JP7835338B2 - Freshness preservation bags for fruits and vegetables, packaging containing fruits and vegetables, and method for preserving the freshness of fruits and vegetables. - Google Patents

Description

This invention relates to a freshness-preserving bag for fruits and vegetables, a package containing fruits and vegetables, and a method for preserving the freshness of fruits and vegetables.

Traditionally, a method for preserving the freshness of harvested fruits and vegetables has been known, which involves adjusting oxygen and carbon dioxide concentrations to moderately suppress respiration. Packaging materials used for preserving the freshness of fruits and vegetables in this way are known as MA (Modified Atmospheric) packaging.
In recent years, with the growing interest in MA packaging, there is a demand for improved performance in various aspects of packaging materials, including not only gas permeability but also processability, strength, packaging workability, and appearance.

For example, Patent Document 1 (Japanese Patent Application Publication No. 2023-106849) discloses a film for preserving the freshness of fruits and vegetables, in which the coefficient of dynamic friction μ' between the inner surfaces is controlled at a 40°C environment, taking into account that the packaging film may come into direct contact with the fruits and vegetables, and in order to suppress the deterioration of the freshness of the fruits and vegetables caused by the film itself.
Furthermore, Patent Document 2 (Japanese Patent Publication No. 2022-119289) discloses a freshness-preserving film that is thin, has excellent conformability to contents, does not reduce seal strength, is less prone to whitening due to anti-fogging agent bleeding, and has deodorizing properties. Specifically, it discloses that the freshness-preserving film uses a specific polypropylene resin and a specific deodorizing nanofiller.

Japanese Patent Publication No. 2023-106849 Japanese Patent Publication No. 2022-119289

However, the technologies disclosed in Patent Documents 1 and 2 did not focus on the state of the packaging bag after the produce has been packed inside. The present inventor focused on the fact that after the produce has been packed inside, a portion of the packaging bag deforms due to localized stress, such as when transporting heavy objects, resulting in a reduced appearance.

Therefore, the inventors diligently conducted research to suppress deformation of the packaging bag under localized load. As a result, they devised a new index related to the ratio of elastic recovery rates and found that by controlling this index, deformation under localized load can be suppressed while maintaining good freshness preservation, thus completing the present invention.

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

[1] A fresh produce preservation bag made of synthetic resin film,
The aforementioned synthetic resin film contains polypropylene,
A fresh produce freshness preservation bag in which the ratio of elastic recovery rates (elastic recovery rate _MD / elastic recovery rate _TD ), measured by the following procedure a of the fresh produce freshness preservation bag, is 1.00 or less.
(Procedure a)
(i) Cut out the fresh produce preservation bag so that the MD direction of the synthetic resin film is in the length direction, and prepare a strip-shaped sample with a width of 5 mm. Using a tensile testing machine, the distance between the chucks when both ends of the sample are fixed with chucks is defined as the gauge length _L0 (mm) of the sample. Stretch the sample until the gauge length _L0 (mm) becomes 1.2 times, and hold it in that position for 3 minutes. Then, release the fixation of the sample, and measure the gauge length _L1 (mm) of the sample 20 seconds after release. Calculate the elastic recovery rate _MD (%) from the following formula (1).
[L ₀ ×1.2−L ₁ ]/L ₀ ×0.2 (1)
(ii) The same procedure as in (i) above is used for measurement, except that the fresh produce preservation bag is cut out so that the TD direction of the synthetic resin film is in the length direction, and a 5 mm wide strip-shaped sample is prepared, and the elastic recovery rate _TD (%) is calculated from formula (1).
[2] The freshness preservation bag for fruits and vegetables described in [1],
A fresh produce preservation bag with an elastic recovery rate _TD (%) of 60.0% or higher.
[3] A fresh produce preservation bag as described in [1] or [2],
A fresh produce freshness preservation bag, wherein the loop stiffness measured by the following procedure b is 2.5 to 30 mN.
(Procedure b) Cut out the fresh produce preservation bag so that the TD direction of the synthetic resin film is the length direction, and prepare a 25 mm wide strip-shaped sample. Overlap the two ends of the sample facing each other and roll it into a loop shape so that the loop length is 55 mm, and secure both ends by clamping them from the outside with a chuck. With the sample secured, compress it by 20 mm at a speed of 3.3 mm/s with an indenter, from the top of the loop towards the chuck, and measure the pressure applied to the indenter.
[4] A fresh produce preservation bag described in any one of [1] to [3],
The aforementioned synthetic resin film is a single-layer film containing polypropylene, or a multilayer film having a layer containing polypropylene, as described in any one of the fresh produce freshness preservation bags [5] [1] to [4],
The synthetic resin film is a fresh produce freshness preservation bag according to any one of the fresh produce freshness preservation bags [6] [1] to [5], which includes a stretched polypropylene film.
The aforementioned fresh produce preservation bag is a fresh produce preservation bag having through holes.
[7] A package containing fresh produce, in which fresh produce is contained in a fresh produce preservation bag as described in any one of [1] to [6].
[8] In the fruit and vegetable packaging described in [7],
A package containing fresh produce weighing 300g or more.
[9] A method for preserving the freshness of fruits and vegetables,
A method for preserving the freshness of fruits and vegetables, comprising the step of placing the fruits and vegetables in a freshness-preserving bag for fruits and vegetables described in any one of [1] to [6].

According to the present invention, a technology is provided for a packaging bag that can suppress deformation due to localized stress while maintaining good freshness preservation of fruits and vegetables.

The embodiments of the present invention will be described in detail below.

In this specification, the notation "X to Y" in descriptions of numerical ranges means "X or greater and Y or less" unless otherwise specified. For example, "1 to 5 mass%" means "1 mass% or greater and 5 mass% or less".
Furthermore, in this specification, the MD direction refers to the Machine Direction, meaning the direction of resin flow, and the TD direction refers to the Transverse Direction, meaning the direction perpendicular to the MD direction.

<Freshness-preserving bags for fruits and vegetables>
The fresh produce preservation bag of this embodiment (hereinafter also referred to as "packaging bag") is made of a synthetic resin film, and the synthetic resin film contains polypropylene.
The ratio of the elastic recovery rates (elastic recovery rate _MD / elastic recovery rate _TD ) measured by the following procedure a of the fresh produce preservation bag is 1.00 or less.
(Procedure a)
(i) Cut out the fresh produce preservation bag so that the MD direction of the synthetic resin film is in the length direction, and prepare a strip-shaped sample with a width of 5 mm. Using a tensile testing machine, the distance between the chucks when both ends of the sample are fixed with chucks is defined as the gauge length _L0 (mm) of the sample. Stretch the sample until the gauge length _L0 (mm) becomes 1.2 times, and hold it in that position for 3 minutes. Then, release the fixation of the sample, and measure the gauge length _L1 (mm) of the sample 20 seconds after release. Calculate the elastic recovery rate _MD (%) from the following formula (1).
[L ₀ ×1.2−L ₁ ]/L ₀ ×0.2 (1)
(ii) The same procedure as in (i) above is used for measurement, except that the fresh produce preservation bag is cut out so that the TD direction of the synthetic resin film is in the length direction, and a 5 mm wide strip-shaped sample is prepared, and the elastic recovery rate _TD (%) is calculated from formula (1).

This results in a packaging bag that maintains the freshness of fruits and vegetables while suppressing deformation under localized stress. The detailed reasons for this are not clear, but they are thought to be as follows.
The elastic recovery rate refers to the recovery of the synthetic resin film from tension. If there is an imbalance in the elastic recovery rate, the packaging bag is likely to deform easily under localized stress. It is presumed that by reducing the elastic recovery rate ratio (elastic recovery rate _MD / elastic recovery rate _TD ) in that area, the tendency of the packaging bag to deform locally can be highly suppressed. Furthermore, by using polypropylene, a good balance of good bag-making properties and appropriate gas permeability can be obtained, making it easier to obtain packaging bags that maintain freshness.

The ratio of elastic recovery rates (elastic recovery rate _MD / elastic recovery rate _TD ) is 1.00 or less, preferably 0.99 or less.
By keeping the ratio of elastic recovery rates below the above upper limit, deformation due to localized loads becomes easier to suppress.

The elastic recovery rate _MD is preferably 60.0 to 70.0%, more preferably 62.0 to 68.0%, and even more preferably 62.0 to 66.0%.
The elastic recovery rate _TD is preferably 61.0% or more, more preferably 62.0 to 70.0%, and even more preferably 63.0 to 69.0%.

The packaging bag is further preferably such that the loop stiffness measured by the following procedure b is 2.5 to 30 mN, and more preferably 2.6 to 29 mN.
stomach.
(Procedure b) Cut out the fresh produce preservation bag so that the TD direction of the synthetic resin film is the length direction, and prepare a 25 mm wide strip-shaped sample. Overlap the two ends of the sample facing each other and roll it into a loop shape so that the loop length is 55 mm, and secure both ends by clamping them from the outside with a chuck. With the sample secured, compress it by 20 mm at a speed of 3.3 mm/s with an indenter, from the top of the loop towards the chuck, and measure the pressure applied to the indenter.

By controlling the loop stiffness in this way, the packaging bag gains appropriate rigidity, which is thought to distribute and reduce localized stress on the packaging bag and suppress deformation.

Furthermore, the loop stiffness (mN) measured in step b with respect to the thickness (μm) of the synthetic resin film is preferably 0.13 to 1.00, and more preferably 0.14 to 0.8.
This allows for more precise control over the stiffness of the packaging bag, which is thought to enable more stable distribution of local stresses and suppress deformation.

In this embodiment, a packaging bag that satisfies the above-mentioned elastic recovery rate _MD , elastic recovery rate _TD , and loop stiffness can be achieved, for example, by selecting polypropylene, adjusting the polyethylene content, or by devising the layer structure of the synthetic resin film or the 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 and annealing the synthetic resin film.

[Bag shape]
The packaging bag of this embodiment is a bag formed from a synthetic resin film, and its shape is not particularly limited; it can be a two-sided bag, a three-sided bag, a back-sealed bag (gusseted bag), a pouch, a gusseted bag, etc. A two-sided bag is a bag in which a synthetic resin film is folded in half, with the folded part as the bottom and both sides sealed. A three-sided bag is a bag in which two layers of synthetic resin film are overlapped and the bottom and both sides are sealed.

The size of the packaging bag in this embodiment can be approximately 100 mm x 100 mm to 250 mm x 350 mm for packaging fresh produce intended for general consumers.

[Through hole]
The packaging bag may or may not have through holes. The presence or absence of through holes allows for stable adjustment of water vapor permeability and oxygen permeability.

The planar shape of the through-hole may be, for example, circular, polygonal, or a slit. A circular shape is not limited to a perfect circle, but includes approximately circular shapes. It may also be a semicircular or crescent shape. A polygon is any shape enclosed by three or more line segments, such as a triangle, quadrilateral, or pentagon. A slit is a cut or narrow gap penetrating the synthetic resin sheet constituting the packaging material, and may be a straight line, curve, L-shaped, or X-shaped, with no particular limitations on its length, etc.

If through-holes are formed, the average diameter of the through-holes is preferably 10 μm to 200 μm, more preferably 20 to 100 μm, even more preferably 40 to 80 μm, and especially preferably 60 to 75 μm. Setting it above the lower limit improves the oxygen permeability of the packaging and makes it easier to suppress the generation of off-odors. On the other hand, setting it below the upper limit prevents the entry of foreign matter while maintaining the MA effect, making it easier to preserve the freshness of fruits and vegetables.
The average diameter of the through-hole is calculated by assuming the through-hole is a perfect circle, based on the area of the opening.

Furthermore, the packaging bag may have through-holes with a diameter of 4 mm or more. It may also have so-called punch holes.

The number of punch 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 2, in order to suppress increased respiration and drying due to excessive gas permeability, and to facilitate the preservation of freshness.

The above-mentioned through-holes may be formed in the resin film beforehand during the manufacturing of the packaging bag, or they may be formed after the resin film has been formed into the packaging bag, or they may be formed before or after the resin film has been formed into the packaging bag.

The method for forming the through-hole described above is not particularly limited, and known methods can be employed. Examples of such known methods include laser processing, needle processing methods including hot needles, and methods utilizing molds such as roll cutters.

[Oxygen permeability]
The oxygen permeability (cc/ ^m² ·day·atm) of the packaging bag at 23°C and 60% RH is preferably 500 to 30,000, more preferably 600 to 20,000, and even more preferably 800 to 10,000.

Oxygen permeability can be calculated, for example, by measuring the oxygen concentration inside a packaging bag immediately after filling it with nitrogen, and then measuring the oxygen concentration gradient inside the packaging bag after it has been left for a certain period of time after filling it with nitrogen.

[Water vapor transmission rate]
The water vapor permeability of the packaging bag at 40°C is preferably 1 g/( ^m² ·day) or more, and more preferably 3 g/( ^m² ·day) or more, from the viewpoint of releasing water vapor due to the respiration of fresh produce.
On the other hand, the water vapor permeability of the packaging bag at 40°C is preferably 300 g/( ^m² ·day) or less, more preferably 100 g/( ^m² ·day) or less, even more preferably 50 g/( ^m² ·day) or less, and especially preferably 9 g/( ^m² ·day) or less, from the viewpoint of suppressing the respiration of fresh produce.

Water vapor transmission can be measured using a method compliant with JIS Z 0208 (Cup method).

Furthermore, in this 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 film's layer structure, the presence or absence of through holes and the average diameter of the through holes, and the presence or absence of unpenetrated grooves.

[Synthetic resin film]
(raw materials)
The synthetic resin film is preferably transparent or semi-transparent, and more preferably transparent, from the viewpoint of allowing the fruits and vegetables to be seen from the outside. It may also be printed with information for the purpose of identifying the fruits and vegetables. The synthetic resin may also use biomass-derived raw materials in part.

The synthetic resin constituting the synthetic resin film does not need to contain polypropylene, and is not particularly limited as long as it can be used for packaging fruits and vegetables; known synthetic resins can be used. This allows for good freshness preservation while suppressing deformation under localized stress.

The polypropylenes mentioned above include homopolymers, random copolymers, and block copolymers. 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.

The synthetic resin film may have a film made of polypropylene, or it may have a film made of a resin material mixed with polypropylene and other resins.

Other resins include, for example, polyethylene resin, polyamide resin, polyvinyl chloride, polystyrene, acrylic resin, polyester resins such as polyethylene terephthalate and polylactic acid.

Examples of polyethylene resins mentioned above include various polyethylenes and ethylene copolymers. Specific examples include 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, ethylene-α-olefin copolymer, and other copolymers or ionomers.
The linear low-density polyethylene described above is typically a copolymer of ethylene and a small amount of α-olefin. The type of α-olefin is not particularly limited. Typical α-olefins include 1-propylene, 1-butene, 1-hexene, 4-methylpentene-1, and 1-octene, which have 3 to 10 carbon atoms. The ethylene content of the ethylene-propylene copolymer is typically 4.5% or less.

Examples of the polyamide resins mentioned above include nylon. Nylon can be used individually or in combination of two or more types, including 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). Among these, nylon 6, nylon 11, nylon 12, and nylon 66 individually or in combination of two or more types are preferred, and nylon 6 and nylon 66 individually or in combination of two types are even more preferred.

The synthetic resin film may contain additives such as anti-fogging agents, anti-blocking agents, heat stabilizers, lubricants, impact modifiers, processing aids, antistatic agents, UV absorbers, antioxidants, weather degradation inhibitors, fillers, and pigments, as needed, within limits that do not impair the performance of the synthetic resin film.

The anti-fogging agents mentioned above are those that wet and spread water through hydrogen bonding via hydroxyl groups. Specific examples of anti-fogging agents include glycerin laurate, diglycerin laurate, decaglycerin laurate, glycerin monostearate, and sorbitan stearate.

Examples of the above antiblocking agents include particulate inorganic compounds such as silica, alumina, alumina silicate, and diatomaceous earth; and particulate organic compounds such as polyethylene, cross-linked polyethylene, polymethyl methacrylate, and cross-linked polymethyl methacrylate.
By using an antiblocking agent, the handling properties of synthetic resin films can be improved, such as when winding the film into a roll during molding.

(Film manufacturing method)
The method for obtaining the synthetic resin film is not particularly limited. Examples of known methods for obtaining a synthetic resin film include extrusion, inflation, and calendering.
Furthermore, the synthetic resin film may be subjected to stretching or annealing. Stretching is usually biaxial stretching. The stretching ratio is not particularly limited, but for example, it can be about 2 to 10 times in both the MD and TD directions. Annealing can be carried out at a temperature of 130 to 175°C for several tens of seconds to several hours.
Furthermore, the conditions may be adjusted as appropriate to achieve the above-mentioned elastic recovery rate _MD , elastic recovery rate _TD , and loop stiffness.

(layer structure)
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 mixed with polypropylene and another resin, or a multilayer film including a layer made of a resin material mixed with polypropylene and another resin. Among 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.
Furthermore, it is even more preferable that the film be a stretched polypropylene film.

By creating a multi-layered synthetic resin film, desired functionality can be enhanced. For example, by adding properties such as slipperiness to the surface layer of the synthetic resin film, the handling and heat-sealability of the film can be improved, and packaging bags with an excellent balance of stretchability and rigidity can be reliably obtained. Furthermore, for example, by creating a two- or three-layer structure of the synthetic resin film and including an anti-blocking agent in at least one of the surface layers, slipperiness can be achieved.

In the case of a multilayered synthetic resin film, the base resins of each layer may be the same or different. From the viewpoint of obtaining good adhesion between layers, it is preferable that each layer uses the same resin.

When a synthetic resin film is multilayered, the thickness of each layer may be the same or different. For example, in a three-layer structure, the thickness of the intermediate layer may be the highest, and the thickness of the surface layer may be the lowest. The surface layer is preferably 10-20% of the total thickness of the synthetic resin film, and more preferably 12-17%.

As methods for obtaining multilayer films, known methods such as dry lamination, extrusion lamination, co-extrusion, and coating can be used as appropriate. From the viewpoint of improving interlayer adhesion and controlling layer thickness, co-extrusion is preferable.

(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 most preferably 20 to 50 μm.
By making the thickness of the synthetic resin film greater than or equal to the lower limit mentioned above, the strength of the packaging bag is increased, suppressing deformation due to external stress while ensuring a stable freshness preservation effect. By making the thickness of the synthetic resin film greater than or equal to the upper limit mentioned above, the flexibility (suppleness) of the packaging bag can be maintained.

[Fruits and vegetables]
In this embodiment, "fresh produce" refers to uncooked vegetables from which non-edible parts of soil-grown or hydroponically grown vegetables, such as roots, peels, cores, stems, seeds, and flowers, have been removed, with the edible portion of the vegetable being prepared with consideration for ease of eating and simple preparation.

As for fruits and vegetables, there are no particular limitations, but for example, semi-heading and heading vegetables such as cabbage, Chinese cabbage, lettuce (lettuce, leaf lettuce, romaine lettuce, sunny lettuce, salad lettuce, ssamjang, etc.), and Brussels sprouts; spinach, komatsuna, mizuna, bok choy, rapeseed (kakina), loose-leaf lettuce (romaine lettuce, sunny lettuce, etc.), garland chrysanthemum, stem vine, santouna, rapeseed, curly lettuce, kousaitai, urui, field wasabi, flower wasabi, watercress, arugula, shepherd's purse, petit vert, ice plant, leaf radish, etc.; root vegetables such as sweet potato, potato, nagaimo, yamaimo, taro, jinenjo, and yamatoimo, radish, carrot, burdock, turnip, ginger; leeks, ta Examples include: onions, chives, and other Allium vegetables; broccoli, cauliflower, and other Brassicaceae flower buds; cucurbitaceae fruit vegetables such as cucumbers and pumpkins; nightshade fruit vegetables such as eggplants, tomatoes, cherry tomatoes, bell peppers, and paprikas; and fruit vegetables such as okra, bitter melon, zucchini, and sweet corn; immature legumes such as edamame, snow peas, green beans, and broad beans; stem vegetables such as celery, asparagus, and wasabi; herbs such as myoga ginger, perilla, water dropwort, mitsuba, and herbs (thyme, sage, parsley, Italian parsley, rosemary, oregano, lemon balm, chives, lavender, salad burnet, lamb's ear, arugula, dandelion, and nasturtium); and mushrooms. These may be packaged individually or in combination of two or more types.

Fresh produce may be cut as appropriate, taking into consideration factors such as purchasing and consumption. For example, cabbage, Chinese cabbage, and pumpkin may be roughly divided into 1/8 to 1/2 portions for ease of purchase. Furthermore, they may be cut into bite-sized pieces or julienned for use in salads or stir-fries.

<Packaged fruit and vegetable product>
The fruit and vegetable packaging of this embodiment (hereinafter also referred to as "packaging") contains fruit and vegetable in the fruit and vegetable freshness preservation bag described above. This improves the freshness preservation effect of the fruit and vegetable.

It is preferable that the packaging has a sealed opening after the fruits and vegetables have been packaged.
Sealing may be achieved, for example, by heat-sealing the opening of the bag, or by using materials such as back sealing tape, cable ties, rubber bands, or crimping.

The amount of produce contained in the packaging bag may vary depending on the size of the container, the type of produce, and the intended use of the packaging. For produce intended for general consumers, for example, from the viewpoint of easy consumption immediately after opening and ease of carrying and handling, the amount is preferably 50 to 1000 g, more preferably 100 to 800 g. Furthermore, from the viewpoint of obtaining a more significant effect in suppressing deformation under localized load, the amount of produce contained in the packaging bag is preferably 300 g or more, and more preferably 400 g or more.

<Methods for maintaining freshness>
The freshness preservation method of this embodiment includes the step of storing the produce using the above-described package containing the produce.
Storage can be carried out by known methods, but it is preferable to store the packaged product at an ambient temperature of 2 to 20°C. Ambient temperature refers to, for example, the temperature setting of the refrigerator or refrigerator where the packaged product is stored, or the temperature control setting of the display case where the packaged product is displayed in a store. It does not refer to a precisely measured temperature around the packaged product. Furthermore, it is sufficient for the average ambient temperature to be between 2 and 20°C, and it may temporarily drop to around 10°C due to unavoidable circumstances such as opening and closing doors during transport of the packaged product.

The embodiments of the present invention have been described above, but these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above; modifications, improvements, etc., within the scope of achieving the objectives of the present invention are included.

The present invention will be described in detail below based on examples and comparative examples. It should be noted that the present invention is not limited to the examples provided.

<Measurement and Physical Properties>
- Measurement of tensile elongation (i) A fresh produce preservation bag was cut out of the synthetic resin film so that the MD direction was in the length direction, and a 5 mm wide strip-shaped sample was prepared. Using a tensile testing machine, the distance between the chucks when both ends of the sample were fixed with chucks was defined as the gauge length _L0 (mm) of the sample. The sample was stretched until the gauge length _L0 (mm) was 1.2 times, and held in that position for 3 minutes. After that, the fixation of the sample was released, and the gauge length _L1 (mm) of the sample was measured 20 seconds after release. The elastic recovery rate _MD (%) was calculated from the following formula (1).
[L ₀ ×1.2−L ₁ ]/L ₀ ×0.2 (1)
(ii) The same procedure as in (i) was followed to perform the measurements, except that the fresh produce preservation bag was cut out so that the TD direction of the synthetic resin film was in the length direction, and a 5 mm wide strip-shaped sample was prepared, and the elastic recovery rate _TD (%) was calculated from formula (1).
• Tensile testing machine: TENSILON RTH-1225 (manufactured by A&D Company, Limited)
・Environment: 23℃, 50%RH

Loop Stiffness: A 25 mm wide strip of the fresh produce preservation bag was cut out of the synthetic resin film so that the TD direction of the film was the length direction. The ends of the sample were overlapped and rolled into a loop shape, with a loop length of 55 mm, and both ends were clamped and fixed from the outside with a chuck. With the sample fixed, it was compressed by 20 mm at a speed of 3.3 mm/s from the top of the loop towards the chuck, and the pressure applied to the chuck was measured.
Three test samples were used, and measurements were taken three times. The average value was defined as the loop stiffness (mN).
• Device name: Loop stiffness tester (manufactured by Toyo Seiki Co., Ltd.)
・Environment: 23℃, 50%RH

- Measurement of oxygen permeability (cc/ ^m²・day・atm) at 23°C and 60% RH (1) Nitrogen gas filling A bag for measurement was prepared using a synthetic resin film with the raw materials and thickness shown in Table 1. After sealing the bag by heat sealing, the bag was degassed using an aspirator. Degassing was continued until both sides of the bag 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 size of the bag, and as much as possible was injected while ensuring that the film constituting the bag was not under tension due to the injected nitrogen gas and was slightly loose. The amount was measured using the scale on the white hard syringe. Nitrogen gas degassing and injection were performed, for example, by piercing the bag with a needle. When piercing with a needle, double-sided tape was applied to the film constituting the bag, and then polypropylene film adhesive tape (hereinafter referred to as "PP tape") was applied on top of this. Furthermore, after removing the injection needle, the needle hole was immediately sealed with PP tape. The tape applied to the bag was made to cover an area of 4.5 ^cm² or less.
Furthermore, if the film used to make up the bag is a microporous film, the tape was not used to block the micropores.
(2) Measurement of initial oxygen concentration 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 by gas chromatography (TCD). C0 was 0.2% or less; if it exceeded this, the procedure was repeated. The sampled gas for oxygen concentration measurement was 10 cc or less. When injecting into the gas chromatograph, a constant amount of about 1 cc was injected. Measurements of standard gases (two or more points containing approximately 1% and approximately 10% oxygen) were also performed by injecting the same amount of gas to create a calibration curve.
(3) Storage of the bags The bags, whose initial oxygen concentration was measured, were stored at 23°C and 60% RH (in a constant temperature and humidity chamber). At this time, the bags were left undisturbed so that nothing was placed on top of them and the airflow from the constant temperature and humidity chamber's fan did not directly hit the bags.
(4) Measurement of oxygen concentration inside the bag during storage and calculation of oxygen permeation rate The oxygen concentration inside the bag was measured at a total of 3 to 5 points, with at least two points, immediately after filling with nitrogen gas and again at least 3 hours later, within the range of 1% to 7%. A proportional relationship (correlation coefficient of 0.98 or higher) must be established between the elapsed time t (hr) and the oxygen concentration inside the bag. If the correlation coefficient was not established, the test was repeated. If the oxygen permeation rate of the film constituting the bag was too high, causing the oxygen concentration inside the bag to rise too quickly and failing to meet this condition, a bag could be created by laminating a portion of the film with a known film of the same material that has a smaller oxygen permeation rate than the film being measured, and the same procedure was followed. In this case, the surface area of the bag was calculated excluding the portion laminated with the other known film, and the oxygen permeation rate of the measured film was obtained by subtracting the oxygen permeation rate of the known film portion from the calculated oxygen permeation rate.
The oxygen permeation rate was calculated using the value obtained over the longer elapsed time, as shown in the following formula (i).
F=1.143×(Ct-C0)×V/t (i)
F: Oxygen permeation rate (cc/bag/day/atm)
Ct: Oxygen concentration inside the bag t hours after nitrogen gas filling (%)
C0: Oxygen concentration inside the bag immediately after filling with nitrogen gas (%)
V: Amount of nitrogen gas filled (cc)
t: Time elapsed since gas filling (hr)

- Measurement of water vapor transmission rate (g/ ^m² ·day) at 40°C: Measurement was performed using synthetic resin films with the raw materials and thicknesses shown in Table 1, in accordance with JIS Z 0208 (cup method).

<Example 1>
First, commercially available polypropylene resin (homopolymer) was prepared as the raw material. Next, the molten material was extruded from a T-die at a temperature of 230°C and stretched using a roll stretcher (5 times in the MD direction and 6 times in the TD direction) to obtain a biaxially oriented polypropylene film (synthetic resin film) with the thickness (μm) shown in Table 1. At this time, the temperature of the rolls of the roll stretcher was set to 140°C. After that, an annealing treatment was performed to obtain a synthetic resin film.
Next, using the obtained synthetic resin film, two sheets were stacked with the inner layer facing inward, and heat-sealed on three sides using an impulse sealer (Fuji Impulse Co., Ltd., FI-400Y-10PK) to form a 10 mm wide heat-sealed section at 160°C for a sealing time of 1 second, thereby producing a packaging bag with the bag size (inner dimensions) shown in Table 1.

<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 to achieve the thickness (μm) shown in Table 1.
Next, the synthetic resin form was cut to the bag size (internal dimensions) shown in Table 1, and a packaging bag was manufactured in the same manner as in Example 1.

<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 to achieve the thickness (μm) shown in Table 1.
Next, the synthetic resin form was cut to the bag size (internal dimensions) shown in Table 1, and a packaging bag was made in the same manner as in Example 1, with one through hole (hole diameter 70 μm) provided.

<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 to achieve the thickness (μm) shown in Table 1, the stretching treatment was performed four times in the MD direction and four times in the TD direction, and no annealing treatment was performed.
Next, the synthetic resin form was cut to the bag size (internal dimensions) shown in Table 1, and a packaging bag was made in the same manner as in Example 1, with one through hole (hole diameter 120 μm) provided.

<Example 5>
A synthetic resin film was obtained in the same manner as in Example 1, except that the stretching treatment was performed four times in the MD direction and four times in the TD direction, and no annealing treatment was performed.
Next, the synthetic resin form was cut to the bag size (internal dimensions) shown in Table 1, and a packaging bag was made in the same manner as in Example 1, with one through hole (hole diameter 120 μm) provided.

<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 to achieve the thickness (μm) shown in Table 1, and stretching and annealing treatments were not performed.
Next, the synthetic resin form was cut to the bag size (internal dimensions) shown in Table 1, and a packaging bag was manufactured in the same manner as in Example 1.

<Comparative Example 2>
A synthetic resin film was obtained in the same manner as in Example 1, except that the stretching treatment was performed six times in the MD direction and four times in the TD direction, and no annealing treatment was performed.
Next, the synthetic resin form was cut to the bag size (internal dimensions) shown in Table 1, and a packaging bag was made in the same manner as in Example 1, with one through hole (hole diameter 120 μm) provided.

<Comparative Example 3>
A three-layer synthetic resin film was obtained by co-extruding commercially available polypropylene resin (homopolymer) and ethylene-propylene copolymer (random copolymer, ethylene content 3%) from a T-die (multi-die) at a temperature of 230°C, with the layer structure shown in Table 1, without stretching or annealing treatment.
Next, the synthetic resin form was cut to the bag size (internal dimensions) shown in Table 1, and a packaging bag was made in the same manner as in Example 1, with one through hole (hole diameter 120 μm) provided.

<Evaluation>
The following evaluations were performed on the obtained packaging.
[Freshness preservation]
150g of fresh shredded cabbage was placed in each of the resulting packaging bags, and the bags were sealed to create fruit and vegetable packages, which were then stored at 10°C for 3 days.
Afterward, the cabbage was removed, its appearance was observed, and its freshness retention was evaluated according to the following criteria.
• Freshness retention (standard)
◎: No loss of freshness at all 〇: Slight loss of freshness △: Clear loss of freshness ×: Significant loss of freshness

[Deformation resistance]
After grasping only a portion of the packaged goods preserved using the freshness-preserving properties described above, and shaking it up and down 10 times to the point where the fruits and vegetables inside moved vigorously, the strength of the packaging bag was evaluated according to the following criteria.
• Bag strength (standard)
◎: No deformation of the bag 〇: Slight deformation of the bag △: Deformation of the bag ×: Significant deformation of the bag

Claims (9)

A fresh produce preservation bag made of synthetic resin film,
The aforementioned synthetic resin film contains polypropylene,
The aforementioned synthetic resin film is a single layer,
The oxygen permeability of the aforementioned fresh produce preservation bag at 23°C and 60% RH is between 1900 (cc/m² ^· day·atm) and 30000 (cc/m² ^· day·atm).
The water vapor permeability of the aforementioned fresh produce preservation bag at 40°C is 1 g/(m² ^· day) or more and 300 g/(m² ^· day) or less.
A fresh produce freshness preservation bag (excluding a fresh produce freshness preservation bag to which a breathable material covering holes with a diameter of 1 to 10 mm is attached) wherein the ratio of elastic recovery rates (elastic recovery rate _MD / elastic recovery rate _TD ) measured by the following procedure a of the fresh produce freshness preservation bag is 1.00 or less, and the elastic recovery rate _TD ( %) is 61.0% or more .
(Procedure a)
(i) Cut out the fresh produce preservation bag so that the MD direction of the synthetic resin film is in the length direction, and prepare a strip-shaped sample with a width of 5 mm. Using a tensile testing machine, the distance between the chucks when both ends of the sample are fixed with chucks is defined as the gauge length _L0 (mm) of the sample. Stretch the sample until the gauge length _L0 (mm) becomes 1.2 times, and hold it in that position for 3 minutes. Then, release the fixation of the sample, and measure the gauge length _L1 (mm) of the sample 20 seconds after release. Calculate the elastic recovery rate _MD (%) from the following formula (1).
[L ₀ ×1.2−L ₁ ]/L ₀ ×0.2 (1)
(ii) The same procedure as in (i) above is used for measurement, except that the fresh produce preservation bag is cut out so that the TD direction of the synthetic resin film is in the length direction, and a 5 mm wide strip-shaped sample is prepared, and the elastic recovery rate _TD (%) is calculated from formula (1). A fresh produce preservation bag according to claim 1 ,
A fresh produce freshness preservation bag, wherein the loop stiffness measured by the following procedure b is 2.5 to 30 mN.
(Procedure b) Cut out the fresh produce preservation bag so that the TD direction of the synthetic resin film is the length direction, and prepare a 25 mm wide strip-shaped sample. Overlap the two ends of the sample facing each other and roll it into a loop shape so that the loop length is 55 mm, and secure both ends by clamping them from the outside with a chuck. With the sample secured, compress it by 20 mm at a speed of 3.3 mm/s with an indenter, from the top of the loop towards the chuck, and measure the pressure applied to the indenter. A fresh produce preservation bag according to claim 1 or 2,
The aforementioned synthetic resin film is made of stretched polypropylene film, and is used for fresh produce preservation bags. A fresh produce preservation bag according to claim 1 or 2,
The aforementioned fresh produce preservation bag is a fresh produce preservation bag having through holes. A package containing fresh produce, comprising fresh produce contained in a freshness-preserving bag according to claim 1 or 2. In the package containing fresh produce according to claim 5 ,
A package containing fresh produce weighing 300g or more. In the package containing fresh produce according to claim 5,
The aforementioned produce is cabbage; the package contains produce. A method for preserving the freshness of fruits and vegetables,
A method for preserving the freshness of fruits and vegetables, comprising the step of placing the fruits and vegetables in a freshness-preserving bag for fruits and vegetables described in claim 1 or 2. In the method for preserving the freshness of fruits and vegetables according to claim 8,
A method for preserving the freshness of fruits and vegetables, wherein the process of storing the fruits and vegetables is carried out under atmospheric pressure.