Polyolefin resin film

Abstract

To provide a polyolefin-based resin film from which a packaging bag obtained from a laminate laminated on a base material film is excellent in rectilinear cutting properties, easy tearing properties and bag making workability, is less likely to be broken at the time of falling even after retort, and is less likely to generate whiskers at the time of opening, even in a case in which the base material film has large distortion of a molecular orientation axis.SOLUTION: A polyolefin-based resin film is composed of a polypropylene-based resin composition, contains 40 to 97 pts. wt. of a propylene-ethylene block copolymer composed of propylene and ethylene having an ethylene content of 20 to 50 pts. wt, and 3 to 10 pts. wt. of one or more kinds of elastomers selected from an ethylene-propylene copolymerization elastomer, a propylene-butene copolymerization elastomer, and an ethylene-butene copolymerization elastomer, and has a heat shrinkage percentage in a longitudinal direction 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.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] A packaging bag is mainly manufactured by heat-sealing (hereinafter referred to as heat-sealing) the peripheral portion of a laminate of a base film such as a polyamide resin film, a polyester resin film, or a polypropylene resin film and a polyolefin resin film at a temperature near the melting point of the polyolefin resin film with the polyolefin resin film surfaces in contact with each other. In food packaging bags, so-called retort pouches that are suitable for long-term preservation of food and are sterilized with pressurized steam at about 130°C after filling the food have become widespread. In recent years, due to social backgrounds such as the advancement of women into society, the trend towards nuclear families, or the progress of aging, the demand for retort pouches has been increasing, and at the same time, further improvement in characteristics has been demanded. For example, in recent years, such retort pouches are often boxed, transported, and sold at retail stores. Therefore, it is required that they are not easily broken even if they fall during the process, especially not easily broken even if they fall under refrigeration.

[0003] Also, when taking out the food contents from a packaging bag, especially a retort pouch, it is often necessary to tear the packaging bag by hand from a cut portion, so-called notch portion, provided in the heat-sealed portion around the packaging bag. However, when using a conventional laminate, the packaging bag cannot be torn parallel to one side, usually the horizontal direction, and it may be opened obliquely, or a phenomenon called "crying separation" occurs where the direction of the tear progression is reversed between the front and back laminates of the packaging bag, making it difficult to take out the food contents and risking soiling hands and clothes with the food contents or getting burned if the contents were heated.

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

[0005] This problem would not occur if the molecular orientation axis of the base film could be made the same as the tearing direction of the packaging bag. The molecular orientation axis of the center of the widthwise stretched film that is manufactured coincides with the direction of film travel, making it possible to tear it parallel to one side of the packaging bag. However, at the widthwise edges of the base film, the molecular orientation axis is tilted from the direction of film travel, and even if the direction of film travel is processed to coincide with the longitudinal or transverse direction of the packaging bag, the tearing direction of the packaging bag will be tilted in the direction of the molecular orientation axis of the base film. It is not practical to procure base film that completely avoids using the widthwise edges of the film, and as the production speed of base film increases and the width increases, the degree of distortion tends to become even greater than before. Therefore, attempts are being made to solve these problems by improving the polyolefin resin film that is laminated with the base film.

[0006] Patent Document 1 describes a film obtained by uniaxially stretching a polyolefin resin sheet containing an ethylene-propylene block copolymer and an ethylene-propylene copolymer at a ratio of 3.0 or less. However, there was room for improvement in tear strength, and it had the problem of being prone to splitting.

[0007] Furthermore, Patent Documents 2 and 3 describe films 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 ethylene-butene elastomer by approximately five times. However, it had problems with poor dimensional stability against heat, causing the packaging to deform and damage its appearance due to the heat applied during retort processing, and also with being prone to tearing at low temperatures. Furthermore, Patent Document 4 describes a film made by uniaxially stretching a polyolefin resin sheet, mainly composed of a propylene-ethylene block copolymer, to about four times its original size. However, when tearing open a four-sided sealed bag made from a laminate of biaxially oriented polyamide film or the like at the notch, there was a problem in that thread-like film fragments would separate from the heat-sealed area (commonly known as "whiskers"). [Prior art documents] [Patent Documents]

[0008] Patent Document 1: Patent No. 5790497 Patent Document 2: Japanese Unexamined Patent Publication No. 2014-141302 Patent Document 3: Special Publication No. 2012-500307 Patent document 4: WO2019 / 123944A1 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The present invention aims to provide a polyolefin resin film that, even when laminated with a base film having a large distortion of the molecular orientation axis, such as a biaxially oriented polyamide resin film, produces packaging bags that exhibit excellent straight-line cutting ability, tearability, and bag-making processability, are less prone to tearing when dropped after retorting, and are less likely to produce whiskers when opened. [Means for solving the problem]

[0010] As a result of diligent research to achieve the above objective, the present inventors have found that a polypropylene resin composition comprising a propylene-ethylene block copolymer, a propylene-α-olefin random copolymer, an ethylene-propylene copolymer elastomer, and a propylene-butene copolymer elastomer, which primarily orients the polymer molecules in one direction by stretching, reduces the thermal shrinkage rate in each direction, and limits the orientation of the molecular chains in the longitudinal direction to a specific range, can be obtained. This results in a polyolefin resin film that, even when laminated with a base film with a large distortion of the molecular orientation axis, such as a biaxially oriented polyamide resin film, exhibits excellent straight-line cutting ability, tearability, and bag-making processability, is less prone to tearing when dropped after retorting, and is less likely to produce whiskers when opened. This led to the completion of the present invention. In other words, the present invention has the following aspects.

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

[0012] [2] The polyolefin resin film according to [1], comprising at least two or more layers.

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

[0014] [4] The laminate described in [3], wherein the straight-line cutting ability is 5 mm or less.

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

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

[0017] The polyolefin resin film of the present invention exhibits excellent straight-line cutting properties, tearability, and bag-making processability. It is also resistant to tearing when dropped after retorting and less prone to generating burrs when opened. It is particularly suitable for retort pouches. [Modes for carrying out 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 consisting of a first polymerization step consisting of a copolymer component of a large amount of propylene and a small amount of ethylene, and a second polymerization step consisting of a copolymer component of a small amount of propylene and a large amount of ethylene. Specifically, it is preferable to use one that has been polymerized by a gas-phase method, as shown in Japanese Patent Application Publication No. 2000-186159. That is, a block copolymer obtained by polymerizing a polymer portion mainly composed of propylene (component A) in the first step in the substantially inactive solvent-free state, and then polymerizing a copolymer portion of propylene and ethylene (component B) with an ethylene content of 20 to 50 parts by weight in the gas phase in the second step, is an example, but is not limited to these.

[0019] The melt flow rate (MFR) (measured at 230°C under a load of 2.16 kg) of the above propylene-ethylene block copolymer is preferably 1 to 10 g / 10 min, more preferably 2 to 7 g / 10 min. When it is 1 g / 10 min or more, extrusion with a T-die is easy. On the contrary, when it is 10 g / 10 min or less, it is easy to increase the impact strength.

[0020] In the present invention, the xylene-soluble part at 20°C is referred to as CXS, and the xylene-insoluble part at 20°C is referred to as CXIS. In the propylene-ethylene block copolymer used in the present invention, CXS mainly consists of the rubber component (B component), and CXIS mainly consists of the polypropylene component (A component). When 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 for [η]CXS, and more preferably in the range of 2.0 to 3.0 dl / g. When it is 3.0 dl / g or less, fish eyes are less likely to occur in the polyolefin resin film. On the other hand, when it 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 with a T-die is easy. On the contrary, when it is 1.0 dl / g or more, it is easy to increase the impact strength of the film.

[0021] The above [η]CXS and [η]CXIS are values measured by the following measurement method. After completely dissolving 5 g of the sample in 500 ml of boiling xylene, the temperature was lowered to 20°C and left for 4 hours or more. Then, this was filtered into a filtrate and a precipitate, and the intrinsic viscosity ([η]) of the component (CXS) obtained by drying the filtrate and the solid (CXIS) obtained by drying the precipitate under reduced pressure at 70°C was measured in tetralin at 135°C using an Ubbelohde viscometer.

[0022] Generally, it is known that there is a correlation between the 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 an indicator of molecular weight; a larger value indicates a larger molecular weight, and a smaller value indicates a smaller molecular weight. Similarly, MFR is an indicator of molecular weight; a smaller value indicates a larger molecular weight, and a larger value indicates a smaller molecular weight.

[0023] Furthermore, for the propylene-ethylene block copolymer, the copolymerization ratio of the ethylene component in the propylene-ethylene block copolymer is preferably 1 to 15% by weight, and more preferably 3 to 10% by weight. The copolymerization ratio of the propylene component in the propylene-ethylene block copolymer is preferably 85 to 99% by weight, and 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 and more preferably 125°C. Above 120°C, heat resistance is easily obtained, and the inner surfaces of the bags are less likely to fuse together during retort processing. The upper limit of the melting point of the propylene-ethylene block copolymer is not particularly limited, but is preferably 175°C and more preferably 170°C. Below 175°C, the heat seal temperature tends to decrease.

[0025] Examples of propylene-ethylene block copolymers include, for example, a block copolymer polypropylene resin with an ethylene content of 7% by weight and an intrinsic viscosity of CXS 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, manufactured by Sumitomo Chemical Co., Ltd., WFS5293-22), and a block copolymer polypropylene resin with an ethylene content of 6% by weight and an intrinsic viscosity of CXS 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, manufactured by Sumitomo Chemical Co., Ltd., WFS5293-29).

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

[0027] The lower limit of the melt flow rate (MFR) of the propylene-α-olefin random copolymer at 230°C and 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. A MFR of 0.6 g / 10 min or higher increases compatibility with the propylene-ethylene block copolymer, making the film less prone to whitening. 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] For the production of propylene-α-olefin random copolymers, it is preferable to use a polymerization catalyst containing a metallocene-based olefin polymerization catalyst. Propylene-α-olefin random copolymers containing a metallocene-based olefin polymerization catalyst have the characteristic of having low content of components in the low molecular weight and high molecular weight regions. It has also been newly discovered that the generation of whiskers is suppressed when a propylene-α-olefin random copolymer containing a metallocene-based olefin polymerization catalyst is used. A metallocene-based olefin polymerization catalyst is a catalyst comprising (i) a transition metal compound of Group 4 of the periodic table (a so-called metallocene compound) containing a ligand having a cyclopentadienyl skeleton, (ii) a co-catalyst that can be activated into a stable ionic state by reacting with the metallocene compound, and, if necessary, (iii) an organoaluminum compound. Any known catalyst can be used.

[0029] Furthermore, the copolymerization ratio of the ethylene component in the propylene-α-olefin random copolymer is preferably 1 to 15% by weight, and more preferably 3 to 10% by weight. In the propylene-ethylene block copolymer, the copolymerization ratio of the propylene component is preferably 85 to 99% by weight, and 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. Above 120°C, heat resistance is easily obtained, and the inner surfaces of the bags may fuse together during retort processing. The upper limit of the melting point of the propylene-α-olefin random copolymer is preferably 145°C, and more preferably 140°C. Below 145°C, the heat seal temperature tends to decrease.

[0031] Examples of propylene-α-olefin random copolymers include S131 from Sumitomo Chemical Co., Ltd. (ethylene content: 5.5 wt%, density: 890 kg / m³, MFR at 230°C and 2.16 kg load: 1.5 g / 10 m⁸ in, melting point: 132°C, Ziegler-Natta catalyst), WFW4M propylene-ethylene random copolymer from Nippon Polypropylene Co., Ltd. (ethylene content: 7 wt%, density: 900 kg / m³, 230°C, MFR at 2.16 kg: 7.0 g / 10 min, melting point: 136°C, metallocene catalyst), and WFX4M from Nippon Polypropylene Co., Ltd. (ethylene content: 7 wt%, density: 900 kg / m³, 230°C, MFR at 2.16 kg load: 7.0 g / 10 min, melting point: 125°C, metallocene catalyst).

[0032] (Propylene homopolymer) In the present invention, propylene homopolymers can be used. Propylene homopolymers include isotactic polypropylene, which has high crystallinity and excellent rigidity and heat resistance, and atactic polypropylene, which has low crystallinity and excellent flexibility. As the propylene homopolymer to be used, isotactic polypropylene, which has high crystallinity and suppresses deterioration of the thermal shrinkage rate, is preferred. The melt flow rate (MFR) (measured at 230°C and under a load of 2.16 kg) of the above propylene homopolymer is preferably 1 to 10 g / 10 min, and more preferably 2 to 7. A MFR of 1 g / 10 min or higher facilitates extrusion with a T-die, while a MFR of 10 g / 10 min or lower makes it easier to increase the impact strength of the film.

[0033] Propylene homopolymers containing metallocene-based olefin polymerization catalysts have a narrower molecular weight distribution compared to propylene homopolymers containing Ziegler-Natta-based olefin polymerization catalysts, characterized by fewer components on the lower and higher molecular weight sides compared to the weight-average molecular weight used as an indicator. It has also been newly discovered that the formation of whiskers is suppressed when using propylene homopolymers containing metallocene-based olefin polymerization catalysts. Furthermore, they exhibit superior flexibility and strength. A metallocene-based olefin polymerization catalyst is a catalyst consisting of (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 that can be activated into a stable ionic state by reacting with the metallocene compound, and, if necessary, (iii) an organoaluminum compound. Any known catalyst can be used.

[0034] Examples of propylene homopolymers include F300SP manufactured by Prime Polymer Co., Ltd. (ethylene content: 0% by weight, density: 890 kg / m3, MFR at 230°C and a load of 2.16 kg: 3.0 g / 10 min, melting point: 160°C, Ziegler-Natta catalyst).

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

[0036] In the present invention, the copolymerized elastomer preferably has a melt flow rate (MFR) of 0.2 to 5 g / 10 min at 230°C and a load of 2.16 kg, a density of 820 to 930 kg / m3, and a molecular weight distribution (Mw / Mn) of 1.3 to 6.0 determined by GPC method. In the present invention, if the melt flow rate (MFR) of the copolymerized elastomer at 230°C and a load of 2.16 kg is 0.2 g / 10 min or higher, it is easy to knead uniformly and less likely to produce fish eyes. If it is 5 g / min or lower, the bag's tear resistance is easily improved. Furthermore, the intrinsic viscosity [η] of the copolymerized elastomer in the present invention is preferably 1.0 to 5.0, and more preferably 1.2 to 3.0, from the viewpoint of maintaining heat seal strength, impact strength, and bag drop strength. When the intrinsic viscosity [η] is 1.0 or higher, it is easy to knead uniformly and less likely to cause fish eyes, and when it is 5.0 or lower, bag tear resistance and heat seal strength tend to improve.

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

[0038] The ethylene-propylene copolymer elastomer in the present invention specifically includes, for example, an ethylene-propylene copolymer elastomer (Tafmer P0480, manufactured by Mitsui Chemicals, Inc.) with a propylene content of 27% by weight, a density of 870 kg / m3, and an MFR (230°C, 2.16 kg) of 1.8 g / 10 min.

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

[0040] The heat-seal layer is the outermost layer of a polyolefin resin film, and packaging can be manufactured by heat-pressing these two layers together. The layer located on the outermost surface opposite the heat-seal layer is the laminate layer, which can be laminated by bonding it with a base film such as polyester film or polyamide film. In the case of a three-layer structure consisting of a heat-seal layer, an intermediate layer, and a laminate layer, the cost of the film product can be reduced without impairing properties such as straight-line cutting ability, tearability, bag-making processability, and rupture resistance by recovering the edges or the film product itself, and then using the pelletized material as the raw material for the intermediate layer.

[0041] In each layer of the polyolefin resin film of the present invention, the balance of properties such as tear resistance, heat seal strength, and bag breakage 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 propylene-ethylene block copolymer is in the range of 40 to 97 parts by weight per 100 parts by weight of polypropylene resin, preferably 60 parts by weight or more, and more preferably 85 parts by weight or less, from the viewpoint of separation. When the proportion of propylene-ethylene block copolymer is 40 parts by weight or more, the shrinkage rate tends to be lower and the bag's tear resistance tends to improve. When it is 97 parts by weight or less, heat sealability at low temperatures is easily achieved.

[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, 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, heat sealability at low temperatures is easily obtained and the heat seal strength is also easily increased, while when it is 50 parts by weight or less, the heat shrinkage rate is easily reduced.

[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 parts by weight to 10 parts by weight in a total of 100 parts by weight of polypropylene resin, with ethylene-propylene copolymer elastomer preferably in the range of 4 to 9 parts by weight, and more preferably in the range of 5 to 8 parts by weight. By including 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, tearability is imparted, making it easier to obtain heat sealability and tear resistance. By including 10 parts by weight or less, the film appearance (transparency) is improved.

[0045] The polyolefin resin film in this invention exhibits excellent tear resistance by having a sea-island structure consisting of a matrix polymer and domains. The matrix polymer mainly consists of a propylene-based portion of a propylene-ethylene block copolymer and a propylene-α-olefin random copolymer, while the domains mainly consist of an ethylene-propylene copolymer elastomer and the ethylene-based portion of a propylene-ethylene block copolymer.

[0046] (Additives) The polypropylene resin composition of the present invention may contain an antiblocking agent. The antiblocking agent to be incorporated 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 consisting of acrylic, styrene, and styrene-butadiene polymers, and crosslinked versions thereof. Considering ease of controlling particle size distribution, dispersibility, ease of maintaining optical appearance, and prevention of particle detachment from the film, organic particles consisting of crosslinked versions are preferred. As the crosslinked version, crosslinked acrylic polymers consisting of acrylic monomers such as acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters are particularly preferred, and more preferably, crosslinked polymethyl methacrylate is recommended. The surfaces of these particles may be coated with various coatings for the purpose of improving dispersibility and preventing them from falling off. Furthermore, the shape of these particles may be irregular, spherical, ellipsoidal, rod-shaped, angular, polyhedron, conical, or even porous, having cavities on or inside the particle surface. The antiblocking agent is preferably one with an average particle diameter of 3 to 12 μm, in terms of the appearance of the film and its resistance to blocking. While using only one type of antiblocking agent can be effective, incorporating two or more inorganic particles with different particle sizes and shapes can sometimes create more complex protrusions on the film surface, resulting in a higher level of antiblocking effect. When block copolymers are used as the main constituent resin, surface irregularities may be formed due to polymer dispersion, and a high level of anti-blocking effect may be obtained even without the addition of anti-blocking agents.

[0047] The polypropylene resin composition in the present invention may contain an organic lubricant. This improves the lubricity and anti-blocking effect of the laminated film, and improves the handling of the film. This is thought to be because the organic lubricant bleeds out and remains on the film surface, resulting in the 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 oleamide, erucamide, behenamide, ethylenebisoleamide, hexamethylenebisoleamide, and ethylenebisoleamide. These may be used individually, but using two or more in combination is preferable as it may maintain lubricity and anti-blocking effects even in harsher environments.

[0048] The polypropylene resin composition of the present invention may contain, as necessary, appropriate amounts of antioxidants, antistatic agents, antifogging agents, neutralizing agents, nucleating agents, colorants, other additives, and inorganic fillers, without impairing the objectives of the present invention. Examples of antioxidants include the use of phenolic and phosphite-based antioxidants alone or in combination, or the use of a single molecule containing both phenolic and phosphite-based skeletons.

[0049] (Method for manufacturing polyolefin resin film) The present invention allows for the molding of polyolefin resin films using methods such as the inflation method and the T-die method, but the T-die method is preferred for its ability to enhance transparency and facilitate fume facilitation. While the inflation method uses air as a cooling medium, the T-die method uses a cooling roll, making it advantageous for increasing the cooling rate of the unstretched sheet. By increasing the cooling rate, crystallization of the unstretched sheet can be suppressed, resulting in high transparency and easier control of the load required for stretching in subsequent processes. For these reasons, molding using the T-die method is more preferable.

[0050] The lower limit of the cooling roll temperature when casting molten raw resin to obtain an unoriented sheet is preferably 15°C, more preferably 20°C. If the temperature is lower than this, condensation may occur on the cooling roll, resulting in insufficient adhesion between the unstretched sheet and the cooling roll, which can cause poor thickness. The upper limit of the cooling roll temperature 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] Methods for stretching non-oriented sheets include, for example, the inflation method, the tenter transverse stretching method, and the roll longitudinal stretching method, but the roll longitudinal stretching method is preferred due to the ease of controlling orientation. By stretching an unoriented sheet under appropriate conditions, straight-line cutting properties are achieved. This is because the molecular chains are regularly aligned in the direction of stretching. The lower limit of the stretch ratio is preferably 2.8 times, and more preferably 3.3 times. If it is 2.8 times or higher, the tear strength in the stretching direction does not tend to increase, and straight-line cut properties are easily obtained. More preferably it is 3.4 times, and even more preferably 3.5 times. The upper limit of the stretching ratio is preferably 3.9 times. If it is 3.9 times or less, excessive orientation is less likely to occur, and the thermal shrinkage rate in the longitudinal direction is less likely to increase. More preferably, it is 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 on the film does not become too high, and the shrinkage rate does not tend to increase. More preferably, the temperature is 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 on the film does not become too low, the thermal shrinkage rate in the longitudinal direction of the film does not decrease too much, and the film is less likely to fuse to the stretching roll. More preferably, the temperature is 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 preheating roll before introducing it into the stretching process to raise the sheet temperature. The lower limit of the preheating roll temperature when stretching an unoriented sheet is preferably 80°C, more preferably 90°C. Above 80°C, the stretching stress does not become excessively high, and thickness variation is less likely to worsen. The upper limit of the preheating roll temperature is preferably 140°C, more preferably 130°C, and even more preferably 125°C. Below 140°C, the film is less likely to adhere to the roll, and film thickness variation is less likely to become large.

[0054] It is preferable to anneal polyolefin resin films that have undergone a stretching process in order to suppress thermal shrinkage. Annealing methods include roll heating and tenter methods, but the roll heating method is preferred due to the simplicity of the equipment and ease of maintenance. By annealing, the internal stress of the film is reduced, thereby suppressing thermal shrinkage in the longitudinal direction of the film. This does not sacrifice longitudinal thermal shrinkage rate or heat seal strength, as is done in the conventional method of simply increasing the stretching ratio to improve tear resistance. However, this may adversely affect properties other than longitudinal thermal shrinkage rate and heat seal strength. In this invention, adverse effects on properties such as tear resistance can be suppressed by using copolymer elastomers in combination.

[0055] The lower limit of the annealing temperature is preferably 100°C. Below 100°C, the thermal shrinkage rate in the longitudinal direction is less likely to increase, the tear strength is less likely to increase, and the finish of the packaging bag after bag making or retorting may deteriorate. More preferably, it is 115°C, and 125°C is particularly preferred. The upper limit of the annealing temperature is preferably 140°C. Higher annealing temperatures tend to reduce the thermal shrinkage rate in the longitudinal direction, but exceeding this temperature may worsen film thickness variation or cause the film to fuse to the manufacturing equipment. More preferably, the temperature is 135°C.

[0056] In the annealing process, a relaxation step can be incorporated by gradually slowing down the film transport speed, such as by reducing the rotation speed of the rolls after heating. By incorporating a relaxation step, the thermal shrinkage rate of the manufactured polyolefin resin film can be reduced. The upper limit of the relaxation rate in the relaxation process is preferably 10%, and more preferably 8%. If it is 10% or less, the thermal shrinkage rate will not become too small. The lower limit of the relaxation rate is preferably 1%, and more preferably 3%. If it is 1% or more, the thermal shrinkage rate in the longitudinal direction of the polyolefin resin film will not increase easily.

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

[0058] (Properties of polyolefin resin films) (Film thickness) The lower limit of the thickness of the polyolefin resin film of the present invention is preferably 10 μm, and more preferably 30 μm. If it is less than the above, it will be relatively thin compared to the thickness of the base film, which may worsen the straight-line cutting performance of the laminate, and the film may become too stiff, making it difficult to process, as well as reducing impact resistance and worsening tear resistance. The upper limit of the film thickness is preferably 200 μm, and more preferably 130 μm. If it exceeds the above, the film may become too stiff, making it difficult to process, and it may become difficult to manufacture a suitable packaging.

[0059] (Orientation coefficient in the longitudinal direction) The longitudinal orientation coefficient ΔNx used in this invention can be calculated using Equation 1. ΔNx = Nx - (Ny + Nz) / 2 (Equation 1) Nx: Refractive index in the longitudinal direction Ny: Refractive index perpendicular to the longitudinal and thickness directions. 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. A value of 0.0150 or higher makes it easier to obtain straight-line cutability of the packaging. The upper limit of the longitudinal orientation coefficient ΔNx is preferably 0.0250, more preferably 0.0245, even more preferably 0.0240, even more preferably 0.0230, and particularly preferably 0.0220. A value of 0.0250 or lower makes it less likely for the heat seal strength to decrease.

[0060] (Thermal shrinkage rate) The upper limit of the thermal shrinkage rate of the polyolefin resin film of the present invention at 120°C in the longitudinal direction is 9%. If it is 9% or less, the tear strength will decrease, and at the same time, the shrinkage during heat sealing and retort of the package will be reduced, resulting in a superior appearance of the package. Preferably it is 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 higher, the tear strength tends to decrease. Preferably, it is 2%.

[0061] To achieve straight-line cutting performance, the lower limit of the longitudinal orientation coefficient ΔNx needs to be 0.0150. However, if the upper limit of the thermal shrinkage rate at 120°C in the longitudinal direction is 9%, whiskers are less likely to form. This is because when heat-sealed, the orientation is less likely to remain in the sealed area and edges. During heat sealing, the laminated film is constrained by the base film and therefore less likely to shrink. As a result, force is applied to the film, making it difficult for the film to re-orient itself. The upper limit of the thermal 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, and straight-line cutability is easily obtained. Preferably it is 0.5%. The lower limit of the thermal shrinkage rate of the polyolefin resin film of the present invention in the direction perpendicular to the aforementioned one direction is -5%. If it is -5% or more, elongation occurs when heat sealing is performed, which may worsen the appearance of the packaged product. Preferably it is -2%.

[0062] (Hayes) Haze was measured according to JIS K7136. Measurements were taken for N=3 on polyolefin resin films before lamination, 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%. A haze level of 80% or less provides excellent visibility of the contents. 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. Exceeding this limit may make the laminate film difficult to tear. More preferably, it is 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 lower than this, the tear resistance may deteriorate. More preferably it is 0.03 N.

[0064] (Puncture strength) The lower limit of the puncture strength of the polyolefin resin film of the present invention is preferably 10N, more preferably 15N / μm, even more preferably 18N, and even more preferably 20N. A puncture strength of 15N or higher makes it less likely for pinholes to occur when a protrusion strikes the packaging. The upper limit of the puncture strength is preferably 35N. A puncture strength of 35N or lower prevents the film from becoming too stiff, making it easier to handle when made into a film or laminate.

[0065] (Puncture strength) The lower limit of the puncture strength per 1 μm of the polyolefin resin film of the present invention is preferably 0.13 N / μm, and more preferably 0.15 N / μm. If it is less than the above, pinholes may occur when a protrusion strikes the packaging. The upper limit of the puncture strength is preferably 0.40 N / μm. If it exceeds the above, it may become too stiff, making it difficult to handle when made into a film or laminate.

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

[0067] (Laminate structure and manufacturing method) The laminate using the polyolefin resin film of the present invention is a laminate in which the polyolefin resin film is used as a sealant and laminated with at least one film selected from the group consisting of polyamide resin film, polyester resin film, and polypropylene resin film. Furthermore, known techniques may be used to apply coatings or vapor deposition processes to these base films to impart adhesion or barrier properties, or to further laminate aluminum foil. Specifically, 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, with biaxially oriented nylon film, the straight-line cutting performance of the laminate deteriorates significantly when a sealant with small longitudinal orientation is used. By using the polyolefin resin film of the present invention as a sealant, a laminate with good straight-line cutting performance can be manufactured in any configuration. Known lamination methods such as dry lamination and extrusion lamination can be used, and any of these lamination methods can produce laminates with good straight-line cutting properties.

[0068] (Characteristics of laminates) (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. More preferably it is 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-line cutting ability) Straight-cutting ability refers to the ability to tear a film or laminate straight in one direction when it is torn. The measurement was performed using the following method. In this example, the material was stretched in the longitudinal direction, so the thermal shrinkage rate was high in the longitudinal direction, and the aforementioned one direction was the longitudinal direction. Therefore, the straight-line cutting ability was evaluated only in the longitudinal direction. Film or laminate film was cut into strips measuring 150 mm in the longitudinal direction and 60 mm in the longitudinal and perpendicular directions. A 30 mm cut was made from the center of the short side along the longitudinal direction. The sample was torn according to JIS K7128-1:1998. When 120 mm had been torn in the longitudinal direction (excluding the 30 mm cut), the distance traveled in the longitudinal and perpendicular directions was measured and its absolute value was recorded. Measurements were taken with N=3 for both the case where the right-hand section was held in the upper grip and the case where the left-hand section was held in the upper grip, and the average value for each was calculated. The larger of the two measurement results (right or left) was adopted.

[0070] (Straight-line cutting ability) The upper limit of the straight-line cutting ability 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 packaging is less likely to tear apart. The lower limit may be 0.5 mm.

[0071] (Tearful farewell) The upper limit of the separation 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 packaging is torn. The lower limit may be 1 mm.

[0072] (Facial hair growth rate) A laminate film of the polyolefin resin film of the invention and a base film was heat-sealed with the heat-seal film layers facing each other to create a four-sided sealed bag with an inner dimension of 120 mm in the longitudinal direction and 170 mm in the longitudinal and perpendicular directions. A notch was made at the edge of the four-sided sealed bag, and it was torn by hand in the longitudinal direction. The number of times thread-like film fragments (whiskers) were generated and the whisker generation rate calculated from the number of tears were 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 is made using an ester-based adhesive obtained by mixing the polyolefin resin film of the present invention and a base film (Toyobo biaxially oriented nylon film, N1102, 15 μm thick, orientation angle 22° with respect to the longitudinal direction) with 33.6 parts by weight of ester-based dry laminating adhesive (Toyo Morton Co., Ltd., TM569), 4.0 parts by weight of curing agent (Toyo Morton Co., Ltd., CAT10L), and 62.4 parts by weight of ethyl acetate, with an adhesive application amount of 3.0 g / m². 2 The laminated film was dry-laminated to achieve the desired result. The laminated film was kept at 40°C and aged for 3 days to obtain the final laminate film. Beard growth rate = Number of beard growths / Number of tears × 100 (%)

[0073] (Bag manufacturing finish) The polyolefin resin film sides of the laminate film were overlapped, and the two films were heat-sealed at a pressure of 0.2 MPa for 1 second, with a sealing bar width of 10 mm and a heat sealing 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. 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 area, and furthermore, that the bag was perfectly rectangular.

[0074] (Retort shrinkage rate) The upper limit of the retort shrinkage rate of the laminate of the present invention is preferably 5%. If it exceeds this, the appearance of the package after retorting may deteriorate. More preferably it is 4%. The lower limit of the unidirectional retort shrinkage rate is -5%. If it is below this, the elongation after retorting will be large, which may cause the bag to break. More preferably it is -2%, and even more preferably it is 0%.

[0075] (Heat seal strength) The lower limit of the heat seal strength of the laminate of the present invention before retorting is preferably 35 N / 15 mm, and more preferably 40 N / 15 mm. If it is lower than the above, the bag's tear resistance may deteriorate. It is preferable that the heat seal strength remains at 35 N / 15 mm or higher even after retorting at 121°C for 30 minutes. The upper limit of the heat seal strength is preferably 60 N / 15 mm. To exceed the above limits, it may be necessary to increase the film thickness, which can lead to higher costs.

[0076] (Heat seal start temperature) The lower limit of the heat-sealing start temperature of the laminate of the present invention before retorting is preferably 190°C or lower, more preferably 185°C or lower, and even more preferably 180°C or lower. If it exceeds 190°C, the film shrinks significantly during bag making, impairing the appearance, and the bag-making speed may decrease, leading to 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 it is below the above, the heat of the retort process may cause the inner surface of the film to fuse together.

[0077] (packaging) The laminated material, arranged to surround the contents of food products and other items for the purpose of protecting them from dust, gases, and other elements in the natural environment, is called a packaging body. Packaging bodies are manufactured by cutting out the laminated material, bonding the inner surfaces together using a heated heat sealing bar or ultrasonic waves, and forming a bag. For example, a four-sided sealed bag made by stacking two rectangular laminated materials with the sealant side facing inward and heat-sealing all four sides is widely used. The contents may be food products, but may also be other products such as daily necessities, and the shape of the packaging body may also be a shape other than a rectangle, such as a standing pouch or pillow packaging body. Furthermore, packaging that can withstand the heat of heat sterilization using hot water whose boiling point has been raised to 100°C or higher by pressurizing is called retort packaging. Similarly, film intended to provide such packaging is called retort film.

[0078] (Bag resistance) When a four-sided sealed bag made from the laminate of the present invention is dropped and the number of drops is repeated until the bag breaks, it is practically preferable that the number of drops at which the percentage of bags remaining without breaking reaches 50% is 5 or more, more preferably 10 or more, even more preferably 11 or more, and even more preferably 12 or more. [Examples]

[0079] The present invention will be described in detail below with reference to examples, but is not limited to these. The characteristics obtained in each example were measured and evaluated by the following methods. During 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 according to Method D (density gradient tube) of JIS K7112:1999. Measurements were taken with N=3 and the average value was calculated.

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

[0082] (3) Thermal shrinkage The film before lamination was cut into 120mm squares. Markings were made at 100mm intervals in both the MD and TD directions. The samples were suspended in an oven maintained at 120°C and heat-treated for 30 minutes. The distance between the markings was measured, and the thermal shrinkage rate was calculated according to the following formula. Measurements were taken with N=3, and the average value was calculated. Thermal shrinkage rate = (Gauge length before heat treatment - Gauge length after heat treatment) / Gauge length before heat treatment × 100 (%)

[0083] (4) Tear strength Tear strength was measured in accordance with JIS K7128-1:1998. Evaluation was performed on both the base film before lamination and the laminated film. Measurements were taken in both the MD and TD directions with N=3 each, and the average value was calculated.

[0084] (5) Orientation coefficient in the longitudinal direction The refractive index was evaluated in accordance with JIS K 0062:1999, the method for measuring the refractive index of chemical products. Measurements were taken 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 perpendicular to the longitudinal and thickness directions. Nz: Refractive index in the thickness direction

[0085] (6) Straight-line cutting ability Straight-cutting ability refers to the ability of a laminate film (laminated material) to tear straight in one direction. The measurement was performed using the following method. In this example, since the material was stretched in the MD direction, the thermal shrinkage rate was high in the MD direction, and the aforementioned one direction was the MD direction. Therefore, straight-cutting ability was evaluated only in the MD direction. Laminate film was cut into strips measuring 150 mm in the MD direction and 60 mm in the TD direction. A 30 mm cut was made along the MD direction from the center of the short side. The sample was torn according to JIS K7128-1:1998. When 120 mm had been torn in the MD direction (excluding the 30 mm cut), the distance moved in the TD direction was measured and its absolute value was recorded. Measurements were taken with N=3 for both the case where the right section was held in the upper grip and the case where the left section was held in the upper grip, and the average value for each was calculated. The larger of the two measurement results (right or left) was adopted.

[0086] (7) A tearful farewell A four-sided sealed bag with inner dimensions of 120mm in the MD direction and 170mm in the TD direction was created by heat-sealing laminate film with two heat-seal films facing each other. A notch was made at the edge of the four-sided sealed bag and torn by hand in the MD direction. The cutting was continued to the opposite end, and the misalignment of the tear lines of the film on the front and back sides of the bag was measured. The average value was calculated for both the direction with the right hand facing forward and the direction with the left hand facing forward, with N=3 for each direction, and the larger measurement value was adopted.

[0087] (8) Retort shrinkage rate Laminating film was cut into 120mm squares. Markings were made at 100mm intervals in both the MD and TD directions. The films were retorted in hot water at 121°C for 30 minutes. The distance between the markings was measured, and the retort shrinkage rate was measured according to the following formula. Measurements were taken for each N=3 sample, and the average value was calculated. Retort shrinkage rate = (Mark length before processing - Mark length after processing) / Mark length before processing × 100 (%)

[0088] (9) Heat seal strength The heat sealing and strength measurement conditions were as follows: The polyolefin resin film sides of the laminate films obtained in the examples and comparative examples were overlapped, and heat-sealed at a pressure of 0.2 MPa for 1 second with a sealing bar width of 10 mm and a heat sealing temperature of 220°C, followed by cooling. Next, the films were retorted in hot water at 121°C for 30 minutes. Test pieces measuring 80 mm in the MD direction and 15 mm in the TD direction were cut from the heat-sealed films at each temperature, and the peel strength was measured when the heat-sealed portion was peeled off at a crosshead speed of 200 mm / min for each test piece. An Instron Instruments 5965 universal material tester was used as the testing machine. Measurements were taken N=3 times for each test, and the average value was calculated.

[0089] (10) Sealing start temperature The sealing start temperature is a factor related to productivity when assuming continuous production in a bag-making machine. Good bag-making suitability means that sufficient sealing is achieved within a temperature range where the base film does not shrink or break. The heat seal temperature was evaluated as follows. In the aforementioned measurement of 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 setting with N=3. The heat seal strength was calculated by weighting the heat seal temperature at the temperature just before it exceeded 30N and the heat seal temperature immediately after it exceeded 30N.

[0090] (11) The rate of beard occurrence A four-sided sealed bag with inner dimensions of 120mm in the MD direction and 170mm in the TD direction was created by heat-sealing two laminate films facing each other. A notch was made at the edge of the four-sided sealed bag and it was torn by hand in the MD direction. The occurrence rate was calculated from the number of times thread-like film fragments (whiskers) were generated. The test was performed with n=100 for both the direction with the right hand facing the front and the direction with the left hand facing the front, and the larger measurement value was adopted. Beard growth rate = Number of beard growths / Number of tears × 100 (%)

[0091] (12) Bag making finish The polyolefin resin film sides of the laminate film were overlapped, and the film was heat-sealed at a pressure of 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. ○: There is no deformation near the heat-sealed area, and the bag is perfectly rectangular. △: Minimal deformation near the heat-sealed area. ×: The area near the heat seal is significantly deformed, causing the edges of the bag to be wavy.

[0092] (13) Bag breakage resistance A four-sided sealed bag with internal dimensions of 170 mm (length) x 120 mm (width) was prepared by cutting out laminate film and sealing 300 ml of saturated saline solution inside. The heat sealing conditions were 0.2 MPa pressure for 1 second, a seal bar width of 10 mm, and a heat sealing temperature of 220°C. After bag making, the ends of the four-sided sealed bag were trimmed to a seal width of 5 mm. The four-sided sealed bag was retorted at 121°C for 30 minutes. Next, it was left in a -5°C environment for 8 hours, and under that environment, the four-sided sealed bag was dropped from a height of 1.0 m onto a flat concrete floor. The dropping was repeated until the bag ruptured, and the number of repeated drops was measured, establishing stages as follows. The number of bags at each level was 20. ◎: The number of drops resulting in a 50% survival rate is 13 or more. ○: The number of drops at which the survival rate is 50% is between 10 and 12. △: The number of drops required to achieve a 50% survival rate is between 5 and 9. ×: The number of drops that result in a 50% survival rate is 4 or less.

[0093] (14) Orientation angle The orientation angle (°) of the substrate film was measured using a molecular orientation meter MOA-6004 manufactured by Oji Instruments Co., Ltd. Samples were cut to 120 mm in the MD direction and 100 mm in the TD direction, placed in the measuring instrument, and the measured Angle value was defined as the orientation angle. Note that the MD direction is 0°. Measurements were taken with N=3 and the average value was calculated.

[0094] (15) Puncture strength The puncture strength of the film before lamination and the laminate was measured at 23°C in accordance with "2. Strength Test Methods" of "Standards and Criteria for Food, Food Additives, etc. Article 3: Utensils and Containers and Packaging" (Ministry of Health and Welfare Notification No. 20 of 1982) under the Food Sanitation Law. A needle with a tip diameter of 0.7 mm was pierced into the film at a piercing 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 thickness of the film to calculate the puncture strength per 1 μm of film [N / μm]. Measurements were taken with N=3, 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, the raw materials were prepared based on the resin composition and proportions of each layer shown in Tables 1 and 2 below. These raw materials were mixed uniformly to obtain a mixed raw material for producing polyolefin resin films. 1) Raw material A: Sumitomo Chemical's propylene-ethylene block copolymer WFS5293-22 (ethylene content 7% by weight, resin density 891 kg / m3, MFR 3.0 g / 10 min at 230°C, 2.16 kg, melting point 164°C) 2) Raw material B: Mitsui Chemicals' ethylene-propylene copolymer elastomer Toughmer P0480 (propylene content 27% by weight, resin density 870 kg / m3, MFR 1.8 g / 10 min at 230°C, 2.16 kg, melting point 48°C) 3) Raw material C: Sumitomo Chemical's propylene-ethylene random copolymer S131 (ethylene content 5.5% by weight, resin density 890 kg / m3, MFR 1.5 g / 10 min at 230°C, 2.16 kg, melting point 132°C, Ziegler-Natta catalyst) 29 4) Raw material D: WFW4M propylene-ethylene random copolymer manufactured by Nippon Polypropylene (ethylene content 7% by weight, resin density 900 kg / m3, MFR 7.0 g / 10 min at 230°C, melting point 136°C, metallocene catalyst) 5) Raw material E: WFX4M propylene-ethylene random copolymer manufactured by Nippon Polypropylene (ethylene content 7% by weight, resin density 900 kg / m3, MFR 7.0 g / 10 min at 230°C, melting point 125°C, metallocene catalyst)

[0096] (Melting extrusion) The mixed raw materials for the intermediate layer were introduced using a 3-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 introduced using 3-stage single-screw extruders with diameters of 45 mm and 65 mm, respectively. The materials were introduced in the order of laminate layer / intermediate layer / heat seal layer, and introduced into a T-slot type die with a width of 800 mm and two stages of pre-landing, and the shape of the stepped section was curved to ensure uniform flow of molten resin within the die. The die outlet temperature was 230°C for extrusion. 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. During 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. Simultaneously, a vacuum chamber was applied to prevent air from being trapped between the molten resin sheet and the cooling roll. The air nozzles were installed in series at both ends in the direction of film travel. The die was surrounded by a sheet to prevent air from blowing onto the molten resin sheet.

[0097] (preheat) The unstretched sheet was guided into a group of heated rolls, and the sheet was preheated by bringing the sheet into contact with the rolls. The temperature of the preheating rolls was set to 105°C. Multiple rolls were used to preheat both sides of the film. (Longitudinal extension) The aforementioned unstretched sheet was fed into a longitudinal stretcher and stretched to a thickness of 60 μm by a difference in roll speed, resulting in a 3.5-fold increase in thickness. The stretching roll temperature was set to 105°C. (Annealing treatment) The film was heat-treated at 130°C using an annealing roll. Multiple rolls were used to heat-treat both sides of the film. (relaxation process) The speed of the roll installed immediately after the annealing roll was reduced by 5% relative to the annealing roll as a relaxation factor, thereby relaxing the film.

[0098] (Corona treatment) One side of the film (the laminated side) was treated with corona. (winding up) The film deposition process was carried out with a winding roll speed of 20 m / min. The deposited film was trimmed at the edges and wound into a roll. The thickness of the resulting film was 60 μm.

[0099] (Creating laminating film) In Example 1, the polyolefin resin film obtained in Example 1 and a base film (Toyobo biaxially oriented nylon film, N1102, 15 μm thick, orientation angle 22° relative to the MD direction) were mixed with 33.6 parts by weight of ester-based dry laminating adhesive (Toyo Morton Co., Ltd., TM569), 4.0 parts by weight of curing agent (Toyo Morton Co., Ltd., CAT10L), and 62.4 parts by weight of ethyl acetate to obtain an ester-based adhesive, and the adhesive application amount was 3.0 g / m². 2 The laminated film was dry-laminated to achieve the desired result. The laminated film was kept at 40°C and aged for 3 days to obtain the final laminate film.

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

[0101] (Example 3) In Example 1, a 60 μm polyolefin resin film was obtained using the same method 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 using the same method 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) In Example 1, a 60 μm polyolefin resin film was obtained using the same method 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 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 using the same method 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) In Example 1, a 60 μm polyolefin resin film was obtained using the same method 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, a 60 μm polyolefin resin film was obtained using the same method as in Example 1, except that the raw materials shown in Table 2 were used, the thickness of the unstretched polyolefin resin film was set to 60 μm, and longitudinal stretching, annealing, and relaxation steps were omitted. A laminate was obtained in the same manner as in Example 1.

[0107] (Comparative Example 3) In Example 1, a 60 μm polyolefin resin film was obtained using the same method as in Example 1, except that the raw materials shown in Table 2 were used, the thickness of the unstretched polyolefin resin film was set to 240 μm, the longitudinal stretching ratio was set to 4.0 times, and no relaxation step was provided. 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 using the same method as in Example 1, except that the raw materials shown in Table 2 were used, the thickness of the unstretched polyolefin resin film was set to 270 μm, the longitudinal stretching ratio was set to 4.5, the annealing temperature was set to 120°C, and no relaxation step was provided. A laminate was obtained in the same manner as in Example 1.

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

[0110] (Comparative Example 6) In Example 1, using the raw materials shown in Table 2, a 60 μm polyolefin resin film was obtained using the same method 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 included. A laminate was obtained in the same manner as in Example 1.

[0111] (Comparative Example 7) A 60 μm polyolefin resin film was obtained using the same method as in Example 1, except that a relaxation step was omitted. A laminate was obtained in the same manner as in Example 1.

[0112] (Comparative Example 8) A 60 μm polyolefin resin film was obtained using the same method as in Example 1, except that the annealing step and the relaxation step after stretching were omitted. A laminate was obtained in the same manner as in Example 1.

[0113] (Comparative Example 9) In Example 1, a 60 μm polyolefin resin film was obtained using the same method as in Example 1, except that the raw materials shown in Table 2 were used, the thickness of the unstretched polyolefin resin film was set to 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) In Example 1, a 60 μm polyolefin resin film was obtained using the same method as in Example 1, except that the raw materials shown in Table 2 were used, the thickness of the unstretched polyolefin resin film was set to 300 μm, and the stretching ratio was 5.0 times. A laminate was obtained in the same manner as in Example 1.

[0115] Comparative Examples 1 and 2 were unstretched films, and therefore had poor straight-line cutting properties. In Comparative Example 3, the high stretching ratio and large x-axis orientation coefficient of the film made it prone to developing whiskers upon opening. Furthermore, the lack of relaxation after annealing resulted in poor thermal dimensional stability. In Comparative Example 4, the low-temperature sealing performance was poor because at least the heat seal layer did not contain ethylene-propylene random copolymer, and the stretch ratio was high. In Comparative Example 5, the stretching ratio was low and the x-axis orientation coefficient of the film was small, resulting in poor straight-line cutting performance. Comparative Examples 6-8 exhibited poor thermal dimensional stability due to the lack of relaxation after annealing. In Comparative Example 9, the x-axis orientation coefficient was small, resulting in poor straight-line cutting performance. In Comparative Example 10, the x-axis orientation coefficient was large, which made it prone to developing whiskers when 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 "Unmeasurable*" indicate that the film tore in the MD direction during the characterization process, making it impossible to obtain measurement values. [Industrial applicability]

[0119] This invention provides a retort pouch that can be opened straight with minimal tearing in the opening direction and that is less prone to generating whiskers during opening, thereby making a significant contribution to industry.

Claims

1. A polyolefin resin film having a heat-seal layer made of a polypropylene resin composition and a laminate layer made of a polypropylene resin composition, A polypropylene resin composition consists of a polypropylene resin, or a polypropylene resin and additives. In a total of 100 parts by weight of polypropylene resin constituting the heat seal layer, the heat seal layer contains 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 with an ethylene content of 20 to 50 parts by weight, and having a copolymerization ratio of ethylene component of 1 to 15% by weight; 5 to 50 parts by weight of a propylene-α-olefin random copolymer; and 3 to 10 parts by weight of at least one elastomer selected from the group consisting of ethylene-propylene copolymer elastomers and ethylene-butene copolymer elastomers. The propylene-ethylene block copolymer has a polymer portion mainly composed of propylene, the propylene-α-olefin random copolymer has a matrix polymer mainly composed of propylene, and the propylene-ethylene block copolymer has a copolymer portion of propylene and ethylene with an ethylene content of 20 to 50 parts by weight, and the elastomer has a sea-island structure consisting of domains mainly composed of ethylene. In a total of 100 parts by weight of the polypropylene resin constituting the laminate layer, The present invention contains 40 to 97 parts by weight of a propylene-ethylene block copolymer, which consists of a polymer portion mainly composed of propylene and a copolymer portion of propylene and ethylene with an ethylene content of 20 to 50 parts by weight, and in which the copolymerization ratio of the ethylene component is 1 to 15% by weight; 0 to 50 parts by weight of a propylene-α-olefin random copolymer; and 3 to 10 parts by weight of at least one elastomer selected from the group consisting of ethylene-propylene copolymer elastomers and ethylene-butene copolymer elastomers. The matrix polymer comprises at least the polymer portion of the propylene-ethylene block copolymer mainly composed of propylene, and the elastomer has a sea-island structure consisting of domains mainly composed of the copolymer portion of propylene and ethylene with an ethylene content of 20 to 50 parts by weight of the propylene-ethylene block copolymer and the ethylene portion of the elastomer. A polyolefin resin film having a thermal shrinkage rate of 1% to 9% after heating at 120°C for 30 minutes in the longitudinal direction, and an x-axis orientation coefficient ΔNx calculated from the refractive index of 0.0180 to 0.0220.

2. A laminate comprising a polyolefin resin film as described in claim 1 and at least one base film selected from the group consisting of a polyamide resin film, a polyester resin film, and a polypropylene resin film.

3. The laminate according to claim 2, wherein the straight-line cutting ability is 5 mm or less.

4. A packaging body comprising the laminate described in claim 3.

5. The packaging according to claim 4, which is for retort packaging.