rate after treatment at 130 ° C. for 15 minutes in the main shrinkage direction to 4% or more and 30% or less, the composition of the raw material and the laminated structure should be within the range described later, and the longitudinal stretching condition and the transverse stretching condition. It is preferable that the heat fixing condition and the relaxation condition are within the range described later.

In the present invention, the direction parallel to the film-forming direction 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 main contraction direction in the present invention is 15 °, 30 °, 45 °, 60 °, 75 °, 90 ° with respect to the MD direction when the MD direction is 0 ° in the film surface. The direction showing the highest value when the heat shrinkage rate after treatment at 130 ° C. for 15 minutes is measured in each direction forming an angle of 105 °, 120 °, 135 °, 150 °, and 165 °. If it is not possible to determine which direction is the MD direction from the appearance of the film, measure the heat shrinkage rate after treatment at 130 ° C. for 15 minutes in 15 ° increments from any direction, and mainly the direction with the highest heat shrinkage rate. The contraction direction.

The polypropylene film of the present invention has a melting peak at 155 ° C. or higher when the temperature is raised from 30 ° C. to 260 ° C. at 20 ° C./min with a differential scanning calorimeter DSC. The temperature of the melting peak when the temperature is raised from 30 ° C. to 260 ° C. at 20 ° C./min with a differential scanning calorimeter DSC is more preferably 160 ° C. or higher, further preferably 165 ° C. or higher, and most preferably 170 ° C. or higher. Is. If the melting peak temperature is less than 155 ° C, it becomes difficult to perform stretching and heat treatment at a high temperature, so that the heat shrinkage rate after 15 minutes of treatment at 100 ° C, which will be described later, may increase, and during the film forming process. There is a risk of shrinkage during the coating process and storage after winding, resulting in reduced flatness. The upper limit of the melting peak temperature is not particularly limited, but is set to 180 ° C. because the heat shrinkage rate after treatment at 130 ° C. for 15 minutes may be low. In order to set the melting peak temperature to 155 ° C. or higher, it is preferable that the raw material composition and the laminated structure are within the range described later, and the longitudinal stretching condition, the transverse stretching condition, the heat fixing condition, and the relaxation condition are within the range described later. In particular, in addition to using a high-crystal raw material having a high mesopentad fraction, it is important to biaxially stretch in the longitudinal direction and the width direction.

The polypropylene film of the present invention preferably has a heat shrinkage rate of 10% or less after treatment at 100 ° C. for 15 minutes in the main shrinkage direction. The heat shrinkage rate after treatment at 100 ° C. for 15 minutes in the main shrinkage direction is more preferably 8% or less, further preferably 7% or less, and particularly preferably 6% or less. The lower limit of the heat shrinkage rate after treatment at 100 ° C. for 15 minutes is preferably more than 1%, more preferably more than 2%. The heat shrinkage rate after treatment at 100 ° C. for 15 minutes in the main shrinkage direction refers to a value measured by the method described in the column of Examples. In order to reduce the heat shrinkage rate after treatment at 100 ° C. for 15 minutes in the main shrinkage direction to 10% or less, the composition of the raw material and the laminated structure should be within the range described later, and the longitudinal stretching condition, the transverse stretching condition, the heat fixing condition, and the relaxation It is preferable that the conditions are within the range described later.

The polypropylene film of the present invention preferably has an elastic modulus in the thickness direction of at least one side at 23 ° C. measured by the nanoindentation method of 2.0 GPa or more. The elastic modulus in the thickness direction is more preferably 2.1 GPa or more, still more preferably 2.2 GPa or more. The elastic modulus in the thickness direction is not limited as long as it is 2.0 GPa or more, but in order to increase the elastic modulus in the thickness direction, it is necessary to increase the crystallinity of the film, and from the viewpoint of compatibility with film forming property. The upper limit is substantially 5.0 GPa. In order to set the elastic modulus in the thickness direction to 2.0 GPa or more, the raw material composition of the film and the laminated structure of the film should be within the range described later, and the casting (melt-extruded resin sheeting step) conditions at the time of film formation. It is preferable that the vertical / horizontal stretching conditions are within the range described later. The elastic modulus in the thickness direction is preferably 2.0 GPa or more on one side, but more preferably 2.0 GPa on both sides.

The polypropylene film of the present invention preferably has a stress (hereinafter, also referred to as an F2 value) at an elongation of 2% in both the main contraction direction and the direction orthogonal to the main contraction direction, which is 24 MPa or more. The F2 value in the main contraction direction and the direction orthogonal to the main contraction direction is more preferably 26 MPa or more, still more preferably 28 MPa or more. In order to set the F2 value in the main shrinkage direction of the film and the direction orthogonal to the main shrinkage direction to 24 MPa or more, the raw material composition and the laminated composition should be within the range described later, and the longitudinal stretching condition, the transverse stretching condition, the heat fixing condition, It is preferable that the relaxation condition is within the range described later.

From the viewpoint of windability, the polypropylene film of the present invention preferably has a thickness unevenness in the main contraction direction of 2.0% or less, more preferably 1.5% or less, still more preferably 1.0% or less. .. The smaller the thickness unevenness in the main contraction direction, the more preferable, and the lower limit is not particularly limited, but is substantially 0.1%. In order to reduce the thickness unevenness in the main contraction direction to 2.0% or less, it is preferable that the transverse stretching condition, the heat fixing condition, and the relaxation condition at the time of film formation are within the range described later. The thickness unevenness is an index showing the unevenness of the thickness, and the thickness at 10 points is measured every 50 mm in the main shrinkage direction of the polypropylene film and calculated from the following formula.
Thickness unevenness (%) = ((maximum thickness value-minimum thickness value) / average thickness value) x 100

The polypropylene film of the present invention preferably has a heat shrinkage stress of 1.0 MPa or more at 130 ° C. in the main shrinkage direction. It is more preferably 1.5 MPa or more, still more preferably 2.0 MPa or more. The higher the thermal shrinkage stress at 130 ° C., the more preferably it can be used for a shrinkable base material, but the upper limit is 10 MPa in order to suppress natural shrinkage.

The polypropylene film of the present invention preferably has a heat shrinkage stress of 0.5 MPa or less at 100 ° C. in the main shrinkage direction. It is more preferably 0.3 MPa or less, still more preferably 0.1 MPa or less. The lower the thermal shrinkage stress at 100 ° C. is, the more preferable it is from the viewpoint of flatness during high-temperature storage, but from the viewpoint of dimensional stability, the lower limit is −0.5 MPa.

In the polypropylene film of the present invention, the number of fish eyes having a long side length of 50 μm or more is preferably 20 pieces / m ² or less. In the present invention, the long side means the long side of a rectangle circumscribing the fish eye when measuring the size of the fish eye. The number of fish eyes is more preferably 15 / m ² or less, still more preferably 10 / m ² , and particularly preferably 5 / m ² or less. The lower limit is not particularly limited, but it is substantially 0.001 piece / m ² or more because there are problems of cost increase and productivity decrease due to cleanliness of production equipment and foreign matter control. To reduce the number of fish eyes to 20 / m ² or less, the raw material composition and melt extrusion conditions are set within the ranges described below, and foreign matter generation due to resin deterioration and poor dispersion is suppressed. The number of fish eyes in the present invention means a value measured by the method described in the column of Examples.

The polypropylene film of the present invention preferably has a dynamic friction coefficient μd of 0.4 or less measured by superimposing one surface of the film and the back surface thereof. More preferably, it is 0.3 or less. The lower limit of the dynamic friction coefficient μd is substantially about 0.1, and if it is less than 0.1, the roll may be easily miswound. In order to set the coefficient of kinetic friction μd to 0.4 or less, the raw material composition of the film and the laminated composition of the film should be within the range described later, and the cast (melt-extruded resin sheeting process) conditions and vertical / vertical / It is preferable that the transverse stretching condition is within the range described later.

Subsequently, a polypropylene raw material preferable to be used for the polypropylene film of the present invention will be described.
For the polypropylene film of the present invention, it is preferable to use at least two kinds of polypropylene raw materials (for convenience, these two kinds of polypropylene raw materials are referred to as polypropylene raw material A and polypropylene raw material B, respectively). The polypropylene raw material A, which is one of the polypropylene raw materials, is preferably a polypropylene raw material having high crystallinity in order to improve the strength and slipperiness of the film surface. On the other hand, the polypropylene raw material B, which is another polypropylene raw material, is preferably a polypropylene raw material having a low crystallinity and a low melting point in order to improve the heat shrinkage of the film.

The mesopentad fraction of the polypropylene raw material A is preferably 0.95 or more, more preferably 0.97 or more. The mesopentad fraction is an index showing the stereoregularity of the polypropylene crystal phase measured by nuclear magnetic resonance spectroscopy (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 obtained resin powder with a solvent such as n-heptane, a method of appropriately 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 preferably 0.5 to 20 g / 10 minutes (230 ° C., 21.18 N load), and more preferably the melt flow rate (MFR) is 1 to 10 g / 10. Minutes (230 ° C., 21.18N load), particularly preferably 2 to 5g / 10 minutes (230 ° C., 21.18N load) are preferable from the viewpoint of film forming property and tensile rigidity of the film. In order to set the MFR to the above value, a method of controlling the average molecular weight or the molecular weight distribution is adopted.

Polypropylene preferably used as the polypropylene raw material A has a melting point of 150 ° C. or higher, preferably 155 ° C. or higher, and more preferably 160 ° C. or higher. If the melting point is less than 150 ° C, the heat shrinkage rate after treatment at 100 ° C for 15 minutes becomes large, and the film may shrink during the film forming process, coating process, and storage after winding, resulting in deterioration of flatness. is there. There is no particular upper limit to the melting point, but generally 170 ° C is the upper limit.

Subsequently, the polypropylene raw material B will be described.
The polypropylene raw material B is preferably a polypropylene raw material having a low crystallinity and a low melting point in order to improve the heat shrinkage of the film. As such polypropylene raw material B, homopolypropylene such as low stereoregular polypropylene and syndiotactic polypropylene, polypropylene-α-olefin copolymer, and the like can be used, but they are metallocene-based from the viewpoint of suppressing fish eyes. Polypropylene is preferable, and metallocene-based homopolypropylene is more preferable.

When a polypropylene-α-olefin copolymer is used as the polypropylene raw material B, the α-olefin may be, for example, ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1,1-hexene, etc. 4-Methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene, etc. can be used. it can. The molar fraction of α-olefin contained in the copolymer is preferably 15% or less, more preferably 10% or less, still more preferably less than 5%. If the mole fraction of α-olefin contained in the copolymer exceeds 15%, the quality may deteriorate due to the generation of fish eyes.

Polypropylene preferably used as the polypropylene raw material B has a melting point of 135 ° C. or lower, preferably 120 ° C. or lower, more preferably 110 ° C. or lower, and further preferably 90 ° C. or lower. If the melting point is higher than 135 ° C., the shrinkage of the polypropylene film may be insufficient. On the other hand, the melting point of polypropylene preferably used as the polypropylene raw material B is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, still more preferably 65 ° C. or higher. If the melting point is less than 50 ° C., the obtained polypropylene film may have poor strength.

Polypropylene, which is preferably used as the polypropylene raw material B, preferably has a weight average molecular weight (Mw) of 500,000 or less, more preferably 400,000 or less, and further preferably 300,000 or less. When the weight average molecular weight exceeds 500,000, an increase in melt viscosity may become a problem. On the other hand, polypropylene preferably used as the polypropylene raw material B preferably has a weight average molecular weight of 10,000 or more, more preferably 30,000 or more, and further preferably 50,000 or more. When the weight average molecular weight is less than 10,000, the obtained film may be inferior in shrinkage. Further, the Z + 1 average molecular weight (Mz + 1) is preferably 2.5 million or less, more preferably 2.2 million or less, and 1.5 million or less. Is even more preferable. On the other hand, the lower limit of Mz + 1 is preferably 100,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more.

Examples of the polypropylene raw material (polypropylene raw material B) having the above characteristics include "WELNEX" and "WINTEC" manufactured by Japan Polypropylene Corporation, which are metallocene-based propylene-ethylene copolymers, and Idemitsu Kosan Co., Ltd., which is a metallocene-based homopolypropylene. Commercially available products such as "El Modu" (registered trademark) manufactured by the manufacturer can be appropriately selected and used.

The polypropylene raw material used in the present invention includes various additives such as antioxidants, heat stabilizers, slip agents, antistatic agents, antiblocking agents, fillers and viscosity modifiers as long as the object of the present invention is not impaired. , Anti-coloring agent and the like can also be contained.

Among these, selection of the type and amount of antioxidant is important from the viewpoint of long-term stability. As such an antioxidant, a phenolic agent having steric hindrance is preferable, and when a plurality of types of antioxidants are used in combination, at least one type is preferably a high molecular weight type having a molecular weight of 500 or more. Specific examples thereof include various examples. For example, 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 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. 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 poor. 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.

Further, a crystal nucleating agent can be added to the polypropylene raw material used in the present invention within a range not contrary to the object of the present invention. Crystal nucleating agents include α-crystal nucleating agents (dibenzylideneacetone, sodium benzoate, etc.) and β-crystal nucleating agents (potassium 1,2-hydroxystearate, magnesium benzoate, N, N'-dicyclohexyl-2,6- Amide compounds such as naphthalenedicarboxamide, quinacridone compounds, etc.) are exemplified. However, since excessive addition of the nucleating agent may cause a decrease in stretchability and a decrease in transparency and strength due to void formation and the like, the amount added is usually 0.5% by mass or less, preferably 0.1% by mass. Hereinafter, it is more preferably 0.05% by mass or less.

The polypropylene film of the present invention preferably has a film thickness of 30 μm or more and 100 μm or less. The lower limit is more preferably 40 μm or more, still more preferably 50 μm or more. If the film thickness is smaller than 30 μm, wrinkles may occur or the flatness may deteriorate, resulting in poor appearance. On the other hand, the upper limit of the thickness is more preferably 90 μm or less, still more preferably 80 μm or less. If the film thickness exceeds 100 μm, the amount of resin used may increase and productivity may decrease, or the film may become difficult to bend and workability may deteriorate.

Subsequently, the configuration of the polypropylene film of the present invention will be described with specific examples.
The polypropylene film of the present invention is composed of at least two layers having different properties, and is composed of a layer A containing the polypropylene raw material A as a main component described above as a preferable propylene raw material and a polypropylene raw material described above as a preferable propylene raw material. It is preferable to include two layers of a B layer containing A and the polypropylene raw material B described above as a preferable propylene raw material. The principal component described here refers to the component having the highest mass% (high content) among the components constituting each layer of the film.

The layer A constituting the polypropylene film of the present invention is mainly composed of a polypropylene raw material A composed of a homopolymer of propylene, but a copolymerization component with other unsaturated hydrocarbons such as polypropylene-is not impaired the object of the present invention. It may contain an α-olefin copolymer or the like. With respect to the preferably used polypropylene-α-olefin copolymer, as the α-olefin, for example, ethylene, 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. The mole fraction of α-olefin in the copolymer is preferably 5% or less from the viewpoint of controlling the heat shrinkage after treatment at 130 ° C. for 15 minutes and the melting peak temperature of the film within a preferable range and suppressing fish eyes. , More preferably less than 3%.

The A layer constituting the polypropylene film of the present invention preferably contains 90% by mass or more of the polypropylene raw material A when the mass of the A layer is 100% by mass from the viewpoint of controlling heat shrinkage and slipperiness. The content of the polypropylene raw material A in the layer A is more preferably 95% by mass or more, further preferably 97% by mass or more, and most preferably 99% by mass or more. When the content of the polypropylene raw material A in the layer A is less than 90% by mass, the dimensional stability at 100 ° C. and 15 minutes described above may be deteriorated, or the slipperiness at high temperature may be lowered.

The raw material of the layer A constituting the polypropylene film of the present invention preferably has a weight average molecular weight (Mw) of 800,000 or less, more preferably 600,000 or less, and further preferably 400,000 or less. When the weight average molecular weight exceeds 800,000, an increase in melt viscosity may become a problem. On the other hand, the lower limit of Mw is preferably 100,000 or more, more preferably 150,000 or more, and further preferably 200,000 or more. If the weight average molecular weight is less than 100,000, the resulting film may be poorly shrinkable. Further, the polypropylene raw material of the A layer preferably has a Z + 1 average molecular weight (Mz + 1) of 2.5 million or less, more preferably 2 million or less, and further preferably 1.7 million or less. The lower limit of Mz + 1 is preferably 1 million or more, more preferably 1.2 million or more, and even more preferably 1.4 million or more.

When the mass of the B layer is 100% by mass, the B layer constituting the polypropylene film of the present invention preferably contains 20% by mass or more of the polypropylene raw material A, more preferably 30% by mass or more, and further preferably 40% by mass. % Or more. When the polypropylene raw material A is less than 20% by mass, the dimensional stability at 100 ° C. for 15 minutes may be deteriorated, or the stacking disorder with the A layer may occur. On the other hand, since sufficient heat shrinkage after treatment at 130 ° C. for 15 minutes may not be obtained, the ratio of the polypropylene raw material A in the layer B is preferably 95% by mass or less, more preferably 90% by mass. % Or less, more preferably 80% by mass or less.

When the mass of the B layer is 100% by mass, the B layer constituting the polypropylene film of the present invention preferably contains 10% by mass or more of the polypropylene raw material B, more preferably 15% by mass or more, and further preferably 25% by mass. % Or more. When the polypropylene raw material B is less than 10% by mass, sufficient heat shrinkage after treatment at 130 ° C. for 15 minutes may not be obtained. On the other hand, the proportion of the polypropylene raw material B in the layer B is preferably 95% by mass or less, more preferably 90% by mass or less, because the dimensional stability after the treatment at 100 ° C. for 15 minutes may deteriorate. More preferably, it is 80% by mass or less.

The raw material of the B layer constituting the polypropylene film of the present invention preferably has a weight average molecular weight (Mw) of 500,000 or less, more preferably 400,000 or less, and further preferably 300,000 or less. When the weight average molecular weight exceeds 500,000, an increase in melt viscosity may become a problem. On the other hand, the lower limit of Mw is preferably 100,000 or more, more preferably 150,000 or more, and further preferably 200,000 or more. If the weight average molecular weight is less than 100,000, the resulting film may be poorly shrinkable. Further, the polypropylene raw material of the B layer preferably has a Z + 1 average molecular weight (Mz + 1) of 2 million or less, more preferably 1.7 million or less, and further preferably 1.4 million or less. The lower limit of Mz + 1 is preferably 500,000 or more, more preferably 600,000 or more, and even more preferably 800,000 or more.

The ratio of the weight average molecular weight of the A layer to the weight average molecular weight of the B layer (Mw (A) / Mw (B)) in the polypropylene film of the present invention is preferably 0.2 to 3.0. It is more preferably 0.4 to 2.5, still more preferably 0.6 to 2.0.

In the polypropylene film of the present invention, the ratio of the Z + 1 average molecular weight of the A layer to the Z + 1 average molecular weight of the B layer (Mz + 1 (A) / Mz + 1 (B)) is preferably 0.2 to 5.0. It is more preferably 0.4 to 4.5, still more preferably 0.5 to 4.0.

The thickness ratio of the A layer and the B layer to the total thickness of the polypropylene film of the present invention is preferably 10% or more, more preferably 15% or more, and further preferably 20% or more, respectively.

In the polypropylene film of the present invention, it is preferable that the surface layer (outermost layer) is the A layer described above from the viewpoint of slipperiness. When the B layer is on the surface layer, the slipperiness may decrease due to blocking or the like.

The polypropylene film of the present invention may contain particles on at least one surface layer for the purpose of imparting slipperiness. Such 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.

The average particle size of the particles added to the surface layer is preferably 0.1 μm or more and less than 1.0 μm. If the average particle size is less than 0.1 μm, the particles may aggregate into coarse particles, and the shape may be transferred to the bonded substrate. 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 shape may be transferred to the coated functional layer. In addition, the particles added to the surface layer may fall off during film formation, resulting in an increase in surface roughness. 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.

Next, the method for producing a polypropylene film of the present invention will be described with specific examples, but the present invention is not necessarily construed as being limited to this.
First, the raw material for the A layer is supplied to the single-screw extruder for the A layer, the raw material for the B layer is supplied to the single-screw extruder for the B layer, 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, 1/20/1 to 1/5 with a multi-manifold type A layer / B layer / A layer composite T die. Laminated so as to have a laminated thickness ratio of 1/1, and discharged onto a cast drum to obtain a laminated unstretched sheet having a layer structure of A layer / B layer / A layer. At this time, the surface temperature of the cast drum is preferably 10 to 130 ° C, more preferably 20 to 100 ° C. 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.

Subsequently, the cast sheet obtained as described above is biaxially stretched to obtain a film having desired strength and heat shrinkage characteristics. As the biaxial stretching method, any method such as an inflation simultaneous biaxial stretching method, a stent simultaneous biaxial stretching method, and a stent sequential biaxial stretching method can be selected, but film forming stability, thickness uniformity, and film heat From the viewpoint of shrinkage control, it is preferable to adopt the stenter sequential biaxial stretching method, and it is particularly preferable to stretch in the MD direction and then in the TD direction from the viewpoint of heat shrinkage control.

Subsequently, a specific stretching method will be described. The following description is an example of a stretching method and is not limited to this method.
First, in order to stretch the obtained unstretched cast sheet in the longitudinal direction, the unstretched cast sheet is controlled to a stretchable temperature. As the temperature control method, a method using a temperature-controlled rotary roll, a method using a hot air oven, or the like can be adopted. The stretching temperature in the longitudinal direction is 100 to 150 ° C., more preferably 110 to 140 ° C., and most preferably 130 to 140 ° C. from the viewpoint of film characteristics and its uniformity. When the stretching temperature is less than 100 ° C, uneven stretching or film breakage occurs, or the heat shrinkage rate after treatment at 100 ° C for 15 minutes increases, and during the film forming process, coating process, and storage after winding. The film may shrink and the flatness may decrease. When the stretching temperature exceeds 150 ° C., the orientation of the film is weak and the heat shrinkage at high temperature may decrease. The stretching ratio in the longitudinal direction is preferably 2 to 7 times, more preferably 2.5 to 6.5 times, still more preferably 3 to 6 times. If the draw ratio is less than 2 times, the orientation of the film is weakened, and the heat shrinkage and tensile rigidity may be lowered. On the other hand, if it exceeds 7 times, film breakage may occur.

Subsequently, the uniaxially stretched film obtained by stretching in the longitudinal direction is stretched in the width direction. A biaxially stretched film is obtained by guiding the uniaxially stretched film to a tenter type stretching machine, grasping the end portion of the film with a clip, and stretching the film in the width direction. The stretching temperature in the width direction is preferably 125 to 175 ° C., more preferably 135 ° C. to 170 ° C., and even more preferably 145 ° C. to 165 ° C. Further, the stretching temperature in the width direction is preferably higher than the melting point of the polypropylene raw material B, more preferably 30 ° C. or higher than the melting point, and further preferably 50 ° C. or higher. When the stretching temperature is less than 125 ° C., or when the melting point of the polypropylene raw material B is lower than the melting point, the film breaks or uneven stretching occurs, or the heat shrinkage rate after the treatment at 100 ° C. for 15 minutes increases. During the filming process, coating process, and storage after winding, the film may shrink and the flatness may deteriorate. On the other hand, if the temperature exceeds 175 ° C., the orientation of the film is weak and the tensile rigidity may decrease, or film rupture may occur due to resin melting. The stretching ratio in the width direction is preferably 1.5 to 15 times, more preferably 2.5 to 12 times, still more preferably 6 to 10 times. If the draw ratio is less than 1.5 times, the tensile rigidity may decrease and the productivity may deteriorate. On the other hand, when the draw ratio exceeds 15 times, the film may be easily broken.

Subsequently, in order to improve the dimensional stability of the film, it is preferable to perform a relaxation treatment and a heat fixing treatment. In the relaxation treatment and heat fixing treatment, while tensioning the width direction with a clip and giving relaxation at a relaxation rate of 0 to 8% in the width direction, heat fixing is performed at a temperature of 100 ° C. or higher and lower than 160 ° C., and then 80 to 80 to After a cooling step at 100 ° C., the film is guided to the outside of the tenter to release the clip at the edge of the film. Here, the heat treatment temperature is more preferably 110 ° C. or higher and lower than 155 ° C., and further preferably 120 ° C. or higher and lower than 150 ° C. The heat treatment temperature is preferably higher than the melting point of the polypropylene raw material B, more preferably 30 ° C. or higher than the melting point, and further preferably 50 ° C. or higher. Here, the relaxation rate is more preferably 0 to 6%, further preferably 0 to 4%. If the relaxation rate exceeds 6%, the heat shrinkage after treatment at 130 ° C. for 15 minutes may be insufficient. Here, when the temperature at which relaxation is applied is 160 ° C. or higher, the heat shrinkage after treatment at 130 ° C. for 15 minutes may be insufficient. On the other hand, if the temperature is lower than 100 ° C, the dimensional stability of the film at a temperature of 100 ° C or lower may be insufficient.

The polypropylene film of the present invention obtained as described above has excellent heat shrinkage at a high temperature (130 ° C.) and at the same time has good flatness at a high temperature (100 ° C.). Therefore, for example, it has a design property. It can be preferably used for label packaging for the purpose of imparting and protecting the contents, and for a mold release base material that is required to have heat shrinkage after forming a functional layer. In particular, it can be suitably used as a release film.

Hereinafter, the present invention will be described in detail with reference to Examples. Physical properties and characteristics were measured and evaluated by the following methods.
(1) Film Thickness Five points were measured using a microthickness meter (manufactured by Anritsu Co., Ltd.), and the value was calculated as an arithmetic mean value.

(2) Heat shrinkage rate after treatment at 130 ° C. in the main shrinkage direction for 15 minutes Five samples with a length of 200 mm and a width of 10 mm were cut out and marked as marked lines at positions 25 mm from both ends. Measure the distance between the marked lines with a universal projector and set the test length (l ₀ , 150 mm). Next, a load of 3 g is applied to one end (the lower end) of the test piece in the length direction, and the test piece is heated in an oven kept at 130 ° C. for 15 minutes while suspended, and the test piece is taken out and at room temperature. After cooling with, measure the dimension (l ₁ ) between the marked lines attached earlier with a universal projector, calculate the heat shrinkage rate of each sample by the following formula, and calculate the heat shrinkage of each sample with the five arithmetic mean values in the measurement direction. Calculated as shrinkage rate.
Heat shrinkage = {(l _{0 −} l ₁ ) / l ₀ } × 100 (%)
The measurement is performed in the film plane when the MD direction is 0 °, 15 °, 30 °, 45 °, 60 °, 75 °, 90 °, 105 °, 120 °, 135 ° with respect to the MD direction. The heat shrinkage rate was measured in each direction forming an angle of 150 ° and 165 °, and the direction showing the highest value was shown in the table as the main shrinkage direction. When the MD direction is unknown, the heat shrinkage rate is measured in 15 ° increments from any direction, and the highest direction is set as the main shrinkage direction. The main contraction direction in the examples coincided with the width direction in all the examples. For reference, the values in the longitudinal direction are also shown in the table.

(3) Heat shrinkage rate after treatment at 100 ° C. for 15 minutes in the main shrinkage direction Long so that the main shrinkage direction defined in the section "(2) Heat shrinkage rate after treatment at 130 ° C. for 15 minutes" is the long side. Five samples with a size of 200 mm and a width of 10 mm are cut out, marked as marked lines at positions 25 mm from both ends, and the distance between the marked lines is measured with a universal projector to obtain the test length (l ₂ , 150 mm). Next, a load of 3 g is applied to one end (the lower end) of the test piece in the length direction, and the test piece is heated in an oven kept at 100 ° C. for 15 minutes while suspended, and the test piece is taken out and at room temperature. After cooling with, measure the dimension (l ₃ ) between the marked lines attached earlier with a universal projector, calculate the heat shrinkage rate of each sample by the following formula, and calculate the heat shrinkage of each sample with the five arithmetic mean values in the measurement direction. Calculated as shrinkage rate.
Heat shrinkage = {(l _{2 −} l ₃ ) / l ₂ } × 100 (%)

(4) Melting peak temperature of film Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), a 3 mg sample is heated from 30 ° C to 260 ° C at 20 ° C / min in a nitrogen atmosphere. To do. The peak temperature of the endothermic curve obtained at the time of this temperature rise was defined as the melting peak temperature. When there were multiple melting peaks, the melting peak temperature of the hottest melting peak was used. The n number of measurements was performed three times, and the arithmetic mean value was used.

(5) Heat shrinkage stress at 130 ° C. and 100 ° C. in the main shrinkage direction The width is 4 mm so that the main shrinkage direction defined in the section "(2) Heat shrinkage rate after treatment at 130 ° C. for 15 minutes" is the long side. A rectangular sample having a length of 50 mm was cut out, and a film was sandwiched between metal chucks so as to have a trial length of 20 mm. The sample sandwiched between the chucks was set in the following device, and the stress curve in the longitudinal direction of the film in which the test length was kept constant was obtained by the following temperature program. From the obtained stress curve, the shrinkage stress of the film at 130 ° C. and 100 ° C. was read.
Equipment: Thermomechanical analyzer TMA / SS6000 (manufactured by Seiko Instruments Inc.)
Test mode: L control mode Test length: 20 mm
Temperature range: 23-200 ° C
Temperature rise rate: 10 ° C./min SS program: 0.1 μm / min Measurement atmosphere: In nitrogen Measurement thickness: The film thickness of (1) above was used.

(6) Elastic modulus (EIT) in the thickness direction measured by the nanoindentation method
For the measurement, a nano indenter "ENT-2100" manufactured by Elionix Inc. was used, and the measurement was performed according to the method specified in ISO 14577 (2002). Apply one drop of "Aron Alpha" (registered trademark) professional impact resistance "manufactured by Toagosei Co., Ltd. to the polypropylene film, and fix the biaxially oriented polypropylene film to the dedicated sample fixing base via instant adhesive. The measurement was performed with the surface layer side as the measurement surface. A triangular pyramid diamond indenter (Berkovich indenter) having an interridge angle of 115 ° was used for the measurement. The measurement data was processed by the dedicated analysis software (version 6.18) of "ENT-2100", and the indentation elastic modulus EIT (GPa) was measured. The measurement was performed on both sides of the film at n = 10, and the average value was obtained. The larger value of the average values of the measured values on both sides was shown in the table.
Measurement mode: Load-unloading test Maximum load: 0.5mN
Holding time when the maximum load is reached: 1 second Load speed, unloading speed: 0.05 mN / sec

(7) Stress at 2% elongation in the main contraction direction and in the direction orthogonal to it (F2 value)
Five films each in a rectangle with a length of 150 mm and a width of 10 mm so that the main shrinkage direction of the film specified in the section "(2) Heat shrinkage rate after treatment at 130 ° C. for 15 minutes" and the direction orthogonal to it are long sides. The samples were cut out one by one.
Using a tensile tester (Tencilon UCT-100 manufactured by Orientec), in an atmosphere of room temperature of 23 ° C. and relative humidity of 65%, the initial tensile chuck distance is 50 mm and the tensile speed is 300 mm / min, and the sample for measurement in the main contraction direction is used. Tensile tests were performed on each of the measurement samples in the direction orthogonal to the main contraction direction. The load applied to the film when the sample was stretched by 2% (when the distance between chucks was 51 mm) was read, and the value divided by the cross-sectional area (film thickness × 10 mm) of the sample before the test was defined as the F2 value. The test was performed 5 times in each of the main contraction direction and the direction orthogonal to the main contraction direction, and the F2 value was calculated by calculating the arithmetic mean value in each direction.

(8) Thickness unevenness in the main shrinkage direction The thickness is measured every 50 mm in the main shrinkage direction of the polypropylene film specified in the section "(2) Heat shrinkage rate after treatment at 130 ° C. for 15 minutes", and the maximum value is measured. , The minimum value and the average value were used to determine the thickness unevenness from the following formula. The measurement is performed 10 times, but if the sample width in the main contraction direction is 500 mm or less and the number of measurements is less than 10, the measurement location is shifted by 5 to 10 mm in the direction orthogonal to the main contraction direction to increase the number of measurements. May be good.
Thickness unevenness (%) = ((maximum thickness value-minimum thickness value) / average thickness value) x 100

(9) Number of fish eyes having a long side of 50 μm or more Five square film samples having a side of 20 cm or more were cut out, and the number of fish eyes having a long side of 50 μm or more was counted using an illumination magnifying glass. The total number of 5 samples was calculated, and this was multiplied by 5 to calculate the number of fish eyes per 1 m ² . In the fisheye count, if a clear image can be taken, a photograph may be taken and obtained.

(10) Dynamic friction coefficient (μd)
The measurement was carried out at 25 ° C. and 65% RH according to JIS K 7125 (1999) using a slip tester manufactured by Toyo Seiki Co., Ltd. The measurement was carried out in the direction orthogonal to the main shrinkage direction defined in the section "(2) Heat shrinkage rate after treatment at 130 ° C. for 15 minutes" and on different surfaces. The same measurement was performed 5 times for each sample, and the average value of the obtained values was calculated and used as the coefficient of kinetic friction (μd) of the sample.

(11) Molecular weight measurement
Measurement was performed by gel permeation chromatography (GPC) method using 150 C / GPC manufactured by Waters. The elution temperature was 140 ° C., TSKgelGMH6-HT (3 pieces) manufactured by Tosoh Co., Ltd. was used as the column, and polystyrene (manufactured by Tosoh Co., Ltd., molecular weight 500 to 6,770,000) was used as the molecular weight standard substance. In the measurement sample, about 5 mg of polypropylene resin was dissolved in 5 ml of o-dichlorobenzene to a concentration of about 1 mg / ml. 400 μl of the obtained sample solution was injected. The elution solvent flow rate was 1.0 ml / min, and it was detected by a refractive index detector. Tables 1 and 2 show the weight average molecular weight (Mw) and Z + 1 average molecular weight (Mz + 1) of each of the A layer and the B layer, respectively.

(12) Flatness of film A polypropylene film having a width of 500 mm wound around a core is unwound by 1 m, and free tension (in a state of hanging vertically due to the weight of the film) and 1 kg / kg evenly over the entire width of the film. With the tension of m and 3 kg / m applied, the presence or absence of poor flatness such as dents and swells was visually confirmed.
⊚: There is no part with poor flatness in free tension ○: There is a part with poor flatness in free tension and disappears in tension of 1 kg / m width △: There is a part of poor flatness in tension of 1 kg / m width Seen, things that disappear with a tension of 3 kg / m width ×: Things that do not disappear even with a tension of 3 kg / m width

(13) Evaluation of transfer to an adherend A polypropylene film as a sample and a 40 μm-thick “Zeonoa film” (registered trademark) manufactured by Nippon Zeon Co., Ltd. were sampled into squares having a width of 100 mm and a length of 100 mm, respectively, and the polypropylene film was sampled. The rough surface and the "Zeonoa film" are stacked so that they are in contact with each other, sandwiched between two acrylic plates (width 100 mm, length 100 mm) with smooth surfaces, placed on a table, and 3 kg from the top of the acrylic plate. 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 polypropylene film) was visually observed and evaluated according to the following criteria.
A: Clean and equivalent to before applying load B: Weak unevenness is confirmed C: Strong unevenness is confirmed Ryoka System Co., Ltd. is used to distinguish between the rough and smooth surfaces of polypropylene film. VertScan2.0 R5300GL-Lite-AC manufactured by the company was used. The surface shape of the film was obtained by surface-correcting the shooting screen by polynomial fourth-order approximation using the attached analysis software. The measurement conditions are as follows.
Measurement conditions: CCD camera SONY HR-57 1/2 inch (12.7 mm)
Objective lens 5x
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
The measurement was performed on both the front and back surfaces of the film at n = 3, the average value of Sz (maximum height) of each surface was obtained, and the surface having a large Sz was defined as the rough surface side of the polypropylene film.

(Example 1)
Highly crystalline PP (manufactured by Prime Polymer Co., Ltd., MFR: 2.9 g / 10 minutes, melting point 164 ° C.) was supplied to the A layer as a polypropylene raw material A to a single-screw melt extruder for the A layer, and B In the layer, 65 parts by mass of the polypropylene raw material A and low stereoregular PP (manufactured by Idemitsu Kosan Co., Ltd., "El Modu" (registered trademark) S901, MFR: 50 g / 10 minutes, melting point: 80 ° C.) as the polypropylene raw material B ) A dry blend of 35 parts by mass is supplied to a single-screw melt extruder for layer B, melt-extruded at 240 ° C., and after removing foreign matter with a 60 μm cut sintering filter, feed block type A A three-layer composite T-die composed of layers / B layers / A layers was laminated at a thickness ratio of 3/4/3 and discharged to a cast drum whose surface temperature was controlled at 30 ° C. to obtain a cast sheet. .. Next, the film was preheated to 130 ° C. using a plurality of ceramic rolls, stretched 4.5 times at 130 ° C. in the longitudinal direction of the film, and introduced by gripping the end with a clip into a tenter type stretching machine at 160 ° C. After preheating for 3 seconds, the film was stretched 8.0 times in the width direction of the film at 150 ° C. In the subsequent heat treatment step, the heat treatment is performed at 130 ° C. without giving relaxation, and then the film is guided to the outside of the tenter through a cooling step of 110 ° C., and after releasing the clip at the end of the film, the end is slit and wound around the core. A polypropylene film having a thickness of 20 μm was obtained. Table 1 shows the physical properties of the polypropylene film and the evaluation results.

(Example 2)
A polypropylene film was obtained in the same manner as in Example 1 except that the laminated thickness ratio was 1/8/1, the preheating temperature in the width direction was 170 ° C., the stretching temperature was 160 ° C., and the film thickness was 30 μm. ..

(Example 3)
Highly crystalline PP (manufactured by Prime Polymer Co., Ltd., MFR: 2.9 g / 10 minutes, melting point: 164 ° C.) 80 parts by mass as polypropylene raw material A, and low stereoregular PP (Idemitsu) as polypropylene raw material B in layer A. A dry blend of 20 parts by mass of "El Modu" (registered trademark) S901, MFR: 50 g / 10 minutes, melting point: 80 ° C. manufactured by Kosan Co., Ltd. is used as a raw material for the A layer, and the laminated thickness ratio is 2 /. 6/2, except that the stretching temperature in the longitudinal direction was 125 ° C, the preheating temperature in the width direction was 170 ° C, the stretching temperature was 160 ° C, the heat treatment temperature was 120 ° C, and the film thickness was 15 μm. A polypropylene film was obtained in the same manner.

(Example 4)
"WELNEX" RFG4VM (MFR: 6.0 g / 10 minutes, melting point: 130 ° C.) manufactured by Japan Polypropylene Corporation was used as the polypropylene raw material B, the lamination thickness ratio was 2/6/2, and the film thickness was 40 μm. A polypropylene film was obtained in the same manner as in Example 1 except for the above.

(Example 5)
A polypropylene film was obtained in the same manner as in Example 1 except that the mixing ratios of the polypropylene raw material A and the polypropylene raw material B for the B layer were 55 parts by mass and 45 parts by mass, respectively, and the film thickness was 12 μm. It was.

(Example 6)
Highly crystalline PP (manufactured by Prime Polymer Co., Ltd., MFR: 2.9 g / 10 minutes, melting point: 164 ° C.) 90 parts by mass as polypropylene raw material A on layer A, polypropylene ethylene random copolymer as polypropylene raw material B (Sumitomo Chemical) Noblen S131 manufactured by Co., Ltd., MFR: 1.5 g / 10 minutes, melting point: 132 ° C.) A dry blend of 10 parts by mass was supplied to a single-screw melt extruder for layer A, and the above was applied to layer B. 50 parts by mass of polypropylene raw material A and 40 parts by mass of low stereoregular PP (manufactured by Idemitsu Kosan Co., Ltd., "El Modu" (registered trademark) S901, MFR: 50 g / 10 minutes, melting point: 80 ° C.) as polypropylene raw material B , And polypropylene ethylene random copolymer (manufactured by Sumitomo Chemical Co., Ltd., Nobleen S131, MFR: 1.5 g / 10 minutes, melting point: 132 ° C.) 10 parts by mass of dry blend was used as the raw material for the B layer. A polypropylene film was obtained in the same manner as in Example 1 except for the exception.

(Comparative Example 1)
Highly crystalline PP (manufactured by Prime Polymer Co., Ltd., MFR: 2.9 g / 10 minutes, melting point: 164 ° C.) 20 parts by mass as polypropylene raw material A in layer A, and low stereoregular PP (Idemitsu) as polypropylene raw material B. Kosan Co., Ltd., "El Modu" (registered trademark) S901, MFR: 50 g / 10 minutes, melting point: 80 ° C., 30 parts by mass, and polypropylene ethylene random copolymer (Sumitomo Chemical Co., Ltd., Noblen S131, MFR: 1) .5 g / 10 minutes, melting point: 132 ° C.) 50 parts by mass was dry-blended and supplied to a single-screw melt extruder for layer A, and 50 parts by mass of the polypropylene raw material A and polypropylene were added to layer B. A dry blend of 50 parts by mass of ethylene random copolymer was used as a raw material for the B layer, and the same as in Example 1 except that the laminated thickness ratio was 1/8/1 and the film thickness was 15 μm. A polypropylene film was obtained.

(Comparative Example 2)
In layer A, as polypropylene raw material B, 50 parts by mass of low stereoregular PP (manufactured by Idemitsu Kosan Co., Ltd., "El Modu" (registered trademark) S901, MFR: 50 g / 10 minutes, melting point: 80 ° C.), and polypropylene ethylene random A dry blend of 50 parts by mass of a copolymer (Noblen S131, MFR: 1.5 g / 10 minutes, melting point: 132 ° C.) manufactured by Sumitomo Chemical Co., Ltd. was supplied to a single-screw melt extruder for layer A, and B As a layer, 100 parts by mass of highly crystalline PP (manufactured by Prime Polymer Co., Ltd., MFR: 2.9 g / 10 minutes, melting point: 164 ° C.), which is a polypropylene raw material A, is used as a raw material for the B layer, and the laminated thickness ratio. A polypropylene film was obtained in the same manner as in Example 1 except that the film thickness was set to 2/6/2, the film thickness was set to 25 μm, and the relaxation rate in the width direction was set to 10%.

(Comparative Example 3)
A layer is a dry blend of 30 parts by mass of syndiotactic PP described in JP-A-7-329177 and 70 parts by mass of an ethylene-propylene copolymer described in JP-A-7-329177 as polypropylene raw material B. It was supplied to a single-screw melt extruder for the layer, and 30 parts by mass of the syndiotactic PP and 70 parts by mass of the ethylene-propylene copolymer were dry-blended as the B layer and laminated as a raw material for the B layer. A polypropylene film was obtained in the same manner as in Example 1 except that the thickness ratio was 1/8/1 and the film thickness was 18 μm.

Claims (8)

The heat shrinkage after treatment at 130 ° C. for 15 minutes in the main shrinkage direction is 4% or more and 30% or less.
When the temperature is raised from 30 ° C. to 260 ° C. at 20 ° C./min with a differential scanning calorimeter DSC, it has a melting peak temperature of 155 ° C. or higher.
The stress (F2 value) at an elongation of 2% in both the main contraction direction and the direction orthogonal to the main contraction direction is 24 MPa or more.
It has a laminated structure consisting of at least A layer and B layer, and the A layer contains 90% by mass or more of polypropylene raw material A having a melting point of 150 ° C. or more and 170 ° C. or less in 100% by mass of all the components constituting the layer. The B layer is a polypropylene film which contains 15% by mass or more and 95% by mass or less of a polypropylene raw material B having a melting point of 50 ° C. or more and 135 ° C. or less in 100% by mass of all the components constituting the layer. The heat shrinkage after treatment at 130 ° C. for 15 minutes in the main shrinkage direction is 4% or more and 30% or less.
When the temperature is raised from 30 ° C. to 260 ° C. at 20 ° C./min with a differential scanning calorimeter DSC, it has a melting peak temperature of 155 ° C. or higher.
The thickness unevenness in the main contraction direction is 2.0% or less,
It has a laminated structure consisting of at least A layer and B layer, and the A layer contains 90% by mass or more of polypropylene raw material A having a melting point of 150 ° C. or more and 170 ° C. or less in 100% by mass of all the components constituting the layer. The B layer is a stretched film containing 15% by mass or more and 95% by mass or less of a polypropylene raw material B having a melting point of 50 ° C. or more and 135 ° C. or less in 100% by mass of all the components constituting the layer. The polypropylene film according to claim 1 or 2, wherein the heat shrinkage rate after treatment at 100 ° C. in the main shrinkage direction for 15 minutes is 10% or less. The polypropylene film according to any one of claims 1 to 3, wherein the heat shrinkage stress at 130 ° C. in the main shrinkage direction is 1.0 MPa or more, and the heat shrinkage stress at 100 ° C. is 0.5 MPa or less. The polypropylene film according to any one of claims 1 to 4, wherein the elastic modulus in the thickness direction at at least one side at 23 ° C. measured by the nanoindentation method is 2.0 GPa or more. The polypropylene film according to any one of claims 1 to 5, wherein the number of fish eyes having a long side length of 50 μm or more is 20 pieces / m ² or less. The polypropylene film according to any one of claims 1 to 6, wherein the dynamic friction coefficient measured by superimposing one front surface of the film and the back surface thereof is 0.4 or less. A release film using the polypropylene film according to any one of claims 1 to 7.