Oxygen absorptive resin composition, molding and multilayer structure

Abstract

To provide an oxygen absorptive resin composition which can exhibit excellent oxygen absorption performance while contributing to SDGs, and a molding and a multilayer structure using the same.SOLUTION: An oxygen absorptive resin composition contains a deoxidant agent composition containing pregelatinized starch and iron powder as main components, and a polyolefin resin.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an oxygen-absorbing resin composition, and a molded article and a multilayer structure using the same. [Background technology]

[0002] Oxygen absorbers that remove oxygen have been used for the purpose of preventing oxidation of various products that are easily deteriorated by oxygen, such as food, medicine, and metal products. The form of this oxygen absorber that was developed early and is still widely used today is a granular or powdered oxygen absorber composition packed in a small bag. As an improvement over this, a film or sheet form in which the oxygen absorber composition is fixed has been considered as a safe oxygen absorber that is easier to handle, has a wide range of applications, and is free from problems such as accidental ingestion. Such a film or sheet-like oxygen absorber can be used, for example, as a packaging container or packaging bag, and the packaging container or packaging bag itself can be provided with oxygen absorbing properties.

[0003] In general, in order to form an oxygen absorbing composition into a film or sheet, a method is simply used in which a granular or powdery oxygen absorbing composition is compounded using a thermoplastic resin as a matrix component (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-72941 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the Sustainable Development Goals (SDGs) have been proposed as a way to overcome the environmental problems caused by the excessive use of fossil fuels while promoting new industrial development and economic growth, and the use of biomass has been attracting attention as part of this.

[0006] Biomass is organic matter produced by living organisms through photosynthesis using solar energy from water and carbon dioxide, and is a sustainable, renewable resource as long as life and solar energy exist. Furthermore, the carbon dioxide released when biomass is burned differs from that released when fossil fuels are burned; it is carbon dioxide absorbed from the atmosphere through photosynthesis during the growth of living organisms, and does not contribute to the release of new carbon dioxide into the atmosphere. This type of biomass can be called a "carbon neutral" resource.

[0007] For example, even in the case of the above-mentioned film or sheet-shaped oxygen absorbers, if at least a part of the thermoplastic resin used as the matrix component could be switched from fossil fuel-derived raw materials to biomass-derived raw materials, it may be possible to contribute to the achievement of the SDGs by reducing the amount of fossil fuel used and plastic waste.

[0008] Therefore, an object of the present invention is to provide an oxygen-absorbing resin composition that can exhibit excellent oxygen-absorbing performance while contributing to the SDGs, and a molded article and a multilayer structure using the same. [Means for solving the problem]

[0009] That is, the gist of the present invention is as follows. [1] An oxygen-absorbing resin composition comprising pregelatinized starch, an oxygen scavenger composition containing iron powder as a main component, and a polyolefin resin. [2] The oxygen-absorbing resin composition according to the above [1], wherein the total content of the pregelatinized starch and the oxygen scavenger composition is 10% by mass or more and 60% by mass or less. [3] The oxygen-absorbing resin composition according to [1] or [2] above, wherein the mass ratio of the pregelatinized starch to the oxygen scavenger composition [pregelatinized starch / oxygen scavenger composition] is 0.15 or more and 2.5 or less. [4] The oxygen-absorbing resin composition according to any one of the above [1] to [3], wherein the pregelatinized starch is pregelatinized rice. [5] The oxygen-absorbing resin composition according to any one of [1] to [4] above, wherein the polyolefin resin is at least one selected from the group consisting of polyethylene, polypropylene, and ethylene-propylene copolymer. [6] A molded article comprising the oxygen-absorbing resin composition according to any one of [1] to [5] above. [7] The molded article according to [6] above, wherein the molded article is a film or a sheet. [8] A multilayer structure comprising an oxygen-absorbing layer made of the molded article according to [6] or [7] above. [Advantages of the Invention]

[0010] According to the present invention, it is possible to provide an oxygen-absorbing resin composition that can exhibit excellent oxygen absorption performance while contributing to the SDGs, as well as a molded article and a multilayer structure using the same. [Embodiments for Carrying Out the Invention]

[0011] Embodiments of the oxygen-absorbing resin composition according to the present invention, as well as a molded article and a multilayer structure using the same, will be described in detail below. In this 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). Further, in the present invention, a combination of preferred embodiments is a more preferred embodiment.

[0012] [Oxygen-Absorbing Resin Composition] The oxygen-absorbing resin composition of the present invention contains alpha-starch, a deoxidizer composition containing iron powder as a main component, and a polyolefin resin. Due to the above configuration, the oxygen-absorbing resin composition of the present invention can exhibit excellent oxygen absorption performance while contributing to the SDGs.

[0013] Hitherto, polyolefin resins derived from fossil fuels have been widely used as thermoplastic resins as matrix components. However, if at least a portion of the thermoplastic resin used as the matrix component could be switched from fossil fuel-derived raw materials to biomass-derived raw materials, it could contribute to the achievement of the SDGs by reducing fossil fuel consumption and plastic waste. Therefore, as a result of intensive research, the present inventors focused on a resin using pregelatinized starch as a raw material derived from biomass, and investigated replacing at least a part of a thermoplastic resin used as a matrix component with a resin using pregelatinized starch. As a result, they surprisingly found that the oxygen absorbing performance was dramatically improved by blending pregelatinized starch into an oxygen absorbing resin composition, and thus completed the present invention.

[0014] The reason why the oxygen absorbing performance of the oxygen absorbing resin composition of the present invention is dramatically improved is not clear, but is presumed to be as follows. Normally, in order for an oxygen-absorbing resin composition to exhibit excellent oxygen absorption performance, it is desired that the oxygen scavenger composition contained in the oxygen-absorbing resin composition, in particular the iron powder which is the main agent in the oxygen scavenging reaction, come into contact with and react with a larger amount of water and oxygen. However, in the case of an oxygen-absorbing resin composition, the oxygen absorbing composition is fixed in a resin matrix, so that the oxygen absorbing composition has limited opportunities to come into contact with water and oxygen, and the oxygen absorbing performance that the oxygen absorbing composition inherently has tends not to be fully exhibited. In contrast, in the oxygen absorbing resin composition of the present invention, since pregelatinized starch is kneaded into the resin matrix together with the oxygen absorbing agent composition, it is believed that the moisture held or absorbed by the pregelatinized starch is appropriately and continuously supplied to the adjacent particles of the oxygen absorbing agent composition. As a result, it is presumed that the oxygen absorbing performance inherent to the oxygen absorbing agent composition is fully exhibited, and the oxygen absorbing performance is dramatically improved compared to when the oxygen absorbing resin composition does not contain pregelatinized starch.

[0015] Hereinafter, the oxygen absorbing resin composition according to this embodiment will be described in detail.

[0016] <Pregelatinized starch> The pregelatinized starch used in the present invention functions as a matrix component and a filler of the oxygen-absorbing resin composition. In particular, since the oxygen-absorbing resin composition of the present invention contains pregelatinized starch together with the oxygen scavenger composition, the moisture retained or absorbed by the pregelatinized starch can be appropriately and continuously supplied to the adjacent particles of the oxygen scavenger composition, so that the inherent oxygen absorbing performance of the oxygen scavenger composition can be fully exhibited, and the oxygen absorbing performance of the oxygen absorbing resin composition as a whole is dramatically improved.

[0017] In this specification, "pregelatinized starch" refers to starch that has been gelatinized (gelatinized) by the addition of moisture and heat, and has been given thermoplastic properties.

[0018] Examples of raw materials for such gelatinized starch include grains containing starch as a main component, such as rice, wheat, sugarcane, buckwheat, corn, potatoes, sweet potatoes, and other tubers, and beans such as soybeans and red beans. Among these, rice is preferably used. The above raw materials may be used alone or in combination of two or more.

[0019] Among them, pregelatinized starch is preferably pregelatinized rice made from rice as a raw material. The rice used as the raw material is not particularly limited, but in consideration of food issues, "non-edible rice" that is not eaten, such as old rice or broken rice, is usually used.

[0020] The content of gelatinized starch in the oxygen-absorbing resin composition is, for example, 1% by mass or more and 55% by mass or less, and from the viewpoints of contributing to the SDGs, oxygen absorption performance, and molding processability, it is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 15% by mass or more and 35% by mass or less.

[0021] <Oxygen Absorber Composition> The oxygen scavenger composition used in the present invention contains iron powder as a main component. The iron powder in the oxygen scavenger composition is a main agent for the oxygen scavenging reaction. The oxygen scavenger composition is used in a granular or powdered form and is dispersed in a resin matrix to exhibit oxygen absorbing performance.

[0022] The oxygen absorbing composition is not particularly limited as long as it contains iron powder as a main component, and any known oxygen absorbing composition can be used. In this specification, the oxygen absorbing composition "containing iron powder as a main component" means that the content of iron powder in the oxygen absorbing composition is 60 mass % or more. The content of iron powder in the oxygen absorbing composition is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and the upper limit is, for example, 100% by mass, preferably 99% by mass or less. Specifically, the content of iron powder in the oxygen absorbing composition is preferably 80% by mass or more and 100% by mass or less, more preferably 85% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 99% by mass or less, and even more preferably 95% by mass or more and 99% by mass or less.

[0023] The iron powder used in the oxygen scavenger composition is not particularly limited as long as it can be dispersed in a resin and can cause an oxygen scavenging reaction, and any iron powder that is usually used in oxygen scavenger compositions can be used. The iron powder is preferably one in which the surface of iron (zero-valent metallic iron) is exposed, but may also have a very thin oxide film like a normal metal surface, as long as it does not impair the effects of the present invention. Specific examples of the iron powder that can be used include reduced iron powder, sponge iron powder, sprayed iron powder, ground iron powder, electrolytic iron powder, and pulverized iron. In addition, iron powder with a low content of oxygen and silicon as impurities is preferred, and iron powder with a metallic iron content of 95% by mass or more is particularly preferred.

[0024] The average particle size of the iron powder is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 10 μm to 200 μm, and even more preferably 20 μm to 100 μm. The maximum particle size of the iron powder is preferably 500 μm or less, more preferably 400 μm or less, even more preferably 50 μm to 350 μm, and even more preferably 50 μm to 300 μm. From the viewpoint of obtaining a molded product with good appearance, the smaller the particle size of the iron powder, the smoother the oxygen absorbing layer can be formed, which is preferable, but from the viewpoint of cost, the particle size of the iron powder may be somewhat larger as long as it does not significantly affect the appearance of the molded product. The maximum particle size and average particle size of the iron powder are measured by the method described in the Examples.

[0025] The oxygen scavenger composition may contain components other than the above-mentioned main component (base agent) as necessary. Specifically, the oxygen scavenger composition is preferably an oxygen scavenger composition comprising, for example, iron powder and a metal halide, and more preferably an oxygen scavenger composition in which a metal halide is adhered to iron powder.

[0026] The metal halide acts catalytically on the oxygen absorption reaction of metallic iron. Preferable specific examples of the metal constituting the metal halide include at least one selected from the group consisting of alkali metals, alkaline earth metals, copper, zinc, aluminum, tin, iron, cobalt, and nickel. In particular, at least one selected from the group consisting of lithium, potassium, sodium, magnesium, calcium, barium, and iron is preferred. Preferable specific examples of the halide include chloride, bromide, and iodide, with chloride being particularly preferred, and calcium chloride being more preferred. The content of the metal halide in the oxygen scavenger composition is preferably 0.01 parts by mass or more and 20 parts by mass or less, more preferably 0.2 parts by mass or more and 5 parts by mass or less, and even more preferably 1 part by mass or more and 3 parts by mass or less, relative to 100 parts by mass of iron powder. The metal halide is preferably dissolved in water and then coated on the iron powder.

[0027] The content of the oxygen scavenger composition in the oxygen absorbing resin composition is, for example, 5% by mass or more and 59% by mass or less, preferably 10% by mass or more and 55% by mass or less, more preferably 15% by mass or more and 50% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less. When the content of the oxygen scavenger composition is within the above range, the oxygen absorbing performance is improved and the molding processability is also good.

[0028] The content of the iron powder in the oxygen absorbing resin composition is, for example, 4% by mass or more and 59% by mass or less, preferably 8% by mass or more and 55% by mass or less, more preferably 15% by mass or more and 50% by mass or less, and even more preferably 15% by mass or more and 40% by mass or less. When the content of the oxygen scavenger composition is within the above range, the oxygen absorbing performance is improved and the moldability is also good.

[0029] The total content of the pregelatinized starch and the oxygen scavenger composition in the oxygen absorbing resin composition is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 55% by mass or less, and even more preferably 30% by mass or more and 55% by mass or less. When the content of the oxygen scavenger composition is within the above range, the oxygen absorbing performance is improved and the molding processability is also good.

[0030] The mass ratio of pregelatinized starch to the oxygen scavenger composition in the oxygen absorbing resin composition [pregelatinized starch / oxygen scavenger composition] is preferably 0.15 to 2.5, more preferably 0.5 to 2.0, and even more preferably 0.7 to 1.7. By being within the above range, the oxygen absorbing resin composition can exhibit excellent oxygen absorbing performance while contributing to the SDGs.

[0031] <Polyolefin resin> The polyolefin resin is a thermoplastic resin, and functions as a matrix component of the oxygen-absorbing resin composition.

[0032] The polyolefin resin used in the present invention preferably has a melting point of 50° C. or more and 200° C. or less. Such a polyolefin resin can disperse pregelatinized starch well and has good moldability. The melting point of the polyolefin resin is more preferably 80° C. or more and 200° C. or less, and even more preferably 100° C. or more and 180° C. or less. The melting point of the polyolefin resin is measured by the method described in the examples.

[0033] Specifically, the polyolefin resin used in the present invention includes polyolefins such as polyethylene, polypropylene, polybutene, polybutadiene, ethylene-propylene random copolymer, and ethylene-propylene block copolymer; polyolefin copolymers such as ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid copolymer, and ethylene-methacrylic acid ester copolymer; and graft polymers of the above polyolefins or the above polyolefin copolymer with silicone resin. Among these, preferably, one or more selected from the group consisting of polyethylene, polypropylene, polybutene, polybutadiene, and ethylene-propylene copolymer, more preferably, one or more selected from the group consisting of polyethylene, polypropylene, and ethylene-propylene copolymer, even more preferably, one or more selected from the group consisting of polyethylene and polypropylene, and even more preferably, polyethylene. Among polyethylene, low-density polyethylene is preferred from the viewpoint of gas permeability, and linear low-density polyethylene is more preferred. The polyolefin resin may be used alone or in combination of two or more of the above components.

[0034] The content of the polyolefin resin in the oxygen absorbing resin composition is, for example, 30% by mass or more and 90% by mass or less, preferably 35% by mass or more and 80% by mass or less, and more preferably 40% by mass or more and 70% by mass or less.

[0035] The mass ratio of pregelatinized starch to polyolefin resin in the oxygen-absorbing resin composition [pregelatinized starch / polyolefin resin] is, for example, 0.10 to 1.80, preferably 0.10 to 1.25, more preferably 0.15 to 1.00, and even more preferably 0.20 to 1.00. By being within the above range, excellent oxygen absorption performance can be exhibited while contributing to the SDGs.

[0036] <Other ingredients> The oxygen absorbing resin composition may contain other components in addition to the above-mentioned pregelatinized starch, oxygen scavenger composition and polyolefin resin. Examples of other components include thermoplastic resins other than polyolefin resins and various additives. Other thermoplastic resins include polyesters such as polyethylene terephthalate; polyamides such as nylon 6 and nylon 66; ionomers; and elastomers. Examples of additives include antifoaming agents such as calcium oxide, lubricants such as zinc stearate and calcium stearate, antioxidants such as phenols or phosphorus-based agents, colorants such as organic or inorganic dyes or pigments such as titanium oxide, dispersants such as silanes or titanates, water absorbents such as polyacrylic acid, fillers such as silica or clay, and gas adsorbents such as zeolite or activated carbon.

[0037] When the oxygen-absorbing resin composition contains the above-mentioned pregelatinized starch and other thermoplastic resins other than the polyolefin resin, the mass ratio of the other thermoplastic resins to the polyolefin resin in the oxygen-absorbing resin composition [other thermoplastic resins / polyolefin resins] is, for example, 0.5 / 99.5 or less, preferably 0.1 / 99.9 or less. In addition, it is preferable that the oxygen-absorbing resin composition does not contain other thermoplastic resins other than the above-mentioned polyolefin resin.

[0038] Furthermore, when the oxygen absorbing resin composition contains the additives as described above, the content of the additives in the oxygen absorbing resin composition is, for example, 10 mass % or less.

[0039] <Manufacturing method> The method for producing the oxygen absorbing resin composition of the present invention is not particularly limited, but the following preferred examples can be mentioned. The oxygen-absorbing resin composition can be obtained by kneading pregelatinized starch, an oxygen scavenger composition containing iron powder as a main component, and a polyolefin resin, and further kneading other thermoplastic resins and additives as necessary, to uniformly disperse the pregelatinized starch and the oxygen scavenger composition in the resin.

[0040] As the pregelatinized starch, a resin composition in which the pregelatinized starch is kneaded in advance with a resin to form a composite (hereinafter referred to as a "pregelatinized starch-containing resin composition") can be suitably used. The gelatinized starch-containing resin composition is not particularly limited, but examples thereof include those prepared by feeding grains containing starch as the main component, water, and a polyolefin resin into a twin-screw extrusion kneader, and while gelatinizing the starch in the grains in the kneader, melt-kneading the starch with the polyolefin resin to form a composite, and then pelletizing the resulting mixture.

[0041] In such a gelatinized starch-containing resin composition, the content of gelatinized starch is not particularly limited, but from the viewpoint of contributing to the SDGs and the uniformity and stability of the resin composition, it is, for example, 20% by mass or more and 80% by mass or less, preferably 40% by mass or more and 70% by mass or less, and more preferably 45% by mass or more and 70% by mass or less. Furthermore, the pregelatinized starch-containing resin composition may further contain additives such as a solubilizing agent, if necessary.

[0042] When the gelatinized starch is gelatinized rice, it is preferable to use a gelatinized rice-containing resin composition. Commercially available examples of gelatinized rice-containing resin compositions preferably used in the present invention include the rice resin series "R50E-4", "R55J-1", and "R70J-1" manufactured by Minami-Uonuma Biomass Resin Co., Ltd.

[0043] From the viewpoint of obtaining a uniform oxygen-absorbing resin composition, the following production method is more preferable. Providing a pregelatinized starch-containing resin composition (X); A step of preparing an oxygen scavenger-containing resin composition (Y) containing an oxygen scavenger composition and a polyolefin resin; and kneading the pregelatinized starch-containing resin composition (X) with an oxygen scavenger-containing resin composition (Y) to obtain an oxygen absorbing resin composition.

[0044] The step of preparing the pregelatinized starch-containing resin composition (X) may be, for example, a step of kneading pregelatinized starch with a resin to obtain the pregelatinized starch-containing resin composition (X), or a step of obtaining a commercially available pregelatinized starch-containing resin composition (X) and using it as is. In order to further improve the compatibility with the oxygen scavenger-containing resin composition (Y), it is preferable to further include a step of kneading the pregelatinized starch-containing resin composition (X) with a polyolefin resin in advance to obtain the pregelatinized starch-containing resin composition (X').

[0045] The step of preparing the oxygen scavenger-containing resin composition (Y) may be, for example, a step of kneading the oxygen scavenger composition with a polyolefin resin to obtain the oxygen scavenger-containing resin composition (Y), or a step of obtaining a commercially available oxygen scavenger-containing resin composition (Y) and using it as is.

[0046] In addition, when additives are blended as necessary, for example, in the step of obtaining the oxygen scavenger-containing resin composition (Y), the additive-containing resin composition obtained by previously kneading the additive with the polyolefin resin may be blended and kneaded together with the oxygen scavenger composition and the polyolefin resin, or a commercially available pregelatinized starch-containing resin composition (X) or oxygen scavenger-containing resin composition (Y) containing additives may be obtained and used as is.

[0047] [Molded body] The molded article of the present invention is made of the oxygen-absorbing resin composition of the present invention. Such a molded article can exhibit excellent oxygen absorption performance while contributing to the SDGs.

[0048] The present molded article is not particularly limited as long as it is a molded product of the oxygen-absorbing resin composition of the present invention, but is preferably, for example, a film or sheet. In this specification, based on the "Packaging Terminology" standard of JIS Z0108:2012, a membrane-like molded product with a thickness of less than 250 μm is referred to as a "film," and a plate-like molded product with a thickness of 250 μm or more is referred to as a "sheet."

[0049] The thickness and shape of the molded article are not particularly limited, but when the molded article is a film, the thickness is, for example, 10 μm or more and less than 250 μm, preferably 10 μm or more and 200 μm or less, more preferably 50 μm or more and 200 μm or less, and when the molded article is a sheet, the thickness is, for example, 250 μm or more and 1000 μm or less, preferably 300 μm or more and 600 μm or less. The thickness of the molded article is preferably selected appropriately depending on the application.

[0050] The above molded body can be produced by a known method. For example, there may be mentioned a method for producing a molded article, which includes a step of melt-kneading an oxygen-absorbing resin composition and a step of molding the oxygen-absorbing resin composition. Specifically, when the molded product is a film or sheet, (1) the oxygen-absorbing resin composition may be melt-kneaded in an extruder, then extruded through a strand die, cooled, pelletized in a pelletizer, and the pellets of the oxygen-absorbing resin composition are pressed to obtain a film or sheet, or (2) the oxygen-absorbing resin composition may be melt-kneaded in an extruder, then formed into a film through a T-die to obtain a film or sheet. From the viewpoint of stable productivity, the above (2) is preferred.

[0051] Since the oxygen-absorbing resin composition of the present invention contains pregelatinized starch, from the viewpoints of preventing the pregelatinized starch from burning and of improving moldability, the heating temperature during kneading and extrusion is preferably from 170° C. to 195° C., more preferably from 180° C. to 190° C. Within the above range, the state of the pregelatinized starch can be maintained well.

[0052] [Multilayer structure] The multilayer structure of the present invention includes a film or sheet which is the molded article of the present invention. Such a multilayer structure has excellent oxygen absorption performance and can contribute to the SDGs. Such a multilayer structure may be any structure containing an oxygen absorbing layer made of the molded article of the present invention, and more preferably has a multilayer structure in which, for example, a gas barrier layer, an adhesive layer and an oxygen absorbing layer are laminated in this order.

[0053] <Gas barrier layer> The gas barrier layer plays a role in blocking oxygen entering from the outside. The gas barrier layer may be one layer or two or more layers in the multilayer structure depending on the purpose. By providing two or more layers, the intrusion of oxygen from the outside can be more efficiently suppressed. The gas barrier layer is preferably a layer containing one or more types selected from an inorganic vapor deposition film, a metal thin film, or a gas barrier resin such as an ethylene-vinyl alcohol copolymer or a polyamide resin, and from the viewpoint of gas barrier properties, an inorganic vapor deposition film is more preferable.

[0054] The thickness of the gas barrier layer varies depending on the constituent material. For example, when it is an inorganic vapor deposition film, it is preferably 0.01 μm or more and 100 μm or less, more preferably 0.5 μm or more and 50 μm or less, and even more preferably 1 μm or more and 30 μm or less. From the viewpoints of gas barrier properties, transparency and cost, the thickness of the gas barrier layer in the multilayer structure is preferably 2 to 20% of the total thickness of the multilayer structure, more preferably 5 to 15%, and even more preferably 5 to 10%. The gas barrier layer may be made of one material or a plurality of materials. When made of a plurality of materials, the materials may be laminated, and by using the materials in a laminated state, a higher barrier effect can be exhibited.

[0055] <Adhesive layer> The adhesive layer contains an adhesive resin as a main component. The adhesive resin is not particularly limited, and known adhesive thermoplastic resins can be used. For example, acid-modified polyolefins obtained by modifying olefin resins with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and maleic anhydride, polyester resins, and polyisocyanate resins can be used. These may be used alone or in combination of two or more. From the viewpoints of adhesion and cost, the thickness of the adhesive layer in the multilayer structure is preferably 0.1 to 15%, more preferably 1 to 10%, and even more preferably 3 to 8% of the total thickness of the multilayer structure.

[0056] <Oxygen absorbing layer> The oxygen absorbing layer is made of a film or sheet which is the molded article of the present invention. That is, the oxygen absorbing layer is made of an oxygen absorbing resin composition containing pregelatinized starch, an oxygen scavenger composition, and a polyolefin resin. Therefore, the oxygen absorbing layer preferably contains the components and the ratios described in the section [Oxygen absorbing resin composition] above.

[0057] The preferred thickness of the oxygen absorbing layer of the present invention is similar to the thickness when the molded article is a film or sheet. When the molded article is a film, the thickness is, for example, 10 μm or more and less than 250 μm, preferably 10 μm or more and 200 μm or less, more preferably 50 μm or more and 200 μm or less, and when the molded article is a sheet, the thickness is, for example, 250 μm or more and 1000 μm or less, preferably 250 μm or more and 600 μm or less. The thickness ratio of the oxygen absorbing layer in the multilayer structure is preferably 10 to 40%, more preferably 15 to 25%, and even more preferably 15 to 20% of the total thickness of the multilayer structure. Within this range, good oxygen absorbing performance can be exhibited without adversely affecting the moldability and appearance of the multilayer structure.

[0058] <Other layers> Furthermore, the multilayer structure may have layers other than the gas barrier layer, adhesive layer, and oxygen absorbing layer, if necessary. Examples of the other layers include a surface substrate layer, an oxygen permeable layer, and a sealant layer.

[0059] The surface substrate layer is a layer disposed on the gas barrier layer side, and serves as a protective layer for the gas barrier layer and also serves to improve the design and strength of the present multilayer laminate. The oxygen permeable layer is a layer that is placed on the oxygen absorbing layer side, and serves as an isolating layer to prevent items stored in the container from coming into direct contact with the oxygen absorbing layer, while also serving to quickly and efficiently allow oxygen within the container to pass through so that the oxygen absorbing layer can fully exert its oxygen absorption function. The sealant layer is a layer disposed on the oxygen-absorbing layer side, and serves as the innermost layer for heat sealing when the multilayer structure of the present invention is used as, for example, a bag-shaped packaging material. The oxygen-permeable layer may also serve as the sealant layer. The other layers are not particularly limited, and known layers can be used for each layer.

[0060] The multilayer structure of the present invention is not particularly limited as long as it contains an oxygen absorbing layer made of the molded article of the present invention, but is preferably a multilayer film or sheet, and more preferably a multilayer film. In this specification, based on the "Packaging Terminology" standard of JIS Z0108:2012, a film-like multilayer structure having a thickness of less than 250 μm is referred to as a "multilayer film," and a plate-like multilayer structure having a thickness of 250 μm or more is referred to as a "multilayer sheet."

[0061] Furthermore, the thickness of the multilayer structure is not particularly limited, but when the multilayer structure is a multilayer film, the thickness is, for example, 20 μm or more and less than 250 μm, preferably 50 μm or more and less than 250 μm, and more preferably 100 μm or more and 220 μm or less, and when the multilayer structure is a multilayer sheet, the thickness is, for example, 250 μm or more and 1000 μm or less, and preferably 250 μm or more and 600 μm or less.

[0062] The multilayer structure can be prepared by a known method. For example, the above layers can be laminated by appropriately combining known methods such as co-extrusion, various lamination methods, and various coating methods depending on the properties of the materials of each layer, the processing purpose, the processing step, etc. Specifically, there are (1) a method in which a film or sheet corresponding to each layer of the gas barrier layer and the oxygen absorbing layer is produced or prepared in advance, an adhesive obtained by dissolving an adhesive resin in a solvent such as ethyl acetate is applied to at least one layer, dried, and the two layers are dry laminated with a laminator to obtain a multilayer structure having a layer configuration in which the gas barrier layer, the adhesive layer, and the oxygen absorbing layer are laminated in this order from the outer layer to the inner layer, and (2) a method in which the materials constituting each layer are melt-kneaded with an extruder corresponding to each layer of the gas barrier layer, the adhesive layer, and the oxygen absorbing layer, and then simultaneously melt-extruded through a multilayer die such as a T-die or a circular die to obtain a multilayer structure having a layer configuration in which the gas barrier layer, the adhesive layer, and the oxygen absorbing layer are laminated in this order from the outer layer to the inner layer.

[0063] The multilayer structure of the present invention can contribute to the SDGs and has excellent oxygen absorption performance, making it suitable for packaging containers for various goods. The form of the container made of the multilayer structure of the present invention is not particularly limited, and examples thereof include a lid, a tray, a pouch, and a laminate tube, with a tray being preferred among these.

[0064] Examples of items to be stored in the container include beverages such as milk, dairy products, juice, coffee, tea, and alcoholic beverages; liquid condiments such as sauces, soy sauce, and dressings; cooked foods such as soup, stew, curry, cooked foods for infants, and cooked foods for the elderly; paste-like foods such as jam, mayonnaise, ketchup, and jelly; seafood products such as tuna, fish and shellfish; dairy products such as cheese and butter; processed meat products such as meat, salami, sausage, and ham; vegetables such as carrots and potatoes; eggs; noodles; processed rice products such as uncooked rice, cooked rice, and rice porridge; chemicals such as pesticides and insecticides; pharmaceuticals; cosmetics; pet food; miscellaneous items such as shampoo, conditioner, and detergent; and various other items. Among these, it is suitable for jellies, yokan, cooked rice, processed rice products, cooked foods for infants, cooked foods for the elderly, curries, soups, stews, jams, mayonnaise, ketchup, pet foods, and processed marine products using fruit pulp, fruit juice, coffee, etc., which are subjected to heat sterilization treatment such as boiling or retort treatment.

[0065] The container can be produced by a known method. For example, the multilayer sheet of the present invention can be molded into a container of a predetermined shape by hot molding. The molding method can be vacuum molding, compressed air molding, plug assist molding, etc. The heating temperature during molding is preferably 170°C or higher and 190°C or lower.

[0066] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention. EXAMPLES

[0067] The present embodiment will be described in detail below using examples and comparative examples, but the present embodiment can be modified as appropriate as long as the effects of the present invention are achieved.

[0068] <Material> The materials used in the examples and comparative examples are shown below. Pregelatinized starch-containing resin composition (X): Rice resin, which is a pregelatinized rice-containing resin composition ("R50E-4" manufactured by Minamiuonuma Biomass Resin Co., Ltd., composition: pregelatinized rice 50% by mass, polyethylene 50% by mass). Deoxidant-containing resin composition (Y): manufactured by Mitsubishi Gas Chemical Co., Ltd., composition: Deoxidant composition (iron powder: 98.5% by mass, calcium chloride: 1.5% by mass) 60% by mass, polyethylene (melting point 126.9°C) 22.9% by mass, other additives 17.1% by mass <Melt point measurement> The melting point of the polyethylene was measured in accordance with JIS K 0129:2005 using a differential scanning calorimeter ("DSC-60" manufactured by Shimadzu Corporation). Linear low-density polyethylene (LLDPE): "KC580S" manufactured by Japan Polyethylene Co., Ltd., melting point: 111.0°C (measurement method is the same as above.)

[0069] <Production of oxygen-absorbing resin composition and molded article thereof> Example 1 The gelatinized starch-containing resin composition (X) and the oxygen scavenger-containing resin composition (Y) were mixed in a mass ratio [(X) / (Y)] of 2 / 1 and dry-blended, and then kneaded and extruded at 180°C to 190°C using a Labo Plastomill ("4C150" manufactured by Toyo Seiki Seisakusho Co., Ltd.) and formed into a film using a T-die, to obtain a film (single layer, thickness: 150 μm) which is a molded product made of the oxygen-absorbing resin composition.

[0070] Example 2 In Example 2, a film, which is a molded body made of an oxygen-absorbing resin composition, was obtained in the same manner as in Example 1, except that a pregelatinized starch-containing resin composition (X') prepared by the following method was used instead of the pregelatinized starch-containing resin composition (X). [Preparation of pregelatinized starch-containing resin composition (X')] The pregelatinized starch-containing resin composition (X) and LLDPE were mixed and dry-blended at a mass ratio [composition (X) / LLDPE] of 1 / 1, and then the mixture was kneaded and extruded at 180°C to 190°C using a small twin-screw segment extruder ("2D15W" manufactured by Toyo Seiki Seisakusho, Ltd.), extruded through a strand die, cooled, and cut with a pelletizer to obtain pellets (pregelatinized starch-containing resin composition (X')).

[0071] Example 3 In Example 3, a film, which is a molded body made of an oxygen-absorbing resin composition, was obtained in the same manner as in Example 2, except that the mass ratio of the pregelatinized starch-containing resin composition (X) to LLDPE [composition (X) / LLDPE] for the pregelatinized starch-containing resin composition (X') was changed to 1 / 2.

[0072] Comparative Example 1 In Comparative Example 1, a film, which was a molded article made of an oxygen-absorbing resin composition, was obtained in the same manner as in Example 1, except that LLDPE was used instead of the pregelatinized starch-containing resin composition (X).

[0073] <Evaluation> The films prepared in the examples and comparative examples were subjected to the following evaluations. The results are shown in Table 1.

[0074] (oxygen absorption) The amount of oxygen absorbed was measured by the following method. First, the films (thickness: 150 μm) produced in the examples and comparative examples were cut into pieces measuring 10 mm×10 mm to obtain six samples for measurement. The two measurement samples were placed in an aluminum foil laminated plastic film bag (manufactured by San-A Chemical Co., Ltd., size 180 mm x 250 mm, hereinafter referred to as "aluminum barrier bag") together with 500 ml of air at 40°C and absorbent cotton moistened with 10 ml of ion-exchanged water, and the opening was heat-sealed. Furthermore, the oxygen concentration (initial oxygen concentration) in the aluminum barrier bag at this time was measured. The aluminum barrier bag was then immediately placed in a thermostatic chamber at 40° C. and kept there for 7 days. During this time, the oxygen concentration inside the aluminum barrier bag (oxygen concentration after storage) was measured at 3 days and 7 days, and the amount of oxygen absorbed at each time point (initial oxygen concentration−oxygen concentration after storage) was calculated. The oxygen concentration was measured using a gas analyzer (MOCON's "Check Mate 3") by inserting a hollow needle at the tip of a sampling silicon tube attached to the gas analyzer into the aluminum barrier bag through a sampling rubber sheet that had been attached to the aluminum barrier bag in advance, and measuring the oxygen concentration inside the aluminum barrier bag. The above measurement was carried out three times for each of the Examples and Comparative Examples, and the average value was calculated. The results are shown in Table 1. A larger oxygen absorption amount means a more excellent oxygen absorption performance.

[0075] [Table 1]

[0076] As shown in Table 1, it was confirmed that the oxygen absorbing resin composition containing pregelatinized rice (pregelatinized starch), an oxygen scavenger composition containing iron powder as the main component, and a polyolefin resin had excellent oxygen absorption performance (Examples 1 to 3).

[0077] On the other hand, it was confirmed that the oxygen-absorbing resin composition not containing pregelatinized starch had inferior oxygen-absorbing performance compared to the oxygen-absorbing resin compositions of the present invention (Examples 1 to 3) (Comparative Example 1).

[0078] Furthermore, the oxygen-absorbing resin compositions of the present invention (Examples 1 to 3) can contribute to the SDGs because part of the resin matrix is ​​made of pregelatinized starch, which is a raw material derived from biomass.

Claims

1. An oxygen-absorbing resin composition comprising: a pregelatinized starch; an oxygen scavenger composition containing iron powder as a main component; and a polyolefin resin.

2. 2. The oxygen-absorbing resin composition according to claim 1, wherein the total content of the pregelatinized starch and the oxygen scavenger composition is 10% by mass or more and 60% by mass or less.

3. 3. The oxygen-absorbing resin composition according to claim 1, wherein the mass ratio of the pregelatinized starch to the oxygen absorbing composition [pregelatinized starch / oxygen absorbing composition] is 0.15 or more and 2.5 or less.

4. 3. The oxygen-absorbing resin composition according to claim 1, wherein the pregelatinized starch is pregelatinized rice.

5. 3. The oxygen-absorbing resin composition according to claim 1, wherein the polyolefin resin is at least one selected from the group consisting of polyethylene, polypropylene, and ethylene-propylene copolymer.

6. A molded article comprising the oxygen-absorbing resin composition according to claim 1 or 2.

7. The molded article according to claim 6 , which is a film or a sheet.

8. A multilayer structure comprising an oxygen-absorbing layer made of the molded article according to claim 6.