Method for evaluating container filled with content

Abstract

To provide a method for evaluating of the quality of a container filled with a content which is subjected to sterilization by heating and pressurizing after carbon gas replacement, in a container having an oxygen absorption layer containing a ferrous oxygen absorbent.SOLUTION: A method for evaluating of the quality of a container filled with a content that is filled with a content in the container, is subjected to carbon gas replacement, is sealed by a lid, and then is subjected to sterilization by heating and pressurizing includes at least an oxygen absorption layer containing a base material layer composed of an olefinic resin, a barrier layer and an oxygen absorbent including reduced ion, and has a contact part and a bottom having a variable part surrounded by the contact part, wherein the lid has flexibility, after the sterilization treatment by heating and pressurizing, after a decompressed state is maintained for 24 hours, the method evaluates the quality of the container filled with the content, on the basis of the displacement between a container axial direction position at the center of the variable part or the vicinity of the lid center of the container filled with the content, and container axial direction positions at the center of the variable part and the vicinity of the lid center of the container filled with the content after the lapse of two weeks after the sterilization treatment by heating and pressurizing.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating filled containers, and more specifically to a method for evaluating filled containers that have been filled with contents and have an oxygen absorbing layer containing a barrier layer and an iron-based oxygen absorber, and have been subjected to a heat and pressure sterilization process after carbon dioxide substitution. [Background technology]

[0002] BACKGROUND ART Multilayer containers having a barrier layer and an oxygen absorbing layer containing an iron-based oxygen absorber have been known as containers having excellent storage properties for the contents. For example, Patent Document 1 below describes a multilayer plastic container having inner and outer layers made of polypropylene, a first intermediate layer (barrier layer) made of EVOH located on the outer layer side, and a second intermediate layer (oxygen absorbing layer) made of a resin composition containing an iron-based oxygen absorber located on the inner layer side.

[0003] It is also known that the headspace inside a container can be substituted with carbon dioxide or nitrogen gas to improve the shelf life of the contents. For example, Patent Document 2 listed below describes a liquid processed food in which the headspace of the package after heat-sealing or heat-sterilization is substantially free of oxygen gas, by replacing the oxygen dissolved in the liquid food with nitrogen gas and / or carbon dioxide gas before the liquid food is heated and sealed and packaged in a packaging material made of an oxygen-absorbing laminated material, or by replacing the air in the headspace with nitrogen gas and / or carbon dioxide gas after filling.

[0004] Purging the container with carbon dioxide or other gas not only maintains quality, but also removes oxygen from the container. When the container is subjected to a heated and pressurized sterilization process such as retort sterilization after carbon dioxide substitution, the carbon dioxide dissolves in the contents, creating a negative pressure inside the container and causing the bottom and lid to deform into a concave shape, making it possible to see at a glance that the container is sealed; this fact is used to determine whether the container is airtight or not (Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3630706 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-14374 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-3445 Summary of the Invention [Problem to be solved by the invention]

[0006] However, it has been found that in containers equipped with an oxygen absorbing layer containing the above-mentioned iron-based oxygen absorber, when carbon dioxide gas replacement is followed by heat and pressure sterilization, the carbon dioxide gas reacts with the iron in the oxygen absorber to generate hydrogen, and this hydrogen gas causes the container to swell. In particular, in tray-shaped containers with wide bottoms or containers sealed with flexible lids, the swelling caused by the hydrogen gas is easily noticeable on the flat bottom or lid, and even if the seal is ensured, this raises suspicions that the contents may have spoiled or that bacteria have proliferated. Even if there is no problem with the contents, the contents may be deemed unshippable, making it difficult to carry out accurate inspections.

[0007] Therefore, an object of the present invention is to provide a method for evaluating the quality of a filled container that has been subjected to carbon dioxide gas replacement and then heat-pressure sterilization in a container equipped with an oxygen absorbing layer containing an iron-based oxygen absorber. Another object of the present invention is to provide a method for evaluating the quality of a filled container in which hydrogen gas generated by the reaction between reduced iron and carbon dioxide during heat and pressure sterilization has been released outside the container. [Means for solving the problem]

[0008] According to the present invention, there is provided a method for evaluating the quality of a filled container which has been filled with contents, subjected to carbon dioxide gas replacement, sealed with a lid, and then subjected to heat and pressure sterilization, wherein the container comprises at least a base layer made of an olefin-based resin, a barrier layer, and an oxygen absorbing layer containing an oxygen absorber including reduced iron, and has a bottom with a grounding portion and a variable portion surrounded by the grounding portion, and the lid is flexible, and after maintaining a reduced pressure state for 24 hours after the heat and pressure sterilization treatment, the quality of the filled container is evaluated based on the displacement between the axial position of the container near the center of the variable portion or the center of the lid of the filled container and the axial position of the container near the center of the variable portion or the center of the lid of the filled container two weeks after the heat and pressure sterilization treatment.

[0009] In the method for evaluating a content-filled water container of the present invention, (1) The container is filled with a water-containing material, and hydrogen generated in the container by the reaction of water, carbon dioxide, and iron is released to the outside of the container by permeating the container wall during the heat and pressure sterilization treatment. (2) The displacement occurs in accordance with the amount of hydrogen generated in the container by a reaction between the water in the contents, the carbon dioxide gas, and the reduced iron. (3) The displacement occurs due to spoilage of the contents. (4) The carbon dioxide concentration in the carbon dioxide substitution is less than 55%. (5) The oxygen absorbing layer contains 1 to 30 parts by mass of an oxygen absorber per 100 parts by mass of the base resin of the oxygen absorbing layer. (6) The barrier layer is made of an ethylene-vinyl alcohol copolymer and has a thickness of 120 μm or less. (7) The thickness of the oxygen absorbing layer is 1.5 times or more the thickness of the barrier layer. (8) The olefin-based resin is polypropylene. (9) The substrate layer is an inner layer and an outer layer, and the oxygen absorbing layer is located on the inner layer side of the barrier layer. is preferred. [Effects of the Invention]

[0010] According to the evaluation method of the present invention, a container having at least a substrate layer made of an olefin resin, a barrier layer, and an oxygen absorbing layer containing an iron-based oxygen absorber is filled with contents, and the sealed container is subjected to carbon dioxide gas replacement and heat and pressure sterilization. After this, the quality of the filled container can be easily evaluated based on the displacement near the center of the adjustable part at the bottom of the container and / or the center of the lid. Note that, in the evaluation method of the present invention, the displacement occurs due to the amount of hydrogen generated by the reaction between carbon dioxide due to carbon dioxide replacement and reduced iron in the oxygen absorbing layer, or the amount of methane gas generated by spoilage of the contents, and therefore, it is possible to select containers in which such gases are present. In particular, in the evaluation method of the present invention, by setting the carbon dioxide concentration in the container during carbon dioxide substitution to less than 55% and setting the amount of oxygen absorbent in the oxygen absorbing layer to 1 to 30 parts by mass per 100 parts by mass of base resin, it is possible to reduce the amount of reaction between carbon dioxide and the reduced iron in the oxygen absorbent, suppress the occurrence of displacement due to hydrogen gas, and detect displacement caused by spoilage of the contents, making it easy to identify defective products. Furthermore, by using an ethylene-vinyl alcohol copolymer as the barrier layer of the container, hydrogen gas generated by the reaction between carbon dioxide and reduced iron in the oxygen absorbing layer during heat-pressure sterilization can escape to the outside of the container during the heat-pressure sterilization process, while excellent barrier properties can be maintained after the heat-pressure sterilization process. Therefore, in this case as well, displacement due to hydrogen gas can be suppressed, and displacement caused by spoilage of the contents can be detected, making it easier to identify defective products. [Brief explanation of the drawings]

[0011] [Figure 1] 10A and 10B are diagrams illustrating a method for measuring the degree of bulging (displacement) caused by the bottom of a sealed container. [Figure 2] 10 is a diagram illustrating a method for measuring the degree of swelling (displacement) caused by a lid material of a sealed container. FIG. [Figure 3] FIG. 1 is a cross-sectional view illustrating an example of a laminated structure of a container according to the present invention. [Figure 4] 1 is a cross-sectional view showing another example of the laminated structure of a container of the present invention. [Figure 5] 3 is a photograph of the sealed containers obtained in Example 1 and Comparative Example 2 taken from above. [Figure 6] 1 is a photograph of the sealed container obtained in Comparative Example 1 taken from above. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the method of the present invention for evaluating the quality of a filled container, an important feature is that the container to be evaluated has at least a substrate layer made of an olefin-based resin, a barrier layer, and an oxygen absorbing layer containing an oxygen absorber including reduced iron, and that the bottom of the container has a grounding portion and a variable portion surrounded by the grounding portion, or that the lid is flexible. In the present invention, the container is filled with the contents, carbon dioxide gas is replaced, the container is sealed with a lid, and then the filled container is subjected to heat and pressure sterilization.The quality of the filled container is evaluated based on the displacement between the axial position of the center of the variable part or near the center of the lid of the filled container 24 hours after the heat and pressure sterilization process and the axial position of the center of the variable part or near the center of the lid of the filled container 2 weeks after the heat and pressure sterilization process.

[0013] FIG. 1 is a diagram for explaining a method of evaluation based on the displacement of the bottom of a container in the evaluation method of the present invention. FIG. 1(A) is a schematic cross-sectional view showing an example of a container to be evaluated. Container 10 generally comprises body 11 and bottom 12. Bottom 12 is formed with base 13 and panel-shaped variable portion 14, which is surrounded by base 13 and located a distance H above base 13 in the axial direction of the container. As shown in FIG. 1(B), immediately after container 10 is filled with contents, carbon dioxide gas is purged, and the container is sealed with lid 15, panel-shaped variable portion 14 protrudes downward in the axial direction of the container, with its apex near the center. When the container is then cooled by being stored at room temperature, the pressure inside the container is reduced, and after this reduced pressure state is maintained for 24 hours, panel-shaped variable portion 14 protrudes upward in the axial direction of the container, with its apex near the center, as shown in FIG. 1(C), and is elevated a distance H0 above base 13 in the axial direction of the container. After the sealed container has cooled, if hydrogen gas is generated inside the container or the contents are spoiled, the distance H1 from the grounding portion of the panel-shaped variable portion 14 in the axial direction of the container will be as shown in Figure 1(D), and the panel-shaped variable portion 14 will protrude downward. In the evaluation method of the present invention, the quality of a filled container can be determined based on the displacement ΔH (H0-H1) of the axial position of the variable bottom portion of the container. Although it cannot be determined in general terms depending on the material and thickness of the container or the type of contents, if this displacement ΔH is 0.1 mm or less, it can be determined to be a good product with no practical problems.

[0014] If the container bottom does not have a grounding portion or a panel-shaped variable portion, the quality of the filled container can be evaluated by the displacement of the flexible lid, as shown in FIG. Specifically, after a flat-bottomed container 10 is filled with contents, carbon dioxide gas is purged, and the container is sealed with lid 15 (FIG. 2(A)), immediately after heat and pressure sterilization, lid 15 protrudes upward in the axial direction of the container, with its apex near the center, as shown in FIG. 2(B). When the container is then cooled by being stored at room temperature, the pressure inside the container is reduced, and after this reduced pressure state is maintained for 24 hours, the sealed container becomes depressed in the axial direction of the container, with its apex near the center, as shown in FIG. 2(C), and lid 15 is displaced by a distance H0 from the state shown in FIG. 2(A). If hydrogen gas is generated inside the sealed container or the contents spoil, the displacement of lid 15, which is the distance H1, will be as shown in FIG. 2(D), and lid 15 will have an upward protruding portion. In the evaluation method of the present invention, the quality of a filled container can also be determined based on the displacement ΔH (H0-H1) of the axial position of the flexible lid material, and although this cannot be determined in general terms depending on the material or thickness of the lid material or the type of contents, if this displacement ΔH is 0.1 mm or less, it can be determined to be a good product with no practical problems.

[0015] (container) The containers that are the subject of the evaluation method of the present invention are made of a laminate including at least a substrate layer made of an olefin-based resin, a barrier layer, and an oxygen absorbing layer containing an oxygen absorber containing reduced iron, and are sealed after being filled with the contents and subjected to carbon dioxide gas replacement and heat-pressure sterilization. As described above, when the above-mentioned container is filled with the contents, carbon dioxide gas is replaced, and then the container is subjected to a heat and pressure sterilization process such as retort sterilization, the reduced iron contained in the oxygen absorbing layer reacts with carbon dioxide to generate hydrogen, which causes a problem of bulging at the bottom or lid of the container, which has been made negative pressure by the heat and pressure sterilization process. To solve this problem, it is necessary to efficiently release the hydrogen generated inside the container to the outside of the container and to reduce the amount of reduced iron in the oxygen absorbing layer to suppress the reaction with carbon dioxide and thereby reduce the generation of hydrogen. However, if the permeability of the container wall is increased, the amount of oxygen that permeates from outside the container increases, and if the amount of reduced iron is reduced, the oxygen absorbing performance decreases, increasing the oxygen concentration inside the container, resulting in a new problem of reduced shelf life of the contents.

[0016] In order to solve such problems, in the evaluation method of the present invention, the oxygen permeability (ml / m) of the laminate constituting the container to be evaluated at 20°C and 100% RH is 2 ·day·MPa) and oxygen absorption at 50℃ (ml / cm 2 It is preferable to use a container made of a laminate having a product of heat resistance, humidity, and humidity (H2O / H2O·hr) of 6.0 or more. The oxygen permeability and oxygen absorption of the laminate can be approximated to those measured by the method described in the Examples below using a sample cut out from the bottom of a container, because the bottom of the container is hardly stretched and maintains the properties of the laminate even when the container is formed by vacuum forming or the like.

[0017] Furthermore, in the evaluation method of the present invention, it is preferable that the carbon dioxide concentration in the container filled with the contents to be evaluated during carbon dioxide replacement is less than 55%. This reduces the amount of reaction between reduced iron and carbon dioxide in the oxygen absorbing layer, thereby suppressing the amount of hydrogen gas generated. Furthermore, by setting the content of reduced iron in the oxygen absorbing layer to 1 to 30 parts by mass per 100 parts by mass of base resin, combined with the reduction in the carbon dioxide concentration in the container as described above, the amount of hydrogen gas generated is suppressed, suppressing displacement caused by hydrogen gas, and making it possible to determine displacement due to spoilage of the contents and detect defective products. Furthermore, the containers that can be used in the evaluation method of the present invention are those that allow hydrogen generated inside the container to escape through the container wall during heat and pressure sterilization, while at the same time exhibiting barrier properties after heat and pressure sterilization, and are equipped with a barrier layer that can maintain the reduced pressure inside the container. This suppresses displacement due to hydrogen gas and makes it possible to detect displacement due to spoilage of the contents. An example of such a barrier layer is a layer made of ethylene vinyl alcohol copolymer (EVOH). EVOH tends to have reduced barrier properties under high-temperature, high-humidity conditions such as those used in retort sterilization, but it can efficiently expel hydrogen gas generated during retort sterilization from the container under hydrothermal conditions, while exhibiting favorable oxygen barrier properties in environments other than these conditions.

[0018] [Oxygen absorption layer] In the container that is the subject of the evaluation method of the present invention, the oxygen absorbing layer is made of an oxygen absorbing resin composition in which an iron-based oxygen absorber having reduced iron is contained in a base resin. Any known iron-based oxygen absorbent can be used, and those containing reduced iron and metal halide can be preferably used. Rotary reduced iron powder can be preferably used as the reduced iron. Rotary reduced iron powder has high purity and a large specific surface area, and therefore has excellent oxygen absorption performance. The reduced iron content in the oxygen absorber is preferably in the range of 1 to 30 mass %, more preferably 10 to 30 mass %. The metal halide may be a chloride, bromide, or iodide of an alkali metal or alkaline earth metal, with calcium chloride being particularly preferred. The metal halide is preferably contained in an amount of 0.1 to 10 parts by mass per 100 parts by mass of reduced iron, and it is preferred to use a mixture of these metal halides in advance so that the metal halide does not easily separate from the reduced iron powder.

[0019] In addition to reduced iron and metal halide, the oxygen absorber may further contain an alkaline substance such as calcium hydroxide or calcium oxide, which is a dehydrated product of calcium hydroxide. The inclusion of an alkaline substance can reduce the amount of hydrogen generated by the reaction between iron and water. The alkaline substance is preferably blended in an amount of 0.5 to 2 parts by mass, particularly 1 to 2 parts by mass, per 100 parts by mass of reduced iron.

[0020] The oxygen absorber can be prepared by a conventionally known method. For example, reduced iron is coarsely pulverized, and then a metal halide and, if necessary, an alkaline substance are added thereto and the resulting mixture is finely pulverized while being mixed. The finely pulverized product is then classified to remove coarse particles, and then heat-treated. After the heat treatment, the product is further classified, if necessary, to remove coarse particles, thereby obtaining the oxygen absorber.

[0021] The oxygen absorber is preferably contained in an amount of 1 to 30 parts by mass, particularly 10 to 30 parts by mass, per 100 parts by mass of the base resin. If the amount of oxygen absorber is less than the above range, there is a risk that sufficient oxygen absorption performance will not be exhibited compared to when it is within the above range, while if the amount of oxygen absorber is more than the above range, there is a risk that the amount of hydrogen generated by reaction with carbon dioxide will be greater compared to when it is within the above range. From the viewpoint of interlayer adhesion, the base resin is preferably made of an olefin-based resin similar to that used for the substrate layer described below. In addition, since the base resin is made of an olefin-based resin with high gas permeability, the remaining oxygen can be easily transferred to the oxygen absorbing layer, and the oxygen absorbing reaction can be carried out efficiently.

[0022] [Barrier layer] The barrier layer of the container to be evaluated by the present invention can be made of a conventionally known barrier resin. Suitable examples of such barrier resins include ethylene vinyl alcohol copolymer (EVOH) and polyamide resins. Examples of polyamide resins include nylon 6, nylon 6,6, nylon 6 / 6,6 copolymer, nylon 6,10, nylon 11, nylon 12, nylon 13, and xylylene group-containing polyamides such as metaxylylene adipamide and metaxylylene sebacamide. Among these, as mentioned above, EVOH is particularly suitable for satisfying the requirement of blocking the permeation of oxygen from outside the container while allowing hydrogen generated inside the container during heat and pressure sterilization to permeate outside the container. Any known ethylene-vinyl alcohol copolymer can be used without limitation. However, from the viewpoint of barrier properties and recyclability in particular, a saponified copolymer obtained by saponifying an ethylene-vinyl acetate copolymer having an ethylene content of 20 to 50 mol% to a degree of saponification of 96 mol% or more, particularly 99 mol% or more, can be preferably used.

[0023] [Base material layer] In the containers that are the subject of the evaluation method of the present invention, the base layer is made of an olefin-based resin, and resins that have traditionally been used as packaging materials can be used. Examples include, but are not limited to, polyethylenes such as low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and linear very-low-density polyethylene (LVLDPE), as well as polypropylene, ethylene-propylene copolymers, polybutene-1, ethylene-butene-1 copolymers, propylene-butene-1 copolymers, ethylene-propylene-butene-1 copolymers, ethylene-vinyl acetate copolymers, and ionically crosslinked olefin copolymers (ionomers). Among these, polypropylene is preferred because it is desirable for it to have heat resistance that can withstand heat-pressure sterilization processes such as retort sterilization.

[0024] [Laminated structure] As described above, the container has at least a substrate layer, a barrier layer, and an oxygen absorbing layer. The thickness of the base layer is preferably, but not limited to, in the range of 50 to 90% of the total thickness. This ensures the mechanical strength of the container. The base layer may have at least one layer, but may be made up of multiple layers, and it is preferable that both the outer layer and the inner layer are base layers, for example. When multiple base layers are used, the total thickness of the multiple layers should be within the above range. The thickness of the barrier layer can be changed depending on the type of barrier resin that constitutes the barrier layer, but it is preferable that the thickness is in the range of 1 to 12% of the total thickness of the laminate. The barrier layer may also be formed in multiple layers, in which case the thickness of each layer should be within the above range. Furthermore, the thickness of the oxygen absorbing layer cannot be generally determined depending on the content of the oxygen absorber in the oxygen absorbing layer, but in the case of the oxygen absorber content relative to the base resin described above, it is preferable that the thickness be in the range of 1 to 22% of the total thickness of the laminate.

[0025] As mentioned above, it is preferable to use ethylene vinyl alcohol copolymer (EVOH) as the barrier layer. In this case, it is preferable that the EVOH is contained in an amount of less than 13 parts by mass, particularly 1 to 10 parts by mass, per 100 parts by mass of the laminate. The thickness of the EVOH is preferably 150 μm or less, more preferably 120 μm or less, more preferably 80 μm or less, and even more preferably 70 μm or less. In the present invention, it is desirable for the barrier layer to be extremely thin, but from the viewpoint of long-term storage stability of the contents, it is possible to ensure oxygen barrier performance by increasing the thickness of the oxygen absorbing layer. It is preferable that the thickness of the oxygen absorbing layer is 0.8 times or more, 1.0 to 3.0 times, particularly 1.5 to 2.5 times the thickness of the EVOH barrier layer. That is, according to this embodiment, by reducing the amount of EVOH, the gas barrier properties of the container are reduced, allowing hydrogen in the container to be efficiently discharged outside the container, while the oxygen absorbing layer can efficiently capture oxygen that permeates from outside the container. This makes it possible to discharge generated hydrogen and prevent the container from swelling without reducing the stability of the contents.

[0026] The container includes at least a substrate layer, a barrier layer, and an oxygen absorbing layer, and may also include other layers such as an adhesive layer and a reproduction layer (regrind layer). For the adhesive layer, an adhesive resin having excellent adhesion between an ethylene-vinyl alcohol copolymer and the olefin resin constituting the base resin of the substrate layer and the oxygen absorbing layer can be used. Examples of such adhesive resins include ethylene-acrylic acid copolymer, ion-crosslinked olefin copolymer, maleic anhydride grafted polyethylene, maleic anhydride modified polypropylene, maleic anhydride grafted polypropylene, acrylic acid grafted polyolefin, ethylene-vinyl acetate copolymer, and those formed from a blend of an ethylene-vinyl alcohol copolymer and a maleic anhydride modified olefin resin. In particular, maleic anhydride modified polypropylene and maleic anhydride grafted polypropylene can be preferably used.

[0027] The reproduction layer is preferably made of a sheet containing a resin primarily made of olefin-based resin, or crushed scraps generated during the molding process of containers such as cups and bottles. While it is possible to use only the reproduction resin, it is preferable to mix it with virgin olefin-based resin in an amount of 75% by mass or less in terms of transparency, flow unevenness, color, and other container appearance, as well as moldability, such as the occurrence of eye irritation, gelation, and burnt areas. Furthermore, in the laminate used in the present invention, the barrier layer, oxygen absorbing layer, and base layer may be blended, as necessary, with known resin compounding agents such as fillers, colorants, heat stabilizers, weather stabilizers, antioxidants, antiaging agents, light stabilizers, ultraviolet absorbers, antistatic agents, lubricants such as metal soaps and waxes, modifying resins or rubbers, etc., according to known formulations. In particular, since the oxygen absorbing layer contains an iron-based oxygen absorber, it is preferable that the inner and / or outer layer contain a white pigment to conceal it.

[0028] The container may have a variety of layer configurations as long as it has a base layer, a barrier layer, and an oxygen-absorbing layer, but it is preferred that the inner and outer layers be base layers, with the barrier layer and oxygen-absorbing layer positioned as intermediate layers. Specifically, as shown in Figure 3, the container has, from the outside in, an outer layer 1 which is a base layer made of an olefin-based resin, an adhesive layer 2a, a barrier layer 3, an adhesive layer 2b, an oxygen-absorbing layer 4, and an inner layer 5 made of an olefin-based resin, and it is preferred that the oxygen-absorbing layer 4 be positioned closer to the inner layer than the barrier layer, which allows the oxygen that has permeated the barrier layer to be captured by the oxygen-absorbing layer, improving the shelf life of the contents. When the reproduced layer 6 is included, it is preferable that the reproduced layer 6 is located between the outer layer 1 and the barrier layer 3 as shown in FIG.

[0029] The container can have any known form as long as it has a base layer, a barrier layer, and an oxygen absorbing layer, and can be a cup-shaped or tray-shaped container. It is particularly suitable for cups and trays with a large bottom or opening relative to the height of the container, in which swelling due to hydrogen generation or the like is noticeable under reduced pressure.

[0030] (lid material) The lid material applicable to the containers that are the subject of the evaluation method of the present invention may be a rigid lid material if a variable portion is formed at the bottom of the container, but it may also be a flexible sheet-like lid material, or a molded lid whose top surface is flexible and can be deformed into a dome shape. Since the lid material also needs to have barrier properties, it needs to have a barrier layer, and in addition to the barrier resin described above for the container, it is desirable that it has a light metal foil such as aluminum, an inorganic vapor deposition layer, etc. Furthermore, like the container, it preferably has a base layer and a heat seal layer. The base layer is preferably made of an olefin-based resin as in the container described above, and the heat seal layer can also be made of an olefin-based resin such as polypropylene or polyethylene that has been used in conventional heat seal layers.

[0031] (carbon dioxide replacement) In order to improve the shelf life of the contents of the filled containers that are the subject of the evaluation method of the present invention, the air in the headspace after filling is replaced with carbon dioxide gas. In this case, it is preferable to use a replacement gas with a carbon dioxide gas concentration of less than 95%, particularly less than 55%, at 1% or more. This reduces the amount of reaction with iron in the oxygen absorbent, making it possible to suppress the generation of hydrogen.

[0032] (heat and pressure sterilization) The container is filled with the contents, the air is replaced with carbon dioxide gas, and the filled sealed container is sealed with a lid, and then the sealed container is subjected to a known heat-pressure sterilization process such as retort sterilization. The heat-pressure sterilization process may be performed under known conditions, and is not limited thereto, but is preferably performed at a temperature of 105 to 150°C for 2 to 120 minutes. After the heat-pressure sterilization process, the carbon dioxide gas in the container dissolves in the contents, and the container is placed in a reduced pressure state. When a container that suppresses hydrogen gas generation after the above-mentioned heat-pressure sterilization process is used as the container, the hydrogen gas concentration inside the sealed container after cooling at room temperature for 24 hours after heat-pressure sterilization is controlled to 0.1 to 20%. As a result, it can be determined that the displacement of the bottom or lid measured by the method described below is due to gas generated due to spoilage of the contents.

[0033] (Contents) In the evaluation method of the present invention, when evaluation is performed based on the above-mentioned variation in the amount of generated hydrogen gas, the contents are not limited, but from the viewpoint of identifying defective filled containers due to spoilage of the contents, etc., it is desirable that the variation due to hydrogen gas be reduced. Therefore, the evaluation method of the present invention is particularly suitable for use with filled containers that are filled with contents having a solubility parameter for carbon dioxide of less than 55. As mentioned above, the filled containers that are the subject of evaluation in this invention must undergo carbon dioxide gas replacement after filling with the contents. [80- (carbon dioxide concentration in the container 24 hours after replacing the headspace with 80% carbon dioxide and sterilizing with heat and pressure)] If the carbon dioxide solubility parameter of the content calculated in (2) is high, the content will dissolve a large amount of carbon dioxide gas due to carbon dioxide gas substitution, resulting in an excess amount of carbon dioxide in the container. As a result, the amount of reaction with iron in the oxygen absorbent will increase, and the amount of hydrogen generated will also increase. Therefore, it is desirable to fill the container with a content with a low carbon dioxide solubility parameter.

[0034] Examples of contents with a carbon dioxide solubility parameter of less than 55 include, but are not limited to, contents with a lipid content of 0.1% or more, i.e., contents with a high oil content (high lipid content), tend to have a lower carbon dioxide solubility. In the examples described below, water is used as the content because the solubility parameter of carbon dioxide in water is greater than 55, and the reaction between carbon dioxide and reduced iron is accelerated, creating harsh conditions that result in a large amount of hydrogen gas being generated. Therefore, if the amount of hydrogen gas generated can be reduced by using water as the content, hydrogen gas generation can also be suppressed with other contents. [Example]

[0035] (Calculation method of oxygen permeability) Toyobo PPS Packaging Film Overview 5th Edition P.53 (Publisher: Toyobo PPS, Publication Date: 2022 / 02 / 28) Oxygen permeability coefficient [ml·mm / m 2 ·day·MPa] MXD-6(MxNy) 2.58 EVOH(Et32%) 3.75 The oxygen permeability of the barrier material at each thickness was calculated from each value.

[0036] (Method for measuring oxygen absorption amount) The bottom of the container obtained as described below was cut into a 30 cm x 30 cm piece and placed inside a gas-impermeable plastic cup container with an internal volume of 85 ml and laminated with steel foil. The container was then heat-sealed in air using a gas-impermeable metal foil laminated film. After storing the container at 50°C for 1 day, the oxygen concentration inside the container was measured using an oxygen concentration meter (Toray Engineering; LC-750F), and the oxygen absorption amount per 1 g of film was calculated.

[0037] (Measurement of maximum displacement fluctuation and inspection suitability) The distance from the flange near the center of the lid material (lid H0) and the distance from the ground near the center of the panel-shaped bottom variable part (bottom H0) were measured 24 hours after retort sterilization, and the distance from the flange near the center of the lid material (lid H1) and the distance from the ground near the center of the panel-shaped bottom variable part (bottom H1) were measured after the lid was left to cool at room temperature for two weeks after retort sterilization. Note that upward movement from the flange in the container axial direction was considered positive (+), and downward movement from the flange in the container axial direction was considered negative (-), and lid H0 - lid H1 was defined as the maximum lid displacement fluctuation. Downward movement from the ground to the container axial direction was considered positive (+), and downward movement from the container axial direction was considered negative (-), and bottom H0 - bottom H1 was defined as the maximum bottom displacement fluctuation. If the maximum displacement fluctuation amount of both the lid material and the bottom variable part was 0.1 mm or less, it was determined that the inside of the container was in a reduced pressure state and was rated as passed (◯); if the maximum displacement fluctuation amount was greater than 0.1 mm, it was determined that the inside of the container was not in a reduced pressure state and was rated as failed (×), and the suitability for testing was evaluated.

[0038] (Measurement of hydrogen concentration inside the container) The hydrogen concentration in the sealed containers, which had been left for two weeks after retort sterilization, was measured using a micro gas chromatograph (GC-323, manufactured by GL Sciences).

[0039] Example 1 Using polypropylene for the inner and outer layers, a polypropylene oxygen-absorbing resin composition containing 29% by mass of reduced iron for the oxygen-absorbing layer, EVOH for the barrier layer, and an adhesive layer, a laminate with an outer layer (255 μm) / barrier layer (80 μm) / oxygen-absorbing layer (70 μm) / inner layer (550 μm) structure was produced by coextrusion, as shown in Figure 3. The oxygen permeability (20°C, 100% RH) and oxygen absorption rate (50°C, 24 hours) of this laminate are shown in Table 1. The resulting laminate was then formed into a flanged cup-shaped container with a diameter of 84 mm, height of 5.7 mm, drawing ratio of 0.33, and full capacity of 105 ml using plug-assisted pressure forming. The container was filled with water (carbon dioxide solubility parameter 63) at room temperature. Carbon dioxide gas was purged to 80% carbon dioxide and 20% nitrogen gas concentrations in the container according to standard procedures, and the container was then sealed with a gas-impermeable lid containing aluminum foil. The sealed container was retort sterilized at 123°C for 40 minutes, slowly cooled to room temperature, and then measured for displacement from the flange and ground after 24 hours and two weeks after retort sterilization using laser irradiation. The results are shown in Table 1 and Figure 5. Visual inspection of the lid revealed no lifting.

[0040] Examples 2 to 6 Barrier layer (50 μm) / oxygen absorption layer (115 μm) Barrier layer (60 μm) / oxygen absorption layer (100 μm) Barrier layer (60 μm) / oxygen absorption layer (110 μm) Barrier layer (65 μm) / Oxygen absorption layer (105 μm) Barrier layer (70 μm) / oxygen absorption layer (110 μm) Except for changing the thickness of each layer and adjusting the outer layer thickness so that the total thickness of the laminate was 1 mm, sealed containers were produced in the same manner as in Example 1. Examples 2 to 6 were performed in the same order as above. When the lid material was visually inspected, no lifting was observed.

[0041] (Comparative Example 1) Instead of replacing the air with carbon dioxide, nitrogen gas replacement was performed so that the nitrogen gas in the container was 100%, and the container was then sealed with the same lid as in Example 1. This sealed container was stored at room temperature. The results are shown in Table 1 and Figure 6. Because the air was not replaced with carbon dioxide, the pressure inside the container was not negative, and it was not possible to determine whether the container was airtight. When the lid was visually inspected, sagging was confirmed.

[0042] (Comparative Example 2) A sealed container was prepared in the same manner as in Example 1, except that the barrier layer was an 80 μm thick layer made of MAXD6, and retort sterilization and cooling were performed. The distance from the flange near the center of the lid was measured in the same manner as in Example 1. The results are shown in Table 1 and Figure 5. When the lid was visually inspected, lifting was confirmed.

[0043] [Table 1]

[0044] (Consideration) In Example 1, the air was replaced with a gas containing carbon dioxide, so the carbon dioxide dissolved in the contents during heat sterilization, and after heat sterilization, the container was cooled to room temperature and the pressure inside the container was reduced. Although hydrogen gas was generated when the carbon dioxide dissolved in the contents came into contact with the oxygen absorber in the container, the barrier properties of the barrier layer were reduced during heat sterilization, so the hydrogen gas easily permeated outside the container, and the reduced pressure state was maintained unless the contents were spoiled. Therefore, spoilage of the contents could be accurately determined. In Comparative Example 1, the air was not replaced with a gas containing carbon dioxide, and the contents were filled at room temperature, so the pressure inside the container was not reduced, and therefore it was not possible to determine whether the contents had spoiled based on the reduced pressure state. In Comparative Example 2, the air was replaced with a gas containing carbon dioxide, so the carbon dioxide dissolved in the contents during heat sterilization, and the container was cooled to room temperature after heat sterilization, resulting in a reduced pressure inside the container. However, hydrogen gas was generated when the carbon dioxide dissolved in the contents came into contact with the oxygen absorber inside the container, and because the barrier properties of the barrier material were high during and immediately after heat sterilization, the hydrogen gas could not be sufficiently released outside the container, and the reduced pressure inside the container could not be maintained without the contents spoiling. Therefore, spoilage of the contents could not be accurately determined. [Explanation of symbols]

[0045] 1 outer layer, 2a, 2b adhesive layers, 3 barrier layer, 4 oxygen absorbing layer, 5 inner layer, 6 reproduction layer, 10 container, 11 body, 12 bottom, 13 grounding portion, 14 panel-shaped variable portion, 15 lid material.

Claims

1. A method for evaluating the quality of a container filled with contents, which has been subjected to carbon dioxide gas replacement, sealed with a lid, and then subjected to heat and pressure sterilization, comprising: the container includes at least a substrate layer made of an olefin-based resin, a barrier layer, and an oxygen absorbing layer containing an oxygen absorber including reduced iron, and has a bottom including a ground portion and a variable portion surrounded by the ground portion, and the lid is flexible; A method for evaluating filled containers, characterized in that the sealed container has a headspace, carbon dioxide and nitrogen gas are introduced into the headspace to perform gas replacement, and then, after the heat and pressure sterilization treatment, a reduced pressure state is maintained for 24 hours, and the quality of the filled container is evaluated based on the displacement between the axial position of the center of the variable part or near the center of the lid of the filled container and the axial position of the center of the variable part or near the center of the lid of the filled container two weeks after the heat and pressure sterilization treatment.

2. 2. A method for evaluating a filled container as described in claim 1, wherein the container is filled with a water-containing material, and hydrogen generated in the container by a reaction between water, carbon dioxide, and iron is allowed to escape to the outside of the container by passing through the container wall during heat and pressure sterilization.

3. 3. The evaluation method according to claim 1, wherein the displacement occurs in accordance with an amount of hydrogen generated in the container by a reaction between the water in the content, the carbon dioxide gas, and the reduced iron.

4. The evaluation method according to claim 1 or 2, wherein the displacement occurs due to spoilage of the contents.

5. 3. The evaluation method according to claim 1, wherein the carbon dioxide concentration in the carbon dioxide substitution is less than 55%.

6. 3. The evaluation method according to claim 1, wherein the oxygen absorbing layer contains 1 to 30 parts by mass of an oxygen absorbent per 100 parts by mass of the base resin of the oxygen absorbing layer.

7. 3. The evaluation method according to claim 1, wherein the barrier layer is made of an ethylene-vinyl alcohol copolymer and has a thickness of 120 μm or less.

8. 8. The evaluation method according to claim 7, wherein the thickness of the oxygen absorbing layer is at least 1.5 times the thickness of the barrier layer.

9. 3. The evaluation method according to claim 1, wherein the olefin resin is polypropylene.

10. 3. The evaluation method according to claim 1, wherein the substrate layer comprises an inner layer and an outer layer, and the oxygen absorbing layer is located closer to the inner layer than the barrier layer.

Images