JP2023013958A - Biaxially oriented laminated polypropylene film - Google Patents

Abstract

To provide a biaxially oriented laminated polypropylene film which has a low heat shrinkage rate at 150°C equivalent to a biaxially oriented PET film and has excellent laminate strength.SOLUTION: A biaxially oriented laminated polypropylene film includes at least a base material layer A and a surface layer B, and is composed of a resin composition which contains a polypropylene resin as a main component, and satisfies the following requirements 1) to 6): 1) a ratio of thickness of the base material layer A to thickness of the whole film is 70-98%; 2) a mesopentad fraction of the polypropylene resin constituting the base material A is 97.0-99.9%; 3) a mesopentad fraction of the polypropylene resin constituting the surface layer B is 80.0-96.5%; 4) a coefficient of surface orientation measured from the surface layer B side of the film is 0.0134 or less; 5) a low heat shrinkage rate at 150°C in a film longitudinal direction is 6.0% or less; and 6) a low heat shrinkage rate at 150°C in a film width direction is 5.0% or less.SELECTED DRAWING: None

Description

The present invention relates to a biaxially oriented polypropylene film having excellent heat resistance and lamination strength.

A biaxially oriented polypropylene film is characterized by excellent moisture resistance and has the necessary heat resistance and rigidity.
Moreover, recently, due to the environmental impact of packaging materials (ease of recycling), the realization of mono-material packaging made of a single resin is expected. Therefore, it is expected to realize a single polypropylene packaging material using a biaxially oriented polypropylene film as a base film and an unstretched polypropylene film as a sealant film.

In order to increase the heat resistance and rigidity of the biaxially oriented polypropylene film, in the production process of the biaxially oriented polypropylene film, a method of stretching in the longitudinal direction after stretching in the width direction (see Patent Document 1 etc.), or a biaxially oriented polypropylene film. In the manufacturing process of an oriented polypropylene film, after stretching in the width direction, the first heat treatment is performed while the film is relaxed at a temperature below the stretching temperature in the width direction, and in the second step, the heat treatment is performed at the first temperature to the temperature for stretching in the width direction. A method (see, for example, Patent Document 2, etc.) has been proposed.
However, the films described in Patent Documents 1 and 2 tend to wrinkle at the sealed portion after heat sealing, and it has been difficult to replace the biaxially oriented PET film for all uses. Moreover, since the crystallinity of the film is high, there is a problem that the lamination strength is low when the sealant film is laminated.

Furthermore, an oriented polypropylene film having heat resistance at 150° C. comparable to that of a biaxially oriented PET film has been proposed (see, for example, Patent Documents 3 and 4), but further improvements in laminate strength are expected. .

JP 2013-177645 A WO2016/182003 international publication WO2013/111779 international publication WO2017/169952 international publication

An object of the present invention is to solve the problems described above. That is, it relates to a biaxially oriented polypropylene film which is excellent in heat resistance and lamination strength. More specifically, it relates to a biaxially oriented polypropylene film having heat resistance at 150° C. comparable to that of a biaxially oriented PET film and excellent lamination strength.

As a result of intensive studies in order to achieve such an object, the present invention has been made by controlling the lamination structure of the biaxially oriented polypropylene film, the raw material composition of each layer, and the film properties, thereby achieving excellent rigidity and lamination strength. An axially oriented polypropylene film could be obtained.
That is, the biaxially oriented polypropylene film according to the present invention has the following structure.
[1]
A biaxially oriented laminated polypropylene film comprising at least a substrate layer A and a surface layer B, wherein the biaxially oriented laminated polypropylene film satisfies the following requirements 1) to 6).
1) The ratio of the thickness of the substrate layer A to the thickness of the entire film is 70% or more and 98% or less.
2) The mesopentad fraction of the polypropylene resin constituting the base material layer A is 97.0 or more and 99.9% or less.
3) The mesopentad fraction of the polypropylene resin constituting the surface layer B is 80.0 or more and 96.5% or less.
4) The plane orientation coefficient measured from the surface layer B side of the film is 0.0134 or less.
5) The 150°C heat shrinkage in the longitudinal direction of the film is 6.0% or less.
6) The 150°C heat shrinkage in the width direction of the film is 5.0% or less.

[2]
The biaxially oriented laminated polypropylene film according to [1], wherein the biaxially oriented laminated polypropylene film satisfies the following requirements 7) and 8).
7) F5 in the longitudinal direction of the film is 35 MPa or more.
8) F5 in the width direction of the film is 95 MPa or more.

[3]
The biaxially oriented laminated polypropylene film according to [1] or [2], wherein the film surface of the surface layer B of the biaxially oriented laminated polypropylene film has a wet tension of 38 mN/m or more.

[4]
The biaxially oriented laminated polypropylene film according to any one of [1] to [3], wherein the biaxially oriented laminated polypropylene film has a haze of 5.0% or less.

[5]
The biaxially oriented laminated polypropylene film according to any one of [1] to [4], wherein the thickness of the entire biaxially oriented laminated polypropylene film is 5 μm or more and 60 μm or less.

[6]
A laminate comprising the biaxially oriented laminated polypropylene film according to any one of [1] to [5] and an unstretched polypropylene film.
[7]
The laminate strength, which is represented by the peel strength when the laminate is peeled at 90° (T-shape), is 1.9 N/15 mm or more and 10 N/15 mm or less in both the longitudinal direction and the width direction of the laminate [6] The laminate according to .

The biaxially oriented laminated polypropylene film of the present invention has a low thermal shrinkage comparable to that of a biaxially oriented PET film at 150°C, and has excellent lamination strength. It can be suitably used as a packaging material.

The biaxially oriented laminated polypropylene film according to the present invention will be described in more detail below.
The biaxially oriented laminated polypropylene film according to the present invention is a biaxially oriented laminated polypropylene film comprising at least a substrate layer A and a surface layer B. The base material layer A and the surface layer B are made of a polypropylene resin composition, and the polypropylene resin composition contains a polypropylene resin as a main component. The "main component" means that the proportion of the polypropylene resin in the polypropylene resin composition is 90% by mass or more, more preferably 93% by mass or more, more preferably 95% by mass or more, and particularly preferably is 97% by mass or more.
The base material layer A and the surface layer B are described below.

[Base material layer A]
(Steric regularity of polypropylene resin constituting base material layer A)
The mesopentad fraction ([mmmm]%), which is an index of stereoregularity of the polypropylene resin constituting the base material layer A in the present invention, is 97.0% or more, 99.9% or less, and 97.5% or more. , is preferably 99.7% or less, more preferably 98.0% or more and 99.5% or less, and even more preferably 98.5% or more and 99.3% or less. When the polypropylene resin used for the substrate layer A is a mixture of a plurality of polypropylene resins, the mesopentad fraction of the mixture is preferably within the same range as above.
When the mesopentad fraction of the polypropylene resin constituting the substrate layer A in the present invention is 97.0% or more, the crystallinity of the polypropylene resin is enhanced, and the crystal melting point, crystallinity, and crystal orientation of the film are improved. , rigidity and heat resistance at high temperatures are easily obtained. When it is 99.9% or less, it is preferable in terms of less breakage during film production and in that the production cost of the polypropylene resin can be easily suppressed. The mesopentad fraction is measured by a nuclear magnetic resonance method (so-called NMR method).
In order to make the mesopentad fraction of the polypropylene resin within the above-mentioned range, there are a method of washing the obtained polypropylene resin powder with a solvent such as n-heptane, a selection of a catalyst and / or a co-catalyst, and a polypropylene resin composition. A method of appropriately selecting components is preferably adopted.

(Polypropylene resin used for base material layer A)
The polypropylene resin used for the base material layer A in the present invention can be a polypropylene homopolymer or a copolymer with ethylene and/or an α-olefin having 4 or more carbon atoms. A propylene homopolymer substantially free of ethylene and/or an α-olefin having 4 or more carbon atoms is preferred, and even if it contains ethylene and/or an α-olefin component having 4 or more carbon atoms, ethylene and/or The amount of α-olefin components having 4 or more carbon atoms is preferably 1 mol % or less. The upper limit of the component amount is more preferably 0.5 mol %, still more preferably 0.3 mol %, particularly preferably 0.1 mol %, and most preferably 0%. Within the above range, rigidity and heat resistance are likely to be improved. Examples of α-olefin components having 4 or more carbon atoms constituting such copolymers include 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene, Thene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene and the like. As the polypropylene resin, two or more different polypropylene homopolymers, copolymers with ethylene and/or α-olefins having 4 or more carbon atoms, and mixtures thereof can be used.

(Melting temperature of polypropylene resin constituting base material layer A)
The lower limit of the melting temperature (Tm) measured by DSC of the polypropylene resin used for the base material layer A: hereinafter sometimes abbreviated as TmA) is preferably 160 ° C., more preferably 161 ° C., and further It is preferably 162°C, and even more preferably 163°C.
When TmA is 160° C. or higher, rigidity and heat resistance at high temperatures are easily obtained.
The upper limit of TmA is preferably 180°C, more preferably 178°C. When the TmA is 180°C or less, it is easy to suppress cost increase in terms of production of polypropylene resin.
When the polypropylene resin used for the substrate layer A is a mixture of a plurality of polypropylene resins, the TmA of the mixture is preferably within the same range as above.
About 5 mg of a sample was packed in an aluminum pan, set in a differential scanning calorimeter (DSC), heated to 230°C at a scanning rate of 10°C/min in a nitrogen atmosphere, and melted at 230°C for 5 minutes. , is the main peak temperature of the endothermic peak accompanying melting observed when the temperature is lowered to 30°C at a scanning rate of -10°C/min, held for 5 minutes, and then heated at a scanning rate of 10°C/min. When multiple peaks are observed, the peak temperature on the low temperature side is taken as Tm.

(Crystallization temperature of polypropylene resin constituting base material layer A)
The lower limit of the crystallization temperature (Tc: hereinafter sometimes abbreviated as Tc) measured by DSC of the polypropylene resin used for the base material layer A is 105°C, preferably 108°C, more preferably 110°C. °C, more preferably 114°C. When Tc is 105° C. or higher, crystallization is likely to proceed, and rigidity and heat resistance at high temperatures are likely to be obtained.
The upper limit of Tc is preferably 135°C, more preferably 133°C, still more preferably 132°C, even more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. is. When Tc is 135° C. or less, cost increase can be suppressed in terms of polypropylene production, and breakage during film formation can be easily suppressed.
When the polypropylene resin used for the substrate layer A is a mixture of a plurality of polypropylene resins, the crystallization temperature of the mixture is preferably within the same range as above.
Tc is about 5 mg of a sample packed in an aluminum pan, set in a DSC, heated to 230 ° C. at a scanning rate of 10 ° C./min under a nitrogen atmosphere, and melted at 230 ° C. for 5 minutes, scanning speed -10 ° C. This is the main peak temperature of the exothermic peak observed when the temperature is lowered to 30° C./min. When multiple peaks are observed, the peak temperature on the low temperature side is defined as Tc.
The crystallization temperature can be further increased by adding a crystal nucleating agent to the polypropylene resin described above.

(Melt flow rate of polypropylene resin used for base material layer A)
The melt flow rate (MFR: hereinafter sometimes abbreviated as MFR) of the polypropylene resin used for the base material layer A is measured according to Condition M (230 ° C., 2.16 kgf) of JISK7210 (1995). , preferably 6.0 g/10 min or more and 10 g/10 min or less, more preferably 6.2 g/10 min or more and 9.0 g/10 min or less, 6.3 g/10 min or more, It is more preferably 8.5 g/10 minutes or less, particularly preferably 6.4 g/10 minutes or more and 8.0 g/10 minutes or less, and 6.5 g/10 minutes or more and 7.5 g/10 minutes or less. Most preferably.
Further, when the polypropylene resin used for the base material layer A is a mixture of a plurality of polypropylene resins, the MFR of the mixture is preferably 6.0 g/10 min or more and 10 g/10 min or less, and 6.2 g/10 min. Above, it is more preferably 9.0 g/10 min or less, more preferably 6.3 g/10 min or more and 8.5 g/10 min or less, 6.4 g/10 min or more and 8.0 g/10 min. It is particularly preferable that it is less than or equal to 6.5 g/10 minutes, and most preferably 6.5 g/10 minutes or more and 7.5 g/10 minutes or less.
When the MFR of the polypropylene resin is 6.0 g/10 minutes or more, it is easy to obtain a biaxially oriented polypropylene film with low heat shrinkage. Moreover, when the MFR of the polypropylene resin is 10 g/10 minutes or less, it is easy to improve the film formability.
When the polypropylene resin used for the base material layer A is a mixture of a plurality of polypropylene resins, the MFR of each polypropylene resin is preferably 2.5 g/10 min or more and 30 g/10 min or less, and 3.5 g/10 min. minutes or more and 25 g/10 minutes or less, more preferably 4.5 g/10 minutes or more and 22 g/10 minutes or less, and particularly 5.5 g/10 minutes or more and 20 g/10 minutes or less. Preferably, it is 6.0 g/10 minutes or more and 20 g/10 minutes or less, most preferably.
In order to keep the MFR of the polypropylene resin within the above range, a method of controlling the average molecular weight and molecular weight distribution of the polypropylene resin is preferably adopted.

(Antistatic agent used for base material layer A)
The propylene resin composition constituting the substrate layer A may contain an antistatic agent such as a diethanolamine fatty acid ester compound, an amine compound, or a glycerin mono-fatty acid ester compound. By using these together in a specific ratio, the initial antistatic property is sufficient, the excellent antistatic property is maintained for a long period of time, and even when exposed to high temperatures, the initial transparency hardly deteriorates, and the composition is sticky. A biaxially oriented polypropylene film free of marks is obtained.
The antistatic agent contained in the substrate layer A can migrate to the film surface of the surface layer B by bleeding and exist there.

(Other additives used in base material layer A)
In addition to the antistatic agent, the polypropylene resin composition constituting the base material layer A contains various additives for quality improvement, such as productivity improvement, as long as it does not impair the effects of the present invention. For this reason, anti-blocking agents such as fine particles, lubricants such as waxes and metal soaps, plasticizers, processing aids, and known heat stabilizers, antioxidants, and UV absorbers that are usually added to polypropylene films are blended. It is also possible to

Inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, zeolite, etc., and the shape of these particles may be spherical, elliptical, conical, or irregular. , and its particle size can also be used and blended according to the application and method of use of the film.
As organic fine particles, crosslinked particles obtained by cross-linking acrylic resin, methyl acrylate resin, styrene-butadiene resin, etc. can be used, and the shape and size are the same as inorganic fine particles. Various can be used. Moreover, various surface treatments can be applied to the surfaces of these inorganic or organic fine particles, and these can be used alone or in combination of two or more.

[Surface layer B]
(Steric regularity of polypropylene resin constituting surface layer B)
The mesopentad fraction ([mmmm]%), which is an index of the stereoregularity of the polypropylene resin constituting the surface layer B, is 80.0% or more and 96.5% or less, and 85.0% or more and 96.5%. % or less, more preferably 90.0% or more and 96.5% or less.
When the polypropylene resin used for the surface layer B is a mixture of a plurality of polypropylene resins, the stereoregularity of the mixture is preferably within the same range as above.
When the polypropylene resin used for the surface layer B is a mixture of a plurality of polypropylene resins, the mesopentad fraction of each polypropylene resin is preferably 80.0% or more and 98.0% or less.
When the mesopentad fraction of the polypropylene resin constituting the surface layer B is 96.5% or less, the lamination strength of the laminate obtained by laminating the sealant film can be easily increased. Further, when the mesopentad fraction of the polypropylene resin constituting the surface layer B is 80.0% or more, the rigidity and heat resistance of the film can be easily obtained. The mesopentad fraction is measured by a nuclear magnetic resonance method (so-called NMR method).

(Polypropylene resin used for surface layer B)
As the polypropylene resin used for the surface layer B, a polypropylene homopolymer or a copolymer with ethylene and/or an α-olefin having 4 or more carbon atoms can be used. A propylene homopolymer substantially free of ethylene and/or an α-olefin having 4 or more carbon atoms is preferred, and even if it contains ethylene and/or an α-olefin component having 4 or more carbon atoms, ethylene and/or The upper limit of the amount of α-olefin components having 4 or more carbon atoms is preferably 1 mol% or less, more preferably 0.5 mol%, still more preferably 0.3 mol%, particularly preferably 0 .1 mol %, most preferably 0%. Within the above range, rigidity and heat resistance are likely to be improved. Examples of α-olefin components having 4 or more carbon atoms constituting such a copolymer include 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4 -methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene and the like. As the polypropylene resin, two or more different polypropylene homopolymers, copolymers with ethylene and/or α-olefins having 4 or more carbon atoms, and mixtures thereof can be used.

(Melting temperature of polypropylene resin used for surface layer B)
The lower limit of the melting temperature (Tm) (hereinafter abbreviated as TmB) measured by DSC of the polypropylene resin used for the surface layer B is preferably 152°C, more preferably 154°C, and even more preferably 156°C. and more preferably 158°C. When TmB is 154° C. or more, rigidity and heat resistance at high temperatures are easily obtained.
The upper limit of TmB is preferably 170°C, more preferably 169°C, even more preferably 168°C, even more preferably 167°C, and particularly preferably 166°C. When TmB is 170° C. or less, cost increase can be suppressed in terms of production of polypropylene resin, and breakage during film formation can be easily suppressed. In addition, lamination strength tends to increase. When the polypropylene resin used for the surface layer B is a mixture of a plurality of polypropylene resins, the TmB of the mixture is preferably within the same range as above.
About 5 mg of a sample was packed in an aluminum pan, set in a differential scanning calorimeter (DSC), heated to 230°C at a scanning rate of 10°C/min in a nitrogen atmosphere, and melted at 230°C for 5 minutes. , is the main peak temperature of the endothermic peak accompanying melting observed when the temperature is lowered to 30°C at a scanning rate of -10°C/min, held for 5 minutes, and then heated at a scanning rate of 10°C/min. When multiple peaks are observed, the peak temperature on the low temperature side is taken as Tm.

(Crystallization temperature of polypropylene resin used for surface layer B)
The lower limit of the crystallization temperature (Tc) measured by DSC of the polypropylene resin used for the surface layer B is 95°C, preferably 100°C, more preferably 105°C. When Tc is 95° C. or higher, crystallization is likely to proceed, and rigidity and heat resistance at high temperatures are likely to be obtained.
The upper limit of Tc is preferably 115°C, more preferably 113°C. When Tc is 115° C. or less, the crystal orientation of the surface layer B is suppressed, and the lamination strength tends to increase.
When the polypropylene resin used for the surface layer B is a mixture of a plurality of polypropylene resins, the Tc of the mixture is preferably within the same range as above.
Tc is about 5 mg of a sample packed in an aluminum pan, set in a DSC, heated to 230 ° C. at a scanning rate of 10 ° C./min under a nitrogen atmosphere, and melted at 230 ° C. for 5 minutes, scanning speed -10 ° C. This is the main peak temperature of the exothermic peak observed when the temperature is lowered to 30° C./min. When multiple peaks are observed, the peak temperature on the low temperature side is defined as Tc.

(Melt flow rate of polypropylene resin used for surface layer B)
The melt flow rate (MFR) of the polypropylene resin used for the surface layer B is 2.8 g/10 min or more, 5 0 g/10 min or less, more preferably 3.0 g/10 min or more and 5.0 g/10 min or less, and 3.0 g/10 min or more and 4.5 g/10 min or less and more preferably 3.0 g/10 minutes or more and 4.0 g/10 minutes or less.
When the polypropylene resin used for the surface layer B is a mixture of a plurality of polypropylene resins, the MFR of the polypropylene resin mixture is preferably 2.8 g/10 minutes or more and 5.0 g/10 minutes or less. It is more preferably 0 g/10 min or more and 5.0 g/10 min or less, more preferably 3.0 g/10 min or more and 5.0 g/10 min, and 3.0 g/10 min or more and 4.0 g. /10 minutes or less is even more preferable.
When the MFR of the polypropylene resin is 2.8 g/10 minutes or more, it is easy to obtain a biaxially oriented polypropylene film with low heat shrinkage. Further, when the MFR of the polypropylene resin is 5.0 g/10 min or less, the film formability tends to be improved, and defects are less likely to occur during film formation.
When the polypropylene resin used for the surface layer B is a mixture of a plurality of polypropylene resins, the MFR of each polypropylene resin is preferably 2.0 g/10 minutes or more and 5.0 g/10 minutes or less, and 2.2 g/10 minutes or more and 5.0 g/10 minutes or less. It is more preferably 10 minutes or more and 5.0 g/10 minutes or less, and even more preferably 2.3 g/10 minutes or more and 4.5 g/10 minutes or less.
The MFR of the polypropylene resin used for the surface layer B is preferably close to the MFR of the polypropylene resin used for the base layer A from the viewpoint of the uniformity of the thickness of the laminated film.

(Additives used in surface layer B)
The polypropylene resin composition constituting the surface layer B contains various additives for improving quality such as slipperiness and antistatic properties, as long as the effects of the present invention are not impaired, for example, for improving productivity. Anti-blocking agents such as fine particles, lubricants such as waxes and metal soaps, plasticizers, processing aids, and known heat stabilizers, antioxidants, UV absorbers, inorganic and organic substances that are usually added to polypropylene films. It is also possible to mix fine particles and the like.

Inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, zeolite, etc., and the shape of these particles may be spherical, elliptical, conical, or irregular. , and its particle size can also be used and blended according to the application and method of use of the film.
As organic fine particles, crosslinked particles such as acryl, methyl acrylate, styrene-butadiene, etc. can be used, and in terms of shape and size, various particles can be used like inorganic fine particles. It is possible. Moreover, various surface treatments can be applied to the surfaces of these inorganic or organic fine particles, and these can be used alone or in combination of two or more.

(Anti-fog agent used for base layer A and surface layer B)
In the biaxially oriented laminated polypropylene film of the present invention, an antifogging agent such as fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, ethylene oxide adducts of higher fatty acid amines and amides is added to the film. By adding the content in the range of 0.2 to 5% by mass, it is possible to make it suitable for packaging vegetables, fruits, flowers, etc. that require freshness retention. The anti-fogging agent can be added to both the substrate layer A and the surface layer B. The antifogging agent contained in the substrate layer A migrates to the film surface of the surface layer B by bleeding and can exhibit antifogging properties.

[Thickness configuration of base layer A and surface layer B]
The total layer thickness of the biaxially oriented laminated polypropylene film of the present invention varies depending on its application and usage method, but from the viewpoint of film strength and resource saving, the lower limit is preferably 5 μm, more preferably 6 μm, further preferably 8 μm, and 10 μm. is particularly preferred. The upper limit is preferably 60 μm, more preferably 40 μm, still more preferably 35 μm, particularly preferably 25 μm, most preferably 19 μm. If the total layer thickness of the film is within this range, it is possible to contribute to resource saving by making the film thinner while ensuring strength. Depending on the application, the total layer thickness of the film may be preferably larger than 60 μm, and generally a film having a total layer thickness of up to 200 μm can be used.

Although the lower limit of the thickness of the base layer A varies depending on its application and usage, it is preferably 5 μm in terms of film rigidity and water vapor barrier properties. The upper limit of the thickness of the substrate layer A is preferably 50 μm, more preferably 35 μm, still more preferably 20 μm or less, and particularly preferably 18 μm, from the viewpoint of transparency and environmental impact. The thickness of the base material layer A may be preferably more than 50 μm depending on the application, and generally up to 200 μm can be used.

The lower limit of the thickness of the surface layer B varies depending on its application and method of use, but is preferably 0.3 μm, more preferably 0.5 μm, and even more preferably 0.8 μm or more from the viewpoint of film lamination strength and antistatic properties. .
The upper limit of the thickness of the surface layer B is preferably 4 μm, more preferably 2 μm, from the viewpoint of the rigidity of the film and heat resistance at high temperatures, although it varies depending on the application and the method of use. Also, if the thickness of the surface layer B is large, it is easy to reduce the plane orientation coefficient.

The lower limit of the ratio of the thickness of the base layer A to the thickness of the entire film is 70%, more preferably 75%, even more preferably 80%, and particularly preferably 85% from the viewpoint of rigidity and heat resistance at high temperatures. .
The upper limit of the ratio of the thickness of the substrate layer A to the thickness of the entire film is preferably 98% or less, more preferably 95% or less, and even more preferably 92% or less in order to maintain the function of the surface layer B.

The lower limit of the ratio of the thickness of the surface layer B to the thickness of the entire film is preferably 2%, more preferably 3%, still more preferably 5%, and more preferably 8% or more from the viewpoint of the laminate strength and antistatic property of the film. .
The upper limit of the ratio of the thickness of the base layer B to the thickness of the entire film is preferably 30% or less, more preferably 23% or less, still more preferably 20% or less, and 15% or less from the viewpoint of rigidity and heat resistance at high temperatures. Especially preferred.

(Layer structure)
The layer structure of the biaxially oriented laminated polyolefin film of the present invention includes surface layer B/base layer A and surface layer B/base layer A/surface layer B. Although it is preferable that the base layer A and the surface layer B are in direct contact with each other, an intermediate layer may be provided between the base layer A and the surface layer B. In order to prevent separation between the layers of the surface layer B, it is preferable to use a raw material composition that is intermediate between the substrate layer and the surface layer.

[Method for forming biaxially oriented laminated polypropylene film]
The biaxially oriented laminated polypropylene film of the present invention is obtained by preparing an unstretched sheet made of the polypropylene resin composition containing the above polypropylene resin as a main component, and biaxially stretching the sheet. As the method of biaxial stretching, any of inflation simultaneous biaxial stretching method, tenter simultaneous biaxial stretching method, and tenter sequential biaxial stretching method may be adopted. It is preferable to employ a sequential biaxial stretching method. In particular, it is preferable to stretch in the width direction after stretching in the longitudinal direction, but a method of stretching in the longitudinal direction after stretching in the width direction may also be used.

Next, the method for producing the biaxially oriented laminated polypropylene film of the present invention will be described, but the method is not necessarily limited to this.
An example of surface layer B/substrate layer A/surface layer B will be described below in the case of adopting the tenter sequential biaxial stretching method.
First, a multi-sheet of a molten polypropylene resin composition composed of surface layer B/substrate layer A/surface layer B is extruded from a T-die.
As a method thereof, for example, a method of co-extrusion while laminating polypropylene resins fed from different flow paths using two or more extruders into multiple layers using a multilayer feed block, a static mixer, a multilayer multi-manifold die, etc. etc. can be used.
It is also possible to use only one extruder and introduce the multi-layering device described above into the melt line from the extruder to the T-die.
In addition, from the viewpoint of stabilizing the back pressure and suppressing thickness fluctuations, a method of installing a gear pump in the polymer flow path is preferable.
The molten sheet co-extruded from the T-die into a sheet shape is grounded on a metal cooling roll and solidified by cooling. For the purpose of promoting the solidification, it is preferable to further cool the sheet cooled by the chill roll by immersing it in a water tank or the like.

Then, the sheet is stretched in the longitudinal direction by two pairs of heated stretching rolls by increasing the rotational speed of the rear stretching rolls to obtain a uniaxially stretched film.
Subsequently, after preheating the uniaxially stretched film, it is stretched in the width direction at a specific temperature while gripping the ends of the film with a tenter type stretching machine to obtain a biaxially stretched film.
After the width direction stretching step is completed, the biaxially stretched film is heat-treated at a specific temperature. In the heat treatment step, the film may be relaxed in the width direction.
The biaxially oriented polypropylene film thus obtained may be subjected, for example, to corona discharge treatment on at least one side, if necessary, and then wound up with a winder to obtain a film roll.

Each step will be described in more detail below.
(Extrusion process)
First, a polypropylene resin composition containing polypropylene resin as a main component is heated and melted in a range of 200 ° C. or higher and 300 ° C. or lower with a single-screw or twin-screw extruder, and a sheet-like molten polypropylene resin composition coming out of the T die. is brought into contact with a metal cooling roll to cool and solidify. The obtained unstretched sheet is preferably put into a water tank.
The temperature of the cooling roll or the temperature of the cooling roll and the water bath is preferably a temperature that can suppress crystallization, and if it is desired to increase the transparency of the film, it is preferable to cool and solidify with a cooling roll of 50° C. or less. When the cooling temperature is 50°C or lower, the transparency of the unstretched sheet tends to increase, and the cooling temperature is preferably 40°C or lower. It is also preferable to set the cooling temperature to 30° C. or higher in order to increase the degree of crystal orientation after successive biaxial stretching.
The thickness of the unstretched sheet is preferably 3500 μm or less in terms of cooling efficiency, more preferably 3000 μm or less, and can be appropriately adjusted according to the thickness of the film after successive biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition, the lip width of the T-die, and the like.

(Longitudinal stretching process)
The lower limit of the draw ratio in the longitudinal direction is preferably 3 times, more preferably 3.5 times, and particularly preferably 3.8 times. Within the above range, it is easy to increase the strength, and thickness unevenness is reduced.
The upper limit of the draw ratio in the longitudinal direction is preferably 4.3 times, more preferably 4.2 times, and particularly preferably 4.1 times. Within the above range, the stretchability in the width direction stretching step is good, and the productivity is improved.

In the present invention, by using a polypropylene resin with high stereoregularity as a raw material and lowering the draw ratio in the longitudinal direction and suppressing the degree of orientation in the longitudinal direction, it is possible to form a film that has both heat resistance and film-forming properties. Become.

The reason for this is presumed as follows. By lowering the stretching ratio in the longitudinal direction, the degree of orientation of the polypropylene molecular chains in the longitudinally stretched film is suppressed, making it difficult to suppress the mobility of the polypropylene molecular chains. A biaxially oriented laminated polypropylene film having a structure with a high degree of crystallinity is finally obtained by stretching at a high magnification and further performing heat treatment at a high temperature for a sufficient time in the next heat treatment step. . As a result, a biaxially oriented laminated polypropylene film having a high Young's modulus and stress at 5% elongation, particularly high stress at 5% elongation, can be obtained.
Conventionally, if one of heat resistance (heat shrinkability) and rigidity is improved, the other tends to be lowered, but the present invention can achieve both.

The lower limit of the stretching temperature in the longitudinal direction is preferably TmA-40°C, more preferably TmA-37°C, still more preferably TmA- 35°C. Within the above range, the heat shrinkage rate can be easily reduced, the subsequent width direction stretching can be easily performed, and thickness unevenness can be reduced. The upper limit of the longitudinal stretching temperature is preferably Tm-7°C, more preferably TmA-10°C, still more preferably TmA-12°C. Within the above range, it is less likely that the resin will be fused to the stretching rolls to make stretching difficult, or that the film quality will be reduced due to increased surface roughness.
The longitudinal stretching may be carried out in two or more stages using three or more pairs of stretching rolls.

(Preheating process for width direction stretching)
Before the width direction stretching step, it is necessary to heat the uniaxially stretched film after longitudinal stretching in the range of TmA+5° C. or more and TmA+20° C. or less to soften the polypropylene resin composition. By making it TmA or more, the softening of the uniaxially stretched film progresses and the stretching in the width direction becomes easy. By adjusting the temperature to be Tm+20° C. or lower, orientation during stretching in the width direction proceeds, and rigidity is easily exhibited. More preferably, it is TmA+8°C or higher and TmA+15°C or lower. Here, the maximum temperature in the preheating step is defined as the preheating temperature.

(Width direction stretching process)
In the widthwise stretching step, it is preferable to stretch at a temperature of TmA-8°C or higher and a preheating temperature or lower. At this time, the stretching in the width direction may be started when the preheating temperature is reached, or when the temperature is lowered after reaching the preheating temperature to reach a temperature lower than the preheating temperature.
The lower limit of the temperature in the width direction stretching step is more preferably TmA-5°C. When the width direction stretching temperature is within this range, the heat shrinkage of the resulting biaxially oriented film is likely to be reduced.
The upper limit of the temperature in the width direction stretching step is preferably TmA+10°C, more preferably TmA+7°C, and particularly preferably TmA+5°C. Stretching unevenness is less likely to occur when the width direction stretching temperature is within this range.

The lower limit of the final width direction draw ratio in the width direction stretching step is preferably 9 times, more preferably 9.5 times, and still more preferably 10 times. When it is 9 times or more, the rigidity tends to be increased, and thickness unevenness tends to be reduced. The upper limit of the width direction draw ratio is preferably 20 times, more preferably 15 times, and still more preferably 11 times. When it is 20 times or less, the heat shrinkage rate is easily reduced, and the film is less likely to break during stretching.

(Heat treatment process)
The biaxially stretched film is heat treated. The lower limit of the heat treatment temperature is preferably TmA+8°C, particularly preferably TmA+10°C. When the temperature is TmA+5° C. or higher, the orientation of the amorphous portion is easily relaxed, the heat shrinkage rate is easily reduced, and the laminate strength is easily increased.
The upper limit of the heat treatment temperature is preferably TmA+20°C, more preferably TmA+15°C, and particularly preferably TmA+12°C. By setting the temperature at TmA+20° C. or lower, the highly oriented crystals generated in the biaxial stretching process are less likely to melt, and the rigidity of the obtained film can be easily improved. In addition, the roughness of the film surface does not become too large, and the film is less likely to whiten.
Moreover, in order to further reduce the thermal shrinkage, the film can be relaxed (relaxed) in the width direction during the heat treatment. The upper limit of the relaxation rate is 15%, preferably 10%, and still more preferably 8%. When the above is exceeded, thickness unevenness may become large. The lower limit of the relaxation rate is preferably 0%, more preferably 2%, and the relaxation in the width direction tends to reduce the thermal shrinkage rate.

The film surface of the surface layer B of the obtained biaxially oriented laminated polypropylene film is preferably subjected to corona treatment. The watt density at this time is preferably 11 W/m ² ·min, more preferably 12 W/m ² ·min, still more preferably 13 W/m ² ·min.

[Film characteristics]
The biaxially oriented laminated polypropylene film of the present invention is characterized by the following properties.
The "longitudinal direction" in the biaxially oriented laminated polypropylene film of the present invention is the direction corresponding to the flow direction in the film manufacturing process, and the "width direction" is perpendicular to the flow direction in the film manufacturing process. is the direction. Hereinafter, "longitudinal direction" may be abbreviated as "MD direction" and "width direction" as "TD direction".

(plane orientation factor)
The upper limit of the plane orientation coefficient (ΔP) measured from the surface layer B side of the biaxially oriented laminated polypropylene film of the present invention is preferably 0.0134, more preferably 0.0132. If it is 0.0134 or less, the laminate strength can be increased. Also, the thermal shrinkage rate at high temperatures can be reduced. The lower limit of the plane orientation coefficient (ΔP) is preferably 0.0112, more preferably 0.0116, still more preferably 0.0120, still more preferably 0.0122, and particularly preferably 0 0.0124 and most preferably 0.0126. If it is 0.0122 or more, the thickness unevenness of the film tends to be improved.
The plane orientation coefficient (ΔP) can be set within a range by adjusting the draw ratio, relaxation rate, and temperature conditions during film formation. In particular, it is important to set the mesopentad fraction of the polypropylene resin constituting the surface layer B to 96.5% or less, and it is preferable to set the heat treatment temperature after biaxial stretching to TmA+8° C. or higher.
The plane orientation coefficient (ΔP) was calculated using the formula [(Nx+Ny)/2]-Nz.

(150°C heat shrinkage rate)
The upper limit of the thermal shrinkage in the longitudinal direction at 150°C of the biaxially oriented laminated polypropylene film of the present invention is 6.0%, preferably 5.0%, more preferably 4.8%, especially Preferably, it is 4.6% or less.
The upper limit of the heat shrinkage rate in the width direction at 150°C is 5.0%, preferably 4.5%, more preferably 4.0%, still more preferably 3.5%, and more More preferably 3.0%, particularly preferably 2.7%, most preferably 2.1%, most preferably 1.7%.
If the heat shrinkage rate at 150° C. is 6.0% or less in the longitudinal direction and 5.0% or less in the width direction, wrinkles are less likely to occur in the sealed portion during heat sealing.

(stress at 5% elongation)
The lower limit of the stress at 5% elongation in the longitudinal direction of the biaxially oriented laminated polypropylene film of the present invention (F5, hereinafter, the stress at 5% elongation is abbreviated as F5) is preferably 35 MPa, more preferably 36 MPa. Yes, more preferably 38 MPa, even more preferably 40 MPa, and particularly preferably 42 MPa. At 35 MPa or more, the rigidity is high, so that the shape of the packaging bag can be easily maintained, and deformation of the film during processing such as printing does not easily occur, so printing pitch deviation does not easily occur when printing ink is transferred.
The upper limit of F5 in the longitudinal direction of the film is preferably 70 MPa, more preferably 65 MPa, still more preferably 62 MPa, particularly preferably 61 MPa, most preferably 60 MPa. Realistic production is easy at 70 MPa or less.
The lower limit of F5 in the width direction of the biaxially oriented laminated polypropylene film of the present invention is preferably 95 MPa, more preferably 100 MPa, even more preferably 105 MPa, and even more preferably 110 MPa. When the film is 95 MPa or higher, the rigidity is high, so that the shape of the packaging bag can be easily maintained, and deformation of the film during processing such as printing is difficult to occur, so printing pitch deviation is less likely to occur when printing ink is transferred.
The upper limit of F5 in the width direction is preferably 200 MPa, more preferably 190 MPa, even more preferably 180 MPa. If it is 200 MPa or less, realistic production is easy. In addition, the balance of physical properties in the longitudinal direction and width direction of the film tends to be improved.
F5 can be set within a range by adjusting the draw ratio, relaxation rate, and temperature conditions during film formation.

(Young's modulus)
The lower limit of Young's modulus in the longitudinal direction of the biaxially oriented laminated polypropylene film of the present invention is preferably 1.6 GPa, more preferably 1.7 GPa, even more preferably 1.8 GPa, and particularly preferably 1.9 GPa. and most preferably 2.0 GPa.
At 1.6 GPa or more, the rigidity is high, so that the shape of the packaging bag can be easily maintained, and deformation of the film during processing such as printing is unlikely to occur, so printing pitch deviation is unlikely to occur when printing ink is transferred.
The upper limit of the Young's modulus in the longitudinal direction of the film is preferably 3.0 GPa, more preferably 2.9 GPa, still more preferably 2.8 GPa, particularly preferably 2.7 GPa, most preferably 2 .6 GPa. Realistic production is easy at 3.0 GPa or less.
The lower limit of the Young's modulus in the width direction of the biaxially oriented laminated polypropylene film of the present invention is preferably 3.5 GPa, more preferably 3.6 GPa, still more preferably 3.7 GPa, and particularly preferably 3.8 GPa. is. At 3.6 GPa or more, the rigidity of the film is high, so that the shape of the bag can be easily maintained.
The upper limit of Young's modulus in the width direction is preferably 5.0 GPa, more preferably 4.9 GPa, even more preferably 4.8 GPa, and even more preferably 4.5 MPa or less. If it is 5.0 GPa or less, realistic production is easy. In addition, the balance of physical properties in the longitudinal direction and width direction of the film tends to be improved.
The Young's modulus can be set within a range by adjusting the draw ratio, relaxation rate, and temperature conditions during film formation.

(Tensile breaking strength)
The lower limit of the tensile breaking strength in the longitudinal direction of the biaxially oriented laminated polypropylene film of the present invention is preferably 90 MPa, more preferably 95 MPa, even more preferably 100 MPa, still more preferably 110 MPa. When it is 90 MPa or more, the durability of the packaging bag tends to be excellent. A higher tensile strength at break in the longitudinal direction is preferable in terms of durability, but the upper limit is 300 MPa as a realistic value for manufacturing.
The lower limit of the tensile breaking strength in the width direction of the biaxially oriented laminated polypropylene film of the present invention is preferably 240 MPa, more preferably 260 MPa, still more preferably 280 MPa, still more preferably 300 MPa, and particularly preferably. is 340 MPa. When it is 240 MPa or more, the durability of the packaging bag tends to be excellent. A higher tensile strength at break in the width direction is preferable in terms of durability, but the upper limit is 500 MPa as a realistic value for manufacturing.
The tensile strength at break can be set within a range by adjusting the draw ratio, relaxation rate, and temperature conditions during film formation.

(Tensile breaking elongation)
The lower limit of the tensile elongation at break in the longitudinal direction of the biaxially oriented laminated polypropylene film of the present invention is preferably 200%, more preferably 220%, even more preferably 240%, and even more preferably 250%. or more, particularly preferably 280% or more, and most preferably 300% or more. If it is 200% or more, the breakage of the film and the breakage of the packaging bag tend to decrease. As a practical value, the upper limit of the tensile elongation at break in the longitudinal direction is preferably 350%, more preferably 340%.
The lower limit of the tensile elongation at break in the width direction of the biaxially oriented laminated polypropylene film of the present invention is preferably 25%, more preferably 30%, still more preferably 35%, and even more preferably 40%. and particularly preferably 50%. If it is 25% or more, breakage of the film and breakage of the packaging bag tend to be reduced. As a practical value, the upper limit of the tensile elongation at break in the width direction is preferably 70%, more preferably 65%, and even more preferably 60%.
The tensile elongation at break can be set within a range by adjusting the draw ratio, relaxation rate, and temperature conditions during film formation.

(Haze)
The upper limit of the haze of the biaxially oriented laminated polypropylene film of the present invention is preferably 5.0%, more preferably 4.5%, even more preferably 4.0%, and particularly preferably 3.5%. and most preferably 3.0%. When it is 5.0% or less, it is easy to use in applications where transparency is required. As a realistic value, the lower limit of haze is preferably 0.1%, more preferably 0.2%, still more preferably 0.3%, and particularly preferably 0.4%. It is easy to manufacture as it is 0.1% or more.
The haze can be kept within the range by adjusting the temperature conditions during film formation, such as the temperature of the cooling roll (CR).

(wetting tension)
The wetting tension of the film surface of the surface layer B of the biaxially oriented laminated polypropylene film of the present invention is preferably 38 mN/m or more, more preferably 39 mN/m or more, and even more preferably 40 mN/m or more. When the wet tension is 38 mN/m or more, the adhesion with the printing ink or the adhesive used for lamination with other member films is improved.
In order to obtain a wetting tension of 38 mN/m or more, it is preferable to perform a physicochemical surface treatment such as corona treatment or flame treatment. For example, in the corona treatment, it is preferable to heat the film using a preheating roll and a treatment roll, and discharge the film in the air. The wetting tension is related to the strength of the corona treatment, and since the wetting tension is also related to the amount of bleeding out of the antistatic agent, it is effective to set each of them within a suitable range.

[Practical properties of film]
Practical properties of the biaxially oriented laminated polypropylene film of the present invention will be described.
(film processing)
The biaxially oriented laminated polypropylene film of the present invention can be printed by letterpress printing, planographic printing, intaglio printing, stencil printing, or transfer printing, depending on the application.
In addition, heat sealability is imparted by laminating unstretched sheets, uniaxially oriented films, and biaxially oriented films made of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, and polyester as sealant films. It can also be used as a laminated body. If you want to further improve gas barrier properties and heat resistance, use unstretched sheets, uniaxially stretched films, and biaxially stretched films made of aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, or polyvinyl alcohol as biaxially oriented polypropylene films. and the sealant film as an intermediate layer. An adhesive applied by a dry lamination method or a hot melt lamination method can be used for bonding the sealant film.
In order to improve the gas barrier property, the biaxially oriented polypropylene film, the intermediate layer film, or the sealant film can be vapor-deposited with aluminum or inorganic oxide. Vacuum vapor deposition, sputtering, and ion plating can be used as vapor deposition methods, but vacuum vapor deposition of silica, alumina, or a mixture thereof is particularly preferred.

(Laminate strength)
The lower limit of the laminate strength in the longitudinal direction and width direction of the laminate of the biaxially oriented laminated polypropylene film and the sealant film of the present invention is preferably 1.9 N/15 mm, more preferably 2.1 N/15 mm, and even more preferably. is 2.3 N/15 mm, even more preferably 2.4 N/15 mm, particularly preferably 2.5 N/15 mm, most preferably 2.6 N/15 mm, most preferably 2.8 N /15 mm or more. When it is 1.9 N/15 mm or more, the breakage of the packaging bag tends to decrease. As a practical value, the upper limit of the laminate strength in the longitudinal direction is preferably 4.0 N/15 mm, more preferably 3.5 N/15 mm.
In addition, the lamination strength here is a laminate film (laminate ) is the peel strength when T-shaped peeling is performed between the base material layer and the sealant layer.
Laminate strength is determined by adjusting the mesopentad fraction of the polypropylene resin that constitutes the surface layer B to 96.5% or less, adjusting the draw ratio, relaxation rate, and temperature conditions during film formation to increase the plane orientation coefficient (ΔP). It can be increased by setting it to 0.0134 or less.

(Appearance of heat seal part)
In order to form a bag for packaging food, there is a method of filling a pre-made bag with contents, heating and melting the film, and fusing and sealing the films. There is a way to seal it. Usually, a base film is laminated with a sealant film made of polyethylene, polypropylene, or the like, and the sealant film surfaces are fused together. As for the heating method, pressure is applied from the base film side with a heating plate to press and seal the film, and the sealing width is often about 10 mm. Since the base film is also heated at this time, the shrinkage at that time generates wrinkles. For the durability of the bag, the less wrinkles the better, and the less wrinkles the better to increase the willingness to buy. Although the sealing temperature may be about 120° C., a higher sealing temperature is required in order to increase the speed of the bag-making process, and even in that case the shrinkage is preferably small. When the zipper is to be fused to the opening of the bag, sealing at a higher temperature is required.
In order to maintain a good appearance of the heat-sealed portion when heat-sealed at high temperatures, it is important that the film has excellent dimensional stability at high temperatures and high film rigidity at high temperatures.

(Print pitch deviation)
As for the structure of the packaging film, as a basic structure, it is often composed of a laminated film of a printed base film and a sealant film. The print pitch deviation is considered to occur because tension and heat are applied to the film during the printing process, and the base material of the film expands and contracts. Eliminating defective products due to printing pitch deviation is important in terms of effective use of resources, and is also important in increasing purchasing motivation.
In order to reduce printing pitch deviation, it is important to have high film rigidity at high temperature and excellent film dimensional stability at high temperature.

The present invention will be described in detail below with reference to examples. The properties were measured and evaluated by the following methods.
(1) Melt flow rate Melt flow rate (MFR) was measured according to JISK7210 at a temperature of 230°C and a load of 2.16 kgf.

(2) Mesopentad Fraction The mesopentad fraction ([mmmm]%) of the polypropylene resin was measured using ¹³ C-NMR. The mesopentad fraction was calculated according to the method described in Zambelli et al., Macromolecules, 6:925 (1973). 13C-NMR measurement was carried out at 110°C by dissolving 200 mg of a sample in a 8:2 mixture of o-dichlorobenzene and deuterated benzene at 135°C using AVANCE500 manufactured by BRUKER.

(3) Crystallization temperature (Tc), melting temperature (Tm)
Thermal measurements were performed under a nitrogen atmosphere using a PerkinElmer DSC8500 Differential Scanning Calorimeter. About 5 mg was cut out from the polypropylene resin pellet and enclosed in an aluminum pan for measurement. After the temperature was raised to 230° C. and held for 5 minutes, it was cooled to 30° C. at a rate of −10° C./min, and the exothermic peak temperature was defined as the crystallization temperature (Tc). The temperature was maintained at 30° C. for 5 minutes, and the temperature was raised to 230° C. at 10° C./min, and the main endothermic peak temperature was defined as the melting temperature (Tm).

(4) Film thickness The thickness of the film was measured using a Seiko EM Millitron 1202D.
The thicknesses of the base layer A and the surface layer B were calculated based on the ratio of the discharge amount of the base layer A and the discharge amount of the surface layer B from the total thickness of the laminated polypropylene film measured by the above method.

(5) Haze Measured according to JISK7105 at 23° C. using NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd.

(6) Tensile test Based on JISK7127, the tensile strength of the film in the longitudinal direction and the width direction was measured at 23°C. The sample was cut into a size of 15 mm×200 mm, the chuck width was 100 mm, and the sample was set in a tensile tester (Instron 5965 dual-column desktop tester manufactured by Instron Japan Company Limited). A tensile test was performed at a tensile speed of 200 mm/min. From the obtained strain-stress curve, the stress at 5% elongation was defined as F5.
Also, the Young's modulus was obtained from the slope of the linear portion at the initial stage of elongation. The tensile strength at break and the tensile elongation at break were the strength and elongation at the time when the sample broke, respectively.

(7) Thermal shrinkage rate It was measured by the following method based on JISZ1712. The film was cut into pieces of 20 mm width and 200 mm length in the longitudinal direction and the width direction of the film, and hung in a hot air oven at 150° C. for 5 minutes. The length after heating was measured, and the thermal shrinkage rate was determined as the ratio of the shrinkage length to the original length.

(8) Refractive Index and Plane Orientation Coefficient Measured from the surface layer B side of the film at a wavelength of 589.3 nm and a temperature of 23° C. using an Atago Abbe refractometer. Nx and Ny are the refractive indices along the longitudinal direction and the width direction, respectively, and Nz is the refractive index in the thickness direction. The plane orientation coefficient was calculated using the formula [(Nx+Ny)/2]-Nz.
When the surface layer B is present on both sides, the average value of the respective plane orientation coefficients was calculated and used as the plane orientation coefficient.

(9) Wetting Tension According to JIS K6768-1999, the film was aged at 23° C. and 50% relative humidity for 24 hours, and the corona-treated surface of the film was measured according to the following procedure.
1) Measurement is performed in a standard laboratory atmosphere (see JIS K7100) at a temperature of 23°C and a relative humidity of 50%.
2) Place the test piece on the substrate of the hand coater, drop a few drops of the test mixture on the test piece, and immediately pull the wire bar to spread the test mixture evenly. If using a cotton swab or brush to spread the test mixture, spread the liquid quickly over an area of at least 6 cm ² .
The amount of liquid should be such that it forms a thin layer without pooling. The wetting tension is determined by observing the liquid film of the mixed liquid for testing in a bright place and observing the state of the liquid film after 3 seconds. If the liquid film does not break and the state of application is maintained for 3 seconds or longer, it is determined to be wet. If the wetness is maintained for 3 seconds or longer, the next higher surface tension mixture is selected. Conversely, if the liquid film breaks in 3 seconds or less, the next lower surface tension mixture is selected. Repeat this operation and choose a mixture that can wet the surface of the test piece exactly for 3 seconds.
3) Wire bars are cleaned with methanol and dried between uses.
4) The operation of selecting a mixture that can wet the surface of the test piece for 3 seconds is performed at least 3 times. The surface tension of the liquid mixture thus selected is taken as the wetting tension of the film.

(10) Laminate Strength of Laminate Film (Laminate) Laminate strength was measured by the following procedure.
1) Production of laminated film with sealant film A continuous dry laminator was used as follows. First, the corona-treated surface of the surface layer B of the obtained biaxially oriented laminated polypropylene film was gravure-coated with an adhesive so that the dry coating amount was 3.0 g/m ² . Dried in 5 seconds. Subsequently, it was laminated with a sealant film between rolls provided downstream (roll pressure: 0.2 MPa, roll temperature: 60°C). The obtained laminated film was subjected to aging treatment at 40° C. for 3 days in a wound state.
The adhesive was obtained by mixing 28.9% by mass of a main agent (TM569, manufactured by Toyo-Morton Co., Ltd.), 4.00% by mass of a curing agent (CAT10L, manufactured by Toyo-Morton Co., Ltd.), and 67.1% by mass of ethyl acetate. A dry laminate adhesive was used, and a non-stretched polypropylene film (Pylen (registered trademark) CT P1128, thickness 30 μm) manufactured by Toyobo Co., Ltd. was used as the sealant film.
2) Measurement of lamination strength of laminate film (laminate) The laminate film (laminate) obtained above is a biaxially oriented polypropylene film having long sides in the longitudinal direction and the width direction. 15 mm) and peeled 90° (T-shaped) at a tensile speed of 200 mm / min in an environment of 23 ° C. using a tensile tester (Instron 5965, a dual column desktop tester manufactured by Instron Japan Company Limited). The peel strength (N/15 mm) at the time was measured. The measurement was performed three times each in the longitudinal direction and the width direction, and the average value was taken as the laminate strength in the longitudinal direction and the width direction.

(11) Appearance evaluation of heat-sealed portion The seal strength of the laminate film (laminate) was measured according to JIS Z1707 by the following method, and the appearance of the sealed portion when heat-sealed at the reached heat-sealing temperature was evaluated.
The sealant films of the laminate film (laminate) are heat-sealed with a heat sealer. At this time, the sealing pressure was 10 N/cm ² , the sealing time was 1 second, and the temperature was 100°C to 250°C.
The heat-sealed laminate film (laminate) was cut into a size of 15 mm in width and 200 mm in length, and the initial distance between chucks was 100 mm. , and the T-peel strength was measured at a tensile speed of 200 mm/min. A graph was drawn with the temperature on the horizontal axis and the heat sealing strength on the vertical axis. The appearance of the sealed portion when heat-sealed at the reached heat-sealing temperature was evaluated in the following two stages from the degree of peeling and wrinkling of the base material layer.
Good: No peeling or wrinkling of the film.
x: Peeling and/or wrinkling of the film occurred.

(Example 1)
[Base layer A]
Propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., FLX80E4) having MFR = 7.5 g/10 min, [mmmm] = 98.9%, Tc = 116°C, and Tm = 163°C as the polypropylene resin and 80 parts by mass of propylene homopolymer PP-2 (manufactured by Sumitomo Chemical Co., Ltd., FS2012) was blended with 20 parts by mass.
To 100 parts by mass of a mixture of these propylene homopolymers, 1.4 parts by mass of a mixture of stearyldiethanolamine monostearate, stearyldiethanolamine distearate, and stearyldiethanolamine (manufactured by Matsumoto Yushi Co., Ltd., KYM-4K) was blended and mixed. , using an extruder with a pelletizer, melted, kneaded and granulated to obtain pellets of the polypropylene composition to obtain a polypropylene resin composition for the substrate layer A. This polypropylene resin composition had a mesopentad fraction of 98.8%, a TmA of 163° C., and an MFR of 6.5 g/10 minutes.
[Surface layer B]
Propylene homopolymer PP-3 (manufactured by Prime Polymer Co., Ltd., F- 300SP) and 58 parts by mass of propylene homopolymer PP-4 (Japan Polypropylene Corporation) having MFR = 4.2 g / 10 minutes, [mmmm] = 97.3%, Tc = 112 ° C., Tm = 165 ° C. A blend of 42 parts by mass of FL4) was melt-kneaded and granulated using an extruder with a pelletizer to obtain pellets of the polypropylene composition, which was used as the polypropylene resin composition for the surface layer B. This polypropylene resin composition had a mesopentad fraction of 95.3%, a TmB of 161° C., and an MFR of 3.5 g/10 minutes. First, using a multi-layer feed block, the polypropylene resin composition constituting each of the base material layer A and the surface layer B is heated and melted at 250 ° C. with an extruder, and the molten polypropylene resin composition is transferred from a T-die at 250 ° C. to the surface layer. It was co-extruded into a sheet while laminating in a configuration of B/base layer A/surface layer B.
The melted sheet was brought into contact with a cooling roll at 37°C and then put into a water bath at 29°C to obtain an unstretched sheet. After that, the unstretched sheet was stretched 4.0 times in the longitudinal direction with two pairs of rolls at 140°C, then clipped at both ends, led into a hot air oven, preheated at 174°C, and then stretched to 160°C in the width direction. and then heat-treated at 175° C. in the width direction while being relaxed by 7%.
One side surface of the obtained biaxially oriented polypropylene film was subjected to corona treatment using a corona treatment machine manufactured by Kasuga Denki Co., Ltd. under the conditions of 13 W / m ² · min, and then wound up with a winder to form two films having a thickness of 17 μm. An axially oriented polypropylene film was obtained. The thickness composition of the film was surface layer B/base layer A/surface layer B=1/15/1 μm.
Table 1 shows the properties of the polypropylene resin raw materials used, Table 2 shows the raw material compositions and film-forming conditions for each layer, and Table 3 shows the film properties. As shown in Table 3, no peeling or wrinkling of the laminated film from the unstretched polypropylene film occurred during heat sealing, the rigidity was high, and the lamination strength was excellent.

(Example 2)
As shown in Table 2, a film having a thickness of 19 μm was obtained in the same manner as in Example 1 except that the thickness composition and the relaxation rate during heat treatment were changed. The thickness structure was surface layer B/base layer A/surface layer B=1/17/1 μm. As shown in Table 3, no peeling or wrinkling of the laminated film from the unstretched polypropylene film occurred during heat sealing, the rigidity was high, and the lamination strength was excellent.

(Example 3)
As shown in Table 2, a film having a thickness of 19 μm was obtained in the same manner as in Example 2, except that the preheating temperature, width direction stretching temperature, and heat treatment temperature were changed. The thickness structure was surface layer B/base layer A/surface layer B=1/17/1 μm. As shown in Table 3, no peeling or wrinkling of the laminated film from the unstretched polypropylene film occurred during heat sealing, the rigidity was high, and the lamination strength was excellent.

(Example 4)
As shown in Table 2, a film having a thickness of 16 μm was obtained in the same manner as in Example 3 except that the thickness composition and preheating temperature were changed. The thickness structure was surface layer B/base layer A/surface layer B=1/14/1 μm. As shown in Table 3, no peeling or wrinkling of the laminated film from the unstretched polypropylene film occurred during heat sealing, the rigidity was high, and the lamination strength was excellent.

(Example 5)
As shown in Table 2, a film having a thickness of 17 μm was obtained in the same manner as in Example 4 except that the thickness composition and heat treatment temperature were changed. The thickness composition was surface layer B/base layer A/surface layer B=1/15/1 μm. As shown in Table 3, no peeling or wrinkling of the laminated film from the unstretched polypropylene film occurred during heat sealing, the rigidity was high, and the lamination strength was excellent.

(Example 6)
As shown in Table 2, the same procedure as in Example 2 was performed except that the thickness of the film was changed to 19 μm and the thickness structure was changed to surface layer B/base layer A/surface layer B=2/15/2 μm. As shown in Table 3, no peeling or wrinkling of the laminate film occurred during heat sealing, the rigidity was high, and the laminate strength was excellent.

(Comparative example 1)
As shown in Table 2, a film having a thickness of 19 μm was obtained in the same manner as in Example 2, except that the same raw material with a high mesopentad fraction as in the base layer A was used as the raw material for the surface layer B. The thickness structure was surface layer B/base layer A/surface layer B=1/17/1 μm. As shown in Table 3, no peeling or wrinkling of the laminate film occurred during heat sealing, and although the rigidity was high, the laminate strength was poor.

(Comparative example 2)
As shown in Table 2, a film having a thickness of 19 μm was obtained in the same manner as in Example 2 except that the draw ratio in the longitudinal direction was changed. The thickness structure was surface layer B/base layer A/surface layer B=1/17/1 μm. As shown in Table 3, the laminate film had high rigidity and excellent lamination strength, but peeling and wrinkling occurred at the sealed portion of the laminate film during heat sealing.

(Comparative Example 3)
As shown in Table 2, a film having a thickness of 19 μm was obtained in the same manner as in Example 2 except that the heat treatment temperature was changed. The thickness structure was surface layer B/base layer A/surface layer B=1/17/1 μm. As shown in Table 3, the laminate film had high rigidity and excellent lamination strength, but peeling and wrinkling occurred at the sealed portion of the laminate film during heat sealing.

(Comparative Example 4)
As shown in Table 2, a film having a thickness of 17 μm was obtained in the same manner as in Example 1 except that the draw ratio in the longitudinal direction and the heat treatment temperature were changed. The thickness composition was surface layer B/base layer A/surface layer B=1/15/1 μm. As shown in Table 3, the laminate film had high rigidity and excellent lamination strength, but peeling and wrinkling occurred at the sealed portion of the laminate film during heat sealing.

(Comparative Example 5)
Propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., FLX80E4) having MFR = 7.5 g/10 min, [mmmm] = 98.9%, Tc = 116°C, and Tm = 163°C as the polypropylene resin and 50 parts by mass of propylene homopolymer PP-3 (manufactured by Prime Polymer Co., Ltd., F-300SP) was blended with 50 parts by mass.
To 100 parts by mass of a mixture of these propylene homopolymers, 1.4 parts by mass of a mixture of stearyldiethanolamine monostearate, stearyldiethanolamine distearate, and stearyldiethanolamine (manufactured by Matsumoto Yushi Co., Ltd., KYM-4K) was blended and mixed. , using an extruder with a pelletizer, melted, kneaded and granulated to obtain pellets of the polypropylene composition to obtain a polypropylene resin composition for the substrate layer A. This polypropylene resin composition had a mesopentad fraction of 96.4%, a TmA of 161° C., and an MFR of 5.3 g/10 minutes.
As shown in Table 2, a film having a thickness of 19 μm was obtained in the same manner as in Example 2 except that the above polypropylene resin composition was used for the substrate layer A. The thickness structure was surface layer B/base layer A/surface layer B=1/17/1 μm. As shown in Table 3, the lamination strength was excellent, but the rigidity was low, and peeling and wrinkling occurred at the seal portion of the laminate film during heat sealing.

(Comparative Example 6)
As shown in Table 2, the same procedure as in Example 1 was repeated except that the thickness of the film was changed to 19 μm and the thickness composition was changed to surface layer B/base layer A/surface layer B=3/13/3 μm. As shown in Table 3, the lamination strength was excellent, but the rigidity was low, and peeling and wrinkling occurred at the seal portion of the laminate film during heat sealing.

(Comparative Example 7)
Propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., FLX80E4) having MFR = 7.5 g/10 min, [mmmm] = 98.9%, Tc = 116°C, and Tm = 163°C as the polypropylene resin and 58 parts by mass of propylene homopolymer PP-4 (FL4 manufactured by Japan Polypropylene Co., Ltd. ) was blended with 42 parts by mass of the mixture, which was melt-kneaded and granulated using an extruder with a pelletizer to obtain pellets of the polypropylene composition, which was used as the polypropylene resin composition for the surface layer B. This polypropylene resin composition had a mesopentad fraction of 98.2%, a TmB of 164° C., and an MFR of 6.1 g/10 min.
As shown in Table 2, a film having a thickness of 19 μm was obtained in the same manner as in Comparative Example 1 except that the above polypropylene resin composition was used as the raw material for the surface layer B. As shown in Table 3, no peeling or wrinkling of the laminate film occurred during heat sealing, and although the rigidity was high, the laminate strength was poor.

Since the biaxially oriented laminated polypropylene film of the present invention is excellent in heat resistance and lamination strength, it can be preferably used as a packaging material. In addition to being widely used as a substitute for biaxially oriented PET film, it has excellent moisture resistance, and when combined with a sealant film made of polypropylene resin, it is highly recyclable and suitable as an environmentally friendly mono-material packaging material. can be used for
In addition to packaging materials, it is also used at higher temperatures such as insulating films for capacitors and motors, back sheets for solar cells, high barrier films with inorganic oxide layers, and base films for transparent conductive films such as ITO. It is also suitable for applications that require higher rigidity, such as separate films.
Furthermore, it is possible to use coating agents, inks, lamination adhesives, etc., which have been difficult to use in the past, and to perform coating and printing at high temperatures, which is expected to improve production efficiency.

Claims (7)

A biaxially oriented laminated polypropylene film comprising at least a substrate layer A and a surface layer B, wherein the biaxially oriented laminated polypropylene film satisfies the following requirements 1) to 6).
1) The ratio of the thickness of the substrate layer A to the thickness of the entire film is 70% or more and 98% or less.
2) The mesopentad fraction of the polypropylene resin constituting the base material layer A is 97.0% or more and 99.9% or less.
3) The mesopentad fraction of the polypropylene resin constituting the surface layer B is 80.0% or more and 96.5% or less.
4) The plane orientation coefficient measured from the surface layer B side of the film is 0.0134 or less.
5) The 150°C heat shrinkage in the longitudinal direction of the film is 6.0% or less.
6) The 150°C heat shrinkage in the width direction of the film is 5.0% or less. The biaxially oriented laminated polypropylene film according to claim 1, wherein the biaxially oriented laminated polypropylene film satisfies the following requirements 7) and 8).
7) F5 in the longitudinal direction of the film is 35 MPa or more.
8) F5 in the width direction of the film is 95 MPa or more. 3. The biaxially oriented laminated polypropylene film according to claim 1, wherein the film surface of the surface layer B of the biaxially oriented laminated polypropylene film has a wet tension of 38 mN/m or more. The biaxially oriented laminated polypropylene film according to any one of claims 1 to 3, wherein the biaxially oriented laminated polypropylene film has a haze of 5.0% or less. The biaxially oriented laminated polypropylene film according to any one of claims 1 to 4, wherein the thickness of the entire biaxially oriented laminated polypropylene film is 5 µm or more and 60 µm or less. A laminate comprising the biaxially oriented laminated polypropylene film according to any one of claims 1 to 5 and an unstretched polypropylene film. 6. Laminate strength represented by peel strength when the laminate is peeled at 90° (T-shape) is 1.9 N/15 mm or more and 10 N/15 mm or less in both the longitudinal direction and the width direction of the laminate. The laminate according to .