Polyethylene multilayer shrink film

Abstract

To provide a polyethylene-based multilayer shrink film that can extend the freshness preservation period of shrink-wrapped fruits and vegetables, and has good transparency and gloss. [Solution] Two surface layers X, One or more internal layers Y are provided between the two surface layers X. A polyethylene-based multilayer shrink film comprising at least three layers, The two surface layers X are each formed from a surface layer-forming composition containing a polyethylene resin and an anti-fogging agent, and not containing inorganic porous particles. The inner layer Y is a layer formed from an inner layer forming composition containing a polyethylene resin, an anti-fogging agent, and inorganic porous particles. The content of the inorganic porous particles is greater than 0.2 parts by mass and less than 3 parts by mass, based on 100 parts by mass of the internal layer forming composition. Polyethylene-based multilayer shrink film.

Description

[Technical Field]

[0001] This invention relates to polyethylene-based multilayer shrink film. [Background technology]

[0002] Even after harvesting, fresh produce continues to perform vital activities such as respiration and transpiration, leading to a decrease in nutrients, moisture, and pigments, resulting in discoloration, wilting, and a decline in freshness and quality. Furthermore, stress from cutting during processing and ethylene gas released from the produce itself stimulate respiration after harvesting, and these factors are known to significantly affect the decline in freshness. In other words, the decline in freshness of fresh produce is caused not only by the internal reactions such as respiration and transpiration mentioned above, but also by external stresses such as vibrations and shocks.

[0003] Producers and retailers of fruits and vegetables take measures to suppress the deterioration of freshness, such as controlling temperature and humidity during storage and packaging in bags and trays. Packaging fruits and vegetables in bags and trays not only reduces the impact during transportation but also prevents consumers from directly touching the produce at the point of sale and prevents foreign objects from getting into the produce during store displays, thereby reducing the risk of damage to the produce. For this reason, development is underway to create packaging materials that have special functions to suppress the deterioration of freshness of fruits and vegetables through respiration and transpiration.

[0004] For example, a film has been proposed that provides anti-fogging properties to suppress fogging and condensation inside the packaging bag due to moisture evaporation from fruits and vegetables, thereby preventing spoilage caused by water droplets falling on the fruits and vegetables after packaging, and preventing defects in the appearance of the packaged product due to fogging (Patent Document 1).

[0005] Furthermore, a polyethylene-based multilayer film for overlap heat-shrinkable packaging has been proposed in which the respiration process can be suppressed by incorporating a specific zeolite into the surface layer of the film to adsorb ethylene gas (Patent Document 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-231899 [Patent Document 2] Patent No. 7108266 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, while respiration significantly affects the deterioration of fresh produce, the performance of the film proposed in Patent Document 1 was insufficient to adequately suppress respiration, making it difficult to adequately suppress the deterioration of fresh produce. Furthermore, while the polyethylene-based multilayer film for overlap heat-shrink packaging proposed in Patent Document 2 is a film that combines excellent freshness preservation and suitability for automatic packaging machines, there was room to improve the transparency and gloss of the film.

[0008] Furthermore, compared to films without zeolite, films containing zeolite presented a challenge in the manufacturing process: equipment wear was more likely to occur when the film surface came into contact with the cooling device, making it difficult to produce them continuously for extended periods.

[0009] Therefore, the object of the present invention is to provide a polyethylene-based multilayer shrink film that can extend the freshness preservation period of shrink-wrapped fruits and vegetables and has good transparency and gloss. That is the case. Furthermore, an object of the present invention is to provide a polyethylene-based multilayer shrink film that can be produced continuously.

[0010] Furthermore, an objective of the present invention is to provide a polyethylene-based multilayer shrink film that can contribute to reducing the environmental burden, which has become a problem in recent years. [Means for solving the problem]

[0011] As a result of intensive studies to solve the above problems, the inventors of the present invention have found that in a polyethylene-based multilayer shrink film composed of at least three layers having two surface layers and one or more inner layers provided between the two surface layers, by containing inorganic porous particles only in the inner layer, while maintaining freshness retention equivalent to that of the polyethylene-based multilayer film for overlap heat shrink packaging described in Patent Document 2, transparency and gloss are improved, and continuous production is possible, thus completing the present invention.

[0012] In addition, the inventors have found that by using a plant-derived resin as the resin constituting the surface layer and / or inner layer of the polyethylene-based multilayer shrink film, it is possible to contribute to reducing the environmental load, thus completing the present invention.

[0013] That is, the present invention is [1] A polyethylene-based multilayer shrink film composed of at least three layers having two surface layers X and one or more inner layers Y provided between the two surface layers X, wherein the two surface layers X are layers formed from a surface layer-forming composition containing a polyethylene-based resin and an anti-fogging agent and not containing inorganic porous particles, the inner layer Y is a layer formed from an inner layer-forming composition containing a polyethylene-based resin, an anti-fogging agent, and inorganic porous particles, the content of the inorganic porous particles is more than 0.2 parts by mass and less than 3 parts by mass based on 100 parts by mass of the inner layer-forming composition, and the polyethylene-based multilayer shrink film. [2] At least one of the two surface layers X is in contact with the inner layer Y, and when the thickness (μm) of the surface layer X in contact with the inner layer Y is a and the average particle diameter (μm) of the inorganic porous particles in the inner layer Y is D, a ≦ D is satisfied between the thickness of the surface layer X and the average particle diameter of the inorganic porous particles. ​[1] Polyethylene multilayer shrink film as described above, [3] The polyethylene-based multilayer shrink film according to [1] or [2], wherein the inorganic porous particles are zeolite. [4] The polyethylene resin in the two surface layers X is a petroleum-derived polyethylene resin. The polyethylene resin in the inner layer Y comprises 0 to 90 parts by mass of plant-derived polyethylene resin and 10 to 100 parts by mass of petroleum-derived polyethylene resin, based on 100 parts by mass of polyethylene resin. [3] Polyethylene multilayer shrink film as described above, [5] The aforementioned plant-derived polyethylene resin is subject to radiocarbon dating. 14 It is a plant-derived linear low-density polyethylene having a biomass content of 80% to 100% calculated from the measured value of C, Polyethylene multilayer shrink film as described in [4] This provides... [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a polyethylene-based multilayer shrink film with good freshness retention, transparency, and gloss. Furthermore, according to the present invention, it is possible to provide polyethylene-based multilayer shrink film that can be produced continuously.

[0015] Furthermore, according to the present invention, it is possible to provide a polyethylene-based multilayer shrink film that can contribute to reducing environmental impact. [Modes for carrying out the invention]

[0016] The present invention Two surface layers X, One or more internal layers Y are provided between the two surface layers X. A polyethylene-based multilayer shrink film comprising at least three layers, The two surface layers X are each formed from a surface layer-forming composition containing a polyethylene resin and an anti-fogging agent, and not containing inorganic porous particles. The inner layer Y is a layer formed from an inner layer forming composition containing a polyethylene resin, an anti-fogging agent, and inorganic porous particles. The content of the inorganic porous particles is greater than 0.2 parts by mass and less than 3 parts by mass, based on 100 parts by mass of the internal layer forming composition. Polyethylene multilayer shrink film Regarding. The present invention will be described in detail below.

[0017] [Surface layer X] The two surface layers X are each formed from a surface layer-forming composition containing a polyethylene resin and an anti-fogging agent, but without inorganic porous particles. The compositions of the two surface layers X may be the same or different.

[0018] <Polyethylene resin> Examples of polyethylene-based resins include ethylene homopolymers and copolymers of ethylene with small amounts of other monomers (ethylene-α-olefin copolymers). Here, the other monomers are not particularly limited, but examples include α-olefins such as propylene, butene-1, hexene-1, octen-1, and 4-methylpentene-1. The above polyethylene resins can be used individually or in combination of two or more types.

[0019] The density of polyethylene resin is 0.901 g / cm³. 3 ~0.965g / cm 3 Preferably, it is 0.911 g / cm³. 3 Super 0.925g / cm 3 The following is more preferable: In this specification, the density of polyethylene resins is measured in accordance with JIS K 7112-2(2023).

[0020] The melt index (melt flow rate) of the polyethylene resin is preferably 0.2 g / 10 min or more, more preferably 0.3 g / 10 min or more, still more preferably 0.5 g / 10 min or more, and also 20 g / 10 min or less, more preferably 15 g / 10 min or less, and still more preferably 10 g / 10 min or less, from the viewpoints of film-forming property and processability. In this specification, the melt index (melt flow rate) of the polyethylene resin is measured by Method A under the conditions of a temperature of 190 °C and a load of 2.16 kg in accordance with JIS K 7210-1 (2014).

[0021] Examples of the polyethylene resin include ultra-low density polyethylene (density: 0.911 g / cm 3 or less), low density polyethylene (density: 0.911 g / cm 3 exceeding 0.925 g / cm 3 or less), linear low density polyethylene (density: 0.911 g / cm 3 exceeding 0.925 g / cm 3 or less), medium density polyethylene (density: 0.925 g / cm 3 exceeding 0.940 g / cm 3 or less), and high density polyethylene (density: 0.940 g / cm 3 or more). At least one selected from the group consisting of these is preferable, at least one selected from the group consisting of low density polyethylene and linear low density polyethylene is more preferable, and linear low density polyethylene is still more preferable.

[0022] The content of the polyethylene resin is preferably 96 to 99 parts by mass, more preferably 97 to 99 parts by mass, based on 100 parts by mass of the surface layer-forming composition. If the content of the polyethylene resin is more than 99 parts by mass, a sufficient amount of the anti-fogging agent necessary for imparting functions cannot be added. If it is less than 96 parts by mass, the shrinkage finishability and melt-blown sealability during packaging cannot be sufficiently exhibited.

[0023] The polyethylene resin constituting the surface layer X can be at least one selected from petroleum-derived polyethylene resins and plant-derived polyethylene resins.

[0024] <Anti-fogging agent> Examples of anti-fogging agents include polyhydric alcohol partial fatty acid esters such as sorbitan fatty acid esters, glycerin fatty acid esters, glycerin fatty acid succinate esters, polyglycerin fatty acid esters, sorbitan-glycerin condensed fatty acid esters, sorbitan-diglycerin condensed fatty acid esters, pentaerythritol fatty acid esters, and dipentaerythritol fatty acid esters; ethylene oxide adducts such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene glycol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and polyoxyethylene glycerin fatty acid esters; sorbitol derivatives obtained by adding propylene oxide and ethylene oxide to sorbitol and then esterifying it; amines and amides such as alkylamines, alkylamides, alkylethanolamines, and fatty acid diethanolamides, and their ethylene oxide adducts; nonionic surfactants such as polyalkylene glycols; cationic surfactants; anionic surfactants; and other known substances. Anti-fogging agents can be used individually or in combination of two or more types.

[0025] As an anti-fogging agent, at least one selected from the group consisting of glycerin fatty acid esters, polyglycerin fatty acid esters, and polyoxyethylene alkyl ethers is preferred, a mixture of glycerin fatty acid esters, polyglycerin fatty acid esters, and polyoxyethylene alkyl ethers and a mixture of glycerin fatty acid esters and polyglycerin fatty acid esters are more preferred, a mixture of glycerin fatty acid esters, polyglycerin fatty acid esters, and polyoxyethylene alkyl ethers in which the mass ratio of glycerin fatty acid esters, polyglycerin fatty acid esters, and polyoxyethylene alkyl ethers is 20 / 70 / 10 is even more preferred, and a mixture of glycerin fatty acid esters and polyglycerin fatty acid esters in which the mass ratio of glycerin fatty acid esters, polyglycerin fatty acid esters, and polyoxyethylene alkyl ethers is 50 / 50 is even more preferred.

[0026] Fresh produce continues to transpire even after harvesting, and since polyethylene resin films used for packaging fresh produce are hydrophobic, moisture adhering to the film surface forms water droplets, causing clouding and reducing the visibility of the packaged items. Furthermore, water droplets adhering to the fresh produce can contribute to its deterioration. In contrast, the present invention makes the surface of the polyethylene resin film hydrophilic by including an anti-fogging agent in the film, allowing attached moisture to form a water film instead of water droplets. This suppresses the occurrence of fogging and allows for a suitable appearance as a multilayer shrink film for packaging items.

[0027] From the viewpoint of achieving both anti-fogging properties and extrusion moldability of the multilayer shrink film, the content of the anti-fogging agent is preferably 1 to 4 parts by mass, and more preferably 1 to 3 parts by mass, based on 100 parts by mass of the surface layer forming composition. If the content in the surface layer X is less than 1 part by mass, the desired anti-fogging effect may not be sufficiently obtained, and if it exceeds 4 parts by mass, the extrusion moldability may decrease.

[0028] [Inner layer Y] The inner layer Y is a layer formed from an inner layer forming composition containing a polyethylene resin, an antifogging agent, and inorganic porous particles. If the film of the present invention has two or more inner layers Y, the compositions of the inner layers Y may be the same or different.

[0029] <Polyethylene resin> Examples of polyethylene-based resins include ethylene homopolymers and copolymers of ethylene with small amounts of other monomers (ethylene-α-olefin copolymers). Here, the other monomers are not particularly limited, but examples include α-olefins such as propylene, butene-1, hexene-1, octen-1, and 4-methylpentene-1. The above polyethylene resins can be used individually or in combination of two or more types.

[0030] The density of polyethylene resin is, for example, 0.901 g / cm³. 3 ~0.965g / cm 3 That is the case.

[0031] From the viewpoint of film-forming properties and processability, the melt index (melt flow rate) of polyethylene resin is preferably 0.2 g / 10 min or more, more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, preferably 20 g / 10 min or less, more preferably 15 g / 10 min or less, and even more preferably 10 g / 10 min or less.

[0032] As for polyethylene resins, ultra-low density polyethylene (density: 0.911 g / cm³) is an example. 3 (Below) Low-density polyethylene (density: 0.911 g / cm³) 3 Super 0.925g / cm 3 Below) Linear low-density polyethylene (density: 0.911 g / cm³) 3 Super 0.925g / cm 3 Below) Medium-density polyethylene (density: 0.925 g / cm³) 3 Super 0.940g / cm 3 (The following) and high-density polyethylene (density: 0.940 g / cm³)3 At least one selected from the group consisting of ultra-low density polyethylene, linear low density polyethylene, and high density polyethylene is preferred, at least one selected from the group consisting of ultra-low density polyethylene, linear low density polyethylene, and high density polyethylene is more preferred, and mixtures of ultra-low density polyethylene, linear low density polyethylene, and high density polyethylene, as well as mixtures of linear low density polyethylene and high density polyethylene, are even more preferred.

[0033] The polyethylene resin content is preferably 94 to 98 parts by mass, and more preferably 96 to 98 parts by mass, based on 100 parts by mass of the internal layer forming composition. If the polyethylene resin content is greater than 98 parts by mass, the antifogging agent necessary for imparting functionality will be required. If a sufficient amount cannot be added, and the amount is less than 94 parts by mass, the shrinkage finish and heat-sealing properties during packaging cannot be fully exhibited.

[0034] When using a mixture of ultra-low-density polyethylene, linear low-density polyethylene, and high-density polyethylene as the polyethylene resin, it is preferable that, based on 100 parts by mass of the polyethylene resin, the content of ultra-low-density polyethylene is 65 to 80 parts by mass, the content of linear low-density polyethylene is 10 to 30 parts by mass, the content of high-density polyethylene is 1 to 10 parts by mass, the content of ultra-low-density polyethylene is 70 to 75 parts by mass, the content of linear low-density polyethylene is 20 to 25 parts by mass, and the content of high-density polyethylene is 3 to 8 parts by mass.

[0035] When a mixture of linear low-density polyethylene and high-density polyethylene is used as the polyethylene resin, based on 100 parts by mass of polyethylene resin, the linear low-density polyethylene content is preferably 70 to 90 parts by mass, the high-density polyethylene content is preferably 10 to 30 parts by mass, the linear low-density polyethylene content is preferably 75 to 85 parts by mass, and the high-density polyethylene content is preferably 15 to 25 parts by mass.

[0036] The polyethylene resin constituting the inner layer Y can be petroleum-derived polyethylene resin, plant-derived polyethylene resin, or a mixture of petroleum-derived polyethylene resin and plant-derived polyethylene resin. For example, as the polyethylene resin constituting the inner layer Y, based on 100 parts by mass of polyethylene resin, 0 to 90 parts by mass of plant-derived polyethylene resin and 10 to 100 parts by mass of petroleum-derived polyethylene resin can be used.

[0037] As for plant-derived polyethylene resins, radiocarbon dating 14 A plant-derived polyethylene resin having a biomass content of 80% to 100% calculated from the measured value of C is preferred, and radiocarbon dating 14 Plant-derived linear low-density polyethylene having a biomass content of 80% to 100% as calculated from the measured value of C is more preferable. In this specification, biomass content is measured in accordance with ISO 16620-4.

[0038] <Anti-fogging agent> As stated in the section on the <anti-fogging agent> of [Surface layer X].

[0039] <Inorganic porous particles> In this invention, the inorganic porous particles of the inner layer Y efficiently absorb ethylene gas released from fruits and vegetables, thereby suppressing the respiration of the fruits and vegetables and providing them with freshness-preserving properties. Inorganic porous particles are not particularly limited and include zeolites, cristobalites, Oya stone, alumina (aluminum oxide; Al2O3), and zirconia (zirconium dioxide; ZrO2). Inorganic porous particles can be used individually or in combination of two or more types.

[0040] The average particle size of inorganic porous particles is measured using a laser diffraction particle size distribution analyzer (e.g., the Mastersizer 3000 from Malvern Panalytical). The average particle size of the inorganic porous particles is preferably 0.5 μm or more, more preferably 1 μm or more, and even more preferably 5 μm or more. Furthermore, the average particle size of the inorganic porous particles is preferably 30 μm or less, more preferably 10 μm or less, and even more preferably 7 μm or less.

[0041] From the viewpoint of gas adsorption properties and film transparency, zeolites are preferred as inorganic porous particles. Zeolite is a general term for crystalline aluminosilicates, and its general formula is M 2 / n This is represented as O·Al₂O₃·xSiO₂·yH₂O. M is the metal cation, n is the valence of the metal cation, and x and y are the moles of SiO₂ and H₂O, respectively. The term "zeolite" as used here is not particularly limited and may refer to any of the generally classified synthetic zeolites, artificial zeolites, or natural zeolites.

[0042] When the thickness (μm) of the surface layer X in contact with the inner layer Y is a, and the average particle size (μm) of the inorganic porous particles in the inner layer Y is D, it is preferable that the thickness of the surface layer X and the average particle size of the inorganic porous particles satisfy a ≤ D, more preferably a ≤ D / 2, and even more preferably a ≤ D / 4. In the case of inorganic porous particles with an average particle size of a > D, the amount of inorganic porous particles present near the film surface decreases, and the freshness preservation effect is reduced. When the thickness (μm) of the inner layer Y in contact with the surface layer X is b, it is preferable that the thickness of the inner layer Y and the average particle size D of the inorganic porous particles in the inner layer Y satisfy b ≤ D, more preferably b ≤ D / 2, and even more preferably b ≤ D / 3. When b ≤ D, there are more inorganic porous particles near the film surface, which enhances the freshness preservation effect.

[0043] In the present invention, the content of inorganic porous particles is preferably more than 0.2 parts by mass and less than 3 parts by mass, and more preferably between 0.3 parts by mass and 2.5 parts by mass, based on 100 parts by mass of the inner layer forming composition, from the viewpoint of achieving both freshness preservation of fruits and vegetables and aesthetic appeal of the packaging. If the content of inorganic porous particles is 0.2 parts by mass or less, freshness preservation will not be sufficiently achieved, and if the content of inorganic porous particles is 3 parts by mass or more, the transparency and gloss of the film may decrease, potentially impairing the aesthetic appeal of the packaging.

[0044] [Inner layer Z] The film of the present invention may have a layer (internal layer Z) between two surface layers X, having a different composition from the surface layers X and the internal layer Y. If the film of the present invention has internal layers Z, there may be two or more internal layers Z. If the film of the present invention has two or more internal layers Z, the compositions of the internal layers Z may be the same or different. The composition of the inner layer Z is not particularly limited, as long as it does not impair the effects of the present invention. The inner layer Z may be, for example, a layer formed from a composition containing a polyethylene resin and an anti-fogging agent. The polyethylene resin in the inner layer Z is as described in the section on the polyethylene resin in the surface layer X and inner layer Y. Ultra-low density polyethylene is preferred as the polyethylene resin in the inner layer Z. Furthermore, the anti-fogging agent in the inner layer Z is as described in the <Anti-fogging agent> section of the [Surface layer X]. A mixture of glycerin fatty acid ester and polyglycerin fatty acid ester is preferred as the anti-fogging agent in the inner layer Z, and a mixture in which the mass ratio of glycerin fatty acid ester to polyglycerin fatty acid ester is 50 / 50 is more preferred.

[0045] <Polyethylene-based multilayer shrink film> The film of the present invention consists of at least three layers, comprising two surface layers X, one or more internal layers Y provided between these surface layers, and an arbitrary internal layer (e.g., Z). Examples include a three-layer configuration of X / Y / X, a four-layer configuration of X / Y / Z / X, and a five-layer configuration such as X / Y / Y / Y / X, X / Y / Z / Y / X, or X / Y / Z / Z / X.

[0046] Within the limits that do not impair the effects of the present invention, in each layer constituting the film of the present invention Additives such as lubricants, anti-blocking agents, antistatic agents, and antioxidants can be used as appropriate to enhance their respective effective performance.

[0047] Within limits that do not impair the effects of the present invention, the composition used to form the surface layer X may be mixed into the internal layers (such as Y and Z). This makes it easier to adjust various physical properties according to the required characteristics. Furthermore, recycled resins such as trim and off-spec products generated during the manufacture of the film of the present invention may be mixed in, which is preferable in that it reduces the environmental burden.

[0048] The thickness composition ratio of each layer of the film of the present invention is not particularly limited, as long as it is within a range that can achieve the effects of the present invention. The overall thickness of the film of the present invention is not particularly limited, but when used as a heat-shrinkable packaging material, it is preferably 7 μm to 35 μm.

[0049] Regarding the transparency and gloss of the film of the present invention, the haze value is preferably 2.5% or less, and more preferably 2.0% or less. While a haze value of 2.5% or less provides sufficient transparency without reducing the commercial value, a haze value of 2.0% or less can further enhance the commercial value. In this specification, the haze value is measured in accordance with JIS K 7136. The gross value is preferably 145% or higher, and more preferably 150% or higher. If it is less than 145%, it may impair the appearance of the packaging. In this specification, gross values ​​are measured in accordance with JIS Z 8741.

[0050] In packaging fruits and vegetables using the polyethylene-based multilayer shrink film of the present invention, it is preferable, from the viewpoint of transportation efficiency of the packaged goods and suitability for stacking when displayed in stores, etc., to overlap and heat-shrink the fruits and vegetables, whether they are uncut or cut into two or more pieces, or fruits and vegetables placed on a tray.

[0051] For example, the multilayer shrink film of the present invention can be used to shrink-wrap fruits and vegetables in an overlapping manner by using packaging machines such as the PAW-6000B and PAW-9000B vegetable packaging machines manufactured by Nippon Polystar Co., Ltd. As a result, the film of the present invention can tightly wrap the packaged items, making it possible to stack the packages when displaying them in stores. Furthermore, it has the effect of being efficient for transportation because the packages do not take up much space when packed into cardboard boxes or containers for transport. The packaging machine described above is a three-sided heat-sealed pillow-package bag-making method, with a knurled seal for the vertical seal and a seal-and-cut heat seal for the horizontal seal. Furthermore, this packaging machine employs a PAMS system that automatically measures the vertical size of the packaged item and automatically sets the film cut length to a predetermined excess length. This allows for automatic packaging of items with different shapes, producing the optimal bag size for each item. By attaching a heat-shrink tunnel to this packaging machine and performing shrink wrapping, it is possible to produce packages with a tight, shrunk finish.

[0052] <Method for manufacturing polyethylene-based multilayer shrink film> The film of the present invention is obtained by biaxial stretching a multilayer shrink film manufactured using a composition for forming a surface layer X, an internal layer Y, and optionally an internal layer Z. Biaxial stretching can be performed by known stretching methods, such as tubular simultaneous biaxial stretching, tenter simultaneous biaxial stretching, and tenter sequential biaxial stretching. In the embodiments of the present invention, tubular simultaneous biaxial stretching is described as an example, but the invention is not limited thereto. The stretching ratio is preferably 3 to 7 times in both the longitudinal and transverse directions. A ratio of less than 3 times is undesirable because the resulting multilayer shrink film will have a low thermal shrinkage rate and may not have satisfactory shrinkage finish, while a ratio exceeding 7 times will reduce the tear strength of the multilayer shrink film. This is undesirable because it could lead to problems. Furthermore, in this invention, the film can be crosslinked by irradiating one or both sides with an electron beam in order to impart heat resistance and improve shrinkage finish. In addition, the film of this invention can be heat-treated or annealed after stretching, thereby suppressing natural shrinkage during storage. [Examples]

[0053] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. The following ingredients were used in the examples, and are listed in Tables 1 and 2 using abbreviations. A1: Linear low-density polyethylene (density 0.913 g / cm³) 3 Melt Index (hereinafter referred to as MI) 2.4g / 10 min). A2: Linear low-density polyethylene (density 0.920 g / cm³) 3 (MI 0.5g / 10 minutes). A3: Ultra-low density polyethylene (density 0.905 g / cm³) 3 (MI 0.8g / 10 minutes). A4: High-density polyethylene (density 0.964 g / cm³) 3 , MI5.2g / 10min). A5: Plant-derived linear low-density polyethylene (density 0.916 g / cm³) 3 MI 2.3g / 10 mins, biomass content 84%. B1: Synthetic zeolite (average particle size 6 μm). B2: Synthetic zeolite (average particle size 1 μm). C1: Anti-fogging agent (a mixture of glycerin fatty acid ester / polyglycerin fatty acid ester / polyoxyethylene alkyl ether in a mass ratio of 20 / 70 / 10). C2: Anti-fogging agent (a mixture of glycerin fatty acid ester and polyglycerin fatty acid ester in a mass ratio of 50 / 50).

[0054] Furthermore, the measurement and evaluation methods used in the example were as follows. (1) Film thickness: Measured in accordance with JIS Z 1709. (2) Thickness ratio: This was measured by observing the cross-section of the film under a microscope. (3) Haze value: Measured in accordance with JIS K 7136. (4) Gross value: Measured in accordance with JIS Z 8741.

[0055] (5) Packaging evaluation: Commercially available 1 / 4 cut cabbage was pre-packaged using a vegetable packaging machine (model: PAW-9000B) manufactured by Nippon Polystar Co., Ltd. under appropriate bag-making margin conditions. The pre-packaged cabbage was then kept in a shrink tunnel (manufactured by KU System Co., Ltd., model: MS8441-2) set to just 5°C below the film's heat resistance limit, for 5 seconds. Ten samples were randomly selected from the packaged samples after passing through the tunnel, and their freshness retention, heat-sealing ability, shrink finish, transparency, and gloss were evaluated according to the following criteria. <Freshness Preservation> ○: After packaging, the samples were left undisturbed in a 10°C atmosphere immediately after packaging. After 4 days, more than 60% of the packaged cabbage showed no signs of discoloration, wilting, spoilage, or other deterioration of freshness. △: After packaging, the samples were left undisturbed in a 10°C atmosphere immediately after packaging. After 4 days, 40% to less than 60% of the packaged cabbage showed no signs of discoloration, wilting, spoilage, or other deterioration of freshness. ×: After packaging, the sample was left undisturbed in a 10°C atmosphere immediately after packaging. After 4 days, less than 40% of the packaged cabbage showed no signs of discoloration, wilting, spoilage, or other deterioration of freshness. <Heat-sealing properties> ○: When a packaging sample is heat-sealed within the heat-sealing temperature range, no pinholes or seal delaminations are observed in the heat-sealed area. ×: When the packaging sample was heat-sealed within the heat-sealing temperature range, pinholes or seal deformities were observed in the heat-sealed area. <Shrinkage properties> ○: The shrink film has a sufficiently tight fit with the packaged item, and there is almost no sharpness at the corners of the packaged sample. ×: The shrink film does not fit snugly enough against the packaged item, or the corners of the packaged sample are too sharp. <Transparency> ○: The shrink film has good transparency, making it easy to identify the packaged items. ×: The shrink film has poor transparency, making it difficult to identify the packaged items, or even if the items can be identified, the appearance of the packaged items is slightly cloudy, thus reducing the commercial value of the packaged items. <Glossiness> ○: Four or more out of five people examined the packaged items wrapped in shrink film and determined that they were glossy. △: Of the five people who examined the packaged item wrapped in shrink film, 1 to 3 determined that it was glossy. ×: Of the 5 people who examined the packaged items wrapped in shrink film, 0 judged them to be glossy.

[0056] (6) Continuous productivity 〇: We were able to produce film continuously for over 16 hours. ×: During 16 hours of continuous production, equipment wear occurred, requiring equipment replacement.

[0057] Example 1 Compositions forming the surface layer X and composition forming the inner layer Y, as shown in Table 1, were melt-kneaded using three extruders set to 130°C to 250°C. The extrusion rate of each extruder was adjusted so that the thickness ratio of surface layer X / inner layer Y / surface layer X was 2 / 5 / 2, and a three-layer unstretched film was extruded from an annular die. The film was then rapidly cooled with water to obtain a tubular unstretched film. Using an electron beam irradiation device (Curetron® EBC-200) manufactured by NHV Corporation (formerly Nisshin High Voltage Co., Ltd.), both sides of a tubular unstretched film were irradiated with an electron beam at an irradiation condition of 110 kGy to perform crosslinking treatment. Next, the tubular unstretched film was guided to a tubular biaxial stretching apparatus, heated with an annular infrared heater until the temperature of the film surface reached the melting point of the resin, pressurized air was introduced into the tube to form bubbles, and the film was stretched in both the longitudinal and transverse directions at the same magnification to obtain a polyethylene-based multilayer shrink film with a thickness of 10.8 μm. As shown in Table 1, the obtained film exhibited excellent properties in terms of freshness retention, heat sealing, shrinkage finish, transparency, and gloss. Furthermore, it was possible to produce continuously for 72 hours, demonstrating good continuous productivity.

[0058] Example 2 As shown in Table 1, a polyethylene-based multilayer shrink film was obtained in the same manner as in Example 1, except that the content of zeolite (B1) in the inner layer Y was changed to 1.5 parts by mass, and the content of linear low-density polyethylene (A2) in the inner layer Y was changed to 21 parts by mass. As shown in Table 1, the obtained films exhibited excellent properties in terms of freshness retention, heat sealing, shrinkage finish, transparency, and gloss. Furthermore, continuous productivity was also good.

[0059] Example 3 The compositions forming the surface layer X, the interior layer Y, and the interior layer Z, as shown in Table 1, were melt-mixed using three extruders set to 130°C to 250°C, resulting in a thickness ratio of surface layer X / interior layer Y / interior layer Z / interior layer Y / surface layer X of 1 / 1 / 5. The extrusion rate of each extruder was adjusted to be 1 / 1, and a five-layer unstretched film was extruded from the annular die. The film was then rapidly cooled with water to obtain a tubular unstretched film. The subsequent steps were carried out in the same manner as in Example 1 to obtain a polyethylene-based multilayer shrink film. As shown in Table 1, the obtained films exhibited excellent properties in terms of freshness retention, heat sealing, shrinkage finish, transparency, and gloss. Continuous productivity was also good.

[0060] Example 4 As shown in Table 1, a polyethylene-based multilayer shrink film was obtained in the same manner as in Example 3, except that the content of zeolite (B1) in the inner layer Y was changed to 2 parts by mass and the content of linear low-density polyethylene (A2) was changed to 76 parts by mass. As shown in Table 1, the obtained films exhibited excellent properties in terms of freshness retention, heat sealing, shrinkage finish, transparency, and gloss. Continuous productivity was also good.

[0061] Example 5 As shown in Table 1, a polyethylene-based multilayer shrink film was obtained in the same manner as in Example 3, except that the zeolite (B1) of the inner layer Y was changed to B2, and the thickness ratio of surface layer X / inner layer Y / inner layer Z / inner layer Y / surface layer X was changed to 1 / 1 / 6 / 1 / 1. As shown in Table 1, the obtained films exhibited excellent properties in terms of freshness retention, heat sealing, shrinkage finish, transparency, and gloss. Continuous productivity was also good.

[0062] Example 6 As shown in Table 1, a polyethylene-based multilayer shrink film was obtained in the same manner as in Example 3, except that 77.5 parts by mass of linear low-density polyethylene (A2) in the inner layer Y was changed to 7.8 parts by mass of linear low-density polyethylene (A2) and 69.7 parts by mass of plant-derived linear low-density polyethylene (A5) [89.9% of the linear low-density polyethylene (A2) in the inner layer Y in Example 3 was changed to plant-derived linear low-density polyethylene (A5)]. As shown in Table 1, the obtained films exhibited excellent properties in terms of freshness retention, heat sealing, shrinkage finish, transparency, and gloss. Furthermore, continuous productivity was also good.

[0063] Example 7 A polyethylene-based multilayer shrink film was obtained in the same manner as in Example 3, except that the compositions of the surface layer X, inner layer Y, and inner layer Z were changed as shown in Table 2. As shown in Table 2, continuous productivity was good, and the properties of the obtained film were good in terms of heat sealing properties, shrinkage finish, transparency, and gloss, but the lack of synthetic zeolite resulted in insufficient freshness retention.

[0064] Example 8 A polyethylene-based multilayer shrink film was obtained in the same manner as in Example 3, except that the compositions of the surface layer X, inner layer Y, and inner layer Z were changed as shown in Table 2. As shown in Table 2, the obtained film exhibited good characteristics in terms of freshness retention, heat sealing properties, and shrinkage finish, but poor transparency and gloss. Equipment friction occurred after 12 hours of continuous production, resulting in insufficient continuous productivity.

[0065] Example 9 As shown in Table 2, a polyethylene-based multilayer shrink film was obtained in the same manner as in Example 3, except that the content of zeolite (B1) in the inner layer Y was changed to 0.2 parts by mass and the content of linear low-density polyethylene (A2) was changed to 77.8 parts by mass. As shown in Table 2, the properties of the obtained film were good in terms of heat sealing properties, shrinkage finish, transparency, and gloss, but the zeolite content was insufficient, which affected freshness preservation. The endurance performance was poor. Continuous productivity was good.

[0066] Example 10 As shown in Table 2, a polyethylene-based multilayer shrink film was obtained in the same manner as in Example 3, except that the content of zeolite (B1) in the inner layer Y was changed to 3 parts by mass and the content of linear low-density polyethylene (A2) was changed to 75 parts by mass. As shown in Table 2, the obtained film exhibited good characteristics in terms of freshness retention, heat sealing properties, and shrinkage finish, but poor transparency and gloss. Continuous productivity was good.

[0067] Example 11 As shown in Table 2, a polyethylene-based multilayer shrink film was obtained in the same manner as in Example 3, except that the zeolite of the inner layer Y was changed to B2 and the thickness ratio of surface layer X / inner layer Y / inner layer Z / inner layer Y / surface layer X was changed to 2 / 1 / 5 / 1 / 2. As shown in Table 2, the properties of the obtained film were good in terms of heat sealing, shrinkage finish, transparency, and gloss. However, the average particle size of the synthetic zeolite was small, and there was not enough of it near the film surface, resulting in insufficient freshness retention. Continuous productivity was good.

[0068] [Table 1]

[0069] [Table 2] [Industrial applicability]

[0070] The packaging film of the present invention, when used in heat-shrink packaging of fresh produce, can extend the period during which fresh produce is preserved after packaging, and is a shrink packaging material that is excellent in suitability for automatic packaging machines, such as heat sealing properties and shrink finish properties, and does not impair the aesthetic appearance of the packaged product. It can be used in this way.

Claims

1. Two surface layers X, One or more internal layers Y are provided between the two surface layers X. A polyethylene-based multilayer shrink film comprising at least three layers, The two surface layers X are each formed from a surface layer-forming composition containing a polyethylene resin and an anti-fogging agent, and not containing inorganic porous particles. The inner layer Y is a layer formed from an inner layer forming composition containing a polyethylene resin, an anti-fogging agent, and inorganic porous particles. The content of the inorganic porous particles is greater than 0.2 parts by mass and less than 3 parts by mass, based on 100 parts by mass of the internal layer forming composition. Polyethylene-based multilayer shrink film.

2. Of the two surface layers X, at least one surface layer X is in contact with the inner layer Y. When the thickness (μm) of the surface layer X in contact with the inner layer Y is a, and the average particle size (μm) of the inorganic porous particles in the inner layer Y is D, the thickness of the surface layer X and the average particle size of the inorganic porous particles satisfy a ≤ D. The polyethylene-based multilayer shrink film according to claim 1.

3. The polyethylene-based multilayer shrink film according to claim 1 or claim 2, wherein the inorganic porous particles are zeolite.

4. The polyethylene resin in the two surface layers X is a petroleum-derived polyethylene resin. The polyethylene resin in the inner layer Y comprises 100 parts by mass of polyethylene resin, with 0 to 90 parts by mass of plant-derived polyethylene resin and 10 to 100 parts by mass of petroleum-derived polyethylene resin. The polyethylene-based multilayer shrink film according to claim 3.

5. The aforementioned plant-derived polyethylene resin is subject to radiocarbon dating. １４ The polyethylene-based multilayer shrink film according to claim 4, wherein the plant-derived linear low-density polyethylene has a biomass content of 80% to 100% as calculated from the measured value of C.

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