Multilayer container having ferrous oxygen absorbent-containing layer

Abstract

To provide a container having an oxygen absorption layer containing a ferrous oxygen absorbent in which hydrogen concentration is effectively controlled, even when the container is subjected to sterilization by heating and pressurizing after carbon gas replacement.SOLUTION: A container having a ferrous oxygen absorbent-containing layer is composed of a laminate including at least a base material layer composed of an olefinic resin, a barrier layer and an oxygen absorption layer containing an oxygen absorbent containing reduced ion, is sealed by carbon gas replacement after contents are filled, and is subjected to sterilization by heating and pressurizing, wherein a product of oxygen permeability (ml / m2 day MPa) at 20°C and 100 RH% and an oxygen absorption amount (ml / cm2 hr) at 50°C of the laminate is 6.0 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a container provided with an oxygen absorbing layer containing an iron-based oxygen absorber, and more specifically to a container that is effectively prevented from swelling even when carbon dioxide gas is replaced after filling with the contents and the container is subjected to heat and pressure sterilization. [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 with carbon dioxide gas or the like not only has the quality preserving effect of carbon dioxide gas or the like, but also removes oxygen from the container through gas substitution, and has the advantage that when the container is subjected to a heat and pressure sterilization process such as retort sterilization after carbon dioxide substitution, the carbon dioxide gas dissolves in the contents, creating a negative pressure inside the container, making it possible to confirm at a glance that the container is sealed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3630706 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-14374 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 container in which the hydrogen concentration inside the container is effectively controlled even when the container is equipped with an oxygen absorbing layer containing an iron-based oxygen absorber and then subjected to heat and pressure sterilization after carbon dioxide gas replacement. [Means for solving the problem]

[0008] According to the present invention, a container is made of a laminate including at least a substrate layer made of an olefin resin, a barrier layer, and an oxygen absorbing layer containing an oxygen absorber including reduced iron, and is sealed after filling with contents by carbon dioxide gas substitution and then subjected to heat and pressure sterilization. The oxygen permeability (ml / m) of the laminate at 20°C and 100% RH is 2 ·day·MPa) and oxygen absorption at 50℃ (ml / cm 2 ·hr) is 6.0 or greater.

[0009] In the container of the present invention, (1) 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. (2) The barrier layer is made of an ethylene-vinyl alcohol copolymer. (3) The laminate contains an ethylene-vinyl alcohol copolymer in an amount of less than 13 parts by mass per 100 parts by mass of the laminate, and the thickness of the oxygen absorbing layer is 1.5 times or more the thickness of the barrier layer. (4) The olefin-based resin is polypropylene. (5) 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. (6) A repro layer is provided between the barrier layer and the outer layer. (7) The hydrogen gas concentration in the sealed container after the heat and pressure sterilization treatment is 0.1 to 20%. (8) In the sealed container, the maximum displacement fluctuation between the axial positions of the bottom and lid of the sealed container after maintaining a reduced pressure state for 24 hours after the heat-pressure sterilization treatment and the axial positions of the bottom and lid of the sealed container after two weeks have passed since the heat-pressure sterilization treatment is 0.1 mm or less. is preferred. [Effects of the Invention]

[0010] The container of the present invention has a barrier layer made of a barrier resin with gas barrier properties such as an ethylene-vinyl alcohol copolymer that blocks oxygen from entering from outside the container, and an oxygen absorbing layer containing an oxygen absorber that absorbs residual oxygen inside the container, thereby significantly reducing the oxygen concentration inside the container and providing remarkably excellent storage stability for the contents. On the other hand, by controlling the oxygen permeability of the laminate and the oxygen absorption amount of the oxygen absorbing layer to appropriate values, it is possible to reduce the amount of hydrogen generated by the reaction between carbon dioxide due to carbon dioxide substitution and the reduced iron in the oxygen absorbent, and to appropriately release the generated hydrogen to the outside of the container.Even when the contents are filled and carbon dioxide substitution is performed, followed by heat and pressure sterilization such as retort sterilization, swelling of the container due to hydrogen gas can be efficiently suppressed, and appropriate quality inspection can be performed.Furthermore, by selecting contents that dissolve little carbon dioxide gas, swelling of the container can be further suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of a laminated structure of a container according to the present invention. [Figure 2] 1 is a cross-sectional view showing another example of the laminated structure of a container of the present invention. [Figure 3] 10A and 10B are diagrams illustrating a method for measuring the degree of bulging (displacement) caused by the bottom of a sealed container. [Figure 4] 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 5] 1 is a photograph of the sealed containers obtained in Examples 2 and 7 taken from above. [Figure 6] 1 is a photograph of the sealed containers obtained in Comparative Examples 1 and 2 taken from above. DETAILED DESCRIPTION OF THE INVENTION

[0012] The container of the present invention is a laminate comprising at least a substrate layer made of an olefin resin, a barrier layer, and an oxygen absorbing layer containing an oxygen absorber including reduced iron, and is sealed after filling with contents and subjecting to carbon dioxide gas substitution and heat and pressure sterilization. In this container, the oxygen permeability (ml / m) of the laminate at 20°C and 100% RH is 2 ·day·MPa) and oxygen absorption at 50℃ (ml / cm 2 The important feature is that the product of (hr) is 6.0 or more. As mentioned above, when a container is filled with 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. In the present invention, it has been discovered that when the product of the oxygen permeability and oxygen absorption amount of the laminate constituting the container is within the above range, it is possible to achieve both the contradictory effects of preserving the contents and suppressing the expansion of the container after heat-pressure sterilization. The oxygen permeability and oxygen absorption amount of the laminate can be approximated to the oxygen permeability and oxygen absorption amount measured by the methods described in the Examples below.

[0013] (oxygen absorbing layer) In the container 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 5 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.

[0014] 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.

[0015] 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.

[0016] The oxygen absorbent 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 absorbent is less than the above range, the oxygen absorption performance may not be as sufficient as when it is within the above range. On the other hand, if the amount of oxygen absorbent is more than the above range, the reduced iron may aggregate as compared to when it is within the above range. From the viewpoint of interlayer adhesion, etc., it is preferable that the base resin be made of an olefin-based resin similar to that used for the substrate layer described below. In addition, by using an olefin-based resin with high gas permeability, the remaining oxygen can be easily transferred to the oxygen absorbing layer, and the oxygen absorption reaction can be carried out efficiently.

[0017] (barrier layer) The barrier layer of the container of the present invention can be made of a conventionally known barrier resin as long as the product of oxygen permeability and oxygen absorption falls within the above-mentioned range when the laminate is formed. Suitable barrier resins include ethylene vinyl alcohol copolymers (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, ethylene vinyl alcohol copolymer (hereinafter sometimes referred to as "EVOH") is particularly suitable for satisfying the conflicting requirements of blocking oxygen from permeating from outside the container while allowing hydrogen inside the container to permeate out of the container. That is, EVOH tends to lose its barrier properties under high-temperature, high-humidity conditions such as those used in retort sterilization, and is capable of efficiently discharging hydrogen gas generated during retort sterilization treatment out of the container under hydrothermal conditions, while exhibiting favorable oxygen barrier properties in environments other than these conditions. 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.

[0018] (base material layer) In the container of the present invention, the base layer is made of an olefin-based resin, and resins conventionally 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.

[0019] (Laminate) As described above, the laminate constituting the container of the present invention has at least a substrate layer, a barrier layer, and an oxygen-absorbing layer, and it is important that the product of the oxygen permeability and oxygen absorption amount of the laminate is 6.0 or more, particularly in the range of 10.0 to 20. This makes it possible to satisfy the conflicting requirements of blocking the permeation of oxygen from outside the container while allowing hydrogen inside the container to permeate to the outside of the container. In the laminate, the base layer preferably accounts for 50 to 90% of the total thickness. This ensures the mechanical strength of the container. The container may have at least one base layer, but may also have multiple base layers; for example, it is preferable that both the outer layer and the inner layer are base layers. When multiple base layers are present, 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 10% 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 10% of the total thickness of the laminate.

[0020] In the present invention, as described above, it is preferable to use an ethylene-vinyl alcohol copolymer (EVOH) for the barrier layer, and 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, and that the thickness of the oxygen absorbing layer is at least 1.5 times, particularly 1.5 to 2.5 times, and particularly 2 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 inside the container to be efficiently released outside the container, while oxygen that permeates from outside the container can be efficiently captured by the oxygen absorbing layer. Therefore, it is possible to release generated hydrogen and prevent bulging of the container without reducing the shelf life of the contents.

[0021] The laminate that can be used in the container of the present invention 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. 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.

[0022] The layer configuration of the laminate used in the present invention can be various as long as it has a base layer, a barrier layer, and an oxygen-absorbing layer, but it is preferable that the inner and outer layers be base layers, and the barrier layer and the oxygen-absorbing layer be positioned as intermediate layers. Specifically, as shown in Figure 1, the laminate has, from the outside, 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 preferable that the oxygen-absorbing layer 4 is positioned closer to the inner layer than the barrier layer, so that oxygen that has permeated the barrier layer can 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.

[0023] (Containers and their manufacturing methods) The container of the present invention can have any known form, except for the use of the laminate described above, 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, which will tend to bulge due to hydrogen generation. Methods for producing such containers include, but are not limited to, creating a multilayer sheet (laminate) by coextrusion, dry lamination, sandwich lamination, etc., and then subjecting this multilayer sheet to vacuum forming, pressure forming, bulging forming, plug-assist forming, etc., to obtain cup-shaped, tray-shaped, etc. containers.

[0024] (Contents) The container of the present invention can be suitably filled with a content having a carbon dioxide solubility parameter of less than 55. As described above, the container of the present invention requires that carbon dioxide gas substitution be performed after filling with the content, [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 calculated carbon dioxide solubility parameter of the content is high, the content will dissolve a large amount of carbon dioxide gas due to carbon dioxide displacement, and the amount of carbon dioxide that comes into contact with the container will be excessive. 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 content with a low carbon dioxide solubility parameter. Although not limited to this, contents having a carbon dioxide solubility parameter of less than 55 include contents having a lipid content of 0.1 to 3%. In other words, when the oil content in the contents is high (the lipid content is high), the solubility of carbon dioxide tends to decrease. 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.

[0025] (carbon dioxide replacement) In order to improve the shelf life of the contents of the container of the present invention, the air in the headspace after the contents are filled 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% and 1% or more. This reduces the amount of reaction with iron in the oxygen absorbent, making it possible to suppress the generation of hydrogen.

[0026] (sealed container) The container of the present invention is filled with the above-described contents, and the contents are sealed with a lid after replacing the air with carbon dioxide. The filled and sealed container is then subjected to a known heat and pressure sterilization process such as retort sterilization. The heat and pressure sterilization process may be carried out under known conditions, and is not limited thereto, but is preferably carried out at a temperature of 105 to 150°C for 2 to 120 minutes. After the heat and pressure sterilization process, the carbon dioxide gas in the container dissolves in the contents, creating a reduced pressure state. As described above, the container of the present invention suppresses the generation of hydrogen gas after heat-pressure sterilization, and therefore 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, the maximum fluctuation in displacement of the bottom and / or lid measured by the method described below is 0.1 mm or less, and bulging of the container is effectively suppressed even under reduced pressure.

[0027] FIG. 3 illustrates the displacement of the bottom of a container of the present invention before and after heat-pressure sterilization and a method for measuring the displacement. FIG. 3(A) is a schematic cross-sectional view showing an example of a container of the present invention. Container 10 generally comprises body 11 and bottom 12. Bottom 12 is formed with a base portion 13 and a panel-shaped variable portion 14 that is surrounded by base portion 13 and located a distance H above base portion 13 in the axial direction of the container. As shown in FIG. 3(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 as shown in FIG. 3(C), panel-shaped variable portion 14 protrudes upward in the axial direction of the container, with its apex near the center, rising a distance H0 above base portion 14 in the axial direction of the container. After the sealed container has been left to cool for 24 hours, if hydrogen gas is generated inside the container, 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 3(D), and the panel-shaped variable portion 14 will protrude downward. In the container of the present invention, since hydrogen gas generation is suppressed, this displacement (H0 - H1) is 0.1 mm or less.

[0028] As shown in Figure 4, it can also be determined that the bulging of the container is suppressed by the displacement of the lid material. That is, after the contents are filled into the container 10, carbon dioxide gas is replaced, and the container is sealed with the lid member 15 (FIG. 4(A)), immediately after the heat-pressure sterilization process, the lid member 15 protrudes upward in the axial direction of the container, with its apex near the center, as shown in FIG. 4(B). When the container is then cooled by being stored at room temperature, the pressure inside the container is reduced, and the sealed container becomes concave in the axial direction of the container, with its apex near the center, as shown in FIG. 4(C). The lid member 15 is displaced by a distance H0 from the state shown in FIG. 4(A). If hydrogen gas is generated inside the sealed container after being left to cool for 24 hours, the displacement of the lid member 15, which is the distance H1, becomes as shown in FIG. 4(D), and the lid member 15 has a protruding portion. In the container of the present invention, hydrogen gas generation is suppressed, so this displacement (H0 - H1) is 0.1 mm or less. [Example]

[0029] (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.

[0030] (Method for measuring oxygen absorption amount) Sixteen sheets of the laminate cut into 30 mm x 30 mm pieces were placed in a gas-impermeable plastic cup container with an internal volume of 85 ml and laminated with steel foil, together with 0.5 ml of water. The container was then heat-sealed in air using a gas-impermeable metal foil laminated film. After storing the container at 50°C for 24 hours, 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.

[0031] (Container characteristics) The product of the oxygen permeability and oxygen absorption amount measured by the above method (oxygen permeability x oxygen absorption amount) was evaluated as "◯" when it was 6.0 or more, and "X" when it was less than 6.0.

[0032] (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.

[0033] (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).

[0034] (Container characteristics and inspection characteristics) The container characteristics were evaluated as "good" when the value of oxygen permeability x oxygen absorption was 6.0 or more, and "poor" when it was less than 6.0.

[0035] Example 1 A laminate was prepared by coextrusion using polypropylene for the inner and outer layers, a polypropylene oxygen-absorbing resin composition containing 29% by mass of reduced iron (denoted as "OXY" in the table) for the oxygen-absorbing layer, an ethylene-vinyl alcohol copolymer (ethylene content 32 mol%, denoted as "EVOH" in the table) for the barrier layer, and an adhesive layer, with the structure of outer layer (255 μm) / barrier layer (50 μm) / oxygen-absorbing layer (115 μm) / inner layer (550 μm), as shown in Figure 1. The oxygen permeability (20°C, 100% RH) and oxygen absorption (50°C, 24 hours) of this laminate are shown in Table 2. 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 an 80% carbon dioxide concentration 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 the flange displacement was measured 24 hours later and 2 weeks after retort sterilization. The results are shown in Table 2 and Figure 5. Visual inspection of the lid revealed no lifting.

[0036] Examples 2 to 6 A sealed container was produced and subjected to retort sterilization and cooling in the same manner as in Example 1, except that the thicknesses of the barrier layer and oxygen absorbing layer were as shown in Table 1 and the outer layer thickness was adjusted so that the total thickness of the laminate was 1 mm. 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 2 and Figure 5. When the lid was visually inspected, no lifting was observed.

[0037] Example 7 A sealed container was produced in the same manner as in Example 6, except that the barrier layer was a 40 μm thick layer made of MXNy (MXD-6) and the thickness of the outer layer was adjusted so that the total thickness of the laminate was 1 mm, and then 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 2 and Figure 5. Visual inspection of the lid revealed no lifting.

[0038] (Comparative Examples 1 and 2) A sealed container was prepared in the same manner as in Example 7, except that the thickness of the barrier layer made of MxNy (MXD-6) was as shown in Table 1 and the thickness of the outer layer was adjusted so that the total thickness of the laminate was 1 mm, and then retort sterilization and cooling were carried out. 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 2 and Figure 6. In Comparative Example 1, it was not possible to determine whether or not the lid had lifted by visual inspection alone. In Comparative Example 2, lifting was clearly confirmed when the lid was visually inspected. In Figure 6, Comparative Example 1 is the container on the left, and Comparative Example 2 is the container on the right.

[0039] [Table 1]

[0040] [Table 2] [Industrial Applicability]

[0041] The container of the present invention has a barrier layer and an oxygen-absorbing layer, and therefore has excellent preservation properties for the contents. Furthermore, even when the container is subjected to a heat-pressure sterilization process such as carbon dioxide gas replacement and retort sterilization after filling the contents, hydrogen gas generation is suppressed and there is no swelling of the container due to hydrogen gas, so that accurate testing can be performed without any suspicion of spoilage or bacterial growth of the contents. Therefore, the container can be suitably used for sealed containers that require long-term storage and require carbon dioxide gas replacement and retort sterilization. [Explanation of symbols]

[0042] 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 container comprising a laminate including at least a substrate layer made of an olefin resin, a barrier layer, and an oxygen absorbing layer containing an oxygen absorber including reduced iron, which is sealed after being filled with contents and subjected to carbon dioxide gas substitution and heat-pressure sterilization, The oxygen permeability (ml / m ２ · day · MPa) and oxygen absorption at 50 ° C (ml / cm ２ A container characterized in that the product of (hr) is 6.0 or more.

2. 2. The container according to claim 1, wherein the oxygen absorbing layer contains 1 to 30 parts by weight of an oxygen absorbent per 100 parts by weight of the base resin of the oxygen absorbing layer.

3. 3. The container according to claim 1, wherein the barrier layer comprises an ethylene vinyl alcohol copolymer.

4. 4. The container according to claim 3, wherein the ethylene-vinyl alcohol copolymer is contained in an amount of less than 13 parts by mass per 100 parts by mass of the laminate, and the thickness of the oxygen absorbing layer is 1.5 times or more the thickness of the barrier layer.

5. 3. The container according to claim 1, wherein the olefin resin is polypropylene.

6. 3. The container 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.

7. 7. The container according to claim 6, further comprising a repro layer between the barrier layer and the outer layer.

8. 3. The container according to claim 1, wherein the hydrogen gas concentration in the sealed container after the heat and pressure sterilization treatment is 0.1 to 20%.

9. 9. The container according to claim 8, wherein the maximum variation in displacement between the axial positions of the bottom and lid of the sealed container after maintaining a reduced pressure state for 24 hours following the heat-and-pressure sterilization treatment and the axial positions of the bottom and lid of the sealed container two weeks after the heat-and-pressure sterilization treatment is 0.1 mm or less.

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