Olefinic resin packaging material

Abstract

To provide a packaging material that reduces the amount of an ethylene-vinyl alcohol copolymer used and has improved recyclability, without impairing the oxygen barrier property of the packaging material.SOLUTION: In an olefinic resin packaging material including at least a base material layer having an olefinic resin, a barrier layer having an ethylene-vinyl alcohol copolymer, and an oxygen absorption layer containing an oxygen absorbent containing reduced iron, a ratio of the sum of the barrier layer and the oxygen absorption layer to 100 pts.mass of the packaging material is 9 pts.mass or more, a thickness of the barrier layer is less than 40 μm, and 50 pts.mass or more of the oxygen absorbent is used with respect to 100 pts.mass of the ethylene-vinyl alcohol copolymer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an olefin-based resin packaging material, and more specifically to an olefin-based resin packaging material that has an ethylene-vinyl alcohol copolymer-containing barrier layer and an iron-based oxygen absorber-containing oxygen absorbing layer, and that has excellent not only barrier properties but also recyclability. [Background technology]

[0002] Olefin resins such as polyethylene and polypropylene have excellent properties such as moldability, transparency, mechanical strength, and chemical resistance, and are particularly suitable for use as packaging materials for cups, trays, bottles, and the like. In the field of packaging materials, blocking oxygen is required to prevent oxidation and deterioration of the contents. However, plastic packaging materials have poorer oxygen barrier properties than glass or metal, so their oxygen barrier properties are generally improved by using a multilayer structure with an intermediate layer of an oxygen-barrier resin.

[0003] In the above-described multilayer structure, a typical example of the oxygen barrier resin is an ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as "EVOH"). However, such an oxygen barrier resin layer physically suppresses oxygen permeation, and its oxygen barrier performance is lower than that of glass, etc., so it has conventionally been used in combination with an oxygen absorber that actively absorbs permeating oxygen or residual oxygen within the container. For example, Patent Document 1 below describes a multilayer plastic container having inner and outer layers made of polypropylene, a first intermediate layer (barrier layer) made of EVOH located on the outer layer side, and a second intermediate layer (oxygen absorbing layer) made of a resin composition containing an oxygen scavenger located on the inner layer side. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3630706 Summary of the Invention [Problem to be solved by the invention]

[0005] A plastic container having the above layer structure has an excellent ability to keep the contents fresh and retain their flavor, since the barrier layer blocks permeating oxygen and the oxygen absorber absorbs permeating oxygen and remaining oxygen in the container. However, while a barrier layer of a certain thickness is necessary to improve the oxygen barrier property of a packaging material, the recent demand for recycling of plastic products has made it necessary to reduce the content of barrier resins that are different from the olefin-based resin that forms the base material of the packaging material, such as the inner and outer layers. Ethylene-vinyl alcohol copolymers in particular are susceptible to thermal decomposition, and may become discolored or generate low-molecular-weight components when heated, which may hinder the recyclability of the packaging material. On the other hand, if the barrier layer is made thinner, the oxygen barrier properties of the packaging material will be deteriorated, and there is a risk that the preservation quality of the contents will be reduced.

[0006] Therefore, an object of the present invention is to provide a packaging material in which the amount of ethylene-vinyl alcohol copolymer used is reduced without impairing the oxygen barrier properties of the packaging material, and which has improved recyclability. [Means for solving the problem]

[0007] According to the present invention, there is provided an olefin-based resin packaging material comprising at least a substrate layer having an olefin-based resin, a barrier layer having an ethylene-vinyl alcohol copolymer, and an oxygen absorbing layer containing an oxygen absorber containing reduced iron, wherein the sum of the barrier layer and the oxygen absorbing layer is contained in an amount of 9 parts by mass or more per 100 parts by mass of the packaging material, the thickness of the barrier layer is less than 40 μm, and the oxygen absorber is used in an amount of 50 parts by mass or more per 100 parts by mass of the ethylene-vinyl alcohol copolymer.

[0008] In the packaging material of the present invention, (1) The oxygen absorbing layer contains 1 to 40 parts by mass of an oxygen absorbent per 100 parts by mass of the base resin of the oxygen absorbing layer. (2) The packaging material contains an ethylene-vinyl alcohol copolymer in an amount of less than 10 parts by mass per 100 parts by mass of the packaging material, and the thickness of the oxygen absorbing layer is 1.5 times or more the thickness of the barrier layer. (3) The olefin-based resin is polypropylene. (4) The container has an inner layer and an outer layer, each of which is made of an olefin-based resin, and the oxygen absorbing layer is located on the inner layer side of the barrier layer. (5) A repro layer is provided between the barrier layer and the outer layer. (6) An easily peelable layer is provided on the outer side of the innermost layer. is preferred. [Effects of the Invention]

[0009] In the packaging material of the present invention, by providing an oxygen absorbing layer containing a specific amount of oxygen absorber relative to the EVOH content in the packaging material, it is possible to maintain excellent oxygen barrier properties despite the reduced thickness of the barrier layer made of EVOH, and to create a packaging container with excellent storage properties for the contents. The packaging material of the present invention has a reduced amount of EVOH, and therefore the recyclability of the olefin resin is improved. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing an example of the layer structure of a packaging material of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The packaging material of the present invention comprises at least a substrate layer containing an olefin-based resin, a barrier layer containing an ethylene-vinyl alcohol copolymer, and an oxygen-absorbing layer containing an oxygen absorber containing reduced iron. Fig. 1 is a cross-sectional view showing an example of the layer structure of the packaging material of the present invention, which comprises an outer layer 1, an adhesive layer 2a, a barrier layer 3, an adhesive layer 2b, an oxygen absorbing layer 4, and an inner layer 5. The outer layer 1 and the inner layer 5 each correspond to a base layer and are made of an olefin resin. The barrier layer 3 is made of EVOH, and the oxygen absorbing layer 4 is made of an oxygen absorbing layer containing an oxygen absorber including reduced iron. In the present invention, a first important feature is that the thickness of the barrier layer 3 made of the EVOH is less than 40 μm, and a second important feature is that the oxygen absorbing layer 4 contains an oxygen absorber containing reduced iron, and that the oxygen absorber is used in an amount of 50 parts by mass or more per 100 parts by weight of the EVOH used in the barrier layer. As a result, even in packaging materials with a reduced EVOH content, the oxygen absorbing layer captures permeated oxygen or oxygen within the packaging material, so that the oxygen barrier properties are not reduced and the shelf life of the contents is guaranteed.

[0012] (barrier layer) In the packaging material of the present invention, the barrier layer is made of an ethylene-vinyl alcohol copolymer (saponified ethylene-vinyl acetate copolymer), and as described above, it is important that the thickness thereof is less than 40 μm, and particularly preferably in the ranges of 1.5 to 39 μm, 3 to 30 μm, 3 to 25 μm, 3 to 20 μm, 3 to 15 μm, or 4 to 15 μm. The proportion of the barrier layer relative to 100 parts by mass of the packaging material is preferably in the range of 1.2 to 10 parts by mass. Any known ethylene-vinyl alcohol copolymer can be used for the barrier layer without any restrictions. However, from the viewpoint of barrier properties and recyclability in particular, a saponified copolymer obtained by saponifying an ethylene-vinyl acetate copolymer having an ethylene content of 20 to 60 mol % to a saponification degree of 96 mol % or more, particularly 99 mol % or more, can be preferably used. In the present invention, as described above, it is preferable to use ethylene vinyl alcohol copolymer (EVOH) as the barrier layer. In this case, it is preferable that the EVOH is contained in an amount of 10 parts by mass or less, particularly 2 to 6 parts by mass, per 100 parts by mass of the packaging material, and it is also preferable that the thickness of the oxygen absorbing layer is 1.5 times or more, 1.5 to 10 times, particularly 1.5 to 5 times the thickness of the EVOH barrier layer.

[0013] (oxygen absorbing layer) In the packaging material of the present invention, the oxygen absorbing layer is made of an oxygen absorbing resin composition containing an oxygen absorber containing reduced iron in a base resin. As described above, the oxygen absorbing layer contains an oxygen absorber containing reduced iron. It is important that the oxygen absorber is used in an amount of 50 parts by mass or more per 100 parts by weight of EVOH, and it is particularly preferable that the oxygen absorber be contained in an amount in the range of 50 to 150 parts by mass. The oxygen absorbent preferably contains reduced iron and a metal halide. By containing a metal halide, it is possible to improve the oxygen absorption performance. Rotary reduced iron powder is preferably used as the reduced iron, which has high purity and a large specific surface area, and therefore has excellent oxygen absorption performance. The content of reduced iron in the oxygen absorbent is preferably 1 to 40 mass %, and more preferably 10 to 40 mass %.

[0014] Examples of metal halides include halides of alkali metals, alkaline earth metals, copper, zinc, iron, etc. Specific examples include sodium chloride, sodium bromide, sodium iodide, potassium chloride, potassium bromide, potassium iodide, calcium chloride, magnesium chloride, barium chloride, etc. Among these, sodium chloride is preferred. These metal halides may be used alone or in combination of two or more. The metal halide is preferably blended in an amount of 0.1 to 10 parts by mass, particularly 1 to 5 parts by mass, per 100 parts by mass of reduced iron, which is the main component of the oxygen absorber.

[0015] The oxygen absorbent may further contain an alkaline substance in addition to reduced iron and a metal halide. By including an alkaline substance, the amount of hydrogen generated by the reaction between iron and water can be reduced. Examples of alkaline substances include magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, magnesium carbonate, calcium carbonate, strontium carbonate, and barium carbonate. Among these, calcium hydroxide and calcium oxide, which is a dehydrated product of calcium hydroxide, are preferred. These alkaline substances may be used alone or in combination of two or more. When the oxygen absorber contains an alkaline substance, the alkaline substance is preferably blended in an amount of 0.5 to 2 parts by mass, particularly 1 to 2 parts by mass, per 100 parts by mass of reduced iron.

[0016] The oxygen absorber can be prepared by a conventionally known method. For example, reduced iron is coarsely pulverized, and then a metal halide and, if necessary, an alkaline substance are added thereto and the resulting mixture is finely pulverized while being mixed. The finely pulverized product is then classified to remove coarse particles, and then heat-treated. After the heat treatment, the product is further classified, if necessary, to remove coarse particles, thereby obtaining the oxygen absorber.

[0017] The base resin in the oxygen absorbing layer can be a conventionally known thermoplastic resin, but from the viewpoint of the recyclability of the packaging material, it is preferable to use an olefin-based resin similar to that used in the inner and outer layers. The olefin-based resin will be described later. As mentioned above, it is important to determine the amount of oxygen absorber used based on the EVOH standard for the barrier layer, but it is also preferable that the oxygen absorbing layer contain an amount of 1 to 40 parts by mass, particularly 10 to 40 parts by mass, per 100 parts by mass of the base resin. If the amount of oxygen absorber is less than the above range, there is a risk that the oxygen absorbing performance will not be as sufficient as when it is within the above range, while if the amount of oxygen absorber is more than the above range, there is a risk that the moldability of the container will be impaired. The oxygen-absorbing resin composition can be prepared by a conventionally known method. When a small amount of oxygen absorbent is blended, it is preferable to prepare and use a masterbatch. The thickness of the oxygen absorbing layer is preferably in the range of 3 to 200 μm, 9 to 120 μm, 9 to 50 μm, or 9 to 40 μm. In particular, the ratio of the oxygen absorbing layer to 100 parts by mass of the packaging material is preferably 6 to 20 parts by mass.

[0018] (base material layer) In the packaging material of the present invention, the inner and outer base layers are made of an olefin-based resin, and examples of such an olefin-based resin include low-, medium-, or high-density polyethylene, polypropylene, polybutene-1, poly4-methyl-1-pentene, or polyolefins such as random or block copolymers of α-olefins such as ethylene, propylene, 1-butene, and 4-methyl-1-pentene, and cyclic olefin copolymers, with polypropylene being particularly preferred. The materials for the inner and outer layers may be the same or different.

[0019] Furthermore, the raw materials or part of the raw materials of the olefin resin are not limited to petroleum-derived materials, but may be chemically recycled materials from waste plastics by monomerization techniques such as gasification or liquefaction, or olefin resins produced from biomass materials such as plant-derived materials. The biomass content can be measured by measuring the radioactive carbon concentration, etc. Furthermore, when manufacturing olefin resins, from the perspective of reducing environmental impact, SVHC substances (listed under the European Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulations) such as phthalate ester compounds are not used in the polymerization stage from raw materials. S ubstance of V ery H igh C It is desirable to produce it using a catalyst system that does not use an oxidizer. Recycled materials can also be used, which are made by collecting, sorting, and cleaning multi-layer packaging materials and processed plastic materials that have been used once, then melting them down and turning them into pellets.

[0020] The inner layer and / or outer layer preferably contains a white pigment such as titanium oxide to conceal the black color of the oxygen absorbing layer derived from the iron powder. The amount of such a white pigment is preferably 1 to 20 parts by mass per 100 parts by mass of the olefin resin constituting the inner layer and / or outer layer. The thickness of the inner or outer layer is not particularly limited, but is preferably in the range of 50 to 400 μm, and is preferably 8 to 90% of the total thickness of the packaging material.

[0021] (Other layers) In addition to the barrier layer, oxygen absorbing layer, and base layer described above, the packaging material of the present invention may also be provided with an adhesive layer, a layer made of a reproduction resin (hereinafter referred to as the "reproduction layer"), an easily peelable layer, a deodorizing layer, etc. The adhesive layer may be made of a conventionally known adhesive resin, including, but not limited to, ethylene-acrylic acid copolymer, ion-crosslinked olefin copolymer, maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, acrylic acid grafted polyolefin, ethylene-vinyl acetate copolymer, etc. The thickness of the adhesive layer is not particularly limited, but is preferably in the range of 1 to 30 μm.

[0022] The reproduced resin is a resin obtained by pulverizing and reducing resins and films discharged during the process of producing the packaging material of the present invention, and is a resin primarily composed of an olefin-based resin such as polypropylene. Alternatively, due to growing environmental awareness, recycled material, chemical recycled material, or biomass material may be blended. In particular, with recycled material, it is preferable to use less EVOH and nylon-based resins in terms of deterioration of physical properties and compatibility with olefins. The reproduced resin may also contain virgin olefin-based resins. The thickness of the recycled layer is preferably in the range of 1 to 300 μm.

[0023] Furthermore, the easily peelable layer may be a conventionally known blend capable of cohesive failure, including, but not limited to, a blend of polypropylene and polyethylene, or a blend of the above blends with a rubber-based compatibilizer such as EPR, if necessary. The thickness of the easily peelable layer is not particularly limited, but is preferably in the range of 1 to 100 μm. Furthermore, a layer containing a deodorizer can be formed to prevent flavor degradation due to the oxygen absorber in the oxygen absorbing layer, and is composed of a resin composition in which an adsorbent component such as activated carbon or diatomaceous earth is blended with a base resin.

[0024] (Layer composition) The packaging material of the present invention is not limited to the layer structure shown in FIG. 1, and various layer structures can be adopted depending on the application and structure. For example, examples include outer layer / recycling layer / adhesive layer / barrier layer / adhesive layer / oxygen absorbing layer / inner layer / easy peeling layer, outer layer / recycling layer / adhesive layer / barrier layer / adhesive layer / oxygen absorbing layer / deodorizing layer / inner layer, etc. Furthermore, a plurality of repro layers, barrier layers, or oxygen absorbing layers may be provided as long as the constitution of the present invention is satisfied, and in that case, the total thickness of the respective layers is taken as the thickness.

[0025] (Manufacturing method) The packaging material of the present invention can be produced by a method known per se, except for the layer structure described above. In multilayer coextrusion, the resin layers are melt-mixed in extruders corresponding to the respective resin layers and then extruded into a desired shape through a multilayer die such as a T-die or circular die. Alternatively, the resin layers are melt-mixed in injectors corresponding to the respective resin layers and then co-injected or sequentially into an injection mold to produce a multilayer container or a preform for a container. Other lamination methods, such as dry lamination, sandwich lamination, and extrusion coating, can also be used.

[0026] The packaging material may take the form of a film, a sheet, a parison or pipe for forming a bottle or tube, a preform for forming a bottle or tube, etc. A bottle can be formed from the parison, pipe, or preform by pinching off the extrudate with a pair of split dies and blowing a fluid into the interior. Alternatively, a stretch-blown bottle or the like can be obtained by cooling the pipe or preform, heating it to a stretching temperature, stretching it axially, and blowing it circumferentially with fluid pressure.

[0027] Furthermore, the film or sheet can be subjected to vacuum forming, pressure forming, bulging forming, plug assist forming or the like to obtain a packaging container in the shape of a cup, tray or the like. Furthermore, the multilayer film can be laminated or folded into a bag-like shape and the periphery heat-sealed to form a bag-like container. [Example]

[0028] (Resin used and layer structure) From the inner layer, the layers were an easy-peel layer made of a mixture of polyethylene and polypropylene, a base layer made of block polypropylene with added titanium white pigment, an oxygen-absorbing layer made of a polypropylene oxygen-absorbing resin composition prepared by blending a base resin made of random polypropylene with an oxygen absorber (containing 2 parts by mass of sodium chloride per 100 parts by mass of reduced iron, indicated as "OXY" in the table), an adhesive layer (10 μm thick) modified with maleic anhydride, a barrier layer made of ethylene-vinyl alcohol copolymer (ethylene content 32 mol%, indicated as "EVOH" in the table), an adhesive layer (15 μm thick) modified with maleic anhydride, a repro layer (85 μm thick) made of a mixture of crushed decorative material scraps and block polypropylene, and a base layer made of block polypropylene with added titanium white pigment.

[0029] (Evaluation of the shelf life of the contents) Cooked rice was placed inside the container, and the container was heat-sealed using a gas-impermeable metal foil laminated film under an atmosphere with an oxygen concentration of 0.5%. At this time, the internal volume of the container was 220 cm 3The headspace inside the container was 50 ml. After storing the container at 30°C and 80% RH for 100 days, the oxygen concentration inside the container was measured using a gas chromatograph (product name: CP4900, manufactured by Agilent). The shelf life of the contents was evaluated based on the oxygen concentration inside the container after storage according to the following criteria. ○: The oxygen concentration inside the container after storage is less than 0.5%. △: The oxygen concentration inside the container after storage is 0.5% or more and less than 1.0%. ×: The oxygen concentration in the container after storage is 1.0% or more.

[0030] (Recyclability evaluation) The proportion of functional material layers (EVOH layer and OXY layer) contained in 100 parts by mass of packaging material was evaluated as recyclability using the following criteria. The proportion of EVOH and OXY in the recyclable layer can cause foaming due to EVOH degradation and problems with film formation, which affect recyclability. ○: The ratio of functional material to 100 parts by mass of packaging material is less than 20 parts by mass △: The ratio of functional materials to 100 parts by mass of packaging material is 20 parts by mass or more and less than 30 parts by mass

[0031] (Examples 1 to 12, Comparative Example 1) The packaging material (multilayer sheet) shown in FIG. 1 was produced by coextrusion lamination using the above-mentioned resin and an oxygen-absorbing resin composition with an adjusted oxygen absorber content. The center of the produced sheet was cut out in the width direction, and the thickness of each layer was measured using an optical microscope. The results are shown in Table 1. This multilayer sheet was also used to form a multilayer container with an outer opening diameter of 140 × 105 mm, a height of 40 mm, and a capacity of 330 ml using a vacuum / pressure molding machine. The resulting container had a flange, and the minimum wall thickness in Example 1 was 150 μm. The thickness of each layer was generally 3 / 10 of the thickness in Table 1. (For example, in Example 1, the thickness of the EVOH layer was 30 μm in the sheet but 9 μm in the molded container. The oxygen-absorbing layer was also 100 μm in the sheet but 30 μm in the molded container. The same applies to the other layers.) The thickness of the flange was the same as the thickness of the produced packaging material (multilayer sheet).

[0032] [Table 1]

[0033] (Consideration) The container obtained in Comparative Example 1 had poor storage stability. On the other hand, containers obtained using a packaging material (Example 9) with a barrier layer thickness of 12 μm and an oxygen-absorbing layer thickness of 40 μm had a minimum barrier layer thickness of 3.6 μm and a minimum oxygen-absorbing layer thickness of 12.0 μm. The containers obtained in Example 9 had excellent storage stability and recyclability by setting the thickness of the oxygen absorber to be 3 to 4 times the thickness of the barrier layer and the ratio (parts by mass) [A] + [B] of (barrier layer + oxygen-absorbing layer) per 100 parts by mass of the packaging material to be 9.0 parts by mass or more. Furthermore, containers obtained using a packaging material (Example 7) with a barrier layer thickness of 15 μm and an oxygen-absorbing layer thickness of 30 μm had a minimum barrier layer thickness of 4.5 μm and a minimum oxygen-absorbing layer thickness of 9.0 μm. In the container obtained in Example 7, by making the thickness of the oxygen absorber more than twice the thickness of the barrier layer, a container with excellent storage stability and recyclability was obtained even when the ratio (parts by mass) [A] + [B] of (barrier layer + oxygen absorbing layer) to 100 parts by mass of packaging material was 9.0 parts by mass. Although a certain barrier layer is necessary for preservation, it is believed that the oxygen that permeated through the barrier layer was absorbed by the oxygen absorbing layer. Therefore, it was found that the amount of oxygen absorbing layer and barrier layer contained in the entire packaging material could be reduced, achieving both preservation and recyclability. [Industrial Applicability]

[0034] The packaging material of the present invention, which is primarily made of an olefin-based resin, has excellent barrier properties and also exhibits excellent recyclability of the olefin-based resin, even when the content of ethylene-vinyl alcohol copolymer constituting the barrier layer is reduced. Therefore, the packaging material can be suitably used for food containers that require the contents to be preserved for a long period of time, and in particular for general-purpose containers that are mass-produced and require recyclability. [Explanation of symbols]

[0035] 1 outer layer, 2a, 2b adhesive layers, 3 barrier layer, 4 oxygen absorbing layer, 5 inner layer.

Claims

1. An olefin-based resin packaging material comprising at least a substrate layer having an olefin-based resin, a barrier layer having an ethylene-vinyl alcohol copolymer, and an oxygen absorbing layer containing an oxygen absorber including reduced iron, The sum of the barrier layer and the oxygen absorbing layer is 9 parts by mass or more relative to 100 parts by mass of the packaging material; and the barrier layer has a thickness of less than 40 μm; An olefin-based resin packaging material, characterized in that the oxygen absorber is used in an amount of 50 parts by mass or more per 100 parts by mass of ethylene-vinyl alcohol copolymer.

2. 2. The olefin-based resin packaging material according to claim 1, wherein the oxygen absorbing layer contains 1 to 40 parts by weight of an oxygen absorbent per 100 parts by weight of the base resin of the oxygen absorbing layer.

3. 3. The olefin-based resin packaging material according to claim 1, wherein the packaging material contains an ethylene-vinyl alcohol copolymer in an amount of less than 10 parts by mass per 100 parts by mass of the packaging material, and the thickness of the oxygen absorbing layer is 1.5 times or more the thickness of the barrier layer.

4. 3. The olefin-based resin packaging material according to claim 1, wherein the olefin-based resin is polypropylene.

5. 3. The olefin-based resin packaging material according to claim 1, wherein the substrate layer containing the olefin-based resin is an inner layer and an outer layer, and the oxygen absorbing layer is located on the inner layer side of the barrier layer.

6. 6. The olefin-based resin packaging material according to claim 5, further comprising a repro layer between the barrier layer and the outer layer.

7. 6. The olefin-based resin packaging material according to claim 5, further comprising an easily peelable layer on the outer side of the innermost layer.

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