Biaxially oriented laminated polypropylene film

Abstract

[Problem] To provide a biaxially oriented polypropylene film having low thermal shrinkage at 150°C comparable to that of a biaxially oriented PET film, exceptional rigidity, and exceptional laminate strength. [Solution] A biaxially oriented laminated polypropylene film including at least a substrate layer A and a surface layer B and comprising a resin composition having a polypropylene resin as a main component, wherein the biaxially oriented laminated polypropylene film satisfies the following requirements 1) to 7).　1) The proportion of the thickness of the substrate layer A to the thickness of the entire film is 70-98%.　2) The mesopentad fraction of the polypropylene resin constituting the substrate layer A is 97.0-99.9%.　3) The mesopentad fraction of the polypropylene resin constituting the surface layer B is 80.0-96.5%.　4) The longitudinal-direction F5 of the film is 35 MPa or greater.　5) The width-direction F5 of the film is 95 MPa or greater.　6) The longitudinal-direction 150°C thermal shrinkage of the film is 6.0% or less.　7) The width-direction 150°C thermal shrinkage of the film is 5.0% or less.

Description

Technical Field

[0001] The present invention relates to a biaxially oriented polypropylene film having excellent heat resistance and rigidity.

Background Art

[0002] Biaxially oriented polypropylene films have the characteristics of excellent moisture resistance, and moreover, have the required heat resistance and rigidity. Therefore, they are used in packaging applications and industrial applications, and the applications used are becoming increasingly widespread. Moreover, recently, in consideration of the impact of packaging materials on the environment (ease of recycling), the realization of a monomaterial packaging material composed of a single resin is expected. Therefore, the realization of a polypropylene single-layer packaging material using a biaxially oriented polypropylene film as a base film and an unstretched polypropylene film as a sealant film is expected.

[0003] In order to improve the heat resistance and rigidity of biaxially oriented polypropylene films, in the manufacturing process of biaxially oriented polypropylene films, after stretching in the width direction, a method of further stretching in the longitudinal direction (see Patent Document 1, etc.) or, in the manufacturing process of biaxially oriented polypropylene films, after stretching in the width direction, a first-stage heat treatment is performed while relaxing the film at a temperature below the stretching temperature in the width direction, and a heat treatment is performed at the first-stage temperature to the stretching temperature in the width direction in the second stage (for example, see Patent Document 2, etc.) have been proposed. However, in the films described in Patent Document 1 and Patent Document 2, wrinkles are likely to occur in the seal portion after heat sealing, and it was difficult to replace all applications of biaxially oriented PET films.

[0004] Furthermore, a stretched polypropylene film having heat resistance at 150 °C comparable to that of biaxially oriented PET films has been proposed (for example, see Patent Document 3, Patent Document 4, etc.), but further improvement in laminate strength is expected.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-177645 [Patent Document 2] WO2016 / 182003 International Publication [Patent Document 3] WO2013 / 111779 International Publication [Patent Document 4] WO2017 / 169952 International Publication [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] The problem of the present invention is to solve the above-mentioned problems. That is, it relates to a biaxially oriented polypropylene film excellent in heat resistance and rigidity. Specifically, it relates to a biaxially oriented polypropylene film having heat resistance at 150 ° C comparable to that of a biaxially oriented PET film, excellent rigidity, and excellent laminate strength. [Means for Solving the Problems]

[0007] As a result of intensive studies to achieve such an object, the present invention has obtained a biaxially oriented polypropylene film excellent in heat resistance, rigidity, and laminate strength by controlling the laminated structure of the biaxially oriented polypropylene film, the raw material composition of each layer, and the film properties. That is, the biaxially oriented polypropylene film according to the present invention has the following configuration. [1] A biaxially oriented laminated polypropylene film containing at least a base material layer A and a surface layer B, which satisfies the following requirements 1) to 7). 1) The ratio of the thickness of the base material 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 F5 in the longitudinal direction of the film is 35 MPa or more. 5) The F5 in the width direction of the film is 95 MPa or more. 6) The 150 °C heat shrinkage rate in the longitudinal direction of the film is 6.0% or less. 7) The 150 °C heat shrinkage rate in the width direction of the film is 5.0% or less.

[0008] [2] The biaxially oriented laminated polypropylene film according to [1], wherein the surface orientation coefficient measured from the surface layer B side of the biaxially oriented laminated polypropylene film is 0.0134 or less.

[0009] [3] The biaxially oriented laminated polypropylene film according to [1] or [2], wherein the wetting tension of the film surface of the surface layer B of the biaxially oriented laminated polypropylene film is 38 mN / m or more.

[0010] [4] The biaxially oriented laminated polypropylene film according to any one of [1] to [3], wherein the haze of the biaxially oriented laminated polypropylene film is 5.0% or less.

[0011] [5] The biaxially oriented laminated polypropylene film according to any one of [1] to [4], wherein the total thickness of the biaxially oriented laminated polypropylene film is 5 μm or more and 60 μm or less.

[0012] [6] A laminate including the biaxially oriented laminated polypropylene film according to any one of [1] to [5] and an unstretched polypropylene film. [7] The laminate according to [6], wherein the laminate strength represented by the peel strength when the laminate is peeled at 90 ° (T-shaped) 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.

Advantages of the Invention

[0013] The biaxially oriented laminated polypropylene film of the present invention has a low heat shrinkage rate comparable to that of a biaxially oriented PET film at 150°C, excellent rigidity, and excellent laminate strength. Therefore, when combined with a sealant film made of a polypropylene-based resin, it can be suitably used as a monomaterial packaging material.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, the biaxially oriented laminated polypropylene film according to the present invention will be described in more detail. The biaxially oriented laminated polypropylene film according to the present invention is a biaxially oriented laminated polypropylene film including at least a base material 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 is mainly composed of a polypropylene resin. The term "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, still more preferably 95% by mass or more, and particularly preferably 97% by mass or more. Hereinafter, the base material layer A and the surface layer B will be described.

[0015] 〔Base material layer A〕 (Tacticity of the polypropylene resin constituting the base material layer A) The mesopentad fraction ([mmmm]%) which is an index of the tacticity of the polypropylene resin constituting the base material layer A in the present invention is 97.0% or more and 99.9% or less, preferably 97.5% or more and 99.7% or less, more preferably 98.0% or more and 99.5% or less, and still more preferably 98.5% or more and 99.3% or less. When the polypropylene resin used for the base material layer A is a mixture of a plurality of polypropylene resins, the mesopentad fraction of the mixture is preferably in the same range as described above. When the mesopentad fraction of the polypropylene resin constituting the base material layer A in the present invention is 97.0% or more, the crystallinity of the polypropylene resin increases, and the melting point, crystallinity, and crystal orientation degree of the crystals in the film improve, and rigidity and heat resistance at high temperatures are easily obtained. When it is 99.9% or less, it is preferable in terms of reducing breakage in film production and easily suppressing the production cost of the polypropylene resin. The mesopentad fraction is measured by nuclear magnetic resonance method (so-called NMR method). In order to make the mesopentad fraction of the polypropylene resin within the above range, a method of washing the obtained polypropylene resin powder with a solvent such as n-heptane, or a method of appropriately selecting a catalyst and / or a cocatalyst and a method of selecting components of the polypropylene resin composition are preferably employed.

[0016] (Polypropylene resin used for the base material layer A) As the polypropylene resin used for the base material layer A in the present invention, 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 preferable. Even when it contains an ethylene and / or an α-olefin component having 4 or more carbon atoms, the amount of the ethylene and / or the α-olefin component 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%. When it is within the above range, rigidity and heat resistance are easily improved. Examples of the α-olefin component 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, etc. Different two or more kinds of polypropylene homopolymers, copolymers with ethylene and / or an α-olefin having 4 or more carbon atoms, and mixtures thereof can be used as the polypropylene resin.

[0017] (Melting temperature of the polypropylene resin constituting the base material layer A) The lower limit of the melting temperature (Tm) (hereinafter abbreviated as TmA) measured by DSC of the polypropylene resin used for the base material layer A is preferably 160°C, more preferably 161°C, still more 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 TmA is 180°C or lower, it is easy to suppress cost increase in terms of the production of the polypropylene resin. When the polypropylene resin used for the base material layer A is a mixture of a plurality of polypropylene resins, it is preferable that the TmA of the mixture is also in the same range as described above. Tm is the main peak temperature of the endothermic peak accompanying melting observed when a sample of about 5 mg is 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, melted at 230°C for 5 minutes, cooled 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.

[0018] (Crystallization temperature of the polypropylene resin constituting the base material layer A) The lower limit of the crystallization temperature (Tc: hereinafter may be 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, and still more preferably 114°C. When Tc is 105°C or higher, crystallization easily proceeds, and rigidity and heat resistance at high temperatures are easily 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. When Tc is 135°C or lower, cost increase in polypropylene production can be suppressed, and breakage during film formation is also easily suppressed. When the polypropylene resin used for the base material layer A is a mixture of a plurality of polypropylene resins, the crystallization temperature of the mixture is preferably in the same range as described above. Tc is the main peak temperature of the exothermic peak observed when a sample of about 5 mg is packed in an aluminum pan, set in a DSC, heated to 230 °C at a scanning rate of 10 °C / min in a nitrogen atmosphere, melted at 230 °C for 5 minutes, and then cooled to 30 °C at a scanning rate of -10 °C / min. When multiple peaks are observed, the peak temperature on the low temperature side is taken as Tc. By blending a nucleating agent with the aforementioned polypropylene resin, the crystallization temperature can also be further increased.

[0019] (Melt flow rate of the polypropylene resin used for the base material layer A) The melt flow rate (MFR: hereinafter, may be abbreviated as MFR) of the polypropylene resin used for the base material layer A, when measured in accordance with condition M (230 °C, 2.16 kgf) of JIS K7210 (1995), is 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, still more preferably 6.3 g / 10 min or more and 8.5 g / 10 min or less, particularly preferably 6.4 g / 10 min or more and 8.0 g / 10 min or less, and most preferably 6.5 g / 10 min or more and 7.5 g / 10 min or less. Also, 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, more preferably 6.2 g / 10 min or more and 9.0 g / 10 min or less, still more preferably 6.3 g / 10 min or more and 8.5 g / 10 min or less, particularly preferably 6.4 g / 10 min or more and 8.0 g / 10 min or less, and most preferably 6.5 g / 10 min or more and 7.5 g / 10 min or less. When the MFR of the polypropylene resin is 6.0 g / 10 min or more, it is easy to obtain a biaxially oriented polypropylene film with low heat shrinkage. Also, when the MFR of the polypropylene resin is 10 g / 10 min or less, it is easy to improve the film-forming property. 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, more preferably 3.5 g / 10 min or more and 25 g / 10 min or less, still more preferably 4.5 g / 10 min or more and 22 g / 10 min or less, particularly preferably 5.5 g / 10 min or more and 20 g / 10 min or less, and most preferably 6.0 g / 10 min or more and 20 g / 10 min or less. In order to make the MFR of the polypropylene resin within the above range, methods such as controlling the average molecular weight and molecular weight distribution of the polypropylene resin are preferably adopted.

[0020] (Antistatic agent used for the base material layer A) The propylene resin composition constituting the base material layer A can contain antistatic agents such as diethanolamine fatty acid ester compounds, amine compounds, and glycerin monofatty acid ester compounds. By using these in combination at a specific ratio, the initial antistatic property is sufficient, and the excellent antistatic property can be maintained for a long time. Moreover, even when exposed to high temperatures, there is almost no decrease in the initial transparency, and a non-sticky biaxially oriented polypropylene film can be obtained. The antistatic agent contained in the base material layer A can move to the film surface of the surface layer B by bleeding and exist there.

[0021] (Other additives used for the base material layer A) Also, within a range that does not impair the effects of the present invention, in addition to the antistatic agent, the propylene resin composition constituting the base material layer A can be blended with various additives for improving quality, for example, antiblocking agents such as fine particles for improving productivity, lubricants such as waxes and metal soaps, plasticizers, processing aids, and known heat stabilizers, antioxidants, ultraviolet absorbers, etc. that are usually added to polypropylene-based films.

[0022] Examples of the inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, zeolite, etc. The shape of these particles is not limited to spherical, elliptical, conical, or amorphous, and the particle size can be selected as desired according to the use and usage method of the film. In addition, as the organic fine particles, cross-linked particles obtained by cross-linking acrylic resins, methyl acrylate resins, styrene-butadiene resins, etc. can be used, and various shapes and sizes can be used as in the case of inorganic fine particles. Further, 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.

[0023] [Surface layer B] (Tacticity of the polypropylene resin constituting the surface layer B) The mesopentad fraction ([mmmm]%) which is an index of the tacticity of the polypropylene resin constituting the surface layer B is 80.0% or more and 96.5% or less, preferably 85.0% or more and 96.5% or less, and 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 tacticity of the mixture is preferably in the same range as described 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, it is easy to increase the laminate strength of the laminate with the sealant film. 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 are easily obtained. The mesopentad fraction is measured by nuclear magnetic resonance method (so-called NMR method).

[0024] (Polypropylene resin used for the 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. Even when it contains ethylene and / or an α-olefin component having 4 or more carbon atoms, the upper limit of the amount of the ethylene and / or α-olefin component 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%, and most preferably 0%. When it is within the above range, the rigidity and heat resistance are likely to be improved. Examples of the α-olefin component 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, etc. 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.

[0025] (Melting temperature of the polypropylene resin used for the surface layer B) The lower limit of the melting temperature (Tm) measured by DSC of the polypropylene resin used for the surface layer B (hereinafter abbreviated as TmB) is preferably 152°C, more preferably 154°C, still more preferably 156°C, and even more preferably 158°C. When TmB is 154°C or higher, rigidity and heat resistance at high temperatures are likely to be obtained. The upper limit of TmB is preferably 170°C, more preferably 169°C, still more preferably 168°C, even more preferably 167°C, and particularly preferably 166°C. When TmB is 170°C or lower, an increase in cost can be suppressed in terms of the production of the polypropylene resin, and breakage during film formation is also likely to be suppressed. Also, the laminating strength is likely to be increased. When the polypropylene resin used for the surface layer B is a mixture of a plurality of polypropylene resins, the TmB of the mixture preferably falls within the same range as described above. Tm refers to the main peak temperature of the endothermic peak accompanying melting, which is observed when about 5 mg of a sample is packed into an aluminum pan, set in a differential scanning calorimeter (DSC), heated to 230°C at a scanning rate of 10°C / min under a nitrogen atmosphere, melted at 230°C for 5 minutes, cooled 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.

[0026] (Crystallization temperature of the polypropylene resin used for the surface layer B) The lower limit of the crystallization temperature (Tc) of the polypropylene resin used for the surface layer B, measured by DSC, is 95°C, preferably 100°C, and more preferably 105°C. When Tc is 95°C or higher, crystallization easily proceeds, and rigidity and heat resistance at high temperatures are easily obtained. The upper limit of Tc is preferably 115°C, and more preferably 113°C. When Tc is 115°C or lower, the crystallization orientation of the surface layer B is suppressed, and the laminate 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 preferably falls within the same range as described above. Tc refers to the main peak temperature of the exothermic peak observed when about 5 mg of a sample is packed into an aluminum pan, set in a DSC, heated to 230°C at a scanning rate of 10°C / min under a nitrogen atmosphere, melted at 230°C for 5 minutes, and cooled to 30°C at a scanning rate of -10°C / min. When multiple peaks are observed, the peak temperature on the low-temperature side is taken as Tc.

[0027] (Melt flow rate of the polypropylene resin used for the surface layer B) The melt flow rate (MFR) of the polypropylene resin used for the surface layer B is preferably 2.8 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 or less, still more preferably 3.0 g / 10 min or more and 4.5 g / 10 min or less, and even more preferably 3.0 g / 10 min or more and 4.0 g / 10 min or less when measured in accordance with Condition M (230 °C, 2.16 kgf) of JIS K7210 (1995). When the polypropylene resin used for the surface layer B is a mixture of a plurality of polypropylene resins, the MFR of the mixture of polypropylene resins is preferably 2.8 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 or less, still more preferably 3.0 g / 10 min or more and 5.0 g / 10 min, and even more preferably 3.0 g / 10 min or more and 4.0 g / 10 min or less. When the MFR of the polypropylene resin is 2.8 g / 10 min or more, it is easy to obtain a biaxially oriented polypropylene film with low heat shrinkage. When the MFR of the polypropylene resin is 5.0 g / 10 min or less, the film-forming property is likely to be good, 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 min or more and 5.0 g / 10 min or less, more preferably 2.2 g / 10 min or more and 5.0 g / 10 min or less, and still more preferably 2.3 g / 10 min or more and 4.5 g / 10 min or less. From the viewpoint of the thickness uniformity of the laminated film, the MFR of the polypropylene resin used for the surface layer B is preferably closer to the MFR of the polypropylene resin used for the base material layer A.

[0028] (Additives used for the surface layer B) As long as the effects of the present invention are not impaired, various additives for improving qualities such as slipperiness and antistatic properties can be added to the polypropylene resin composition constituting the surface layer B. For example, antiblocking agents such as fine particles for improving productivity, lubricants such as waxes and metal soaps, plasticizers, processing aids, and known heat stabilizers, antioxidants, ultraviolet absorbers, inorganic and organic fine particles, etc. that are usually added to polypropylene-based films can also be blended.

[0029] Examples of the inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, zeolite, etc. Their shapes are not limited to spherical, elliptical, conical, or amorphous, and the particle diameter can also be selected as desired according to the use and usage method of the film. In addition, as the organic fine particles, crosslinked particles such as acrylic, methyl acrylate, and styrene-butadiene can be used, and various shapes and sizes can be used in the same way as the inorganic fine particles. Also, 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.

[0030] (Antifogging agent used for the base material layer A and the surface layer B) In the biaxially oriented laminated polypropylene film of the present invention, by adding 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 amines and amides of higher fatty acids in an amount of 0.2 to 5% by mass in the film, it can be made suitable for packaging fresh agricultural products such as vegetables, fruits, and flowers that require freshness retention. The antifogging agent can be added to either the base material layer A or the surface layer B. The antifogging agent contained in the base material layer A can move to the film surface of the surface layer B by bleeding and exhibit antifogging properties.

[0031] 〔Thickness configuration of the base material layer A and the surface layer B〕 The total layer thickness of the biaxially oriented laminated polypropylene film of the present invention varies depending on its use and usage method. From the viewpoints of film strength and resource saving, the lower limit is preferably 5 μm, more preferably 6 μm, even more preferably 8 μm, and particularly preferably 10 μm. The upper limit is preferably 60 μm, more preferably 40 μm, even more preferably 35 μm, particularly preferably 25 μm, and 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 thickness thinner while ensuring strength. Depending on the application, the total layer thickness of the film may preferably be greater than 60 μm, and generally can be used if the total layer thickness of the film is up to 200 μm.

[0032] The lower limit of the thickness of the base material layer A varies depending on its use and usage method. From the viewpoints of film rigidity and water vapor barrier properties, 5 μm is preferred. The upper limit of the thickness of the base material layer A is preferably 50 μm, more preferably 35 μm, even more preferably 20 μm or less, and particularly preferably 18 μm, in terms of transparency and impact on the environment. Depending on the application, the thickness of the base material layer A may preferably be greater than 50 μm, and generally can be used if it is up to 200 μm.

[0033] The lower limit of the thickness of the surface layer B varies depending on its use and usage method. From the viewpoints of film laminating strength and antistatic properties, 0.3 μm is preferred, 0.5 μm is more preferred, and 0.8 μm or more is even more preferred. The upper limit of the thickness of the surface layer B varies depending on its use and usage method. From the viewpoints of film rigidity and heat resistance at high temperatures, 4 μm is preferred, and 2 μm is more preferred. Also, when the thickness of the surface layer B is large, it is easy to reduce the surface orientation coefficient.

[0034] The lower limit of the ratio of the thickness of the base material layer A to the total thickness of the film is 70% from the viewpoints of rigidity and heat resistance at high temperatures, more preferably 75%, even more preferably 80%, and particularly preferably 85%. The upper limit of the ratio of the thickness of the base material layer A to the total thickness of the 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.

[0035] From the viewpoints of the lamination strength and antistatic property of the film, 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 even more preferably 8% or more. From the viewpoints of rigidity and heat resistance at high temperatures, the upper limit of the ratio of the thickness of the base material layer B to the thickness of the entire film is preferably 30% or less, more preferably 23%, still more preferably 20% or less, and particularly preferably 15% or less.

[0036] (Layer structure) The layer structure of the biaxially oriented laminated polyolefin film of the present invention includes surface layer B / base material layer A and surface layer B / base material layer A / surface layer B. It is preferable that the base material layer A and the surface layer B are in direct contact, but an intermediate layer may be provided between the base material layer A and the surface layer B. The raw material composition of the intermediate layer is preferably such that it is in the middle of the base material layer and the surface layer in order to make peeling less likely to occur between the base material layer A and the surface layer B.

[0037] 〔Method for producing a biaxially oriented laminated polypropylene film〕 The biaxially oriented laminated polypropylene film of the present invention is obtained by producing an unstretched sheet composed of a polypropylene resin composition mainly composed of the above-described polypropylene resin and performing biaxial stretching. As the method of biaxial stretching, any of an inflation simultaneous biaxial stretching method, a tenter simultaneous biaxial stretching method, and a tenter sequential biaxial stretching method may be employed, but it is preferable to employ the tenter sequential biaxial stretching method from the viewpoints of film formation stability and thickness uniformity. 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.

[0038] Next, the manufacturing method of the biaxially oriented laminated polypropylene film of the present invention will be described, but it is not necessarily limited thereto. Below, the case where the tenter sequential biaxial stretching method is employed will be described for the example of surface layer B / base material layer A / surface layer B. First, a multilayer sheet of a molten polypropylene resin composition having a structure of surface layer B / base material layer A / surface layer B is extruded from a T-die. As a method, for example, a co-extrusion method can be used in which polypropylene resins fed from different flow paths using two or more extruders are laminated in multiple layers using a multilayer feed block, a static mixer, a multilayer multi-manifold die, etc. It is also possible to introduce the above-described multilayer device into the melt line from the extruder to the T-die using only one extruder. Also, 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 in a sheet shape from the T-die is grounded on a metal cooling roll and cooled and solidified. For the purpose of accelerating solidification, it is preferable to further cool by immersing the sheet cooled by the cooling roll in a water tank or the like.

[0039] Next, the sheet is stretched in the longitudinal direction by increasing the rotational speed of the rear stretching roll with two pairs of heated stretching rolls to obtain a uniaxially stretched film. Subsequently, after preheating the uniaxially stretched film, while gripping the film ends with a tenter-type stretching machine, stretching is performed in the width direction at a specific temperature to obtain a biaxially stretched film. After the width direction stretching step, 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 can be wound with a winder to obtain a film roll, for example, after performing a corona discharge treatment on at least one side as necessary.

[0040] Each of the following steps will be described in more detail. (Extrusion step) First, a polypropylene resin composition mainly composed of polypropylene resin is heated and melted in a single-screw or twin-screw extruder in the range of 200°C or higher and 300°C or lower, and the sheet-like molten polypropylene resin composition discharged from a T-die is brought into contact with a metal cooling roll to be cooled and solidified. It is preferable to further put the obtained unstretched sheet into a water tank. The temperature of the cooling roll or the cooling roll and the water tank is preferably a temperature that can suppress crystallization. When it is desired to increase the transparency of the film, it is preferable to cool and solidify with a cooling roll at 50°C or lower. When the cooling temperature is 50°C or lower, the transparency of the unstretched sheet is likely to increase, preferably 40°C or lower. To increase the degree of crystal orientation after sequential biaxial stretching, it is also preferable to set the cooling temperature to 30°C or higher. 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 film thickness after sequential 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, etc.

[0041] (Longitudinal stretching step) The lower limit of the longitudinal stretching ratio is preferably 3 times, more preferably 3.5 times, and particularly preferably 3.8 times. When it is within the above range, it is easy to increase the strength and the thickness unevenness is reduced. The upper limit of the longitudinal stretching ratio is preferably 4.3 times, more preferably 4.2 times, and particularly preferably 4.1 times. When it is within the above range, the stretchability in the widthwise stretching step is good and the productivity is improved.

[0042] In the present invention, by using a polypropylene resin with high stereoregularity as a raw material, reducing the longitudinal stretching ratio, and suppressing the degree of orientation in the longitudinal direction, it is possible to produce a film that achieves both heat resistance and film-forming properties.

[0043] The reason is presumed as follows. By reducing the longitudinal stretching ratio, the orientation degree of the polypropylene molecular chains in the longitudinally stretched film is suppressed, making it difficult to suppress the mobility of the polypropylene molecular chains. By stretching at a high magnification in the subsequent widthwise stretching step and performing heat treatment at a high temperature for a sufficient time in the further subsequent heat treatment step, a biaxially oriented laminated polypropylene film having a high crystallinity structure can be finally obtained. As a result, a biaxially oriented laminated polypropylene film having a high Young's modulus, stress at 5% elongation, particularly stress at 5% elongation can be obtained. Conventionally, when either heat resistance (heat shrinkability) or rigidity is improved, the other property tends to deteriorate, but in the present invention, both can be achieved simultaneously.

[0044] The lower limit of the longitudinal stretching temperature is preferably TmA - 40°C, more preferably TmA - 37°C, and still more preferably TmA - 35°C with respect to the melting point of the base material layer A (hereinafter abbreviated as TmA). When within the above range, it is easy to reduce the heat shrinkage rate, the subsequent widthwise stretching becomes easier, and thickness unevenness also decreases. The upper limit of the longitudinal stretching temperature is preferably TmA - 7°C, more preferably TmA - 10°C, and still more preferably TmA - 12°C. When within the above range, it is less likely that the resin fuses to the stretching roll and becomes difficult to stretch, or the surface roughness increases, resulting in a decrease in film quality. Note that the longitudinal stretching may be performed in two or more stages using three or more pairs of stretching rolls.

[0045] (Preheating step for widthwise stretching) Before the widthwise stretching step, it is necessary to heat the uniaxially stretched film after longitudinal stretching in the range of TmA + 5°C or higher and TmA + 20°C or lower to soften the polypropylene resin composition. By doing the above, the softening of the uniaxially stretched film progresses, and the widthwise stretching becomes easier. By setting it to TmA + 20°C or lower, the orientation during widthwise stretching progresses, and rigidity is likely to be exhibited. More preferably, it is TmA + 8°C or higher and TmA + 15°C or lower. Here, the highest temperature in the preheating step is defined as the preheating temperature.

[0046] (Width direction stretching step) In the width direction stretching step, it is preferable to stretch at a temperature of TmA - 8°C or higher and lower than the preheating temperature. At this time, the start of the width direction stretching may be at the time when the preheating temperature is reached, or may be at the time when the temperature is lowered after reaching the preheating temperature and reaches 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, it is easy to reduce the thermal shrinkage rate of the obtained biaxially oriented film. 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. When the width direction stretching temperature is within this range, stretching unevenness is less likely to occur.

[0047] The lower limit of the final width direction stretching 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, it is easy to increase the rigidity and the thickness unevenness is also likely to decrease. The upper limit of the width direction stretching ratio is preferably 20 times, more preferably 15 times, and still more preferably 11 times. When it is 20 times or less, it is easy to reduce the thermal shrinkage rate and it is difficult to break during stretching.

[0048] (Heat treatment step) The biaxially stretched film is heat-treated. The lower limit of the heat treatment temperature is preferably TmA + 8°C, and particularly preferably TmA + 10°C. When it is TmA + 5°C or higher, it is easy to relax the orientation of the amorphous part, reduce the thermal shrinkage rate, and increase the lamination strength. 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 it to TmA + 20°C or lower, the highly oriented crystals generated in the biaxial stretching step are less likely to melt, and it is easy to improve the rigidity of the obtained film. Also, the roughness of the film surface does not become too large and the film is less likely to turn white. In addition, in order to further reduce the heat shrinkage rate, the film can be relaxed in the width direction during the heat treatment. The upper limit of the relaxation rate is 15%, more preferably 10%, and even more preferably 8%. If it exceeds the above, thickness unevenness may increase. The lower limit of the relaxation rate is preferably 0%, more preferably 2%, and relaxation in the width direction makes it easier to reduce the heat shrinkage rate.

[0049] It is preferable to perform a corona treatment on the film surface of the surface layer B of the obtained biaxially oriented laminated polypropylene film. The watt density at this time is preferably 11 W / m 2 ·min, more preferably 12 W / m 2 ·min, and even more preferably 13 W / m 2 ·min.

[0050] 〔Film Properties〕 The biaxially oriented laminated polypropylene film of the present invention is characterized by the following properties. In the biaxially oriented laminated polypropylene film of the present invention, the "longitudinal direction" corresponds to the flow direction in the film manufacturing process, and the "width direction" is the direction orthogonal to the flow direction in the film manufacturing process. Hereinafter, the "longitudinal direction" may be abbreviated as "MD direction" and the "width direction" as "TD direction".

[0051] (Stress at 5% elongation) The lower limit of the stress (F5, hereinafter abbreviated as F5 for the stress at 5% elongation) at 5% elongation in the longitudinal direction of the biaxially oriented laminated polypropylene film of the present invention is 35 MPa, preferably 36 MPa, more preferably 38 MPa, even more preferably 40 MPa, and even more preferably 42 MPa. When it is 35 MPa or more, the rigidity is high, so it is easy to maintain the bag shape when used as a packaging bag, and deformation of the film hardly occurs during processing such as printing, so that printing pitch deviation hardly occurs when transferring printing ink. 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, and most preferably 60 MPa. When it is 70 MPa or less, realistic production is easy. The lower limit of F5 in the width direction of the biaxially oriented laminated polypropylene film of the present invention is 95 MPa, preferably 100 MPa, more preferably 105 MPa, and still more preferably 110 MPa. When it is 95 MPa or more, since the rigidity is high, it is easy to maintain the bag shape when used as a packaging bag, and since deformation of the film hardly occurs during processing such as printing, printing pitch deviation hardly occurs when transferring printing ink. The upper limit of F5 in the width direction is preferably 200 MPa, more preferably 190 MPa, and still more preferably 180 MPa. When it is 200 MPa or less, realistic production is easy. Also, the balance of physical properties in the longitudinal and width directions of the film is likely to be improved. F5 can be set within the range by adjusting the draw ratio, relaxation ratio, and temperature conditions during film formation.

[0052] (Heat shrinkage rate at 150 °C) The upper limit of the heat shrinkage rate in the longitudinal direction of the biaxially oriented laminated polypropylene film of the present invention at 150 °C is 6.0%, preferably 5.0%, more preferably 4.8%, and particularly preferably 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%, even more preferably 3.0%, particularly preferably 2.7, most preferably 2.1%, and particularly most preferably 1.7%. When 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 in the seal part hardly occur during heat sealing.

[0053] (Young's modulus) The lower limit of the 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, still more preferably 1.8 GPa, particularly preferably 1.9 GPa, and most preferably 2.0 GPa. When it is 1.6 GPa or more, since the rigidity is high, it is easy to maintain the bag shape when used as a packaging bag, and since deformation of the film hardly occurs during processing such as printing, printing pitch deviation hardly occurs when transferring printing ink. 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, and most preferably 2.6 GPa. When it is 3.0 GPa or less, realistic production is easy. 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. When it is 3.6 GPa or more, since the rigidity is high, it is easy to maintain the bag shape when used as a packaging bag, and since deformation of the film hardly occurs during processing such as printing, printing pitch deviation hardly occurs when transferring printing ink. The upper limit of the Young's modulus in the width direction is preferably 5.0 GPa, more preferably 4.9 GPa, still more preferably 4.8 GPa, and even more preferably 4.5 MPa or less. When it is 5.0 GPa or less, realistic production is easy. Also, the balance of the physical properties in the longitudinal direction and the width direction of the film is likely to be improved. The Young's modulus can be made within the range by adjusting the draw ratio, relaxation ratio, and temperature conditions during film formation.

[0054] (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, still more preferably 100 MPa, and even more preferably 110 MPa. If it is 90 MPa or more, the durability of the packaging bag is likely to be excellent. The higher the tensile breaking strength in the longitudinal direction, the more preferable it is in terms of durability and the like. However, as a realistic value in manufacturing, the upper limit is 300 MPa. 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, even more preferably 300 MPa, and particularly preferably 340 MPa. If it is 240 MPa or more, the durability of the packaging bag is likely to be excellent. The higher the tensile breaking strength in the width direction, the more preferable it is in terms of durability and the like. However, as a realistic value in manufacturing, the upper limit is 500 MPa. The tensile breaking strength can be made within a range by adjusting the draw ratio, relaxation ratio, and temperature conditions during film formation.

[0055] (Tensile elongation at break) 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%, still more preferably 240%, 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 bursting of the packaging bag are likely to decrease. The upper limit of the tensile elongation at break in the longitudinal direction is preferably 350% as a realistic value, 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%, even more preferably 40%, and particularly preferably 50%. If it is 25% or more, the breakage of the film and the bursting of the packaging bag are likely to decrease. The upper limit of the tensile elongation at break in the width direction is preferably 70% as a realistic value, more preferably 65%, and still more preferably 60%. The tensile elongation at break can be made within a range by adjusting the draw ratio, relaxation ratio, and temperature conditions during film formation.

[0056] (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%, still more preferably 4.0%, 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. The lower limit of the haze is preferably 0.1%, more preferably 0.2%, still more preferably 0.3%, and particularly preferably 0.4% as a realistic value. When it is 0.1% or more, it is easy to manufacture. The haze can be made within a range by adjusting the temperature conditions during film formation such as the temperature of the cooling roll (CR).

[0057] (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 still more preferably 40 mN / m or more. When the wetting tension is 38 mN / m or more, the adhesion to printing ink and adhesives used for laminating with other member films is improved. To make the wetting tension 38 mN / m or more, it is preferable to perform physicochemical surface treatments such as corona treatment and flame treatment. For example, in corona treatment, it is preferable to heat the film using a preheating roll and a treatment roll and perform discharge in the air. The wetting tension is related to the degree of the strength of corona treatment, but since the wetting tension is also related to the bleed-out amount of the antistatic agent, it is effective to set each within a suitable range.

[0058] (Surface orientation coefficient) The lower limit of the in-plane orientation coefficient (ΔP) measured from the surface layer B side of the biaxially oriented laminated polypropylene film of the present invention is preferably 0.0122, more preferably 0.0124, and even more preferably 0.0126. When it is 0.0122 or more, the film thickness unevenness tends to improve. The upper limit of the in-plane orientation coefficient (ΔP) is preferably 0.0134, more preferably 0.0132. When it is 0.0134 or less, it is likely to have excellent heat resistance at high temperatures and the laminating strength is likely to increase. The in-plane orientation coefficient (ΔP) can be made within the range by adjusting the draw ratio, relaxation ratio, and temperature conditions during film formation. Further, the in-plane orientation coefficient (ΔP) is calculated using the formula [(Nx + Ny) / 2] - Nz.

[0059] [Practical characteristics of the film] The practical characteristics of the biaxially oriented laminated polypropylene film of the present invention will be described. (Film processing) The printing of the biaxially oriented laminated polypropylene film of the present invention can be performed by letterpress printing, lithographic printing, gravure printing, screen printing, or transfer printing according to the application. Further, an unstretched sheet, uniaxially oriented film, or biaxially oriented film made of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, or polyester can be bonded as a sealant film to form a laminate with heat sealability. Further, when it is desired to enhance the gas barrier property and heat resistance, an unstretched sheet, uniaxially stretched film, or biaxially stretched film made of aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, or polyvinyl alcohol can be provided as an intermediate layer between the biaxially oriented polypropylene film and the sealant film. For bonding the sealant film, an adhesive applied by a dry lamination method or a hot melt lamination method can be used. To enhance the gas barrier property, aluminum or inorganic oxides can also be vapor-deposited on a biaxially oriented polypropylene film, an intermediate layer film, or a sealant film. Vacuum evaporation, sputtering, or ion plating methods can be employed for the vapor deposition method, but it is particularly preferable to vacuum-evaporate silica, alumina, or a mixture thereof.

[0060] (Lamination strength) The lower limit of the lamination strength in the longitudinal direction and the 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, still more preferably 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, and particularly 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 is likely to be reduced. The upper limit of the lamination strength in the longitudinal direction is preferably 4.0 N / 15 mm, more preferably 3.5 N / 15 mm as a realistic value. Here, the lamination strength is the peel strength at the time of T-peel between the base film and the sealant layer for a laminate film (laminate) in which an unstretched polypropylene film (sealant layer) is bonded to a biaxially oriented polypropylene film (base film) described in the examples via an adhesive.

[0061] (Appearance of heat seal part) To form a bag for packaging food, there are methods such as filling a pre-made bag with contents, heating and melting the film, and fusing and sealing the films together, or making and sealing the bag while filling the food. Usually, a sealant film made of polyethylene, polypropylene, etc. is laminated on a base film, and the sealant film surfaces are fused together. The heating method is to apply pressure with a heating plate from the base film side to hold the film and seal it, and the seal width is often about 10 mm. At this time, since the base film is also heated, the shrinkage at that time causes wrinkles. In terms of the durability of the bag, fewer wrinkles are better, and fewer wrinkles are also better to enhance the purchasing desire. The sealing temperature may be about 120 °C, but a higher sealing temperature is required to increase the bag-making processing speed, and in that case, it is preferable that the shrinkage is small. When fusing a chuck to the opening of the bag, a seal at an even higher temperature is required.

[0062] (Printing pitch deviation) As the structure of the packaging film, it often consists of a laminated film of a base film with printing and a sealant film as a basic structure. The printing pitch deviation is considered to occur because tension and heat are applied to the film during the printing process, causing the base material of the film to expand and contract. Eliminating defective products due to printing pitch deviation is important in terms of the effective utilization of resources and also important to enhance the purchasing desire.

Examples

[0063] Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods. (1) Melt flow rate The melt flow rate (MFR) was measured in accordance with JIS K7210 at a temperature of 230 °C and a load of 2.16 kgf.

[0064] (2) Mesopentad fraction The measurement of the mesopentad fraction ([mmmm]%) of the polypropylene resin was 13It was carried out using 13C-NMR. The mesopentad fraction was calculated according to the method described by Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). 13 The 13C-NMR measurement was performed using AVANCE500 manufactured by BRUKER. 200 mg of the sample was dissolved in a mixed solution of o-dichlorobenzene and deuterated benzene at a ratio of 8:2 at 135 °C and the measurement was carried out at 110 °C.

[0065] (3) Crystallization temperature (Tc), melting temperature (Tm) Thermal measurement was carried out under a nitrogen atmosphere using a DSC8500 differential scanning calorimeter manufactured by PerkinElmer. Approximately 5 mg was cut out from the pellets of the polypropylene resin and sealed in an aluminum pan for measurement. After heating to 230 °C and holding for 5 minutes, it was cooled to 30 °C at a rate of -10 °C / min, and the exothermic peak temperature was taken as the crystallization temperature (Tc). Then, it was held at 30 °C for 5 minutes and heated to 230 °C at 10 °C / min, and the main endothermic peak temperature was taken as the melting temperature (Tm).

[0066] (4) Film thickness The thickness of the film was measured using Militron 1202D manufactured by Seiko E&M. The thicknesses of the base material layer A and the surface layer B were calculated from the total thickness of the laminated polypropylene film measured by the above method based on the ratio of the discharge amount of the base material layer A and the discharge amount of the surface layer B.

[0067] (5) Haze It was measured at 23 °C in accordance with JIS K7105 using NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0068] (6) Tensile test In accordance with JIS K7127, the tensile strength in the longitudinal and width directions of the film was measured at 23 °C. The sample was cut into a size of 15 mm × 200 mm, the chuck width was 100 mm, and it was set on a tensile testing machine (Dual Column Tabletop Testing Machine Instron 5965 manufactured by Instron Japan Co., Ltd.). The tensile test was carried out at a tensile speed of 200 mm / min. From the obtained strain-stress curve, the stress at 5% elongation was taken as F5. Also, the Young's modulus was determined from the slope of the linear portion at the initial stage of elongation. The tensile breaking strength and the tensile breaking elongation were defined as the strength and elongation at the time when the sample broke, respectively.

[0069] (7) Heat shrinkage rate It was measured by the following method in accordance with JIS Z1712. The film was cut into lengths of 200 mm with a width of 20 mm in the longitudinal and width directions of the film, respectively, and hung in a hot air oven at 150 °C and heated for 5 minutes. The length after heating was measured, and the heat shrinkage rate was determined as the ratio of the shrunk length to the original length.

[0070] (8) Refractive index, surface orientation coefficient It was measured at a wavelength of 589.3 nm and a temperature of 23 °C using an Abbe refractometer manufactured by Atago Co., Ltd. from the surface layer B side of the film. The refractive indices along the longitudinal and width directions were designated as Nx and Ny, respectively, and the refractive index in the thickness direction was designated as Nz. The surface orientation coefficient was calculated using the formula [(Nx + Ny) / 2] - Nz. When the surface layer B is on both sides, the average value of the respective surface orientation coefficients was calculated and taken as the surface orientation coefficient.

[0071] (9) Wetting tension In accordance with JIS K6768-1999, after the film was aged for 24 hours at 23 °C and a relative humidity of 50%, the corona-treated surface of the film was measured by the following procedure. 1) The measurement was carried out in a standard test chamber atmosphere (see JIS K7100) at a temperature of 23 °C and a relative humidity of 50%. 2) The test piece was placed on the substrate of a hand coater, and several drops of the test mixture were dropped onto the test piece, and immediately the wire bar was pulled to spread the test mixture evenly. When using a cotton swab or a brush to spread the test mixture, the liquid should be at least 6 cm 2Quickly spread it over the above area. The amount of the liquid should be such that it forms a thin layer without creating puddles. The wettability tension is determined by observing the liquid film of the test mixture in a bright place and judging based on the state of the liquid film after 3 seconds. If the liquid film does not break and maintains its state when applied for more than 3 seconds, it is judged to be wet. If the wet state is maintained for more than 3 seconds, further proceed to the mixture with a higher surface tension. Conversely, if the liquid film breaks in less than 3 seconds, proceed to the mixture with a lower surface tension. Repeat this operation to select the mixture that can accurately wet the surface of the test piece for 3 seconds. 3) The wire bar is washed with methanol and dried after each use. 4) Perform the operation of selecting the mixture that can wet the surface of the test piece for 3 seconds at least 3 times. The surface tension of the mixture thus selected is taken as the wettability tension of the film.

[0072] (10) Laminating strength of the laminate film (laminated body) The laminating strength was measured according to the following procedure. 1) Preparation of a laminate (laminate film) of a biaxially oriented laminated polypropylene film and a sealant film This was carried out as follows using a continuous dry laminating machine. 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 / m2, and then it was led to a drying zone and dried at 80°C for 5 seconds. Subsequently, it was laminated with the sealant film between the rolls provided on the downstream side (roll pressure 0.2 MPa, roll temperature: 60°C). The obtained laminate film was subjected to an aging treatment at 40°C for 3 days in a wound state. Note that the adhesive used was a dry laminating system adhesive obtained by mixing 28.9% by mass of the main agent (manufactured by Toyo Morton Co., Ltd., TM569), 4.00% by mass of the curing agent (manufactured by Toyo Morton Co., Ltd., CAT10L), and 67.1% by mass of ethyl acetate. The sealant film used was an unstretched polypropylene film (Pyren (registered trademark) CT P1128, thickness 30 μm) manufactured by Toyobo Co., Ltd. 2) Measurement of the laminating strength of the laminate film (laminated body) The laminated film (laminate) obtained above was cut into strips (length 200 mm, width 15 mm) with the long side in the longitudinal and width directions of the biaxially oriented polypropylene film, and using a tensile testing machine (dual-column tabletop testing machine Instron 5965 manufactured by Instron Japan K.K.), the peel strength (N / 15 mm) when peeling at 90° (T-shaped) at a tensile speed of 200 mm / min in an environment of 23°C was measured. The measurement was performed 3 times in each of the longitudinal and width directions, and the average value was taken as the laminate strength in the longitudinal and width directions.

[0073] (11) Appearance evaluation of heat seal part In accordance with JIS Z1707, the seal strength of the laminated film (laminate) was measured by the following method, and the appearance of the sealed part when heat-sealed at the reaching heat seal temperature was evaluated. The sealant films of the laminated film (laminate) were heat-sealed with a heat sealer. At this time, the seal pressure was 10 N / cm2, the seal time was 1 second, and the temperature was carried out from 100°C to 250°C. The heat-sealed laminated film (laminate) was cut into a size of width 15 mm × length 200 mm, the initial chuck distance was 100 mm, and it was set on a tensile testing machine (dual-column tabletop testing machine Instron 5965 manufactured by Instron Japan K.K.), and the T-peel strength was measured at a tensile speed of 200 mm / min. A graph with temperature on the horizontal axis and heat seal strength on the vertical axis was drawn, the maximum value of the heat seal strength was taken as the reaching seal strength, and the temperature at that time was taken as the reaching heat seal temperature. The appearance of the sealed part when heat-sealed at the reaching heat seal temperature was evaluated in the following two levels from the peeling of the base material layer and the degree of wrinkles. ○: No peeling of the film and no occurrence of wrinkles. ×: Peeling of the film or / and occurrence of wrinkles.

[0074] (Example 1) [Base material layer A] As the polypropylene resin, 80 parts by mass of propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., FLX80E4) with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116 °C, and Tm = 163 °C was blended with 20 parts by mass of propylene homopolymer PP-2 (manufactured by Sumitomo Chemical Co., Ltd., FS2012) with MFR = 3.0 g / 10 min, [mmmm] = 98.4%, Tc = 116 °C, and Tm = 163 °C. To 100 parts by mass of the mixture of these propylene homopolymers, 1.4 parts by mass of a mixture of stearyldiethanolamine monostearate, stearyldiethanolamine distearate, and stearyldiethanolamine (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., KYM-4K) was added and mixed. After that, it was melt-kneaded and pelletized using an extruder equipped with a pelletizer to obtain pellets of a polypropylene composition, which was used as the polypropylene resin composition for the base layer A. The mesopentad fraction of this polypropylene resin composition was 98.8%, TmA was 163 °C, and MFR was 6.5 g / 10 min. [Surface layer B] As the polypropylene resin, a blend of 58 parts by mass of propylene homopolymer PP-3 (manufactured by Prime Polymer Co., Ltd., F-300SP) with MFR = 2.5 g / 10 min, [mmmm] = 93.8%, Tc = 112 °C, and Tm = 159 °C and 42 parts by mass of propylene homopolymer PP-4 (FL4 manufactured by Nippon Polypropylene Co., Ltd.) with MFR = 4.2 g / 10 min, [mmmm] = 97.3%, Tc = 112 °C, and Tm = 165 °C was melt-kneaded and pelletized using an extruder equipped with a pelletizer to obtain pellets of a polypropylene composition, which was used as the polypropylene resin composition for the surface layer B. The mesopentad fraction of this polypropylene resin composition was 95.3%, TmB was 161 °C, and MFR was 3.5 g / 10 min. First, the polypropylene resin compositions constituting the base layer A and the surface layer B were heated and melted at 250 °C using a multi-layer feed block and an extruder, and co-extruded into a sheet form while laminating the molten polypropylene resin compositions from a T-die in the configuration of surface layer B / base layer A / surface layer B at 250 °C. The molten sheet was brought into contact with a cooling roll at 37°C and then directly put into a water bath at 29°C to obtain an unstretched sheet. Subsequently, the unstretched sheet was longitudinally stretched 4.0 times with a pair of rolls at 140°C, and then both ends were clamped with clips and introduced into a hot air oven. After preheating at 174°C, it was stretched 10 times in the width direction at 160°C, and then heat-treated while relaxing 7% at 175°C in the width direction. On the surface of the inner layer B of the obtained biaxially oriented polypropylene film, a corona treatment was performed using a corona treatment machine manufactured by Kasuga Electric Co., Ltd. at a condition of 13 W / m 2 ·min. After that, it was wound up with a winder to obtain a biaxially oriented polypropylene film with a thickness of 17 μm. The thickness structure of the film was surface layer B / substrate layer A / surface layer B = 1 / 15 / 1 μm. The characteristics of the polypropylene resin raw materials used in Table 1, the raw material compositions and film-forming conditions of each layer in Table 2, and the film characteristics in Table 3 were shown. As shown in Table 3, there were no peeling or wrinkles in the laminated film with the unstretched polypropylene film during heat sealing, it had high rigidity, and excellent lamination strength.

[0075] (Example 2) As shown in Table 2, a film with a thickness of 19 μm was obtained in the same manner as in Example 1 except that the thickness structure and the relaxation rate during heat treatment were changed. The thickness structure was surface layer B / substrate layer A / surface layer B = 1 / 17 / 1 μm. As shown in Table 3, there were no peeling or wrinkles in the laminated film with the unstretched polypropylene film during heat sealing, it had high rigidity, and excellent lamination strength.

[0076] (Example 3) As shown in Table 2, a film with a thickness of 19 μm was obtained in the same manner as in Example 2 except that the preheating temperature, the stretching temperature in the width direction, and the heat treatment temperature were changed. The thickness structure was surface layer B / substrate layer A / surface layer B = 1 / 17 / 1 μm. As shown in Table 3, there were no peeling or wrinkles in the laminated film with the unstretched polypropylene film during heat sealing, it had high rigidity, and excellent lamination strength.

[0077] (Example 4) As shown in Table 2, a film with a film thickness of 16 μm was obtained in the same manner as in Example 3 except that the thickness configuration and the preheating temperature were changed. The thickness configuration was surface layer B / substrate layer A / surface layer B = 1 / 14 / 1 μm. As shown in Table 3, there was no peeling or wrinkling of the laminated film with the un-stretched polypropylene film during heat sealing, and it had high rigidity and excellent lamination strength.

[0078] (Example 5) As shown in Table 2, a film with a film thickness of 17 μm was obtained in the same manner as in Example 4 except that the thickness configuration and the heat treatment temperature were changed. The thickness configuration was surface layer B / substrate layer A / surface layer B = 1 / 15 / 1 μm. As shown in Table 3, there was no peeling or wrinkling of the laminated film with the un-stretched polypropylene film during heat sealing, and it had high rigidity and excellent lamination strength.

[0079] (Example 6) As shown in Table 2, it was carried out in the same manner as in Example 2 except that the film thickness was changed to 19 μm and the thickness configuration was changed to surface layer B / substrate layer A / surface layer B = 2 / 15 / 2 μm. As shown in Table 3, there was no peeling or wrinkling of the laminated film during heat sealing, and it had high rigidity and excellent lamination strength.

[0080] (Comparative Example 1) As shown in Table 2, a film with a film thickness of 19 μm was obtained in the same manner as in Example 2 except that a raw material with the same high mesopentad fraction as the substrate layer A was used as the raw material for the surface layer B. The thickness configuration was surface layer B / substrate layer A / surface layer B = 1 / 17 / 1 μm. As shown in Table 3, there was no peeling or wrinkling of the laminated film during heat sealing, and although it had high rigidity, its lamination strength was inferior.

[0081] (Comparative Example 2) As shown in Table 2, a film with 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 composition was surface layer B / substrate layer A / surface layer B = 1 / 17 / 1 μm. As shown in Table 3, it had high rigidity and excellent laminating strength, but peeling and wrinkles occurred in the seal portion of the laminated film during heat sealing.

[0082] (Comparative Example 3) As shown in Table 2, a film with 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 composition was surface layer B / substrate layer A / surface layer B = 1 / 17 / 1 μm. As shown in Table 3, it had high rigidity and excellent laminating strength, but peeling and wrinkles occurred in the seal portion of the laminated film during heat sealing.

[0083] (Comparative Example 4) As shown in Table 2, a film with 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 / substrate layer A / surface layer B = 1 / 15 / 1 μm. As shown in Table 3, it had high rigidity and excellent laminating strength, but peeling and wrinkles occurred in the seal portion of the laminated film during heat sealing.

[0084] (Comparative Example 5) As the polypropylene resin, 50 parts by mass of propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., FLX80E4) with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116 °C, and Tm = 163 °C was blended with 50 parts by mass of propylene homopolymer PP-3 (manufactured by Prime Polymer Co., Ltd., F-300SP) with MFR = 3.0 g / 10 min, [mmmm] = 93.8%, Tc = 112 °C, and Tm = 159 °C. To 100 parts by mass of the mixture of these propylene homopolymers, 1.4 parts by mass of stearyldiethanolamine monostearate, stearyldiethanolamine distearate, and a stearyldiethanolamine mixture (manufactured by Matsumoto Yushi Co., Ltd., KYM-4K) were added and mixed. Then, using an extruder equipped with a pelletizer, the mixture was melt-kneaded and granulated to obtain pellets of a polypropylene composition, which was used as the polypropylene resin composition for the base layer A. The mesopentad fraction of this polypropylene resin composition was 96.4%, the TmA was 161 °C, and the MFR was 5.3 g / 10 min. As shown in Table 2, a film with 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 base layer A. The thickness configuration was surface layer B / base layer A / surface layer B = 1 / 17 / 1 μm. As shown in Table 3, although it had excellent laminating strength, it had low rigidity, and peeling and wrinkles occurred in the seal part of the laminated film during heat sealing.

[0085] (Comparative Example 6) As shown in Table 2, the procedure was the same as in Example 1 except that the film thickness was changed to 19 μm and the thickness configuration was changed to surface layer B / base layer A / surface layer B = 3 / 13 / 3 μm. As shown in Table 3, although it had excellent laminating strength, it had low rigidity, and peeling and wrinkles occurred in the seal part of the laminated film during heat sealing.

[0086] (Comparative Example 7) As the polypropylene resin, 58 parts by mass of a propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., FLX80E4) with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116 °C, and Tm = 163 °C and 42 parts by mass of a propylene homopolymer PP-4 (manufactured by Nippon Polypropylene Co., Ltd., FL4) with MFR = 4.2 g / 10 min, [mmmm] = 97.3%, Tc = 112 °C, and Tm = 165 °C were blended. Using an extruder equipped with a pelletizer, the blend was melt-kneaded and granulated to obtain pellets of a polypropylene composition, which was used as the polypropylene resin composition for the surface layer B. The mesopentad fraction of this polypropylene resin composition was 98.2%, the TmB was 164 °C, and the MFR was 6.1 g / 10 min. As shown in Table 2, a film with 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 wrinkles occurred in the seal portion of the laminate film during heat sealing, and although the rigidity was high, the laminate strength was inferior.

[0087]

Table 1

[0088]

Table 2

[0089]

Table 3

Industrial Applicability

[0090] The biaxially oriented laminated polypropylene film of the present invention is excellent in heat resistance and rigidity, and also excellent in laminate strength, so it can be preferably used as a packaging material. In addition, it can not only be widely used as a substitute for biaxially oriented PET film, but is also extremely excellent in moisture resistance. Furthermore, by combining it with a sealant film made of polypropylene resin, it has excellent recyclability and can be suitably used as an environmentally considerate monomaterial packaging material. Moreover, not limited to packaging materials, it is also suitable for applications used at higher temperatures, such as insulating films for capacitors and motors, backsheets for solar cells, base films for high-barrier films provided with inorganic oxide layers and transparent conductive films such as ITO, and applications that require higher rigidity, such as separator films. Furthermore, by using coating agents, inks, laminate adhesives, etc. that were previously difficult to use, coating and printing processes at high temperatures become possible, and an improvement in production efficiency can be expected.

Claims

1. A biaxially oriented laminated polypropylene film comprising at least a base material layer A and a surface layer B, the biaxially oriented laminated polypropylene film satisfying the following requirements 1) to 8). 1) The ratio of the thickness of the base layer A to the thickness of the biaxially oriented laminated polypropylene film is 70% or more and 98% or less. 2) The mesopentad fraction of the polypropylene resin constituting the base layer A is 97.0% or more and 99.9% or less. 3) The polypropylene resin constituting the surface layer B is a propylene homopolymer, and the mesopentad fraction is 90.0% or more and 96.5% or less. 4) F5 at a tensile speed of 200 mm / min in the longitudinal direction of the biaxially oriented laminated polypropylene film is 35 MPa or more. 5) F5 at a tensile speed of 200 mm / min in the width direction of the biaxially oriented laminated polypropylene film is 95 MPa or more. 6) The heat shrinkage rate after heating at 150 °C for 5 minutes in the longitudinal direction of the biaxially oriented laminated polypropylene film is 6.0% or less. 7) The heat shrinkage rate after heating at 150 °C for 5 minutes in the width direction of the biaxially oriented laminated polypropylene film is 5.0% or less. 8) The wetting tension of the film surface of the surface layer B of the biaxially oriented laminated polypropylene film is 38 mN / m or more.

2. The biaxially oriented laminated polypropylene film according to Claim 1, wherein the haze of the biaxially oriented laminated polypropylene film is 5.0% or less.

3. The biaxially oriented laminated polypropylene film according to Claim 1 or 2, wherein the total thickness of the biaxially oriented laminated polypropylene film is 5.3 μm or more and 202 μm or less.

4. A laminate including the biaxially oriented laminated polypropylene film according to any one of Claims 1 to 3, an unstretched polypropylene film, and an adhesive layer therebetween.

5. The laminate according to Claim 4, wherein the lamination strength 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.

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