JP7471053B2 - Film used for packaging bags for fruits and vegetables - Google Patents

Description

The present invention relates to a film used for packaging bags for fruits and vegetables.

Vegetables, fruits, potatoes, mushrooms, and other fresh produce are packaged in plastic film processed into bags and distributed to maintain their freshness and protect them from damage caused by contact with the outside world.

Packaging machines such as vertical pillow machines are used to process this resin film into bags and automatically package fresh produce such as raw vegetables. A vertical pillow machine is a machine that first forms the resin film into a cylindrical shape, then seals the bottom of the bag, then pours the contents into the bag from above, and finally seals the top of the bag, packaging the contents in a bag-shaped resin film. If the weight of the contents is applied to the sealed part (bottom of the bag) immediately after sealing, there is a risk that in the case of heavy items such as raw vegetables, problems such as the sealed part opening may occur.

The applicant has therefore provided a film for packaging fruits and vegetables (Patent Document 1). This polypropylene-based packaging film has excellent heat seal strength and excellent hot tack when filled with contents, so the seal is unlikely to open even if the contents are relatively heavy items such as raw vegetables, and it can be efficiently packaged using a vertical pillow packaging machine.

Furthermore, among fruits and vegetables, bean sprouts are packaged in bags made of polyethylene film, polypropylene film, etc. after harvesting, and are distributed and sold at low temperatures. Even though bean sprouts are distributed and sold at low temperatures, they are susceptible to deterioration.

The applicant has therefore provided a packaging film that extends the shelf life of bean sprouts and the like (Patent Document 2). This bean sprout packaging film has an excellent deodorizing effect against methyl sulfide, which is generated when bean sprouts deteriorate.

In addition, a freshness-preserving packaging bag for bean sprouts or mushrooms has been disclosed that prevents the package from expanding over time when the bean sprouts or mushrooms are vacuum-packaged and stored after harvest (Patent Document 3).

Patent No. 6302726 Patent No. 4854881 JP 2018-76081 A

The present invention aims to provide a film for use in packaging bags for fruits and vegetables that can suppress the expansion (return of air after degassing) of evacuated packaging bags.

The present invention relates to packaging bags for fruits and vegetables, particularly bean sprouts. Films such as polyethylene and polypropylene are used as materials for packaging bags for fruits and vegetables, particularly bean sprouts. Bean sprouts are easily spoiled, even though they are distributed at low temperatures. When packaging bags for bean sprouts, they are packaged in a vacuum-packaged state with the air removed from the bag.

This has the effect of suppressing the breathing of the bean sprouts. This vacuum packaging gives the entire bag a firm feel, improving the ease of handling and display of the bag. However, some vacuum bags contain air when they are put on store shelves, resulting in a slightly bulging state. As a result, they lose their "firmness" when picked up and are less suitable for display.

The inventors have discovered that bulging of vacuum-packaged bags cannot occur unless the amount of gas entering and leaving the bag exceeds the gas permeability of the synthetic resin used in the film. As a result, they have come up with a film that can be used for vacuum packaging and that can suppress bulging of vacuum-packaged bags (return of gas after degassing).

Gas enters and exits through the sealed area when the bag is made. Gas enters and exits through defective areas of the seal. By achieving stable sealing, it is possible to reduce swelling of the vacuum packaging bag (return of gas after degassing).

The inventors have discovered that films used in packaging bags for fruits and vegetables can suppress the expansion (return of air after deaeration) of evacuated packaging bags by providing the following characteristics:

Item 1.
A film used for packaging bags for fruits and vegetables,
The film is characterized by having at least one seal layer containing a propylene-based random copolymer and a polyethylene-based resin.

Item 2.
The film is a biaxially oriented polypropylene film having at least three layers: a surface layer, a base layer, and a seal layer;
2. The film according to item 1, wherein the sealing layer contains 60% by weight to 95% by weight of a propylene-based random copolymer and 5% by weight to 40% by weight of a polyethylene-based resin.

Item 3.
3. The film according to item 1 or 2, wherein the fruit or vegetable is bean sprouts.

Item 4.
3. A vacuum packaging bag for bean sprouts using the film according to item 1 or 2.

Item 5.
Using film used for packaging bags for fruits and vegetables,
The film is a biaxially oriented polypropylene film having at least three layers: a surface layer, a base layer, and a seal layer;
The sealing layer contains 60% by weight to 95% by weight of a propylene-based random copolymer and 5% by weight to 40% by weight of a polyethylene-based resin,
Packaging fruits and vegetables with the fill.
A method for preventing re-release of degassed products after vacuum packaging.

The present invention provides a film for use in packaging bags for fruits and vegetables that can suppress the expansion (return of air after degassing) of evacuated packaging bags.

The present invention relates to a film used for packaging bags for fruits and vegetables.

In the present invention, in the film used for the packaging bag for the fruit and vegetable, the fruit and vegetable is preferably bean sprouts.

The present invention also relates to a degassing packaging bag for bean sprouts using the film.

The present invention relates to a method for preventing re-gassing after vacuum packaging, which includes a process of packaging fruits and vegetables using a film used for packaging bags for fruits and vegetables.

(1) Film for use in packaging bags for fruits and vegetables The present invention is a film for use in packaging bags for fruits and vegetables,
The film is characterized by having at least one seal layer containing a propylene-based random copolymer and a polyethylene-based resin.

In the present invention, the film is a biaxially oriented polypropylene film having at least three layers, namely, a surface layer, a base layer, and a seal layer,
The sealing layer preferably contains 60% to 95% by weight of a propylene-based random copolymer and 5% to 40% by weight of a polyethylene-based resin.

In the present invention, the fruit or vegetable is preferably bean sprouts.

The present invention is a degassing packaging bag for bean sprouts that uses the above film.

(1-1) Sealing Layer The film of the present invention has at least one sealing layer.

For example, when packaging fruits and vegetables using a vertical pillow machine, the sealing layer is the layer that becomes the inside of the tube when the plastic film is first formed into a cylindrical shape, and the sealing layers are bonded to each other at the sealing section.

The sealing layer contains a propylene-based random copolymer and a polyethylene-based resin. It is preferable that the sealing layer contains 60% to 95% by weight of the propylene-based random copolymer and 5% to 40% by weight of the polyethylene-based resin.

Propylene-Based Random Copolymers Propylene-based random copolymers are copolymers of propylene and other α-olefins.

Examples of α-olefins other than propylene include α-olefins having 2 to 20 carbon atoms other than propylene. Specific examples 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, and 2-ethyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene.

Among these, those 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.

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.

The propylene-based random copolymer is not particularly limited as long as it is a random copolymer of propylene and other α-olefins, but specific examples include propylene-ethylene random copolymers, propylene-butene random copolymers, and propylene-ethylene-butene random copolymers. Among these, propylene-ethylene-butene random copolymers are preferred.

Among propylene random copolymers, those having a melt flow rate (MFR) value in the range of 0.5 g/10 min to 20 g/10 min when measured in accordance with ISO1133 (1997) at 230°C and a load of 21.18 N (2.16 kg) are preferred. Propylene random copolymers having an MFR value in the range of 4 g/10 min to 8 g/10 min are more preferred. The MFR value of the polymer can be adjusted as appropriate by changing the type and content of α-olefins other than propylene, the molecular weight of the polymer, and the degree of polymerization.

Polyethylene resins Polyethylene resins are copolymers of ethylene and other α-olefins.

Examples of α-olefins other than ethylene include α-olefins having 3 to 20 carbon atoms, such as 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, and 1-eicosene.

Among these, those 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.

The content ratio of ethylene and other α-olefins in polyethylene resins is usually 75% to 100% by weight of ethylene and 0% to 25% by weight of other α-olefins, preferably 85% to 99.9% by weight of ethylene and 0.1% to 15% by weight of other α-olefins, more preferably 90% to 99.5% by weight of ethylene and 0.5% to 10% by weight of other α-olefins, and even more preferably 90% to 99% by weight of ethylene and 1% to 10% by weight of other α-olefins.

Among polyethylene resins, those with a melt flow rate (MFR) value measured in accordance with ISO1133 (1997) at 190°C and a load of 21.18N (2.16kg) within the range of 0.5g/10min to 20g/10min are preferred. Furthermore, those with an MFR value within the range of 2g/10min to 4g/10min are even more preferred.

Furthermore, among polyethylene resins, those having a density measured in accordance with JIS K 7112 within the range of 850 kg/m ³ to 900 kg/m ³ are preferred, and those having a density within the range of 860 kg/m ³ to 890 kg/m ³ are more preferred.

Content Ratio In the film of the present invention, the sealing layer preferably contains 60% to 95% by weight of a propylene-based random copolymer and 5% to 40% by weight of a polyethylene-based resin.

The content of the propylene-based random copolymer in the seal layer is more preferably 62% to 94% by weight, even more preferably 63% to 93% by weight, and particularly preferably 65% to 91% by weight. If the content of the propylene-based random copolymer is more than 95% by weight, sufficient heat seal strength may not be obtained, and if it is less than 60% by weight, hot tack properties may decrease.

The content of the polyethylene resin in the seal layer is more preferably 6% to 38% by weight, even more preferably 7% to 37% by weight, and particularly preferably 9% to 35% by weight. If the content of the polyethylene resin is less than 5% by weight, sufficient heat seal strength may not be obtained, and if it is more than 40% by weight, hot tack properties may decrease.

The antiblocking agent or lubricant seal layer may contain an antiblocking agent or lubricant to the extent that transparency 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 in combination of two or more.

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

(1-2) Substrate layer In the present invention, the film is preferably a biaxially oriented polypropylene film having at least three layers, namely, a surface layer, a substrate layer, and a seal layer. The substrate layer is an intermediate layer sandwiched between the seal layer and the surface layer described below.

The base layer preferably contains a crystalline polypropylene resin as a main component.

Crystalline Polypropylene Resin The crystalline polypropylene resin is not particularly limited as long as it is a crystalline propylene resin, but a crystalline polypropylene resin having a melting point of 155°C to 165°C is preferred.

Examples of crystalline polypropylene resins with a melting point of 155°C to 165°C include propylene homopolymers and copolymers of propylene and other α-olefins.

Examples of α-olefins other than propylene include α-olefins other than propylene having 2 to 10 carbon atoms, specifically, for example, 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 kinds.

The content of α-olefins other than propylene is preferably 1.3% by weight or less, and more preferably 0.8% by weight or less.

The main component is usually 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more of crystalline polypropylene resin with a melting point of 155°C to 165°C in the base layer.

The anti-fog agent substrate layer can contain an anti-fog agent for the purpose of imparting anti-fog performance to the film. Such an anti-fog agent is generally added to the substrate layer, but after the film of the present invention is formed, it diffuses into the surface layer and the seal layer, so that when it is used for packaging contents with a lot of moisture, it exhibits good anti-fog properties. Such an anti-fog agent is not particularly limited as long as it is suitable for the purpose, and anti-fog agents that have been used in anti-fog films in the past can be used as they are. Specifically, for example, three types of anti-fog agents can be mentioned: 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 bonded to the -OH of glycerin.

The above anti-fogging agents are preferably 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. It is particularly preferable to use anti-fogging agents 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 ppm to 15,000 ppm is appropriate, and 4,000 ppm 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 bleed-out to the surface may occur, resulting in a deterioration in transparency.

(1-3) Surface layer In the present invention, the film is preferably a biaxially oriented polypropylene film having at least three layers, namely, a surface layer, a base layer, and a seal layer. The surface layer is a layer that becomes the outer surface when the resin film is formed into a packaging bag.

The surface layer preferably contains a polypropylene resin.

Polypropylene-based resins Polypropylene-based resins are propylene homopolymers or copolymers of propylene and other α-olefins. Examples of α-olefins other than propylene include α-olefins having 2 to 10 carbon atoms other than propylene. Specific examples include α-olefins such as ethylene, 1-butene, 1-pentene, and 1-hexene. 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 the α-olefin other than propylene is suitably 14% by weight or less, and preferably 10% by weight or less.

Among polypropylene-based resins, it is preferable that the melt flow rate (MFR) value, measured in accordance with ISO1133 (1997) at 230°C and a load of 21.18N (2.16Kg), is within the range of 0.5g/10min to 20g/10min. Furthermore, polypropylene-based resins with an MFR value within the range of 4g/10min to 8g/10min are more preferable. The MFR value of the polymer can be adjusted as appropriate by the type and content of α-olefins other than propylene, the molecular weight of the polymer, and the degree of polymerization.

Furthermore, it is preferable that the melting point of the polypropylene resin is within the range of 120°C to 165°C.

The antiblocking agent or lubricant surface layer may contain an antiblocking agent or lubricant to the extent that transparency is not impaired in order to smooth the surface of the resin film and prevent the resin films from adhering to each other. The preferred types and amounts of the antiblocking agent or lubricant are the same as those described for the seal layer.

(1-4) Film Structure The film of the present invention has at least three layers, namely, a surface layer, a base layer, and a seal layer. When the film of the present invention is formed into a packaging bag, these layers are arranged in the following order: the surface layer on the outer surface, the base layer in the middle, and the seal layer on the inner surface.

Thickness of Each Layer of the Film The total thickness of the film of the present invention is usually within the range of 10 μm to 80 μm, and preferably within the range of 10 μm to 40 μm.

The sealing layer is usually in the range of 1.0 μm to 12 μm, preferably in the range of 1.2 μm to 6 μm.

The substrate layer is usually in the range of 1 μm to 40 μm, preferably in the range of 2 μm to 25 μm.

The surface layer is usually in the range of 0.3 μm to 40 μm, preferably in the range of 0.5 μm to 37 μm.

If the thickness of the sealing layer and surface layer are within this range, the film will have good sealing strength and be easy to handle.

Various additives can be further mixed in appropriate amounts into the film of the present invention. Such additives include nucleating agents, antioxidants, flame retardants, antistatic agents, fillers, pigments, etc.

In addition to the three layers, the film of the present invention may have other layers such as an opening-imparting layer and a gas barrier layer.

(2) Film manufacturing method By using the film of the present invention, stable sealing can be achieved and degassing return can be reduced. By using the film of the present invention, there are no defective parts in the sealed part and gas does not enter or exit through the sealed part when the film is made into a bag.

There are no particular limitations on the method for producing the film of the present invention, and any known method can be used.

In consideration of productivity and the physical properties of the finished film, the preferred method for producing the film of the present invention is to extrude a flat sheet and then sequentially biaxially stretch it to produce the film.

More specifically, the resins constituting the surface layer, the resin constituting the base material layer, and the resin constituting the seal layer are fed into three extruders set to appropriate temperatures, and after the resins are melted and kneaded in the extruders, they are extruded into a sheet from a T-die at 210°C to 250°C. In this case, either the feed block method or the multi-manifold method may be used to form a three-layer structure.

The extruded sheet is cooled and solidified by cooling rolls at 25°C, and then sent to the longitudinal stretching process. The longitudinal stretching is performed using heating rolls set at 130°C to 140°C, and the sheet is stretched in the longitudinal direction (hereinafter referred to as 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 are required, one on the low speed side and one on the high speed side. The stretching ratio for longitudinal stretching is 4 to 6 times, and preferably 4.5 to 5.5 times.

The film is then sent to a transverse stretching process using a tenter, where it is stretched in the transverse direction (hereafter 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 around 6 to 10 times. After stretching, 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 the film leaves the annealing zone of the tenter and before it is wound up by the winder, it is preferable to perform a known surface treatment such as corona discharge treatment, flame treatment, or ultraviolet irradiation treatment, and from the viewpoint of simplicity, it is particularly preferable to perform corona discharge treatment. By performing such a surface treatment, it is possible to impart wetting tension to the surface of the film and enhance the anti-fogging effect, as well as to improve the adhesion of the film to printing ink when printing is performed on the film surface.

The corona discharge treatment may be performed on both the surface layer surface and the sealing layer surface, or on only one of the surface layer surface or the sealing layer surface. The intensity of the corona discharge treatment is preferably within the range of 1.8× ¹⁰² J/ ^m2 to 9.0× ¹⁰² J/ ^m2 , and when both surfaces are treated, the intensity may be the same or different.

The surface wetting tension of the biaxially oriented polypropylene film of the present invention is preferably 38 mN/m to 44 mN/m. If the wetting tension is less than 38 mN/m, the anti-fogging properties are not sufficiently expressed, and when printing, the adhesion of the printing ink is poor, which is undesirable. If the wetting tension exceeds 44 mN/m, the anti-fogging agent bleeds out to the surface excessively, causing whitening and blocking, as well as causing a decrease in the melt-cutting seal strength, which is undesirable.

(3) Method of processing the film into a bag The present invention includes packaging bags for fruits and vegetables using the film.

The present invention includes a degassing packaging bag for bean sprouts that uses the film.

The packaging bag of the present invention can be formed by an automatic packaging machine or the like using the film of the present invention. A packaging machine such as a vertical pillow machine is used as a device for processing the film into a bag shape and automatically packaging fruits and vegetables such as raw vegetables. A vertical pillow machine is a device that first forms a (resin) film into a cylindrical shape, then seals the bottom of the bag, then pours the contents into the bag from above, sandwiches the bag and the contents with a sponge, pushes out the air inside the bag to degas it, and finally seals the top of the bag, thereby packaging the contents in a bag-shaped (resin) film.

The film of the present invention has excellent hot tack when filled with contents, and is therefore particularly suitable for use when forming packaging bags using a vertical pillow packaging machine. The film of the present invention can also be used when forming bags using other packaging machines, such as a horizontal pillow packaging machine.

The contents to be packaged in the packaging bag of the present invention are not particularly limited as long as they can be packaged, but examples include agricultural products such as fruits and vegetables (e.g., raw vegetables, fruits, potatoes, mushrooms, etc.), with agricultural products being preferred.

Examples of agricultural products include vegetables such as green onions, bean sprouts, spinach, broccoli, and bell peppers; cut vegetables such as cabbage, lettuce, and carrots; fruits such as strawberries, bananas, and lemons; and mushrooms such as enoki mushrooms, maitake mushrooms, shimeji mushrooms, and shiitake mushrooms. Of these, bean sprouts and cut vegetables are preferred.

By using the film of the present invention, a stable seal can be achieved and degassing back can be reduced. By using the film of the present invention, there are no defects in the sealed area, and gas does not enter or exit through the sealed area when the bag is made.

(4) Method for preventing return of air after vacuum packaging The present invention includes a method for preventing return of air after vacuum packaging by using a film used for packaging bags for fruits and vegetables.

The present invention uses a film used for packaging bags for fruits and vegetables,
The film is a biaxially oriented polypropylene film having at least three layers: a surface layer, a base layer, and a seal layer;
The sealing layer contains 60% by weight to 95% by weight of a propylene-based random copolymer and 5% by weight to 40% by weight of a polyethylene-based resin,
Packaging fruits and vegetables with the fill.
The method for preventing re-gassing after vacuum packaging is characterized in that:

Details of the film are as above.

The process of packaging fruits and vegetables using fillers is carried out, for example, using a packaging machine such as a vertical pillow machine, as described above.

In the present invention, the fruit or vegetable is preferably bean sprouts.

By using the film of the present invention, a stable seal can be achieved and degassing back can be reduced. By using the film of the present invention, there are no defects in the sealed area, and gas does not enter or exit through the sealed area when the bag is made.

The present invention will be explained with reference to examples. The present invention is not limited to these examples in any way.

(1) Raw materials for packaging film
PP-1: Propylene-ethylene copolymer Ethylene content: 0.5% by weight, MFR: 3.0g/10min, melting point: 161°C, density: 900Kg/ ^m3
PP-2: Propylene-ethylene copolymer
Ethylene content: 0.4% by weight, MFR: 2.3g/10min, melting point: 160℃, density: 900Kg/ ^m3
PP-3: Propylene-ethylene-butene copolymer
Ethylene component: 3.4% by weight, butene component: 1.4% by weight,
MFR: 5.0g/10min, Melting point: 125℃, Density: 900Kg/ ^m3
LLDPE: Linear low density polyethylene
MFR: 3.5g/10min, Melting point: 60℃, Density: 880Kg/ ^m3

(2) Conditions for manufacturing packaging bags The packaging bags were manufactured under the following conditions using an automatic weighing and packaging machine DT-1080 (manufactured by Taisei Machinery).
Number of shots: 56 shots/min Bag making pitch: 224mm
Amount in package: 200g bean sprouts
Vertical seal temperature: 220℃
Horizontal seal temperature: 140℃
Deaeration sponge: Yes

(3) Example (Example 1)
Resin that constitutes the surface layer: PP-1 (100% by weight)
Resin constituting the base layer: PP-2 (100% by weight)
Resins constituting the sealing layer: PP-3 (80% by weight) and PE-1 (20% by weight)
The resins constituting each layer were fed into three extruders, and were laminated in the order of surface layer/base material layer/seal layer, co-extruded from a three-layer T-die at 230° C., cooled and solidified with a cooling roll at 25° C. to obtain a raw sheet. The sheet was then heated to 130° C. and roll-stretched 4.6 times in the MD direction, and then preheated in a tenter at a set temperature of 165° C. and stretched 10 times in the TD direction at a set temperature of 165° C.

The film was then annealed at a set temperature of 165°C, and after leaving the tenter, the surface layer side was subjected to a corona discharge treatment at 6.6 x ¹⁰² J/ ^m2 and the seal layer side was subjected to a corona discharge treatment at 4.8 x ¹⁰² J/ ^m2 . The film was wound up on a winder to obtain a film of the present invention. The total thickness of the obtained film was 25 μm, and the thicknesses of the respective layers were surface layer/base layer/seal layer = 2 μm/19 μm/4 μm.

Example 2
A film of the present invention was obtained in the same manner as in Example 1, except that the total thickness of the film was 20 μm and the thicknesses of the individual layers were surface layer/base layer/seal layer=2 μm/15 μm/3 μm.

(Comparative Example 1)
A film was obtained in the same manner as in Example 1, except that the resin constituting the seal layer was 100% by weight of PP-3.

A method of processing the film into a bag shape: Using a vertical pillow machine as an automatic packaging machine, the film obtained above was processed into a bag shape to package fresh vegetables and other fruits and vegetables. Using the vertical pillow machine, first, the (resin) film was made into a cylindrical shape, then the bottom of the bag was sealed, and the contents were then poured into the bag from above, and the bag and contents were sandwiched between a sponge to push out the air inside the bag and degas it. Finally, the top of the bag was sealed to package the contents in the bag-shaped (resin) film.

(4) Evaluation test of packaging bags
Heat seal strength measurement
The two films were stacked with the seal layer surfaces facing each other, and then heat sealed using a heat seal tester (HG-100, manufactured by Toyo Seiki Seisakusho) under conditions of a temperature of 140° C., a pressure of 0.2 MPa, and a sealing time of 1.0 second.

The obtained samples were cut to a length of 200 mm and a width of 15 mm, and the heat seal strength was measured in a T-peel test at a tensile speed of 200 mm/min using a peel tester (Peeling TESTER HEIDON-17, manufactured by Shinto Scientific Co., Ltd.). The measurement was carried out five times, and the average value was calculated.

Products with a seal strength of 6N/15mm or more were judged to be "good."

A deaeration return confirmation test was carried out. The percentage of bags containing fruit and vegetables that had air infiltration was investigated. The deaeration return was checked by visually checking whether air had entered the bag and by touching whether the bean sprouts in the bag had shifted. It was determined that deaeration return had occurred when the bag was inflated and the bean sprouts moved.

By using the film of the present invention, a stable seal can be achieved and degassing back can be reduced. By using the film of the present invention, there are no defects in the sealed area, and gas does not enter or exit through the sealed area when the bag is made.

Claims (6)

A film used for packaging bags for fruits and vegetables,
The total thickness of the film is 15 μm or more and less than 30 μm,
The packaging of the fruits and vegetables using the packaging bag is carried out by an automatic packaging machine,
The film is a biaxially oriented polypropylene film having at least three layers: a surface layer, a base layer, and a seal layer;
The polypropylene resin of the surface layer has a melting point of 120°C to 165°C,
The sealing layer contains a propylene-based random copolymer and a polyethylene-based resin,
A film characterized in that when two sheets of the film are stacked with the sealing layer faces facing each other and heat sealed under conditions of a temperature of 140°C, a pressure of 0.2 MPa, and a sealing time of 1.0 second, the heat seal strength is 7 N/15 mm or more and 10 N/15 mm or less. The film according to claim 1, characterized in that the thickness of the sealing layer is 3 μm or more and 4 μm or less. The film according to claim 1 or 2, characterized in that the sealing layer contains 60% to 95% by weight of a propylene-based random copolymer and 5% to 40% by weight of a polyethylene-based resin. The film according to any one of claims 1 to 3, wherein the fruit or vegetable is bean sprouts. A vacuum packaging bag for bean sprouts using the film described in any one of claims 1 to 3. Using film used for packaging bags for fruits and vegetables,
The total thickness of the film is 15 μm or more and less than 30 μm,
The film is a biaxially oriented polypropylene film having at least three layers: a surface layer, a base layer, and a seal layer;
The polypropylene resin of the surface layer has a melting point of 120°C to 165°C,
The sealing layer contains 60% by weight to 95% by weight of a propylene-based random copolymer and 5% by weight to 40% by weight of a polyethylene-based resin,
When two sheets of the film are stacked with the sealing layer surfaces facing each other and heat sealed under conditions of a temperature of 140°C, a pressure of 0.2 MPa, and a sealing time of 1.0 second, the heat seal strength is 7 N/15 mm or more and 10 N/15 mm or less,
packaging fruits and vegetables with the film,
A method for preventing re-gassing after vacuum packaging, characterized in that the packaging of the fruits and vegetables with the film is carried out by an automatic packaging machine.