Polyolefin resin film

Abstract

Provided is a polyolefin resin film such that, when laminated with a substrate film having large distortion of the molecular orientation axis, such as a biaxially stretched polyamide resin film, a packaging pouch obtained from said laminate has excellent straight-line cuttability, tearing properties and pouch-making properties, and does not tend to break when dropped even after retorting.　A polyolefin resin film comprising a polypropylene resin composition, wherein: 100 parts by weight of the polypropylene resin composition contains 40-97 parts by weight of a propylene-ethylene block copolymer, 0-50 parts by weight of a propylene-α olefin random copolymer or a propylene homopolymer, and 3-10 parts by weight of at least one elastomer selected from the group consisting of ethylene-propylene copolymer elastomers, propylene-butene copolymer elastomers and ethylene-butene copolymer elastomers; the heat shrinkage in the length direction is 1-9%; and the x-axis orientation factor ΔNx calculated from the refractive index is 0.0150-0.0250.

Description

[Technical Field]

[0001] The present invention relates to a polyolefin resin film and at least one base film selected from the group consisting of polyamide resin films, polyester resin films, and polypropylene resin films. [Background technology]

[0002] Packaging bags are manufactured by heat-sealing (hereinafter referred to as heat sealing) the periphery of a laminate of a base film, such as a polyamide resin film, polyester resin film, or polypropylene resin film, and a polyolefin resin film, with the polyolefin resin film surfaces in contact with each other at a temperature close to the melting point of the polyolefin resin film. In food packaging bags, so-called retort pouches are widely used, which are filled with food and then sterilized with pressurized steam at about 130°C, making them suitable for storing food for long periods of time. In recent years, the demand for retort pouches has increased due to social factors such as the increasing participation of women in the workforce, the trend toward nuclear families, and the aging of the population, and at the same time, there is a demand for further improvement in their properties. For example, in recent years, these retort pouches have often been packed in boxes, transported, and sold in stores, so they are required to be resistant to breakage even if dropped during this process, particularly when dropped under refrigeration.

[0003] Furthermore, when removing food contents from a packaging bag, particularly a retort pouch, the packaging bag is often torn by hand from a slit made in the heat-sealed portion around the periphery of the bag, known as a notch. However, when a conventional laminate is used, the bag cannot be torn parallel to one side, which is usually the horizontal direction, and the bag ends up being opened at an angle, or the tearing direction of the laminate on the front and back of the packaging bag is reversed on the top and bottom, a phenomenon known as tear separation, occurs, making it difficult to remove the food contents and posing a risk of staining hands and clothes with the food contents, or of causing burns if the contents are heated.

[0004] The reason why it is difficult to tear a packaging bag parallel to one side of the packaging bag is that the base film used in the laminate is distorted, i.e., the molecular orientation axis direction of the base film is not parallel to one side of the package.

[0005] This problem would not occur if the molecular orientation axis direction of the base film could be made the same as the tear direction of the packaging bag. The molecular orientation axis direction of the produced wide-width stretched film in the widthwise center portion is aligned with the running direction of the film, making it possible to tear the packaging bag parallel to one side. However, at the widthwise ends of the base film, the molecular orientation axis direction is tilted from the running direction of the film. Even if the running direction of the film is processed to be aligned with the longitudinal or transverse direction of the packaging bag, the tear direction of the packaging bag will be tilted toward the molecular orientation axis direction of the base film. It is not practical to completely avoid procuring base film using the widthwise ends of the film, and the degree of distortion tends to become even greater than before as the production speed of base film increases and the width of the film increases. Therefore, attempts have been made to solve these problems by improving the polyolefin resin film that is laminated onto the substrate film.

[0006] Patent Document 1 discloses a film obtained by uniaxially stretching a polyolefin resin sheet containing an ethylene-propylene block copolymer and an ethylene-propylene copolymer at a stretch ratio of 3.0 or less. However, there is room for improvement in tear strength, and there are problems with the film being prone to tearing.

[0007] Furthermore, Patent Documents 2 and 3 disclose a film obtained by uniaxially stretching a polyolefin resin sheet containing a propylene-ethylene block copolymer or a propylene-ethylene random copolymer and a propylene-butene elastomer and / or an ethylene-butene elastomer at a stretching ratio of about 5. However, this film has problems such as poor dimensional stability against heat, which causes the package to deform due to heat applied during retort treatment, damaging the appearance, and the bag is prone to tearing at low temperatures. Also, Patent Document 4 discloses a film obtained by uniaxially stretching a polyolefin resin sheet mainly composed of a propylene-ethylene block copolymer at a stretching ratio of about four times. However, when a four-side sealed bag manufactured from a laminate with a biaxially stretched polyamide film or the like is torn open from the notch, a problem occurs in which thread-like pieces of film separate from the heat-sealed edge (commonly known as whiskers). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5790497 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-141302 [Patent Document 3] Special Publication No. 2012-500307 [Patent Document 4] WO2019 / 123944A1 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a polyolefin resin film that, even when laminated with a base film having a large distortion in the molecular orientation axis, such as a biaxially oriented polyamide resin film, provides a packaging bag obtained from the laminate that has excellent straight-line cutting properties, tearability, and bag-making processability, is resistant to bag tearing when dropped after retorting, and is resistant to whisker formation when opened. [Means for solving the problem]

[0010] As a result of intensive research into achieving this object, the present inventors have found that a polyolefin resin film can be obtained that is made from a polypropylene resin composition containing, in addition to a propylene-ethylene block copolymer and a propylene-α-olefin random copolymer, an ethylene-propylene copolymer elastomer and a propylene-butene copolymer elastomer, and that while the polymer molecules are primarily oriented in one direction by stretching, the heat shrinkage rates in each direction are reduced and the orientation of the molecular chains in the longitudinal direction is within a specific range. This finding led to the completion of the present invention. That is, the present invention has the following aspects.

[0011] [1] A polyolefin-based resin film made of a polypropylene-based resin composition, which contains, in a total of 100 parts by weight of polypropylene-based resin, 40 to 97 parts by weight of a propylene-ethylene block copolymer, 0 to 50 parts by weight of a propylene-α-olefin random copolymer or a propylene homopolymer, and 3 to 10 parts by weight of at least one elastomer selected from the group consisting of an ethylene-propylene copolymer elastomer, a propylene-butene copolymer elastomer, and an ethylene-butene copolymer elastomer, and which has a heat shrinkage rate in the longitudinal direction of 1% or more and 9% or less, and an x-axis orientation coefficient ΔNx calculated from the refractive index of 0.0150 or more and 0.0250 or less.

[0012] [2] The polyolefin resin film according to [1], which has a multi-layer structure of at least two layers.

[0013] [3] A laminate with at least one base film selected from the group consisting of the polyolefin resin film according to [1] or [2], a polyamide resin film, a polyester resin film, and a polypropylene resin film.

[0014] [4] The laminate according to [3], having a straight cut ability of 5 mm or less.

[0015] [5] A packaging body comprising the laminate described in [4].

[0016] [6] The packaging described in [5], which is for retort use. [Effects of the Invention]

[0017] The polyolefin resin film of the present invention has excellent straight-line cutting properties, tearability, and processability for bag formation, and is resistant to tearing when dropped after retorting, and is also resistant to creases when opened. It is particularly suitable for retort pouches. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below. (propylene-ethylene block copolymer) In the present invention, a propylene-ethylene block copolymer can be used. The propylene-ethylene block copolymer in the present invention is a multi-stage copolymer obtained by a first polymerization step using a copolymerization component of a large amount of propylene and a small amount of ethylene, and a second polymerization step using a copolymerization component of a small amount of propylene and a large amount of ethylene. Specifically, as disclosed in JP-A-2000-186159, it is preferable to use a block copolymer obtained by gas-phase polymerization. That is, a block copolymer obtained by polymerizing a polymer portion (component A) mainly composed of propylene in the first step substantially in the absence of an inert solvent, and then polymerizing a copolymer portion (component B) of propylene and ethylene having an ethylene content of 20 to 50 parts by weight in the gas phase in the second step, is an example of such a block copolymer, but is not limited thereto.

[0019] The melt flow rate (MFR) of the propylene-ethylene block copolymer (measured at 230°C under a load of 2.16 kg) is preferably 1 to 10 g / 10 min, more preferably 2 to 7 g / 10 min. If the MFR is 1 g / 10 min or more, extrusion through a T-die is easy, and conversely, if the MFR is 10 g / 10 min or less, impact strength (impact strength) can be easily increased.

[0020] In the present invention, the xylene-soluble portion at 20°C is referred to as CXS, and the xylene-insoluble portion at 20°C is referred to as CXIS. In the propylene-ethylene block copolymer used in the present invention, CXS is mainly composed of a rubber component (component B), and CXIS is mainly composed of a polypropylene component (component A). If the intrinsic viscosities of each are [η]CXS and [η]CXIS, the values ​​of [η]CXS and [η]CXIS are preferably in the range of 1.8 to 3.8 dL / g, more preferably 2.0 to 3.0 dL / g. If the viscosity is 3.0 dL / g or less, fisheyes are less likely to occur in the polyolefin resin film. On the other hand, if the viscosity is 1.8 dL / g or more, the heat seal strength between polyolefin resin films is less likely to decrease significantly. On the other hand, [η]CXIS is preferably in the range of 1.0 to 3.0 dl / g. When it is 3.0 dl / g or less, extrusion through a T-die is easy, and conversely, when it is 1.0 dl / g or more, the impact strength of the film is easily increased.

[0021] The above [η]CXS and [η]CXIS values ​​were measured using the following method. Five grams of sample was completely dissolved in 500 ml of boiling xylene, cooled to 20°C, and left to stand for at least four hours. The filtrate and precipitate were then separated by filtration. The filtrate was dried to dryness (CXS) and the precipitate was dried under reduced pressure at 70°C to obtain a solid (CXIS). The intrinsic viscosities ([η]) of these components were measured in tetralin at 135°C using an Ubbelohde viscometer.

[0022] It is generally known that there is a correlation between MFR and the intrinsic viscosity η of the entire film. By knowing the η of the film, it is possible to roughly determine the MFR of the resin used. η is a measure of molecular weight, with larger numbers indicating larger molecular weights and smaller numbers indicating smaller molecular weights. MFR is a measure of molecular weight, with smaller numbers indicating larger molecular weights and larger numbers indicating smaller molecular weights.

[0023] The propylene-ethylene block copolymer preferably has a copolymerization ratio of the ethylene component of 1 to 15% by weight, more preferably 3 to 10% by weight, and more preferably 85 to 99% by weight, more preferably 90 to 97% by weight.

[0024] The lower limit of the melting point of the propylene-ethylene block copolymer is not particularly limited, but is preferably 120°C, more preferably 125°C. At 120°C or higher, heat resistance is easily achieved, and the inner surfaces of the bag are less likely to fuse together during retort treatment. The upper limit of the melting point of the propylene-ethylene block copolymer is not particularly limited, but is preferably 175°C, more preferably 170°C. If it is 175°C or lower, the heat-sealing temperature is likely to decrease.

[0025] Specific examples of the propylene-ethylene block copolymer include a block copolymer polypropylene resin having an ethylene content of 7% by weight and a CXS intrinsic viscosity η=3.0 dL / g (MFR=3.0 g / 10 min at 230°C and a load of 2.16 kg, melting point: 164°C, WFS5293-22 manufactured by Sumitomo Chemical Co., Ltd.), and a block copolymer polypropylene resin having an ethylene content of 6% by weight and a CXS intrinsic viscosity η=2.3 dL / g (MFR=3.0 g / 10 min at 230°C and a load of 2.16 kg, melting point: 164°C, WFS5293-29 manufactured by Sumitomo Chemical Co., Ltd.).

[0026] (Propylene-α-olefin random copolymer) In the present invention, it is preferable to add a propylene-α-olefin random copolymer for the purpose of lowering the heat sealing temperature of the polyolefin resin film. The propylene-α-olefin random copolymer may be a copolymer of propylene and at least one α-olefin other than propylene having 2 to 20 carbon atoms. Examples of such α-olefin monomers having 2 to 20 carbon atoms that can be used include ethylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, and octene-1. While not particularly limited, ethylene is preferred in terms of compatibility with propylene-ethylene block copolymers. Two or more types of propylene-α-olefin random copolymers can be mixed and used as needed. A propylene-ethylene random copolymer is particularly preferred. In this paper, the monomers constituting the random copolymers are named and described in descending order of their composition ratio.

[0027] The lower limit of the melt flow rate (MFR) of the propylene-α-olefin random copolymer at 230°C under a load of 2.16 kg is preferably 0.6 g / 10 min, more preferably 1.0 g / 10 min, and even more preferably 1.2 g / 10 min. If it is 0.6 g / 10 min or higher, the compatibility with the propylene-ethylene block copolymer is improved and the film is less likely to whiten. The upper limit of the melt flow rate of the propylene-α-olefin random copolymer is preferably 10.0 g / 10 min, more preferably 8.0 g / 10 min, and even more preferably 7.0 g / 10 min.

[0028] It is preferable to use a propylene-α-olefin random copolymer containing a metallocene-based olefin polymerization catalyst as the polymerization catalyst used in the production of propylene-α-olefin random copolymers. Propylene-α-olefin random copolymers containing a metallocene-based olefin polymerization catalyst are characterized by a low content of components in the low molecular weight region and the high molecular weight region. It has also been newly discovered that the use of a propylene-α-olefin random copolymer containing a metallocene-based olefin polymerization catalyst suppresses the occurrence of whiskers. The metallocene olefin polymerization catalyst is a catalyst comprising (i) a transition metal compound of Group 4 of the periodic table containing a ligand having a cyclopentadienyl skeleton (a so-called metallocene compound), (ii) a co-catalyst capable of reacting with the metallocene compound to activate it to a stable ionic state, and, if necessary, (iii) an organoaluminum compound, and any known catalyst can be used.

[0029] The copolymerization ratio of the ethylene component in the propylene-α-olefin random copolymer is preferably 1 to 15% by weight, more preferably 3 to 10% by weight, and the copolymerization ratio of the propylene component in the propylene-ethylene block copolymer is preferably 85 to 99% by weight, more preferably 90 to 97% by weight.

[0030] The lower limit of the melting point of the propylene-α-olefin random copolymer is preferably 120°C, more preferably 125°C. At 120°C or higher, heat resistance is likely to be achieved, and the inner surfaces of the bag may fuse together during retort treatment. The upper limit of the melting point of the propylene-α-olefin random copolymer is preferably 145°C, more preferably 140°C. At 145°C or lower, the heat sealing temperature is likely to decrease.

[0031] Specific examples of the propylene-α-olefin random copolymer include S131 (ethylene content: 5.5% by weight, density: 890 kg / m) manufactured by Sumitomo Chemical Co., Ltd. 3, MFR: 1.5 g / 10 min at 230 °C, load: 2.16 kg, melting point: 132 °C, Ziegler-Natta catalyst), propylene-ethylene random copolymer WFW4M (ethylene content: 7 wt%, density: 900 kg / m 3 , MFR 7.0 g / 10 min at 230 °C and 2.16 kg, melting point 136 °C, metallocene catalyst), WFX4M (ethylene content: 7 wt%, density: 900 kg / m) manufactured by Japan Polypropylene Corporation 3 , 230°C, MFR: 7.0 g / 10 min under a load of 2.16 kg, melting point: 125°C, metallocene catalyst).

[0032] (propylene homopolymer) In the present invention, propylene homopolymers can be used, including isotactic polypropylene, which has high crystallinity and excellent rigidity and heat resistance, and atactic polypropylene, which has low crystallinity and excellent flexibility. The propylene homopolymer to be used is preferably isotactic polypropylene, which has high crystallinity and is less susceptible to deterioration in heat shrinkage. The melt flow rate (MFR) of the propylene homopolymer (measured at 230°C under a load of 2.16 kg) is preferably 1 to 10 g / 10 min, more preferably 2 to 7. If it is 1 g / 10 min or more, it is easy to extrude it through a T-die, and conversely, if it is 10 g / 10 min or less, it is easy to increase the impact strength (impact strength) of the film.

[0033] Propylene homopolymers containing metallocene-based olefin polymerization catalysts are characterized by a narrower molecular weight distribution and fewer components lower and higher than the weight-average molecular weight (MW). We have also discovered that the use of propylene homopolymers containing metallocene-based olefin polymerization catalysts suppresses the formation of whiskers. Furthermore, they exhibit excellent flexibility and strength. A metallocene-based olefin polymerization catalyst is a catalyst consisting of (i) a transition metal compound from Group 4 of the periodic table containing a cyclopentadienyl-based ligand (a so-called metallocene compound), (ii) a cocatalyst capable of activating the metallocene compound to a stable ionic state, and, optionally, (iii) an organoaluminum compound. Any known catalyst can be used.

[0034] Specifically, the propylene homopolymer is F300SP (ethylene content: 0% by weight, density: 890 kg / m) manufactured by Prime Polymer Co., Ltd. 3 , MFR: 3.0 g / 10 min at 230°C and a load of 2.16 kg, melting point: 160°C, Ziegler-Natta catalyst).

[0035] (copolymer elastomer) In the present invention, a copolymer elastomer is used as a constituent component of the polyolefin resin film of the present invention in order to improve the drop-breakage resistance of the packaging bag of the present invention. Examples of copolymer elastomers include olefin-based thermoplastic elastomers, which are olefin-based thermoplastic copolymers that exhibit rubber-like elasticity at around room temperature, and / or olefin-based thermoplastic copolymer elastomers that exhibit relatively high Shore hardness and good transparency. As such copolymer elastomer, at least one elastomer selected from the group consisting of ethylene-propylene copolymer elastomer, propylene-butene copolymer elastomer, and ethylene-butene copolymer elastomer may be used, but ethylene-propylene copolymer elastomer is preferred from the viewpoint of impact resistance and heat seal strength. The ethylene-propylene copolymer elastomer refers to a thermoplastic elastomer that is an amorphous or low-crystalline elastomer obtained by copolymerizing ethylene and propylene.

[0036] The copolymer elastomer in the present invention has a melt flow rate (MFR) of 0.2 to 5 g / 10 min at 230°C and a load of 2.16 kg, and a density of 820 to 930 kg / m 3 In a preferred embodiment, the molecular weight distribution (Mw / Mn) determined by GPC is 1.3 to 6.0. When the copolymer elastomer of the present invention has a melt flow rate (MFR) of 0.2 g / 10 min or more at 230°C under a load of 2.16 kg, it is easy to knead uniformly and fish eyes are less likely to occur, and when it is 5 g / min or less, bag rupture resistance is likely to be improved. The intrinsic viscosity [η] of the copolymer elastomer in the present invention is preferably 1.0 to 5.0, and more preferably 1.2 to 3.0, from the viewpoints of maintaining heat seal strength, impact strength, and bag drop strength. When the intrinsic viscosity [η] is 1.0 or more, uniform mixing is facilitated and fisheyes are less likely to occur, while when it is 5.0 or less, bag breakage resistance and heat seal strength are likely to be improved.

[0037] The copolymerization ratio of the ethylene component in the ethylene-propylene copolymer elastomer, propylene-butene copolymer elastomer, and ethylene-propylene copolymer elastomer is preferably 55 to 85% by weight, and more preferably 60 to 80% by weight.The copolymerization ratio of the propylene component in the ethylene-propylene copolymer elastomer is preferably 15 to 45% by weight, and more preferably 20 to 40% by weight.

[0038] Specifically, the ethylene-propylene copolymer elastomer in the present invention has a propylene content of 27% by weight and a density of 870 kg / m 3 and an ethylene-propylene copolymer elastomer having a MFR (230° C., 2.16 kg) of 1.8 g / 10 min (Tafmer P0480, manufactured by Mitsui Chemicals, Inc.).

[0039] (Polyolefin resin film) The polyolefin resin film of the present invention may be a single layer or may be composed of two or more layers, for example, a three-layer structure of a heat seal layer / laminate layer or a heat seal layer / intermediate layer / laminate layer, and each layer may be composed of multiple layers.

[0040] The heat seal layer is a layer located on the outermost surface side of the polyolefin resin film, and a package can be produced by placing the two surfaces of the heat seal layer face to face and thermocompressing them together. The layer located on the outermost surface opposite to the heat seal layer is a laminate layer, which can be laminated by being stuck to a base film such as a polyester film or a polyamide film. In the case of a three-layer structure of heat seal layer / intermediate layer / laminate layer, the end portion of the film product of the present invention or the film itself can be recovered and re-pelletized to be used as the raw material for the intermediate layer, thereby reducing the cost of the film product without impairing properties such as straight cuttability, ease of tearing, bag-making processability, and bag-breaking resistance.

[0041] In each layer of the polyolefin resin film of the present invention, the balance of properties such as tearability, heat seal strength, and bag rupture resistance can be adjusted by changing the mixing ratio of at least one elastomer selected from the group consisting of propylene-ethylene block copolymer, propylene-α-olefin random copolymer or propylene homopolymer, ethylene-propylene copolymer elastomer, propylene-butene copolymer elastomer, and ethylene-butene copolymer elastomer in each layer.

[0042] (propylene-ethylene block copolymer) In each layer of the polyolefin resin film of the present invention, the content of the propylene-ethylene block copolymer in a total of 100 parts by weight of polypropylene resin is in the range of 40 to 97 parts by weight, preferably 60 parts by weight or more, and more preferably 85 parts by weight or less, from the viewpoint of separation. When the ratio of the propylene-ethylene block copolymer is 40 parts by weight or more, the shrinkage rate tends to be small and the resistance to bag breakage tends to be improved.When the ratio is 97 parts by weight or less, heat sealing properties at low temperatures tend to be obtained.

[0043] (Propylene-α-olefin random copolymer or propylene homopolymer) In each layer of the polyolefin resin film of the present invention, the content of propylene-α-olefin random copolymer or propylene homopolymer in a total of 100 parts by weight of polypropylene resin is in the range of 0 to 50 parts by weight from the viewpoint of separation, preferably 5 parts by weight or more and 40 parts by weight or less, and more preferably 15 parts by weight or more. When the content of propylene-α-olefin random copolymer or propylene homopolymer is 5 parts by weight or more, it is easy to obtain heat sealability at low temperatures and the heat seal strength is also easy to increase, and when it is 50 parts by weight or less, it is easy to reduce the heat shrinkage rate.

[0044] (copolymer elastomer) In each layer of the polyolefin resin film of the present invention, the content of at least one elastomer selected from the group consisting of ethylene-propylene copolymer elastomer, propylene-butene copolymer elastomer, and ethylene-butene copolymer elastomer is in the range of 3 to 10 parts by weight, preferably 4 to 9 parts by weight, more preferably 5 to 8 parts by weight, per 100 parts by weight of polypropylene resin in total. By incorporating 3 parts by weight or more of at least one elastomer selected from the group consisting of ethylene-propylene copolymer elastomer, propylene-butene copolymer elastomer, and ethylene-butene copolymer elastomer, heat sealability and bag rupture resistance are easily achieved when ease of tearing is imparted, and by incorporating 10 parts by weight or less, the appearance (transparency) of the film is improved.

[0045] The polyolefin resin film of the present invention has a sea-island structure consisting of a matrix polymer and domains, which allows it to exhibit good bag-rupture resistance. The matrix polymer is mainly composed of a propylene-based portion of a propylene-ethylene block copolymer and a propylene-α-olefin random copolymer, and the domains are mainly composed of an ethylene-propylene copolymer elastomer and the ethylene-based portion of each of the propylene-ethylene block copolymers.

[0046] (additives) The polypropylene resin composition of the present invention may contain an antiblocking agent. The antiblocking agent to be added is not particularly limited, but examples include inorganic particles such as calcium carbonate, silicon dioxide, titanium dioxide, barium sulfate, magnesium oxide, talc, and zeolite, as well as organic particles made of acrylic, styrene, and styrene-butadiene polymers, and crosslinked versions of these. Considering ease of particle size distribution control, dispersibility, ease of maintaining optical appearance, and prevention of particle detachment from the film, crosslinked organic particles are preferred. As the crosslinked polymer, crosslinked acrylic polymers made of acrylic monomers such as acrylic acid, methacrylic acid, acrylic esters, and methacrylic esters are particularly preferred, with crosslinked polymethyl methacrylate being more preferred. The surfaces of these particles may be coated with various coatings for the purposes of improving dispersibility and preventing falling off. The shape of these particles may be irregular, spherical, oval, rod-like, angular, polyhedral, conical, or even porous with cavities on the particle surface or inside. From the viewpoints of film appearance and blocking resistance, the antiblocking agent preferably has an average particle size of 3 to 12 μm. Although using only one type of anti-blocking agent is effective, blending two or more types of inorganic particles with different particle sizes and shapes can sometimes result in more complex protrusions being formed on the film surface, resulting in a more advanced anti-blocking effect. When a block copolymer is used as the main constituent resin, the dispersion of the polymer may result in the formation of surface irregularities, and a high level of anti-blocking effect may be obtained even without the addition of an anti-blocking agent.

[0047] An organic lubricant may be added to the polypropylene resin composition of the present invention. This improves the lubrication and anti-blocking properties of the laminated film, improving film handling. The reason for this is believed to be that the organic lubricant bleeds out and is present on the film surface, thereby exerting its lubricating and release effects. Furthermore, it is preferable to add an organic lubricant with a melting point above room temperature. Examples of suitable organic lubricants include fatty acid amides and fatty acid esters. More specifically, these include oleic acid amide, erucic acid amide, behenic acid amide, ethylene bisoleic acid amide, hexamethylene bisoleic acid amide, and ethylene bisoleic acid amide. While these may be used alone, using two or more of them in combination can sometimes maintain lubrication and anti-blocking properties even under harsh environments, making this preferable.

[0048] The polypropylene resin composition of the present invention may contain, as needed, appropriate amounts of antioxidants, antistatic agents, antifogging agents, neutralizing agents, nucleating agents, colorants, other additives, inorganic fillers, etc., within the scope of the object of the present invention. Examples of antioxidants include phenolic and phosphite antioxidants, which may be used alone or in combination, or antioxidants having both phenolic and phosphite skeletons in one molecule.

[0049] (Method of manufacturing polyolefin resin film) The polyolefin resin film of the present invention can be formed using, for example, an inflation method or a T-die method, but the T-die method is preferred for its enhanced transparency and ease of drafting. While the inflation method uses air as the cooling medium, the T-die method uses a cooling roll, making it an advantageous production method for increasing the cooling rate of the unstretched sheet. Increasing the cooling rate not only suppresses crystallization of the unstretched sheet, but also provides the advantage of easily controlling the load applied to stretching in the subsequent process. For these reasons, molding using the T-die method is more preferable.

[0050] The lower limit of the cooling roll temperature when the molten raw resin is cast to obtain a non-oriented sheet is preferably 15°C, more preferably 20°C. If the temperature is lower than the above, condensation occurs on the cooling roll, resulting in insufficient adhesion between the unstretched sheet and the cooling roll, which may cause thickness defects. The upper limit of the cooling roll is preferably 50°C, more preferably 40°C. If the temperature is 50°C or lower, the transparency of the polyolefin resin film is less likely to deteriorate.

[0051] The non-oriented sheet can be stretched by, for example, inflation, tenter transverse stretching, or roll longitudinal stretching, but roll longitudinal stretching is preferred because of ease of control of orientation. By stretching a non-oriented sheet under appropriate conditions, straight cut properties are achieved because the molecular chains are regularly aligned in the stretching direction. The lower limit of the stretching ratio is preferably 2.8 times, more preferably 3.3 times. If the stretching ratio is 2.8 times or more, the tear strength in the stretching direction is unlikely to increase, and straight cuttability is easily obtained. The lower limit is more preferably 3.4 times, and even more preferably 3.5 times. The upper limit of the stretching ratio is preferably 3.9 times. At 3.9 times or less, excessive orientation is unlikely to proceed and the thermal shrinkage in the longitudinal direction is unlikely to increase. The upper limit is more preferably 3.8 times.

[0052] The lower limit of the stretching roll temperature is preferably 80° C. If the temperature is 80° C. or higher, the stretching stress applied to the film will not be too high, and the shrinkage rate will not be large. The temperature is more preferably 90° C. The upper limit of the stretching roll temperature is preferably 140°C. If the temperature is 140°C or lower, the stretching stress applied to the film will not be too low, and the thermal shrinkage rate of the film in the longitudinal direction will not be too low, and the film will not easily fuse to the stretching roll. The upper limit is more preferably 130°C, even more preferably 125°C, and particularly preferably 115°C.

[0053] It is preferable to bring the unstretched sheet into contact with a preheat roll to raise the sheet temperature before introducing it into the stretching step. The lower limit of the preheating roll temperature when stretching a non-oriented sheet is preferably 80°C, more preferably 90°C. If the temperature is 80°C or higher, the stretching stress does not become too high, and thickness fluctuation is unlikely to worsen. The upper limit of the preheating roll temperature is preferably 140°C, more preferably 130°C, and even more preferably 125°C. If the temperature is 140°C or lower, the film is unlikely to stick to the roll, and film thickness fluctuation is unlikely to increase.

[0054] It is preferable to anneal the polyolefin resin film after the stretching process to suppress thermal shrinkage. Annealing methods include roll heating and tentering, with roll heating being preferred due to the simplicity of the equipment and ease of maintenance. Annealing reduces the internal stress of the film, thereby suppressing thermal shrinkage in the longitudinal direction of the film. This does not sacrifice the longitudinal heat shrinkage rate or heat seal strength compared to the conventional method of simply increasing the stretch ratio to improve tearability. However, while this may adversely affect properties other than the longitudinal heat shrinkage rate and heat seal strength, the present invention can suppress adverse effects on bag rupture resistance by using a copolymer elastomer in combination.

[0055] The lower limit of the annealing temperature is preferably 100°C. If the temperature is below 100°C, the heat shrinkage rate in the longitudinal direction is unlikely to increase, the tear strength is unlikely to increase, and the finish of the packaging bag after bag making or retorting may deteriorate. 115°C is more preferable, and 125°C is particularly preferable. The upper limit of the annealing temperature is preferably 140°C. A higher annealing temperature tends to reduce the thermal shrinkage in the longitudinal direction, but if the annealing temperature exceeds this limit, the film thickness fluctuation may worsen or the film may fuse to the manufacturing equipment. A more preferred upper limit is 135°C.

[0056] In the annealing step, a relaxation step can be provided by gradually slowing down the film transport speed, for example, by reducing the rotation speed of the roll after heating. By providing the relaxation step, the thermal shrinkage rate of the produced polyolefin resin film can be reduced. The upper limit of the relaxation rate in the relaxation step is preferably 10%, more preferably 8%. If it is 10% or less, the heat shrinkage rate will not be too small. The lower limit of the relaxation rate is preferably 1%, more preferably 3%. If it is 1% or more, the heat shrinkage rate in the longitudinal direction of the polyolefin resin film is unlikely to become high.

[0057] In the present invention, it is preferable to activate the surface of the polyolefin resin film to be laminated by corona treatment or the like. This improves the lamination strength with the base film. The laminate surface is provided on the opposite side of the heat-sealed surface.

[0058] (Properties of polyolefin resin film) (film thickness) The lower limit of the thickness of the polyolefin resin film of the present invention is preferably 10 μm, more preferably 30 μm. If the thickness is less than this, the film will be relatively thin compared to the thickness of the base film, which may result in poor straight-cutting properties as a laminate, and the film may be too weak and difficult to process, and may also result in reduced impact resistance and poor bag-breaking resistance. The upper limit of the film thickness is preferably 200 μm, more preferably 130 μm. If the thickness exceeds this limit, the film may be too strong and difficult to process, and may also result in difficulty in producing a suitable package.

[0059] (Longitudinal orientation coefficient) The longitudinal orientation coefficient ΔNx used in the present invention can be calculated by Equation 1. ΔNx=Nx-(Ny+Nz) / 2 (Equation 1) Nx: refractive index in the longitudinal direction Ny: Refractive index in the longitudinal direction and perpendicular to the thickness direction Nz: Refractive index in the thickness direction The lower limit of the longitudinal orientation coefficient ΔNx of the polyolefin resin film of the present invention is 0.0150, more preferably 0.0180, and even more preferably 0.0200. If it is 0.0150 or more, the straight cuttability of the package is easily obtained. The upper limit of the longitudinal orientation coefficient ΔNx is preferably 0.0250, more preferably 0.0245, even more preferably 0.0240, still more preferably 0.0230, and particularly preferably 0.0220. If it is 0.0250 or less, the heat seal strength is less likely to decrease.

[0060] (Thermal shrinkage rate) The upper limit of the heat shrinkage rate in the longitudinal direction of the polyolefin resin film of the present invention at 120°C is 9%. If it is 9% or less, the tear strength is reduced, and at the same time, shrinkage during heat sealing or retort of the package is reduced, resulting in excellent appearance of the package. The upper limit is preferably 8%, more preferably 7%, more preferably 6%, even more preferably 5%, and particularly preferably 4%. The lower limit of the longitudinal heat shrinkage rate of the polyolefin resin film of the present invention is 1%. If it is 1% or more, the tear strength tends to be low. It is preferably 2%.

[0061] (Moving from below) To achieve straight cutability, the lower limit of the longitudinal orientation coefficient ΔNx must be 0.0150, but whisker formation is less likely to occur if the upper limit of the longitudinal heat shrinkage rate at 120°C is 9%. The reason for this is that when the film is heat-melted by heat sealing, orientation is less likely to remain in the sealed area or at the sealed edge, so the film laminated to the base film is restrained by the base film during heat sealing and is less likely to shrink. This is thought to be because force is applied to the film, making it difficult to re-orient the film. The upper limit of the heat shrinkage rate of the polyolefin resin film of the present invention in the direction perpendicular to the longitudinal direction (width direction) is preferably 1%. If it is 1% or less, the tear strength in the longitudinal direction tends to be low, making it easier to achieve straight cuttability. It is preferably 0.5%. The lower limit of the heat shrinkage rate of the polyolefin resin film of the present invention in the direction perpendicular to the one direction is -5%. If it is -5% or more, elongation may occur during heat sealing, which may deteriorate the appearance of the package. It is preferably -2%.

[0062] (Hayes) Haze was measured according to JIS K 7136. Measurements were made on the polyolefin resin film before lamination (N=3), and the average value was calculated. The upper limit of the haze is preferably 80%, more preferably 70%, even more preferably 60%, and even more preferably 50%. When it is 80% or less, the visibility of the contents is excellent. The lower limit of the haze is preferably 20%.

[0063] (tear strength) The upper limit of the longitudinal tear strength of the polyolefin resin film of the present invention is preferably 0.30 N. If this limit is exceeded, the laminate film may become difficult to tear. The upper limit is more preferably 0.16 N. The lower limit of the longitudinal tear strength of the polyolefin resin film of the present invention is preferably 0.02 N. If it is smaller than this, the resistance to bag rupture may deteriorate. It is more preferably 0.03 N.

[0064] (Puncture strength) The lower limit of the puncture strength of the polyolefin resin film of the present invention is preferably 10 N, more preferably 15 N / μm, even more preferably 18 N, and even more preferably 20 N. If the puncture strength is 15 N or more, pinholes are less likely to occur when a protrusion hits the package. The upper limit of the puncture strength is preferably 35 N. If the puncture strength is 35 N or less, the film or laminate will not be too stiff and will be easy to handle.

[0065] (Puncture strength) The lower limit of the puncture strength per μm of the polyolefin resin film of the present invention is preferably 0.13 N / μm, more preferably 0.15 N / μm. If it is less than this, pinholes may occur when the protrusion hits the package. The upper limit of the puncture strength is preferably 0.40 N / μm. If it exceeds this, the film may be too stiff, making it difficult to handle when made into a film or laminate.

[0066] (wet tension) The lower limit of the wet tension of the surface of the polyolefin resin film of the present invention to be laminated with at least one film selected from the group consisting of polyamide resin films, polyester resin films, and polypropylene resin films is preferably 30 mN / m, more preferably 35 mN / m. If the wet tension is less than this, the laminate strength may decrease. The upper limit of the wet tension is preferably 55 mN / m, more preferably 50 mN / m. If the wet tension exceeds this, blocking of the roll of the polyolefin resin film may occur.

[0067] (Structure of laminate and manufacturing method) The laminate using the polyolefin resin film of the present invention is a laminate of the polyolefin resin film as a sealant and at least one film selected from the group consisting of polyamide resin film, polyester resin film, and polypropylene resin film. Furthermore, these substrate films may be coated or vapor-deposited using known techniques to impart adhesiveness or barrier properties, or may be further laminated with aluminum foil. Specific examples include biaxially oriented PET film / aluminum foil / sealant, biaxially oriented PET film / biaxially oriented nylon film / sealant, biaxially oriented nylon film / sealant, biaxially oriented polypropylene film / sealant, and biaxially oriented PET film / biaxially oriented nylon film / aluminum foil / sealant. Among these, when a sealant with low longitudinal orientation is used with biaxially oriented nylon film, the straight-cutting ability of the laminate is significantly impaired. By using the polyolefin resin film of the present invention as a sealant, laminates with good straight-cutting ability can be produced in any configuration. As the lamination method, known methods such as dry lamination and extrusion lamination can be used, but any lamination method can produce a laminate with good straight cutability.

[0068] (Laminate properties) (tear strength) The upper limit of the longitudinal tear strength of the laminate of the present invention is preferably 0.50 N. If it is 0.50 N or less, the laminate is easily torn. It is more preferably 0.40 N, even more preferably 0.35 N, and even more preferably 0.30 N. The lower limit of the longitudinal tear strength may be 0.05 N.

[0069] (Straight cutting ability) The straight cuttability refers to the ability of a film or laminate to be torn straight in one direction. Measurement was carried out by the following method. In this example, the film was stretched in the longitudinal direction, so the heat shrinkage rate was high in the longitudinal direction, and the one direction was the longitudinal direction. Therefore, the straight cuttability was evaluated only in the longitudinal direction. The film or laminate film was cut into strips measuring 150 mm in the longitudinal direction and 60 mm perpendicular to the longitudinal direction, and a 30 mm slit was made along the longitudinal direction from the center of the short edge. The sample was torn in accordance with JIS K7128-1:1998. At the point where the sample had been torn 120 mm in the longitudinal direction, excluding the 30 mm slit, the distance traveled in the longitudinal and perpendicular directions was measured and the absolute value was recorded. Measurements were performed in triplicate for both cases, with the right-hand piece clamped in the upper grip and the left-hand piece clamped in the upper grip, and the average value for each was calculated. The larger value of the measurement results for the right or left side was used.

[0070] (Straight cutting ability) The upper limit of the straight cuttability of the laminate of the present invention is preferably 8 mm, more preferably 5 mm, and even more preferably 3 mm. If it is 8 mm or less, the package is less likely to tear apart. The lower limit may be 0.5 mm.

[0071] (Tearful farewell) The upper limit of the tear-off thickness of the laminate of the present invention is not particularly limited, but is preferably 15 mm, more preferably 10 mm, even more preferably 6 mm, and particularly preferably 5 mm. If it is 15 mm or less, the contents are less likely to spill when the package is torn. The lower limit may be 1 mm.

[0072] (beard incidence) A laminate film of the polyolefin resin film and the base film of the invention was heat-sealed with the heat-sealable film layers facing each other to create a four-sided sealed bag with internal dimensions of 120 mm in the longitudinal direction and 170 mm perpendicular to the longitudinal direction. A notch was made at the end of the four-sided sealed bag, which was then manually torn in the longitudinal direction. The whisker occurrence rate, calculated from the number of times thread-like film fragments (whiskers) appeared and the number of times the bag was torn, is preferably 30% or less, more preferably 25% or less, even more preferably 20% or less, particularly preferably 16% or less, and most preferably 10% or less. The laminate film was prepared by mixing the polyolefin resin film of the present invention and a substrate film (biaxially oriented nylon film N1102 manufactured by Toyobo Co., Ltd., thickness 15 μm, orientation angle 22° relative to the longitudinal direction) with 33.6 parts by weight of an ester-based dry laminating adhesive (TM569 manufactured by Toyo Morton Co., Ltd.), 4.0 parts by weight of a curing agent (CAT10L manufactured by Toyo Morton Co., Ltd.), and 62.4 parts by weight of ethyl acetate, with an adhesive coating amount of 3.0 g / m. 2 The laminated film was kept at 40°C and aged for 3 days to obtain a laminated film. Hair growth rate = number of hair growths / number of tears × 100 (%)

[0073] (Finished bag) The polyolefin resin film sides of the laminate films were overlapped and heat-sealed at 0.2 MPa for 1 second with a seal bar width of 10 mm and a heat seal temperature of 220°C to create a four-sided sealed bag with internal dimensions of 120 mm in the MD and 170 mm in the TD. When the finished state of this four-sided sealed bag was visually inspected, it was preferable that there was no deformation near the heat-sealed areas, and it was also preferable that the bag was perfectly rectangular.

[0074] (retort shrinkage rate) The upper limit of the retort shrinkage of the laminate of the present invention is preferably 5%. If it exceeds this limit, the appearance of the package after retort may deteriorate. It is more preferably 4%. The lower limit of the retort shrinkage in one direction is -5%. If it is less than this limit, the elongation after retort may be too great, which may cause the bag to break. It is more preferably -2%, and even more preferably 0%.

[0075] (Heat seal strength) The lower limit of the heat seal strength of the laminate of the present invention before retort is preferably 35 N / 15 mm, more preferably 40 N / 15 mm. If it is less than this, the bag rupture resistance may deteriorate. The heat seal strength preferably remains at 35 N / 15 mm or more even after retort treatment at 121°C for 30 minutes. The upper limit of the heat seal strength is preferably 60 N / 15 mm. To exceed this limit, it may be necessary to increase the thickness of the film, which may result in higher costs.

[0076] (Heat seal starting temperature) The lower limit of the heat-sealing initiation temperature before retort of the laminate of the present invention is preferably 190°C or lower, more preferably 185°C or lower, and even more preferably 180°C or lower. If the temperature exceeds 190°C, the film will shrink significantly during bag formation, impairing the appearance, and the bag-making speed may decrease, resulting in higher costs. The lower limit of the heat-sealing temperature is preferably 150°C or higher, and even more preferably 160°C or higher. If the temperature is lower than the above, the heat of the retort treatment may cause the inner surface of the film to fuse.

[0077] (packaging) The laminate, which is arranged to enclose the contents, such as food, for the purpose of protecting the contents from natural dust, gases, and the like, is called a package. Packages are manufactured by cutting out the laminate, bonding the inner surfaces together using a heated heat seal bar or ultrasonic waves, and forming them into a bag. A commonly used example is a four-sided sealed bag, in which two rectangular laminates are stacked with the sealant side facing inward and the four sides are heat-sealed. The contents may be food, but may also be other products such as daily necessities, and the shape of the package may be a shape other than rectangular, such as a stand-up pouch or pillowcase. Furthermore, packaging that can withstand the heat of thermal sterilization using hot water whose boiling point has been raised to 100°C or higher by pressurization or other methods is called a retort packaging, and films intended to provide such packaging are called retort films.

[0078] (Bag resistance) A four-side sealed bag made from the laminate of the present invention is dropped and repeatedly dropped until the bag breaks, and the number of repeated drops is measured. From a practical standpoint, it is preferable that the number of drops at which 50% of the bags remain unbroken is 5 or more, more preferably 10 or more, even more preferably 11 or more, and even more preferably 12 or more. [Example]

[0079] The present invention will be described in detail below with reference to examples, but is not limited to these. The properties obtained in each example were measured and evaluated by the following methods. In the evaluation, the longitudinal direction of the film was defined as the MD direction, and the direction perpendicular to the longitudinal direction (width direction) was defined as the TD direction.

[0080] (1) Resin density The density was evaluated in accordance with JIS K7112:1999 D method (density gradient tube). N=3 measurements were taken and the average value was calculated.

[0081] (2) Melt flow rate (MFR) Measurements were carried out in accordance with JIS K-7210-1 at 230°C and a load of 2.16 kg. N=3 measurements were taken, and the average value was calculated.

[0082] (3) Heat shrinkage rate The film before lamination was cut into 120mm squares. Marked lines were marked at 100mm intervals in both the MD and TD directions. The sample was hung in an oven maintained at 120°C and heat-treated for 30 minutes. The distance between the marked lines was measured, and the thermal shrinkage was calculated according to the following formula. N=3 measurements were made, and the average value was calculated. Heat shrinkage rate = (gauge length before heat treatment - gauge length after heat treatment) / gauge length before heat treatment x 100 (%)

[0083] (4) Tear strength The tear strength was measured according to JIS K7128-1:1998. Evaluation was carried out on the base film before lamination and on the laminate film. Measurements were made in the MD direction and the TD direction with N=3 each, and the average value was calculated.

[0084] (5) Longitudinal orientation coefficient The refractive index was evaluated in accordance with JIS K 0062:1999, a method for measuring the refractive index of chemical products. Measurements were made with N=3, and the average value was calculated. The longitudinal orientation coefficient ΔNx was calculated using Equation 1. ΔNx=Nx-(Ny+Nz) / 2 (Equation 1) Nx: refractive index in the longitudinal direction Ny: Refractive index in the longitudinal direction and perpendicular to the thickness direction Nz: Refractive index in the thickness direction

[0085] (6) Straight cutting ability The straight cut property indicates the ability of a laminate film (laminate) to tear straight in one direction when torn. Measurement was performed as follows. In this example, the film was stretched in the MD direction, so the heat shrinkage rate was high in the MD direction, and the one direction was the MD direction. Therefore, the straight cut property was evaluated only in the MD direction. The laminate film was cut into strips measuring 150 mm in the MD direction and 60 mm in the TD direction, and a 30 mm slit was made in the MD direction from the center of the short edge. The sample was torn in accordance with JIS K7128-1:1998. The distance traveled in the TD direction was measured after 120 mm of tearing in the MD direction, excluding the 30 mm slit, and the absolute value was recorded. Measurements were performed with N=3 for both cases, where the right-hand piece was clamped in the upper grip and where the left-hand piece was clamped in the upper grip, and the average value for each was calculated. The larger of the measurement results for the right and left sides was used.

[0086] (7) Tearful Parting The laminated films were placed face-to-face and heat-sealed to create a four-sided sealed bag with an internal dimension of 120 mm in the MD and 170 mm in the TD. A notch was made at the edge of the four-sided sealed bag, and it was torn by hand in the MD. The cut was continued to the opposite end, and the deviation of the tear lines between the film on the front and back of the bag was measured. Measurements were taken in both the right-hand side facing and left-hand side facing directions, with N=3 for each direction, and the average value was calculated. The larger measurement was used.

[0087] (8) Retort shrinkage rate The laminate film was cut into 120mm squares. Marked lines were marked at 100mm intervals in both the MD and TD directions. The film was retorted in hot water at 121°C for 30 minutes. The distance between the marks was measured, and the retort shrinkage was calculated according to the following formula. Measurements were performed on N=3 for each film, and the average value was calculated. Retort shrinkage rate = (gauge length before treatment - gage length after treatment) / gage length before treatment x 100 (%)

[0088] (9) Heat seal strength The heat-sealing and strength measurement conditions were as follows. Specifically, the polyolefin resin film sides of the laminate films obtained in the Examples and Comparative Examples were overlapped and heat-sealed at 0.2 MPa for 1 second with a 10 mm seal bar width at 220°C. The films were then allowed to cool. They were then retorted in hot water at 121°C for 30 minutes. Test pieces measuring 80 mm in the MD and 15 mm in the TD were cut from the films heat-sealed at each temperature. The peel strength of each test piece was measured when the heat-sealed portion was peeled at a crosshead speed of 200 mm / min. An Instron Instruments Universal Testing Machine 5965 was used. Measurements were performed three times for each test, and the average value was calculated.

[0089] (10) Sealing start temperature The seal initiation temperature is an item related to productivity when assuming continuous production using a bag making machine. Good bag making suitability means that sufficient sealing properties can be obtained within a temperature range where the base film does not shrink or break. The heat sealing temperature was evaluated as follows. In measuring the heat seal strength, the temperature of the heat seal bar was changed in 5°C increments, and the heat seal strength was measured for each test with N = 3. The heat seal strength was calculated as a weighted average of the heat seal temperature just before the heat seal strength exceeded 30 N and the heat seal temperature just after the heat seal strength exceeded 30 N.

[0090] (11) Beard incidence The laminated films were placed face-to-face with the heat-sealed films and heat-sealed to create a four-sided sealed bag with an internal dimension of 120 mm in the MD and 170 mm in the TD. A notch was made at the edge of the four-sided sealed bag, and it was torn by hand in the MD. The incidence rate was calculated from the number of times that thread-like film fragments (whiskers) appeared. Tests were conducted with n=100 in both the right-hand side and left-hand side facing directions, and the larger measurement value was used. Hair growth rate = number of hair growths / number of tears × 100 (%)

[0091] (12) Finished bag The polyolefin resin film sides of the laminate films were overlapped and heat-sealed at 0.2 MPa for 1 second with a seal bar width of 10 mm and a heat seal temperature of 220°C to create a four-sided sealed bag with inner dimensions of 120 mm in the MD direction and 170 mm in the TD direction. The finished state of this four-sided sealed bag was visually inspected. ○: No deformation near the heat-sealed area, and the bag is perfectly rectangular △: Little deformation near the heat-sealed area ×: Large deformation near the heat-sealed area, causing the bag edge to ripple

[0092] (13) Bag breakage resistance Laminated film was cut out to create four-sided sealed bags with internal dimensions of 170 mm length and 120 mm width, each containing 300 ml of saturated saline solution. The heat-sealing conditions were a pressure of 0.2 MPa for 1 second, a seal bar width of 10 mm, and a heat-sealing temperature of 220°C. After bag production, the edges of the four-sided sealed bag were trimmed to leave a 5 mm seal width. The four-sided sealed bags were retorted at 121°C for 30 minutes. They were then left in a -5°C environment for 8 hours, after which they were dropped from a height of 1.0 m onto a flat concrete floor. The bags were repeatedly dropped until they broke, and the number of repeated drops was measured and classified as follows: 20 bags per level. ◎: 13 or more drops to reach a survival rate of 50% ○: The number of drops required to achieve a 50% survival rate is 10 to 12 times △: The number of drops required to achieve a 50% survival rate is between 5 and 9 times. ×: The number of drops that results in a survival rate of 50% is four or less.

[0093] (14) Orientation angle The orientation angle (°) of the substrate film was measured using a molecular orientation analyzer MOA-6004 manufactured by Oji Scientific Instruments Co., Ltd. A sample was cut out to 120 mm in the MD direction and 100 mm in the TD direction, and placed on the measuring instrument. The measured angle value was taken as the orientation angle. The MD direction was 0°. N=3 measurements were made, and the average value was calculated.

[0094] (15) Piercing strength The puncture strength of the film before lamination and the laminate was measured at 23°C in accordance with "2. Test Methods for Strength, etc." in "Standards for Foods, Food Additives, etc., Part 3: Apparatus and Containers / Packaging" (Ministry of Health and Welfare Notification No. 20, 1982) under the Food Sanitation Act. A needle with a tip diameter of 0.7 mm was pierced into the film at a puncture speed of 50 mm / min, and the strength at which the needle penetrated the film was measured. The obtained measurement value was divided by the film thickness to calculate the puncture strength [N / μm] per 1 μm of film. N=3 measurements were made, and the average value was calculated.

[0095] Example 1 (Polyolefin resin film) (Raw materials used) For the polypropylene resin films of Examples 1 to 7 and Comparative Examples 1 to 10, raw materials were prepared based on the resin compositions and ratios of each layer shown in Tables 1 and 2. These raw materials were mixed uniformly to obtain a mixed raw material for producing a polyolefin resin film. 1) Raw material A: Sumitomo Chemical Co., Ltd. propylene-ethylene block copolymer WFS5293-22 (ethylene content 7% by weight, resin density 891 kg / m 3 , MFR 3.0g / 10min at 230℃, 2.16kg, melting point 164℃) 2) Raw material B: Ethylene-propylene copolymer elastomer Toughmer P0480 (propylene content 27% by weight, resin density 870 kg / m) manufactured by Mitsui Chemicals 3 , MFR 1.8g / 10min at 230℃, 2.16kg, melting point 48℃) 3) Raw material C: Sumitomo Chemical Co., Ltd. propylene-ethylene random copolymer S131 (ethylene content 5.5 wt. %, resin density 890 kg / m 3 (MFR 1.5g / 10min at 230℃, 2.16kg, melting point 132℃, Ziegler-Natta catalyst) 4) Raw material D: Japan Polypropylene propylene-ethylene random copolymer WFW4M (ethylene content 7% by weight, resin density 900 kg / m 3 , 230℃, MFR 7.0g / 10min at 2.16kg, melting point 136℃, metallocene catalyst) 5) Raw material E: Japan Polypropylene propylene-ethylene random copolymer WFX4M (ethylene content 7% by weight, resin density 900 kg / m 3 , 230℃, MFR 7.0g / 10min at 2.16kg, melting point 125℃, metallocene catalyst)

[0096] (melt extrusion) The mixed raw materials for the intermediate layer were extruded in a three-stage single-screw extruder with a screw diameter of 90 mm, while the mixed raw materials for the laminate layer and heat-seal layer were extruded in three-stage single-screw extruders with diameters of 45 mm and 65 mm, respectively, in the order of laminate layer / intermediate layer / heat-seal layer. The extrusion was performed at an outlet temperature of 230°C, with a two-stage preland of 800 mm width and a curved step shape to ensure uniform flow of molten resin within the die. The thickness ratios of the laminate layer / intermediate layer / heat-seal layer were 25% / 50% / 25%, respectively. (cooling) The molten resin sheet emerging from the die was cooled on a cooling roll at 21°C to obtain an unstretched polyolefin resin film with a layer thickness of 210 μm. When cooling on the cooling roll, both ends of the film on the cooling roll were fixed with air nozzles, and the entire width of the molten resin sheet was pressed against the cooling roll with an air knife. At the same time, a vacuum chamber was operated to prevent air from being drawn in between the molten resin sheet and the cooling roll. The air nozzles were installed in series on both ends in the direction of film travel. The die was surrounded by a sheet to prevent the molten resin sheet from being exposed to wind.

[0097] (preheat) The unstretched sheet was preheated by being guided through a group of heated rolls and brought into contact with the rolls. The temperature of the preheating rolls was 105°C. Multiple rolls were used to preheat both sides of the film. (longitudinal stretching) The unstretched sheet was introduced into a longitudinal stretching machine and stretched 3.5 times by the roll speed difference to a thickness of 60 μm. The stretching roll temperature was 105° C. (annealing treatment) The film was heat-treated at 130°C using an annealing roll. Both sides of the film were heat-treated using multiple rolls. (relaxation process) The speed of the roll placed next to the annealing roll was reduced by 5% as a relaxation rate relative to the annealing roll to relax the film.

[0098] (Corona treatment) One side of the film (the laminating side) was subjected to a corona treatment. (winding) The film was formed at a take-up roll speed of 20 m / min. The edge portions of the formed film were trimmed and the film was wound into a roll. The thickness of the obtained film was 60 μm.

[0099] (Creating laminated film) The polyolefin resin film obtained in Example 1 and a substrate film (Toyobo biaxially oriented nylon film, N1102, 15 μm thick, 22° orientation angle relative to the MD direction) were dry-laminated using an ester-based adhesive obtained by mixing 33.6 parts by weight of an ester-based dry laminating adhesive (Toyo-Morton, TM569), 4.0 parts by weight of a curing agent (Toyo-Morton, CAT10L), and 62.4 parts by weight of ethyl acetate, so that the adhesive coating amount was 3.0 g / m2. The laminated film was kept at 40°C and aged for 3 days to obtain a laminate film.

[0100] Example 2 In Example 1, a 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the raw materials shown in Table 1 were used, the thickness of the unstretched polyolefin resin film was 228 μm, the longitudinal stretching ratio was 3.8 times, and the relaxation rate in the relaxation step was 7%. A laminate was obtained in the same manner as in Example 1.

[0101] Example 3 A 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the raw materials shown in Table 1 were used and the relaxation rate in the relaxation step was set to 7%. A laminate was obtained in the same manner as in Example 1.

[0102] Example 4 In Example 1, a 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the raw materials shown in Table 1 were used, the thickness of the unstretched polyolefin resin film was 228 μm, and the longitudinal stretching ratio was 3.8 times. A laminate was obtained in the same manner as in Example 1.

[0103] Example 5 A 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the raw materials shown in Table 1 were used and the relaxation rate in the relaxation step was 6%. A laminate was obtained in the same manner as in Example 1.

[0104] Example 6 In Example 1, a 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the raw materials shown in Table 1 were used, the thickness of the unstretched polyolefin resin film was 228 μm, and the longitudinal stretching ratio was 3.8 times. A laminate was obtained in the same manner as in Example 1.

[0105] Example 7 A 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the raw materials shown in Table 1 were used, the thickness of the unstretched polyolefin resin film was 186 μm, and the longitudinal stretching ratio was 3.1 times. A laminate was obtained in the same manner as in Example 1.

[0106] (Comparative Example 1, Comparative Example 2) In Example 1, the raw materials shown in Table 2 were used, and the thickness of the unstretched polyolefin resin film was 60 μm. A 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the longitudinal stretching, annealing treatment, and relaxation steps were not performed. A laminate was obtained in the same manner as in Example 1.

[0107] (Comparative Example 3) In Example 1, the raw materials shown in Table 2 were used, and a 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the thickness of the unstretched polyolefin resin film was 240 μm, the longitudinal stretching ratio was 4.0 times, and no relaxation step was performed. A laminate was obtained in the same manner as in Example 1.

[0108] Comparative Example 4 In Example 1, a 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the raw materials shown in Table 2 were used, the thickness of the unstretched polyolefin resin film was 270 μm, the longitudinal stretching ratio was 4.5, the annealing temperature was 120° C., and no relaxation step was performed. A laminate was obtained in the same manner as in Example 1.

[0109] (Comparative Example 5) In Example 1, the raw materials shown in Table 2 were used, and a 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the thickness of the unstretched polyolefin resin film was 120 μm, the longitudinal stretching ratio was 2.0 times, the annealing temperature was 120° C., and no relaxation step was performed. A laminate was obtained in the same manner as in Example 1.

[0110] (Comparative Example 6) In Example 1, the raw materials shown in Table 2 were used, and a 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the thickness of the unstretched polyolefin resin film was 186 μm, the longitudinal stretching ratio was 3.1 times, the annealing temperature was 120° C., and no relaxation step was performed. A laminate was obtained in the same manner as in Example 1.

[0111] (Comparative Example 7) A polyolefin resin film having a thickness of 60 μm was obtained in the same manner as in Example 1, except that the relaxation step was not carried out.

[0112] (Comparative Example 8) A polyolefin resin film having a thickness of 60 μm was obtained in the same manner as in Example 1, except that the annealing step and the relaxation step after stretching were not performed.

[0113] Comparative Example 9 A 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the raw materials shown in Table 2 were used, the thickness of the unstretched polyolefin resin film was 150 μm, and the longitudinal stretching ratio was 2.5 times. A laminate was obtained in the same manner as in Example 1.

[0114] (Comparative Example 10) A 60 μm polyolefin resin film was obtained in the same manner as in Example 1, except that the raw materials shown in Table 2 were used, the thickness of the unstretched polyolefin resin film was 300 μm, and the stretching ratio was 5.0 times. A laminate was obtained in the same manner as in Example 1.

[0115] In Comparative Examples 1 and 2, the films were unstretched and therefore had poor straight cuttability. In Comparative Example 3, the high stretching ratio and large x-axis orientation coefficient of the film made it easy for whiskers to form when opened. In addition, the lack of relaxation after annealing made the film poor in thermal dimensional stability. In Comparative Example 4, at least the heat seal layer did not contain an ethylene-propylene random copolymer, and the stretching ratio was high, so that the low-temperature sealability was poor. In Comparative Example 5, the stretching ratio was low and the x-axis orientation coefficient of the film was small, so the straight cuttability was poor. In Comparative Examples 6 to 8, there was no relaxation after annealing, and therefore the thermal dimensional stability was poor. In Comparative Example 9, the x-axis orientation coefficient was small, and therefore the straight cutting property was poor. In Comparative Example 10, the x-axis orientation coefficient was large, and therefore whiskers were likely to occur when the package was opened. The results are shown in Tables 1 and 2.

[0116] [Table 1]

[0117] [Table 2]

[0118] In Tables 1 and 2, the evaluation results marked as "Not measurable*" indicate that the film was torn in the MD direction during the property evaluation, and no measurement value could be obtained. [Industrial Applicability]

[0119] The present invention can provide a retort pouch that can be opened straight with only a slight crease in the opening direction and is less likely to produce creases when opened, making a great contribution to industry.

Claims

1. A polyolefin resin film made of a polypropylene resin composition, the polypropylene resin composition being made of a polypropylene resin or a polypropylene resin and an additive, and containing, in a total of 100 parts by weight of the polypropylene resin, 40 to 97 parts by weight of a propylene-ethylene block copolymer consisting of a polymer portion mainly composed of propylene and a copolymer portion of propylene and ethylene having an ethylene content of 20 to 50 parts by weight, and having a copolymerization ratio of the ethylene component of 1 to 15% by weight, 0 to 50 parts by weight of a propylene-α-olefin random copolymer or a propylene homopolymer, and ethylene-propylene copolymer elastomer. a propylene-butene copolymer elastomer, and an ethylene-butene copolymer elastomer, and the polyolefin resin film has a sea-island structure consisting of a portion of the propylene-ethylene block copolymer mainly composed of propylene, a matrix polymer mainly composed of the propylene-α-olefin random copolymer, and domains mainly composed of a portion of the elastomer mainly composed of ethylene, the polyolefin resin film having a heat shrinkage rate of 1% or more and 9% or less, and an x-axis orientation coefficient ΔNx calculated from a refractive index of 0.0180 or more and 0.0220 or less.

2. The polyolefin resin film according to claim 1, which has a multi-layer structure of at least two layers.

3. A laminate of the polyolefin resin film according to claim 1 or 2 with at least one substrate film selected from the group consisting of a polyolefin resin film, a polyamide resin film, a polyester resin film, and a polypropylene resin film.

4. The laminate according to claim 3, having a straight cut ability of 5 mm or less.

5. A package comprising the laminate according to claim 4.

6. The package according to claim 5, which is for retort packaging.

Images