Vegetable and fruit freshness keeping bag, vegetable and fruit-containing package, and vegetable and fruit freshness keeping method

Abstract

To provide a vegetable and fruit freshness keeping bag which can achieve both easy openability and durability of a packaging bag, while keeping good freshness keeping property of vegetables and fruits.SOLUTION: A vegetable and fruit freshness keeping bag is composed of a synthetic resin film, wherein the synthetic resin film contains polypropylene, a ratio (MD / TD) of tear strength (N / cm) in an MD direction of the synthetic resin film measured by a right angled tear method according to JIS K 7128-3 to tear strength (N / cm) in a TD direction of the synthetic resin film is 2.2 or more, and a coefficient of static friction measured by a friction test according to JIS K 7125 of outside faces of the vegetable and fruit freshness keeping bag is 0.23 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a freshness-keeping bag for fruits and vegetables, a package containing fruits and vegetables, and a method for keeping fruits and vegetables fresh, and more particularly to a freshness-keeping bag for fruits and vegetables, a package containing fruits and vegetables, a method for keeping fruits and vegetables fresh, a synthetic resin film used for manufacturing the freshness-keeping bag for fruits and vegetables, and a roll of synthetic resin film. [Background technology]

[0002] A conventional method for preserving the freshness of harvested fruits and vegetables is to moderately suppress the respiration of the fruits and vegetables by adjusting the oxygen and carbon dioxide concentrations. This type of packaging used to preserve the freshness of fruits and vegetables is known as modified atmosphere (MA) packaging. In recent years, with the growing interest in MA packaging, there is a demand for packaging materials to have improved performance in various aspects, including gas permeability, processability, strength, packaging workability, and appearance.

[0003] For example, Patent Document 1 (JP 2023-106849 A) ​​discloses a film for freshness-keeping bags for fruits and vegetables in which the dynamic friction coefficient μ' between the inner surfaces at 40°C is controlled in order to prevent the film itself from reducing the freshness of the fruits and vegetables, taking into account that the packaging film may come into direct contact with the fruits and vegetables. Furthermore, Patent Document 2 (JP 2022-119289 A) discloses a freshness-keeping film that is thin and has excellent content tracking properties, yet does not reduce seal strength, is resistant to whitening due to anti-fog agent bleeding, and has deodorizing properties. Specifically, it discloses that the freshness-keeping film uses a specific polypropylene resin and a specific deodorizing nanofiller. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-106849 [Patent Document 2] Japanese Patent Application Publication No. 2022-119289 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technologies disclosed in Patent Documents 1 and 2 do not focus on the condition or usability of the packaging bag after the fruit and vegetables have been packaged in it. The inventors noticed that after the fruit and vegetables have been packaged in the packaging bag, the outer surface of the bag may be easily torn due to friction when the package containing the fruit and vegetables is transported, or the packaging bag may be difficult to tear and open.

[0006] Therefore, the inventors conducted extensive research to improve the durability of the outer surface of the packaging bag against friction, etc. while maintaining the easy-open properties of the packaging bag. As a result, they discovered that it is effective to simultaneously control the tear strength and static friction coefficient of the synthetic resin film, and thus completed the present invention. [Means for solving the problem]

[0007] According to the present invention, the following technology relating to packaging bags for fruits and vegetables is provided.

[0008] [1] A freshness-keeping bag for fruits and vegetables made of synthetic resin film, the synthetic resin film includes polypropylene, the ratio (MD / TD) of the tear strength (N / cm) in the MD direction of the synthetic resin film to the tear strength (N / cm) in the TD direction of the synthetic resin film, as measured by a right-angle tear method in accordance with JIS K7128-3, is 2.2 or more; The static friction coefficient between the outer surfaces of the fruit and vegetable freshness-keeping bag measured by a friction test in accordance with JIS K7125 is 0.23 or less. [2] The freshness-keeping bag for fruits and vegetables according to [1], The freshness-keeping bag for fruits and vegetables has a tensile strength of 130 MPa or more and 170 MPa or less, measured in the MD direction at a tensile speed of 500 mm / min, in accordance with JIS K7127 for freshness-keeping bags for fruits and vegetables. [3] The freshness-keeping bag for fruits and vegetables according to [1] or [2], The synthetic resin film is a monolayer film containing polypropylene or a multilayer film having a layer containing polypropylene. [4] The fruit and vegetable freshness-keeping bag according to any one of [1] to [3], The fruit and vegetable freshness-keeping bag has through holes with a pore diameter of 100 μm or more. [5] A package containing fresh produce, in which fresh produce is contained in a fresh produce freshness-keeping bag described in any one of [1] to [4]. [6] A method for preserving the freshness of fruits and vegetables, comprising a step of storing fruits and vegetables in a fruit and vegetable freshness preservation bag described in any one of [1] to [4]. [7] A synthetic resin film used to manufacture the fruit and vegetable freshness-keeping bag according to any one of [1] to [4], A synthetic resin film configured so that the static friction coefficient between at least one of its surfaces, measured by a friction test conforming to JIS K7125, is 0.2 or less, and that surface is the outer surface of a fruit and vegetable freshness-keeping bag. [8] A rolled body in which the synthetic resin film according to [7] is wound into a roll. [Effects of the Invention]

[0009] According to the present invention, a freshness-keeping bag for fruits and vegetables is provided that can maintain the freshness of fruits and vegetables well while achieving both easy opening and durability of the packaging bag. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail.

[0011] In this specification, unless otherwise specified, the expression "X to Y" in the description of a numerical range means at least X and at most Y. For example, "1 to 5% by mass" means "at least 1% by mass and at most 5% by mass." In this specification, MD direction refers to the machine direction and indicates the direction in which the resin flows, and TD direction refers to the transverse direction and indicates the direction perpendicular to the MD direction.

[0012] <Fruit and vegetable freshness preservation bag> The fruit and vegetable freshness-keeping bag (hereinafter also referred to as "packaging bag") of this embodiment is made of a synthetic resin film, and the synthetic resin film contains polypropylene, the ratio (MD / TD) of the tear strength (N / cm) in the MD direction of the synthetic resin film to the tear strength (N / cm) in the TD direction of the synthetic resin film, as measured by a right-angle tear method in accordance with JIS K7128-3, is 2.2 or more; The coefficient of static friction between the outer surfaces of the fruit and vegetable freshness-keeping bags is 0.23 or less as measured by a friction test in accordance with JIS K7125.

[0013] This allows the packaging bag to maintain the freshness of the fruit and vegetables while also achieving a high level of ease of opening and durability. The details of the reason for this are not clear, but it is thought to be as follows. When synthetic resin films are extruded, the molecules are oriented in the direction the resin flows, which tends to increase tensile strength in the MD direction. The higher the tear strength (N / cm) ratio (MD / TD), the more anisotropic the synthetic resin film is. Therefore, by making the tear strength (N / cm) ratio (MD / TD) 2.2 or higher, the film will be more likely to tear in the MD direction, making it easy to tear by hand and also tear in a straight line from the cutout, which is thought to result in good easy-to-open properties. In addition, by controlling the coefficient of static friction between the outer surfaces of the packaging bags, it is possible to reduce friction when packages containing fresh produce rub against each other, preventing excessive force and friction from being applied to the packaging bags, and it is thought that this will make it easier to improve the durability of the packaging bags.

[0014] The ratio (MD / TD) of the tear strength (N / cm) is 2.2 or more, preferably 2.3 or more, and more preferably 2.4 or more. The upper limit of the ratio (MD / TD) of the above tear strength (N / cm) is not particularly limited, but in order to maintain good processability and formability of the packaging bag, it is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.0 or less.

[0015] The tear strength (N / cm) in the MD direction is preferably 1000 to 5000 N / cm, more preferably 1500 to 4000 N / cm, and even more preferably 2000 to 3500 N / cm.

[0016] The static friction coefficient between the outer surfaces of the packaging bag as measured by a friction test in accordance with JIS K7125 is 0.23 or less, preferably 0.22 or less, more preferably 0.21 or less, and even more preferably 0.20 or less.

[0017] The packaging bag preferably has a tensile strength of 130 to 170 MPa, more preferably 135 to 165 MPa, measured in the MD direction at a tensile speed of 500 mm / min in accordance with JIS K7127 for freshness-keeping bags for fruits and vegetables.

[0018] By controlling the tensile strength, the packaging bag can be given appropriate strength against tension, thereby increasing the durability of the packaging bag during transportation, etc., while maintaining the strength of the packaging bag, thereby preventing deformation or damage to the bag when opened.

[0019] In this embodiment, a packaging bag that satisfies the above tear strength (N / cm) ratio, static friction coefficient, and tensile strength can be realized by, for example, selecting polypropylene, adjusting the polyethylene content, or devising the thickness, layer structure, and manufacturing method of the synthetic resin film. Examples of manufacturing methods for the synthetic resin film include adjusting the stretching conditions of the synthetic resin film, particularly controlling the stretching ratios in the MD and TD directions, and annealing the synthetic resin film.

[0020] [Bag shape] The packaging bag of this embodiment is a bag formed from a synthetic resin film, and the bag shape is not particularly limited, and can be a two-sided bag, a three-sided bag, a back-sealed bag (a palm-shaped bag), a pouch, a gusset bag, etc. A two-sided bag is a bag made by folding a synthetic resin film in half, using the folded part as the bottom, and sealing both sides. A three-sided bag is a bag made by sealing the bottom and both sides of two overlapping synthetic resin films.

[0021] (Manufacturing method of packaging bags) The manufacturing method of the packaging bag is appropriately set depending on the bag shape, etc., and a known method can be used. The static friction coefficient of the outer surface of the packaging bag can be achieved by appropriately combining the synthetic resin film and the manufacturing method of the packaging bag.

[0022] The size of the packaging bag of this embodiment can be about 100 mm×100 mm to 300 mm×450 mm when used to pack fruits and vegetables for general consumers.

[0023] [Through hole] The packaging bag may have through holes formed therein, or may have no through holes. The presence or absence of through holes makes it possible to stably adjust the water vapor permeability and oxygen permeability.

[0024] The planar shape of the through-hole may be, for example, a circle, a polygon, or a slit. The circle is not limited to a perfect circle and includes an approximate circle. In addition to a circle, the through-hole may be a semicircle or a crescent shape. The polygon may be any shape surrounded by three or more line segments, such as a triangle, a rectangle, or a pentagon. The slit is a cut or narrow gap that penetrates the synthetic resin sheet that constitutes the packaging material, and may be a straight line, a curve, an L-shape, an X-shape, or the like, and its length is not particularly limited.

[0025] When through-holes are formed, the average diameter of the through-holes is preferably 10 μm to 200 μm, more preferably 50 to 180 μm, even more preferably 100 to 150 μm, and particularly preferably 110 to 130 μm. By setting the diameter at or above the lower limit, the oxygen permeability of the package is improved and the generation of unpleasant odors is easily suppressed. On the other hand, by setting the diameter at or below the upper limit, the MA effect can be maintained while preventing the intrusion of foreign matter, making it easier to maintain the freshness of fruits and vegetables. The average diameter of the through holes is calculated from the open area of ​​the through holes, assuming that the through holes are perfect circles.

[0026] The packaging bag may also have a through hole with a diameter of 4 mm or more, or may have so-called punched holes.

[0027] The number of punched holes is preferably 1 to 20 per packaging bag, more preferably 1 to 10, even more preferably 1 to 5, and especially preferably 1 to 3, in order to suppress increased respiration and drying due to excessive gas permeability and to make it easier to maintain freshness.

[0028] The above-mentioned through holes may be formed in the resin film in advance when manufacturing the packaging bag, or may be formed after the resin film is formed into the packaging bag, or may be formed before or after the resin film is formed into the packaging bag.

[0029] The method for forming the through holes is not particularly limited, and any known method can be used, such as a laser processing method, a needle processing method including a hot needle, or a method using a mold such as a roll cutter.

[0030] [Oxygen permeability] Oxygen permeability (cc / m) of packaging bag at 23°C and 60% RH 2·day·atm) is preferably 500 or more and 30,000 or less, more preferably 800 or more and 20,000 or less, even more preferably 1,000 or more and 10,000 or less, and even more preferably 1,000 or more and 6,000 or less.

[0031] The oxygen permeability can be calculated, for example, by measuring the oxygen concentration inside the packaging bag immediately after filling it with nitrogen and after leaving it for a certain period of time after filling it with nitrogen, and then calculating it from the oxygen concentration gradient.

[0032] [Water vapor permeability] The water vapor permeability of the packaging bag at 40°C is preferably 1 g / (m 2 ·day) or more, and more preferably 3g / (m 2 ·day) or more. On the other hand, the water vapor permeability of the packaging bag at 40°C is preferably 300 g / (m 2 ·day) or less, and more preferably 100g / (m 2 ·day) or less, and more preferably 50 g / (m 2 ·day) or less, and particularly preferably 10 g / (m 2 ·day) or less.

[0033] The water vapor permeability can be measured by a method in accordance with JIS Z 0208 (cup method).

[0034] In addition, in the present invention, the oxygen permeability and water vapor permeability (moisture permeability) of the packaging bag can be adjusted by controlling the selection of the synthetic resin film material, the film manufacturing method, the layer structure of the film, the presence or absence of through holes and the average diameter of the through holes, the presence or absence of non-through grooves, etc.

[0035] <Synthetic resin film> The synthetic resin film is used to produce the above-mentioned freshness-keeping bag for fruits and vegetables. The synthetic resin film is a long sheet wound into a sheet or roll. From the viewpoint of increasing the production efficiency of packaging bags, the synthetic resin film is preferably a long sheet wound into a roll. The roll may be one in which the synthetic resin film is wound around a core, or one rolled into a roll without using a core. The synthetic resin film may have a front and back, or may have no front and back, and can be appropriately selected depending on the manufacturing method, shape, use, etc. of the packaging bag.

[0036] The coefficient of static friction between at least one surface of the synthetic resin film, measured by a friction test in accordance with JIS K7125, is preferably 0.23 or less, more preferably 0.22 or less, even more preferably 0.21 or less, and especially preferably 0.20 or less, and it is preferable that this surface be configured as the outer surface of the fruit and vegetable freshness-keeping bag, which makes it easier to increase the durability of the packaging bag.

[0037] (raw materials) The synthetic resin film is preferably transparent or translucent, more preferably transparent, so that the fruit or vegetable can be visually recognized from the outside. It may also be printed with information for identifying the fruit or vegetable. The synthetic resin may be partially made from raw materials derived from biomass.

[0038] The synthetic resin constituting the synthetic resin film is not particularly limited as long as it contains at least polypropylene, and any known synthetic resin can be used as long as it can be used for packaging fruits and vegetables. This allows the film to maintain good freshness while suppressing deformation due to local loads.

[0039] The polypropylene may be a homopolymer, a random copolymer, or a block copolymer. More specifically, homopolymers include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene, while random copolymers include ethylene-propylene copolymers, propylene-1-butene copolymers, and propylene-octene copolymers. Among these, homopolymers are preferred.

[0040] The synthetic resin film may have a film made of polypropylene, or may have a film made of a resin material in which polypropylene is mixed with another resin.

[0041] Examples of other resins include polyethylene resin, polyamide resin, polyvinyl chloride, polystyrene, acrylic resin, and polyester resins such as polyethylene terephthalate and polylactic acid.

[0042] Examples of the polyethylene resin include various polyethylenes and ethylene copolymers, and specific examples include copolymers such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene (L-LDPE), metallocene-linear low-density polyethylene, ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid copolymer, and ethylene-α-olefin copolymer, as well as ionomers. The linear low-density polyethylene is usually a copolymer of ethylene and a small amount of an α-olefin. The type of α-olefin is not particularly limited. Typical α-olefins include α-olefins having 3 to 10 carbon atoms, such as 1-propylene, 1-butene, 1-hexene, 4-methylpentene-1, and 1-octene. The ethylene content of the ethylene-propylene copolymer is typically 4.5% or less.

[0043] Examples of the polyamide resin include nylon. Nylon includes nylon 6, nylon 11, nylon 12, nylon 66, nylon 6·10, nylon 6·12, nylon 6·T, nylon 6·I, nylon 9T, nylon M5T, and polymetaxylylene adipamide (MXD nylon), which can be used alone or in combination of two or more. Among these, nylon 6, nylon 11, nylon 12, and nylon 66, either alone or in combination of two or more, are preferred, and nylon 6 and nylon 66, either alone or in combination, are more preferred.

[0044] The synthetic resin film may contain additives such as anti-fogging agents, anti-blocking agents, heat stabilizers, lubricants, impact modifiers, processing aids, anti-static agents, ultraviolet absorbers, antioxidants, weather-resistant agents, fillers, and pigments, as needed, within the range that does not impair the performance of the synthetic resin film.

[0045] The anti-fogging agent may be one that wets and spreads water by hydrogen bonding through hydroxyl groups. Specific examples of the anti-fogging agent include glycerin laurate, diglycerin laurate, decaglycerin laurate, glycerin monostearate, and sorbitan stearate.

[0046] Examples of the antiblocking agent include fine particle inorganic compounds such as silica, alumina, alumina silicate, and diatomaceous earth; and fine particle organic compounds such as polyethylene, cross-linked polyethylene, polymethyl methacrylate, and cross-linked polymethyl methacrylate. Use of an anti-blocking agent can improve the handling properties of the synthetic resin film when it is wound into a roll during molding.

[0047] (film manufacturing method) The method for obtaining the synthetic resin film is not particularly limited, and examples of the method for obtaining the synthetic resin film include known methods such as extrusion, inflation, and calendering. The synthetic resin film may also be stretched or annealed. Stretching is typically biaxial stretching. The stretching ratio is not particularly limited, but can be, for example, about 2 to 10 times in both the MD and TD directions. Annealing can be performed at a temperature of 130 to 175°C for a period of several tens of seconds to several hours. The conditions may be adjusted as appropriate so as to achieve the above-mentioned tear strength (N / cm) ratio, static friction coefficient, and tensile strength.

[0048] (Layer composition) The synthetic resin film may be a single layer or a multilayer film of two or more layers. It may be a single layer film made of polypropylene, a multilayer film including a layer made of polypropylene, a single layer film made of a resin material in which polypropylene and other resins are mixed, or a multilayer film including a layer made of a resin material in which polypropylene and other resins are mixed. Of these, a single layer film made of polypropylene or a multilayer film including a layer made of polypropylene is preferred, and a single layer film made of polypropylene is more preferred. A stretched polypropylene film is more preferred.

[0049] By making the synthetic resin film multilayered, it is possible to enhance the desired functionality. For example, by adding a function such as slipperiness to the surface layer of the synthetic resin film, the handleability and heat sealability of the synthetic resin film can be improved, and packaging bags with an excellent balance of elongation and rigidity can be consistently obtained. Furthermore, for example, by making the synthetic resin film into a two-layer or three-layer structure and making a layer containing an antiblocking agent at least one of the surface layers, slipperiness can be obtained.

[0050] When the synthetic resin film is multi-layered, the base resins of the layers may be the same or different from each other. From the viewpoint of obtaining good adhesion between the layers, it is preferable that the same resin is used for each layer.

[0051] When the synthetic resin film is multilayered, the thickness of each layer may be the same or different. For example, in the case of a three-layer structure, the thickness of the middle layer may be the greatest and the thickness of the surface layer may be the smallest. The surface layer preferably accounts for 10 to 20% of the total thickness of the synthetic resin film, and more preferably 12 to 17%.

[0052] As a method for obtaining a multilayer film, known methods such as dry lamination, extrusion lamination, coextrusion, coating, etc. can be appropriately used. From the viewpoint of improving adhesion between layers and controlling layer thickness, coextrusion is preferred.

[0053] (Thickness) The thickness of the synthetic resin film is preferably 5 to 200 μm, more preferably 10 to 100 μm, even more preferably 15 to 80 μm, and particularly preferably 20 to 50 μm. By making the thickness of the synthetic resin film equal to or greater than the above lower limit, the strength of the packaging bag is increased, suppressing deformation due to external stress, while stably achieving a freshness-preserving effect.By making the thickness of the synthetic resin film equal to or greater than the above upper limit, the flexibility (suppleness) of the packaging bag can be maintained.

[0054] [Fruits and vegetables] In this embodiment, fruits and vegetables refer to uncooked vegetables that have been grown in soil or hydroponically, from which inedible parts such as roots, skin, core, stem, seeds, and flowers have been removed, leaving the edible parts of the vegetables in a state that is easy to eat and can be easily cooked.

[0055] Examples of fruits and vegetables include, but are not limited to, semi-heading and heading vegetables such as cabbage, Chinese cabbage, lettuce (lettuce, leaf lettuce, cos lettuce, sunny lettuce, salad lettuce, and lettuce), and Brussels sprouts; spinach, komatsuna, mizuna, bok choy, turnip (kakina), non-heading lettuce (romaine lettuce, sunny lettuce, and the like); non-heading leafy vegetables such as chrysanthemum, kukitachina, shinobu-na, santona, rapeseed, chijirena, kousai-tai, urui, field wasabi, flower wasabi, watercress, arugula, shepherd's purse, petit vert, ice plant, and leaf radish; root vegetables such as sweet potato, potato, nagaimo (Japanese yam), yam, taro, jinenjo (Japanese yam), daikon radish, carrot, burdock, turnip, and ginger; leek, tuna, and the like. Examples of suitable vegetables include Allium vegetables such as onions and chives; Brassicaceae flower buds such as broccoli and cauliflower; Cucurbitaceae fruit vegetables such as cucumbers and pumpkins; Solanaceae fruit vegetables such as eggplant, tomato, cherry tomato, bell pepper, and paprika; okra, bitter melon, zucchini, bitter gourd, and sweet corn; immature beans such as edamame, snow peas, green beans, and broad beans; stem vegetables such as celery, asparagus, and wasabi; herbs such as myoga (ginger), myoba (Japanese parsley), Japanese water dropwort, mitsuba (Japanese parsley), and herbs (thyme, sage, parsley, Italian parsley, rosemary, oregano, lemon balm, chives, lavender, salad burnet, lamb's ear, rocket, dandelion, and nasturtium); and fungi and mushrooms. These may be packaged singly or in a mixture of two or more types.

[0056] Fruits and vegetables may be appropriately cut in consideration of purchase and consumption, and may be roughly divided into 1 / 8 to 1 / 2 in the case of cabbage, Chinese cabbage, pumpkin, etc. Furthermore, they may be cut into bite-sized pieces or shredded for eating raw in salads or for cooking in stir-fries.

[0057] <Packaging containing fruits and vegetables> The fruit and vegetable package of this embodiment (hereinafter also referred to as "package") is made by storing fruit and vegetables in the fruit and vegetable freshness-keeping bag described above, thereby improving the freshness-keeping effect of the fruit and vegetables.

[0058] It is preferable that the opening of the package be sealed after packaging the fruits and vegetables. The sealing may be achieved, for example, by heat sealing the opening of the bag, or by using a back sealing tape, a cable tie, a rubber band, or a member such as a caulking member.

[0059] The amount of fruit or vegetable contained in a packaging bag may vary depending on the size of the container, the type of fruit or vegetable, the purpose of the package, etc. For fruit or vegetable intended for general consumers, the amount is preferably 50 to 1,000 g, more preferably 100 to 800 g, from the viewpoints of ease of consumption immediately after opening and convenient carry-out and handling. Furthermore, in order to obtain a more significant effect of suppressing deformation due to local loads, the amount of fruit or vegetable contained in a packaging bag is preferably 300 g or more, more preferably 400 g or more.

[0060] <How to maintain freshness> The freshness preservation method of this embodiment includes a step of storing fruits and vegetables in the above-described package containing the fruits and vegetables. Storage can be carried out by known methods, but it is preferable to store the package at an ambient temperature of 2 to 20°C. The ambient temperature refers to, for example, the temperature setting of a refrigerator or refrigerated room in which the package is stored, or the temperature setting of a showcase in which the package is displayed in a store, etc. It does not refer to a strict measurement of the temperature around the package. Furthermore, the average ambient temperature should be 2 to 20°C, and temporary temperatures of around 10°C are acceptable due to unavoidable circumstances such as the opening and closing of doors during transport of the package.

[0061] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. [Example]

[0062] The present invention will be described in detail below with reference to examples and comparative examples. However, it should be noted that the present invention is not limited to the examples.

[0063] <Measurement> -Tear strength (N / cm) measurement Right-angle tear test specimens were prepared based on the right-angle tear method in accordance with JIS K7128-3 "Plastics - Test methods for tear strength of films and sheets - Part 3: Right-angle tear test method." Test specimens were prepared with the longitudinal direction of the right-angle tear test specimen aligned with the MD direction of the synthetic resin film, and with the longitudinal direction of the right-angle tear test specimen aligned with the TD direction of the synthetic resin film. Each of the prepared test pieces was pulled under the following conditions, and the maximum load when the test piece was completely torn was determined and taken as the tear strength (N / cm). (conditions) Tensile testing machine: ENSILON RTH-1225 manufactured by A&D Co., Ltd. Pulling speed: 200mm / min ·Environment: 23℃, 50%RH

[0064] Coefficient of static friction The static friction coefficient between the outer surfaces of fruit and vegetable freshness-keeping bags was measured using a friction test in accordance with JIS K 7125. Specifically, the synthetic resin films that form the outer surfaces of the fruit and vegetable freshness-keeping bags were stacked one on top of the other so that they faced each other, and the static friction coefficient was measured by sliding the upper synthetic resin film over the lower synthetic resin film under the following conditions with a weight placed on the upper synthetic resin film. (conditions) Upper synthetic resin film: 80 x 200 mm Tensile testing machine: "TENSILON RTH-1225" A&D Co., Ltd. Weight of weight: 200g Contact area between the weight and the upper synthetic resin film: 40cm 2 Pulling speed: 100mm / min ·Environment: 23℃, 50%RH

[0065] Tensile strength (MPa) measurement According to JIS K7127, rectangular test pieces were prepared with the longitudinal direction of the synthetic resin film aligned with the MD direction. Each test piece was pulled in the longitudinal direction under the following conditions to measure the tensile strength (MPa). (conditions) Tensile testing machine: "TENSILON RTH-1225" A&D Co., Ltd. Pulling speed: 200mm / min ·Environment: 23℃, 50%RH Test specimen shape: No. 1 dumbbell

[0066] Oxygen permeability at 23°C and 60% RH (cc / m 2 ·day·atm) measurement (1) Nitrogen gas filling A measurement bag was prepared using a synthetic resin film made from the raw materials and thickness shown in Table 1. The bag was sealed using a heat seal or similar method, and then degassed using an aspirator or similar device. Degassing was continued until both sides of the bag were stuck together. Next, nitrogen gas (purity 99.9% or higher) was filled into the bag using a white hard syringe. The amount of nitrogen gas injected was adjusted to the bag size, and as much as possible was injected so that the injected nitrogen gas did not apply tension to the film constituting the bag and left it slightly loose. The amount was measured using the scale on the white hard syringe. The degassing and injection of nitrogen gas was carried out, for example, by piercing the bag with a syringe needle. When inserting the syringe needle, double-sided tape was attached to the film constituting the bag, and then adhesive tape made of polypropylene film (hereinafter referred to as "PP tape") was attached on top of this. After the syringe needle was removed, the pinhole was quickly sealed with PP tape. The tape attached to the bag was 4.5 cm long. 2 It fits within the following area: In addition, when the film constituting the bag was a microporous film, the micropores were not blocked with tape. (2) Initial oxygen concentration measurement The initial oxygen concentration (C0) inside the bag was measured immediately after filling with nitrogen gas (t=0). The gas inside the bag was sampled and the initial oxygen concentration (C0) inside the bag was determined using gas chromatography (TCD). C0 was 0.2% or less, and if it exceeded this, the process was repeated. The amount of sampled gas used for oxygen concentration measurement was 10cc or less. When injecting into gas chromatography, a fixed amount of approximately 1cc was injected. In addition, measurements of standard gases (two or more points including approximately 1% and approximately 10% oxygen) were also performed by injecting the same amount of gas, and a calibration curve was created. (3) Storage of bags The bags used to measure the initial oxygen concentration were stored at 23°C and 60% RH (in a temperature and humidity chamber) while being kept stationary so that no objects were placed on top of the bags and the air from the temperature and humidity chamber fan did not directly hit the bags. (4) Measurement of oxygen concentration inside the bag during storage and calculation of oxygen transmission rate The oxygen concentration inside the bag is measured immediately after filling with nitrogen gas and after three or more hours, with the oxygen concentration between 1% and 7%. Two or more measurements are taken at three to five points in total. A proportional relationship (a correlation coefficient of 0.98 or greater) must be established between the elapsed time (t) and the oxygen concentration inside the bag. If the correlation coefficient is not established, the test is repeated. If the oxygen transmission rate of the film making up the bag is too high, causing the oxygen concentration inside the bag to rise too quickly, and this condition cannot be met, a bag can be created by laminating a portion of the film with a smaller, known film of the same material. The surface area of ​​the bag is then excluded from the portion laminated with the known film. The oxygen transmission rate of the measured film is calculated by subtracting the oxygen transmission rate of the known film from the calculated oxygen transmission rate. The oxygen transmission rate was calculated using the value for the longer elapsed time using the following formula (i). F=1.143×(Ct-C0)×V / t (i) F: Oxygen permeation rate (cc / bag day atm) Ct: Oxygen concentration in the bag t hours after filling with nitrogen gas (%) C0: Oxygen concentration in the bag immediately after filling with nitrogen gas (%) V: Amount of nitrogen gas filled (cc) t: Time elapsed since gas filling (hr)

[0067] Water vapor permeability at 40°C (g / m 2 ·day) measurement Using synthetic resin films made of the raw materials and having the thicknesses shown in Table 1, measurements were carried out in accordance with JIS Z 0208 (cup method).

[0068] [Examples and Comparative Examples] (1) Preparation of synthetic resin film Example 1 First, a commercially available polypropylene resin (homopolymer) was prepared as a raw material. Next, the melt obtained by melting the raw material was extruded through a T-die at a temperature of 230°C and stretched (8 times in the MD direction and 4 times in the TD direction) using a roll stretching machine to obtain a biaxially stretched polypropylene film (synthetic resin film) with the thickness (μm) shown in Table 1. At this time, the roll temperature of the roll stretching machine was set to 140°C. After that, an annealing treatment was performed to obtain a synthetic resin film. Next, two sheets of the obtained synthetic resin film were stacked together with the inner layer facing outwards, and heat-sealed on three sides using an impulse sealer (manufactured by Fuji Impulse Co., Ltd., FI-400Y-10PK) to form a 10 mm wide heat-sealed area at 160°C for a sealing time of 1 second, to produce packaging bags with the bag size (inner dimensions) shown in Table 1.

[0069] <Example 2> A synthetic resin film was obtained in the same manner as in Example 1, except that the extrusion conditions from the T-die were adjusted so that the thickness (μm) shown in Table 1 was obtained. Next, the synthetic resin form was cut to have the bag size (inner dimensions) shown in Table 1, and packaging bags were produced in the same manner as in Example 1.

[0070] Example 3 A synthetic resin film was obtained in the same manner as in Example 1, except that the extrusion conditions from the T-die were adjusted so as to give a thickness (μm) shown in Table 1, and annealing treatment was not performed. Next, the synthetic resin form was cut to have the bag size (inner dimensions) shown in Table 1, and packaging bags were produced in the same manner as in Example 1.

[0071] Example 4 A synthetic resin film was obtained in the same manner as in Example 1, except that the extrusion conditions from the T-die were adjusted so as to give a thickness (μm) shown in Table 1, and annealing treatment was not performed. Next, the synthetic resin form was cut to have the bag size (internal dimensions) shown in Table 1, and a packaging bag was produced in the same manner as in Example 1, with one through-hole (hole diameter 120 μm) formed.

[0072] <Example 5> A synthetic resin film was obtained in the same manner as in Example 1, except that the extrusion conditions from the T-die were adjusted so that the thickness (μm) shown in Table 1 was obtained. Next, the synthetic resin form was cut to have the bag size (inner dimensions) shown in Table 1, and packaging bags were produced in the same manner as in Example 1.

[0073] <Comparative Example 1> A synthetic resin film was obtained in the same manner as in Example 1, except that the extrusion conditions from the T-die were adjusted so as to give a thickness (μm) shown in Table 1, and the stretching treatment and annealing treatment were not carried out. Next, the synthetic resin form was cut to have the bag size (inner dimensions) shown in Table 1, and packaging bags were produced in the same manner as in Example 1.

[0074] <Comparative Example 2> A synthetic resin film was obtained in the same manner as in Example 1, except that the stretching conditions were 4 times in the MD direction and 6 times in the TD direction, and no annealing treatment was performed. Next, the synthetic resin form was cut to have the bag size (inner dimensions) shown in Table 1, and packaging bags were produced in the same manner as in Example 1.

[0075] <Evaluation> The resulting package was evaluated as follows. [Freshness retention] 150 g of freshly shredded cabbage was placed in each of the resulting packaging bags, and the packaging bags were sealed to prepare packages containing fruits and vegetables, which were then stored at 10°C for 3 days. Thereafter, the cabbage was taken out, and changes in appearance were observed, and freshness retention was evaluated according to the following criteria. (standard) ◎: No loss of freshness 〇: Slight decrease in freshness △: Clear decrease in freshness ×: Significant decrease in freshness

[0076] [Easy to open] The fruit and vegetable-containing packages prepared for the evaluation of freshness retention were evaluated for ease of opening. Specifically, the package was opened by applying force so as to tear it horizontally from the cut edge at the top of the bag, and the ease of opening was evaluated according to the following criteria. (standard) ◎: Can be opened manually in a straight, horizontal direction 〇: Can be opened manually horizontally △: The bag bends horizontally when opened manually, but can still be opened. ×: Difficult to open manually

[0077] [Durability] Ten packs of fruit and vegetable packages prepared for the freshness-keeping evaluation were placed in a cardboard box and subjected to a 5-hour vibration test during transportation. After that, the condition of the packages was evaluated according to the following criteria. (standard) ◎: No folds, wrinkles, tears, or pinholes in any of the bags 〇: No tears or pinholes in any of the bags △: At least one of tears and pinholes occurred in some bags ×: At least one of tears and pinholes occurred in all bags

[0078] [Table 1]

Claims

1. A freshness-keeping bag for fruits and vegetables made of a synthetic resin film, the synthetic resin film includes polypropylene, the ratio (MD / TD) of the tear strength (N / cm) in the MD direction of the synthetic resin film to the tear strength (N / cm) in the TD direction of the synthetic resin film, as measured by a right-angle tear method in accordance with JIS K7128-3, is 2.2 or more; The freshness-keeping bag for fruits and vegetables has a static friction coefficient of 0.23 or less between the outer surfaces of the freshness-keeping bag for fruits and vegetables, as measured by a friction test in accordance with JIS K7125.

2. The fruit and vegetable freshness-keeping bag according to claim 1, The fruit and vegetable freshness-keeping bag has a tensile strength of 130 MPa or more and 170 MPa or less, measured in the MD direction at a tensile speed of 500 mm / min in accordance with JIS K7127 for fruit and vegetable freshness-keeping bags.

3. The fruit and vegetable freshness-keeping bag according to claim 1 or 2, The synthetic resin film is a single-layer film containing polypropylene or a multi-layer film having a layer containing polypropylene.

4. The fruit and vegetable freshness-keeping bag according to claim 1 or 2, The fruit and vegetable freshness-keeping bag has through holes with a pore diameter of 100 μm or more.

5. A package containing fruits and vegetables, in which fruits and vegetables are housed in the fruit and vegetable freshness-keeping bag according to claim 1 or 2.

6. A method for preserving the freshness of fruits and vegetables, comprising the step of storing fruits and vegetables in the fruit and vegetable freshness-preserving bag according to claim 1 or 2.

7. A synthetic resin film used to manufacture the fruit and vegetable freshness-keeping bag according to claim 1 or 2, A synthetic resin film configured so that the static friction coefficient between at least one of its surfaces, measured by a friction test conforming to JIS K7125, is 0.2 or less, and that surface is the outer surface of a fruit and vegetable freshness-keeping bag.

8. A roll of the synthetic resin film according to claim 7.

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