JP7495251B2 - Freshness preserving film - Google Patents

Description

The present invention belongs to the technical field of biaxially oriented polypropylene resin films. The present invention relates to a freshness-preserving film or packaging bag made of such a resin film. The present invention also relates to a package in which fruits and vegetables (cut vegetables), in particular cut cabbage, are enclosed in such a packaging bag.

More and more households are using pre-washed and pre-cut fresh foods, known as "cut vegetables," to make meals easier to eat and to shorten meal preparation times as more couples work. In addition, efforts to reduce waste are driving demand for films that can keep food fresh for longer.
The freshness of cut vegetables is evaluated by bacterial count and each cut vegetable manufacturer's own evaluation (odor, color, taste, etc.). If there is a problem with the freshness, the vegetables are discarded. As a countermeasure, gas-regulating film that can adjust the atmosphere inside the packaging bag and extend the freshness is considered.

As a package made of a gas regulating film, for example, a package for cut cabbage is known, which is made of a 20 to 50 μm synthetic resin film characterized by an oxygen transmission rate of 120 to 400 cc/100 g day atm, a carbon dioxide transmission rate of 120 to 600 cc/100 g day atm, and a water vapor transmission rate of 50 g/ ^m2 day atm (at 40° C., 90% RH) or less through the effective surface area of the package (Patent Document 1).
Also known is a freshness-preserving packaging bag for bean sprouts or fungi, which is made of a synthetic resin film having an oxygen transmission rate of 1500 cc/ ^m2 -day-atm or more and 7000 cc/ ^m2 -day-atm or less at 23°C and 60% RH, and an elastic modulus of 150 MPa or more and 1600 MPa or less at 23°C (Patent Document 2).
The synthetic resin films and packaging bags made of the same described in Patent Documents 1 and 2 basically have holes physically made in the film to increase gas permeability, so there is a risk of microorganisms and the like entering the film.

Also, as a freshness-preserving packaging film for fruits and vegetables, a gas permeation control film is known which is characterized by containing a layer containing polypropylene (A), an ethylene-1-octene random copolymer (B) and a styrene-ethylene/butylene-styrene block copolymer (C), the content of (A) being 55-95% by weight, the total content of (B) and (C) being 5-45% by weight, and the weight ratio of (B) to (C) being within the range of 80/20 to 20/80 (Patent Document 3). According to Patent Document 3, this film is said to have high oxygen permeability and carbon dioxide permeability, and low haze.

JP 2004-242504 A JP 2018-076081 A JP 2008-133350 A

The main objective of the present invention is to provide a novel freshness-preserving film or a packaging bag formed from said film that can maintain freshness by preventing the deterioration of odors inside the packaging bag.

As a result of extensive research, the inventors discovered that the above problems could be solved by devising the composition of the resin film, and thus completed the present invention.

The present invention can include, for example, the following.
[1] A biaxially oriented polypropylene-based resin film comprising a sealing layer and a base layer, wherein the sealing layer is mainly composed of a propylene-based random copolymer and a gas-permeable resin, and the base layer is mainly composed of a polypropylene-based resin and a gas-permeable resin, and wherein the sealing layer and the base layer do not have through holes penetrating the sealing layer and the base layer.
[2] The freshness-preserving film described in [1] above, wherein the gas-permeable resin is a polyethylene-based resin or a vinyl aromatic hydrocarbon-based resin.
[3] The freshness-preserving film according to [1] or [2] above, further comprising a deodorant, an antibacterial agent, or both.

[4] A packaging bag formed from the freshness-preserving film described in any one of [1] to [3] above.
[5] A package in which cut vegetables are enclosed in the packaging bag described in [4] above.

According to the present invention, it is possible to suppress the deterioration of odors generated from fruits and vegetables, mainly cut vegetables (particularly cut cabbage), and to maintain the freshness of the vegetables for a relatively long period of time.

The freshness-preserving film of the present invention (hereinafter referred to as "the film of the present invention") is a biaxially oriented polypropylene-based resin film including a sealing layer and a base layer, characterized in that the sealing layer is mainly composed of a propylene-based random copolymer and a gas-permeable resin, the base layer is mainly composed of a polypropylene-based resin and a gas-permeable resin, and the sealing layer and the base layer do not have through holes penetrating the sealing layer and the base layer.
The term "not having through holes" means that in a test using a penetrating liquid, the penetrating liquid does not penetrate from one side of the packaging film to the other side, and there are no particular limitations on the size or shape.
The inventive film may further include a deodorant, an antimicrobial agent, or both, which are preferably included in the seal layer.

Here, "mainly composed of" means that other components are permitted to be contained within a range that does not impair the effects of the present invention, and does not limit the content of the components, but generally means that the content of the essential component in the total layer components is 50% by weight or more. Preferably, the content is 70% by weight or more, and more preferably, the content is 80% by weight or more to 90% by weight or more. The content may be 100% by weight.
The present invention will be described in detail below.

1. Film of the Invention The film of the invention comprises a seal layer and a substrate layer.
The "sealing layer" of the film of the present invention is the layer (innermost layer) that becomes the inside of the tube that comes into contact with the contents when the film of the present invention is formed into a cylindrical shape, and the sealing layers are bonded to each other when heat is applied. The "substrate layer" of the film of the present invention is the layer that faces the sealing layer directly or with an intermediate layer in between, and becomes the outside of the tube when the film of the present invention is formed into a cylindrical shape, and is the layer (outermost layer) that comes into contact with the outside world.

1.1 Sealing Layer The sealing layer is mainly composed of a propylene-based random copolymer and a gas-permeable resin.
The propylene-based random copolymer is not particularly limited as long as it is a copolymer of propylene and another α-olefin, which is processed into a film layer and has a sealability that allows the film layers to be bonded together when heat is applied to the film layer.
Examples of the α-olefin other than propylene include α-olefins having 2 to 20 carbon atoms other than propylene, and specific examples thereof include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, 3-methyl-1-butene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, cyclopentene, cycloheptene, norbornene, 5-ethyl-2-norbornene, tetracyclododecene, 2-ethyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, and the like. Among these, α-olefins having 2 to 4 carbon atoms, such as ethylene and butene, are preferred, and ethylene is more preferred. These α-olefins other than propylene may be used alone or in combination of two or more kinds.

The content of α-olefins other than propylene in the propylene random copolymer is preferably 14% by weight or less, more preferably 10% by weight or less.

Specific examples of the propylene-based random copolymer include propylene-ethylene random copolymer, propylene-butene random copolymer, and propylene-ethylene-butene random copolymer. Among these, propylene-ethylene-butene random copolymer is preferred.

Among these propylene random copolymers, those having a melt flow rate (MFR) value in the range of 0.5 to 20 g/10 min when measured according to ISO1133 (1997) at 230° C. and a load of 21.18 N (2.16 kg) are preferred. Propylene random copolymers having a melt flow rate value in the range of 4 to 8 g/10 min are more preferred. The melt flow rate (MFR) value of the polymer can be appropriately adjusted depending on the type and content of α-olefin other than propylene, the molecular weight of the polymer, and the degree of polymerization.
Furthermore, among the propylene random copolymers, those having a density measured according to ISO1183 (1987) in the range of 850 to 950 kg/ ^m3 are preferred, and those having a density in the range of 860 to 920 kg/ ^m3 are more preferred.

The sealing layer contains a gas-permeable resin. Here, "gas-permeable resin" refers to a resin that, when added to a raw material to form a film layer, can form a film layer that can increase the permeation of gases such as oxygen, carbon dioxide, and odors compared to when the raw material is not added. Specific examples of gas-permeable resins in the sealing layer include polyethylene-based resins, vinyl aromatic hydrocarbon-based resins, silicone rubber, natural rubber, polyurethane, polybutadiene, and butadiene rubber. Among these, polyethylene-based resins are preferred from the viewpoints of gas permeability and heat sealability.

The polyethylene resin is a copolymer of ethylene and other α-olefins. Examples of such α-olefins other than ethylene include α-olefins having 3 to 20 carbon atoms, specifically, for example, propylene, 1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, and the like. Among these, α-olefins having 3 to 8 carbon atoms, such as 1-hexene, 4-methyl-1-pentene, and 1-octene, are preferred. These α-olefins other than ethylene may be used alone or in combination of two or more kinds.

The content ratio of ethylene and other α-olefins in the polyethylene resin is usually 65 to 100% by weight of ethylene and 0 to 35% by weight of other α-olefins, preferably 70 to 99.9% by weight of ethylene and 0.1 to 30% by weight of other α-olefins, more preferably 72 to 99.5% by weight of ethylene and 0.5 to 27% by weight of other α-olefins, and even more preferably 75 to 99% by weight of ethylene and 1 to 25% by weight of other α-olefins.

Among these polyethylene resins, those having a melt flow rate (MFR) value measured in accordance with ISO 1133 (1997) at 190°C under a load of 21.18 N (2.16 kg) are preferred within the range of 0.5 to 20 g/10 min. Also, polyethylene resins having a melt flow rate value within the range of 2 to 4 g/10 min are more preferred.
Furthermore, among the polyethylene resins, those having a density measured in accordance with ISO1183 (1987) within the range of 850 to 900 kg/ ^m3 are preferred, and those having a density within the range of 860 to 890 kg/ ^m3 are more preferred.

Examples of the vinyl aromatic hydrocarbon resin include a hydrogenated copolymer of a vinyl aromatic hydrocarbon and a conjugated diene hydrocarbon, a copolymer of a vinyl aromatic hydrocarbon and a conjugated diene hydrocarbon, and a copolymer of a vinyl aromatic hydrocarbon and an aliphatic unsaturated carboxylic acid ester. Among these, a copolymer of a vinyl aromatic hydrocarbon and a conjugated diene hydrocarbon (e.g., a polystyrene resin) or a hydrogenated copolymer thereof is preferred.
Examples of hydrogenated copolymers of vinyl aromatic hydrocarbons and conjugated diene hydrocarbons include hydrogenated random copolymers of styrene monomers and diene monomers, and hydrogenated block copolymers of styrene monomers and diene monomers. These are also called "hydrogenated styrene elastomers,""hydrogenated random copolymers," or "hydrogenated block copolymers."

Specifically, the hydrogenated random copolymer is, for example, a copolymer in which styrene monomer units represented by the formula -CH(C ₆ H ₅ )CH ₂ -, ethylene units represented by the formula -CH ₂ CH ₂ CH ₂ CH ₂ -, and butylene units represented by the formula -CH(C ₂ H ₅ )CH ₂ - are randomly bonded.
The hydrogenated block copolymer may be one having a block segment derived from a vinyl aromatic hydrocarbon at one or both ends of the copolymer and further having a block segment derived from a conjugated diene hydrocarbon, or a hydrogenated product of a blend of these. Specific examples of the hydrogenated block copolymer include one having a block segment derived from a styrene monomer represented by the formula -CH(C ₆ H ₅ )CH ₂ - at one end of the copolymer, and a block segment containing an ethylene unit represented by the formula -CH ₂ CH ₂ CH ₂ CH ₂ - and/or a butylene unit represented by the formula -CH(C ₂ H ₅ )CH ₂ - in the middle of the block segment. Alternatively, the copolymer may have a segment containing an ethylene unit represented by the formula -CH ₂ CH ₂ CH ₂ CH ₂ - at the other end.

Among the vinyl aromatic hydrocarbon resins, as the hydrogenated block copolymer (hydrogenated styrene elastomer), a styrene-ethylene-butylene-olefin crystalline block copolymer (SEBC) or a styrene-ethylene-butylene-styrene block copolymer (SEBS) is particularly preferred.
The density of the vinyl aromatic hydrocarbon resin (SEBS, etc.) is preferably within the range of 850 kg/m ³ to 1,100 kg/m ³ , more preferably within the range of 880 kg/m ³ to 1,050 kg/m ³ , in accordance with ISO 1183-1:2004.
The MFR (melt flow rate) value of the vinyl aromatic hydrocarbon resin (SEBS, etc.) measured at a temperature of 230° C. and a load of 21.18 N in accordance with ISO 1133 is preferably within the range of 1 g/10 min to 20 g/10 min, more preferably within the range of 3 g/10 min to 15 g/10 min.
The styrene content in 100% by weight of the hydrogenated styrene-based elastomer is preferably within a range of 5 to 70% by weight, and more preferably within a range of 9 to 67% by weight.

The content of the propylene-based random copolymer in the resin of the seal layer varies depending on the specific type of resin, but may be, for example, in the range of 65 to 97% by weight, preferably in the range of 70 to 95% by weight, and more preferably in the range of 72 to 93% by weight.
The blending ratio of the propylene-based random copolymer and the gas-permeable resin (polyethylene-based resin) in the resin of the seal layer varies depending on the specific types of resins, but is suitably within a weight ratio range of 1.5 to 20 (propylene-based random copolymer/gas-permeable resin), preferably within a range of 2 to 15, and more preferably within a range of 2.5 to 14.

The sealing layer may further contain one or more deodorants, which will be described later, in an appropriate amount, and it is preferable to do so. In addition, the sealing layer may further contain one or more antibacterial agents, which will be described later, in an appropriate amount, and it is preferable to do so. The incorporation of a deodorant or antibacterial agent is more effective in suppressing unpleasant odors.
The deodorant may be blended in the sealing layer in an amount of, for example, 1 to 6 parts by weight per 100 parts by weight of the resin constituting the layer, and the antibacterial agent may be blended in the sealing layer in an amount of, for example, 0.1 to 1 part by weight per 100 parts by weight of the resin constituting the layer.

The sealing layer may contain an antiblocking agent or a lubricant to the extent that the effect of the present invention is not impaired, in order to smooth the surface of the resin film and prevent the resin films from adhering to each other. Examples of such antiblocking agents include commonly used inorganic silica, kaolin, zeolite, etc., and organic crosslinked acrylic beads, etc. Examples of lubricants include calcium stearate, etc. The antiblocking agent and the lubricant may each be used alone, or two or more types may be used in combination.

The amount of the antiblocking agent or lubricant added can be adjusted as appropriate depending on the type of resin, etc., but is preferably 0.05 to 30 parts by weight, and more preferably 0.5 to 20 parts by weight, per 100 parts by weight of the resin that constitutes the layer.

1.2 Substrate Layer The substrate layer is mainly made of a polypropylene-based resin.
Examples of the polypropylene-based resin include polypropylene homopolymers and crystalline polypropylene-based resins, of which crystalline polypropylene-based resins are preferred.
The crystalline polypropylene resin preferably has a melting point of 155° C. to 165° C. Furthermore, among the crystalline polypropylene resins having a melting point of 155° C. to 165° C., those having an isotactic pentad fraction (IP) of 89.0% to 96.0% as determined by ¹³ C nuclear magnetic resonance spectroscopy are more preferred.

Crystalline polypropylene resins are copolymers of propylene and other α-olefins. Examples of α-olefins other than propylene include α-olefins having 2 to 10 carbon atoms, specifically, ethylene, 1-butene, 1-pentene, 1-hexene, and other α-olefins. Among these, α-olefins having 2 to 4 carbon atoms, such as ethylene and 1-butene, are preferred, and ethylene is more preferred. These α-olefins other than propylene may be used alone or in combination of two or more. The content of α-olefins other than propylene is suitably 1.3% by weight or less, and preferably 0.5% by weight or less.

Among these polypropylene-based resins, the melt flow rate (MFR) value measured in accordance with ISO 1133 (1997) at 230°C and a load of 21.18 N (2.16 kg) is preferably within the range of 0.5 to 20 g/10 min., and more preferably within the range of 2 to 4 g/10 min.
Furthermore, among the polypropylene-based resins, those having a density measured in accordance with ISO1183 (1987) within the range of 850 to 950 kg/ ^m3 are preferred, and those having a density within the range of 860 to 920 kg/ ^m3 are more preferred.

The base layer may also contain an appropriate amount of gas-permeable resin. The gas-permeable resin is the same as that in the sealing layer, but the gas-permeable resin in the base layer is preferably a vinyl aromatic hydrocarbon resin, and more preferably a styrene resin or a hydrogenated styrene elastomer. In particular, from the viewpoint of transparency (haze) when made into a film, a styrene-ethylene-butylene-styrene block copolymer (SEBS) is preferred.

The content of the polypropylene-based resin in the resin of the base layer varies depending on the specific type of resin, but can be, for example, in the range of 70 to 98% by weight, preferably in the range of 75 to 95% by weight, and more preferably in the range of 78 to 92% by weight.
The blending ratio of the polypropylene-based resin (crystalline polypropylene-based resin) to the gas-permeable resin (vinyl aromatic hydrocarbon-based resin or hydrogenated styrene-based elastomer) in the resin of the base layer varies depending on the specific types of these resins, but is suitably within a weight ratio range of 1.5 to 20 (polypropylene-based resin/gas-permeable resin), preferably within a range of 2.5 to 15, and more preferably within a range of 3 to 12.

The base layer may further contain one or more deodorants as described below in appropriate amounts. If necessary, one or more antibacterial agents as described below may also be contained in appropriate amounts.
The deodorant may be blended in the sealing layer in an amount of, for example, 1 to 6 parts by weight per 100 parts by weight of the resin constituting the layer, and the antibacterial agent may be blended in the sealing layer in an amount of, for example, 0.1 to 1 part by weight per 100 parts by weight of the resin constituting the layer.

The base layer may further contain an anti-fogging agent for the purpose of imparting anti-fogging properties to the film. Such an anti-fogging agent is not particularly limited as long as it is suitable for the purpose, and anti-fogging agents that have been conventionally used in anti-fogging films may be used as is. Specific examples include three types of anti-fogging agents: alkyldiethanolamine, alkyldiethanolamine fatty acid ester, and glycerin fatty acid ester.

The alkyl group in the alkyldiethanolamine usually has 8 to 22 carbon atoms, preferably 12 to 18 carbon atoms. Specific examples of alkyldiethanolamine include lauryldiethanolamine, myristyldiethanolamine, palmityldiethanolamine, stearyldiethanolamine, and oleyldiethanolamine.

The fatty acid ester group in the alkyldiethanolamine fatty acid ester is usually a saturated or unsaturated fatty acid ester having 8 to 22 carbon atoms, preferably 12 to 22 carbon atoms, and preferably the latter unsaturated fatty acid ester. Specific examples of alkyldiethanolamine fatty acid esters include lauryldiethanolamine monostearate, myristyldiethanolamine monooleate, lauryldiethanolamine monostearate, palmityldiethanolamine monostearate, stearyldiethanolamine monopalmitylate, stearyldiethanolamine monostearate, and oleyldiethanolamine monostearate.

The fatty acid ester group in the glycerin fatty acid ester can be the same as the fatty acid ester group in the alkyldiethanolamine fatty acid ester described above. In addition, the number of fatty acid ester groups bonded to the -OH of glycerin is preferably 1 or 2, and more preferably, it is a fatty acid ester monoglyceride with one fatty acid ester group.

The above anti-fogging agents are used in the form of one type or a mixture of two or three types in the same system, or in the form of a mixture of two or three types in a different system, but it is more preferable to use them in the form of a mixture of three types in a different system, that is, a three-component mixture of alkyldiethanolamine, alkyldiethanolamine fatty acid ester, and fatty acid ester monoglyceride, with alkyldiethanolamine fatty acid ester as the main component.

The amount of anti-fog agent added can be adjusted as appropriate depending on the type of anti-fog agent, but 5,000 to 15,000 ppm is appropriate, and 4,000 to 10,000 ppm is preferable. If the amount of anti-fog agent added is less than 5,000 ppm, sufficient anti-fog effect may not be obtained, and if it exceeds 15,000 ppm, excessive bleeding out to the surface may occur, resulting in deterioration of transparency.

1.3 Deodorant and antibacterial agent The film of the present invention may contain a suitable amount of deodorant and/or antibacterial agent. The deodorant can eliminate the generated odor, and the antibacterial agent can suppress the generation of the odor.

Examples of deodorants include inorganic deodorants. Examples of inorganic deodorants include zirconium phosphate; aluminosilicates (zeolites), zinc aluminosilicate; carbonates such as sodium carbonate, sodium bicarbonate, and calcium carbonate; and metal oxides such as calcium oxide, magnesium oxide, aluminum oxide, zinc oxide, copper oxide, iron oxide, titanium oxide, and alum. Examples also include composites of these compounds, and compounds in which metals such as copper, silver, zinc, and titanium are supported on these compounds. Among these, silicon dioxide/zinc oxide composites (composites), zinc aluminosilicate, and silver ion-containing aluminosilicates are preferred. Silicon dioxide/zinc oxide composites (composites) are particularly preferred. Commercially available deodorants of this type include Sumerclin PC-504ZB (G), PC-504ZB (GF), PC-504ZB (GFD), PC-504ZB (GFAD), and PC-504ZB (GUD) from Fuji Chemical Co., Ltd., Lionite SF (zinc aluminosilicate) from Kao Corporation, Zeomic HW10N (silver ion-containing aluminosilicate) from Shinan Zeomic Co., Ltd., Kesmon NS-10N (zirconium phosphate) from Toagosei Co., Ltd., and Kyoward 500 and 1000 from Kyowa Chemical Industry Co., Ltd.

Examples of the antibacterial agent include inorganic antibacterial agents and organic antibacterial substances.
Examples of inorganic antibacterial agents include metal compounds containing metal ions, specifically, metal compounds containing silver ions, copper ions, or zinc ions. Among these, metal compounds containing silver ions and zinc ions are preferred. Specific examples of such metal compounds include silver-zinc zeolite. Commercially available products include Bactekiller from Fuji Chemical Co., Ltd., Zeomic (registered trademark) from Sinanen Zeomic Co., Ltd., and Novalon (registered trademark) from Toa Gosei Co., Ltd.

The average particle diameter of the metal compound containing metal ions is not particularly limited, but is preferably 0.5 μm or more and 10 μm or less, and more preferably 1 μm or more and 8 μm or less. When the average particle diameter is 0.5 μm or more, the dispersion state in the resin becomes good, and when the average particle diameter is 10 μm or less, the film formation stability of the film becomes excellent. Here, the "average particle diameter" refers to a particle diameter obtained by measuring the maximum length (Dmax: the maximum length at two points on the outline of the particle image) of the antibacterial agent using a transmission electron microscope and measuring the maximum length perpendicular length (DV-max: the shortest length between two straight lines parallel to the maximum length when the particle image is sandwiched between these two straight lines), and taking the geometric mean value (Dmax x DV-max) ^1/2 as the particle diameter of one antibacterial agent, for example, for 100 antibacterial agents by this method, and calculating the arithmetic mean of the particle diameters.

Organic antibacterial substances can be appropriately selected by those skilled in the art from the viewpoint of safety, and specific examples include terpenes such as allyl isothiocyanate and hinokitiol.

1.4 Others The film of the present invention has at least two layers, the seal layer and the base layer. The film of the present invention may also have an intermediate layer between the seal layer and the base layer.

The thickness of each layer in the film of the present invention is as follows:
When the total thickness of the film is in the range of 10 to 50 μm, preferably in the range of 20 to 45 μm, the seal layer is in the range of 1 to 8 μm, preferably in the range of 1.5 to 6 μm, and the base layer is in the range of 2 to 49 μm, preferably in the range of 14 to 43.5 μm.

The film of the present invention may further contain various additives in appropriate amounts, such as nucleating agents, antioxidants, flame retardants, antistatic agents, fillers, pigments, etc.
In addition to the above layers, the film of the present invention may have other layers such as an aperture-imparting layer and a gas barrier layer.

2. Manufacturing method of the film of the present invention The film of the present invention can be manufactured by a known manufacturing method. However, taking into consideration the productivity and the physical properties of the finished film, it is preferable to manufacture the film of the present invention by forming a flat sheet by extrusion molding and then sequentially biaxially stretching it.

More specifically, the resin constituting the sealing layer and the resin constituting the base material layer are fed into each extruder set at an appropriate temperature, and the resin is melted and kneaded in the extruder, and then extruded into a sheet from a T-die at 210°C to 250°C. In this case, a feed block method or a multi-manifold method may be used to form a multi-layer structure of two or three layers. The extruded sheet is cooled and solidified by a cooling roll at 25°C and sent to the longitudinal stretching process. The longitudinal stretching is performed by a heating roll set at 130°C to 140°C, and the sheet is stretched in the longitudinal direction (hereinafter referred to as the MD direction) depending on the speed difference between the rolls. There is no particular limit to the number of heating rolls, but at least two rolls, one on the low speed side and one on the high speed side, are required. The stretching ratio of the longitudinal stretching is 4 to 6 times, preferably 4.5 to 5.5 times. The sheet is then sent to a transverse stretching process using a tenter, where it is stretched in the transverse direction (hereinafter referred to as the TD direction). The tenter is divided into preheating, stretching, and annealing zones, with the preheating zone set at 165°C to 170°C, the stretching zone at 165°C to 170°C, and the annealing zone at 165°C to 170°C. The stretching ratio in the stretching zone is preferably about 6 to 10 times. After being stretched, the film is cooled and fixed in the annealing zone, and then wound up on a winder to become a film roll.

In the production of the film of the present invention, after leaving the annealing zone of the tenter and before being wound up by a winder, it is preferable to perform a known surface treatment such as a corona discharge treatment, a flame treatment, or an ultraviolet irradiation treatment, and in particular, it is preferable to perform a corona discharge treatment from the viewpoint of convenience. By performing the surface treatment, it is possible to impart wetting tension to the surface of the film and enhance the anti-fogging effect, and also to enhance the adhesion to printing ink when printing is performed on the film surface. This corona discharge treatment may be performed on both the surface layer surface and the substrate layer surface, or on either one of the surface layer surface or the substrate layer surface. The strength of the corona discharge treatment is preferably within the range of 1.8×10 ² to 9.0×10 ² J/m ² , and when both sides are treated, both sides may have the same strength or different strengths.

The surface wet tension of the biaxially oriented polypropylene resin film (film of the present invention) thus obtained is preferably 38 to 44 mN/m. If the wet tension is less than 38 mN/m, the antifogging properties are not sufficiently exhibited, and in the case of printing, the adhesion of the printing ink is poor, which is undesirable. If the wet tension exceeds 44 mN/m, the antifogging agent bleeds out to the surface severely, which causes whitening and blocking, and also causes a decrease in the melt-cutting and sealing strength, which is undesirable.

3. Packaging Bag and Package Formed from the Film of the Invention Next, the packaging bag (hereinafter referred to as "the bag of the invention") and package formed from the film of the invention will be described in detail.

The bag of the present invention can be produced by using the film of the present invention with an automatic packaging machine or the like.
The film of the present invention can be used not only when formed using a vertical pillow packaging machine, but also when formed using other packaging machines such as a horizontal pillow packaging machine.
Specifically, the bag of the present invention can be produced, for example, in a former of a vertical pillow packaging machine, by forming a tubular film with a sealing layer on the inner surface, heat sealing the ends of the film along the machine direction (MD direction), and then heat sealing the lower end of the tubular film in a direction perpendicular to the machine direction (TD direction).
Next, a certain amount of contents is weighed out and placed in the bag of the present invention, and the bag is heat-sealed in a direction (TD) perpendicular to the machine direction (MD) of the film, thereby producing a package containing the contents. Hereinafter, a package containing the contents sealed in the bag of the present invention will be referred to as the "package of the present invention."

The contents to be enclosed in the bag of the present invention include, for example, agricultural products such as fresh vegetables, fruits, potatoes, mushrooms, etc., and preferably fresh vegetables. Examples of such fresh vegetables include vegetables such as green onions, bean sprouts, spinach, broccoli, and green peppers; or cut vegetables such as cabbage, lettuce, and carrots. In particular, the bag of the present invention can be suitably used for cut vegetables such as cut cabbage, and is particularly suitable for cut cabbage.

The present invention will be explained below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

The raw materials used in the production of biaxially oriented polypropylene film are as follows:
PP-1: propylene-ethylene-butene copolymer (MFR: 5.0 g/10 min, melting point: 125° C., density: 0.9 g/cm ³ )
PP-2: crystalline polypropylene resin (MFR: 2.5 g/10 min, melting point: 160° C., density: 0.9 g/cm ³ )
PE: ethylene/1-octene copolymer (MFR: 3.0 g/10 min, melting point: 68° C., density: 0.875 g/cm ³ )
SEBS: styrene-ethylene-butylene-styrene block copolymer (MFR: 4.5 g/10 min, styrene content: 12 wt%, density: 0.89 g/cm ³ )
Deodorant: Smerclean PC-504ZB: Silicon dioxide/zinc oxide composite (manufactured by Fuji Chemical Co., Ltd.)
Antibacterial agent: Bactekiler BM-102NSC: inorganic antibacterial agent (manufactured by Fuji Chemical Co., Ltd.)

A biaxially oriented polypropylene film consisting of a seal layer and a base layer was produced by the following procedure using the resin, deodorant, and antibacterial agent blends shown in Table 1 below.
The resins constituting each layer were put into each extruder, and were laminated in the order of base layer/seal layer, and were co-extruded from a multi-layer T-die at a temperature of 230 ° C., and then cooled and solidified with a cooling roll at 25 ° C. to obtain a raw sheet. The sheet was then heated to 130 ° C., roll-stretched 4.6 times in the MD direction, preheated in a tenter at a set temperature of 165 ° C., stretched 10 times in the TD direction at a set temperature of 165 ° C., and annealed at a set temperature of 165 ° C. After leaving the tenter, the base layer side was subjected to corona discharge treatment at 6.6 × 10 ² J / m ² and the surface layer side was subjected to 4.8 × 10 ² J / m ² , and then wound up with a winder to obtain a biaxially stretched polypropylene film (film of the present invention, etc.) with a total thickness of 30 μm (seal layer: 2 μm, base layer 28 μm).
The produced film did not have any through holes penetrating the seal layer and the base layer.

[Example 1, Comparative Examples 1 and 2] Production of Packages Using the film of the present invention obtained above, the package of the present invention (Example 1) and comparative packages (Comparative Examples 1 and 2) were produced according to the following procedure.
The film was set in a vertical pillow packaging machine (manufactured by Taisei Machinery Co., Ltd.) and made into a bag. First, a former was used to make a cylindrical film (200 mm wide) with the seal layer on the inner surface, and the end of the film was heat-sealed at a temperature of 130° C. along the machine direction (MD), and then the lower end of the heat-sealed cylindrical film was heat-sealed at a temperature of 210° C. in the direction perpendicular to the machine direction (TD), forming a cylindrical film (bag) with the bottom and back heat-sealed and the top open.
Next, a certain amount of the contents (cut cabbage, 130 g) was put into the cylindrical film (bag) obtained above, and then heat-sealed at a temperature of 210° C. at intervals of 250 mm in the direction (TD) perpendicular to the machine direction (MD) of the film, and the center of the heat-sealed portion was cut horizontally.

The bags filled with the contents by the above process were sealed at the top and bottom to form the present invention package and the comparative package (the present invention package, etc.). The heat seal width in this production is 10 mm. The bag size of the produced package is 250 mm in the machine direction (MD) x 200 mm in the width direction (TD).
In addition, in Comparative Example 2, one through hole having a diameter of 60 μm was formed in each bag. In Example 1 and Comparative Example 1, no through hole was formed.

The obtained packaging of the present invention was used to evaluate odor as follows.

<Odor evaluation test>
The packages of the present invention containing cut cabbage as the content were stored in a refrigerator set at 10° C. for 6 days to prepare samples. The number of specimens was 6 for each sample (N=6). The cut cabbage was purchased randomly from a marketed store (contents: 130 g), and was opened on the second day after the date of manufacture to be used in each of the packages.
The air from each of the odor samples was filled into a collection tube to a volume of 200 mL, and the peak areas of dimethyl disulfide and ethanol were measured using a gas chromatogram mass spectrometer (Shimadzu Corporation: QP2010ULRT) (N=6).

As shown in the above results (Table 1), the packaging of the present invention (Example) produced less dimethyl disulfide and ethanol than the comparative packaging (Comparative Example), demonstrating excellent odor suppression effect.

The film or bag of the present invention can, for example, suppress the deterioration of odors emanating from fruits and vegetables, particularly cut vegetables such as cut cabbage, and can maintain their freshness for a long time. Therefore, the package of the present invention in which these or cut vegetables are enclosed is useful, for example, for distribution and sales in the fruit and vegetable market.

Claims (3)

A biaxially oriented polypropylene-based resin film comprising a seal layer and a base layer,
the sealing layer is mainly composed of a propylene-based random copolymer and a gas-permeable resin,
the base layer is mainly made of a polypropylene-based resin and a gas-permeable resin,
The gas-permeable resin contained in the sealing layer is a polyethylene-based resin,
the gas-permeable resin contained in the base layer is a vinyl aromatic hydrocarbon-based resin,
the sealing layer comprises a deodorant and an antibacterial agent;
A freshness-preserving film characterized in that it has no through holes penetrating the sealing layer and the base layer. A packaging bag formed from the freshness-preserving film according to claim 1 . A package comprising cut vegetables sealed in the packaging bag according to claim 2 .