JP7585735B2 - Resin composition, molded body, and method for disposing of polyamide resin - Google Patents

Description

The present invention relates to a resin composition, a molded body, and a method for disposing of polyamide resin.

Polyamide resins have excellent physical and chemical properties. For this reason, they are widely used in a variety of applications, including electrical and electronic equipment components and packaging materials for food and medicine. For example, Patent Document 1 discloses a so-called high-barrier container in which a layer containing a transition metal salt such as organic cobalt is provided in a polyamide resin, and metaxylylene group-containing polyamide resin is catalytically oxidized to absorb oxygen, thereby imparting oxygen absorption properties in addition to gas barrier properties.

JP 2002-321774 A

As described above, polyamide resins are used for various applications. However, as part of the recent efforts for environmental conservation, there is a demand for polyamide resins to be biodegradable.
The present invention aims to solve the above problems, and has an object to provide a resin composition having excellent biodegradability, a molded body formed from the resin composition, and a method for disposing of polyamide resin.

In view of the above problems, the present inventors have conducted research and found that the above problems can be solved by blending a cobalt salt with a specific type of polyamide resin.
Specifically, the above problems were solved by the following means.
<1> A resin composition comprising a polyamide resin and a cobalt salt, the polyamide resin comprising diamine-derived structural units and dicarboxylic acid-derived structural units, 50 mol % or more of the diamine-derived structural units being derived from xylylenediamine, 50 mol % or more of the dicarboxylic acid-derived structural units being derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, and a xylylenediamine-based polyamide resin, wherein 0.1 mol % or more of the xylylenediamine is paraxylylenediamine.
<2> The resin composition according to <1>, wherein the mass ratio of the xylylenediamine structure in the xylylenediamine-based polyamide resin is 20 to 70 mass%; here, the mass ratio of the xylylenediamine structure is a value calculated by [(mass of the xylylenediamine structure in the xylylenediamine-based polyamide resin)/(total mass of the xylylenediamine-based polyamide resin)]×100.
<3> The resin composition according to <1> or <2>, wherein the α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms includes sebacic acid and/or dodecanedioic acid.
<4> The resin composition according to <1> or <2>, wherein the α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms includes dodecanedioic acid.
<5> The resin composition according to any one of <1> to <4>, in which 20 mol % or more of the diamine-derived structural units are derived from paraxylylenediamine.
<6> The resin composition according to any one of <1> to <5>, wherein the cobalt salt includes a carboxylate of cobalt.
<7> The resin composition according to any one of <1> to <5>, wherein the cobalt salt includes cobalt stearate.
<8> The resin composition according to any one of <1> to <7>, wherein the content of the cobalt salt is 10 to 2000 ppm by mass based on cobalt atoms relative to 100 parts by mass of the xylylenediamine-based polyamide resin.
<9> The resin composition according to any one of <1> to <8>, which is biodegradable.
<10> The resin composition according to any one of <1> to <9>, wherein the resin composition has a biodegradability of 10% or more after storage for 90 days in a compost environment, where the biodegradability (%) is [(total amount of _CO2 generated during storage for 90 days in a compost environment)/(theoretical amount of carbon dioxide generated calculated from the composition formula)]×100.
<11> A molded article formed from the resin composition according to any one of <1> to <10>.
<12> The molded article according to <11>, which is a fishing net.
<13> A method for disposing of a polyamide resin, comprising biodegrading the resin composition according to any one of <1> to <10> or the molded article according to <11> or <12>.

The present invention makes it possible to provide a resin composition with excellent biodegradability, a molded body formed from the resin composition, and a method for disposing of polyamide resin.

Hereinafter, an embodiment of the present invention (hereinafter, simply referred to as the present embodiment) will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to the present embodiment.
In this specification, the word "to" is used to mean that the numerical values before and after it are included as the lower limit and upper limit.
In this specification, various physical properties and characteristic values are those at 23° C. unless otherwise specified.
In this specification, ppm means ppm by mass.

The resin composition of the present embodiment is characterized in that it contains a polyamide resin and a cobalt salt, the polyamide resin contains a diamine-derived structural unit and a dicarboxylic acid-derived structural unit, 50 mol % or more of the diamine-derived structural unit is derived from xylylenediamine, 50 mol % or more of the dicarboxylic acid-derived structural unit is derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, and the xylylenediamine-based polyamide resin contains 0.1 mol % or more of the xylylenediamine as paraxylylenediamine. By adopting such a configuration, it is possible to provide a resin composition with excellent biodegradability. The reason for this is presumed to be as follows.
For example, if the resin is left in a compost environment for a long period of time to biodegrade, microorganisms act on the resin and reduce the molecular weight of the resin. As a result, it becomes easier for microorganisms to penetrate further into the resin, and biodegradation progresses, decomposing it into oligomers, monomers, and even further low molecules. However, polyamide resins generally have strong amide bonds and are usually crystalline resins, so they are not easily affected by microorganisms and are less likely to reduce in molecular weight. Therefore, polyamide resins are less likely to be decomposed by microorganisms. In this embodiment, it was speculated that by using a specific xylylenediamine-based polyamide resin as the polyamide resin, the NH ₂ -CH ₂ -benzene ring site of xylylenediamine is first oxidized and decomposed by cobalt, and is cleaved between the benzyl site and NH _2. As a result, it is speculated that the molecular weight reduction of the xylylenediamine-based polyamide resin is promoted, and then biodegradation by microorganisms is promoted.
Hereinafter, the resin composition of the present embodiment will be described in detail.

<Polyamide resin>
The resin composition of the present embodiment contains a xylylenediamine-based polyamide resin. The xylylenediamine-based polyamide resin is a polyamide resin that contains diamine-derived structural units and dicarboxylic acid-derived structural units, in which 50 mol % or more of the diamine-derived structural units are derived from xylylenediamine, and 50 mol % or more of the dicarboxylic acid-derived structural units are derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms. By using such a xylylenediamine-based polyamide resin and blending it with a cobalt salt, a resin composition with excellent biodegradability can be obtained.

In the xylylenediamine-based polyamide resin, 50 mol% or more of the diamine-derived structural units are derived from xylylenediamine, preferably 70 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, and even more preferably 99 mol% or more. The upper limit may be 100 mol%.

The xylylenediamine contains 0.1 mol % or more of paraxylylenediamine. By including paraxylylenediamine, biodegradability can be improved. One of the reasons is presumed to be that the paraxylylenediamine skeleton tends to be more susceptible to decomposition by microorganisms than the metaxylylenediamine skeleton. It is generally known that the susceptibility to decomposition by microorganisms depends greatly on the molecular structure, and it is presumed that linear paraxylylenediamine is more susceptible to decomposition by microorganisms among xylylenediamines. Therefore, it is presumed that the biodegradability of the resin is improved by replacing metaxylylenediamine with paraxylylenediamine. In addition, it is presumed that the paraxylylenediamine skeleton serves as the starting point for decomposition by microorganisms, which further reduces the molecular weight of the resin, thereby promoting biodegradation.
The proportion of paraxylylenediamine in the xylylenediamine is preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 25 mol% or more. The upper limit is 100 mol%, but may be, for example, 80 mol% or less, further 60 mol% or less, and particularly 45 mol% or less.
In this embodiment, the xylylenediamine preferably contains 0 to 99.9 mol % metaxylylenediamine and 0.1 to 100 mol % paraxylylenediamine, more preferably 0 to 80 mol % metaxylylenediamine and 20 to 100 mol % paraxylylenediamine. In the xylylenediamine, the total of metaxylylenediamine and paraxylylenediamine preferably accounts for 95 mol % or more, more preferably 99 mol % or more, and even more preferably 100 mol %.
In addition, in this embodiment, the xylylenediamine-based polyamide resin contains a constitutional unit derived from paraxylylenediamine, which tends to promote decomposition of the xylylenediamine-based polyamide resin by cobalt atoms.

Diamine components other than xylylenediamine include aliphatic diamines such as tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethyl-hexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine, 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane. Examples of the diamines include alicyclic diamines such as bis(4-aminocyclohexyl)cyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decalin, and bis(aminomethyl)tricyclodecane; and diamines having an aromatic ring such as bis(4-aminophenyl)ether, paraphenylenediamine, and bis(aminomethyl)naphthalene. These can be used alone or in combination of two or more kinds.

In the xylylenediamine-based polyamide resin, 50 mol % or more of the dicarboxylic acid-derived constitutional units are derived from α,ω-linear aliphatic dicarboxylic acids having 8 to 22 carbon atoms, preferably 70 mol % or more, more preferably 90 mol % or more, even more preferably 95 mol % or more, and even more preferably 99 mol % or more. The upper limit may be 100 mol %.
The number of carbon atoms in the α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms is preferably 10 or more, and more preferably 11 or more. By making the number of carbon atoms equal to or more than the lower limit, the compound tends to be more susceptible to biodegradation by microorganisms. Furthermore, the number of carbon atoms in the α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms is preferably 21 or less, more preferably 20 or less, even more preferably 18 or less, and even more preferably 14 or less. By making the number of carbon atoms equal to or less than the upper limit, the compound tends to be more susceptible to hydrophilicity and more susceptible to decomposition by microorganisms. It is particularly more preferable that the number of carbon atoms in the α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms is 12.
Specific examples of the α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms include suberic acid, azelaic acid, sebacic acid, 1,11-undecanedioic acid, 1,12-dodecanedioic acid, 1,13-tridecanedioic acid, 1,14-tetradecanedioic acid, 1,15-pentadecanedioic acid, 1,16-hexadecanedioic acid, 1,17-heptadecanedioic acid, 1,18-octadecanedioic acid, 1,19-nonadecanedioic acid, 1,20-eicosanediic acid, 1,21-heneicosanediic acid, 1,2 Examples include 2-docosane diacid, more preferably sebacic acid, 1,12-dodecanedioic acid, 1,14-tetradecanedioic acid, 1,16-hexadecanedioic acid, 1,18-octadecanedioic acid, 1,20-eicosane diacid, 1,21-heneicosane diacid, 1,22-docosane diacid, 1,14-tetradecanedioic acid, 1,16-hexadecanedioic acid, 1,18-octadecanedioic acid, eicosane diacid, and docosane diacid, and even more preferably sebacic acid and/or dodecanedioic acid. When the α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms is 1,12-dodecanedioic acid, the above-mentioned effect is particularly remarkable.

Examples of dicarboxylic acid components other than α,ω-linear aliphatic dicarboxylic acids having 8 to 22 carbon atoms include α,ω-linear aliphatic dicarboxylic acids having 7 or less carbon atoms such as adipic acid, phthalic acid compounds such as isophthalic acid, terephthalic acid, and orthophthalic acid, and naphthalenedicarboxylic acids such as 1,2-naphthalenedicarboxylic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid, and these can be used alone or in combination of two or more.

The phrase "including diamine-derived structural units and dicarboxylic acid-derived structural units" means that at least a part of the amide bonds constituting the xylylenediamine-based polyamide resin is formed by the bond between the dicarboxylic acid and the diamine, and further, other sites such as terminal groups may be included in addition to the dicarboxylic acid-derived structural units and diamine-derived structural units. In addition, repeating units having amide bonds not derived from the bond between the dicarboxylic acid and the diamine, or trace amounts of impurities, may be included. Specifically, in addition to the diamine component and the dicarboxylic acid component, the xylylenediamine-based polyamide resin may also contain lactams such as ε-caprolactam and laurolactam, and aliphatic aminocarboxylic acids such as aminocaproic acid and aminoundecanoic acid as copolymerization components constituting the xylylenediamine-based polyamide resin, as long as the effect of this embodiment is not impaired. In this embodiment, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more of the xylylenediamine-based polyamide resin is a diamine-derived structural unit or a dicarboxylic acid-derived structural unit.

The xylylenediamine-based polyamide resin used in this embodiment preferably has a mass ratio of the xylylenediamine structure of 20 to 70 mass %. This configuration tends to facilitate biodegradation. Here, the mass ratio of the xylylenediamine structure is a value calculated from [(mass of the xylylenediamine structure in the polyamide resin)/(mass of the entire polyamide resin)]×100. The xylylenediamine structure refers to the portion represented by "-HN-CH ₂ -benzene ring-CH ₂ -NH-".
The lower limit of the mass ratio of the xylylenediamine structure is preferably 35% by mass or more, more preferably 40% by mass or more. By making it equal to or more than the lower limit, the starting points of decomposition increase, and low molecular weight components that are more susceptible to biodegradation tend to be generated. In addition, the upper limit of the mass ratio of the xylylenediamine structure is preferably 60% by mass or less, more preferably 50% by mass or less. By making it equal to or less than the upper limit, the xylene skeleton that is less susceptible to biodegradation decreases, and the biodegradability of the resin as a whole tends to be improved.

The content of the xylylenediamine-based polyamide resin in the resin composition of this embodiment is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more. By making it equal to or more than the lower limit, the performance derived from the xylylenediamine-based polyamide resin, such as high gas barrier properties and high strength, tends to be more effectively achieved. The upper limit is the amount at which all components other than the cobalt salt become xylylenediamine-based polyamide resin.
The resin composition of the present embodiment may contain only one type of xylylenediamine-based polyamide resin, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

The resin composition of the present embodiment may or may not contain a polyamide resin other than the xylylenediamine-based polyamide resin.
The other polyamide resin may be one or more of aliphatic polyamide resins, alicyclic polyamide resins, semi-aromatic polyamide resins, etc., with aliphatic polyamide resins and alicyclic polyamide resins being preferred, and aliphatic polyamide resins being more preferred. More specifically, polyamide 4, polyamide 6, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 6/66, polyamide 610, polyamide 612, polyamide 6T, polyamide 6/6T, polyamide 66/6T, polyamide 6I, polyamide 66/6I/6, polyamide 66/6I, polyamide 6T/6I, polyamide 6T/12, polyamide 66/6T/6I, polyamide 9T, polyamide 9I, polyamide 9T, 9I, polyamide 10T, 1,3-BAC10I (a polyamide resin composed of 1,3-bisaminomethylcyclohexane, sebacic acid, and isophthalic acid), and 1,4-BAC10I (a polyamide resin composed of 1,4-bisaminomethylcyclohexane, sebacic acid, and isophthalic acid), and polyamide 6 and/or polyamide 66 are preferred.
When these other polyamide resins are contained, the content thereof in the resin composition is preferably 5 to 15% by mass.

<Cobalt salts>
The resin composition of the present embodiment contains a cobalt salt. By containing the cobalt salt, biodegradation of the resin composition of the present embodiment is promoted when the resin composition is placed in a compost environment. In particular, the cobalt salt hardly has any adverse effect on the xylylenediamine-based polyamide resin before being placed in a compost environment, and is therefore preferable in that it is unlikely to impair the inherent performance (particularly strength) of the resin composition when the resin composition is used.
The type of cobalt salt is not particularly limited, and may be either a divalent salt or a trivalent salt, with a divalent salt being preferred.
The cobalt salt is preferably a cobalt carboxylate. The use of a carboxylate tends to more effectively promote the reduction in molecular weight due to oxidative decomposition at the benzyl position. Furthermore, the reduction in molecular weight of the polyamide resin promotes subsequent biodegradation by microorganisms.
In the case of a cobalt carboxylate, the carboxylic acid is preferably an aliphatic carboxylic acid. The aliphatic carboxylic acid is not particularly specified because it does not significantly affect the oxidative decomposition behavior of the resin by cobalt, but either a linear or branched aliphatic carboxylic acid can be preferably adopted, and a linear aliphatic carboxylic acid is more preferable. The carbon number of the aliphatic carboxylic acid is not particularly specified because it does not significantly affect the oxidative decomposition behavior of the resin by cobalt, but it is preferably 2 or more, may be 10 or more, and is preferably 40 or less, more preferably 30 or less, and even more preferably 24 or less. In particular, an aliphatic dicarboxylic acid having an even number of carbon atoms is preferable.
Specific examples of aliphatic carboxylic acids include acetic acid, neodecanoic acid, lauric acid, neodecanoic acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melissic acid. From the viewpoint of physical properties, acetic acid, neodecanoic acid, and stearic acid are preferred, and stearic acid is more preferred.
In this embodiment, the cobalt salt is preferably cobalt stearate, and the cobalt stearate is preferably (C ₁₇ H ₃₅ COO) ₂ Co.

The content of the cobalt salt (preferably cobalt stearate) in the resin composition of this embodiment is preferably 10 ppm by mass or more, more preferably 50 ppm by mass or more, and even more preferably 80 ppm by mass or more, based on the cobalt atom, relative to 100 parts by mass of the xylylenediamine-based polyamide resin. By making it equal to or more than the lower limit, the polyamide resin can be more effectively decomposed to a molecular weight that is easily biodegradable. In addition, the content of the cobalt salt in the resin composition of this embodiment is preferably 2000 ppm by mass or less, more preferably 1800 ppm by mass or less, even more preferably 1500 ppm by mass or less, even more preferably 1200 ppm by mass or less, even more preferably 1000 ppm by mass or less, and even more preferably 800 ppm by mass or less, based on the cobalt atom, relative to 100 parts by mass of the xylylenediamine-based polyamide resin. By making it equal to or less than the upper limit, there is a tendency that deterioration and poor appearance during the preparation of the polyamide resin can be effectively suppressed.
The resin composition of the present embodiment may contain only one type of cobalt salt, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Other Ingredients>
The resin composition of this embodiment may contain other components other than the polyamide resin and the cobalt salt, as long as the purpose and effect of this embodiment are not impaired. Specific examples of the other components include thermoplastic resins other than polyamide resins, antioxidants, heat stabilizers, hydrolysis resistance improvers, weathering stabilizers, matting agents, UV absorbers, nucleating agents, plasticizers, dispersants, flame retardants, antistatic agents, coloring inhibitors, gelling inhibitors, colorants, release agents, surface activators, dyes, and the like. For details of these, please refer to the descriptions in paragraphs 0130 to 0155 of Japanese Patent No. 4894982, the descriptions in paragraph 0021 of Japanese Patent Publication No. 2010-281027, and the descriptions in paragraph 0036 of Japanese Patent Publication No. 2016-223037, and the contents of these are incorporated herein.
Examples of thermoplastic resins other than polyamide resins include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polycarbonate resins, polyoxymethylene resins, polyether ketones, polyether sulfones, thermoplastic polyether imides, etc. In the resin composition of this embodiment, it is possible to have a configuration that does not substantially contain thermoplastic resins other than polyamide resins. "Substantially does not contain" means, for example, that in the resin composition of this embodiment, the content of thermoplastic resins other than polyamide resins is 5% by mass or less of the mass of polyamide resin.
The resin composition of the present embodiment may contain a filler such as a glass resin composition or carbon fiber, but is preferably substantially free of the filler. The term "substantially free of the filler" means that the amount of the filler is 3% by mass or less of the resin composition of the present embodiment, for example.
In addition, the resin composition of the present embodiment can be given any surface property by performing a plasma treatment. For details, refer to the descriptions in paragraphs 0019 to 0022 of JP-A-06-182195, the contents of which are incorporated herein by reference.

<Characteristics and properties of resin composition>
The resin composition of the present embodiment preferably has a molecular weight that decreases when placed under constant temperature conditions. Specifically, when stored for 28 days under an environment of 55° C. and 90% relative humidity, the reduction rate of the number average molecular weight of the resin composition ((Mn of polyamide resin after storage/Mn of polyamide resin before storage)×100) is preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less. The lower limit of the reduction rate is ideally 0%, and even if it is 0.01% or more, the required performance is sufficiently met.
The resin composition of the present embodiment is preferably biodegradable. Biodegradability refers to the ability to be ultimately decomposed into water and carbon dioxide by microorganisms, and includes, for example, those in which a decrease in molecular weight is observed when stored for a certain period of time in a compost environment.
The resin composition of this embodiment preferably has a biodegradability of 10% or more after storage in a compost environment for 90 days, more preferably 25% or more, even more preferably 30% or more, even more preferably 35% or more, and even more preferably 40% or more. The upper limit of the biodegradability is ideally 100%, but for example, 80% or less, or even 70% or less, is sufficient to satisfy the required performance. Here, the biodegradability (%) is [(total _CO2 generation during storage for 90 days in a compost environment) / (theoretical carbon dioxide generation calculated from the composition formula)] × 100.
The resin composition of the present embodiment preferably has a number average molecular weight of 8,000 or more, more preferably 10,000 or more. The upper limit of the number average molecular weight is not particularly limited, but is, for example, 100,000 or less, and further 50,000 or less. The number average molecular weight here is that before biodegradation.

<Method of producing resin composition>
As a method for producing the resin composition of the present embodiment, any method may be adopted.
For example, a polyamide resin, a cobalt salt, and other components that are added as necessary are mixed using a mixing means such as a V-type blender to prepare a lump-sum blend, which is then melt-kneaded in a vented extruder and pelletized.

The heating temperature during melt kneading can usually be selected appropriately from the range of 180 to 360°C. If the temperature is too high, decomposition gas is likely to be generated, which may cause extrusion defects such as strand breakage. Therefore, it is desirable to select a screw configuration that takes shear heat generation, etc. into consideration.

<Molded body>
The resin composition of the present embodiment is molded into a molded article. The molded article may be a part or a finished product.
In the present embodiment, the manufacturing method of the molded body is not particularly limited, and any molding method generally used for resin compositions can be used. Examples include injection molding, ultra-high speed injection molding, injection compression molding, two-color molding, gas-assisted hollow molding, molding using a heat-insulating mold, molding using a rapid heating mold, foam molding (including supercritical fluid), insert molding, IMC (in-mold coating molding) molding, extrusion molding, sheet molding, thermoforming, rotational molding, lamination molding, press molding, blow molding, etc. Also, a molding method using a hot runner system can be used.

The molded article of the present embodiment is widely used in automobile and other transport machinery parts, general machine parts, precision machine parts, electronic and electrical equipment parts, office equipment parts, building materials and housing-related parts, medical devices, leisure and sporting goods (e.g., fishing lines), agricultural, forestry and fishery products, play equipment, medical products, food packaging films, everyday items such as clothing, defense and aerospace products, and the like.
In particular, the resin composition or molded article of the present embodiment is preferably used for food packaging films, filter cloths, and leisure sports goods (e.g., fishing lines and fishing nets, and more preferably used for fishing nets) because of its excellent biodegradability.

The resin composition of this embodiment and the molded article of this embodiment can be disposed of by biodegrading them. The resin composition and molded article of this embodiment can be decomposed to the molecular level by the action of microorganisms, and ultimately turned into carbon dioxide and water, which can be circulated back into nature. This is therefore advantageous in that they can be disposed of naturally without destroying nature. In other words, this specification also discloses a method for disposing of polyamide resin, which includes biodegrading the resin composition or molded article of this embodiment.

The resin composition of this embodiment is stored at 55°C and 90% relative humidity for 28 days, and the number average molecular weight is reduced. The composition (low Mn composition) after the number average molecular weight is reduced contains a polyamide resin decomposition product and a cobalt salt, the polyamide resin contains a diamine-derived structural unit and a dicarboxylic acid-derived structural unit, 50 mol% or more of the diamine-derived structural unit is derived from xylylenediamine, 50 mol% or more of the dicarboxylic acid-derived structural unit is derived from a xylylenediamine-based polyamide resin derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, and 0.1 mol% or more of the xylylenediamine is paraxylylenediamine, and the number average molecular weight of the composition is less than 3000 (preferably less than 2000, more preferably less than 1000). The number average molecular weight of the low Mn composition is preferably 950 or less, more preferably 900 or less, even more preferably 850 or less, and even more preferably 800 or less. The lower limit of the number average molecular weight is better, but 150 or more is practical, and even 200 or more will fully satisfy the required performance.

The present invention will be described in more detail below with reference to examples. The materials, amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.
If the measuring instruments used in the examples are difficult to obtain due to discontinuation or the like, measurements can be made using other instruments with equivalent performance.

1. Raw materials <Synthesis example of MP10>
Sebacic acid was dissolved by heating in a reaction vessel under a nitrogen atmosphere, and then a mixed diamine of metaxylylenediamine (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and paraxylylenediamine (manufactured by Mitsubishi Gas Chemical Co., Ltd.) in a molar ratio of 7:3 was gradually added dropwise under pressure (0.35 MPa) so that the molar ratio of diamine to sebacic acid was about 1:1, while the temperature was raised to 235°C. After the dropwise addition was completed, the reaction was continued for 60 minutes to adjust the amount of components with a molecular weight of 1,000 or less. After the reaction was completed, the contents were taken out in the form of strands and pelletized with a pelletizer to obtain a polyamide resin (MP10). The melting point of the obtained polyamide was 215°C.

<Synthesis Example of PXD10>
A precisely weighed amount of 60.00 mol of sebacic acid was placed in a jacketed reactor equipped with a stirrer, a partial condenser, a cooler, a thermometer, a dropping tank and a nitrogen gas inlet tube, and the atmosphere was fully replaced with nitrogen. The temperature was raised to 170°C under a small amount of nitrogen gas flow, and the sebacic acid was dissolved and made into a uniform fluid state. 60 mol of paraxylylenediamine was dropped into the reactor while stirring for 160 minutes. During this time, the pressure inside the reaction system was kept at normal pressure, the internal temperature was continuously raised to 285°C, and water distilled together with the dropping of paraxylylenediamine was removed from the system through the partial condenser and the cooler. After the dropping of paraxylylenediamine was completed, the liquid temperature was kept at 290°C and the reaction was continued for 10 minutes. Thereafter, the pressure inside the reaction system was continuously reduced to 600 Torr over 10 minutes, and the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 305°C. After the reaction was completed, the inside of the reactor was pressurized to 0.3 MPa with nitrogen gas, and the polymer was taken out as a strand from the nozzle at the bottom of the polymerization tank. After cooling with water, the polymer was cut into pellets to obtain pellets of a molten polymer. The pellets were dried in a vacuum dryer at 150°C for 5 hours. The melting point of the obtained polyamide resin (PXD10) measured by DSC was 290°C.

<Synthesis Example of MP12>
A precisely weighed amount of 60.00 mol of 1,12-dodecanedioic acid was placed in a jacketed reactor equipped with a stirrer, a partial condenser, a cooler, a thermometer, a dropping tank and a nitrogen gas inlet tube, and the mixture was thoroughly replaced with nitrogen. The temperature was raised to 180°C under a small amount of nitrogen gas flow, and 1,12-dodecanedioic acid was dissolved and made into a uniform fluid state. 60 mol of para/meta-xylylenediamine, in which 40 mol% of the diamine component was para-xylylenediamine and 60 mol% was meta-xylylenediamine, was dropped into the reactor over a period of 160 minutes while stirring. During this time, the internal pressure of the reaction system was kept at normal pressure, and the internal temperature was continuously raised to 250°C. Water distilled with the dropping of para/meta-xylylenediamine was removed from the system through the partial condenser and the cooler. After the dropping of para/meta-xylylenediamine was completed, the liquid temperature was kept at 250°C and the reaction was continued for 10 minutes. Thereafter, the pressure inside the reaction system was continuously reduced to 600 Torr over 10 minutes, and the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 260°C. After the reaction was completed, the inside of the reactor was pressurized with nitrogen gas at 0.3 MPa, and the polymer was taken out as a strand from a nozzle at the bottom of the polymerization tank, and after cooling with water, it was cut into pellets to obtain pellets of a molten polymerized product. The obtained pellets were charged at room temperature into a tumbler (rotary vacuum tank) having a jacket for heating a heat medium. While rotating the tumbler, the inside of the tank was reduced in pressure (0.5 to 10 Torr), the circulating heat medium was heated to 150°C, and the pellet temperature was raised to 130°C and maintained at that temperature for 3 hours. Thereafter, nitrogen was again introduced to return to normal pressure, and cooling was started. When the temperature of the pellets became 70°C or less, the pellets were taken out of the tank, and a solid-phase polymerized product was obtained.
The melting point of the resulting polyamide resin (MP12) was 216° C. as measured by DSC.

<Synthesis of 1,3-BAC6>
A precisely weighed amount of adipic acid (50.8 mol) was placed in a jacketed reactor equipped with a stirrer, a partial condenser, a cooler, a thermometer, a dropping tank and a nitrogen gas inlet tube, and the atmosphere was fully replaced with nitrogen. The temperature was raised to 190°C under a small amount of nitrogen flow, and the adipic acid was dissolved and made into a uniform fluid state. 1,3-bis(aminomethyl)cyclohexane (cis-isomer/trans-isomer: 72.7/27.3, hereinafter referred to as 1,3-BAC) (50.5 mol) was dropped into the reactor while stirring for 160 minutes. During this time, the internal pressure of the reaction system was normal pressure, the internal temperature was continuously raised to 223°C, and water distilled with the dropping of metaxylylenediamine was removed from the system through the partial condenser and the cooler. After the dropping of metaxylylenediamine was completed, the liquid temperature was kept at 235°C and the reaction was continued for 10 minutes. Thereafter, the pressure inside the reaction system was continuously reduced to 600 Torr over 10 minutes, and the reaction was continued for 50 minutes. During this time, the reaction temperature was continuously raised to 250°C. After the reaction was completed, the inside of the reactor was pressurized with nitrogen gas at 0.3 MPa, and the polymer was taken out as a strand from a nozzle at the bottom of the polymerization vessel, cooled with water, and cut into pellets to obtain pellets of a molten polymer. The melting point of the obtained polyamide resin (1,3-BAC6) measured according to DSC was 230°C. The mass ratio of the xylylenediamine structure was 0 mass%.

Cobalt stearate (StCo): Kanto Chemical Co., Ltd., product number: 07423-02

2. Examples 1 to 3 and Comparative Examples 1 to 4
<Compound>
The polyamide resin and cobalt stearate were weighed out and blended in a tumbler to obtain the composition shown in Table 1 below, and the blend was fed into the base of a twin-screw extruder (TEM26SS, manufactured by Shibaura Machine Co., Ltd.), melted, and pelletized. The temperature of the twin-screw extruder was set to melting point + 20°C. Each component in Table 1 is shown in mass ratio. The content of cobalt stearate (StCo) is the amount of cobalt atoms (ppm by mass) relative to 100 parts by mass of polyamide resin.

<Molecular weight reduction after storage at 55°C for 28 days>
The obtained polyamide resin pellets were stored for 28 days in an environment of 55° C. and 90% relative humidity. The number average molecular weight and weight average molecular weight were measured before and after storage.
In addition, "Mn (%) after 28 days" is an index showing the rate of decrease in the number average molecular weight of the polyamide resin, and is a value expressed as (Mn of polyamide resin after storage/Mn of polyamide resin before storage) x 100.

The number average molecular weight (Mn) was measured according to the following gel permeation chromatography (GPC) method.
The GPC measurement was performed using a Shodex GPC SYSTEM-11 manufactured by Showa Denko K.K. Hexafluoroisopropanol (HFIP) was used as the solvent, and 10 mg of the polyamide resin sample was dissolved in 10 g of HFIP and used for the measurement. The measurement conditions were two HFIP-806M GPC standard columns (column size 300 x 8.0 mm I.D.) manufactured by the same company, two HFIP-800 reference columns, a column temperature of 40°C, and a solvent flow rate of 1.0 mL/min. PMMA (polymethyl methacrylate) was used as the standard sample, and the number average molecular weight (Mn) was obtained using SIC-480II manufactured by the same company as the data processing software.

<Biodegradability>
The biodegradability was measured according to JIS K 6953-1 (aerobic compost biodegradability test method). 10 g of powder obtained by freeze-pulverizing the pellets (resin composition) was mixed with 60 g of compost with a dry mass of 45 to 50% by mass. This mixture was placed in a compost environment at 58±2°C and 100% relative humidity, and a biodegradation test was performed for 90 days by saturating the air with water and ventilating it with gas that had been deprived of carbon dioxide. The amount of carbon dioxide generated was measured, and the biodegradability was calculated from the total amount of theoretical carbon dioxide generated according to the following formula.
Biodegradability (%) = [(total amount of _CO2 generated during storage for 90 days in a compost environment) / (theoretical amount of carbon dioxide generated calculated from the composition formula)] x 100
The theoretical amount of carbon dioxide generated was calculated from the composition formula according to the following formula using the total organic carbon (TOC) amount of the test material previously measured with a CHN analyzer and a sample weight of 10 g.
Theoretical amount of carbon dioxide generated (g) = [(total organic carbon (TOC) of test material / 100)] x 3.67 x 10
The compost was made using a YK-11 manufactured by Yawata Bussan Co., Ltd. The amount of carbon dioxide was measured using a non-dispersive infrared analyzer (LI-830 manufactured by LI-COR Co., Ltd.) and the CHN analyzer was a PE2400 series II manufactured by PerkinElmer Co., Ltd.

As is clear from Table 1, when the resin compositions of the present invention (Examples 1 to 3) were stored for 28 days at 55° C. and a relative humidity of 90%, the cobalt salt acted to effectively reduce the number average molecular weight of the polyamide resin. Furthermore, when the resin compositions were stored for 90 days in a compost environment, the decomposition of the polyamide resin proceeded more effectively through biodegradation in addition to the oxidative decomposition action of the cobalt salt.
In contrast, when no cobalt salt was included (Comparative Examples 1 to 3), no decrease in the number average molecular weight of the polyamide resin was observed even after storage at 55° C. and a relative humidity of 90% for 28 days.Furthermore, biodegradation did not progress.
On the other hand, when the polyamide resin was not the specified polyamide resin even if a cobalt salt was blended (Comparative Example 4), no decrease in the number average molecular weight of the polyamide resin was observed even after storage at 55° C. and a relative humidity of 90% for 28 days.Furthermore, biodegradation did not progress.

Claims (12)

Contains a polyamide resin and a cobalt salt,
the polyamide resin comprises a xylylenediamine-based polyamide resin containing a diamine-derived structural unit and a dicarboxylic acid-derived structural unit, in which 50 mol % or more of the diamine-derived structural units are derived from xylylenediamine, and 50 mol % or more of the dicarboxylic acid-derived structural units are derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms;
0.1 mol % or more of the xylylenediamine is paraxylylenediamine,
A resin composition that is biodegradable . The resin composition according to claim 1, wherein the mass ratio of the xylylenediamine structure in the xylylenediamine-based polyamide resin is 20 to 70 mass%; here, the mass ratio of the xylylenediamine structure is a value calculated by [(mass of the xylylenediamine structure in the xylylenediamine-based polyamide resin)/(total mass of the xylylenediamine-based polyamide resin)]×100. The resin composition according to claim 1 or 2, wherein the α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms includes sebacic acid and/or dodecanedioic acid. The resin composition according to claim 1 or 2, wherein the α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms includes dodecanedioic acid. The resin composition according to any one of claims 1 to 4, wherein 20 mol% or more of the diamine-derived structural units are derived from paraxylylenediamine. The resin composition according to any one of claims 1 to 5, wherein the cobalt salt comprises a carboxylate of cobalt. The resin composition according to any one of claims 1 to 5, wherein the cobalt salt includes cobalt stearate. The resin composition according to any one of claims 1 to 7, wherein the content of the cobalt salt is 10 to 2000 ppm by mass based on cobalt atoms per 100 parts by mass of the xylylenediamine-based polyamide resin. The resin composition according to any one of claims 1 to 8 , wherein the resin composition has a biodegradability of 10% or more after storage in a compost environment for 90 days, where the biodegradability (%) is [(amount of _CO2 generated during storage in a compost environment)/(theoretical amount of carbon dioxide generated calculated from the composition formula)]×100. A molded article formed from the resin composition according to any one of claims 1 to 9 . The molded article according to claim 10 , which is a fishing net. A method for disposing of a polyamide resin, comprising biodegrading the resin composition according to any one of claims 1 to 9 or the molded article according to claim 10 or 11 .