Polyamide resin, polyamide resin composition, molded body and method for producing polyamide resin

Abstract

The present invention provides a polyamide resin which is a copolymer of a biodegradable polyamide such as polyamide 2 to polyamide 4, and another polyamide, and which has further enhanced biodegradability. This polyamide resin comprises a structural unit represented by formula (1) and another polyamide structural unit; and the difference between the degree of randomness in the case where it is assumed that the structural units are in an ideal random arrangement as determined by the proportions of the structural units obtained by 1H-NMR analysis and the degree of randomness obtained from the ratio of carbonyl carbon atoms of amide groups that connect different structural unit to each other to the integral value of all peaks of the carbonyl carbon atoms as obtained by 13C-NMR analysis is 0.10 or less. (In formula (1), x is an integer of 1 to 3.)

Description

Polyamide resin, polyamide resin composition, molded article, and method for producing polyamide resin

[0001] The present invention relates to a polyamide resin, a polyamide resin composition, a molded article, and a method for producing a polyamide resin.

[0002] Polyamide 4 has a high melting point, which gives it high heat resistance and mechanical strength. Furthermore, it can be synthesized from a biomass-derived raw material (2-pyrrolidone), and polyamide 4 itself is biodegradable, which means it has a low environmental impact.

[0003] Non-Patent Document 1 describes the introduction of a special structure derived from an initiator and a structure derived from ε-caprolactam into polyamide 4 to modify the mechanical and thermal properties of polyamide 4. Non-Patent Document 1 also indicates that this copolymer is slightly biodegradable. However, Non-Patent Document 1 also describes that when the structure derived from polyamide 4 was 40 mol % or less, there was almost no biodegradation.

[0004] Kawasaki, Journal of Applied Polymer Science, 2020, Volume 137, Issue 39, 49165

[0005] Polyamide 4 has a problem in that its melting point and thermal decomposition temperature are close to each other, making it prone to thermal decomposition during melt molding, making it difficult to mold. In response to this problem, it is expected that moldability can be improved by copolymerizing polyamide 4 with other polyamides to lower the melting point, as described in Non-Patent Document 1.

[0006] Incidentally, Non-Patent Document 1 states that the copolymer of 2-pyrrolidone and ε-caprolactam synthesized therein exhibited biodegradability. Considering that polyamide 4 synthesized from 2-pyrrolidone is readily biodegradable, while polyamide 6 synthesized from ε-caprolactam is not, it is presumed that the biodegradability of the copolymer is due to the structural units derived from 2-pyrrolidone. Furthermore, copolymers of glycine (polyamide 2 copolymers) and copolymers of α-alanine (2-aminopropanoic acid), β-alanine (3-aminopropanoic acid), and β-lactam (2-azetidinone) (polyamide 3 copolymers) are also expected to exhibit similar biodegradability due to their protein-like structures.

[0007] However, the copolymer described in Non-Patent Document 1 exhibits only slight biodegradability. Specifically, the degree of biodegradation shown in the experimental results described in Non-Patent Document 1 is lower than the content of structural units derived from 2-pyrrolidone, and in particular, when the structure derived from 2-pyrrolidone is 40 mol% or less, there is almost no biodegradation. Since there is concern that the non-degradable portion will become microplastics, higher biodegradability is desirable in order to reduce environmental pollution caused by waste plastics.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a polyamide resin that is a copolymer of a biodegradable polyamide such as polyamide 2 to polyamide 4 with another polyamide, the polyamide resin having enhanced biodegradability, a polyamide resin composition containing the polyamide resin, a molded article obtained from the polyamide resin composition, and a method for producing the polyamide resin.

[0009] One embodiment of the present invention for solving the above problems relates to the polyamide resins described below in [1] to [4]. [1] A polyamide resin having a first monomer structural unit represented by the following formula (1) and a second monomer structural unit constituting another polyamide structure, １the degree of randomness, calculated from the ratio of the first monomer structural units to the second monomer structural units obtained by H-NMR measurement, assuming that the first monomer structural units are arranged in an ideal random sequence; １３ A polyamide resin, wherein the difference between the degree of randomness calculated from the ratio of the carbonyl carbon of the amide group connecting the first monomer structural unit and the second monomer structural unit to the total peak integral value of the carbonyl carbon, as obtained by C-NMR measurement, is 0.10 or less. (In formula (1), x is an integer of 1 or more and 3 or less.) [2] The polyamide resin according to [1], in which the proportion of the first monomer structural unit represented by the following formula (1) to all structural units is 1 mol % or more and less than 40 mol %. [3] The polyamide resin according to [1] or [2], in which the first monomer structural unit represented by formula (1) includes a structural unit in which x is 3. [4] The polyamide resin according to any of [1] to [3], in which the other polyamide structural unit includes a polyamide 6 structural unit.

[0010] Another embodiment of the present invention for solving the above problems relates to a polyamide resin composition according to the following item [5]. [5] A polyamide resin composition comprising the polyamide resin according to any one of items [1] to [4].

[0011] Another embodiment of the present invention for solving the above problems relates to the polyamide resin compositions of the following [6] and [7]. [6] A molded article obtained by molding the polyamide resin composition of [5]. [7] The molded article of [6], which is a filament.

[0012] Another embodiment of the present invention for solving the above problems relates to the following methods for producing a polyamide resin [8] and [9]. [8] A method for producing a polyamide resin, comprising the steps of: preparing a first monomer that constitutes a structural unit represented by the following formula (1) by polymerization, and a second monomer that constitutes another polyamide structural unit; and polymerizing the first monomer and the second monomer in the presence of a Grignard reagent, which is a basic catalyst, and a polymerization initiator. [9] The method for producing a polyamide resin according to [8], wherein the polymerization step is carried out at 50°C or higher.

[0013] According to the present invention, there are provided a polyamide resin which is a copolymer of a biodegradable polyamide such as polyamide 2 to polyamide 4 with another polyamide, and which has enhanced biodegradability; a polyamide resin composition containing the polyamide resin; a molded article obtained from the polyamide resin composition; and a method for producing the polyamide resin.

[0014] [Polyamide Resin and Production Method Thereof] One embodiment of the present invention relates to a polyamide resin.

[0015] The polyamide resin has a first monomer structural unit represented by the following formula (1) and a second monomer structural unit constituting another polyamide structure.

[0016]

[0017] In formula (1), x is an integer of 1 or more and 3 or less. When x is 2 or 3, the alkylene group in formula (1) may be linear or branched.

[0018] The structural unit represented by formula (1) may contain only structural units in which x is the same number, or may contain a plurality of types of structural units in which x is a different number.

[0019] In the polyamide resin of this embodiment, the first monomer structural units are randomly introduced. In other words, in the polyamide resin of this embodiment, the proportion of blocks formed by consecutive identical first monomer structural units is low, and the proportion of first monomer structural units and second monomer structural units connected adjacently is high. According to the findings of the present inventors, the more randomly the first monomer structural units are introduced into the polyamide resin, the higher its biodegradability. Therefore, the polyamide resin is characterized by its high biodegradability. Note that, as shown in the examples described below, the polyamide resin can generate more carbon dioxide through biodegradation than the theoretical amount when all of the first monomer structural units represented by formula (1) are decomposed. This indicates that in the polyamide resin of this embodiment, not only the first monomer structural units represented by formula (1) but also the second monomer structural units, which are other polyamide structural units, are decomposed.

[0020] From the above viewpoint, the polyamide resin is １ The degree of randomness (hereinafter referred to as "R") is calculated from the ratio of each structural unit obtained by H-NMR measurement, assuming that the first monomer structural unit is an ideal random arrangement. １ Also called "H-theory randomness" １３ The actual randomness (hereinafter referred to as "Ran") is calculated from the ratio of the carbonyl carbon of the amide group connecting the first monomer structural unit and the second monomer structural unit to the total peak integral value of the carbonyl carbon obtained by C-NMR measurement. １３ The difference between the randomness (hereinafter also referred to as "randomness difference Δ") and the randomness (hereinafter also referred to as "randomness C") is preferably 0.10 or less, and more preferably 0.05 or less. The lower limit of the randomness difference Δ is not particularly limited, but can be 0.00 or more.

[0021] where １３ The C randomness is a value calculated by the following formula 1: (total peak integral values ​​derived from the carbonyl carbon peaks of the amide groups connecting the first monomer structural unit and the second monomer structural unit) / (total peak integral values ​​derived from all carbonyl carbon peaks).

[0022] １ The H theoretical randomness is the ratio of carbonyl carbons of amide groups connecting different structural units to the total number of carbonyl carbons when all structural units in the polyamide resin are stochastically randomly selected and arranged, １ It is calculated from the proportion of each structural unit obtained by H-NMR measurement using the following formula 2: (proportion of structural units of the first monomer) x (proportion of structural units of the second monomer) x 2

[0023] The difference Δ in the degree of randomness can be adjusted by the catalyst type, polymerization temperature, etc. For example, by using a Grignard reagent as a catalyst, which increases the reactivity of the monomers, the difference in reactivity between the monomers can be reduced, thereby reducing the difference Δ in the degree of randomness. Furthermore, if the polymerization temperature is high, the monomer that becomes the second monomer structural unit is preferentially consumed, and if the polymerization temperature is low, the monomer that becomes the first monomer structural unit represented by formula (1) is preferentially consumed, and blocks consisting of only the first monomer structural unit in succession tend to be produced. Therefore, by setting the polymerization temperature within an appropriate range depending on the combination of monomers, the difference in reactivity between the monomers can be reduced, thereby reducing the difference Δ in the degree of randomness.

[0024] In addition, the higher the proportion of the first monomer structural unit represented by formula (1) in the polyamide resin, the higher the biodegradability tends to be. On the other hand, the higher the proportion of the second monomer structural unit in the polyamide resin, the more the thermal stability of the polyamide resin during melt processing can be improved. From the viewpoint of balancing these, the proportion of the first monomer structural unit represented by formula (1) to the total structural units of the polyamide resin is preferably 1 mol% or more but less than 90 mol%, more preferably 1 mol% or more but less than 60 mol%, even more preferably 1 mol% or more but less than 40 mol%, even more preferably 3 mol% or more but less than 30 mol%, even more preferably 5 mol% or more but less than 17 mol%, and particularly preferably 5 mol% or more but less than 14 mol%.

[0025] ​From the same viewpoint, the ratio of the second monomer structural units constituting the other polyamide structures to the total structural units of the polyamide resin is preferably more than 10 mol% and not more than 99 mol%, more preferably more than 40 mol% and not more than 99 mol%, even more preferably more than 60 mol% and not more than 99 mol%, even more preferably 70 mol% or more and not more than 97 mol%, even more preferably 83 mol% or more and not more than 95 mol%, and particularly preferably 86 mol% or more and not more than 95 mol%.

[0026] The first monomer structural unit represented by formula (1) may be a structural unit derived from glycine where x = 1 (hereinafter also referred to as a "PA2 structural unit"), a structural unit derived from α-alanine (2-aminopropanoic acid), β-alanine (3-aminopropanoic acid) or β-lactam (2-azetidinone) where x = 2 (hereinafter also referred to as a "PA3 structural unit"), or a structural unit derived from 2-pyrrolidone where x = 3 (hereinafter also referred to as a "PA4 structural unit").

[0027] The second monomer structural unit constituting the other polyamide structure may be a structural unit represented by formula (2) formed by ring-opening polymerization of a lactam compound or polymerization of an amino acid, or may be a structural unit represented by formula (3) and a structural unit represented by formula (4) derived from the diamine and the dicarboxylic acid, respectively, when a moiety formed by condensation of a polyamine and a polycarboxylic acid is contained in the polyamide resin. The structural unit of the other polyamide may contain only one of these, or may contain a plurality of these.

[0028]

[0029] In formula (2), y is an integer of 4 or more and 11 or less. The alkylene group in formula (2) may be linear or branched.

[0030] When the second monomer structural unit constituting the other polyamide structure contains a structural unit represented by formula (2), it may contain only structural units in which y is the same number, or it may contain multiple types of structural units in which y is different numbers.

[0031]

[0032] In formula (3), a is an integer of 1 or more and 10 or less. The alkylene group in formula (3) may be linear or branched.

[0033] When the second monomer structural unit contains a structural unit represented by formula (3), it may contain only structural units in which a is the same number, or may contain multiple types of structural units in which a is different numbers.

[0034]

[0035] In formula (4), b is an integer of 1 or more and 12 or less. The alkylene group in formula (4) may be linear or branched.

[0036] When the second monomer structural unit contains a structural unit represented by formula (4), the second monomer structural unit may contain only structural units in which b is the same number, or may contain multiple types of structural units in which b is different numbers.

[0037] From the viewpoint of further enhancing biodegradability, the second monomer structural unit constituting the other polyamide structure is a structural unit represented by formula (2), and preferably includes a structural unit in which y is 4 or more and 7 or less, more preferably includes a structural unit in which y is 5 (hereinafter also referred to as a "PA6 structural unit"), and even more preferably includes a PA4 structural unit in which x = 3, and the second monomer structural unit is a PA6 structural unit in which y = 5. The ratio of the PA6 structural unit to the second monomer structural unit constituting the other polyamide structure is preferably 50 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, and even more preferably 85 mol% or more and 100 mol% or less.

[0038] Alternatively, from the viewpoint of improving the water resistance of the molded article, the second monomer structural unit constituting the other polyamide structure preferably includes a structural unit in which y is 5 to 11, more preferably a structural unit in which y is 11 (hereinafter also referred to as a "PA12 structural unit"). It is even more preferable that the first monomer structural unit is a PA4 structural unit in which x = 3, and the second monomer structural unit is a PA12 structural unit in which y = 11. The ratio of the PA12 structural unit to the second monomer structural unit constituting the other polyamide structure is preferably 50 mol% to 100 mol%, more preferably 70 mol% to 100 mol%, and even more preferably 85 mol% to 100 mol%. Alternatively, from the viewpoint of achieving both water resistance and heat resistance of the molded article, the ratio of the PA12 structural unit to the second monomer structural unit constituting the other polyamide structure is preferably 1 mol% to 50 mol%, more preferably 1 mol% to 30 mol%, and even more preferably 1 mol% to 15 mol%.

[0039] The structural units derived from the diamine and the dicarboxylic acid may be structural units derived from the diamine and the dicarboxylic acid when the polyamide resin contains a moiety formed by condensation of a diamine such as hexamethylenediamine, nonanediamine, methylpentadiamine, m-xylylenediamine, p-phenylenediamine, or m-phenylenediamine with a dicarboxylic acid such as adipic acid, sebacic acid, terephthalic acid, or isophthalic acid. From the viewpoint of improving the heat resistance of a molded article, the proportion of the structural units derived from the diamine and the dicarboxylic acid to the total structural units of the polyamide resin is preferably 50 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, and even more preferably 85 mol% or more and 100 mol% or less.

[0040] The polyamide resin may be a copolymer consisting only of the first monomer structural unit represented by formula (1) and the second monomer structural unit constituting the other polyamide structure, or may be a copolymer further containing another structural unit. Examples of the other structural unit include a structural unit derived from a polymerization initiator and a structural unit other than polyamide. From the viewpoint of improving biodegradability, the proportion of the other structural unit relative to the total structural units of the polyamide resin is preferably 0 mol% or more and 50 mol% or less, more preferably 0 mol% or more and 30 mol% or less, and even more preferably 0 mol% or more and 15 mol% or less.

[0041] The second monomer structural unit can reduce the thermal decomposition of the polyamide resin. Therefore, the polyamide resin, which is a copolymer with the second monomer structural unit, can suppress the inclusion of decomposed monomers (particularly the monomers that serve as raw materials for the first monomer structural unit represented by formula (1)) during melt processing. Therefore, the polyamide resin can suppress environmental pollution caused by the elution of decomposed monomers from molded articles.

[0042] The types and proportions of the structural units contained in the polyamide resin are as follows: １ H-NMR measurement, or １３ It can be calculated from the integral value of the peaks attributed to each structural unit that appear in the spectrum obtained by C-NMR measurement.

[0043] The polyamide resin may be linear or branched. From the viewpoint of improving the moldability and strength of the molded article, the polyamide resin is preferably linear. If a mono- or di-branched polymerization initiator is used during polymerization as described below, a linear polyamide resin can be obtained.

[0044] From the viewpoint of achieving both biodegradability and the heat resistance and underwater strength of the molded article, the melting point of the polyamide resin is preferably 220°C or less, more preferably 160°C or more and 215°C or less, and even more preferably 190°C or more and 210°C or less. The melting point of the polyamide resin can be measured by a differential scanning calorimeter (DSC). Note that when the difference Δ in the degree of randomness is large (i.e., when blocks of any structural unit are formed), two or more melting points may be observed for the polyamide resin by DSC. Since the difference Δ in the degree of randomness of the polyamide resin of this embodiment is small, only one melting point is often observed.

[0045] Furthermore, the polyamide resin can have a large temperature difference between its melting point and its thermal decomposition temperature due to the second monomer structural unit constituting the other polyamide structure. While a homopolymer of polyamide 4 is difficult to melt-mold because its melting point and thermal decomposition temperature are close, the polyamide can be melt-mold easily.

[0046] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polyamide resin are not particularly limited. For example, from the viewpoint of improving the strength and toughness of molded articles, the Mw of the polyamide resin is preferably 10,000 or more, more preferably 30,000 or more, and particularly preferably 50,000 or more. From the viewpoint of improving processability during molding, the Mw of the polyamide resin is preferably 1,000,000 or less, more preferably 500,000 or less, even more preferably 300,000 or less, even more preferably 200,000 or less, and particularly preferably 100,000 or less. The Mw of the polyamide resin is the Mw converted to polymethyl methacrylate resin (PMMA) and can be determined by known techniques such as gel permeation chromatography (GPC).

[0047] The polydispersity (Mw / Mn) of the polyamide resin is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. The lower limit of Mw / Mn is not particularly limited, but can be 1.0 or more. The smaller the Mw / Mn, the less low-molecular-weight oligomers there are, which makes it possible to suppress changes in properties due to elution of oligomers during use and environmental pollution caused by eluted oligomers. Furthermore, the smaller the Mw / Mn, the higher the mechanical strength of the molded article.

[0048] The polyamide resin can be synthesized by copolymerizing, in the presence of a basic catalyst and a polymerization initiator, a monomer (first monomer) that becomes a first monomer structural unit represented by formula (1) with a monomer (second monomer) that becomes a second monomer structural unit constituting another polyamide structure.

[0049] Examples of the first monomer that can be used include glycine, α-alanine, β-alanine, β-lactam (2-azetidinone), and 2-pyrrolidone. Examples of the second monomer that can be used include lactam compounds having 5 to 12 carbon atoms, such as δ-valerolactam (2-piperidone), ε-caprolactam, ω-octalactam, and ω-laurolactam, amino acids such as 6-aminohexanoic acid and 12-aminododecanoic acid, and adipic acid and hexamethylenediamine or salts thereof.

[0050] The basic catalyst may be any compound capable of generating an anionic species for each monomer. Examples of basic catalysts include Grignard reagents such as ethyl magnesium bromide (EtMgBr), ethyl magnesium chloride (EtMgCl), butyl magnesium chloride (BuMgCl), methyl magnesium chloride (MeMgCl), and methyl magnesium iodide (MeMgI); alkali metals such as lithium, sodium, and potassium, and their hydrides, oxides, hydroxides, carbonates, carboxylates, alkylates, and alkoxides; and alkaline earth metals such as calcium, their hydrides, oxides, hydroxides, carbonates, carboxylates, alkylates, and alkoxides. Examples of alkali metal alkylates include potassium tert-butoxide. Potassium salt of 2-pyrrolidone may also function as both a monomer and a basic catalyst. Among these, Grignard reagents are preferred because they are required in small amounts and are less likely to cause environmental pollution due to residues, can be polymerized in a short time, have a good yield, and can easily reduce the difference in reactivity of monomers and the difference Δ in the degree of randomness.

[0051] The amount of the basic catalyst used (added amount) is not particularly limited, but is preferably 0.01 mol% to 20 mol% relative to the total amount of raw material monomers, more preferably 0.03 mol% to 15 mol% and even more preferably 0.05 mol% to 10 mol%. When a Grignard reagent is used, the amount of the basic catalyst used can be 0.05 mol% to 5 mol%, 0.1 mol% to 2.5 mol%, or even 1 mol% to 1.5 mol% relative to the total amount of raw material monomers, from the viewpoint of balancing the reaction rate and catalyst cost.

[0052] Furthermore, a quaternary ammonium salt such as tetramethylammonium chloride, a quaternary phosphonium salt such as tetrabutylphosphonium bromide, a crown ether, or the like may be used in combination as a co-catalyst. By using these in combination, effects such as a reduction in the amount of catalyst, a shortening of the polymerization time, and an improvement in the yield can be expected.

[0053] Examples of polymerization initiators include ester compounds or derivatives thereof, imide compounds, and carbon dioxide. From the viewpoint of improving the moldability of polyamide resins, ester compounds or derivatives thereof, and imide compounds are preferred. The polymerization initiator may be a monobranched compound, or a di- or tri-branched compound. From the viewpoint of achieving both improved processability during molding and improved strength and toughness of molded articles, bi-branched compounds are preferred, and mono-branched compounds are more preferred. Examples of mono-branched polymerization initiators include tert-butyl acetate, isopropyl myristate, N-acetyl-ε-caprolactam, 1-acetyl-2-pyrrolidone, and N-benzoyl-2-pyrrolidone. Examples of bi- or tri-branched polymerization initiators include diisopropyl adipate and adipoyldipyrrolidone.

[0054] The amount of the polymerization initiator used (added amount) is not particularly limited, but is preferably 0.01 mol % to 1.5 mol % of the total amount of raw material monomers, more preferably 0.03 mol % to 1.0 mol %, even more preferably 0.05 mol % to 0.75 mol %, and particularly preferably 0.2 mol % to 0.3 mol %. If the amount of the polymerization initiator used is within the above range, a high molecular weight polyamide resin can be obtained.

[0055] The polymerization temperature can be, for example, 25° C. or higher and 200° C. or lower. From the viewpoint of reducing the difference in reactivity between monomers and further reducing the difference Δ in the degree of randomness, the polymerization temperature is preferably 50° C. or higher and 180° C. or lower, and more preferably 80° C. or higher and lower than 150° C.

[0056] The method for synthesizing the polyamide resin is not limited to this, and for example, γ-aminobutyric acid (GABA) may be reacted with a lactam compound or ω-aminocarboxylic acid having 5 to 12 carbon atoms.

[0057] [Polyamide Resin Composition and Molded Article] The polyamide resin described above can be molded into various shapes as a polyamide resin composition containing other additives as required.

[0058] In addition to the polyamide resin described above, the polyamide resin composition may contain known additives such as other resins, plasticizers, nucleating agents, antioxidants, ultraviolet absorbers, dyes, pigments, heat stabilizers, light stabilizers, fillers (glass fiber, etc.), internal mold release agents, matting agents, conductivity-imparting agents, charge control agents, antistatic agents, lubricants, and other processing aids.

[0059] From the viewpoint of enhancing the biodegradability of the molded body, the proportion of the polyamide resin in the polyamide resin composition relative to the total mass of the resin components is preferably 30% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less.

[0060] The molding method is not particularly limited, and various molding methods can be used, such as injection molding, extrusion molding, press molding, blow molding, etc. Alternatively, the molten polyamide resin composition may be spun into filaments.

[0061] The shape of the molded product obtained by molding is not particularly limited, and various shapes such as filament, film, particle, and any three-dimensional shape can be used.

[0062] When the polyamide resin composition is melted and molded, it is preferable to melt it at a temperature higher than the melting point of the polyamide resin and lower than the thermal decomposition temperature. In this case, by using a resin with a low melting point as the polyamide resin, the melt-extrudable temperature range can be widened, making molding easier. For example, the melt-extrusion can be carried out at a temperature of 170°C or higher and 270°C or lower.

[0063] The molded article thus obtained has high strength on land and in water, and also has good biodegradability.

[0064] For example, the polyamide resin composition can be molded into a filament shape and conditioned to equilibrium at 25°C and 50% humidity. The knot strength measured at 25°C and 50% humidity can be 100 MPa or more, preferably 300 MPa or more, and more preferably 600 MPa or more. Furthermore, the knot strength of the filament-shaped molded product, immersed in pure water at 25°C for 3 hours, then removed from the pure water and measured at 25°C without drying, can be 100 MPa or more, preferably 300 MPa or more, and more preferably 500 MPa or more. Furthermore, the knot strength of the filament-shaped molded product, immersed in seawater at 25°C for 3 hours, then removed from the seawater and measured at 25°C without drying, can be 100 MPa or more, preferably 300 MPa or more, and more preferably 500 MPa or more. The upper limit of these knot strengths is not particularly limited, but can be 1000 MPa or less.

[0065] The knot strength is a value obtained by dividing the strength at which the knot breaks by the diameter of the filamentous molded article, using a filamentous molded article 300 mm long with a single knot in the center as a test sample, setting the gripping distance to 150 mm, and the crosshead speed of the testing machine to 150 mm / min.

[0066] The seawater used in the measurements may have a NaCl concentration of 3% or more and 4% or less. The seawater used in the measurements may be seawater actually collected from the ocean, or may be commercially available artificial seawater such as MARINE ART (registered trademark) SF-1 manufactured by Osaka Yaken Co., Ltd.

[0067] Furthermore, after knotting, the filamentous molded article is stored at 25°C at the interface between seawater and sediment for one month, and then dried by being left to stand for three days in a dry room at 25°C with a dew point of -40°C or lower. Thereafter, the rate of decrease in knot strength measured at 25°C and 50% relative humidity relative to the knot strength measured at 25°C and 50% humidity is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more. On the other hand, from the viewpoint of suppressing a decrease in strength of the filamentous molded article during use in seawater, the rate of decrease is preferably 80% or less, more preferably 70% or less, and even more preferably 60% or less.

[0068] The interface between seawater and sediments refers to the environment within 5 cm from the interface between seawater and sediments as defined in ISO 19679. The sediments may be sea sand collected from the ocean.

[0069] [Applications] Molded articles of the polyamide resin composition can be used for a variety of applications, including fishing lines, fishing nets, agricultural films, clothing fibers and fabrics made therefrom, cosmetics, paints, functional particles such as antiblocking agents, packaging films, food containers, tableware, and daily necessities such as razors and toothbrushes.

[0070] [Other Embodiments] It goes without saying that the above-described embodiments are exemplary embodiments of the present invention, and the present invention may include embodiments other than the above-described embodiments within the scope of its core technical concept.

[0071] The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

[0072] 1. Preparation of Test Filaments Polymers 1 to 6, polymer 8, and polymer 9 were synthesized by the following method, and test filaments 1 to 9 were prepared from these and polymer 7 by the following method.

[0073] 1-1. Preparation of Test Filament 1 243.8 g (2.86 mol) of 2-pyrrolidone manufactured by Mitsubishi Chemical Corporation and 756.2 g (6.68 mol) of ε-caprolactam manufactured by Tokyo Chemical Industry Co., Ltd. were prepared, mixed, and heated to 80°C to melt, to prepare a homogeneous monomer solution. This monomer solution was divided into two halves, and 8.03 g (0.30 mol % relative to the total moles of 2-pyrrolidone and ε-caprolactam) of separately synthesized adipoyldipyrrolidone was added to one half of the monomer solution and dissolved to prepare an initiator solution. To the other monomer solution, 143.2 ml (1.5 mol % of EtMgBr relative to the total moles of 2-pyrrolidone and ε-caprolactam) of ethyl magnesium bromide (EtMgBr) manufactured by Tokyo Chemical Industry Co., Ltd. in tetrahydrofuran (approximately 1 mol / L) was added dropwise, and then the tetrahydrofuran was removed by distillation under reduced pressure to obtain a catalyst solution. The initiator solution and catalyst solution were mixed and subjected to a polymerization reaction at 100°C to obtain Polymer 1.

[0074] After the polymer was pulverized, it was washed with pure water, an aqueous acetic acid solution, pure water, and pure water in this order to remove unreacted monomers and catalysts, and then dried under reduced pressure to remove water, yielding a polymer powder for spinning.

[0075] The polymer powder obtained above was charged into a small twin-screw extruder, melt-extruded into a fiber, and cooled and solidified by passing through a cold bath to prepare an undrawn monofilament. This monofilament was then appropriately drawn to obtain test filament 1.

[0076] 1-2. Preparation of Test Filament 2 Polymer 2 was obtained in the same manner as in the synthesis of Polymer 1, except that the polymer materials were changed to 1.38 mol of 2-pyrrolidone and 7.80 mol of ε-caprolactam. A monofilament was prepared from this Polymer 2 in the same manner as in the preparation of Test Filament 1, and the monofilament was subjected to a drawing treatment to prepare Test Filament 2.

[0077] 1-3. Preparation of Test Filament 3 Polymer 3 was obtained in the same manner as in the synthesis of Polymer 1, except that the polymer materials were changed to 1.86 mol of 2-pyrrolidone and 7.44 mol of ε-caprolactam, and 0.30 mol % of isopropyl myristate relative to the total moles of 2-pyrrolidone and ε-caprolactam was blended instead of adipoyldipyrrolidone as the initiator. A monofilament was prepared from this polymer 3 in the same manner as in the preparation of Test Filament 1, and the monofilament was drawn to prepare Test Filament 3.

[0078] 1-4. Preparation of Test Filament 4 Polymer 4 was obtained in the same manner as in the synthesis of Polymer 1, except that the polymer materials were changed to 4.03 mol of 2-pyrrolidone and 4.03 mol of ε-caprolactam, 0.20 mol% of N-acetyl-ε-caprolactam was blended relative to the total mol of 2-pyrrolidone and ε-caprolactam instead of adipoyldipyrrolidone as the initiator blended in the initiator solution, the amount of EtMgBr blended in the catalyst solution was changed to 1.0 mol% relative to the total mol of 2-pyrrolidone and ε-caprolactam, and the polymerization reaction temperature was changed to 60°C. A monofilament was prepared from this polymer 4 in the same manner as in the preparation of Test Filament 1, and then drawn to prepare Test Filament 4.

[0079] 1-5. Preparation of Test Filament 5 Polymer 5 was obtained in the same manner as in the synthesis of Polymer 1, except that the polymer materials were changed to 4.03 mol of 2-pyrrolidone and 4.03 mol of ε-caprolactam, 0.20 mol% of N-acetyl-ε-caprolactam was blended relative to the total moles of 2-pyrrolidone and ε-caprolactam instead of adipoyldipyrrolidone as the initiator blended in the initiator solution, the amount of EtMgBr blended in the catalyst solution was changed to 1.0 mol% relative to the total moles of 2-pyrrolidone and ε-caprolactam, and the polymerization reaction temperature was changed to 50°C. A monofilament was prepared from this polymer 5 in the same manner as in the preparation of Test Filament 1, and then drawn to prepare Test Filament 5.

[0080] 1-6. Preparation of Test Filament 6 The polymer materials were changed to 141.00 mol of 2-pyrrolidone and 0.00 mol of ε-caprolactam, and instead of adipoyldipyrrolidone, 0.10 mol% of tert-butyl acetate was added relative to the total moles of 2-pyrrolidone and ε-caprolactam as the initiator incorporated in the initiator solution. Instead of EtMgBr, tert-butoxypotassium (tBuOK) and tetramethylammonium chloride (TMAC) were added, each at 2.0 mol% relative to the total moles of 2-pyrrolidone and ε-caprolactam, respectively. The polymerization reaction temperature was changed to 25 ° C. Polymer 6 was obtained in the same manner as in the synthesis of Polymer 1. A monofilament was prepared from this polymer 6 in the same manner as in the preparation of Test Filament 1, and then stretched to prepare Test Filament 6.

[0081] 1-7. Preparation of Test Filament 7 A commercially available polyamide 6 resin (UBE Nylon 1022B, manufactured by Ube Industries, Ltd.) was used as Polymer 7. This Polymer 7 was pulverized to obtain a polymer powder for spinning, and a monofilament was prepared from the obtained polymer powder in the same manner as in the preparation of Test Filament 1. This monofilament was appropriately stretched to obtain Test Filament 7.

[0082] 1-8. Preparation of Test Filament 8 Polymer 8 was obtained in the same manner as in the synthesis of Polymer 1, except that the polymer materials were changed to 0.95 mol of 2-pyrrolidone and 1.93 mol of ε-caprolactam. A monofilament was prepared from this polymer 8 in the same manner as in the preparation of Test Filament 1, and the monofilament was drawn to prepare Test Filament 8.

[0083] 1-9. Preparation of Test Filament 9 Polymer 9 was obtained in the same manner as in the synthesis of Polymer 1, except that the polymer materials were changed to 1.24 mol of 2-pyrrolidone and 1.72 mol of ε-caprolactam. A monofilament was prepared from this polymer 9 in the same manner as in the preparation of Test Filament 1, and the monofilament was drawn to prepare Test Filament 12.

[0084] The polymerization conditions for polymers 1 to 9 used in the production of test filaments 1 to 9, and the draw ratios for test filaments 1 to 9, are shown in Table 1. Note that "PA4 / 6" for polymer type indicates polyamide 4 / 6, "PA4" for polyamide 4, and "PA6" for polyamide 6. The amounts of initiator and catalyst added are the amounts blended relative to the total moles of monomers, while the monomer "pyrrolidone" indicates the amount of 2-pyrrolidone, and "caprolactam" indicates the amount of ε-caprolactam.

[0085]

[0086] 2. Measurement Polymers 1 to 9 were measured using the following method. １ H-NMR, １３ Measurement by C-NMR, DSC, and TGA, yield calculation, and biodegradability (O ２ Test filaments 1 to 9 were subjected to GPC analysis by the following method.

[0087] 2-1. １ H-NMR measurement: Using a nuclear magnetic resonance spectrometer (JASCO Corporation, JNM-ECZ600R / S1) １ H-NMR spectra were obtained and compared. Specifically, 10 mg of each polymer sample was dissolved in 1 ml of trifluoroethanol (TFE) / d2 chloroform (CDCl ３ The sample was dissolved in a mixed solvent of PA4 and PA6 units at a volume ratio of 1 / 1. Measurement was then performed using tetramethylsilane (TMS) as the standard. Of the peak integrals derived from methylene groups appearing between 1.0 ppm and 2.0 ppm in the obtained spectrum, the ratio of the peak integrals of methylene protons derived from PA4 structural units to the peak integrals of methylene protons derived from PA6 units was determined. The ratio of these peak integrals was used to calculate the ratio of PA4 structural units, which was designated as the "PA4 ratio."

[0088] In addition, from this PA4 ratio and the ratio of PA6 structural units (PA6 ratio) calculated at the same time, the degree of randomness ((PA4 ratio) × (PA6 ratio) × 2) was calculated assuming that each polymer was an ideal random arrangement of PA4 structural units and PA6 structural units. １ H theory randomness.

[0089] 2-2. １３ C-NMR measurement: Using a nuclear magnetic resonance spectrometer (JASCO Corporation, JNM-ECZ600R / S1) １３ Specifically, 10 mg of each polymer sample was dissolved in 1 ml of trifluoroethanol (TFE) / d2 chloroform (CDCl ３ The PA4 structural unit and the PA6 structural unit were dissolved in a mixed solvent of PA6 and PA4 structural units in a volume ratio of 1 / 1. Measurement was then carried out using tetramethylsilane (TMS) as the standard. The ratio of the peak integral value of the carbonyl carbon of the amide group connecting the PA4 structural unit and the PA6 structural unit to the total integral value of all peaks originating from carbonyl carbons appearing between 174 ppm and 177 ppm in the obtained spectrum was calculated, and this was referred to as " １３ C randomness".

[0090] 2-3. DSC Measurement Differential scanning calorimeter (Mettler Toledo, DSC3 ＋ DSC curves were obtained by differential scanning calorimetry (DSC) using a 10 mg sample of each polymer. Specifically, 10 mg of a sample was weighed into an aluminum pan and heated at a rate of 20°C / min in a nitrogen atmosphere within the range of 25°C to 280°C to obtain a DSC curve. The peak top temperature of the endothermic peak based on the melting behavior in this DSC curve was taken as the "melting point" of each polymer.

[0091] 2-4. TGA Measurement A thermogravimetric / differential thermal simultaneous analyzer (TGA / DSC2, manufactured by Mettler Toledo) was used to obtain a thermogravimetric / differential thermal simultaneous analyzer. Specifically, a 10 mg sample of each polymer was weighed into an aluminum pan and heated at a rate of 20°C / min in a nitrogen atmosphere within the range of 25°C to 500°C to obtain a thermogravimetric / differential thermal simultaneous analyzer. The temperature at which 5% weight loss occurred in this thermogravimetric / differential thermal simultaneous analyzer was determined as the "5% thermogravimetric / differential thermal simultaneous analyzer temperature" for each polymer.

[0092] 2-5. GPC Analysis GPC analysis was performed using a gel permeation chromatography (GPC) analyzer (HLC-8420GPC, manufactured by Tosoh Corporation). Specifically, 10 mg of sample for each test filament was dissolved in hexafluoroisopropanol (HFIP) containing 5 mM sodium trifluoroacetate to obtain a 10 mL solution, and then filtered through a membrane filter to obtain a sample solution. 100 μL of this sample solution was injected into the analyzer, and measurements were performed under the following conditions. From the chromatogram obtained by the measurement, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymer constituting each test filament were calculated using a calibration curve obtained with polymethyl methacrylate resin (PMMA) of known molecular weight. Apparatus: HLC-8420GPC, manufactured by Tosoh Corporation Column: HFIP 806M x 2 in series, 40°C Eluent: 5 mM CF ３ COONa / HFIP Flow rate: 1.0 mL / min Detector: differential refractometer (RI)

[0093] 2-6. Yield After the polymerization was completed, the polymer was washed with water five times and dried. The weight of the polymer recovered was then compared to the weight before washing with water, and the ratio was taken as the yield.

[0094] 2-7. Biodegradable (O ２ (Reference) 2000 g of sediment collected from the Pacific coast was added to 4000 ml of seawater collected from the Pacific coast, and microorganisms in the sediment were extracted into seawater by ultrasonic treatment. Nutrient salts, 0.5 g / L of ammonium chloride and 0.1 g / L of potassium dihydrogen phosphate, were dissolved in the extracted seawater, followed by aeration to prepare extracted seawater. Approximately 40 mg of polymer powder was dispersed in 300 ml of the prepared extracted seawater, and the pressure change caused by capturing the generated carbon dioxide with sodium hydroxide in a sealed environment was measured for 4 weeks using a BOD meter (OxiTop i, manufactured by WTW). The biodegradability of the polymer powder was evaluated using the following formula, where the theoretical value is the amount of oxygen required for 100% decomposition of the polymer: Biodegradability (%) = (oxygen consumption from sample / theoretical oxygen demand) x 100

[0095] Tables 2 and 3 show the PA4 ratio, yield, and １ H-theory randomness, １３ C randomness, １ H-theory randomness and １３ the difference Δ between the melting point and the 5% thermal weight loss temperature, the difference ΔT between the melting point and the 5% thermal weight loss temperature, the weight average molecular weight Mw, the number average molecular weight Mn, Mw / Mn, the PA4 ratio of each polymer on a mass basis converted from the molar ratio of PA4, and biodegradability (O ２ (standard).

[0096]

[0097]

[0098] 3. Evaluation 3-1. Strength The knot strength of Test Filament 1 to Test Filament 9 and Polymer 1 to Polymer 9 was measured in an indoor environment, an underwater environment, and a biodegradable environment by the following method.

[0099] The knot strengths were measured in a room environment, an underwater environment, and a biodegradable environment using a tensile tester (Tensilon RTF-1210, manufactured by A&D Co., Ltd.). Specifically, a 300 mm long test filament with a single knot in the center was used as a test sample. The grip distance was set to 150 mm, and the crosshead speed of the tester was set to 150 mm / min. The load at which the knot broke was divided by the diameter of the test filament, and the value obtained was used as the knot strength in each environment.

[0100] The environmental conditions were as follows: Indoor environment: Measurements were made after nodulation at 25°C and a relative humidity of 50%. Underwater environment: After immersion in pure water at 25°C for 3 hours, measurements were made after nodulation at 25°C and a relative humidity of 50% without drying. Biodegradation environment: Stored at the interface between seawater and sediment at 25°C for 1 month, then left to dry for 3 days in a dry room at 25°C with a dew point of -40°C or below, and then measured after nodulation at 25°C and a relative humidity of 50%. Seawater (NaCl concentration: 3.1-3.4%) collected from the Pacific coast and sea sand were used as the seawater and sediment, respectively.

[0101] Furthermore, the difference between the knot strength in the indoor environment and the knot strength in the biodegradable environment was calculated, and the ratio of this difference to the knot strength in the indoor environment ((knot strength in the indoor environment - knot strength in the biodegradable environment) / knot strength in the indoor environment x 100) was calculated to obtain the "strength reduction rate after biodegradation." A strength reduction rate of 10% or more in the biodegradable environment was determined to be "biodegradable (strength standard)."

[0102] 3-2. First Monomer Content Approximately 100 mg of sample was dissolved in 10 ml of HFIP, and then acetone was added to make the total volume 50 ml. The precipitated polymer was removed using a 20 μm membrane filter, and the filtrate was measured. Measurement device: GC-2010 Plus manufactured by Shimadzu Corporation Column: Rix15MS (0.25 mmφ-15 m-0.25 μm df) manufactured by Resteke Corporation Column temperature: 50°C - 5 min → (20°C / min) → 250°C Vaporization chamber temperature: 250°C Detector: FID Split ratio: 50 Injection amount: 1 μl Make-up gas: He Gas flow rate: 30 ml / min

[0103] Table 4 shows the knot strength, strength reduction rate after biodegradation, and biodegradability evaluation results based on the strength reduction rate for test filaments 1 to 9 in each of the indoor environment, underwater environment, and biodegradation environment, as well as the content of 2-pyrrolidone.

[0104]

[0105] As shown in Tables 1 to 4, polymers 1 to 5, 8, and 9, which are polyamide resins having a difference Δ in randomness of 0.10 or less, have a higher O content than the PA4 ratio of each polymer on a mass basis. ２ The biodegradability evaluated by the standard was high, and it biodegraded at a rate higher than that of PA4.

[0106] This application claims priority to Japanese Patent Application No. 2022-158909, filed September 30, 2022, and Japanese Patent Application No. 2023-074569, filed April 28, 2023. The entire disclosures and claims of those applications are incorporated herein by reference.

[0107] The polyamide resin of the present invention enables the production of molded articles having high strength and biodegradability. The polyamide resin of the present invention is applicable to a variety of applications and is expected to contribute to the reduction of environmental pollution caused by waste plastics.

Claims

1. A polyamide resin having a first monomer structural unit represented by the following formula (1) and a second monomer structural unit constituting another polyamide structure, １ the degree of randomness calculated from the ratio of the first monomer structural units and the second monomer structural units obtained by H-NMR measurement, assuming that the first monomer structural units are in an ideal random arrangement; １３ a difference between the degree of randomness calculated from the ratio of the carbonyl carbon of the amide group linking the first monomer structural unit and the second monomer structural unit to the total peak integral value of the carbonyl carbon, as determined by C-NMR measurement, is 0.10 or less; Polyamide resin. 【Chemistry 1】 (In formula (1), x is an integer of 1 or more and 3 or less.)

2. The first monomer structural unit represented by the formula (1) includes a structural unit in which x is 3. The polyamide resin according to claim 1.

3. The second monomer structural unit constituting the other polyamide structure includes a polyamide 6 structural unit. The polyamide resin according to claim 1 or 2.

4. The ratio of the first monomer structural unit represented by the following formula (1) to all structural units is 1 mol% or more and less than 40 mol%. The polyamide resin according to claim 1 or 2.

5. The polyamide resin according to claim 1 or 2 is included. Polyamide resin composition.

6. A molded article obtained by molding the polyamide resin composition according to claim 5.

7. The molded article according to claim 6, which is a filament.

8. A step of preparing a first monomer that constitutes a structural unit represented by the following formula (1) by polymerization, and a second monomer that constitutes other polyamide structural units; polymerizing the first monomer and the second monomer in the presence of a Grignard reagent and a polymerization initiator; The method for producing a polyamide resin comprising the steps of: 【Chemistry 2】 (In formula (1), x is an integer of 1 or more and 3 or less.)

9. The method for producing a polyamide resin according to claim 8, wherein the polymerization step is carried out at 50°C or higher.

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