JP5311344B2 - Oxygen absorbing multilayer pellet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layer pellet having sufficient oxygen-absorbing performance for practical application, suppressing generation of odor by reducing generation of an uncomfortable odor component by absorption of oxygen and having less deactivation of the oxygen-absorbing performance at storage. <P>SOLUTION: The oxygen absorptive multi-layer pellet 10 includes an intermediate layer 11 formed by a resin composition (M) containing a thermoplastic resin (A) substantially having a carbon-carbon double bond only in a main chain and a transition metal salt (C), and a cover layer 12 formed by a thermoplastic resin (B) comprising a hydrocarbon based resin. The resin composition (M) contains the transition metal salt (C) in a range of 0.001-0.5 pt.mass (10-5,000 ppm) in a metal conversion amount based on 100 pts.mass of the thermoplastic resin (A), and the cover layer 12 is superposed so as to cover a periphery of the intermediate layer 11. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a pellet having an oxygen absorption capability that suppresses the deterioration of a resin and the generation of odor due to a transition metal salt, and further has little deactivation of the oxygen absorption capability during storage.

  In recent years, in order to improve the preservability of the contents of packaging containers, especially food, beverages, pharmaceuticals, cosmetics, etc., a container containing a gas barrier resin mixed with an oxygen-absorbing material, an outer layer is provided with a gas barrier resin layer, and an inner layer is provided. A container made of a laminated body provided with an oxygen-absorbing material layer that absorbs residual oxygen in the container has been proposed.

  Conventionally, as an oxygen-absorbing material generally used, for example, an oxygen-absorbing material composed of an iron-based compound, an oxygen-absorbing material composed of an ethylenically unsaturated hydrocarbon polymer, a transition metal salt, and a thermoplastic resin, for example. Examples thereof include a resin composition.

  An oxygen absorbing material made of an iron-based compound has good oxygen absorption performance. However, the presence of moisture is indispensable, and the oxygen absorption performance may vary depending on the water activity of the contents. In addition, when iron-based oxygen absorbers are kneaded into thermoplastic resins and used as packaging materials, the use of microwave ovens is restricted due to the inclusion of metals, or foreign objects using metal detectors after filling foods, etc. There is a problem that contamination inspection cannot be performed. Furthermore, there is a problem that the transparency of the container cannot be ensured and the container cannot be applied to a use requiring transparency (see Patent Document 1).

  On the other hand, an oxygen-absorbing resin composition comprising an ethylenically unsaturated hydrocarbon polymer, a transition metal salt, and a thermoplastic resin is an odor component generated due to oxidative degradation of the thermoplastic resin after oxygen absorption. There are problems such as coloring.

  Patent Document 2 discloses an oxygen-absorbing resin composition containing an ethylenically unsaturated hydrocarbon polymer and a transition metal salt, but there is no description about odor. When an oxygen absorption function is imparted to a thermoplastic resin having poor gas barrier properties, the oxygen absorption rate in the packaging material using the resulting oxygen-absorbing resin composition can achieve the desired performance. However, with the absorption of oxygen, not only the ethylenically unsaturated hydrocarbon polymer but also the thermoplastic resin is oxidized by the action of the transition metal salt. This oxidation generates a low-molecular oxide, which causes a problem in applications where the flavor is particularly important by shifting to packaged contents such as food.

  Patent Document 3 proposes an oxygen-absorbing resin composition having a core-sheath structure. However, the transition metal salt that is an oxidation catalyst is kneaded into a thermoplastic resin that is easily auto-oxidized such as polyethylene, and it is easily guessed that the resin is colored due to oxidative degradation and the generation of odor.

JP 2008-6635 A Japanese Patent Laid-Open No. 5-115776 JP 2007-23193 A

  Therefore, the object of the present invention is to have a practically sufficient oxygen absorption performance, reduce the generation of unpleasant odor components due to oxygen absorption, suppress the generation of odor, and further deactivate the oxygen absorption performance during storage. It is to provide fewer multilayer pellets.

  The present invention provides a transition metal salt (100 parts by mass) with respect to 100 parts by mass of a thermoplastic resin (A) having a carbon-carbon double bond only in the main chain (hereinafter simply referred to as a thermoplastic resin (A)). The resin composition (M) containing C) in a metal conversion amount in the range of 0.001 parts by mass to 0.5 parts by mass (10 ppm to 5000 ppm) is used as an intermediate layer, and the periphery of the intermediate layer is made of a hydrocarbon resin. A multilayer pellet coated with a coating layer made of a thermoplastic resin (B) (hereinafter simply referred to as a thermoplastic resin (B)).

  In one embodiment, the said coating layer is laminated | stacked so that it may adjoin both surfaces of the said intermediate | middle layer.

  In one embodiment, the thermoplastic resin (A) is polyoctenylene.

  In one embodiment, the transition metal salt (C) is at least one metal salt selected from the group consisting of iron salt, nickel salt, copper salt, manganese salt, and cobalt salt.

  In one embodiment, the thermoplastic resin (B) is at least one resin selected from the group consisting of polyethylene, polypropylene, and polystyrene.

  In another embodiment, the amount of the antioxidant contained in the thermoplastic resin (B) is 1000 ppm or less.

  According to the present invention, it has a practically sufficient oxygen absorption capacity, reduces the generation of unpleasant odor components due to oxygen absorption, suppresses the generation of odor, and further reduces the deactivation of oxygen absorption performance during storage Pellets can be provided.

It is a schematic diagram which shows one embodiment of the multilayer pellet of this invention.

  The multilayer pellet of the present invention includes an intermediate layer made of a resin composition (M) containing a thermoplastic resin (A) and a transition metal salt (C), and a coating layer made of a thermoplastic resin (B). FIG. 1 shows an embodiment of the multilayer pellet of the present invention. As shown in FIG. 1, the multilayer pellet 10 of the present invention preferably has a laminated structure in which the coating layer 12 is laminated so as to be adjacent to both surfaces of the intermediate layer 11.

  The multilayer pellet of the present invention can be obtained, for example, by preparing a multilayer sheet in which both surfaces of the intermediate layer are coated with a coating layer, and cutting the resulting multilayer sheet with Cumberland or the like.

  In the multilayer pellet of the present invention, an intermediate layer made of a resin composition (M) containing a thermoplastic resin (A) and a transition metal salt (C) is coated with a coating layer made of a thermoplastic resin (B). Therefore, the transition metal salt (C) works efficiently on the thermoplastic resin (A), and furthermore, oxidative deterioration of the thermoplastic resin (B) due to the transition metal salt (C) can be suppressed. That is, it has excellent oxygen absorption performance, and generation of odorous substances due to deterioration of the thermoplastic resin (B) is extremely reduced. Furthermore, since the resin composition (M) having oxygen absorbability is covered with the thermoplastic resin (B), it becomes possible to prevent inactivation due to oxygen absorption during resin storage.

  Hereinafter, the components contained in the multilayer pellet of the present invention will be described.

(1) Thermoplastic resin (A)
The thermoplastic resin (A) used for the multilayer pellet of the present invention (hereinafter sometimes simply referred to as multilayer pellet) has a carbon-carbon double bond substantially only in the main chain. “Substantially only having a carbon-carbon double bond in the main chain” means that the carbon-carbon double bonds existing in the main chain of the thermoplastic resin (A) are all carbon-carbon double bonds in the molecule. 90% or more, and the carbon-carbon double bond existing in the side chain is 10% or less of the total carbon-carbon double bond in the molecule. The proportion of carbon-carbon double bonds present in the side chain is preferably 7% or less, more preferably 5% or less.

  Examples of the thermoplastic resin (A) include polydienes such as polybutadiene, polyisoprene, polychloroprene, poly (2-ethylbutadiene), and poly (2-butylbutadiene), which are mainly polymerized at positions 1 and 4. Ring-opening metathesis polymers of cycloolefin (polyoctenylene, polypentenylene, polynorbornene, etc.) and the like. Among these, 1,4-polybutadiene and polyoctenylene are preferable, and polyoctenylene is more preferable.

  Since such a thermoplastic resin (A) has a carbon-carbon double bond in the molecule, it can efficiently react with oxygen, and as a result, oxygen absorption performance can be obtained. Here, the “carbon-carbon double bond” does not include multiple bonds contained in the aromatic ring.

Here, the carbon-carbon double bond present in the main chain of the thermoplastic resin molecule has a smaller oxygen absorption amount and a slower oxygen absorption rate than the carbon-carbon double bond present in the side chain. Many. However, in the main chain, the adjacent carbon - having repeating units present methylene chain is more than three between carbon double bond _{(i.e., -C = C- (CH 2)} n ≧ 3 -C = C-) a It was found that the thermoplastic resin has an amount of oxygen absorbed per carbon-carbon double bond larger than expected. Therefore, in the multilayer pellet of the present invention, the adjacent carbon-carbon double bond is preferably used as the thermoplastic resin (A) from the viewpoint that odor is hardly generated and excellent oxygen absorbability can be obtained with a small addition amount. A thermoplastic resin having a repeating unit in which three or more methylene chains are present is used. Examples of such thermoplastic resins include polyoctenylene and polypentenylene, and polyoctenylene is particularly preferable.

  The amount of carbon-carbon double bonds contained in the thermoplastic resin (A) is preferably 0.001 eq / g (equivalent / g) or more, more preferably 0.005 eq / g or more, and 0.01 eq / g. g or more is more preferable. When the content of the carbon-carbon double bond is less than 0.001 eq / g, the resulting multilayer pellet tends not to have sufficient oxygen absorption performance.

  The weight average molecular weight of the thermoplastic resin (A) is preferably 1,000 to 500,000, more preferably 10,000 to 250,000, and even more preferably in the range of 40,000 to 200,000. When the weight average molecular weight of the thermoplastic resin (A) is less than 1000 or more than 500,000, the processability and handling properties of the multilayer pellet, and the mechanical properties such as strength and elongation when formed into a molded product are reduced. Tend to.

  The method for producing the thermoplastic resin (A) varies depending on the type of the thermoplastic resin (A). For example, polyoctenylene uses cyclooctene as a raw material monomer, and uses a tungsten-based catalyst, a ruthenium-based catalyst, or the like as a catalyst. Or a method of performing acyclic diene metathesis polymerization using 1,9-decadiene as a raw material monomer and using a similar catalyst. Examples of the catalyst include [1,3-bis (2,4,6-trimethylphenyl) -2-imidazolidinylidene] dichloro (phenylmethylene) (tricyclohexylphosphine) ruthenium. The polymerization can be performed without a solvent, but a solvent may be used as necessary.

  When the thermoplastic resin (A) is a ring-opening metathesis polymer of a cyclic olefin, it is unavoidable that a certain amount of oligomers are inevitably mixed due to the mechanism of the ring-opening metathesis polymerization. Under normal use conditions, problems such as odor are unlikely to occur if the monomer (cycloolefin monomer) is removed. However, when the packaging material (molded body) obtained from the multi-layer pellets is stored under high temperature and high humidity, odor may be felt in the packaged goods when these oligomers are present. On the other hand, the amount of oligomer is preferably as low as possible from the viewpoint of odor and the like, but if it is attempted to be lower than necessary, the production process becomes complicated. Therefore, in consideration of storage at high temperature and high humidity, the oligomer having a molecular weight of 1000 or less present in the ring-opening metathesis polymer is preferably 6% by mass or less, more preferably 4% by mass or less, and further preferably 2%. It is below mass%.

  Examples of the method for removing the oligomer from the ring-opening metathesis polymer include a method for removing by washing with an organic solvent such as acetone.

  The thermoplastic resin (A) may contain an antioxidant. Examples of the antioxidant include 2,5-di-tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, 4,4′-thiobis (6-tert-butylphenol), 2,2 '-Methylenebis (4-methyl-6-tert-butylphenol), octadecyl-3- (3', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate, 4,4'-thiobis (6-tert -Butylphenol), 2-tert-butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, pentaerythritol tetrakis (3-laurylthiopropionate), 2, 6-di (tert-butyl) -4-methylphenol, 2,2-methylenebis (6-tert Butyl -p- cresol), triphenyl phosphite, tris (nonylphenyl) phosphite, and the like dilauryl thiodipropionate.

  When the thermoplastic resin (A) contains an antioxidant, the amount is appropriately determined in consideration of the type, content, purpose of use, storage conditions, and the like of each component in the multilayer pellet. The amount when the antioxidant is contained is preferably 0.01 to 0.5 parts by mass (100 ppm to 5000 ppm), more preferably 0.02 to 100 parts by mass of the thermoplastic resin (A). 0.08 part by mass (200 ppm to 800 ppm). When the content of the antioxidant exceeds 0.5 parts by mass (5000 ppm), the reaction between the thermoplastic resin (A) and oxygen tends to be hindered. On the other hand, when the content of the antioxidant is less than 0.01 parts by mass (100 ppm), the reaction with oxygen proceeds during storage or melt-kneading of the thermoplastic resin (A), and the resulting resin composition (M) Before actual use, oxygen absorption performance may be reduced.

(2) Transition metal salt (C)
The transition metal salt (C) has an effect of improving the oxygen absorption performance of the resin composition (M) by promoting the oxidation reaction of the thermoplastic resin (A).

  Examples of the transition metal contained in the transition metal salt (C) include, but are not limited to, iron, nickel, copper, manganese, cobalt, rhodium, titanium, chromium, vanadium, and ruthenium. Among these, iron, nickel, copper, manganese, and cobalt are preferable, manganese and cobalt are more preferable, and cobalt is more preferable.

  Examples of the counter ion of the transition metal contained in the transition metal salt (C) include an anion derived from an organic acid or chloride. Examples of the organic acid include acetic acid, stearic acid, acetylacetone, dimethyldithiocarbamic acid, palmitic acid, 2-ethylhexanoic acid, neodecanoic acid, linoleic acid, toluic acid, oleic acid, capric acid, and naphthenic acid. Particularly preferred salts include cobalt 2-ethylhexanoate, cobalt neodecanoate, and cobalt stearate.

  A transition metal salt (C) is mix | blended in 0.001 mass part-0.5 mass part (10 ppm-5000 ppm) by metal conversion amount with respect to 100 mass parts of thermoplastic resins (A). Preferably, the transition metal salt (C) is a metal equivalent, and is 0.01 parts by weight to 0.1 parts by weight (100 to 1000 ppm), more preferably 0.02 parts by weight to 0.08 parts by weight (200 ppm to 800 ppm). ). When the blending amount of the transition metal salt (C) is less than 0.001 part by mass (10 ppm), the resulting multilayer pellet tends to have insufficient oxygen absorption performance and oxygen absorption rate. On the other hand, when the blending amount of the transition metal salt (C) exceeds 0.5 parts by mass (5000 ppm), for example, when melt-kneading the thermoplastic resin (A) and the transition metal salt (C), decomposition accompanied by heat generation The generation of gas, the formation of gels and bumps in the molded product, etc. become remarkable, and the processability tends to deteriorate. Furthermore, the thermal stability of the resin composition obtained by melt-kneading tends to decrease. There is also a concern that the original oxygen absorption performance of the thermoplastic resin (A) may be deactivated due to oxidation during processing.

(3) Thermoplastic resin (B)
In the multilayer pellet of the present invention, a thermoplastic resin (B) made of a hydrocarbon resin is used as a coating layer. This thermoplastic resin (B) has a function of covering the intermediate layer made of the resin composition (M) to prevent oxygen contact, and also provides the multilayer pellet with the characteristics of the thermoplastic resin (B). Have

  Examples of the thermoplastic resin (B) include polyethylene (very low density, low density, linear low density, medium density, high density, etc.), polypropylene (homopolypropylene, random polypropylene, block polypropylene, etc.), and polystyrene (general purpose). Polystyrene (GPPS), high-impact polystyrene (HIPS), etc.), other α-olefin copolymers, and the like, and these commercial products can be used.

  In the multilayer pellet of the present invention, preferably, both surfaces of the intermediate layer made of the resin composition (M) are coated with the thermoplastic resin (B). In the multilayer pellet of the present invention, the compatibilizer (D) may be further contained in the resin composition (M), may be contained in the thermoplastic resin (B), and the resin composition ( You may laminate | stack between the intermediate | middle layer which consists of M), and the coating layer which consists of a thermoplastic resin (B).

  The compatibilizing agent (D) improves the compatibility of these layers (resins) when the intermediate layer and the coating layer in the multilayer pellet of the present invention and other layers as required are laminated. It is contained as necessary for the purpose of giving a stable morphology to a molded product molded from the obtained multilayer pellet. The type of the compatibilizer (D) is appropriately selected depending on the combination of the type of the thermoplastic resin (B) to be used, the thermoplastic resin (A), and the like.

  As the compatibilizing agent (D), for example, in the case where the compatibilizing agent (D) is a hydrocarbon polymer containing a polar group, the compatibilizing agent (D) can be made compatibilized by a hydrocarbon polymer portion serving as a base of the polymer. The affinity between the agent (D) and the thermoplastic resin (A) is improved. Furthermore, the affinity between the compatibilizer (D) and the thermoplastic resin (B) may be improved by the polar group of the compatibilizer (D). As a result, a stable morphology can be formed in the obtained resin composition.

  Examples of the monomer capable of forming the hydrocarbon polymer portion serving as the base of the hydrocarbon polymer containing the polar group include the following compounds: ethylene, propylene, 1-butene, isobutene, 3- Α-olefins such as methylpentene, 1-hexene, 1-octene; styrenes such as styrene, α-methylstyrene, 2-methylstyrene, 4-methylstyrene, 4-propylstyrene; 1-vinylnaphthalene, 2- Vinylnaphthalenes such as vinylnaphthalene; vinylene group-containing aromatic compounds such as indene and acenaphthylene; conjugated diene compounds such as butadiene, isoprene, 2,3-dimethylbutadiene, pentadiene and hexadiene. The hydrocarbon polymer may mainly contain one of these monomers, or may mainly contain two or more.

  Using the monomer, a hydrocarbon polymer containing a polar group is prepared, and the monomer forms a hydrocarbon polymer portion composed of the following polymer: polyethylene (ultra-low Density, low density, linear low density, medium density, high density, etc.), polypropylene (homopolypropylene, random polypropylene, block polypropylene, etc.), polystyrene (general purpose polystyrene (GPPS), high impact polystyrene (HIPS), etc.), Styrene polymers such as styrene-diene block copolymers (styrene-isoprene block copolymers, styrene-butadiene block copolymers, styrene-isoprene-styrene block copolymers, etc.) and hydrogenated products thereof. Of these, styrene-diene block copolymers (styrene-isoprene block copolymers, styrene-butadiene block copolymers, styrene-isoprene-styrene block copolymers, etc.), styrene heavy polymers such as hydrogenated products thereof, and the like. Coalescence is preferred.

The polar group contained in the compatibilizer (D) is not particularly limited, but a functional group containing an oxygen atom is preferable. Specifically, polar groups that contain active hydrogen-containing polar groups (such as —SO ₃ H, —SO ₂ H, —SOH, —CONH ₂ , —CONHR, —CONH—, —OH, etc.) and no active hydrogen. Group (—NCO, —OCN, —NO, —NO ₂ , —CONR ₂ , —CONR—, etc.), epoxy group, carbonyl group-containing polar group (—CHO, —COOH, —COOR, —COR,> C═O , -CSOR, -CSOH, etc.), phosphorus-containing polar groups (-P (OR) ₂ , -PO (OR) ₂ , -PO (SR) ₂ , -PS (OR) ₂ , -PO (SR) (OR) , -PS (SR) (OR), etc.), boron-containing polar groups, and the like. Here, in the above general formula, R represents an alkyl group, a phenyl group, or an alkoxy group.

  When the compatibilizer (D) is a hydrocarbon polymer, particularly preferred polar groups include carboxyl groups such as carboxyl groups, carboxylic anhydride groups, carboxylate groups; boronic acid groups, boronic acid esters And boron-containing polar groups such as boronic acid anhydride groups and boronic acid groups.

  In the multilayer pellet of the present invention, the total mass of the intermediate layer composed of the resin composition (M) and the mass of the coating layer composed of the thermoplastic resin (B) is 90% by mass or more based on the total mass of the multilayer pellet. It is preferable that it is 95 mass% or more. When the compatibilizer (D) is included, the total amount of the thermoplastic resin (B), the resin composition (M), and the compatibilizer (D) is 90% by mass based on the total mass of the multilayer pellet. Preferably, it is more than 95% by mass.

  The multilayer pellet of the present invention may contain various additives as long as the effects of the present invention are not inhibited. Examples of such additives include plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorants, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, fillers, Examples include pigments, dyes, processing aids, flame retardants, antifogging agents, and other polymer compounds.

  When the antioxidant is contained in the thermoplastic resin (B), the oxygen absorption performance of the oxygen-absorbing resin composition obtained by mixing the thermoplastic resin (B) and the resin composition (M) is hindered. Sometimes. This is because the antioxidant contained in the thermoplastic resin (B) also affects the resin composition (M). Therefore, the smaller the amount of the antioxidant contained in the thermoplastic resin (B), the better, but depending on the thermoplastic resin (B) selected when processing into a molded body, deterioration, crosslinking, and gelation may occur. There is. When the oxygen-absorbing performance of the oxygen-absorbing resin composition (P) is not impaired and the processability is taken into consideration, the amount of the antioxidant contained in the thermoplastic resin (B) is preferably 1000 ppm or less.

  The melt flow rate (MFR) (210 ° C., 2160 g load, based on JIS K 7210) of the multilayer pellet of the present invention is preferably 0.1 to 100 g / 10 minutes, more preferably 0.5 to 50 g / 10 minutes, more preferably 1 to 30 g / 10 minutes. When the melt flow rate is out of the above range, workability when processing the multilayer pellet into a molded product may be deteriorated.

  In the case of obtaining a molded product obtained by processing the multilayer pellet of the present invention by, for example, melt molding, an embodiment in which particles made of the resin composition (M) are dispersed in the thermoplastic resin (B) is preferable. The molded body made of multilayer pellets in such a manner is easy to maintain the oxygen absorption performance. At this time, the average particle diameter of the particles composed of the resin composition (M) is preferably 10 μm or less. When the average particle size exceeds 10 μm, the area of the interface between the resin composition (M) and the thermoplastic resin (B) becomes small, and the oxygen absorption performance may be lowered. The average particle size of the resin composition (M) particles is more preferably 5 μm or less, and even more preferably 2 μm or less.

  As an apparatus capable of kneading the thermoplastic resin (A) and the transition metal salt (C), continuous kneading such as continuous intensive mixer, kneading type twin screw extruder (same direction or different direction), mixing roll, and kneader Batch type kneaders such as high-speed mixers, Banbury mixers, intensive mixers, pressure kneaders, etc .; Equipment using a rotating disc having a grinding mechanism such as a millstone such as KCK kneading extruder manufactured by KCK Corporation; Examples include an apparatus provided with a kneading part (such as dull mage) in a machine; a simple kneader such as a ribbon blender or a Brabender mixer. Among these, a continuous kneader is preferable. Commercially available continuous intensive mixers include “FCM” (trade name) manufactured by Farrel, “CIM” (trade name) manufactured by Nippon Steel, Ltd., “KCM”, “LCM” manufactured by Kobe Steel, And “ACM” (both are trade names). Furthermore, as a twin-screw kneading extruder having a kneading disk or a kneading rotor, for example, “TEX” (trade name) manufactured by Nippon Steel Works, “ZSK” (trade name) manufactured by Werner & Pfleiderer, manufactured by Toshiba Machine Co., Ltd. “TEM” (trade name), “PCM” (trade name) manufactured by Ikekai Tekko Co., Ltd., and the like. As a method for producing a multilayer pellet, for example, two or more extruders as described above are used. For example, when two extruders are used, one is an extruder for obtaining a resin composition (M) from a thermoplastic resin (A) and a transition metal salt (C), and the other is a heat An extruder for melt-kneading the plastic resin (B). By connecting a die to these extruders, a multilayer structure such as 2 types, 3 layers, 3 types, 5 layers, and the like can be formed. Before supplying this to the pelletizer, it is cooled in a water bath and cut with a Cumberland pelletizer to obtain a multilayer pellet.

  The kneading of the resin composition (M) is usually performed at a temperature of 40 to 150 ° C. In the kneading of the thermoplastic resin (A) and the transition metal salt (C), the hopper port is preferably purged with nitrogen and extruded at a low temperature of 40 ° C. to 100 ° C. to prevent oxidation. The kneading of the thermoplastic resin (B) is usually performed at a temperature of 140 to 300 ° C., although it depends on the type of the thermoplastic resin (B) to be selected. The longer the kneading time, the better the kneading. However, if the kneading time is too long, an oxidation reaction may occur in the extruder. Therefore, the kneading time is usually 10 to 600 seconds, preferably 15 to 200 seconds, more preferably 15 to 150 seconds, from the viewpoint of antioxidant and production efficiency of the thermoplastic resin (A).

  In the case of obtaining a molded article having a multilayer structure using the multilayer pellet of the present invention, from the viewpoint of facilitating absorption of oxygen inside the molded article, the resin forming the inner layer of the molded article has a relatively high gas permeability and hydrophobicity. Resin is preferable, and heat sealing is preferable depending on the application. Examples of such resins include polyolefins such as polyethylene and polypropylene, and ethylene-vinyl acetate copolymers. On the other hand, the resin forming the outer layer of the molded body is preferably a resin excellent in moldability and mechanical properties. Examples of such resins include polyolefins such as polyethylene and polypropylene, polyamides, polyesters, polyethers, and polyvinyl chloride.

  In order to prevent oxygen from entering from the outside of the container, a layer made of a gas barrier resin such as polyamide or ethylene-vinyl alcohol copolymer is preferably laminated on the outer layer side of the layer made of the multilayer pellet of the present invention. Furthermore, another layer may be included between the layer made of the multilayer pellet of the present invention and the layer made of the gas barrier resin.

  When the multilayer pellet of the present invention is used as a packaging material for retort or a container lid, polyolefin such as polyamide, polyester, or polypropylene is used for the outer layer, and polypropylene is particularly preferably used. Polypropylene is preferably used for the inner layer.

  Polyolefin is preferable in terms of moisture resistance, mechanical properties, economy, heat sealability, and the like. Polyester is preferable in terms of mechanical properties and heat resistance.

  Examples of the method for obtaining a multilayered molded article include, but are not particularly limited to, an extrusion lamination method, a dry lamination method, a co-injection molding method, and a co-extrusion molding method. Examples of the coextrusion molding method include a coextrusion lamination method, a coextrusion sheet molding method, a coextrusion inflation molding method, and a coextrusion blow molding method.

  The sheet, film, parison, etc. having a multilayer structure thus obtained are reheated at a temperature below the melting point of the contained resin, thermoforming methods such as drawing, roll stretching methods, pantograph type stretching methods, A stretched molded product can be obtained by uniaxial or biaxial stretching by an inflation stretching method, a blow molding method, or the like.

  Considering that the multilayer pellet of the present invention is used, for example, as a packaging material and exposed to high humidity, on both sides of the layer made of the multilayer pellet, or on the side where the humidity becomes high when the packaging material is used. It is preferable to provide a layer having a high water vapor barrier property. The molded body provided with such a layer has a particularly long duration of oxygen absorption performance, so that extremely high gas barrier properties are continued for a longer time. On the other hand, the multilayer container having the multilayer pellet of the present invention in the innermost layer exhibits the oxygen absorption performance in the container quickly.

  When the multilayer pellet of the present invention is used as a packaging material, the oxygen absorption rate of the oxygen absorption layer made of the multilayer pellet of the packaging material is 5.0 ml / (g · day) at 23 ° C. and 50% RH (relative humidity). ) Or more. By having such an oxygen absorption rate, when food, pet food, etc. are filled in the packaging material under air at normal room temperature conditions, the oxygen inside the packaging material is deteriorated by oxygen in the flavor of the contents. Can be absorbed efficiently before happens. In addition, an oxygen absorption rate is measured by the method demonstrated in the below-mentioned Example.

  The above-mentioned packaging material has excellent oxygen absorption performance, and generation and movement of odorous substances accompanying oxidation are extremely small, so it is suitable for contents that are susceptible to deterioration due to oxygen, such as foods and pharmaceuticals. Can be used. In particular, it is suitable as a packaging material for foods, beverages, and pet foods sensitive to changes in quality that place an emphasis on flavor.

  The oxygen-absorbing performance of the multilayer pellet of the present invention varies depending on the ratio and type of the thermoplastic resin (A), transition metal salt (C), and thermoplastic resin (B) used. From the viewpoint of positively absorbing oxygen remaining in the material, the oxygen absorption rate is preferably 5.0 ml / g · day or more (23 ° C., 50% RH condition).

  The multilayer pellet of the present invention has improved oxygen absorption performance compared to the multilayer pellet obtained by melting and kneading the thermoplastic resin (A), transition metal salt (C), and thermoplastic resin (B) all together. Furthermore, odor generation after oxygen absorption is suppressed.

  Although the details of such a mechanism for improving the performance are not clear, the resin composition (M) containing the thermoplastic resin (A) and the transition metal salt (C) is used as an intermediate layer, and thermoplastics are formed on both sides of the intermediate layer. By laminating the coating layer made of the resin (B), the transition metal salt (C) is concentrated in the thermoplastic resin (A), and the carbon-carbon double involved in the oxygen absorption performance. It is presumed that the oxygen absorption performance is improved by effectively working for bonding.

  Further, since the transition metal salt (C) is concentrated in the thermoplastic resin (A), the oxidative deterioration of the thermoplastic resin (B) due to the transition metal salt (C) is suppressed. It is estimated that odor is suppressed.

  That is, when the resin composition (M) is used as an intermediate layer and a coating layer made of a thermoplastic resin (B) is laminated on both sides of the intermediate layer, the absolute amount of the transition metal salt in the multilayer pellet is reduced. The oxygen absorption performance is improved. Furthermore, although the oxygen absorption performance is improved, the generation of odor after oxygen absorption is suppressed.

  Furthermore, since the multilayer pellet of the present invention can reduce the area in which the intermediate layer having oxygen absorption performance comes into contact with oxygen, it becomes possible to prevent deactivation of the oxygen absorption performance during storage of the pellet.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to these Examples.

(1) Molecular structure of the thermoplastic resin (A) The molecular structure of the thermoplastic resin (A) was measured by ¹ H-NMR (nuclear magnetic resonance) measurement using deuterated chloroform as a solvent (“JNM-GX-” manufactured by JEOL Ltd.). From the obtained spectrum.

(2) Weight average molecular weight of thermoplastic resin (A) The weight average molecular weight of the thermoplastic resin (A) was measured by gel permeation chromatography (GPC) and indicated as a polystyrene equivalent value. The detailed conditions of measurement are as follows.

<Analysis conditions>
Apparatus: Shodex gel permeation chromatography (GPC) SYSTEM-11
Column: manufactured by Shodex, KF-806L
Column temperature: 40 ° C
Mobile phase: tetrahydrofuran, flow rate 1.0 ml / min Run: 15 minutes Detector: RI
Concentration: 0.1%
Injection volume: 100 μl

(Synthesis Example 1: Synthesis of polyoctenylene (a-1))
The inside of the three-necked flask equipped with a stirrer and a thermometer was replaced with dry nitrogen. To a three-necked flask, 624 parts by mass of heptane in which 110 parts by mass of cis-cyclooctene and 0.187 parts by mass of cis-4-octene were dissolved was added.

  Next, 0.0424 parts by mass of [1,3-bis (2,4,6-trimethylphenyl) -2-imidazolidinylidene] dichloro (phenylmethylene) (tricyclohexylphosphine) ruthenium was dissolved in 3 parts by mass of toluene. A catalyst solution was prepared. This catalyst solution was quickly added to a three-necked flask, and ring-opening metathesis polymerization was performed at 55 ° C. After 1 hour, the reaction solution was analyzed by gas chromatography (manufactured by Shimadzu Corporation, GC-14B; column: manufactured by Chemical Inspection Association, G-100) to confirm the disappearance of cis-cyclooctene. Next, 1.08 parts by mass of ethyl vinyl ether was added to the three-necked flask, and the mixture was further stirred for 10 minutes.

  200 mass parts of water was added to the obtained reaction liquid, and it stirred at 40 degreeC for 30 minutes. Subsequently, it left still at 40 degreeC for 1 hour, and after liquid separation, the water layer was removed. Again, 100 parts by mass of water was added to the reaction solution, and the mixture was stirred at 45 ° C. for 30 minutes. Subsequently, it left still at 40 degreeC for 1 hour, and after liquid separation, the water layer was removed. 800 ppm of Irganox 1076 (trade name: manufactured by Ciba Specialty Chemicals Co., Ltd.) was added to the organic layer as an antioxidant and stirred. Next, heptane was distilled off under reduced pressure, and further dried at 1 Pa and 100 ° C. for 6 hours using a vacuum dryer. The weight average molecular weight (Mw) was 142000 and the ratio of oligomers having a molecular weight of 1000 or less was 9.2 masses. % Of polymer 102.1 parts by mass (yield 92%) was obtained. The ratio of the carbon-carbon double bond in the side chain of this polymer (polyoctenylene) to the total carbon-carbon double bond was 0%.

  The obtained polymer was crushed to about 1 mm square and added to a separable flask equipped with a stirrer, a reflux tube and a thermometer. Next, 300 parts by mass of acetone was added to the separable flask and stirred at 40 ° C. for 3 hours. Acetone was removed by decantation. Again, 300 parts by mass of acetone was added to the separable flask and stirred at 40 ° C. for 3 hours. Acetone was removed by decantation. The remaining acetone was distilled off under reduced pressure, and further dried at 1 Pa and 100 ° C. for 6 hours using a vacuum dryer. The weight average molecular weight (Mw) was 150,000, the number average molecular weight was 37000, and the molecular weight was 1000 or less. 99 parts by mass of a polymer (polyoctenylene (a-1)) having a ratio of 3.1% was obtained.

(Example 1: Preparation of multilayer pellet)
100 parts by mass of polyoctenylene (a-1) and 0.4242 parts by mass of cobalt stearate (II) (400 ppm in terms of cobalt metal) were dry blended. Subsequently, using a 25 mmφ twin screw extruder (LABO PLASTOMIL MODEL 15C300 manufactured by Toyo Seiki Co., Ltd.) (hereinafter simply referred to as a twin screw extruder (L)), the mixture was kneaded at 80 ° C. and supplied to the multilayer die as an intermediate layer. At the same time, linear low-density polyethylene (Harmolex NF325 (trade name), manufactured by Nippon Polyethylene Co., Ltd .; hereinafter referred to as LLDPE) was melt-extruded as a coating layer from a single-screw extruder at 160 ° C. and supplied to a multilayer die. The thickness ratio of the sheet extruded from the die was adjusted to be coating layer / intermediate layer / coating layer = 45/10/45. Next, the obtained sheet was water-cooled and cut finely with a Cumberland pelletizer to obtain a multilayer pellet.

  The multilayer pellets obtained above were stored at 40 ° C. for 1 day under air. Separately, the obtained pellets were placed in an aluminum bag, purged with nitrogen, and stored at room temperature for 3 months. The hue of the resin after storage and the presence or absence of odor generation were confirmed. Almost no change in hue on the outer surface was observed. On the other hand, when quantified by 6-step sensory evaluation based on the odor intensity shown in Table 2, the intensity index was 1 (detection threshold), and the odor was almost felt I couldn't. The results are shown in Table 1.

(Preparation of film)
On the other hand, the obtained multilayer pellet was put into a 20 mmφ single screw extruder (manufactured by Toyo Seiki Co., Ltd .: LABO PLASTOMIL A) and extruded from a coat hanger die while being melt kneaded at 160 ° C. to obtain a film having a thickness of 20 μm. .

  The film obtained above was placed in a standard bottle (internal capacity 260 ml) filled with air at 23 ° C. and 50% RH (relative humidity). The air in the standard bottle had an oxygen: nitrogen volume ratio of 21:79. The mouth of the standard bottle was sealed with an epoxy resin using a multilayer sheet containing an aluminum layer, and then left at 23 ° C. One day, 7 days, 14 days, and 21 days after standing, the air inside the standard bottle was sampled with a syringe, and the oxygen concentration of the air was measured using gas chromatography. The holes generated in the multilayer sheet at the time of sampling were sealed every time using an epoxy resin. From the volume ratio of oxygen and nitrogen obtained by the measurement, the amount of oxygen decrease was calculated, and the oxygen absorption amount of the film in an atmosphere of 23 ° C. and 50% RH was obtained. The results are shown in Table 3.

(Example 2)
The same procedure as in Example 1 was used except that polypropylene (Novatec FY6C (trade name), manufactured by Nippon Polyethylene Co., Ltd .; hereinafter referred to as PP) was used instead of LLDPE, and the extrusion temperature was 180 ° C. Multilayer pellets were obtained. Further, using the obtained pellets, a film having a thickness of 20 μm was obtained in the same procedure as in Example 1.

  Subsequently, the obtained pellets were used to confirm the presence or absence of hue change and odor generation in the same procedure as in Example 1. Furthermore, the oxygen absorption amount was calculated | required in the same procedure as Example 1 using the obtained film. The results are shown in Tables 1 and 3.

(Example 3)
Example 1 except that polystyrene (HF-77 (trade name), manufactured by PS Japan Ltd .; hereinafter referred to as PS) is used as the coating layer instead of LLDPE, and the extrusion temperature is 230 ° C. Multilayer pellets were obtained in the same procedure. Furthermore, a film having a thickness of 20 μm was obtained in the same procedure as in Example 1 except that the obtained pellets were kneaded at 230 ° C.

  Subsequently, the obtained pellets were used to confirm the presence or absence of hue change and odor generation in the same procedure as in Example 1. Furthermore, the oxygen absorption amount was calculated | required in the same procedure as Example 1 using the obtained film. The results are shown in Tables 1 and 3.

(Comparative Example 1)
90 parts by mass of LLDPE, 10 parts by mass of polyoctenylene (a-1), and 0.4242 parts by mass of cobalt stearate (II) (400 ppm in terms of cobalt metal) are collectively charged into a twin screw extruder (L) at 160 ° C. The melt-kneaded and extruded strand was cooled with water and then cut with a pelletizer to obtain pellets.

  Using the pellets obtained above, the hue change and the presence or absence of odor generation were confirmed in the same procedure as in Example 1. After storage at 40 ° C. for 1 day in air, the pellets changed from light purple to light orange yellow. Moreover, when it digitized by 6 steps of sensory evaluation based on the odor intensity | strength shown in Table 2, an intensity | strength index | exponent is 2 (cognitive threshold value), and odor was felt. Furthermore, the pellet after storage at room temperature for 3 months changed to pale yellow, and an acid odor was felt. The strength index was 3 (medium odor). The results are shown in Table 1.

  Further, using the obtained pellets, a film having a thickness of 20 μm was obtained in the same procedure as in Example 1. Using the obtained film, the oxygen absorption amount was determined in the same procedure as in Example 1. The results are shown in Table 3. The oxygen absorption amount itself was not so large as compared with the Examples, but the film was colored.

(Comparative Example 2)
Pellets were obtained in the same procedure as in Comparative Example 1 except that PP was used instead of LLDPE. Furthermore, using the obtained pellets, a film having a thickness of 20 μm was obtained in the same procedure as in Comparative Example 1.

  Using the pellets obtained above, the hue change and the presence or absence of odor generation were confirmed in the same procedure as in Example 1. After storage at 40 ° C. for 1 day in air, the pellets changed from light purple to light orange yellow. On the other hand, when quantified by 6-step sensory evaluation based on the odor intensity shown in Table 2, the strength index was 2 (cognitive threshold), and odor was felt. Furthermore, the pellet after storage at room temperature for 3 months changed to pale yellow, and an acid odor was felt. The strength index was 3 (medium odor). The results are shown in Table 1.

  Using the obtained film, the oxygen absorption amount was determined in the same procedure as in Example 1. The results are shown in Table 3. The oxygen absorption amount itself was not so large as compared with the Examples, but the film was colored.

  From these results, the resin composition (M) containing the thermoplastic resin (A) and the transition metal salt (C) is used as an intermediate layer, and a coating layer made of the thermoplastic resin (B) is laminated on both surfaces of the intermediate layer. It can be seen that the multilayer pellets have excellent oxygen absorption performance and hardly generate odor.

  According to the present invention, oxygen that has a practically sufficient oxygen absorption performance, reduces the generation of unpleasant odor components due to oxygen absorption, suppresses the generation of odors, and further reduces oxygen absorption performance during storage. Absorbent multilayer pellets can be provided. Therefore, the multilayer pellet of the present invention is suitably used as food for which flavor is particularly important, a pet food packaging material for animals with sensitive taste, and a medical packaging material sensitive to oxygen.

10 multilayer pellet 11 intermediate layer 12 coating layer

Claims (6)

  With respect to 100 parts by mass of the thermoplastic resin (A) having a carbon-carbon double bond substantially only in the main chain, the transition metal salt (C) is 0.001 to 0.5 parts by mass in terms of metal. A multi-layer pellet in which the resin composition (M) contained in the range of (10 ppm to 5000 ppm) is used as an intermediate layer, and the periphery of the intermediate layer is coated with a coating layer made of a thermoplastic resin (B) made of a hydrocarbon resin. .   The multilayer pellet according to claim 1, wherein the coating layer is laminated so as to be adjacent to both surfaces of the intermediate layer.   The multilayer pellet according to claim 1 or 2, wherein the thermoplastic resin (A) is polyoctenylene.   The said transition metal salt (C) is at least 1 sort (s) of metal salt selected from the group which consists of iron salt, nickel salt, copper salt, manganese salt, and cobalt salt, The claim in any one of Claim 1 to 3 A multilayer pellet as described in 1.   The multilayer pellet according to any one of claims 1 to 4, wherein the thermoplastic resin (B) is at least one resin selected from the group consisting of polyethylene, polypropylene, and polystyrene.   The multilayer pellet according to any one of claims 1 to 5, wherein an amount of the antioxidant contained in the thermoplastic resin (B) is 1000 ppm or less.

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