Oxygen scavenger composition

Abstract

To provide a ferrous deoxidizing agent composition that does not block a metal detection machine from detecting a metal foreign matter.SOLUTION: A deoxidizing agent composition includes an iron of which metallic iron content is 94 mass% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an oxygen scavenger composition, and more particularly to an iron-based oxygen scavenger composition. [Background technology]

[0002] A method using an oxygen scavenger is known as a preservation technique for foods, medicines, etc. In this method, the preserved item and the oxygen scavenger are enclosed in a gas-barrier sealed container and then sealed, so that the oxygen in the sealed container is absorbed by the oxygen scavenger, and the atmosphere in the sealed container can be kept substantially oxygen-free. Representative oxygen scavengers include iron-based oxygen scavengers, which are mainly made of iron, and non-iron-based oxygen scavengers, which are mainly made of ascorbic acid, glycerin, etc. The type of oxygen scavenger is appropriately selected depending on the application, but iron-based oxygen scavengers are widely used from the viewpoint of oxygen absorption performance.

[0003] From the perspective of maintaining the quality of foods, medicines, etc., it is important to confirm that oxygen absorbers are properly sealed in the products. Since iron-based oxygen absorbers can be detected with a metal detector, it is relatively easy to confirm the presence of the oxygen absorber in the product. In the case of non-ferrous oxygen absorbers, they are generally not detectable by metal detectors, and therefore metal detectors cannot be used as a means for confirming the presence of oxygen absorbers in products, and expensive X-ray foreign body detectors must be used. In this regard, for example, Patent Document 1 discloses an oxygen absorber package containing a non-ferrous oxygen absorbing material and iron oxide, with the aim of providing an oxygen absorber package and a method for confirming its presence, which can detect the presence of the oxygen absorber package in a sealed container with a metal detector and can also detect the presence of stainless steel, which is widely used in the production processes of foods, medicines, etc., even if the stainless steel is mixed in as a foreign body.

[0004] In the manufacturing process of foods, medicines, and other products, metal detectors are used to check for the presence or absence of metallic foreign bodies in products in order to prevent the products from being shipped as is due to contamination with metallic foreign bodies such as metal fragments during the manufacturing process of foods, medicines, and other products. In particular, in recent years, consumer awareness of the safety of foods, medicines, and other products has increased, and foreign body contamination accidents have been attracting attention. Therefore, producers are required to pay even more attention to the contamination of metallic foreign bodies.

[0005] In order to detect metallic foreign bodies in a product containing an iron-based oxygen absorber using a metal detector, it is necessary to distinguish between metallic foreign bodies and the iron contained in the oxygen absorber. In general, when there are multiple detection targets, the detection signals from each of the detection targets are identified and the detection signals of no interest are cancelled as noise, thereby increasing the sensitivity of the detection signal of interest. However, even if an attempt is made to cancel the detection signal from the iron-based oxygen absorber as noise, the detection signals vary widely and the iron-based oxygen absorber cannot be adequately identified. Therefore, currently, a method is generally used in which a product is subjected to detection of metallic foreign bodies using a metal detector, an iron-based oxygen absorber is then sealed in the product, and the presence of the iron-based oxygen absorber is then confirmed using a metal detector. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-030813 A Summary of the Invention [Problem to be solved by the invention]

[0007] It is desirable to efficiently detect metallic foreign bodies using a metal detector for products in which an iron-based oxygen scavenger is enclosed. In particular, in view of the increasing consumer awareness of the safety of foods, medicines, etc., there is a strong demand for detecting metallic foreign bodies even after the oxygen scavenger is enclosed. Therefore, an object of the present invention is to provide an iron-based oxygen absorber that does not impede the detection of metallic foreign matter by a metal detector. [Means for solving the problem]

[0008] The present inventor has studied the reason why the detection signal derived from a conventional iron-based oxygen absorber varies widely. In conventional iron-based oxygen absorbers, the surface of the iron contained in the oxygen absorber is slightly oxidized to improve the oxygen absorption performance, but the iron changes into a mixture of multiple types of iron oxides through oxidation. The inventor has noticed that these iron oxides have different magnetic properties depending on their oxidation number, which results in large variations in the detection signal in a metal detector that uses changes in magnetic force as its detection principle. As a result of further intensive research, the inventor has found that by increasing the purity of iron in the oxygen absorber, the oxidation of iron is suppressed and magnetism is stabilized, thereby making it possible to identify the detection signal derived from iron. The present invention has been completed based on such findings.

[0009] That is, the present invention relates to the following. <1> An oxygen scavenger composition comprising iron, the iron content of which is 94 mass% or more. <2> An oxygen absorbing composition comprising a powder having an α-layer containing a water retention agent, a swelling agent, a metal salt and water, a β-layer containing iron with a metallic iron content of 94% by mass or more, and a γ-layer containing a porous carrier, The powder / granules form a layer structure in which the α layer, the β layer, and the γ layer are arranged in this order from the inside to the outside of the powder / granules. <1> The oxygen scavenger composition according to claim 1. <3> The water retention agent contains at least one selected from the group consisting of diatomaceous earth, silica, and activated carbon. <2> The oxygen scavenger composition according to claim 1. <4> The swelling agent contains at least one selected from the group consisting of calcium carboxymethylcellulose, sodium carboxymethylcellulose, calcium bentonite, and sodium bentonite. <2> or <3> The oxygen scavenger composition according to claim 1. <5> The powder or granule contains, relative to the total amount of the powder or granule, 30% by mass or more and 50% by mass or less of the α layer, 49% by mass or more and 69% by mass or less of the β layer, and 0.1% by mass or more and 5.0% by mass or less of the γ layer. <2> ~ <4> 13. The oxygen scavenger composition according to claim 12, <6> The α layer contains the swelling agent in an amount of 1.0% by mass or more and 10% by mass or less based on the total amount of the α layer. <2> ~ <5> 13. The oxygen scavenger composition according to claim 12, <7> the above <1> ~ <6> A method for inspecting a product containing the oxygen absorbing composition according to any one of the above items using a metal detector, A foreign matter inspection method comprising the step of canceling a detection signal derived from the iron contained in the oxygen absorbing agent composition as noise. <8> the above <1> ~ <6> A method for inspecting a product containing the oxygen absorbing composition according to any one of the above using a metal detector, comprising: An inspection method in which detection is performed using two or more frequency detectors at the same time to simultaneously confirm the presence of an oxygen scavenger composition and inspect for foreign matter. Effect of the Invention

[0010] In the oxygen absorber composition of the present invention, the magnetic properties of the iron contained therein are stable, so that the detection signal of iron derived from the oxygen absorber composition can be canceled as noise with high accuracy, and the detection of metallic foreign matter by a metal detector is not hindered. Therefore, even after the iron-based oxygen absorber composition is enclosed in a product such as food or medicine, the detection of metallic foreign matter can be performed with high sensitivity. Furthermore, by performing detection using a metal detector equipped with two or more frequency detectors, the presence of the oxygen absorber composition can be confirmed and the detection of metallic foreign matter can be performed simultaneously. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present invention will be described below, but the content of the present invention is not limited to the embodiment described below. In the present specification, the term "A to B" regarding the description of numerical values means "A or more and B or less" (when A < B) or "A or less and B or more" (when A > B). In the present invention, a combination of preferred embodiments is a more preferred embodiment.

[0012] 〔Oxygen Absorbent Composition〕 The oxygen absorbent composition of the present invention contains iron having a metallic iron content of 94% by mass or more. The metallic iron content of the iron contained in the oxygen absorbent composition is preferably 95% by mass or more, more preferably 96% by mass or more, still more preferably 96.5% by mass or more, even more preferably 97% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more. The upper limit of the metallic iron content is not particularly limited, and it may be 100% by mass or less, 99.9% by mass or less, or 99.5% by mass or less. When the metallic iron content of the iron contained in the oxygen absorbent composition is 94% by mass or more, the magnetism of the iron is stabilized, and a detection signal derived from the iron can be specified in a metal detector that uses the change in magnetic force as a detection principle.

[0013] The metallic iron content of the iron contained in the oxygen absorbent composition in the present specification was measured in accordance with the bromine-methanol dissolution EDTA titration method described in the commentary 5 of JIS M8213-1995 "Iron Ore - Method for Determination of Acid-Soluble Iron (II)". Specifically, the sample (iron) was dissolved in bromine-methanol, and the residue was filtered. Then, a certain amount of this filtrate was taken, the iron was oxidized with ammonium persulfate, and then an ammonium acetate solution was added to adjust the pH to 2.0 ± 0.2. Finally, titration was performed with a standard EDTA2Na solution using sulfosalicylic acid as an indicator.

[0014] When each manufacturing process is carried out in an inert gas atmosphere such as nitrogen as in one embodiment of the manufacturing method of the oxygen absorbent composition of the present invention described later, the metallic iron of the raw material is not oxidized in the manufacturing process, so the metallic iron content contained in the obtained oxygen absorbent can be quantified as the same content as the metallic iron of the raw material. When the oxygen scavenger composition contains components other than iron, the iron component can be separated in advance with a magnet, and the amount of metallic iron can then be determined by the above-mentioned analytical method. Furthermore, in the case of an oxygen absorbing composition having a multilayer structure such as an α layer, a β layer, and a γ layer, which is one embodiment of the present invention, the oxygen absorbing composition is crushed in advance in a mortar or the like, and then subjected to the above-mentioned analytical method, whereby the purity of metallic iron can be measured.

[0015] In order to make the metallic iron content of the iron contained in the oxygen absorbing composition of the present invention 94% by mass or more, it is preferable to produce the oxygen absorbing composition using, as a raw material, iron having a metallic iron content of 99.0% by mass or more (so-called pure iron) or secondary reduced iron powder having improved purity by carrying out a reduction process twice. Moreover, from the viewpoint of suppressing oxidation of iron during the production of the oxygen absorbing composition, it is preferable to produce the oxygen absorbing composition under a nitrogen atmosphere.

[0016] It is known that the higher the purity of iron, the less likely it is to oxidize. For this reason, conventional iron-based oxygen absorbers are manufactured by intentionally slightly oxidizing the surface of the iron in order to improve oxygen absorption performance, and the metallic iron content is at most about 93% by mass. As described above, in conventional iron-based oxygen absorbers, iron is oxidized to a mixture of multiple types of iron oxides, resulting in a mixture of ferromagnetic, non-magnetic, and non-magnetic materials. Since the magnetic properties of these iron oxides differ depending on their oxidation numbers, the detection signal of a metal detector that detects changes in magnetic force will vary greatly. In contrast, the oxygen absorber composition of the present invention increases the purity of iron in the oxygen absorber to suppress the oxidation of iron, in order to stabilize the magnetism of iron and suppress the variation in the detection signal of a metal detector.

[0017] The form of the iron contained in the oxygen scavenger composition is not particularly limited, but is preferably iron powder from the viewpoints of oxygen absorption performance, availability and ease of handling. The iron powder is not particularly limited as long as the surface of the iron is exposed, and reduced iron powder, electrolytic iron powder, sprayed iron powder, etc. can be suitably used. In addition, crushed or cut products of cast iron, etc. can also be used. The iron powder can be used alone or in combination of two or more types as required. These iron powders are also readily available commercially. When two or more types of iron are used in combination, the metallic iron content in the total iron must be 94 mass% or more. Iron powder coated with a metal halide can also be used, which can be prepared by mixing iron powder with an aqueous solution of the metal halide and then drying to remove moisture.

[0018] The average particle size of the iron powder is preferably 1 mm or less, more preferably 500 μm or less, and even more preferably 100 μm or less from the viewpoint of improving contact with oxygen, and is preferably 1 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, even more preferably 40 μm or more, and particularly preferably 53 μm or more from the viewpoint of suppressing dust generation. Note that the particle size referred to here refers to the particle size measured from the weight fraction based on the size of the sieve openings after vibrating for 5 minutes using a standard sieve conforming to ISO 3310-1:2000 (equivalent to JIS Z8801-1:2006).

[0019] The oxygen scavenger composition of the present invention contains iron as a main component. The content of iron in the oxygen scavenger composition is preferably 40 to 90 mass%, more preferably 45 to 80 mass%, further preferably 50 to 70 mass%, further more preferably 50 to 65 mass%, and particularly preferably 52 to 60 mass%, based on the mass of the oxygen scavenger composition.

[0020] There are two types of oxygen absorbers known: moisture-dependent and self-reacting. Moisture-dependent oxygen absorbers absorb oxygen when they come into contact with moisture that evaporates from products such as food and medicine, while self-reacting oxygen absorbers have moisture necessary for reaction and absorb oxygen when they come into contact with air. The oxygen absorber composition of the present invention may be either the moisture-dependent or self-reacting type, but is preferably the self-reacting type.

[0021] The oxygen scavenger composition of the present invention preferably contains water, a water retention agent, a swelling agent, and a metal salt as components other than iron.

[0022] (water) From the viewpoint of the iron-based oxygen scavenger exhibiting oxygen absorbing performance, the oxygen scavenger composition of the present invention preferably contains water. From the viewpoint of oxygen absorbing performance, the content of water in the oxygen scavenger composition is preferably 20 to 60 parts by mass, more preferably 25 to 55 parts by mass, even more preferably 40 to 50 parts by mass, and even more preferably 44 to 48 parts by mass, relative to 100 parts by mass of iron.

[0023] (Water retention agent) When the oxygen absorbing composition of the present invention contains water, it is preferable that the oxygen absorbing composition of the present invention contains a water retention agent from the viewpoint of improving the handleability of the oxygen absorbing composition. The water retention agent is a substance that can impregnate water into its interior and retain the water without leaking out.

[0024] The water retention agent is not particularly limited as long as it can retain water, but generally available porous materials and superabsorbent resins can be used. The porous material is not particularly limited, but examples thereof include diatomaceous earth, zeolite, sepiolite, cristobalite, porous glass, silica, activated clay, acid clay, activated carbon, vermiculite, and wood flour. The superabsorbent resin is not particularly limited, but examples thereof include polyacrylate resins, polysulfonate resins, polyacrylamide resins, polyvinyl alcohol resins, starch resins, cellulose resins, and polyalginic acid resins. The water retention agent preferably contains at least one selected from the group consisting of diatomaceous earth, silica, and activated carbon, more preferably contains activated carbon, and more preferably uses activated carbon in combination with a porous material or superabsorbent resin other than activated carbon, and even more preferably uses activated carbon in combination with a porous material other than activated carbon, and even more preferably uses activated carbon in combination with diatomaceous earth or silica. The above-mentioned water retention agents can be used alone or in combination of two or more kinds, if necessary. These water retention agents are also readily available as commercial products.

[0025] Among the above water retention agents, activated carbon is particularly preferred because it has a function of promoting the oxidation reaction of iron in addition to a water retention function. The type of activated carbon is not particularly limited, and may be any of wood, coconut shell, coal, etc. Activated carbon containing moisture can be used as is, and the moisture content of the activated carbon is preferably 30% by mass or more, more preferably 40% by mass or more. The water in the oxygen scavenger composition includes the water contained in the activated carbon.

[0026] The properties of the water retention agent are not particularly limited, but from the viewpoint of handling during the manufacture of the oxygen absorber, a powder with high fluidity is preferably used, and a shape close to a sphere is more preferable. In addition, from the viewpoint of handling during the manufacture of the oxygen absorber, the average particle size of the water retention agent is preferably 10 μm or more and 1000 μm or less, more preferably 100 μm or more and 500 μm or less. If the average particle size of the water retention agent is within this range, it is easy to maintain the shape of the α layer described later, and there is a tendency that a more stable powdery granule can be formed. The particles of the water retention agent can be used regardless of whether they are primary particles, aggregated particles, or granulated products, as long as they have a particle size within the above range. The water retention agent having a particle size within the above range can be used alone, or multiple types having different particle sizes can be mixed in any ratio.

[0027] The content of the water retaining agent in the oxygen scavenger composition is not particularly limited, but is preferably 20 to 500 parts by mass, more preferably 30 to 300 parts by mass, and even more preferably 40 to 200 parts by mass, relative to 100 parts by mass of water. When activated carbon is contained, the content of activated carbon in the oxygen scavenger composition is not particularly limited, but is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, still more preferably 6% by mass or less, and even more preferably 5% by mass or less, relative to the total amount of the oxygen scavenger composition. By containing activated carbon, the oxygen absorbing performance of the oxygen scavenger composition in a low humidity atmosphere of 50% RH or less can be further improved, which is preferable.

[0028] (Swelling agent) When the oxygen scavenger composition of the present invention contains water, it is preferable that the oxygen scavenger composition of the present invention contains a swelling agent from the viewpoint of moldability during production of the oxygen scavenger composition. The swelling agent is a component that swells with moisture and prevents the oxygen scavenging reaction from being inhibited by pressure molding, and is preferably used in a substantially dry state or in a semi-swollen or swollen state in which a small amount to a necessary amount of water has been absorbed. In addition to the above functions, the swelling agent preferably has either a function as a lubricant that facilitates extrusion of the mixture during production, particularly when produced by a continuous pressure molding method, or a function as a binder for maintaining the shape of the pressure molded product, and it is particularly preferable that the swelling agent has both functions. The swelling agent can have a binding function for maintaining the shape of the α layer described below.

[0029] The swelling agent is not particularly limited as long as it is a commonly known swelling agent, and known swelling agents used in foods, etc., such as inorganic swelling agents, organic swelling agents, binding agents, adhesives, and binders, can be used. Examples of inorganic swelling agents include clay minerals such as sodium bentonite, calcium bentonite, and sodium montmorillonite. Examples of organic swelling agents include organic bentonite; natural products such as defatted frozen tofu, agar, starch, dextrin, gum arabic, gelatin, and casein; semi-synthetic products such as crystalline cellulose, carboxymethylcellulose, sodium carboxymethylcellulose, calcium carboxymethylcellulose, hydroxyethylcellulose, lignin sulfonic acid, and hydroxyethylated starch; and synthetic products such as water-insoluble polyvinyl alcohol and polyvinyl methyl ether. The above-mentioned swelling agents can be used alone or in combination of two or more types as necessary. Inorganic swelling agents and organic swelling agents are preferred, and it is more preferred to use inorganic swelling agents and organic swelling agents in combination. In addition, these swelling agents can be easily obtained as commercially available products.

[0030] Clay minerals are preferred because they are inexpensive and have excellent performance. Clay minerals are also known as inorganic soaps and function as lubricants. Clay minerals swollen with water are known to exhibit high thixotropy and are preferred because they also exhibit caking properties. Cellulose-based semi-synthetic products are preferred because they exhibit excellent swelling properties. Among these, bentonites such as calcium bentonite and sodium bentonite, and carboxymethylcellulose, sodium carboxymethylcellulose, calcium carboxymethylcellulose, etc. are preferred because they are inexpensive and have strong caking power. The swelling agent preferably contains at least one selected from the group consisting of calcium carboxymethylcellulose, sodium carboxymethylcellulose, calcium bentonite, and sodium bentonite. Among them, it is more preferable to use a clay mineral and a cellulose-based semi-synthetic product in combination, and it is even more preferable to use a bentonite and a cellulose-based semi-synthetic product in combination.

[0031] The average particle size of the swelling agent is preferably from 0.001 μm to 10 μm, more preferably from 0.01 μm to 1.0 μm, from the viewpoint of suppressing dust generation and from the viewpoint of binding function.

[0032] The content of the swelling agent in the oxygen scavenger composition is preferably about 1 to 20% by mass, more preferably about 1 to 15% by mass, and even more preferably about 1.5 to 12% by mass of the oxygen scavenger composition. Also, it is preferably 2 to 15 parts by mass, more preferably about 2 to 10 parts by mass, even more preferably about 3 to 10 parts by mass, and even more preferably about 4 to 10 parts by mass, relative to 100 parts by mass of iron. It is preferably 3 to 30 parts by mass, more preferably 5 to 20 parts by mass, and more preferably 7 to 15 parts by mass, relative to 100 parts by mass of water.

[0033] (Metal Salts) The oxygen absorbing composition of the present invention preferably contains a metal salt from the viewpoint of exhibiting a larger oxygen absorbing ability. The metal salt acts catalytically on the oxidation reaction of iron to improve the activity of iron. In addition, when the oxygen absorbing agent is a moisture-dependent type, it plays a role of attracting moisture from the atmosphere, and when the oxygen absorbing agent is a self-reacting type, it plays a role of preventing moisture from evaporating into a low humidity atmosphere and being lost from the oxygen absorbing agent.

[0034] The metal salt is not particularly limited, but a metal halide is preferred. As the metal halide, any commonly known metal halide can be used without any particular limitation. The metal in the metal halide is not particularly limited, and may be, for example, at least one selected from the group consisting of alkali metals, alkaline earth metals, copper, zinc, aluminum, tin, iron, cobalt, and nickel. Among them, at least one selected from the group consisting of lithium, potassium, sodium, magnesium, calcium, barium, and iron is more preferred, and at least one selected from the group consisting of potassium, sodium, and calcium is more preferred. In addition, the halide in the metal halide is not particularly limited, and may be, for example, chloride, bromide, and iodide.

[0035] As the metal halide, calcium chloride, sodium chloride, calcium bromide, sodium bromide, calcium iodide and sodium iodide are preferred from the viewpoints of handling ease, safety and the like, and calcium chloride and sodium chloride are more preferred. The metal salts can be used alone or in combination of two or more kinds as required. These metal salts are also readily available as commercial products.

[0036] The content of the metal salt in the oxygen scavenger composition is preferably 0.5 to 15 mass %, more preferably 1 to 10 mass %, based on the weight of the composition, and the content of the metal salt is preferably 0.5 to 20 mass parts, more preferably 2 to 10 mass parts, based on 100 mass parts of iron.

[0037] In addition, as a preferred embodiment, the oxygen absorbing agent composition of the present invention preferably contains a powder having an α-layer containing a water retention agent, a swelling agent, a metal salt, and water, a β-layer containing iron with a metallic iron content of 94 mass% or more, and a γ-layer containing a porous carrier, and it is preferable that the powder form a layer structure in the order of the α-layer, the β-layer, and the γ-layer from the inside to the outside of the powder.

[0038] In the oxygen absorber composition of the present invention, by forming the layer structure (core-shell structure), the oxygen absorber composition of the present invention containing iron with high purity and low oxidation resistance has excellent oxygen absorption per unit volume, and in addition to the effect of not hindering the detection of metal foreign matter by a metal detector, it can exhibit high oxygen absorption performance. Furthermore, with the configuration of this embodiment, the oxidation reaction efficiency is high, so the amount of iron used can be reduced. The reason for such high oxygen absorption performance is unclear, but it is thought to be as follows. By having an iron-containing layer adjacent to the outside of the water-containing layer, iron is easily in contact with water and oxygen, promoting the oxidation reaction, and further, it is thought that the outer porous carrier layer improves the fluidity, improving the packing property and increasing the oxygen absorption per unit volume.

[0039] The oxygen absorber composition of the present embodiment having a core-shell structure preferably includes a powder having an α layer (hereinafter also simply referred to as "α layer") containing a water retention agent, a swelling agent, a metal salt, and water, a β layer (hereinafter also simply referred to as "β layer") containing iron, and a γ layer (hereinafter also simply referred to as "γ layer") containing a porous carrier. Here, it is preferable that the iron and the water retention agent in the oxygen absorber composition of the present embodiment are not separated as separate powders as in conventional oxygen absorber compositions, but are integrated as a layer structure of an α layer containing a water retention agent and a β layer containing iron. In addition, it is preferable that the powder form a layer structure in the order of an α layer, a β layer, and a γ layer from the inside to the outside of the powder.

[0040] In addition, the powder particles contained in the oxygen absorber composition of this embodiment preferably form a layer structure in the order of an α layer (inner side), a β layer, and a γ layer (outer side) from the inside to the outside of the powder particles. In the oxygen absorber composition of this embodiment, the powder particles mainly form a layer structure in the order of an α layer containing a water retention agent and a β layer containing iron (hereinafter also referred to as "α layer / β layer / γ layer"). As a result, the β layer containing iron is adjacent to the outside of the α layer containing a water retention agent that supplies moisture, and thus the oxidation reaction of iron is rapid and the oxidation reaction rate of iron and oxygen is also improved. Furthermore, by forming such a layer structure, it is possible to improve the oxidation reaction rate of iron and oxygen without, for example, secondary processing of iron into a flat shape or the like to expand the reaction field of the oxidation reaction of iron and oxygen. In addition, since the gamma layer containing silicas and the like is adjacent to the outside of the beta layer, the slipperiness of the powder particles is improved, and the powder particles are closely packed together, resulting in a high oxygen absorption amount per unit volume of the oxygen absorbing composition.

[0041] Here, "a layer structure in the order of α layer, β layer, γ layer" refers to a structure in which a β layer and an α layer are formed inside the voids of the γ layer, and an α layer is formed inside the voids of the β layer. Therefore, not only a structure in which the surface of the β layer and the α layer are covered with a γ layer, but also a structure in which the β layer and the α layer are filled in a part of the voids of a three-dimensional network structure of the γ layer are included, and similarly, not only a structure in which the surface of the α layer is covered with a β layer, but also a structure in which the α layer is filled in a part of the voids of a three-dimensional network structure of the β layer are included. Therefore, in this specification, "a layer structure in the order of α layer, β layer, γ layer" also includes a powder or granule in which the boundary between the α layer, the β layer, and the γ layer is not strictly clear. In addition, the powder or granule of this embodiment may further have layers other than the α layer, the β layer, and the γ layer. Furthermore, the oxygen absorber composition of this embodiment may contain a powder or granule that forms a "layer structure in the order of α layer, β layer, γ layer", and may further contain a powder or granule that does not form a "layer structure in the order of α layer, β layer, γ layer". Of course, the oxygen absorbing composition of the present embodiment may be an oxygen absorbing composition consisting only of powder particles forming a layer structure in which the α layer, the β layer, and the γ layer are arranged in this order.

[0042] The shape of the powder particles in this embodiment is not particularly limited, but examples include a sphere, an ellipse, and a cylinder, with a sphere being preferred since it tends to have better packing properties.

[0043] The powder or granule of this embodiment preferably contains 30% by mass or more and 50% by mass or less of α-layers, 49% by mass or more and 69% by mass or less of β-layers, and 0.1% by mass or more and 5.0% by mass or less of γ-layers, relative to the total amount of the powder or granules (100% by mass). When the contents of the α-layers, β-layers, and γ-layers in the powder or granules are within these ranges, a sufficient amount of moisture is supplied for the oxidation reaction of iron, the amount of oxygen absorption is increased, and the inclusion of an amount of water not required for the oxidation reaction of iron tends to be suppressed. From the viewpoint of improving oxygen absorption, the α-layer is more preferably 35% by mass to 50% by mass, and even more preferably 40% by mass to 50% by mass. The β-layer is more preferably 49% by mass to 69% by mass, and even more preferably 50% by mass to 65% by mass, and even more preferably 52% by mass to 60% by mass. The γ-layer is more preferably 0.2% by mass to 3.0% by mass, and even more preferably 0.5% by mass to 2.0% by mass.

[0044] [α layer] The α layer in this embodiment is a layer that contains a water retention agent, a swelling agent, a metal salt, and water. The α-layer contains a water retention agent in an amount of preferably 10% by mass to 85% by mass, more preferably 30% by mass to 80% by mass, based on the total amount (100% by mass) of the α-layer. When the water retention agent content is 10% by mass or more, the powder or grain can sufficiently retain water and tends to easily maintain the shape of the α-layer, and when the water retention agent content is 85% by mass or less, the volume ratio of the α-layer in the oxygen absorbing agent composition does not become too large, and the oxygen absorption amount per unit volume of the oxygen absorbing agent composition tends to be higher.

[0045] The α-layer contains a swelling agent in an amount of preferably 0.1% by mass to 20% by mass, more preferably 1.0% by mass to 10% by mass, relative to the total amount (100% by mass) of the α-layer. When the swelling agent content is 0.1% by mass or more, the shape of the α-layer is easily maintained, and when the swelling agent content is 20% by mass or less, the proportion of the water retention agent in the α-layer does not become too small, the amount of moisture supplied to the iron in the β-layer does not decrease, and the amount of oxygen absorption tends to be higher.

[0046] The α-layer contains an aqueous solution of a metal salt in an amount of preferably 30% by mass to 70% by mass, more preferably 40% by mass to 65% by mass, relative to the total amount (100% by mass) of the α-layer. When the content of the aqueous solution of a metal salt is 30% by mass or more, sufficient moisture tends to be supplied to the iron in the β-layer, and when the content of the aqueous solution of a metal salt is 70% by mass or less, the water retention agent retains sufficient water, and water migrates to the β-layer, the surface of the iron becomes wet with water, and contact between the iron and oxygen tends not to be inhibited, and in either case, the amount of oxygen absorbed tends to be higher.

[0047] When the metal salt is used as a raw material in the form of an aqueous solution, the concentration of the salt is preferably 5.0% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 20% by mass or less. The salt concentration of 5.0% by mass or more can prevent the catalytic effect of iron oxidation from being reduced, and the salt concentration of 30% by mass or less can prevent the vapor pressure of moisture from being reduced. In other words, the amount of moisture evaporation is reduced, and sufficient moisture is not supplied to the iron powder in the β layer, and in either case, the amount of oxygen absorption is prevented from being reduced.

[0048] [β layer] The β layer of the present embodiment is a layer containing iron. The iron may be contained as iron powder, and iron powder is preferred from the viewpoints of oxygen absorption performance, availability, and ease of handling. The β layer may contain only iron, or may further contain an auxiliary agent other than iron. The β-layer contains iron in an amount of preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, based on the total amount (100% by mass) of the β-layer. The β-layer may be composed of iron only. When the iron content is 80% by mass or more, the oxygen absorption amount per unit volume of the oxygen absorbing composition tends to be superior.

[0049] (auxiliary agent) The auxiliary of the present embodiment has a function of preventing the iron powder from bonding together as a result of oxidation, and a function of increasing the fluidity of the oxygen absorbing composition, making it easier to fill the oxygen absorbing composition when the oxygen absorbing composition is filled and packaged in a packaging material using a packaging machine. Examples of the auxiliary agent include powders of silica, hydrophobic silica, magnesium stearate, calcium stearate, activated carbon, zeolite, perlite, diatomaceous earth, activated clay, kaolin, talc, bentonite, activated alumina, gypsum, silica alumina, calcium silicate, magnesium oxide, graphite, carbon black, aluminum hydroxide, iron oxide, etc. These are readily available as commercial products.

[0050] The average particle size of the auxiliary is preferably 0.001 μm or more and 10 μm or less, more preferably 0.01 μm or more and 1.0 μm or less. When the average particle size is 0.001 μm or more, the auxiliary is prevented from floating in the air, improving the ease of handling, and when the average particle size is 10 μm or less, there is a tendency to prevent iron particles from bonding to each other.

[0051] [γ layer] The γ layer in this embodiment is a layer that includes a porous carrier. The porous carrier of the present embodiment is not particularly limited as long as it is a carrier having a porous shape. Here, "porous" refers to a state in which a large number of pores that can be confirmed by an electron microscope are present on the surface and inside. The porous carrier may be any of the porous substances used in the water retention agents described above, but is preferably silica. Silica means a substance whose main component is silicon dioxide (SiO2). By using silica, the oxygen absorption amount of the obtained powdery grain is increased.

[0052] The silica used in the present embodiment is not particularly limited, but examples thereof include hydrophobic silica, hydrophilic silica, wet silica, dry silica, silica gel, diatomaceous earth, acid clay, activated clay, perlite, kaolin, talc, and bentonite. The above-mentioned porous carriers can be used alone or in combination of two or more types as necessary. In addition, these porous carriers can be easily obtained as commercial products.

[0053] The γ-layer contains a porous carrier in an amount of preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total amount (100% by mass) of the γ-layer. There is no upper limit and it may be 100% by mass, and the γ-layer may be composed of only the porous carrier. From the viewpoint of improving the oxygen absorption amount per unit volume of the oxygen scavenger composition, it is preferable that the γ-layer is composed of only the porous carrier. When the content of the porous carrier is in such a range, the oxygen absorption amount tends to be higher.

[0054] The average particle size of the oxygen absorber composition of the present invention is preferably 0.3 mm or more and 5.0 mm or less, more preferably 0.5 mm or more and 2.0 mm or less. When the average particle size is 0.3 mm or more, adhesion to the powder contact part of the packaging machine during filling and packaging due to static electricity or the like is suppressed, and when the average particle size is 5.0 mm or less, there is a tendency to suppress the gap between the powder particles from becoming too large, resulting in a decrease in the amount of oxygen absorbed per unit volume. In order to obtain an oxygen absorber composition having an average particle size within the above range, for example, sieving may be performed using sieves with openings of 0.3 mm and 2 mm. The average particle size can be measured, for example, by a commercially available laser diffraction / scattering type particle size distribution measuring device ("LA-960" manufactured by Horiba, Ltd.).

[0055] [Method of producing oxygen scavenger composition] The method for producing the oxygen scavenger composition of the present invention is not particularly limited. The oxygen scavenger composition can be prepared by mixing iron and, if necessary, components other than iron until they are uniformly dispersed. The mixing device is not particularly limited, but as a specific example, a Nauta mixer (manufactured by Hosokawa Micron Corporation) or a conical mixer (manufactured by Ohno Chemical Machinery Co., Ltd.) can be used. Furthermore, the oxygen scavenger composition can be pressure-molded and, if necessary, granulated to form a solid oxygen scavenger composition.

[0056] An example of a method for producing the oxygen absorber composition having the core-shell structure is shown below. The water retention agent and swelling agent are added to a mixer, and while mixing, an aqueous solution of a metal halide salt is added, preferably over several tens of seconds, to prepare a powdery material constituting the α layer. Examples of the mixer include a vertical granulator (made by Powrex Corporation), a high-speed mixer (made by Earth Technica Corporation), and a granulator (made by Akira Kiko Co., Ltd.). Next, iron powder is added to this powdery material (α layer) and mixed, and the iron powder is attached to the outside of the α layer to prepare an (α layer / β layer) powdery material having an α layer and a β layer on the outside of the α layer. Furthermore, a porous carrier, preferably hydrophobic silica, is added to this (α layer / β layer) powdery material and mixed, and the porous carrier is attached to the outside of the β layer to prepare an (α layer / β layer / γ layer) powdery material having an (α layer / β layer) and a γ layer on the outside of the β layer.

[0057] Since iron, which is the main component of the oxygen scavenger, reacts with oxygen, the reaction with oxygen proceeds gradually even in the absence of water, metal salts, etc. Furthermore, in the manufacturing processes such as mixing, pressure molding, and granulation, a large amount of a mixture of the main component and catalyst, etc. is handled. Therefore, it is preferable to carry out each manufacturing process in an inert atmosphere (in the case of a substantially closed system, the system is usually kept in an oxygen-free reducing atmosphere) and to take appropriate measures to remove heat. The inert atmosphere is preferably a nitrogen atmosphere.

[0058] [Foreign body inspection method] Since the iron contained in the oxygen scavenger composition of the present invention has stable magnetic properties, the detection signal derived from the oxygen scavenger composition can be canceled as noise with high accuracy, and the detection of metallic foreign matter by a metal detector is not hindered. Therefore, even after the iron-based oxygen scavenger composition is enclosed in a product such as food or medicine, the detection of metallic foreign matter can be performed with high sensitivity. That is, the foreign matter inspection method of the present invention is a foreign matter inspection method by a metal detector for a product filled with the above-mentioned oxygen absorbing agent composition of the present invention, and includes a step of canceling a detection signal derived from the iron contained in the oxygen absorbing agent composition as noise. Specifically, the foreign matter inspection method of the present invention is a foreign matter inspection method by a metal detector for a product filled with an oxygen absorbing agent composition containing iron with a metallic iron content of 94 mass% or more, and includes a step of canceling a detection signal derived from the iron contained in the oxygen absorbing agent composition as noise.

[0059] In the foreign body inspection method of the present invention, inspection is performed using a metal detector that detects changes in magnetic force. There are no particular limitations on the metal detector, and commercially available ones can be used. Generally, metal detectors detect the presence or absence of metal by detecting changes in electromagnetic waves when non-inspected items pass through the metal detector (see, for example, JP 7-120435 A). If the metal is a magnetic material such as iron, nickel, or cobalt, the metal is magnetized by the magnetic field emitted from the transmitting coil, and the magnetic field lines are attracted to the metal. On the other hand, if the metal is a non-magnetic material such as stainless steel, aluminum, or copper, eddy currents are generated in the metal by the magnetic field emitted from the transmitting coil, the magnetic field emitted from the transmitting coil is consumed as thermal energy, and a magnetic field is generated in the vicinity of the metal. The presence or absence of metal is detected by detecting these with the receiving coil.

[0060] In order to detect metallic foreign bodies using a metal detector in products that contain iron-based oxygen absorbers, it is necessary to distinguish between the metallic foreign body and the iron contained in the oxygen absorber. In particular, if the metallic foreign body is magnetic, the iron contained in the oxygen absorber is also magnetic, so it is not possible to distinguish between the metallic foreign body and the oxygen absorber by simply detecting the presence or absence of a magnetic body. It is necessary to cancel the detection signal derived from the iron-based oxygen absorber as noise and detect only the metallic foreign body. The iron contained in conventional iron-based oxygen absorbers is intentionally slightly oxidized on the surface in order to improve oxygen absorption performance, resulting in a mixture of multiple types of iron oxides. Since these iron oxides have different magnetic properties depending on their oxidation number, even if we try to cancel the detection signal derived from the iron-based oxygen absorber as noise, the detection signal varies greatly and the iron-based oxygen absorber cannot be adequately identified. In contrast, the iron contained in the oxygen absorbing composition of the present invention has a high purity with a metallic iron content of 94% by mass or more and has stable magnetism, so that the detection signal originating from the oxygen absorbing composition can be identified. Therefore, according to the foreign matter inspection method of the present invention, the detection signal originating from the iron contained in the oxygen absorbing composition is canceled as noise, so that metallic foreign matter can be detected with high sensitivity.

[0061] In general, when there are multiple detection targets, the detection signals originating from the respective detection targets are identified, and detection signals of no interest are cancelled as noise, thereby increasing the sensitivity of the detection signal of interest (see, for example, Japanese Patent Application Laid-Open No. 7-120435). In the foreign body inspection method of the present invention, known means can also be applied as a means for cancelling detection signals as noise.

[0062] [Inspection method (simultaneous inspection method for checking the presence of oxygen scavenger composition and inspecting for foreign matter)] The inspection method of the present invention is an inspection method by a metal detector for a product in which the above-mentioned oxygen scavenger composition of the present invention is enclosed, and is a method in which detection is performed simultaneously using two or more frequency detectors to simultaneously check for the presence of the oxygen scavenger composition and inspect for foreign matter. That is, the inspection method of the present invention is an inspection method by a metal detector for a product in which an oxygen scavenger composition containing iron with a metallic iron content of 94 mass% or more is enclosed, and is a method in which detection is performed simultaneously using two or more frequency detectors to simultaneously check for the presence of the oxygen scavenger composition and inspect for foreign matter.

[0063] Non-magnetic materials have higher detection sensitivity at high frequencies than magnetic materials, so by using two or more frequency detectors at the same time, one detector performing detection at low frequencies and the other detector performing detection at high frequencies, it is possible to simultaneously detect magnetic and non-magnetic materials (see, for example, JP 2005-345382 A).

[0064] As described above, the iron contained in the oxygen absorber composition of the present invention has a high purity with a metallic iron content of 94% by mass or more and has stable magnetism, so that the detection signal originating from the oxygen absorber composition can be identified. Therefore, in the inspection method of the present invention, two or more frequency detectors are used to simultaneously detect magnetic bodies and non-magnetic bodies, and the detection signal originating from the iron contained in the oxygen absorber composition is identified, so that the magnetic bodies can be detected as metallic foreign bodies and the iron contained in the oxygen absorber, and the presence of the oxygen absorber composition can be confirmed and foreign body inspection can be performed simultaneously.

[0065] In the inspection method of the present invention, known means can be used to simultaneously detect magnetic and non-magnetic materials (see, for example, JP-A-2005-345382). EXAMPLES

[0066] The present embodiment will be described in detail below using examples and comparative examples, but the present embodiment can be appropriately modified as long as the effects of the present invention are achieved. In the examples and comparative examples, "parts" refers to parts by mass unless otherwise specified.

[0067] Example 1 (Production of oxygen absorber packaging) 1660 parts of diatomaceous earth (Showa Chemical Industry Co., Ltd., granular diatomaceous earth), 1500 parts of activated carbon (Futamura Chemical Co., Ltd., "S-W50", moisture content 50 mass%), 300 parts of calcium bentonite (Kunimine Kogyo Co., Ltd., "Neokunibond"), and 30 parts of sodium carboxymethylcellulose (Nippon Paper Chemicals Co., Ltd., "F350HC-4") were added to a vertical granulator and mixed for 30 seconds. Then, an aqueous sodium chloride solution in which 545 parts of sodium chloride were dissolved in 2915 parts of water was added over 30 seconds, and the mixture was mixed for another 60 seconds to obtain a powder (α layer). Next, 8100 parts of iron powder (manufactured by Höganäs Japan Co., Ltd., average particle size 90 μm) was added, and the atmosphere inside the vertical granulator was replaced with nitrogen, followed by mixing for 3 minutes to obtain a powdered material (α layer / β layer) in which a β layer was formed on the outside of the powdered material (α layer). Furthermore, 120 parts of hydrophobic silica ("D17" manufactured by Evonik Japan Co., Ltd.) was added under a nitrogen atmosphere, followed by mixing for 30 seconds to obtain an oxygen absorber composition containing a powdered material (α layer / β layer / γ layer) in which a γ layer was formed on the outside of the powdered material (α layer / β layer). The average particle size of the obtained oxygen absorber composition was 0.9 mm. In addition, when the cross section of the obtained oxygen absorbing composition was cut with a cutter and photographed with a digital microscope ("VHX-2000" manufactured by Keyence Corporation), it was confirmed that the powder granular material (α layer / β layer / γ layer) had a structure with an α layer in the center, a β layer on the outside of that, and a γ layer on the outside of that.

[0068] The iron powder used to prepare the oxygen scavenger composition was measured for its metallic iron content according to JIS M8213-1995 "Iron ore - acid soluble iron (II) determination method" (Explanation 5: Bromine-methanol dissolution EDTA titration method). As a result, the metallic iron content of the iron used to prepare the oxygen scavenger composition was 97.4% by mass. In addition, since nitrogen substitution was performed in the process of preparing the oxygen absorbing composition, there was almost no reduction in the metallic iron content of iron due to oxidation, and therefore the metallic iron content of the oxygen absorbing composition was 97.4 mass%. 0.8 g of the obtained oxygen absorbing composition was sealed in a three-sided sealed bag measuring 30 mm in length and 40 mm in width, which was made of a breathable packaging material consisting of a low-density polyethylene nonwoven fabric, to prepare an oxygen absorbing package.

[0069] (Magnetic detection test) The obtained oxygen absorber package was enclosed in an oxygen barrier bag measuring 100 mm long x 100 mm wide and sealed to obtain a sealed oxygen absorber. 3,000 of the sealed packages were produced, and a magnetic detection test was performed on the 3,000 sealed packages obtained using a metal detector (manufactured by A&D Co., Ltd., "AD-4971-3517-E") for iron and stainless steel.

[0070] First, a 0.8 mm diameter iron ball test piece was used, and the transmission frequency was set in advance in the metal detector to a sensitivity that could detect iron balls with a diameter of 0.8 mm or more as foreign objects. Five sealed oxygen absorbers were randomly selected, and a 0.8 mm diameter iron ball test piece was enclosed in each one. The sealed oxygen absorbers containing the test pieces were then passed through the metal detector to measure the detection voltage. Based on the measured detection voltage, a sensitivity threshold value was set that could detect the 0.8 mm diameter iron ball test piece. Next, 3,000 sealed oxygen absorbers (without test pieces) were passed through a metal detector to detect foreign objects. As a result of the measurement, no abnormalities were detected in any of the 3,000 sealed objects, and the detection sensitivity was shown to be less than 0.8 mm in diameter (below the threshold). The test piece was changed to an iron ball with a diameter of 1.2 mm, and the transmission frequency was changed accordingly, but the same measurement was performed as above. As a result of the measurement, no abnormality was detected in any of the 3,000 sealed bodies.

[0071] Next, the test piece was changed to a stainless steel ball with a diameter of 1.5 mm, and the transmission frequency was changed to match the test piece, but measurements were performed in the same manner as above. As a result of the measurements, no abnormalities were detected in any of the 3,000 sealed bodies, and the detection sensitivity was shown to be less than the threshold value for stainless steel ball diameters of 1.5 mm. The test piece was changed to a stainless steel ball with a diameter of 2.5 mm, and the transmission frequency was changed accordingly, but the same measurement was performed as above. As a result of the measurement, no abnormality was detected in any of the 3,000 sealed bodies.

[0072] The smaller the diameter of the iron and stainless steel balls, the better the detection sensitivity. In the food industry, the detection sensitivity for iron foreign objects is less than 0.8 mm, and for stainless steel foreign objects it is less than 1.5 mm.

[0073] In addition, when the detection voltage was lowered and 3,000 sealed objects were passed through a metal detector, iron derived from the oxygen absorber was detected in all 3,000 sealed objects, making it possible to detect that an oxygen absorber package was enclosed inside.

[0074] (Oxygen absorption time measurement) One bag of the obtained oxygen absorber package and 250 mL of air were placed in a gas barrier bag made of nylon / polyethylene laminate film and sealed. The bag was stored at 25°C, and the time it took for the oxygen concentration in the gas barrier bag to reach 0.1% or less was measured. The oxygen concentration was measured using a zirconia oxygen concentration meter.

[0075] Comparative Example 1 An oxygen absorbing composition was obtained in the same manner as in Example 1, except that iron powder having a metallic iron content of 89.8 mass % was used as the raw material iron powder. Since nitrogen substitution was also performed in the process of preparing the oxygen absorbing composition of Comparative Example 1, there was almost no decrease in metallic iron in the iron due to oxidation. Therefore, the metallic iron content of the oxygen absorbing composition of Comparative Example 1 was also 89.8 mass%.

[0076] In measurements using 0.8 mm diameter iron balls and 1.5 mm diameter stainless steel balls as test pieces, the detection sensitivity values ​​set as the threshold values ​​for 0.8 mm diameter iron balls and 1.5 mm diameter stainless steel balls were exceeded in all 3,000 oxygen absorber packages, respectively, and iron from the oxygen absorber was mistakenly detected as a foreign matter. In measurements using iron balls with a diameter of 1.2 mm and stainless steel balls with a diameter of 2.5 mm as test pieces, no abnormalities were detected in any of the 3,000 oxygen absorber packages, and the detection sensitivity was shown to be less than 1.2 mm in diameter (below the threshold) for iron balls and less than 2.5 mm in diameter (below the threshold). However, these detection sensitivities are insufficient for use in conjunction with metal inspection.

[0077] In addition, when the detection voltage was lowered and 3,000 sealed objects were passed through a metal detector, iron derived from the oxygen absorber was detected in all 3,000 oxygen absorber packages, making it possible to detect that the oxygen absorber packages were enclosed.

[0078] Comparative Example 2 A magnetic detection test and measurement of oxygen absorption time were carried out in the same manner as in Example 1, except that the oxygen absorber package was changed to "AGELESS GLS-50" (a glycerin-based oxygen absorber manufactured by Mitsubishi Gas Chemical Company, Inc.).

[0079] In the measurement using a 0.8 mm diameter iron ball and a 1.5 mm diameter stainless steel ball as the test pieces, no abnormalities were detected, and the detection sensitivity was shown for iron balls with diameters of less than 0.8 mm (below the threshold) and stainless steel balls with diameters of less than 1.5 mm (below the threshold). The test pieces were changed to iron balls with diameters of 1.2 mm and stainless steel balls with diameters of 2.5 mm, respectively, and the measurement was performed in the same manner as above, except that the transmission frequency was changed to match them. As a result of the measurement, no abnormalities were detected in any of the 3,000 sealed bodies.

[0080] In addition, when the detection voltage was lowered and 3,000 sealed packages were passed through a metal detector, the metal detector was not able to detect that an oxygen absorber package was enclosed inside because Ageless GLS-50 does not contain iron.

[0081] Comparative Example 3 A magnetic detection test and measurement of oxygen absorption time were carried out in the same manner as in Example 1, except that the oxygen absorber packaging was changed to "AGELESS GE-50" (erythorbic acid-based oxygen absorber manufactured by Mitsubishi Gas Chemical Company, Inc.).

[0082] In the measurement using a 0.8 mm diameter iron ball and a 1.5 mm diameter stainless steel ball as the test pieces, no abnormalities were detected, and the detection sensitivity was shown for iron balls with diameters of less than 0.8 mm (below the threshold) and stainless steel balls with diameters of less than 1.5 mm (below the threshold). The test pieces were changed to iron balls with diameters of 1.2 mm and stainless steel balls with diameters of 2.5 mm, respectively, and the measurement was performed in the same manner as above, except that the transmission frequency was changed to match them. As a result of the measurement, no abnormalities were detected in any of the 3,000 sealed bodies.

[0083] In addition, when the detection voltage was lowered and 3,000 sealed packages were passed through a metal detector, the metal detector was not able to detect the presence of an oxygen absorber package inside because Ageless GE-50 does not contain iron.

[0084] [Table 1]

[0085] For the oxygen absorber package of Comparative Example 1 using an iron-based oxygen absorber, the presence of the oxygen absorber package could be confirmed by a metal detector, but the detection sensitivity was insufficient to use in conjunction with metal inspection. Therefore, it is difficult to detect metal foreign matter after the oxygen absorber is enclosed in products such as food and medicine. For the oxygen absorber packages of Comparative Examples 2 and 3 using non-ferrous oxygen absorbers, the presence of the oxygen absorber package cannot be confirmed using a metal detector because the oxygen absorbers do not contain iron. Also, the oxygen absorption time was slower than that of Example 1 using an iron-based oxygen absorber, and the oxygen absorption performance was low. In contrast, with the oxygen absorbing composition of Example 1, the presence of the oxygen absorbing composition could be confirmed by a metal detector, and the iron balls and stainless steel balls could be detected with high sensitivity. [Industrial Applicability]

[0086] According to the oxygen absorber composition of the present invention, the detection of metallic foreign matter by a metal detector is not hindered, and the detection signal derived from the oxygen absorber composition is cancelled as noise, so that the detection of metallic foreign matter can be performed with high sensitivity even after the iron-based oxygen absorber composition is enclosed in products such as food, medicine, etc. Furthermore, by performing detection using a metal detector equipped with two or more frequency detectors, the presence of the oxygen absorber composition can be confirmed and the detection of metallic foreign matter can be performed simultaneously.

Claims

1. A method for producing an oxygen scavenger composition containing iron powder, water, a water retention agent, a swelling agent, and a metal salt as ingredients, comprising the steps of: The iron powder has a metallic iron content of 95% by mass or more and an average particle size of 20 μm or more; The method for producing an oxygen scavenger composition, wherein the components are mixed in a nitrogen atmosphere.

2. The oxygen scavenger composition comprises a powder having an α-layer containing a water retention agent, a swelling agent, a metal salt and water, a β-layer containing iron powder having a metallic iron content of 95% by mass or more, and a γ-layer containing a porous carrier; 2. The method for producing an oxygen absorbing composition according to claim 1, wherein the powder or granule forms a layer structure in which the α layer, the β layer, and the γ layer are arranged in this order from the inside to the outside of the powder or granule.

3. The method for producing an oxygen absorbing composition according to claim 2, wherein the water retention agent contains at least one selected from the group consisting of diatomaceous earth, silica, and activated carbon.

4. The method for producing an oxygen absorbing composition according to claim 2 or 3, wherein the swelling agent contains at least one selected from the group consisting of calcium carboxymethylcellulose, sodium carboxymethylcellulose, calcium bentonite and sodium bentonite.

5. The method for producing an oxygen absorbing composition according to any one of claims 2 to 4, wherein the powder or granule contains, relative to the total amount of the powder or granule, 30% by mass or more and 50% by mass or less of the α layer, 49% by mass or more and 69% by mass or less of the β layer, and 0.1% by mass or more and 5.0% by mass or less of the γ layer.

6. The method for producing an oxygen absorbing composition according to any one of claims 2 to 5, wherein the α layer contains the swelling agent in an amount of 1.0% by mass or more and 10% by mass or less based on the total amount of the α layer.

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