Sterilizing method for package

Abstract

To provide a sterilizing method for a package excellent in sterilizing performance and capable of improving irradiation efficiency and reducing initial number of bacteria.SOLUTION: This invention relates to a sterilizing method for a package which packages a sterilization target with a heat-shrinkable multilayer film. The heat-shrinkable multilayer film has an anti-blocking agent on its internal surface and external surface. In the heat-shrinkable multilayer film, tensile moduli of elasticity in the longitudinal and lateral directions at 23°C are both 50 MPa or more and less than 200 MPa, and thermal shrinkages in the longitudinal and lateral directions at 80°C are both 35% or more and less than 60%. The package is irradiated with ultraviolet rays of a wavelength region of 200-280 nm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for sterilizing a package.

Background Art

[0002] It is known that irradiating the surface of food with deep ultraviolet light (UVC) having a wavelength of about 200 to 280 nm has a sterilizing effect. Therefore, in recent years, a sterilization technique has been developed in which food (mainly raw meat) is packaged with a film that transmits ultraviolet light and then irradiated with UVC to attack the DNA of general viable bacteria and suppress the growth of bacteria. According to this technique, there are advantages such as being able to sterilize without using chemicals, not producing resistant bacteria, and being able to sterilize with a small size and low energy.

[0003] For example, Patent Document 1 discloses a method for sterilizing raw meat vacuum-packed with a film packaging material having ultraviolet light transmissibility and heat shrinkability. After vacuum-packing raw meat with the film packaging material and irradiating it with ultraviolet light, the packaged body is treated in a high-temperature atmosphere for heat shrinkage and sterilization of the film packaging material. A method for sterilizing vacuum-packed raw meat is shown.

[0004] However, when irradiating food packaged in a film with UVC, there is a problem that due to the relationship between the irradiated UVC and the heat generation of the irradiation device, etc., the film deteriorates and the UVC does not penetrate the raw meat, and sufficient sterilization cannot be achieved. In addition, there is also a problem of reduced irradiation efficiency due to sagging or overlapping of the film packaging the food, and further improvement has been desired.

[0005] Techniques for improving the problems of such sterilization techniques using UVC irradiation have also been studied. For example, Patent Document 2 discloses a technique for enhancing sterilization performance by treating food with an organic acid prior to UVC irradiation. In addition, Patent Document 3 discloses a technique related to a film for packaging food, which includes an outer heat-sealing layer, a layer containing an aromatic (co) polyester, and at least one inner barrier layer containing polyvinylidene chloride, and is a multilayer co-extruded biaxially oriented barrier heat-shrinkable packaging film with adjusted heat shrinkage properties.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the technique disclosed in Patent Document 2, since it is necessary to newly provide a sterilization process different from UVC irradiation, there are problems such as complication of the sterilization process and increased cost of using chemicals. Furthermore, since the food is packaged with a film after being treated with an organic acid, contact with the outside occurs during film packaging, and there is also a risk of generating new bacteria, and it has been desired to reduce the number of bacteria before UVC irradiation (initial bacterial count). In addition, in the technique of Patent Document 3, although the sag of the film is improved to some extent by adjusting the heat shrinkage characteristics, it has been desired to further enhance the followability of the film and achieve more excellent irradiation efficiency. Furthermore, since contact with the outside occurs when packaging food with a film, there is also a risk of generating new bacteria, and it has been desired to reduce the initial bacterial count.

[0008] Therefore, an object of the present invention is to provide a method for sterilizing a package that is excellent in sterilization performance and enables improvement of irradiation efficiency and reduction of the initial bacterial count.

Means for Solving the Problems

[0009] The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems regarding a method for sterilizing a package formed by packaging a killed microbial cell with a heat-shrinkable multilayer film. As a result, since the inner surface and the outer surface of the heat-shrinkable multilayer film have an anti-blocking agent, when the heat-shrinkable multilayer film is formed into a bag shape, etc., the opening property of the film is enhanced, so that it becomes possible to smoothly enclose the killed microbial cells (such as raw meat), and the initial bacterial count can be reduced. Furthermore, by optimizing the longitudinal and transverse tensile elastic moduli of the heat-shrinkable multilayer film at 23°C and the longitudinal and transverse heat shrinkage rates at 80°C, the heat shrinkability and the shape followability can be enhanced, so that it has been found that the irradiation efficiency can be significantly enhanced. In addition, it has also been found that excellent sterilization performance can be obtained by setting the wavelength range of the UVC irradiated on the package to the range of 200 to 280 nm, and thus the present invention has been completed.

[0010] The present invention has been made based on the above findings, and the gist thereof is as follows. (1) A method for sterilizing a package formed by packaging a killed microbial cell with a heat-shrinkable multilayer film, wherein the heat-shrinkable multilayer film has an anti-blocking agent on the inner surface and the outer surface, and the longitudinal and transverse tensile elastic moduli of the heat-shrinkable multilayer film at 23°C are both 50 MPa or more and less than 200 MPa, and the longitudinal and transverse heat shrinkage rates at 80°C are both 35% or more and less than 60%, A method for sterilizing a package, characterized in that the package is irradiated with ultraviolet rays having a wavelength range of 200 to 280 nm.

[0011] (2) The method for sterilizing a package according to (1), characterized in that the outer surface layer of the heat-shrinkable multilayer film is a nylon layer.

[0012] (3) The method for sterilizing a package according to (1) or (2), characterized in that the oxygen transmission rate of the heat-shrinkable multilayer film is 1000 cc / (m 2 ·day·atm) or less.

[0013] (4) The method for sterilizing the package according to any one of (1) to (3), characterized in that the antiblocking agent on the inner surface is different from the antiblocking agent on the outer surface.

[0014] (5) The method for sterilizing the package according to any one of (1) to (4), characterized in that the ultraviolet light is irradiated from a position within 50 cm from the package using a UVC-LED.

[0015] (6) The method for sterilizing the package according to any one of (1) to (5), characterized in that the irradiation of the ultraviolet light is carried out after or during the packaging of the package.

[0016] (7) The method for sterilizing the package according to any one of (1) to (6), characterized in that the sterilization of the package sterilizes the general viable bacteria adhering to the package.

Effect of the Invention

[0017] According to the present invention, it is possible to provide a method for sterilizing a package that has excellent sterilization performance and enables improvement of irradiation efficiency and reduction of the initial bacterial count.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments for carrying out the present invention (hereinafter, simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an exemplification for explaining the present invention and is not intended to limit the present invention to the following contents. The present invention can be appropriately modified and implemented within the scope of its gist.

[0019] <Method for Sterilizing a Package> First, the method for sterilizing the package of the present embodiment (hereinafter, sometimes referred to as "the sterilization method of the present embodiment") will be described. The method for sterilizing the package of the present embodiment is a method for sterilizing a package formed by packaging an object to be sterilized with a heat-shrinkable multilayer film.

[0020] (Object to be Sterilized) In the method for sterilizing the package of the present embodiment, the package to be sterilized is one in which the object to be sterilized is packaged with a heat-shrinkable multilayer film. Regarding the type of the object to be sterilized, the package is not particularly limited as long as it can be sterilized. However, from the viewpoint of high sterilization effect by UVC irradiation and better enjoyment of the effect of the sterilization method according to the present invention, it is preferably food, and more preferably raw meat.

[0021] (Heat-shrinkable multilayer film) The heat-shrinkable multilayer film is a film for packaging the object to be sterilized and has heat-shrinkability. Heat-shrinkability means that the film has shrinkage performance by heat. By applying heat to the package by means of warm water, hot air, heating, etc., the heat-shrinkable multilayer film shrinks, thereby enhancing the appearance of the product and the followability to the shape of the object to be sterilized.

[0022] Regarding the shape of the heat-shrinkable multilayer film, there is no particular limitation as long as it can package the object to be sterilized, and it can be appropriately selected according to the required performance. For example, the film can be processed into a bag shape, or the film can be cut and used like a wrap. When the heat-shrinkable multilayer film is used as a bag, it can be used as a two-side seal type bag generally called a bottom seal bag. The bag is mainly manufactured by sealing and cutting one side of a tubular film in the width direction, putting the contents in, and sealing the mouth. Also, it can be used as a bag generally called a side seal bag. The bag is manufactured by fusion sealing or the like of the film.

[0023] The heat-shrinkable multilayer film includes at least an inner surface layer and an outer surface layer. Here, the inner surface layer is the layer that contacts the object to be sterilized among the multilayer films. When the heat-shrinkable multilayer film is processed into a bag shape, it becomes the innermost layer that contacts the object to be sterilized.

[0024] The inner surface layer serves as a heat-sealing layer for sealing the killed cells. The resin used for such an inner surface layer is not particularly limited. For example, it can be selected from polyethylene, an ethylene copolymer such as an ethylene-α-olefin copolymer, an ethylene-vinyl acetate copolymer, or a mixture thereof. Among them, an ethylene-α-olefin copolymer is preferable because it is excellent in stretchability and heat-sealing property.

[0025] Also, the melting temperature of the inner surface layer is preferably from 80°C to 130°C. As the ethylene-α-olefin copolymer, those polymerized using a catalyst called a single-site catalyst or a multi-site catalyst are good. Among them, those polymerized by a single-site catalyst are preferable in terms of good heat-sealing property. Further, a copolymer of ethylene and any one comonomer selected from a butene comonomer, a hexene comonomer, and an octene comonomer is more preferable. Also, in terms of transparency and heat-sealing property, the density range of the ethylene-α-olefin copolymer is preferably 0.88 to 0.92 g / cm3, and more preferably 0.89 to 0.918 g / cm3. Also, the value of the melt index measured under the measurement conditions (190°C, 21.2 N) according to the measurement conditions of JIS-K-7210 for the ethylene-α-olefin copolymer is preferably 0.5 to 7, and more preferably 1 to 4, in terms of heat shrinkage rate and suitable heat shrinkage stress.

[0026] When using an ethylene-α-olefin copolymer as the resin for the inner surface layer, it can be mixed with an ethylene-vinyl acetate copolymer, a high-pressure low-density polyethylene, a petroleum resin, a hydrogenated terpene resin, etc. as other resins within the range of 40% by weight or less. When these are mixed, physical properties such as kneadability with a surfactant such as an anti-fogging agent, transparency, and flexibility can be imparted. In terms of good heat-sealing property, the amount of the ethylene-α-olefin copolymer is preferably 60% by weight or more. The mixing amount range of the other resin is preferably 5% by weight or more and 20% by weight or less.

[0027] In addition, the outer surface layer is the layer that forms the outer surface among the multilayer films. When the heat-shrinkable multilayer film is processed into a bag shape, it constitutes the outer surface and becomes the layer that contacts the outside.

[0028] In order to maintain the strength of the laminated film, a resin with a relatively high melting temperature is used for the outer surface layer. Examples of the resin constituting the outer surface layer include, for example, propylene copolymers, amide resins, ester copolymers, etc. Examples of the ester copolymers include polyethylene terephthalate, polybutylene terephthalate, etc. Among them, a nylon layer made of an amide resin is preferable because it is excellent in the balance of ultraviolet transmittance, heat resistance, transparency, stretchability, etc. Here, examples of the amide resin include aliphatic amide resins such as nylon-6 and nylon-12, aliphatic amide copolymers such as nylon-6,66 and nylon-6,12, and aliphatic ternary copolymers such as nylon-6,66,12. Among them, nylon-6,66 is preferable in terms of obtaining high heat shrinkability.

[0029] The melting temperature of the outer surface layer is not particularly limited, but is preferably from 140°C to 230°C. In the case of an amide resin, the melting temperature (Tm) of the resin is preferably from 140 to 230°C in terms of obtaining high heat shrinkability and preferable heat shrinkage stress. From the same viewpoint, it is more preferably from 155 to 220°C.

[0030] In addition, when the outer surface layer is a nylon layer, it is preferable to mix 5 to 40% by weight of amorphous nylon to obtain better stretchability and appropriate heat shrinkage stress.

[0031] Furthermore, the outer surface layer preferably has a higher melting temperature than the inner surface layer, and is preferably 65 °C or more higher than the inner surface layer, and more preferably 90It is more preferable that it is higher than [temperature value]. When the melting temperature of the outer surface layer is somewhat higher than that of the inner surface layer, when the film is formed into a bag shape, when heat is applied to the portions where multiple bags are overlapped during sealing of the inner surface layer and they are heat-sealed together, the bags (outer surface layers) do not weld to each other. That is, it is because the overlapping sealability is excellent. By having excellent overlapping sealability, the number of packaging bags per unit time can be increased, and productivity can be improved.

[0032] Here, regarding the difference in melting temperature between the outer surface layer and the inner surface layer, since the value of the melting temperature (Tm) measured by a differential scanning calorimeter (DSC) according to JIS-K-7121 is the peak value, some crystals of the resin have started to dissolve even at the temperature until reaching Tm. Some of them may cause stickiness. If stickiness occurs, welding will occur between the overlapping film surface layers even before reaching the melting temperature, and they may adhere depending on the sealing pressure. However, if the melting temperature difference between the outer and inner layers is 65 [temperature value] °C or more, even in such a case, almost no adhesion occurs. Also, if the difference is 100 °C or more, no adhesion occurs, and the heat-sealing temperature range (usually set so that the heat-sealing temperature falls within the range of the above melting temperature difference) may widen, which is preferable. In this case, the operating tolerance range such as the temperature and speed of the packaging machine will widen.

[0033] On the other hand, when the difference in melting temperature between the outer surface layer and the inner surface layer exceeds 150 °C, generally, even if the melting temperature of the resin used as the sealing layer in the inner surface layer is low, it is about 80 °C. Therefore, as the outer surface layer, it may be necessary to use a material with a melting temperature exceeding 230 °C. However, when the melting temperature exceeds 230 °C, whitening may be observed after heat shrinkage. Considering the viewpoint of preventing whitening after shrinkage to ensure good transparency and further suppressing the yellowing of the vinylidene chloride copolymer during co-extrusion, the melting temperature difference is preferably 150 °C or less and 70 °C or more, and more preferably 150 °C or less and 135 °C or more.

[0034] In addition, when the heat-shrinkable multilayer film is made into a bag, even if the heat-applied parts of the bags are overlapped and heat-sealed, the bags will not weld to each other. Packaging of relatively bulky contents such as block meat can also be carried out efficiently. In addition, when a package vacuum-packed with a stretched laminated film is immersed in a hot water bath at 70 to 90 °C for several seconds, for example, the stretched laminated film shrinks thermally and becomes a tight and beautiful package. For example, in the case of raw meat packaging, by tightly tension-packaging, the appearance of the packaged meat is improved and the commercial value is increased. Also, an effect of suppressing the accumulation of gravy and blood and suppressing the growth of bacteria can be obtained.

[0035] And in the sterilization method of the package of the present embodiment, the heat-shrinkable multilayer film has an anti-blocking agent on the inner surface and the outer surface. Since the anti-blocking agent is present on the inner surface and the outer surface of the heat-shrinkable multilayer film, the opening property of the film is enhanced, so that the insertion and packaging of the object to be sterilized such as raw meat become smoother, and as a result, the initial bacterial count of the package can be significantly reduced.

[0036] Here, the anti-blocking agent has an effect of enhancing the opening property by reducing the contact points with the object to be sterilized. The type of the anti-blocking agent is not particularly limited as long as it can enhance the opening property of the film, and it can be appropriately selected according to the required performance and the materials of the inner surface layer and the outer surface layer. As the anti-blocking agent, for example, surfactants such as glycerin fatty acid esters, antioxidants, antistatic agents, petroleum resins, mineral oils, fatty acid amide lubricants, silicon oxides, calcium carbonates, talc, etc. can be used. Furthermore, among the above-described anti-blocking agents, it is preferable that the inner surface and the outer surface have a mixture of silica and starch. This is because more excellent opening property can be obtained and the initial bacterial count can be further reduced.

[0037] In addition, having an anti-blocking agent on the inner surface and the outer surface means that the anti-blocking agent only needs to be present on the inner surface and the outer surface of the film. For example, the anti-blocking agent can be contained in the inner surface layer and the outer surface layer, or the anti-blocking agent can be adhered onto the inner surface layer and the outer surface layer, and it can be appropriately selected according to the use and the required performance.

[0038] Also, the anti-blocking agent on the inner surface and the anti-blocking agent on the outer surface may be the same or different. However, from the perspective of achieving compatibility with equipment and food safety, it is preferably different. Note that the anti-blocking agents being "the same" means that not only the types of the materials of the anti-blocking agents are the same, but also all conditions such as molecular weight and surface treatment are the same. Even when using the same type of anti-blocking agent (for example, both are calcium carbonate), if the molecular weight, processing method, etc. of each anti-blocking agent are different, they are regarded as different.

[0039] Furthermore, the heat-shrinkable multilayer film preferably further includes a barrier layer. By having this barrier layer and having gas barrier properties, particularly oxygen barrier properties, oxidative deterioration of the contents can be prevented. From the perspective of oxygen barrier performance, it is preferable to use a barrier resin, such as a vinylidene chloride copolymer, an ethylene-vinyl alcohol copolymer, etc., in the barrier layer. A vinylidene chloride copolymer is a polymer of vinylidene chloride and other monomers. As the vinylidene chloride copolymer, it is preferably a vinylidene chloride-vinyl chloride copolymer or a vinylidene chloride-methyl acrylate copolymer. In addition, an ethylene-vinyl alcohol copolymer is a copolymer of ethylene and vinyl alcohol. The barrier property can be adjusted according to the copolymerization ratio of ethylene and vinyl alcohol as raw materials. The higher the content of vinyl alcohol, the higher the gas barrier property. However, the gas barrier property decreases under a high humidity environment. Therefore, the copolymerization ratio can be appropriately selected according to the application and the type of the object to be packaged.

[0040] In addition, the oxygen barrier property is also affected by the addition amounts of heat stabilizers and plasticizers mixed in the resin, the thickness of the barrier layer, etc., but also by the oxygen permeability of the resin itself. In the case of a vinylidene chloride copolymer, a vinylidene chloride copolymer with a generally high copolymer ratio of vinylidene chloride comonomer and a high melting temperature is selected in terms of high oxygen barrier property.

[0041] On the other hand, the melting temperature of the barrier layer is preferably 140°C or higher and less than 190°C. This is preferable because whitening after heat shrinkage caused by the difference in the heat shrinkage rate between the inner surface layer and the outer surface layer is less likely to occur, the degree of cloudiness is low, stickiness of the resin is less likely to occur, and stable production can be achieved. More preferably, it is 145°C or higher and less than 185°C.

[0042] In addition, as a factor for adjusting the melting temperature of the barrier layer, the copolymerization ratio of the comonomer of the vinylidene chloride copolymer can be mentioned. The melting temperature decreases by reducing the vinylidene chloride content. When using a vinylidene chloride-vinyl chloride copolymer as the vinylidene chloride copolymer, the vinyl chloride content is preferably 10 to 40% by weight. More preferably, it is more than 10.5% by weight and 34.5% by weight or less, still more preferably more than 11.0% by weight and 32% by weight or less, and most preferably more than 11.5% by weight and 29.5% by weight or less. Further, when using a vinylidene chloride-methyl acrylate copolymer as the vinylidene chloride copolymer, the methyl acrylate content is preferably 6 to 12% by weight, and more preferably 8 to 11% by weight.

[0043] In addition, in order to facilitate melt processing and enable stable production, heat stabilizers and plasticizers may be added to the barrier layer within a range that does not affect the effects of the present invention. It is preferable to add them in the range of 1 to 10% by weight. Heat stabilizers and plasticizers have little effect on the melting temperature of the vinylidene chloride copolymer. Additives such as epoxidized linseed oil and epoxidized soybean oil may be used as heat stabilizer-cum-plasticizers. The preferable addition amount of these is 2 to 5% by weight. Furthermore, lubricants such as fatty acid amide-based lubricants, and powders such as silicon oxide, calcium carbonate, and talc may be added to the vinylidene chloride copolymer. Among them, since it accelerates the crystallization rate as a crystal nucleus of the vinylidene chloride copolymer before stretching and improves the heat shrinkability, it is preferable to add 0.005 to 0.3% by weight of talc. From the viewpoint of good oxygen permeability, the thickness ratio of the barrier layer to the total layer is preferably 5 to 30%, more preferably 6 to 20%.

[0044] Also, the oxygen permeability of the entire heat-shrinkable multilayer film is preferably 1000 cc / (m 2 ·day·atm 23°C 0%RH) or less, more preferably 900 cc / (m 2 ·day·atm 23°C 0%RH) or less. More excellent gas barrier properties can be obtained, and oxidation and deterioration of the cells to be killed can be prevented. In addition, by being able to block oxygen, the sterilized state can be maintained for a long period of time.

[0045] Furthermore, the heat-shrinkable multilayer film may further include an adhesive layer between the barrier layer and the inner surface layer and / or between the barrier layer and the outer surface layer. By further providing an adhesive layer, the interlayer adhesiveness can be enhanced. As the resin that can be used for the adhesive layer, an ethylene copolymer can be used. Preferably, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, polyethylene ionomer, ethylene-ethyl acrylate copolymer, ethylene-maleic anhydride copolymer, etc. can be used. Among them, since the interlayer adhesion strength, stretchability, heat shrinkability, crosslinking characteristics when irradiated with electron beams, etc. between each surface layer and the barrier layer are good, it is preferable to use an ethylene-vinyl acetate copolymer.

[0046] In addition, it is preferable to irradiate the heat-shrinkable multilayer film with ionizing radiation before stretching. Thereby, in particular, the outer surface layer is crosslinked, and the stretchability of the film is enhanced. Since the vinylidene chloride copolymer becomes severely yellowed when strongly irradiated, it is preferable to adjust so that the irradiation does not reach that layer. Generally, the effective depth of ionizing radiation is adjusted by the acceleration voltage. As the ionizing radiation irradiation, ionizing radiation such as α-rays, β-rays, γ-rays, neutron rays, and electron rays is irradiated.

[0047] Further, in the sterilization method of the present embodiment, it is necessary that the tensile elastic modulus in the longitudinal direction and the transverse direction of the heat-shrinkable multilayer film at 23°C is both 50 MPa or more and less than 200 MPa, and the heat shrinkage rate in the longitudinal direction and the transverse direction at 80°C is both 35% or more and less than 60%. In the heat-shrinkable multilayer film, the tensile elastic modulus in the longitudinal direction and the transverse direction at 23°C and the heat shrinkage rate in the longitudinal direction and the transverse direction at 80°C are all very important parameters from the viewpoints of followability and strength when the heat-shrinkable multilayer film is used to package the cells to be killed by heat shrinkage. Therefore, in the sterilization method of the present embodiment, by satisfying the relationship between the tensile elastic modulus and the heat shrinkage rate described above for the heat-shrinkable multilayer film, the heat shrinkability, shape followability, film strength, etc. of the heat-shrinkable multilayer film can be improved well in balance, and thus the irradiation efficiency can be greatly improved.

[0048] Here, the reason for defining the tensile elastic modulus in the longitudinal direction (film flow direction) and the transverse direction (film width direction) of the heat-shrinkable multilayer film at 23°C to be both 50 MPa or more and less than 200 MPa is that when the tensile elastic modulus is 50 MPa or more, the strength of the heat-shrinkable multilayer film can be maintained well, and when it is less than 200 MPa, the followability of the heat-shrinkable multilayer film can be enhanced. In addition, the tensile elastic modulus can be measured in accordance with ASTM-D882.

[0049] In addition, the reason for specifying that the thermal shrinkage rates in the longitudinal direction (the film flow direction) and the transverse direction (the film width direction) of the heat-shrinkable multilayer film at 80°C are both 35% or more and less than 60% is that when the thermal shrinkage rate is 35% or more, the followability of the heat-shrinkable multilayer film can be enhanced, and when it is less than 60%, the strength of the heat-shrinkable multilayer film can be maintained well. Note that the thermal shrinkage rate can be measured in accordance with ASTM D-2732.

[0050] (Ultraviolet rays) The sterilization method of the package of this embodiment irradiates the package with ultraviolet rays having a wavelength range of 200 to 280 nm. The ultraviolet rays (UVC) having a wavelength range of 200 to 280 nm have the highest sterilization effect among ultraviolet rays and can sterilize by inactivating bacteria. Therefore, it is effective in terms of not using chemicals and not generating resistant bacteria. Also, it does not require a large-scale device and has advantages from the viewpoints of energy saving and the cost required for sterilization.

[0051] Here, the irradiation of the ultraviolet rays having a wavelength range of 200 to 280 nm is preferably carried out after or during the packaging of the package. Since the effects of reducing the initial bacterial count and improving the irradiation efficiency by enhancing the shape followability by the sterilization method of this embodiment are exerted after or during the packaging of the package, higher sterilization effects can be obtained by irradiating ultraviolet rays at these timings.

[0052] Note that the sterilization of the package according to this embodiment preferably sterilizes the general viable bacteria attached to the package. General viable bacteria are mesophilic aerobic bacteria that grow by culturing at 35°C for 48 hours under aerobic conditions using a standard agar medium. These bacteria often adhere to the object to be sterilized, and sterilizing these bacteria is desirable from the viewpoint of bactericidal property. Examples of the general viable bacteria include coliform group bacteria, Salmonella bacteria, Staphylococcus aureus, Pseudomonas aeruginosa, etc.

[0053] The irradiation conditions of the ultraviolet rays are not particularly limited. For example, it is preferable to irradiate from a position within 50 cm from the package using a UVC-LED. This is because excellent sterilization performance can be achieved without using a large-scale device or causing a cost increase.

[0054] <Sterilization System for Package> The sterilization system for the package according to the present embodiment is a sterilization system for a package formed by packaging an object to be sterilized with a heat-shrinkable multilayer film, wherein the heat-shrinkable multilayer film has an anti-blocking agent on both the inner surface and the outer surface, wherein both the longitudinal and transverse tensile elastic moduli of the heat-shrinkable multilayer film at 23 °C are 50 MPa or more and less than 200 MPa, and both the longitudinal and transverse heat shrinkage rates at 80 °C are 35% or more and less than 60%, the package is irradiated with ultraviolet rays having a wavelength range of 200 to 280 nm. By having the above configuration, the system of the present embodiment is excellent in sterilization performance, and it is possible to improve the irradiation efficiency and reduce the initial bacterial count.

[0055] Note that the sterilization system for the package according to the present embodiment can be incorporated into the manufacturing process of the package as a sterilization step, or can be implemented as a sterilization device.

[0056] Note that each configuration of the sterilization system for the package of the present embodiment is the same as the content described in the sterilization method for the package of the present embodiment described above.

Examples

[0057] Hereinafter, the present invention will be described in detail with specific examples and comparative examples, but the present invention is not limited to the following examples.

[0058] <Package> The components included in each sample of the examples and comparative examples are shown below. (1) Object to be sterilized Beef was used as the killed cells.

[0059] (2) Heat-shrinkable multilayer film (2-1) As the surface layer (A) (outer surface layer), a 6 / 66 copolymer (Ny-1) was used. The melting point of the 6 / 66 copolymer was 192°C. Regarding the melting points of the surface layer (A), the adhesive layer (B), the adhesive layer (D), and the surface layer (E) described below, in accordance with JIS-K-7121, using a measuring device (DSC8500 manufactured by PerkinElmer), the melting point was measured. Specifically, after holding at 0°C for 1 minute, the temperature was raised from 0°C to 200°C at 10°C / minute and then held for 1 minute, and then, after cooling from 200°C to 0°C at 10°C / minute and holding for 1 minute, the melting point (the melting point during the second heating) when the temperature was raised from 0°C to 200°C at 10°C / minute was measured. Also, for those having multiple peaks, the maximum peak was taken as the melting point. (2-2) For both the adhesive layer (B) between the surface layer (A) and the barrier layer (C) and the adhesive layer (D) between the barrier layer (C) and the inner surface layer (E), a composition containing 20% by mass of an ethylene / vinyl acetate copolymer was used. The melting point of the ethylene / vinyl acetate copolymer was 85°C. (2-3) As the barrier layer, the following vinylidene chloride / vinyl chloride copolymer (manufactured by Asahi Corporation) was used. Regarding the melting points of the following each PVDC, in accordance with JIS-K-7121, using a measuring device (DSC8500 manufactured by PerkinElmer), the melting point was measured. Specifically, after holding at 0°C for 1 minute, the melting point when the temperature was raised from 0°C to 200°C at 10°C / minute was measured. Also, for those having multiple peaks, the maximum peak was taken as the melting point. · PVDC-1: A copolymer with VDC / VC = 83 / 17% by mass and a melting point of 145°C was used. Note that PVDC-1 contains 3.0% by mass of dibutyl sebacate (DBS), 1.0% by mass of epoxidized linseed oil (ELO), and 0.03% by mass of talc as additives. · PVDC-2: A copolymer with VDC / VC = 88 / 12% by mass and a melting point of 163°C was used. In addition, PVDC-2 contains 5.0% by mass of acetyl tributyl citrate (ATBC) and 1.3% by mass of epoxidized soybean oil (ESO) as additives. · PVDC-3: A copolymer of VDC / VC = 88 / 12% by mass with a melting point of 163°C, using a reworked vinylidene chloride (VDC) copolymer (a reworked vinylidene chloride (VDC) copolymer is one that has undergone the process of melting and solidification one or more times). In addition, after forming a film from PVDC-2 by the inflation method, the trim generated during the slit cutting of the resulting film was pulverized so that the bulk density became 0.4 to 0.7 g / cc, and 0.3% by mass of calcium stearate was contained in the pulverized product. · PVDC-4: A mixture of PVDC-1 and PVDC-3 in amounts of 80% by mass and 20% by mass, respectively, was used. · PVDC-5: A mixture of PVDC-1 and PVDC-3 in amounts of 40% by mass and 60% by mass, respectively, was used. · PVDC-6: A copolymer of VDC / VC = 88 / 12% by mass with a melting point of 163°C was used. In addition, PVDC-6 contains 3.0% by mass of dibutyl sebacate (DBS), 1.0% by mass of epoxidized linseed oil (ELO), and 0.03% by mass of talc as additives. (2-4) As the surface layer (E) (inner surface layer), an ethylene / hexene copolymer was used. The melting point of the ethylene / hexene copolymer was 98°C and the MI was 1.2 g / 10 min.

[0060] (3) Antiblocking agent Any of the following antiblocking agents was adhered onto the surface layer (A) and the surface layer (E) in an adhesion amount of 0.1 to 1% by mass. · A mixture of silicone and starch · A mixture of silica and starch · Starch

[0061] [Examples 1 to 7 and Comparative Examples 1 to 4] (1) Production of heat-shrinkable multilayer film Using the materials under the conditions shown in Table 1 and Table 2, resin was melt-extruded from an extruder corresponding to the surface layer (A), adhesive layer (B), barrier layer (C), adhesive layer (D), and surface layer (E), and after passing through a cylindrical die to create a cylindrical laminated tube, it was cooled with a water-cooling ring to obtain an unstretched laminated tube (hereinafter referred to as "parison"). Then, sampling was performed at eight equally spaced locations along a straight line in the width direction of the parison, and the cross-section was observed under a microscope to measure the thickness of each layer, and the average value of the eight locations was calculated. The obtained parison was irradiated with an electron beam at an acceleration voltage of 210 kV while adjusting the irradiation dose to achieve a predetermined gel fraction for crosslinking. Subsequently, the irradiated parison was post-heated at 80 °C and heated with an infrared heater in the stretching section (heating was adjusted to be in the range of 60 - 100 °C near the neck) to perform bubble blowing. The blown tube was folded with a deflator while being cooled with an air-cooling ring to produce a tubular stretched laminated film. The thickness of the stretched laminated film was measured at this time and adjusted with the parison thickness to achieve a predetermined thickness. The stretching ratio was adjusted to 2.5 times in the longitudinal direction and 3.0 times in the transverse direction for biaxial stretching to obtain a stretched laminated film (heat-shrinkable multilayer film) with a width of 300 mm. Note that only for the sample of Comparative Example 3, after folding the blown tube with a deflator, it was heat-set by passing through two heating rollers at 70 °C and then cooled by passing through a cooling roller. (2) Production of bags Samples of the obtained heat-shrinkable multilayer film were used to produce bag samples (bag width 300 mm, bag length 450 mm) by bottom-sealing with a bag-making machine such that the surface layer (A) was the outer layer.

[0062] <Evaluation> Regarding the samples of the heat-shrinkable multilayer film and bag samples obtained as described above, the following evaluations were performed. The evaluation results are shown in Table 1 and Table 2.

[0063] (1) Heat shrinkage rate at 80 °C Regarding the samples of the heat-shrinkable multilayer film, the heat shrinkage rate at 80 °C was measured according to ASTM D - 2732. Specifically, after marking lines or dots of 100 mm in the longitudinal direction (MD direction) and the transverse direction (TD direction), the film was immersed in a warm water bath at 80 °C for 4 seconds for free thermal shrinkage. After thermal shrinkage, the interval between the marks was measured, and the thermal shrinkage rate of the film was calculated from the following formula. Thermal shrinkage rate at 80 °C (%) = ((100 (mm) - dimension after shrinkage (mm)) / 100 (mm)) × 100

[0064] (2) Tensile modulus at 23 °C For samples of the heat-shrinkable multilayer film, in accordance with ASTM D-882, using a measuring device (Tensilon RTG-1210 manufactured by A&D Company Limited), the tensile modulus at 23 °C was measured. Specifically, samples of the heat-shrinkable multilayer film were cut into strips with a width of 10 mm, and under the conditions of a chuck distance of 50 mm, a tensile speed of 5 mm / min, and a temperature of 23 °C, the tensile modulus in the longitudinal direction (MD direction) and the transverse direction (TD direction) was measured from the load at 2% elongation. The number of test times was 5 times for both the MD direction and the TD direction, and the average value was taken as the tensile modulus (%).

[0065] (3) Appearance of meat packaging After putting 4 - 7 kg of block-shaped beef (rib roast or sirloin or outside thigh) into each sample bag, vacuum packaging was performed. Then, it was immersed in a warm water bath at 80 °C for 4 seconds for shrinkage and then cooled in a cooling bath. The appearance after cooling was evaluated according to the following criteria. ◎: The film follows the unevenness of the meat, and there are few wrinkles and the cross-section of the meat can be clearly seen. 〇: The film follows the unevenness of the meat, but there are wrinkles and it is slightly difficult to see the cross-section of the meat. ×: The film does not fully follow the unevenness of the meat. Also, there are many wrinkles and the film sags and it is difficult to see the cross-section of the meat.

[0066] (4) Film opening property When putting 4 - 7 kg of block-shaped beef (rib roast or sirloin or outside thigh) into each sample bag, the time taken was measured and evaluated according to the following criteria. ◎: Within 5 seconds 〇: 5 seconds or more and 15 seconds or less ×: More than 15 seconds

[0067] (5) Oxygen permeability For samples of the heat-shrinkable multilayer film, the amount of oxygen passing through per unit time and per unit area was measured and evaluated according to the following criteria. The machine used for measuring the amount of oxygen was the "Oxygen Permeability Measuring Device (manufactured by MOCON: OX-TRAN 2 / 21SH)" adjusted to either 23°C, 0% relative humidity, or 23°C, 65% relative humidity. ◎: Less than 100 cc / (m 2 ·day·atm) 〇: 100 cc / (m 2 ·day·atm) or more and less than 1000 cc / (m 2 ·day·atm) ×: 1000 cc / (m 2 ·day·atm) or more

[0068] (6) Sterilization performance After putting 4 - 7 kg of block-shaped beef (rib roast or sirloin or outside thigh) into each sample of the bag, vacuum packaging was performed to produce a package. During the production of the produced package (after putting the beef into the bag, sealing the inlet, and until the sealing is completed) and after production (immediately after heat-shrinking the sealed package), ultraviolet light (UVC) was irradiated under the conditions shown in Table 1 and Table 2. For the package using the sample of the bag in Example 1, four types of ultraviolet light with wavelengths of 220 nm, 254 nm, 265 nm, and 280 nm were irradiated. For the packages using the samples of the bags in other Examples and Comparative Examples, only ultraviolet light with a wavelength of 265 nm was irradiated. After ultraviolet irradiation, the package was left at 2°C for 2 months, and then the total viable bacteria present in the package were measured by the pour plate method using a standard agar medium and culturing at 35.0 ± 1.0°C for 48 ± 3 hours. All colonies grown on the medium were counted, and the measured total viable bacteria count was evaluated according to the following criteria. ◎: 10×10 2 or more and less than 10×10 3 〇: 10×10​3 Above, 10×10 5 Less than △: 10×10 5 Above, 10×10 7 Less than ×: 10×10 7 Above

[0069]

Table 1

Table 2

[0070] From the results of Tables 1 and 2, it was found that each sample of the examples showed well-balanced and good results in all evaluation items. On the other hand, it was found that each sample of the comparative examples showed inferior results compared to the examples in at least one evaluation item.

Industrial Applicability

[0071] According to the present invention, it is possible to provide a method for sterilizing a package that is excellent in sterilization performance and enables improvement of irradiation efficiency and reduction of initial bacterial count.

Claims

1. A method for sterilizing a package obtained by packaging a bactericidal target with a heat-shrinkable multilayer film, comprising: the heat-shrinkable multilayer film has an anti-blocking agent on its inner surface and outer surface; the heat-shrinkable multilayer film has a longitudinal and a transverse tensile elastic modulus at 23°C both of which are 50 MPa or more and less than 200 MPa, and a longitudinal and a transverse heat shrinkage rate at 80°C both of which are 35% or more and less than 60%; irradiating the package with ultraviolet rays having a wavelength range of 200 to 280 nm. A method for sterilizing a package, characterized in that.

2. The method for sterilizing a package according to claim 1, characterized in that an outer surface layer of the heat-shrinkable multilayer film is a nylon layer.

3. The oxygen transmission rate of the heat-shrinkable multilayer film is 1000 cc / (m ２ ·day·atm) or less, and the method for sterilizing the package according to claim 1 or 2 is characterized by this.

4. The method for sterilizing a package according to claim 1 or 2, characterized in that the anti-blocking agent on the inner surface is different from the anti-blocking agent on the outer surface.

5. The method for sterilizing a package according to claim 1 or 2, characterized in that the ultraviolet rays are irradiated from a position within 50 cm from the package using a UVC-LED.

6. The method for sterilizing a package according to claim 1 or 2, characterized in that the irradiation of the ultraviolet rays is carried out after or during the packaging of the package.

7. The method for sterilizing a package according to claim 1 or 2, characterized in that the sterilization of the package sterilizes general viable bacteria adhering to the package.

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