Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
  • B29C55/10—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial
  • B29C55/12—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
  • B32B7/02—Physical, chemical or physicochemical properties
  • B32B7/022—Mechanical properties
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets

Definitions

• the present invention relates to a biaxially oriented polypropylene film that has excellent rigidity and heat roll strength at low temperatures. More specifically, the present invention relates to a biaxially oriented polypropylene film that is easy to maintain the shape of a packaging bag when made into it, is less likely to deform during processing such as printing, and is also suitable for automatic packaging.
• a laminated polypropylene-based resin film obtained by laminating a non-oriented polyethylene-based resin film or a non-oriented polypropylene-based resin film and a stretched polypropylene-based resin film has sufficient seal strength, but requires a lamination process that uses organic solvents, etc., and is therefore undesirable both economically and in terms of its impact on the global environment.
• the objective of the present invention is to provide a biaxially oriented polypropylene film that has excellent rigidity and heat seal strength at low temperatures.
• the present invention has been able to solve the above problem by controlling the polypropylene resin composition and film-forming conditions of each layer of a biaxially oriented polypropylene film having at least a base layer A and a seal layer C each made of a polypropylene resin composition. That is, the present invention has the following configuration. [1] A biaxially oriented polypropylene film having a base layer A made of a polypropylene-based resin composition and a seal layer C, which satisfies the following (1) to (3).
• the sum of the stress at 5% elongation in the longitudinal direction and the stress at 5% elongation in the transverse direction of the biaxially oriented polypropylene film at 23° C. is 150 MPa or more.
• the heat seal strength is 1.0 N/15 mm or more.
• the thickness is 10 ⁇ m or more and 50 ⁇ m or less.
• a functional layer D made of a polypropylene-based resin composition is laminated on the surface of the base layer A opposite to the sealing layer C.
• the biaxially oriented polypropylene film of the present invention has high rigidity, so that when it is made into a packaging bag, the bag shape is easily maintained, and even if the film thickness is reduced, the processing workability is good. Furthermore, it has excellent heat seal strength even at low temperatures, making it suitable for automatic packaging.
• the biaxially oriented polypropylene film of the present invention will be described in more detail below.
• the biaxially oriented polypropylene film of the present invention is a biaxially oriented polypropylene film having at least a base layer A and a seal layer C each made of a polypropylene-based resin composition.
• the biaxially oriented polypropylene film of the present invention may have a two-layer structure of substrate layer A/sealing layer C, or a three-layer structure of seal layer C/substrate layer A/sealing layer C, a four-layer structure such as functional layer D/substrate layer A/intermediate layer B/sealing layer C, or functional surface layer E/substrate layer A/intermediate layer B/sealing layer C, or a five-layer structure such as seal layer C/intermediate layer B/substrate layer A/intermediate layer B/sealing layer C, or functional layer D/intermediate layer B/substrate layer A/intermediate layer B/sealing layer C.
• the base layer A, the intermediate layer B, the sealing layer C, and the functional layer D will each be described in detail below.
• the base layer A of the biaxially oriented polypropylene film of the present invention is made of a polypropylene-based resin composition mainly composed of the following polypropylene polymer.
• the term "main component" means that the proportion of the polypropylene polymer in the polypropylene-based resin composition is 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. The proportion is preferably 100% by mass or less, and may be 99% by mass or less.
• the mesopentad fraction ([mmmm]%) which is an index of stereoregularity of the polypropylene resin composition constituting the base layer A, is preferably in the range of 97.0% or more and 99.9% or less, more preferably in the range of 97.5% or more and 99.7% or less, even more preferably in the range of 98.0% or more and 99.5% or less, and particularly preferably in the range of 98.5% or more and 99.3% or less.
• the mesopentad fraction ([mmmm]%) is 97.0% or more, the crystallinity of the polypropylene resin composition is increased, the melting point, crystallinity, and crystal orientation of the crystals in the film are improved, and rigidity and heat resistance at high temperatures are easily obtained.
• the mesopentad fraction is 99.9% or less, the cost of polypropylene production is easily reduced, and the film is less likely to break during film formation.
• the mesopentad fraction is measured by the nuclear magnetic resonance method (the so-called NMR method).
• the lower limit of the MFR (230°C, 2.16 kgf) of the polypropylene resin composition constituting the base layer A is preferably 7.0 g/10 min, more preferably 7.5 g/10 min, even more preferably 8.0 g/10 min, particularly preferably 8.3 g/10 min, and most preferably 8.5 g/10 min.
• MFR Melt flow rate
• the oriented crystallization of the polypropylene-based resin composition is further promoted and the crystallinity of the film is more likely to be increased.
• entanglement of polypropylene molecular chains in the amorphous portion is reduced, making it easier to increase heat resistance.
• the upper limit of the MFR is preferably 11.0 g/10 min, more preferably 10.5 g/10 min, still more preferably 10.0 g/10 min, and particularly preferably 9.5 g/10 min. When the MFR of the polypropylene resin is 11.0 g/10 min or less, the film formability is easily maintained.
• melt flow rate can be measured in accordance with JIS K7210 at a temperature of 230° C. and a load of 2.16 kgf (unit: g/10 min).
• the polypropylene resin composition constituting the base layer A has a lower limit of mass average molecular weight (Mw)/number average molecular weight (Mn), which is an index of the breadth of the molecular weight distribution, of preferably 3.5, more preferably 4.0, even more preferably 4.5, and particularly preferably 4.8.
• the upper limit of Mw/Mn is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20.
• Mw/Mn can be obtained by gel permeation chromatography (GPC). When Mw/Mn is in the above range, it is easy to increase the amount of components having a molecular weight of 100,000 or less.
• the melting point (sometimes abbreviated as Tm) of the polypropylene resin composition constituting the base layer A is preferably 160°C or more and 180°C or less.
• the lower limit of the melting point of the polypropylene resin composition constituting the base layer A is more preferably 161°C, even more preferably 162°C, even more preferably 163°C, and even more preferably 164°C.
• Tm is 160°C or more, rigidity and heat resistance at high temperatures are easily obtained.
• the upper limit of Tm is more preferably 175°C, even more preferably 170°C, and particularly preferably 167°C.
• Tm is 180°C or less, it is easy to suppress cost increase in terms of polypropylene production, and it is difficult to break during film formation.
• the melting point is measured by a differential scanning calorimeter (DSC), and is the main endothermic peak temperature associated with melting observed when 5 mg of a sample is packed and set in an aluminum pan, melted at 230° C. for 5 minutes in a nitrogen atmosphere, 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.
• DSC differential scanning calorimeter
• the polypropylene polymer used in the base layer A is preferably a polypropylene homopolymer substantially free of ethylene and/or an ⁇ -olefin having 4 or more carbon atoms, and/or a polypropylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin having 4 or more carbon atoms content of 0.3 mol % or less.
• the ⁇ -olefin content is more preferably 0.2 mol % or less, and even more preferably 0.1 mol % or less. When the content is within the above range, the crystallinity is likely to be improved.
• Examples of the ⁇ -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, and 1-eicosene.
• the polypropylene homopolymer a blend of two or more different polypropylene homopolymers can be used.
• polypropylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component content of 4 or more carbon atoms of 0.3 mol % or less a blend of two or more different polypropylene- ⁇ -olefin copolymers having an ethylene and/or ⁇ -olefin component content of 4 or more carbon atoms of 0.3 mol % or less can be used.
• the content is preferably 10 mass% or less, more preferably 5 mass% or less, even more preferably 1 mass% or less, and particularly preferably 0 mass% based on the total polypropylene resin used in the base layer A.
• the mesopentad fraction ([mmmm]%) which is an index of stereoregularity of the polypropylene polymer used in the base layer A, is preferably in the range of 97.0% or more and 99.9% or less, more preferably in the range of 97.5% or more and 99.7% or less, even more preferably in the range of 98.0% or more and 99.5% or less, and particularly preferably in the range of 98.5% or more and 99.3% or less.
• the mesopentad fraction ([mmmm]%) is 97.0% or more, the crystallinity of the polypropylene polymer is increased, the melting point, crystallinity, and crystal orientation of the crystals in the film are improved, and rigidity and heat resistance at high temperatures are easily obtained.
• the mesopentad fraction is 99.9% or less, the cost of polypropylene production is easily reduced, and the film is less likely to break during film formation.
• the mesopentad fraction is measured by a nuclear magnetic resonance method (a so-called NMR method).
• the mesopentad fraction is obtained by dissolving 200 mg of a sample in a mixture of o-dichlorobenzene and heavy benzene in an 8:2 ratio at 135°C and measuring 13 C-NMR at 110°C.
• a method of washing the obtained polypropylene polymer powder with a solvent such as n-heptane, a method of appropriately selecting a catalyst and/or a co-catalyst, and a method of appropriately selecting components of a polypropylene resin composition are preferably employed.
• the lower limit of the melting point (Tm) of the polypropylene polymer used in the base layer A is preferably 160 ° C, more preferably 161 ° C, even more preferably 162 ° C, even more preferably 163 ° C, and even more preferably 164 ° C.
• Tm melting point
• the upper limit of Tm is preferably 180 ° C, more preferably 175 ° C, even more preferably 170 ° C, even more preferably 167 ° C, and particularly preferably 165 ° C.
• the melting point can also be further increased by blending a crystal nucleating agent with the above-mentioned polypropylene resin.
• the melting point is measured by a differential scanning calorimeter (DSC), and is the main endothermic peak temperature associated with melting observed when 5 mg of a sample is packed and set in an aluminum pan, melted at 230° C. for 5 minutes in a nitrogen atmosphere, 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.
• DSC differential scanning calorimeter
• the lower limit of the MFR (230°C, 2.16 kgf) of the polypropylene polymer used in the base layer A is preferably 7.0 g/10 min, more preferably 7.5 g/10 min, even more preferably 8.0 g/10 min, particularly preferably 8.3 g/10 min, and most preferably 8.5 g/10 min.
• MFR Melt flow rate
• the upper limit of the MFR is preferably 11.0 g/10 min, more preferably 10.5 g/10 min, still more preferably 10.0 g/10 min, and particularly preferably 9.5 g/10 min.
• the MFR of the polypropylene resin is 11.0 g/10 min or less, the film formability is easily maintained.
• the polypropylene polymer used in the base layer A has a lower limit of mass average molecular weight (Mw)/number average molecular weight (Mn), which is an index of the breadth of the molecular weight distribution, of preferably 3.5, more preferably 4.0, even more preferably 4.5, particularly preferably 4.8, and most preferably 5.0.
• the upper limit of Mw/Mn is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20.
• Mw/Mn can be obtained by gel permeation chromatography (GPC). When Mw/Mn is in the above range, it is easy to increase the amount of components having a molecular weight of 100,000 or less.
• the molecular weight distribution of polypropylene polymers can be adjusted by polymerizing components of different molecular weights in a series of plants in multiple stages, blending components of different molecular weights offline in a kneader, polymerizing by blending catalysts with different performance, or using a catalyst that can achieve the desired molecular weight distribution.
• the shape of the molecular weight distribution obtained by GPC may be a gentle molecular weight distribution with a single peak in a GPC chart with the logarithm (logM) of molecular weight (M) on the horizontal axis and the differential distribution value (weight fraction per logM) on the vertical axis, or a molecular weight distribution with multiple peaks or shoulders.
• the polypropylene resin composition constituting the base layer A preferably contains a polypropylene polymer having a large Mw/Mn value in order to maintain film formability.
• the lower limit of Mw/Mn is preferably 9.0, more preferably 9.2, even more preferably 9.4, and particularly preferably 9.6.
• the upper limit of Mw/Mn is preferably 11.0, more preferably 10.8, even more preferably 10.6, particularly preferably 10.4, and most preferably 10.2.
• the lower limit of the content of the polypropylene polymer having a large Mw/Mn value is preferably 10.0 mass%, more preferably 10.5 mass%, further preferably 11.0 mass%, and particularly preferably 11.5 mass%.
• the upper limit of the content of the polypropylene resin having a large Mw/Mn value is preferably 30.0 mass%, more preferably 29.5 mass%, further preferably 28.0 mass%, and particularly preferably 27.5 mass%.
• the content of the polypropylene resin having a large Mw/Mn value is 30.0 mass% or less, the crystallinity of the polypropylene resin composition can be increased, and rigidity and heat resistance can be obtained.
• the lower limit of the amount of components having a molecular weight of 100,000 or less in the GPC cumulative curve of the polypropylene polymer used in the base layer A is preferably 35 mass%, more preferably 38 mass%, even more preferably 40 mass%, particularly preferably 41 mass%, and most preferably 42 mass%.
• the upper limit of the amount of components having a molecular weight of 100,000 or less in the GPC cumulative curve is preferably 65% by mass, more preferably 60% by mass, and even more preferably 58% by mass. When the amount of components having a molecular weight of 100,000 or less in the GPC cumulative curve is 65% by mass or less, the film strength is unlikely to decrease.
• the amount of components having a molecular weight of 100,000 or less contained in the polypropylene polymer can be easily adjusted without significantly changing the overall viscosity, so that the film formability can be easily improved without significantly affecting the rigidity or heat shrinkage.
• the polypropylene polymer having a large Mw/Mn value used in the base layer A is preferably a polypropylene homopolymer substantially free of ethylene and/or an ⁇ -olefin having 4 or more carbon atoms, and/or a polypropylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin having 4 or more carbon atoms content of 0.3 mol % or less.
• the ⁇ -olefin content is more preferably 0.2 mol % or less, and even more preferably 0.1 mol % or less. When the content is within the above range, the crystallinity is likely to be improved.
• Examples of the ⁇ -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, and 1-eicosene.
• the polypropylene homopolymer having a large Mw/Mn value a blend of two or more different polypropylene homopolymers can be used.
• polypropylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component content of 4 or more carbon atoms of 0.3 mol % or less a blend of two or more different polypropylene- ⁇ -olefin copolymers having an ethylene and/or ⁇ -olefin component content of 4 or more carbon atoms of 0.3 mol % or less can be used.
• the content of the ethylene and/or ⁇ -olefins having 4 or more carbon atoms in the entire polypropylene resin used in the base layer A is preferably 10 mass% or less, more preferably 5 mass% or less, even more preferably 1 mass% or less, and particularly preferably 0 mass%.
• the mesopentad fraction ([mmmm]%) which is an index of stereoregularity of the polypropylene polymer having a large Mw/Mn value used in the base layer A, is preferably in the range of 97.0% or more and 99.9% or less, more preferably in the range of 97.5% or more and 99.7% or less, even more preferably in the range of 98.0% or more and 99.5% or less, and particularly preferably in the range of 98.5% or more and 99.3% or less.
• the mesopentad fraction ([mmmm]%) is 97.0% or more, the crystallinity of the polypropylene polymer is increased, the melting point, crystallinity, and crystal orientation of the crystals in the film are improved, and rigidity and heat resistance at high temperatures are easily obtained. When it is 99.9% or less, the cost of polypropylene production is easily reduced, and the film is less likely to break during film formation.
• the mesopentad fraction is measured by the nuclear magnetic resonance method (the so-called NMR method).
• a method of washing the obtained polypropylene polymer powder with a solvent such as n-heptane, a method of appropriately selecting a catalyst and/or a co-catalyst, and a method of appropriately selecting components of a polypropylene resin composition are preferably adopted.
• the lower limit of the melting point (Tm) of the polypropylene polymer having a large Mw/Mn value used in the base layer A is preferably 160°C, more preferably 161°C, even more preferably 162°C, even more preferably 163°C, and even more preferably 164°C.
• Tm melting point
• the upper limit of Tm is preferably 180°C, more preferably 175°C, even more preferably 170°C, and particularly preferably 167°C.
• the melting point can also be further increased by blending a crystal nucleating agent with the above-mentioned polypropylene resin.
• the melting point is measured by a differential scanning calorimeter (DSC), and is the main endothermic peak temperature associated with melting observed when 5 mg of a sample is packed and set in an aluminum pan, melted at 230° C. for 5 minutes in a nitrogen atmosphere, 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.
• DSC differential scanning calorimeter
• the lower limit of the MFR (230°C, 2.16 kgf) of the polypropylene polymer having a large Mw/Mn value used in the base layer A is preferably 7.0 g/10 min, more preferably 7.5 g/10 min, even more preferably 8.0 g/10 min, particularly preferably 8.3 g/10 min, and most preferably 8.5 g/10 min.
• MFR Melt flow rate
• the upper limit of the MFR is preferably 11.0 g/10 min, more preferably 10.5 g/10 min, still more preferably 10.0 g/10 min, and particularly preferably 9.5 g/10 min.
• the MFR of the polypropylene resin is 11.0 g/10 min or less, the film formability is easily maintained.
• the polypropylene polymer used in the polypropylene resin composition constituting the base layer A preferably has a melting point of 160°C or higher, and the polypropylene polymer having a melting point of 160°C or higher preferably accounts for 70% by mass or more of the entire polypropylene resin composition constituting the base layer A, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.
• the lower limit of the amount of components having a molecular weight of 100,000 or less in the GPC cumulative curve of the polypropylene polymer having a large Mw/Mn value used in the base layer A is preferably 35 mass%, more preferably 38 mass%, even more preferably 40 mass%, particularly preferably 41 mass%, and most preferably 42 mass%.
• the upper limit of the amount of components having a molecular weight of 100,000 or less in the GPC cumulative curve is preferably 65% by mass, more preferably 60% by mass, and even more preferably 58% by mass. When the amount of components having a molecular weight of 100,000 or less in the GPC cumulative curve is 65% by mass or less, the film strength is unlikely to decrease.
• the amount of components having a molecular weight of 100,000 or less contained in the polypropylene polymer can be easily adjusted without significantly changing the overall viscosity, so that the film formability can be easily improved without significantly affecting the rigidity or heat shrinkage.
• An anti-fogging agent may be contained in the polypropylene resin composition constituting the base layer A.
• Typical examples of the anti-fogging agent include fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines or amides of higher fatty acids.
• the amount of the antifogging agent present in the substrate layer A is preferably 0.3 mass % or more and 2.0 mass % or less, more preferably 0.4 mass % or more and 1.9 mass % or less, and even more preferably 0.5 mass % or more and 1.8 mass % or less.
• the polypropylene resin composition constituting the base layer A may contain known heat stabilizers, antioxidants, ultraviolet absorbers, etc., as long as the effects of the present invention are not impaired.
• the anti-fog agent and other additives can be added directly to the extruder during film production, but it is preferable to prepare a masterbatch in advance that contains a high concentration of additives based on a polypropylene polymer as the base resin, and then add this masterbatch to the extruder during film production, as this allows the additives to be mixed uniformly.
• a polypropylene polymer having a melting point of less than 160°C such as a low stereoregular polypropylene polymer or a polypropylene- ⁇ -olefin copolymer, may be used as long as the polypropylene resin composition constituting the base layer A can be within the above-mentioned range, but the content is preferably 5% by mass or less, more preferably 3% by mass or less, based on the entire polypropylene resin composition constituting the base layer A. The content is preferably 0% by mass. In other words, it is preferable not to use a polypropylene polymer having a melting point of less than 160°C as the base resin of the masterbatch.
• the intermediate layer B is preferably made of a polypropylene-based resin composition containing 70% by mass or more of ethylene and/or a propylene- ⁇ -olefin copolymer having an ⁇ -olefin component content of 4 mol% or less.
• the melting point of the polypropylene-based resin composition constituting the intermediate layer B is preferably 150° C. or more and 160° C. or less.
• the lower limit of the melting point (sometimes abbreviated as Tm) of the polypropylene-based resin composition constituting the intermediate layer B is more preferably 152° C., even more preferably 154° C., and even more preferably 156° C.
• Tm is 150° C. or more and 160° C. or less, crystallization of the seal layer C due to the influence of the base layer A can be suppressed, and therefore a decrease in the heat seal strength of the film can be suppressed.
• the melting point is measured by a differential scanning calorimeter (DSC), and is the main endothermic peak temperature associated with melting observed when 5 mg of a sample is packed and set in an aluminum pan, melted at 230° C. for 5 minutes in a nitrogen atmosphere, 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.
• DSC differential scanning calorimeter
• propylene- ⁇ -olefin copolymer having an amount of 4 mol % or less of ethylene and/or an ⁇ -olefin having 4 or more carbon atoms
• at least one propylene-based copolymer selected from the group consisting of a propylene-butene copolymer, a propylene-ethylene-butene copolymer, and a propylene-ethylene copolymer is preferable.
• the propylene- ⁇ -olefin copolymer having ethylene and/or ⁇ -olefins having 4 or more carbon atoms of 4 mol% or less is preferably contained in the polypropylene resin composition constituting the intermediate layer B at 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more.
• the content of the propylene- ⁇ -olefin copolymer having ethylene and/or ⁇ -olefins having 4 or more carbon atoms of 4 mol% or less in the polypropylene resin composition constituting the intermediate layer B is preferably 100% by mass or less, and may be 99% by mass or less.
• the interlayer strength between the seal layer C and the intermediate layer B can be increased.
• the crystallization of the base layer A can be prevented from propagating to the seal layer C, and the heat seal strength as a biaxially oriented polypropylene film can be easily increased.
• the propylene- ⁇ -olefin copolymer containing 4 mol% or less of ethylene and/or ⁇ -olefins having 4 or more carbon atoms contained in the polypropylene resin composition constituting the intermediate layer B at least one polypropylene copolymer selected from the group consisting of propylene-butene copolymer, propylene-ethylene-butene copolymer, and propylene-ethylene copolymer is preferred. Preferred embodiments are shown below.
• the content of ethylene and/or butene in the propylene-ethylene-butene copolymer is preferably 20 mol% or less, more preferably 5 mol% or less.
• the content of ethylene and/or butene is 20 mol% or less, the rigidity and heat resistance are improved by crystallization.
• the lower limit of the content of ethylene and/or butene is not particularly limited, if the content of ethylene and/or butene is too small, the crystallization propagation caused by the base layer A cannot be suppressed completely, and the crystallization of the seal layer C progresses, resulting in a decrease in the heat seal strength of the film.
• the content of ethylene and/or butene in the propylene-ethylene-butene copolymer is preferably 0.1 mol% or more.
• the butene content in the propylene-ethylene-butene copolymer is preferably 20 mol% or less, more preferably 5 mol% or less.
• the rigidity and heat resistance are improved by crystallization.
• the lower limit of the butene content is not particularly limited, if the butene content is too low, the crystallization propagation caused by the base layer A cannot be suppressed completely, and the crystallization of the seal layer C progresses, resulting in a decrease in the heat seal strength of the film. Therefore, the butene content in the propylene-ethylene-butene copolymer is preferably 0.1 mol% or more.
• the butene content in the propylene-butene copolymer is preferably 20 mol% or less, more preferably 5 mol% or less.
• the butene content is 20 mol% or less, the rigidity and heat resistance are improved by crystallization.
• the lower limit of the butene content is not particularly limited, if the butene content is too low, the crystallization propagation caused by the base layer A cannot be suppressed completely, and the crystallization of the seal layer C progresses, resulting in a decrease in the heat seal strength of the film. Therefore, the butene content in the propylene-butene copolymer is preferably 0.1 mol% or more.
• the ethylene content in the propylene-ethylene copolymer is preferably 20 mol% or less, more preferably 7 mol% or less, and even more preferably 4 mol% or less.
• the ethylene content in the propylene-ethylene copolymer is preferably 20 mol% or less, more preferably 7 mol% or less, and even more preferably 4 mol% or less.
• the ethylene content in the propylene-ethylene copolymer is preferably 0.2 mol% or more.
• the lower limit of the melt flow rate (MFR) (230°C, 2.16 kgf) of the propylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component amount of 4 mol% or less contained in the polypropylene resin composition constituting the intermediate layer B is preferably 3.0 g/10 min, more preferably 3.5 g/10 min, even more preferably 4.0 g/10 min, and particularly preferably 4.3 g/10 min.
• the upper limit is preferably 9.0 g/10 min, more preferably 8.5 g/10 min, even more preferably 8.0 g/10 min, and most preferably 7.8 g/10 min.
• An anti-fogging agent may be contained in the polypropylene resin composition constituting the intermediate layer B.
• Typical examples of the anti-fogging agent include fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines or amides of higher fatty acids.
• the amount of the antifogging agent present in the intermediate layer B is preferably 0.3% by mass or more and 2.0% by mass or less, but the antifogging agent which has migrated from the substrate layer A may also be present.
• the polypropylene resin composition constituting the intermediate layer B may contain known heat stabilizers, antioxidants, ultraviolet absorbers, etc., so long as the effects of the present invention are not impaired.
• the sealing layer C is composed of a polypropylene-based resin composition mainly composed of a propylene- ⁇ -olefin copolymer in which the copolymerization component amount of ethylene and/or an ⁇ -olefin having 4 or more carbon atoms is 4 mol % or more.
• the term "main component" means that the proportion of the propylene- ⁇ -olefin copolymer in the polypropylene resin composition is 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. The proportion is preferably 100% by mass or less, and may be 99% by mass or less.
• the heat of fusion of the sealing layer C at 70°C to 140°C in DSC measurement is preferably 10 J/g or more and 40 J/g or less, more preferably 10.5 J/g or more, even more preferably 11 J/g or more, and particularly preferably 11.5 J/g or more.
• the upper limit of the heat of fusion is preferably 40 J/g, more preferably 35 J/g, even more preferably 30 J/g, and particularly preferably 25 J/g.
• the heat of fusion of the sealing layer C from 70°C to 140°C was measured using a differential scanning calorimeter (DSC).
• the surface of the sealing layer C of the biaxially oriented polypropylene film was scraped using a razor blade to prepare a measurement sample, and 5.0 ⁇ 0.2 mg of the sample was packed and set in an aluminum pan.
• the DSC curve was scanned from -30°C to 250°C at a heating rate of 20°C/min under a nitrogen atmosphere, and the heat of fusion from 70°C to 140°C was calculated.
• the low-temperature sealability is a property that allows sufficient heat seal strength to be obtained even when the temperature of the seal bar during heat sealing is relatively low. Specifically, when the heat seal strength of the seal layer C at 115°C obtained by the measurement method described below is 1.0 N/15 mm or more, the low-temperature sealability is good, and even when the temperature of the seal bar during heat sealing is relatively low, sufficient heat seal strength of 3.0 N/15 mm or more is easily obtained. Therefore, it can be operated at high speed during automatic packaging. In addition, since the heat seal processing can be performed at a lower temperature, the entire film is less likely to shrink and wrinkles are less likely to occur in the sealed portion.
• the melting point of the polypropylene resin composition constituting the seal layer C is preferably 110° C. or higher and 135° C. or lower. When the melting point is 135° C. or lower, low-temperature sealability is easily obtained. When the melting point is 110° C. or higher, the rigidity of the seal layer C is prevented from decreasing too much, and as a result, the rigidity of the entire film is easily maintained.
• the melting point is measured by a differential scanning calorimeter (DSC), and is the main endothermic peak temperature associated with melting observed when 1 to 10 mg of a sample is packed and set in an aluminum pan, melted at 230° C. for 5 minutes in a nitrogen atmosphere, 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.
• DSC differential scanning calorimeter
• the propylene- ⁇ -olefin copolymer containing 4 mol % or more of ethylene and/or ⁇ -olefin having 4 or more carbon atoms contained in the polypropylene resin composition constituting the seal layer C is preferably at least one propylene- ⁇ -olefin copolymer selected from the group consisting of a propylene-butene copolymer, a propylene-ethylene-butene copolymer, and a propylene-ethylene copolymer.
• a preferred embodiment is shown below.
• the butene content in the propylene-butene copolymer is preferably 3 mol % or more, and more preferably 20 mol % or more.
• the butene content in the propylene-butene copolymer is preferably 30 mol% or less.
• Examples of the propylene-butene copolymer with a high butene content include "SPX78J1" manufactured by Sumitomo Chemical Co., Ltd. and "XR110H” manufactured by Mitsui Chemicals, Inc.
• the ethylene and/or butene content in the propylene-ethylene-butene copolymer is preferably 3 mol% or more, more preferably 5 mol% or more.
• the upper limit of the ethylene and/or butene content is not particularly limited, but if the ethylene and/or butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so it may be appropriately determined within a range that does not cause such defects.
• the ethylene and/or butene content in the propylene-ethylene-butene copolymer is preferably 20 mol% or less.
• the propylene-ethylene-butene copolymer with a high ethylene and/or butene content is "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd.
• the butene content in the propylene-ethylene-butene copolymer is preferably 3 mol% or more, more preferably 5 mol% or more.
• the upper limit of the ethylene and/or butene content is not particularly limited, but if the ethylene and/or butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so it may be appropriately determined within a range that does not cause such defects.
• the butene content in the propylene-ethylene-butene copolymer is preferably 20 mol% or less.
• An example of the propylene-ethylene-butene copolymer with a high butene content is "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd.
• the ethylene content in the propylene-ethylene copolymer is preferably 3 mol% or more, more preferably 4 mol% or more.
• the upper limit of the ethylene content is not particularly limited, but if the ethylene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so it may be appropriately determined within a range that does not cause such defects.
• the ethylene content in the propylene-ethylene copolymer is preferably 30 mol% or less. Examples of the propylene-ethylene copolymer with a high ethylene content include "PC540R” manufactured by SunAllomer Co., Ltd. and "VM3588FL” manufactured by Mitsui Chemicals, Inc.
• the lower limit of the melt flow rate (MFR) (230°C, 2.16 kgf) of the propylene- ⁇ -olefin copolymer containing 4 mol% or more of ethylene and/or ⁇ -olefins having 4 or more carbon atoms contained in the polypropylene resin composition constituting the seal layer C is preferably 5.0 g/10 min, more preferably 5.5 g/10 min, even more preferably 6.0 g/10 min, and particularly preferably 6.3 g/10 min.
• the upper limit is preferably 8.0 g/10 min, more preferably 7.5 g/10 min, and even more preferably 7.0 g/10 min.
• the maximum heat seal strength can be increased, and the sealability of the bag after bag formation can be easily improved.
• the polypropylene resin composition constituting the seal layer C preferably contains 50% by mass or more and 90% by mass or less of a polypropylene resin having a mid-melting point of 115° C. or more and 145° C. or less, preferably a polypropylene copolymer.
• the lower limit of the melting point of the mid-melting polypropylene copolymer is preferably 120° C., more preferably 125° C.
• the upper limit of the melting point of the mid-melting point polypropylene-based copolymer is preferably 135° C., more preferably 130° C. By setting the melting point to 135° C. or less, it is possible to increase the melting enthalpy in the low-temperature region of the seal layer C, and it is possible to exhibit sealability at low temperatures.
• the lower limit of the proportion of the mid-melting point polypropylene-based copolymer is preferably 53% by mass, more preferably 56% by mass. By making it 50% by mass or more, it is possible to increase the heat of fusion in the low-temperature region of the seal layer C, and it is possible to exhibit sealability at low temperatures.
• the upper limit of the proportion of the mid-melting point polypropylene copolymer is preferably 80% by mass, more preferably 70% by mass. By making it 90% by mass or less, the 5% elongation stress at 23° C. can be kept high and rigidity can be obtained.
• the polypropylene-based copolymer having a medium melting point is preferably a propylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component content of more than 6 mol % having 4 or more carbon atoms, for example, at least one polypropylene-based copolymer selected from the group consisting of a propylene-butene copolymer, a propylene-ethylene-butene copolymer, and a propylene-ethylene copolymer.
• the preferred embodiment is the same as described above, but by increasing the content of the copolymerization component, a polypropylene-based copolymer having a low melting point can be obtained.
• the polypropylene resin composition constituting the seal layer C preferably contains 30% by mass or more and 50% by mass or less of a low-melting polypropylene resin having a melting point of 60° C. or more and 90° C. or less, preferably a polypropylene copolymer.
• the lower limit of the melting point of the low-melting polypropylene copolymer is preferably 60° C., more preferably 64° C., and particularly preferably 68° C.
• the upper limit of the melting point of the low melting point polypropylene-based copolymer is preferably 90° C., more preferably 86° C., and particularly preferably 82° C. By setting the melting point to 90° C. or less, it is possible to increase the melting enthalpy in the low temperature region of the seal layer C, and it is possible to exhibit sealability at low temperatures.
• the lower limit of the proportion of the low melting point polypropylene copolymer is preferably 30% by mass, more preferably 33% by mass, and particularly preferably 36% by mass. By making it 30% by mass or more, it is possible to increase the heat of fusion of the low temperature region of the seal layer C, and it is possible to exhibit sealability at low temperatures.
• the upper limit of the proportion of the low melting point polypropylene copolymer is preferably 50% by mass, more preferably 47% by mass, and particularly preferably 44% by mass. By making it 50% by mass or less, the 5% elongation stress at 23° C. can be kept high and rigidity can be obtained.
• the low melting point polypropylene copolymer is preferably a propylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component content of 4 or more carbon atoms of more than 6 mol%, and is preferably at least one polypropylene copolymer selected from the group consisting of a propylene-butene copolymer, a propylene-ethylene-butene copolymer, and a propylene-ethylene copolymer.
• the preferred embodiment is the same as described above, but by increasing the content of the copolymerization component, a low melting point polypropylene copolymer can be obtained.
• An anti-fogging agent may be contained in the polypropylene resin composition constituting the seal layer C.
• Typical examples of the anti-fogging agent include fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines or amides of higher fatty acids.
• the amount of the antifogging agent present in the sealing layer C is preferably 0.1% by mass or more and 1.0% by mass or less, but may be an antifogging agent that has migrated from the substrate layer A and the intermediate layer B.
• the polypropylene resin composition constituting the sealing layer C can also be blended with various additives for improving qualities such as slipperiness and antistatic properties, such as lubricants such as wax and metal soap, plasticizers, processing aids, and known heat stabilizers, antioxidants, antistatic agents, and ultraviolet absorbers that are commonly added to polypropylene films.
• additives for improving qualities such as slipperiness and antistatic properties, such as lubricants such as wax and metal soap, plasticizers, processing aids, and known heat stabilizers, antioxidants, antistatic agents, and ultraviolet absorbers that are commonly added to polypropylene films.
• the functional layer D is a layer made of a polypropylene-based resin composition laminated on the surface of the base layer A opposite to the seal layer C.
• the functional layer D is a layer for imparting a function not present in the base layer A.
• the functional layer D is a functional layer that imparts easy slippage between films or between a film and a processing tool, a functional layer that is imparted with antistatic functionality, or a functional layer that is imparted with easy adhesion to a coating layer, an adhesive layer, a vapor deposition layer, or the like.
• the functional layer D can also be a functional layer with heat sealability.
• the functional layer D in order to maintain the packaging form, such as gusset packaging, the heat seal portion after bag making is folded to bond the exteriors of the package to each other, and the bag can be easily opened by hand, the functional layer D can be a seal layer having a heat seal reaching strength weaker than that of the seal layer C.
• the heat seal strength of the functional layer D at 130 ° C is preferably 1.0 N / 15 mm or more. If it is 1.0 N / 15 mm or more, the heat seal portion after bag making can be folded to bond the exteriors of the package to each other in order to maintain the packaging form, such as gusset packaging.
• the upper limit of the heat seal strength of the functional layer D at 130 ° C is preferably equal to or less than the heat seal strength of the seal layer C at 130 ° C, for example, 2.5 N / 15 mm or less. If it is 2.5 N / 15 mm or less, the bag can be easily opened by hand at the part where the exteriors of the package are bonded to each other.
• the heat seal strength of the functional layers D can be measured by overlapping the functional layers D facing each other, at each temperature, with a heat seal pressure of 1 kg/cm 2 , a heat seal time of 1 second, and a pulling speed of 200 mm/min.
• polypropylene resin composition constituting the functional layer D in order to impart slipperiness while maintaining high rigidity to the biaxially oriented polypropylene film, it is preferable to use a polypropylene resin composition having a melting point of 160°C or more and 180°C or less, similar to that of the base layer A, as described below.
• the polypropylene polymer used in the functional layer D is preferably a polypropylene homopolymer substantially free of ethylene and/or an ⁇ -olefin having 4 or more carbon atoms, and/or a polypropylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin having 4 or more carbon atoms content of 0.3 mol % or less.
• the ⁇ -olefin content is more preferably 0.2 mol % or less, and even more preferably 0.1 mol % or less. When the content is within the above range, the crystallinity is likely to be improved.
• Examples of the ⁇ -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, and 1-eicosene.
• the polypropylene homopolymer a blend of two or more different polypropylene homopolymers can be used.
• polypropylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component content of 4 or more carbon atoms of 0.3 mol % or less a blend of two or more different polypropylene- ⁇ -olefin copolymers having an ethylene and/or ⁇ -olefin component content of 4 or more carbon atoms of 0.3 mol % or less can be used.
• the mesopentad fraction ([mmmm]%) which is an index of stereoregularity of the polypropylene polymer used in the functional layer D, is preferably in the range of 97.0% or more and 99.9% or less, more preferably in the range of 97.5% or more and 99.7% or less, even more preferably in the range of 98.0% or more and 99.5% or less, and particularly preferably in the range of 98.5% or more and 99.3% or less.
• the mesopentad fraction ([mmmm]%) is 97.0% or more, the crystallinity of the polypropylene polymer is increased, the melting point, crystallinity, and crystal orientation of the crystals in the film are improved, and rigidity and heat resistance at high temperatures are easily obtained. When it is 99.9% or less, the cost of polypropylene production is easily reduced, and the film is less likely to break during film formation.
• the mesopentad fraction is measured by the nuclear magnetic resonance method (the so-called NMR method).
• a method of washing the obtained polypropylene polymer powder with a solvent such as n-heptane, a method of appropriately selecting a catalyst and/or a co-catalyst, and a method of appropriately selecting components of a polypropylene resin composition are preferably employed.
• the lower limit of the melting point (Tm) of the polypropylene polymer used in the functional layer D is preferably 160 ° C, more preferably 161 ° C, even more preferably 162 ° C, even more preferably 163 ° C, and even more preferably 164 ° C.
• Tm melting point
• the upper limit of Tm is preferably 180 ° C, more preferably 175 ° C, even more preferably 170 ° C, and particularly preferably 167 ° C.
• Tm is 180 ° C or less, it is easy to suppress the increase in cost in terms of polypropylene production, and it is difficult to break during film formation.
• the melting point can also be further increased by blending a crystal nucleating agent with the above-mentioned polypropylene resin.
• the melting point is measured by a differential scanning calorimeter (DSC), and is the main endothermic peak temperature associated with melting observed when 5 mg of a sample is packed and set in an aluminum pan, melted at 230° C. for 5 minutes in a nitrogen atmosphere, 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.
• Tm melting point
• the melting point (Tm) is 160° C. or higher, the crystallinity of the polypropylene polymer is increased, the melting point and the degree of crystallization of the crystals in the film are improved, and heat resistance is easily obtained.
• the lower limit of the MFR (230°C, 2.16 kgf) of the polypropylene polymer used in the functional layer D is preferably 7.0 g/10 min, more preferably 7.5 g/10 min, even more preferably 8.0 g/10 min, particularly preferably 8.3 g/10 min, and most preferably 8.5 g/10 min.
• MFR Melt flow rate
• the upper limit of the MFR is preferably 11.0 g/10 min, more preferably 10.5 g/10 min, still more preferably 10.0 g/10 min, and particularly preferably 9.5 g/10 min.
• the MFR of the polypropylene resin is 11.0 g/10 min or less, the film formability is easily maintained.
• the polypropylene polymer used in the functional layer D has a lower limit of mass average molecular weight (Mw)/number average molecular weight (Mn), which is an index of the breadth of the molecular weight distribution, of preferably 3.5, more preferably 4.0, even more preferably 4.5, and particularly preferably 5.0.
• the upper limit of Mw/Mn is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20.
• Mw/Mn can be obtained by gel permeation chromatography (GPC). When Mw/Mn is in the above range, it is easy to increase the amount of components having a molecular weight of 100,000 or less.
• the content is preferably 10 mass% or less, more preferably 5 mass% or less, even more preferably 1 mass% or less, and particularly preferably 0 mass% relative to the total polypropylene resin used in the base layer A.
• the polypropylene polymer used in the functional layer D is preferably a propylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component content of 4 mol % or less, such as at least one propylene-based copolymer selected from the group consisting of a propylene-butene copolymer, a propylene-ethylene-butene copolymer, and a propylene-ethylene copolymer.
• the propylene- ⁇ -olefin copolymer having an amount of ethylene and/or an ⁇ -olefin having 4 or more carbon atoms of 4 mol% or less is preferably contained in the polypropylene-based resin composition constituting the functional layer D at 80 mass% or more, more preferably 90 mass% or more, and particularly preferably 95 mass% or more.
• the interlayer strength between the seal layer C and the intermediate layer B can be increased, while if it is 95 mass% or less, it is easy to increase the interlayer strength between the base layer A and the intermediate layer B.
• propylene- ⁇ -olefin copolymer containing 4 mol% or less of ethylene and/or ⁇ -olefins having 4 or more carbon atoms contained in the polypropylene resin composition constituting the functional layer D at least one polypropylene copolymer selected from the group consisting of propylene-butene copolymer, propylene-ethylene-butene copolymer, and propylene-ethylene copolymer is preferred. Preferred embodiments are shown below.
• the content of ethylene and/or butene in the propylene-ethylene-butene copolymer is preferably 7 mol% or less, more preferably 5 mol% or less.
• the content of ethylene and/or butene is 7 mol% or less, the rigidity and heat resistance are improved by crystallization.
• the lower limit of the content of ethylene and/or butene is not particularly limited, when the content of ethylene and/or butene is too small, the crystallization of the base layer A cannot be prevented from being propagated to the functional layer D, and the surface of the functional layer D cannot be easily adhered to a coating layer, an adhesive layer, a vapor deposition layer, etc.
• the content of ethylene and/or butene in the propylene-ethylene-butene copolymer is preferably 1 mol% or more.
• the butene content in the propylene-ethylene-butene copolymer is preferably 7 mol% or less, more preferably 5 mol% or less.
• the rigidity and heat resistance are improved by crystallization.
• the lower limit of the butene content is not particularly limited, when the butene content is too small, the crystallization of the base layer A cannot be prevented from propagating to the functional layer D, and the surface of the functional layer D cannot be easily adhered to a coating layer, an adhesive layer, a vapor deposition layer, etc. Therefore, the butene content in the propylene-ethylene-butene copolymer is preferably 1 mol% or more.
• the butene content in the propylene-butene copolymer is preferably 20 mol% or less, more preferably 10 mol% or less.
• the rigidity and heat resistance are improved by crystallization.
• the lower limit of the butene content is not particularly limited, when the butene content is too small, the crystallization of the base layer A cannot be prevented from propagating to the functional layer D, and the surface of the functional layer D cannot be easily adhered to a coating layer, an adhesive layer, a vapor deposition layer, etc. Therefore, the butene content in the propylene-butene copolymer is preferably 1 mol% or more.
• the ethylene content in the propylene-ethylene copolymer is preferably 10 mol% or less, more preferably 4 mol% or less.
• the ethylene content in the propylene-ethylene copolymer is preferably 1 mol% or more.
• the lower limit of the melt flow rate (MFR) (230°C, 2.16 kgf) of the propylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component amount of 4 mol% or less contained in the polypropylene resin composition constituting the functional layer D is preferably 3.0 g/10 min, more preferably 3.5 g/10 min, even more preferably 4.0 g/10 min, and particularly preferably 4.3 g/10 min.
• the upper limit is preferably 9.0 g/10 min, more preferably 8.5 g/10 min, even more preferably 8.0 g/10 min, and most preferably 7.8 g/10 min.
• the melting point of the polypropylene resin composition constituting the functional layer D is preferably 110° C. or more and 140° C. or less. When the melting point is 140° C. or less, low-temperature sealability is easily obtained. When the melting point is 110° C. or more, the rigidity of the functional layer D is prevented from decreasing too much, and as a result, the rigidity of the entire film is easily maintained.
• the melting point is measured by a differential scanning calorimeter (DSC), and is the main endothermic peak temperature associated with melting observed when 1 to 10 mg of a sample is packed and set in an aluminum pan, melted at 230° C. for 5 minutes in a nitrogen atmosphere, 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.
• DSC differential scanning calorimeter
• propylene- ⁇ -olefin copolymer containing 4 mol % or more of ethylene and/or ⁇ -olefins having 4 or more carbon atoms contained in the polypropylene resin composition constituting the functional layer D for example, at least one propylene- ⁇ -olefin copolymer selected from the group consisting of propylene-butene copolymer, propylene-ethylene-butene copolymer, and propylene-ethylene copolymer is preferred.
• propylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component content of 4 mol% or more
• at least one propylene- ⁇ -olefin copolymer selected from the group consisting of, for example, propylene-butene copolymer, propylene-ethylene-butene copolymer, and propylene-ethylene copolymer is preferred. Preferred embodiments are shown below.
• the butene content in the propylene-butene copolymer is preferably 3 mol % or more, and more preferably 20 mol % or more. By making it 3 mol % or more, it is easy to increase the heat seal strength and improve the sealability.
• the upper limit of the butene content is not particularly limited, but if the butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so it may be appropriately determined within a range that does not cause such defects.
• the butene content in the propylene-butene copolymer is preferably 30 mol% or less. Examples of the propylene-butene copolymer with a high butene content include "SPX78J1" manufactured by Sumitomo Chemical Co., Ltd. and "XR110H” manufactured by Mitsui Chemicals, Inc.
• the ethylene and/or butene content in the propylene-ethylene-butene copolymer is preferably 3 mol% or more, more preferably 5 mol% or more.
• the upper limit of the ethylene and/or butene content is not particularly limited, but if the ethylene and/or butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so it may be appropriately determined within a range that does not cause such defects.
• the ethylene and/or butene content in the propylene-ethylene-butene copolymer is preferably 20 mol% or less.
• the propylene-ethylene-butene copolymer with a high ethylene and/or butene content is "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd.
• the butene content in the propylene-ethylene-butene copolymer is preferably 3 mol% or more, more preferably 5 mol% or more.
• the upper limit of the butene content is not particularly limited, but if the butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so it may be appropriately determined within a range that does not cause such defects.
• the butene content in the propylene-ethylene-butene copolymer is preferably 20 mol% or less.
• An example of the propylene-ethylene-butene copolymer with a high butene content is "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd.
• the ethylene content in the propylene-ethylene copolymer is preferably 3 mol% or more, more preferably 4 mol% or more.
• the upper limit of the ethylene content is not particularly limited, but if the ethylene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so it may be appropriately determined within a range that does not cause such defects.
• the ethylene content in the propylene-ethylene copolymer is preferably 30 mol% or less. Examples of the propylene-ethylene copolymer with a high ethylene content include "PC540R” manufactured by SunAllomer Co., Ltd. and "VM3588FL” manufactured by Mitsui Chemicals, Inc.
• the lower limit of the melt flow rate (MFR) (230°C, 2.16 kgf) of the propylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component amount of 4 mol% or more contained in the polypropylene resin composition constituting the functional layer D is preferably 5.0 g/10 min, more preferably 5.5 g/10 min, even more preferably 6.0 g/10 min, and particularly preferably 6.3 g/10 min.
• the upper limit is preferably 8.0 g/10 min, more preferably 7.5 g/10 min, even more preferably 7.0 g/10 min, and most preferably 6.8 g/10 min.
• the maximum heat seal strength can be increased, and the sealability of the bag after bag formation can be easily improved.
• the polypropylene resin composition constituting the functional layer D may contain 30% by mass or more and 50% by mass or less of a low-melting polypropylene resin having a melting point of 60° C. or more and 90° C. or less, preferably a polypropylene copolymer.
• the lower limit of the melting point of the low-melting polypropylene copolymer is preferably 60° C., more preferably 64° C., and particularly preferably 68° C.
• the upper limit of the melting point of the low melting point polypropylene-based copolymer is preferably 90° C., more preferably 86° C., and particularly preferably 82° C. By setting the melting point to 90° C. or less, it is possible to increase the melting enthalpy in the low temperature region of the functional layer D, and it is possible to exhibit sealing properties at low temperatures.
• the lower limit of the proportion of the low melting point polypropylene copolymer is preferably 30% by mass, more preferably 33% by mass, and particularly preferably 36% by mass. By making it 30% by mass or more, it is possible to increase the heat of fusion in the low temperature region of the functional layer D, and it is possible to exhibit sealing properties at low temperatures.
• the upper limit of the proportion of the low melting point polypropylene copolymer is preferably 50% by mass, more preferably 47% by mass, and particularly preferably 44% by mass. By making it 50% by mass or less, the 5% elongation stress at 23° C. can be kept high and rigidity can be obtained.
• the low melting point polypropylene copolymer is preferably a propylene- ⁇ -olefin copolymer having an ethylene and/or ⁇ -olefin component content of 4 or more carbon atoms of more than 6 mol%, and is preferably at least one polypropylene copolymer selected from the group consisting of a propylene-butene copolymer, a propylene-ethylene-butene copolymer, and a propylene-ethylene copolymer.
• the preferred embodiment is the same as described above, but by increasing the content of the copolymerization component, a low melting point polypropylene copolymer can be obtained.
• An anti-fogging agent may be contained in the polypropylene resin composition constituting the functional layer D.
• Typical examples of the anti-fogging agent include fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines or amides of higher fatty acids.
• the amount of the antifogging agent present in the functional layer D is preferably 0.1 mass % or more and 1.0 mass % or less, but the antifogging agent may have migrated from the base layer A.
• the polypropylene resin composition constituting the functional layer D may contain known heat stabilizers, antioxidants, ultraviolet absorbers, etc., so long as the effects of the present invention are not impaired.
• the amount of the antifogging agent present in the biaxially oriented polypropylene film of the present invention is preferably 0.1% by weight or more and 10% by weight or less, particularly preferably 0.2% by weight or more and 5% by weight or less.
• an anti-fogging agent is added only to the base layer A during production, so that the anti-fogging agent gradually migrates to the sealing layer C during film production and storage after film formation, and the anti-fogging agent is present on the surface of the sealing layer C, thereby giving the layer anti-fogging properties.
• Fruits and vegetables are characterized by continuing their physiological activity even after harvest, and this is effective in preventing fogging that occurs after packaging.
• Examples of a method for producing the biaxially oriented polypropylene film of the present invention include a method in which melt lamination is performed by a T-die method, an inflation method, or the like using an extruder suitable for the number of layers, and then cooling is performed by a cooling roll method, a water cooling method, or an air cooling method to obtain an unstretched laminated film, and the unstretched laminated film is then stretched by a sequential biaxial stretching method, a simultaneous biaxial stretching method, a tube stretching method, or the like.
• Examples of conditions for producing a biaxially oriented polypropylene film having a structure of functional layer D/base layer A/intermediate layer B/sealing layer C by the sequential biaxial stretching method are given below.
• the polypropylene-based resin compositions constituting the base layer A, intermediate layer B, seal layer C, and functional layer D are preferably as described above.
• the amount of the antifogging agent added to the base layer A, intermediate layer B, and seal layer C is preferably adjusted taking into consideration the amount of the antifogging agent that evaporates into the atmosphere when exposed to high temperatures during the film formation process.
• a multi-layer sheet of a molten polypropylene resin composition having a structure of functional layer D/substrate layer A/intermediate layer B/sealing layer C is extruded from a T-die.
• a method for this for example, a method can be used in which each polypropylene-based resin composition is melted at a temperature of 200°C to 260°C and sent out from different flow paths using four extruders, and the resulting mixture is co-extruded while being laminated in multiple layers using a multi-layer feed block, a static mixer, a multi-layer multi-manifold die, or the like.
• the molten sheet co-extruded from the T-die into a sheet is placed on a metal cooling roll and cooled to solidify.
• a metal cooling roll In order to promote solidification, it is preferable to further cool the sheet cooled by the cooling roll, for example by immersing it in a water bath.
• the cooling roll temperature and water bath temperature are preferably set between 15°C and 40°C in order to suppress crystallization of the polypropylene resin composition and improve transparency.
• the raw sheet is heated to a temperature suitable for stretching, and then the sheet is stretched in the machine direction by utilizing the speed difference between the stretching rolls.
• the uniaxially stretched film is preheated, and then stretched in the width direction at a specific temperature while holding the film ends in a tenter type stretching machine to obtain a biaxially stretched film.
• This width direction stretching step will be described in detail later.
• the biaxially stretched film is heat-treated at a specific temperature to obtain a biaxially oriented film. In the heat treatment step, the film may be relaxed in the width direction.
• the biaxially oriented polypropylene film thus obtained can be subjected to a corona discharge treatment on at least one side, if necessary, and then wound up on a winder to obtain a film roll.
• the polypropylene-based resin compositions constituting each of the functional layer D, base layer A, intermediate layer B and seal layer C are each extruded from a different flow path using four extruders, and each polypropylene-based resin composition is melted at a temperature of 200°C to 260°C.
• the polypropylene-based resin compositions are laminated in multiple layers using a multi-manifold die, and a molten polypropylene-based resin composition multi-layer sheet having a configuration of functional layer D/base layer A/intermediate layer B/seal layer C is extruded from a T-die.
• the molten sheet co-extruded from the T-die into a sheet shape is grounded on a metal cooling roll to be cooled and solidified. At this time, it is preferable to ground the seal layer C side on the cooling roll. Alternatively, if a functional layer D is provided, the functional layer D side may be grounded on the cooling roll.
• the temperature of the cooling roll, or the cooling roll and water bath is preferably in the range of 10° C. to Tc, and when it is desired to increase the transparency of the film, it is preferable to cool and solidify the film with a cooling roll having a temperature in the range of 10 to 50° C. If the cooling temperature is 50° C. or less, the transparency of the unstretched sheet is likely to be increased, and it is preferably 40° C.
• the cooling temperature In order to increase the degree of crystal orientation after sequential biaxial stretching, it may be preferable to set the cooling temperature to 40° C. or more, but as described above, when using a propylene homopolymer having a mesopentad fraction of 97.0% or more, it is preferable to set the cooling temperature to 40° C. or less in order to easily perform the stretching in the next step and to reduce thickness unevenness, and it is more preferable to set the cooling temperature to 30° C. or less.
• the thickness of the unstretched sheet is preferably 3500 ⁇ m or less in terms of cooling efficiency, more preferably 3000 ⁇ m or less, and can be appropriately adjusted depending on the thickness of the film after sequential biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition and the lip width of the T-die, etc.
• the stress at 5% elongation in the longitudinal direction at 23°C is preferably 35 MPa or more, and in order to produce the film stably without unevenness in stretching, it is preferable to set the stretch ratio in the longitudinal direction to 4.0 times or more and 6.0 times or less.
• the lower limit of the stretch ratio in the longitudinal direction is more preferably 4.2 times.
• the upper limit of the stretch ratio in the longitudinal direction is more preferably 5.5 times from the viewpoint of ease of stretching in the transverse direction.
• the lower limit of the longitudinal stretching temperature is preferably 120° C., more preferably 125° C., and even more preferably 135° C. or more.
• the upper limit of the longitudinal stretching temperature is preferably 160° C., more preferably 155° C., and even more preferably 145° C. or less.
• the longitudinal stretching may be carried out in two or more stages using three or more pairs of stretching rolls.
• the upper limit of the temperature in the preheating step is preferably 180° C., more preferably 178° C., still more preferably 176° C., and particularly preferably not more than 172° C.
• the lower limit of the temperature in the preheating step is preferably 160° C., more preferably 162° C., and particularly preferably 164° C.
• the upper limit of the temperature in the width direction stretching step is preferably 170° C., more preferably 168° C., and particularly preferably 166° C.
• the lower limit of the temperature in the width direction stretching step is preferably 155° C., more preferably 157° C., and particularly preferably 159° C.
• the stretch ratio in the transverse direction is preferably 11.0 times or more and 14.0 times or less.
• the lower limit of the stretch ratio in the transverse direction is more preferably 11.5 times, even more preferably 12.0 times, and particularly preferably 12.5 times.
• the upper limit of the stretching ratio in the width direction is preferably 14.0 times, more preferably 13.5 times, and particularly preferably 13.0 times. By setting it to 14.0 times or less, not only can breakage during film formation be suppressed, but also a decrease in heat seal strength can be suppressed. Under a high stretching ratio, the crystallization degree of the base layer A becomes very high.
• the crystallization generated in the base layer A propagates to the seal layer C, and the melting peak of the seal layer C shifts to the high temperature side, reducing the heat of fusion at 70 ° C to 140 ° C, which is a factor that results in a decrease in low-temperature sealability, so 14.0 times or less is preferable.
• Heat treatment process In order to suppress the 120° C. heat shrinkage rate and at the same time increase the tensile elongation at break, it is preferable to carry out a heat treatment step in which the biaxially stretched film stretched in the longitudinal direction is heated while both edge portions are held by tenter clips.
• the upper limit of the temperature in the heat treatment step is preferably 180° C., more preferably 178° C., and particularly preferably 176° C.
• the lower limit of the temperature in the heat treatment step is preferably 160° C., more preferably 162° C., and particularly preferably 164° C.
• the lower limit of the temperature in the heat treatment step is preferably 160° C., more preferably 162° C., and particularly preferably 164° C.
• the molecules of the polypropylene resin in the base layer A are highly aligned in the main orientation direction (which corresponds to the width direction in the above-mentioned width direction stretching process), and therefore, the crystal orientation in the obtained biaxially oriented film is very strong, and crystals with a high melting point are likely to be produced.
• the orientation of the amorphous parts between the crystals is also increased in the main orientation direction (corresponding to the width direction in the width direction stretching process described above), and since there are many crystals with high melting points around the amorphous parts, the stretched polypropylene molecules in the amorphous parts are less likely to relax at temperatures lower than the melting points of the crystals, and tend to maintain their tensed state. Therefore, the entire biaxially oriented film can maintain high rigidity even at high temperatures. It should be noted that the adoption of such a process also tends to reduce the heat shrinkage rate at a high temperature of 120° C.
• the reason for this is that in the base material layer A, since many crystals with high melting points are present around the amorphous parts, the elongated polypropylene molecules in the amorphous parts are less likely to relax at temperatures lower than the melting points of the crystals, and moreover, there is less entanglement between the molecules.
• the orientation of the seal layer C can be weakened, the heat seal strength at low temperatures is also likely to be increased.
• the heat shrinkage rate at a high temperature of 120° C. is also likely to decrease, while the tensile elongation at break is likely to increase.
• an anti-fogging agent is present, the anti-fogging properties of the final biaxially oriented film are also likely to be improved.
• a corona discharge treatment on the surface of the sealing layer C using a corona discharge treatment machine to increase the surface tension of the sealing layer C.
• a corona discharge treatment machine it is preferable to perform a surface treatment on the base layer A or the functional layer D in order to improve printability, lamination property, etc.
• the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, acid treatment, etc., and there is no particular limitation. It is preferable to perform corona discharge treatment, plasma treatment, or flame treatment, which can be performed continuously and can be easily performed before the winding step in the production process of this film.
• the biaxially oriented polypropylene film of the present invention has a base layer A and a seal layer C. It is preferable to provide an intermediate layer B between the base layer A and the seal layer C.
• the layer structure of the biaxially oriented polypropylene film of the present invention is not particularly limited as long as it has the seal layer C on the outermost surface, and may have another layer between the base layer A and the intermediate layer B, or the intermediate layer B may be directly laminated to the base layer A. In addition, another layer may be between the intermediate layer B and the seal layer C, or the seal layer C may be directly laminated to the intermediate layer B.
• seal layer C/base layer A/seal layer C there are three-layer structures of seal layer C/base layer A/seal layer C, base layer A/intermediate layer B/seal layer C, four-layer structure of seal layer C1/base layer A/intermediate layer B/seal layer C2, five-layer structure of seal layer C1/intermediate layer B1/base layer A/intermediate layer B2/seal layer C2, and six-layer structure of seal layer C1/base layer A1/intermediate layer B1/base layer A2/intermediate layer B2/seal layer C2.
• the base layer A1 and the base layer A2 may be made of different polypropylene-based resin compositions or may be the same
• the intermediate layer B1 and the intermediate layer B2 may be made of different polypropylene-based resin compositions or may be the same
• the seal layer C1 and the seal layer C2 may be made of different polypropylene-based resin compositions or may be the same.
• the functional layer D may be directly laminated on the surface of the substrate layer A, or an intermediate layer B may be interposed between the substrate layer A and the functional layer D.
• the functional layer D may also be disposed between the substrate layer A and the intermediate layer B, or between the intermediate layer B and the sealing layer C.
• the film has a functional layer D, it is not particularly limited as long as it has the substrate layer A, intermediate layer B, and sealing layer C in this order, and has the sealing layer C on the outermost surface.
• a four-layer structure of functional layer D/substrate layer A/intermediate layer B/sealing layer C which further has a functional layer D in the structure of substrate layer A/intermediate layer B/sealing layer C
• a five-layer structure of functional layer D/intermediate layer B/substrate layer A/intermediate layer B/sealing layer C which further has a functional layer D in the structure of intermediate layer B/substrate layer A/intermediate layer B/sealing layer C, may be mentioned.
• the overall thickness of the biaxially oriented polypropylene film of the present invention varies depending on the application and method of use, but is 10 ⁇ m or more and 50 ⁇ m or less from the viewpoint of film strength, airtightness, or water vapor barrier properties.
• the thickness is preferably 33 ⁇ m or less, more preferably 28 ⁇ m or less, even more preferably 23 ⁇ m or less, and particularly preferably 18 ⁇ m or less.
• the thickness of the base layer A varies depending on the application and method of use, but is preferably 5 to 48 ⁇ m, more preferably 10 to 40 ⁇ m, and even more preferably 13 to 30 ⁇ m. By making the thickness 5 ⁇ m or more, it is possible to increase the film strength, sealing properties, and water vapor barrier properties. In addition, by making the thickness 48 ⁇ m or less, it is possible to reduce the environmental load by reducing the volume.
• the thickness of the intermediate layer B varies depending on the application and method of use, but is preferably 0.5 to 5 ⁇ m, more preferably 1.0 to 5.0 ⁇ m, and even more preferably 1 to 3 ⁇ m.
• the thickness 0.5 ⁇ m or more it is possible to increase the adhesion between the base layer A and the sealing layer C and increase the heat seal strength.
• the thickness 5 ⁇ m or less it is possible to reduce the environmental load by reducing the volume.
• the thickness of the sealing layer C varies depending on the application and method of use, but is preferably 0.5 to 5 ⁇ m, and more preferably 0.5 to 1.5 ⁇ m. By making the thickness 0.5 ⁇ m or more, the heat seal strength can be increased. Furthermore, by making the thickness 5 ⁇ m or less, the environmental load can be reduced by reducing the volume.
• the thickness of functional layer D varies depending on the application and method of use, but is preferably 0.3 to 2 ⁇ m, and more preferably 0.5 to 1.5 ⁇ m.
• a thickness of 0.3 ⁇ m or more can increase the heat seal strength.
• a thickness of 2 ⁇ m or less can reduce the environmental impact by reducing the volume.
• the biaxially oriented polypropylene film of the present invention is characterized by the following properties.
• the "longitudinal direction" of the biaxially oriented polypropylene film of the present invention is the direction corresponding to the flow direction in the film production process and may be abbreviated as MD.
• the "width direction” is the direction perpendicular to the flow direction in the film production process and may be abbreviated as TD.
• the sum of the stress at 5% elongation in the longitudinal direction and the stress at 5% elongation in the transverse direction of the biaxially oriented polypropylene film of the present invention at 23 ° C. is 150 MPa or more.
• the film has high rigidity, so that even if the film is thinned, the bag shape when made into a packaging bag is easily maintained, and the film is less likely to deform during processing such as printing, making it easy to process.
• the antifogging property is also improved when an antifogging agent is contained. It is presumed that the reason for this is that the crystallinity of the base layer A increases, which promotes the migration of the antifogging agent to the surface layer C.
• the lower limit of the sum of the stress at 5% elongation in the longitudinal direction and the stress at 5% elongation in the transverse direction of the film at 23° C. is more preferably 160 MPa, and even more preferably 170 MPa, when the film is made thinner.
• the upper limit of the sum of the stress at 5% elongation in the longitudinal direction and the stress at 5% elongation in the transverse direction of the film at 23° C. is preferably 200 MPa, more preferably 190 MPa, from the viewpoint of ease of production.
• Methods for adjusting the sum of the stress at 5% elongation in the longitudinal direction and the stress at 5% elongation in the transverse direction of the film at 23°C within the above range include adjusting the raw material composition of each layer described above (particularly the raw material composition of the base layer A), the stretch ratio during film formation, the relaxation rate, and the temperature in each film formation process.
• the stress of the biaxially oriented polypropylene film of the present invention at 23°C when elongated by 5% in the longitudinal direction is preferably 35 MPa, more preferably 40 MPa, and particularly preferably 45 MPa, for the same reasons as the sum of the stress at 23°C when elongated by 5% in the longitudinal direction and the stress at 5% elongation in the transverse direction.
• the upper limit is preferably 70 MPa, more preferably 65 MPa, and particularly preferably 60 MPa.
• the stress of the biaxially oriented polypropylene film of the present invention at 23° C. when elongated by 5% in the width direction is preferably 110 MPa, more preferably 115 MPa, and particularly preferably 120 MPa, for the same reasons as the sum of the stress at 5% elongation in the longitudinal direction and the stress at 5% elongation in the width direction of the film at 23° C.
• the upper limit is preferably 200 MPa, more preferably 180 MPa, and particularly preferably 160 MPa.
• the stress at 5% elongation in the longitudinal and transverse directions (F5) can be kept within the range by adjusting the raw material composition of each layer described above (particularly the raw material composition of the base layer A), the stretch ratio during film formation, the relaxation rate, and the temperature in each film formation step.
• the stress at 5% elongation at 23° C. (F5) can be obtained by measuring the tensile strength in the longitudinal and transverse directions of a film at 23° C. in accordance with JIS K7127. In this case, the measurement can be performed with a sample size of 15 mm ⁇ 200 mm, a chuck width of 100 mm, and a pulling speed of 200 mm/min.
• the heat seal strength of the seal layer C of the biaxially oriented polypropylene film of the present invention at 115° C. is preferably 1.0 N/15 mm or more and 5.0 N/15 mm or less.
• the lower limit of the heat seal strength at 115°C obtained by the measurement method described below is preferably 1.5N/15mm, more preferably 2.0N/15mm.
• the heat seal processing can be performed at a lower temperature, the entire film is less likely to shrink and wrinkles are less likely to occur in the sealed portion.
• the upper limit of the heat seal strength of the seal layer C at 115° C. is about 5.0 N/15 mm. There is little need for it to be greater than that, and if it is too great, it may tend to stick to the seal bar.
• the heat seal strength of the seal layer C can be measured by overlapping the seal layers C facing each other, at each temperature, with a heat seal pressure of 1 kg/cm 2 , a heat seal time of 1 second, and a pulling speed of 200 mm/min.
• the relationship between the sum of the stress at 5% elongation in the longitudinal direction and the stress at 5% elongation in the transverse direction of the film at 23° C. and the heat seal strength of the seal layer C at 115° C. satisfies the following formula (1): Within the range of formula (1), the balance between rigidity and heat seal strength at low temperatures is excellent, and the bag making processability, bag making process speed, and quality of the bags made are further improved. Heat seal strength of seal layer C at 115° C.
• the upper limit of the thermal shrinkage rate in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 2.5%, more preferably 2.0%, even more preferably 1.5%, and particularly preferably 1.0%. If it is 2.5% or less, printing pitch deviation is unlikely to occur when transferring printing ink.
• the lower limit of the thermal shrinkage rate in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 120°C may be 0%.
• the upper limit of the heat shrinkage rate in the width direction at 120° C. is 1.3%, preferably 1.1%, more preferably 0.9%, further preferably 0.7%, and particularly preferably 0.5%.
• the thermal shrinkage rate in the longitudinal direction at 120° C. is smaller than the thermal shrinkage rate in the transverse direction at 120° C., printing pitch deviation is less likely to occur when transferring printing ink.
• the thermal shrinkage rate in the transverse direction at 120° C. of the biaxially oriented polypropylene film of the present invention may have a lower limit of ⁇ 1.0%.
• the thermal shrinkage percentages in the longitudinal and transverse directions at 120°C can be within the ranges by adjusting the raw material composition of each layer described above (particularly the raw material composition of the base layer A), the stretch ratio during film formation, the relaxation rate, and the temperature in each film formation step.
• the heat shrinkage rate can be measured in accordance with JIS Z1712.
• the heat seal strength of the sealing layer C at 115°C depends on the characteristics of each layer. As mentioned above, in addition to the method of lowering the melting point of the sealing layer C so that the heat of fusion of the sealing layer C is large, the method of adding a low melting point polypropylene copolymer is effective. Furthermore, in order to prevent the crystal propagation of the base layer A from reaching the sealing layer C, it is also effective to lower the melting point of the intermediate layer B or to increase the layer thickness. In addition, in order to suppress the crystal propagation of the base layer A to the sealing layer C, it is also effective to keep the stretch ratio low so as not to promote crystallization too much, but since this reduces the F5 value, it is necessary to adjust it appropriately. In addition to the characteristics of each layer mentioned above, the relaxation rate during film formation and the temperature in each film formation process can be adjusted to keep the range within the range.
• the heat of fusion of the sealing layer C at 70°C to 140°C in DSC measurement is preferably 10 J/g or more and 40 J/g or less.
• the lower limit of the heat of fusion is more preferably 11 J/g, and even more preferably 12 J/g.
• the upper limit of the heat of fusion is preferably 40 J/g, and more preferably 35 J/g.
• the heat of fusion of the seal layer C is the heat of fusion (absorbed heat) from 70 ° C to 140 ° C of the DSC curve obtained by scanning the surface of the seal layer C of the biaxially oriented polypropylene film with a razor blade as a measurement sample from -30 ° C to 250 ° C at a heating rate of 20 ° C / min using a differential scanning calorimeter, and is not the heat of fusion when measuring the melting point of the raw material resin composition of the seal layer C.
• the heat of fusion of the seal layer C varies depending on the crystallinity such as the melting point and crystallization temperature of the polypropylene resin composition constituting the seal layer C, but also varies depending on the orientation state and crystallization state of the polypropylene resin composition of the adjacent base layer A and intermediate layer B. That is, it also varies depending on the stretching conditions and heat treatment conditions of the biaxially oriented polypropylene film.
• the properties of the polypropylene resin composition of the seal layer C, intermediate layer B, and base layer A, and the stretching conditions and heat treatment conditions of the biaxially oriented polypropylene film can be set as described above.
• the heat seal strength of the seal layer C of the biaxially oriented polypropylene film of the present invention at 130 ° C is preferably 3.0 N / 15 mm or more and 10.0 N / 15 mm or less.
• the lower limit of the heat seal strength at 130 ° C obtained by the measurement method described later is more preferably 3.5 N / 15 mm, more preferably 4.0 N / 15 mm, and even more preferably 4.5 N / 15 mm in order to prevent the contents from falling off.
• the upper limit of the heat seal strength of the seal layer C at 130 ° C is about 10.0 N / 15 mm.
• the heat seal strength of the sealing layer C at 130°C can be kept within the range by adjusting the raw material composition of each of the above-mentioned layers (which depends particularly on the raw material composition of the sealing layer C, but may also depend on the raw materials of the base layer A and intermediate layer B), the stretch ratio during film formation, the relaxation rate, and the temperature in each film formation process.
• the surface of the seal layer C of the biaxially oriented polypropylene film of the present invention is preferably ranked 3 or less in terms of anti-fogging properties obtained by the measurement method described below. More preferably, it is ranked 2 or less, and even more preferably, it is ranked 1.
• the area of dew on the surface of the seal layer C is 1/4 or less of the area of the biaxially oriented polypropylene film placed at the opening of the container. More preferably, the area is zero, that is, no dew is attached to the surface of the seal layer C.
• the upper limit of the haze of the biaxially oriented polypropylene film of the present invention is preferably 7.0%, more preferably 5.0%, even more preferably 4.0%, particularly preferably 3.5%, and most preferably 3.0%. If it is 7.0% or less, it is easy to use in applications where transparency is required.
• the lower limit of the haze is preferably 0%, and a practical value is 0.1%.
• the haze can be kept within the range by adjusting the cooling roll temperature, the longitudinal stretching temperature, the tenter preheating temperature before widthwise stretching, the widthwise stretching temperature, or the heat setting temperature, or the amount of the component having a molecular weight of 100,000 or less of the polypropylene polymer.
• the haze may be increased by the addition of an antiblocking agent or the composition of the seal layer C.
• the haze can be measured at 23°C according to JIS K7105.
• the biaxially oriented polypropylene film of the present invention or the laminate described above can be used to produce three-sided sealed, pillow-type and gusset-type packaging bags, which have good heat seal strength and good appearance of the sealed area.
• the biaxially oriented polypropylene film of the present invention has a sealing layer C laminated thereon, so it can be made into a packaging bag as is or after printing on the film surface. It is particularly suitable for bag making processing using an automatic packaging machine.
• the pillow-type packaging which is an example of automatic packaging, is described below.
• Horizontal pillow packaging machines for packaging foods and the like are equipped with a center sealer and an end sealer.
• the end sealer which is located downstream, seals and cuts end seal sections located upstream and downstream of the packaged product in the flow direction of the tubular film that wraps the packaged product and is conveyed from the center sealer.
• the center sealer includes a pair of conveying rollers and a pair of heating rollers, and conveys the tubular film by sandwiching the central seal portion where both downstream widthwise ends are joined together.
• a pair of heating rollers disposed downstream sandwich and heat the central seal portion of the conveyed tubular film.
• the center seal portion of the tubular film is heated and pressurized by the pair of heating rollers, thereby being thermally bonded.
• the time required for heating and pressurizing the center seal portion by the pair of heating rollers is considerably shorter than the time required for heating and pressurizing an end sealer that seals the end seal portion using a box motion mechanism or the like.
• the biaxially oriented polypropylene film of the present invention is laminated with the sealing layer C, it can be made into a packaging bag as it is or after printing on the film surface. However, depending on the application, it can also be made into a laminate shown in (1) to (9) below and used as a packaging material.
• Biaxially oriented PP film layer/printed layer/adhesive layer/unoriented PP film sealant layer are examples of the biaxially oriented polypropylene film of the present invention.
• Biaxially oriented PET film layer/printed layer/adhesive layer/biaxially oriented PP film layer/adhesive layer/unoriented PP film sealant layer (3) Biaxially oriented PET film layer/printed layer/adhesive layer/biaxially oriented PP film layer/adhesive layer/unoriented PP film sealant layer.
• Biaxially oriented PP film layer/anchor coat layer/inorganic thin film layer/inorganic thin film protective layer/printed layer/adhesive layer/linear low density PE film sealant layer (5)
• the biaxially oriented PP film of the present invention is printed by letterpress, lithographic, intaglio, stencil or transfer printing, depending on the application.
• An adhesive solution is applied onto the laminate, and an unstretched sheet, uniaxially stretched film, or biaxially stretched film made of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, or polyester is laminated as a sealant film and then dried (dry lamination method).
• the sealant and film are laminated while extruding a molten adhesive resin (hot melt lamination method).
• 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.
• aluminum or inorganic oxides can be vapor-deposited on the biaxially oriented polypropylene film, intermediate layer film, or sealant film. Vacuum deposition, sputtering, and ion plating can be used as the vapor deposition method, but vacuum deposition of silica, alumina, or a mixture thereof is particularly preferred.
• melt flow rate (MFR) was measured in accordance with JIS K7210 at a temperature of 230° C. and a load of 2.16 kgf (unit: g/10 min).
• ⁇ Apparatus HLC-8321PC/HT (manufactured by Tosoh Corporation) Detector: RI Solvent: 1,2,4-trichlorobenzene + dibutylhydroxytoluene (0.05%) Column: TSK gelguard column HHR (30) HT (7.5 mm I.D. x 7.5 cm) x 1 + TSK gel GMHHR-H (20) HT (7.8 mm I.D.
• the number average molecular weight (Mn) and the weight average molecular weight (Mw) are each defined by the number of molecules (N i ) of the molecular weight (M i ) at each elution position of the GPC curve obtained via a molecular weight calibration curve, as shown below.
• Mn ⁇ (N i ⁇ M i )/ ⁇ N i
• Mass average molecular weight: Mw ⁇ (N i ⁇ M i 2 ) / ⁇ (N i ⁇ M i )
• the molecular weight distribution can be obtained by Mw/Mn.
• the proportions of components having a molecular weight of 10,000 or less and components having a molecular weight of 100,000 or less were determined from the integral curve of the molecular weight distribution obtained by GPC.
• Tm Melting point
• Heat shrinkage rate Measured according to JIS Z1712 by the following method. The film was cut into pieces of 20 mm width and 200 mm length in both the longitudinal and transverse directions, and was heated for 5 minutes by hanging in a hot air oven at 120° C. The length after heating was measured, and the heat shrinkage rate was calculated as the ratio of the shrunken length to the original length (unit: %).
• the longitudinal direction of the heat seal bar was parallel to the longitudinal direction of the film and located at the center of the film in the transverse direction.
• the interval between the end of the sample in the transverse direction and the seal bar was 0.5 cm.
• a 15 mm section from the longitudinal center of each sealed portion (3 cm x 1 cm) was cut in the width direction, attached to the upper and lower chucks of a tensile testing machine (Instron 5965 dual column tabletop testing machine), and pulled at a tensile speed of 200 mm/min to measure the heat seal strength of each (unit: N/15 mm).
• functional layers D were stacked facing each other, and the heat seal strength was determined using a thermal gradient tester.
• Anti-Fog Property The anti-fogging property was evaluated by the following procedure. 1) Pour 300cc of 50°C hot water into a 500cc open-top container. 2) The biaxially oriented polypropylene film thus obtained is placed over the opening of the container so that the surface of the sealing layer C faces the inside of the container, thereby sealing the container. 3) Leave in a cold room at 5°C for 30 minutes. 4) After being left in a cold room at 5° C. for 30 minutes, the state of dew adhesion on the surface of the sealing layer C was evaluated on a 5-point scale.
• Grade 1 rating (Rank 1): No dew on the entire surface (0 surface area)
• Grade 2 (Rank 2): Some dew adhesion (the adhesion area is 1 ⁇ 4 or less of the area of the biaxially oriented polypropylene film placed at the opening of the container)
• Grade 3 (Rank 3): Dew adhesion to about 1/2 (adhesion area is more than 1/4 and less than 2/4 of the area of the biaxially oriented polypropylene film placed at the opening of the container)
• Grade 4 (Rank 4): Almost all dew adhesion (adhesion area is more than 2/4 and less than 3/4 of the area of the biaxially oriented polypropylene film placed at the opening of the container)
• Grade 5 (Rank 5): Dew adhesion over the entire surface (the adhesion area is more than 3/4 of the area of the biaxially oriented polypropylene film placed at the opening of the container)
• PP-1 A mixture obtained by mixing propylene homopolymer (manufactured by Sumitomo Chemical Co., Ltd., mesopentad fraction: 98.9%, melting point: 162.5°C, MFR: 7.5 g/10 min, Mw/Mn: 3.7, amount of components having a molecular weight of 10,000 or less: 4.0 mass%, amount of components having a molecular weight of 100,000 or less: 40.5 mass%) with stearyl diethanolamine monostearate, stearyl diethanolamine distearate, and stearyl diethanolamine, all manufactured by Toho Chemical Industry Co., Ltd., as antifogging agents, thereby containing a total of 2.0 mass% of the antifogging agent.
• PP-2 Propylene homopolymer (Sumitomo Chemical Co., Ltd., mesopentad fraction: 98.9%, melting point: 163°C, MFR: 7.5g/10min, Mw/Mn: 3.6, amount of components with molecular weight of 10,000 or less: 4.0% by mass, amount of components with molecular weight of 100,000 or less: 40.5% by mass)
• PP-3 Propylene homopolymer with a large Mw/Mn value (Sumitomo Chemical Co., Ltd., mesopentad fraction: 98.8%, melting point: 162°C, MFR: 11g/10 min, Mw/Mn: 9.6, amount of components with molecular weight of 10,000 or less: 6.9% by mass, amount of components with molecular weight of 100,000 or less: 53.1% by mass)
• PP-4 A mixture obtained by mixing a propylene polymer (manufactured by Sumitomo Chemical Co., Ltd., copolymerized ethylene component
• PP-5 A mixture obtained by mixing a propylene polymer (manufactured by Sumitomo Chemical Co., Ltd., copolymerized ethylene component: 0.6 mol%, melting point: 158°C, MFR: 7.5 g/10 min) with stearyl diethanolamine monostearate, stearyl diethanolamine distearate, and stearyl diethanolamine, all manufactured by Toho Chemical Industry Co., Ltd., as anti-fogging agents, thereby containing a total of 2.0 mass% of the anti-fogging agent.
• a propylene polymer manufactured by Sumitomo Chemical Co., Ltd., copolymerized ethylene component: 0.6 mol%, melting point: 158°C, MFR: 7.5 g/10 min
• PP-6 A mixture obtained by mixing a propylene-ethylene-butene copolymer (manufactured by Sumitomo Chemical Co., Ltd., SP7843, melting point: 128°C, MFR: 6.5 g/10 min) with glycerin monostearate (manufactured by Toho Chemical Industry Co., Ltd.) as an anti-fogging agent, thereby containing a total of 0.5 mass% of the anti-fogging agent.
• glycerin monostearate manufactured by Toho Chemical Industry Co., Ltd.
• PP-7 Propylene-butene copolymer (manufactured by Mitsui Chemicals, Inc., Tafmer XM7070, melting point: 75°C, MFR: 7.0g/10min)
• PP-8 A mixture obtained by mixing a propylene-butene copolymer (manufactured by Sumitomo Chemical Co., Ltd., FSX66M4, melting point: 138°C, MFR: 4.5 g/10 min) with glycerin monostearate (manufactured by Toho Chemical Industry Co., Ltd.) as an anti-fogging agent, containing a total of 0.45 mass% of the anti-fogging agent.
• Example 1 (Base layer A) The raw material was a polypropylene resin composition containing 59 mass% of a mixture of an antifogging agent and a propylene homopolymer PP-1, 18.5 mass% of a propylene homopolymer PP-2, 20.0 mass% of a propylene homopolymer PP-3 having a large Mw/Mn value, and 2.5 mass% of a mixture of an antifogging agent and a propylene homopolymer PP-4. (Intermediate layer B) The raw material was a polypropylene resin composition consisting of an antifogging agent and a mixture of propylene polymers copolymerized with 0.6 mol % ethylene, PP-5.
• (Sealing layer C) A polypropylene resin composition containing 70% by mass of propylene-ethylene-butene copolymer PP-6 and 30% by mass of propylene-butene copolymer PP-7 was used as the raw material.
• (Functional Layer D) A polypropylene resin composition containing 100% by mass of propylene-ethylene-butene copolymer PP-8 was used as the raw material.
• the polypropylene-based resin compositions constituting each of the functional layer D/base layer A/intermediate layer B/sealing layer C were heated and melted in an extruder using a multi-layer feed block at 220°C, 250°C, 240°C, and 210°C, respectively, and the molten polypropylene-based resin composition was then laminated from a T-die at 250°C to form a layer structure of functional layer D/base layer A/intermediate layer B/sealing layer C, and co-extruded so that the thickness ratio of each was 1:16:2:1.
• the functional layer D side of the molten sheet was brought into contact with a cooling roll at 20° C., and then directly put into a water tank at 20° C. Then, between metal rolls heated to 135° C., the sheet was stretched 4.5 times in the longitudinal direction by utilizing the difference in peripheral speed, and then introduced into a tenter stretching machine, where the preheating section temperature was 168° C. and the stretching section temperature was 163° C., and the sheet was stretched 11.2 times in the width direction. Then, the sheet was heat-treated at 165° C. while being relaxed by 6.0% in the width direction.
• the surface of the obtained biaxially oriented polypropylene film on the side of the seal layer C was subjected to a corona treatment using a corona treatment machine manufactured by Softal Corona & Plasma GmbH under conditions of an applied current value of 0.75 A and an applied voltage of 1.8 kW, and then the film was wound up with a winder to obtain the biaxially oriented polypropylene film of the present invention.
• the thickness of the obtained film was 20 ⁇ m.
• the thicknesses of the functional layer D, base layer A, intermediate layer B and seal layer C of the film thus obtained were 1 ⁇ m, 16 ⁇ m, 2 ⁇ m and 1 ⁇ m.
• Table 1 shows the raw material composition of each layer, the film formation conditions, and the film properties.
• the obtained film had high rigidity, yet had low heat shrinkage and good heat seal strength at low temperatures, and was an excellent anti-fogging film.
• Example 2 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the raw material for the seal layer C was a polypropylene-based resin composition containing 80% by mass of propylene-ethylene-butene copolymer PP-6 and 20% by mass of propylene-butene copolymer PP-7. As shown in Table 1, the obtained film had high rigidity, yet had a low thermal shrinkage rate and good heat seal strength at low temperatures, and was an excellent anti-fogging film.
• Example 3 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the raw material for the seal layer C was a polypropylene-based resin composition containing 50% by mass of propylene-ethylene-butene copolymer PP-6 and 50% by mass of propylene-butene copolymer PP-7. As shown in Table 1, the obtained film had high rigidity, yet had a low thermal shrinkage rate and good heat seal strength at low temperatures, and was an excellent anti-fogging film.
• Example 4 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the stretching ratio in the width direction was changed to 13 times. As shown in Table 1, the obtained film had high rigidity, yet had a low thermal shrinkage rate and good heat seal strength at low temperatures, and was an excellent anti-fogging film.
• Example 5 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the thickness of the seal layer C was changed from 1.0 ⁇ m to 0.5 ⁇ m and the thickness of the base layer A was changed from 16 ⁇ m to 16.5 ⁇ m. As shown in Table 1, the obtained film had high rigidity, yet had a low thermal shrinkage rate and good heat seal strength at low temperatures, and was an excellent anti-fogging film.
• Example 6 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the thickness of the seal layer C was changed from 1.0 ⁇ m to 2.0 ⁇ m and the thickness of the base layer A was changed from 16 ⁇ m to 15 ⁇ m. As shown in Table 1, the obtained film had high rigidity, yet had a low thermal shrinkage rate and good heat seal strength at low temperatures, and was an excellent anti-fogging film.
• Example 7 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the thickness of the intermediate layer B was changed from 2.0 ⁇ m to 4.0 ⁇ m, the thickness of the seal layer C was changed from 1.0 ⁇ m to 0.5 ⁇ m, and the thickness of the base layer A was changed from 16 ⁇ m to 14.5 ⁇ m. As shown in Table 1, the obtained film had high rigidity, yet had a low thermal shrinkage rate and good heat seal strength at low temperatures, and was an excellent anti-fogging film.
• Example 8 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the thickness of the intermediate layer B was changed from 2.0 ⁇ m to 3.0 ⁇ m and the thickness of the seal base material layer A was changed from 16 ⁇ m to 15 ⁇ m. As shown in Table 1, the obtained film had high rigidity, yet had a low thermal shrinkage rate and good heat seal strength at low temperatures, and was an excellent anti-fogging film.
• Example 9 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the thickness of the intermediate layer B was changed from 2.0 ⁇ m to 1.0 ⁇ m and the thickness of the base layer A was changed from 16 ⁇ m to 17 ⁇ m. As shown in Table 1, the obtained film had high rigidity, yet had a low thermal shrinkage rate and good heat seal strength at low temperatures, and was an excellent anti-fogging film.
• the biaxially oriented polypropylene films obtained in Examples 1 to 9 were excellent in stiffness and suitability for automatic packaging, and furthermore, when made into packaging bags, they easily maintained their bag shape and were less likely to deform during processing such as printing. In addition, because the thermal shrinkage rate was low, there was little deviation in printing pitch and little wrinkles in the sealed area during heat sealing.
• Example 1 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the raw material for the seal layer C was a polypropylene-based resin composition containing 90% by mass of propylene-ethylene-butene copolymer PP-6 and 10% by mass of propylene-butene copolymer PP-7. As shown in Table 2, the obtained film had high rigidity and low heat shrinkage, but had low heat seal strength at low temperatures and was poorly suited for automatic packaging.
• Example 2 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the raw material for the seal layer C was a polypropylene-based resin composition containing 100% by mass of propylene-ethylene-butene copolymer PP-6 and no low-melting point propylene-butene copolymer PP-7. As shown in Table 2, the obtained film had high rigidity and low heat shrinkage, but had low heat seal strength at low temperatures and was poorly suited for automatic packaging.
• Example 3 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the stretching ratio in the width direction was changed to 10.0 times. As shown in Table 2, the F5 values of the obtained film in both the transverse direction (TD) and longitudinal direction (MD) at 23° C. were low, and the film had a weak stiffness, which made it prone to deformation during processing such as printing, making processing difficult. Furthermore, when made into a packaging bag, it was difficult to maintain the bag shape.
• Example 4 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the thickness of the seal layer C was changed from 1.0 ⁇ m to 0.3 ⁇ m and the thickness of the base layer A was changed from 16 ⁇ m to 16.7 ⁇ m. As shown in Table 2, the obtained film had high rigidity and low heat shrinkage, but had low heat seal strength at low temperatures and was poorly suited for automatic packaging.
• Example 5 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the thickness of the seal layer C was changed from 1.0 ⁇ m to 3.0 ⁇ m and the thickness of the base layer A was changed from 16 ⁇ m to 14 ⁇ m. As shown in Table 2, the F5 values of the obtained film in both the transverse direction (TD) and longitudinal direction (MD) at 23° C. were low, and the film had a weak stiffness, which made it prone to deformation during processing such as printing, making processing difficult. Furthermore, when made into a packaging bag, it was difficult to maintain the bag shape.
• TD transverse direction
• MD longitudinal direction
• Example 6 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the thickness of the intermediate layer B was changed from 2.0 ⁇ m to 0.4 ⁇ m and the thickness of the base layer A was changed from 16 ⁇ m to 17.6 ⁇ m. As shown in Table 2, the obtained film had high rigidity and low heat shrinkage, but had low heat seal strength at low temperatures and was poorly suited for automatic packaging.
• Example 7 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the intermediate layer B was not provided (the thickness was changed from 2.0 ⁇ m to 0 ⁇ m) and the thickness of the base layer A was changed from 16 ⁇ m to 18 ⁇ m. As shown in Table 2, the obtained film had high rigidity and low heat shrinkage, but had low heat seal strength at low temperatures and was poorly suited for automatic packaging.
• Comparative Example 10 A biaxially oriented polypropylene film was obtained in the same manner as in Comparative Example 8, except that the stretching ratio in the width direction was changed to 8.0 times. As shown in Table 2, the obtained film had a low F5 value in the width direction at 23° C. and was a weak film, which was prone to deformation during processing such as printing, making processing difficult. Furthermore, when made into a packaging bag, it was difficult to maintain the bag shape.
• the F5 value in the width direction of the obtained film at 23°C was low, and the film was weak in stiffness, and deformation was likely to occur during processing such as printing, making processing difficult. Furthermore, when made into a packaging bag, the bag shape was difficult to maintain. In addition, printing pitch deviation was likely to occur.
• Example 12 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the raw material for the intermediate layer B was a polypropylene-based resin composition containing 100% by mass of propylene-ethylene-butene copolymer PP-8 having a melting point of 138°C. As shown in Table 2, the F5 values of the obtained film in both the transverse direction (TD) and longitudinal direction (MD) at 23° C. were low, and the film had a weak stiffness, which made it prone to deformation during processing such as printing, making processing difficult. Furthermore, when made into a packaging bag, it was difficult to maintain the bag shape.
• TD transverse direction
• MD longitudinal direction
• Example 13 A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the raw material for the intermediate layer B was the same polypropylene-based resin composition having a melting point of 162° C. as the base layer A. As shown in Table 2, the obtained film had high rigidity and low heat shrinkage, but had low heat seal strength at low temperatures and was poorly suited for automatic packaging.
• the biaxially oriented polypropylene film of the present invention has high rigidity and excellent heat seal strength at low temperatures. Therefore, it has excellent bag-making processability, is easy to maintain the bag shape when made into a packaging bag, and is also excellent in suitability for automatic packaging, and can be preferably used for packaging bags. In particular, by imparting anti-fogging properties, it is particularly suitable for packaging fruits and vegetables. In addition, because of its high rigidity, it is possible to use a thinner film than before, or it can be used without laminating a sealant film, thereby reducing the burden on the environment.

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