Filament for marine resources

Abstract

The present invention addresses the problem of providing a biodegradable filament for marine resources, the filament having high strength equivalent to that of existing nylon filaments.　This filament for marine resources is mainly composed of a nylon resin that contains a nylon 6 structural unit and a nylon 66 structural unit. The ratio of the nylon 6 structural unit to all structural units of the nylon resin is 70 mass% or more but less than 97 mass%, the terminal temperature of the melting peak of the filament as measured by differential scanning calorimetry (DSC) is 190‒220°C, and the heat of fusion of the filament is 80 J / g or less.

Description

Filament for fishery materials

[0001] The present invention relates to a filament for aquatic materials.

[0002] Traditionally, fishing lines have been made of monofilaments such as polyethylene, nylon, and fluorocarbon. Of these, nylon is considered suitable for a variety of fishing styles because it combines flexibility and moderate stretchability with high strength.

[0003] Research and development is also underway to improve the properties of nylon for fishing line. For example, Patent Document 1 describes a fishing line that is integrally spun from a composition in which a polyamide fiber raw material is kneaded with an ultraviolet absorber in order to improve the light resistance that is a drawback of fishing line made from polyamide fibers. Patent Document 2 also describes the production of a fishing line suitable for crucian carp fishing by adjusting the blend ratio of nylon 6 and nylon 6 / 66.

[0004] Japanese Patent Laid-Open No. 10-276639 Japanese Patent Laid-Open No. 2011-101618

[0005] As described in Patent Documents 1 and 2, various nylon fishing lines have been developed and are used for various types of fishing. However, because the high-molecular-weight nylon 6 used in fishing lines is not biodegradable, broken fishing lines remaining in the ocean cause environmental pollution and ghost fishing of marine life, which has become a problem.

[0006] In response to this, fishing lines made of biodegradable materials such as polyesters such as polybutylene succinate (PBS) and nylon 4 are known. However, fishing lines made of these materials have the problem of insufficient strength. This problem is not limited to fishing lines, but also applies to fishing nets made of nylon filaments.

[0007] The present invention has been made in view of the above problems, and has as its object to provide a filament for fishery materials that has high strength equivalent to that of existing nylon filaments and is biodegradable.

[0008] The present invention relates to the following filaments for marine materials and a method for producing the same.

[0009] [1] A filament for fishery materials, the filament being composed primarily of a nylon resin containing nylon 6 structural units and nylon 66 structural units, wherein the ratio of the nylon 6 structural units to all structural units of the nylon resin is 70% by mass or more but less than 97% by mass, and the filament has a melting peak end temperature of 190°C or more but less than 220°C as measured by differential scanning calorimetry (DSC), and a heat of fusion of 80 J / g or less. [2] The filament for fishery materials according to [1], wherein the filament contains 50% by mass or more of the nylon resin relative to the total mass of the filament. [3] The filament for fishery materials according to [1] or [2], wherein the content of an antioxidant in the filament is less than 0.1% by mass. [4] The filament for fishery materials according to any one of [1] to [3], wherein the linear strength of the filament measured at 25°C and a relative humidity of 50% is 700 MPa or more. [5] The filament for fisheries materials according to any one of [1] to [4], wherein the knot strength of the filament measured at 25°C and a relative humidity of 50% is 500 MPa or more. [6] The filament for fisheries materials according to any one of [1] to [5], wherein the linear strength of the filament measured at 25°C and a relative humidity of 50% after storage at an interface between seawater and sediment for three months at 25°C, washing with water, and drying is less than 90% of the linear strength measured at 25°C and a relative humidity of 50% compared to the linear strength measured under the same conditions before storage. [7] A method for producing the filament for fisheries materials according to any one of [1] to [6], comprising the steps of melt-extruding a resin composition containing a nylon resin that contains nylon 6 structural units and nylon 66 structural units, wherein the proportion of the nylon 6 structural units to all structural units is 70% by mass or more but less than 97% by mass, cooling the melt-extruded resin composition into a fiber in a refrigerant at 5°C or less, and stretching the cooled resin composition.

[0010] According to the present invention, a filament for use in fisheries materials is provided which has high strength equivalent to that of existing nylon filaments and is biodegradable.

[0011] The present inventors have discovered that in a filament whose main component is a nylon resin (hereinafter simply referred to as "nylon resin") containing nylon 6 structural units (hereinafter also referred to as "nylon 6 structural units") and nylon 66 structural units (hereinafter also referred to as "nylon 66 structural units"), by setting the content of nylon 6 structural units within a predetermined range and adjusting the spinning conditions, it is possible to obtain a filament having strength equivalent to that of existing filaments while exhibiting good biodegradability. Furthermore, it has been discovered that such a filament has a melting peak end temperature and a heat of fusion that are each below a predetermined value in DSC measurement.

[0012] The reason for this is unclear, but is thought to be as follows: The above-mentioned filament contains an appropriate mixture of nylon 66 structural units and nylon 6 structural units, which weakens the hydrogen bonds between the molecular chains of the nylon 6 structural units, thereby exhibiting biodegradability. Furthermore, by setting the proportion of nylon 6 structural units in the nylon resin within a predetermined range, it is thought that the decrease in strength of the filament due to water absorption can be suppressed, and strength during use can be maintained.

[0013] That is, one embodiment of the present invention provides a filament for use in fisheries materials, which has a filament primarily composed of nylon resin. The nylon resin contains nylon 6 structural units and nylon 66 structural units, with the ratio of nylon 6 structural units to all structural units being 70% by mass or more but less than 97% by mass. Furthermore, the end temperature of the melting peak measured by differential scanning calorimetry (DSC) of the filament can be used as an indicator of nylon structure, and the weaker the hydrogen bonds between nylon molecular chains, the lower the end temperature tends to be. Therefore, the lower the end temperature, the higher the biodegradability tends to be. On the other hand, if the end temperature is too low, the molecular structure becomes fragile and the strength tends to be low. The end temperature of the melting peak measured by DSC is 190°C or more but 220°C or less, and the heat of fusion is 80 J / g or less.

[0014] The filaments included in the filament for fishery materials of this embodiment and the method for producing the same will be specifically described below.

[0015] 1. As described above, the filament contains nylon resin as a main component. "Containing nylon resin as a main component" means that the proportion of nylon resin relative to the total mass of the filament is preferably 50% by mass or more. The proportion of nylon resin relative to the total mass of the filament is more preferably 70% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 95% by mass or more and 100% by mass or less.

[0016] 1-1. Nylon Resin As described above, the nylon resin contains nylon 6 structural units and nylon 66 structural units. The nylon 6 structural units are structural units derived from ε-caprolactam or ε-aminocaproic acid. The nylon 66 structural units are structural units derived from adipic acid and hexamethylenediamine. In the nylon resin, the proportion of nylon 6 structural units to all structural units is 70% by mass or more but less than 97% by mass.

[0017] In the above-mentioned nylon resin, the nylon 66 structural moieties and nylon 6 structural moieties are arranged in an appropriate mixture, which weakens the hydrogen bonds between the molecular chains of the nylon 6 structural moieties and thereby imparts biodegradability to the filaments. On the other hand, by keeping the proportion of nylon 6 structural units within a specified range, it is thought that the decrease in strength of the filaments due to water absorption can be suppressed, thereby increasing the strength during use.

[0018] From the viewpoint of balancing biodegradability and strength during use, the nylon resin has a ratio of nylon 6 structural units to its total structural units of 70% by mass or more but less than 97% by mass. When the ratio of nylon 6 structural units is less than 97% by mass, the nylon 66 structural units and nylon 6 structural units are appropriately mixed and arranged, weakening the hydrogen bonds between the molecular chains of the nylon 6 structural units, which tends to improve the biodegradability of the filaments. When the ratio of nylon 6 structural units is 70% by mass or more, the crystallinity of the nylon 6 structural units is not excessively reduced, which reduces the decrease in filament strength due to water absorption and makes it easier to increase strength during use. In other words, it is believed that the crystallinity of the nylon 6 structural units in the nylon resin tends to decrease as the ratio of nylon 6 structural units approaches approximately 50% by mass and increase as the ratio approaches 100% by mass. Furthermore, by setting the ratio of nylon 6 structural units in the nylon resin to 70% by mass or more but less than 97% by mass, it is possible to appropriately reduce the crystallinity of the nylon 6 structural units in the nylon resin, which is believed to suppress the decrease in filament strength due to water absorption and enable biodegradability to be exhibited. From the viewpoint of achieving both of these, the ratio of nylon 6 structural units to all structural units in the nylon resin is preferably 75% by mass or more and 95% by mass or less, more preferably 80% by mass or more and 95% by mass or less, and even more preferably 80% by mass or more and less than 94% by mass.

[0019] From the same viewpoint, the proportion of nylon 66 structural units relative to all structural units of the nylon resin is preferably more than 3% by mass and not more than 30% by mass, more preferably 5% by mass or more and not more than 25% by mass, even more preferably 5% by mass or more and not more than 20% by mass, and even more preferably more than 6% by mass and not more than 20% by mass.

[0020] From the viewpoint of achieving a better balance between biodegradability and strength, the total proportion of nylon 6 structural units and nylon 66 structural units is preferably 70% by mass or more, more preferably 80% by mass or more, and may be 100% by mass, based on the total structural units of the nylon resin.

[0021] The nylon resin may further contain structural units of nylons other than nylon 6 structural units and nylon 66 structural units. Examples of the structural units of other nylons include structural units of nylon 2 (hereinafter also referred to as "nylon 2 structural units"), structural units of nylon 3 (hereinafter also referred to as "nylon 3 structural units"), structural units of nylon 4 (hereinafter also referred to as "nylon 4 structural units"), structural units of nylon 5 (hereinafter also referred to as "nylon 5 structural units"), structural units of nylon 11 (hereinafter also referred to as "nylon 11 structural units"), and structural units of nylon 12 (hereinafter also referred to as "nylon 12 structural units"), etc. The nylon 2 structural unit is a structural unit derived from glycine, the nylon 3 structural unit is a structural unit derived from β-lactam (2-azetidinone), α-alanine (2-aminopropanoic acid), or β-alanine (3-aminopropanoic acid), the nylon 4 structural unit is a structural unit derived from 2-pyrrolidone or γ-aminobutyric acid, the nylon 5 structural unit is a structural unit derived from 2-piperidone or 5-aminopentanoic acid, the nylon 11 structural unit is a structural unit derived from undecane lactam or 11-aminoundecanoic acid, and the nylon 12 structural unit is a structural unit derived from ω-laurolactam or 12-aminolauric acid.

[0022] The types and proportions of each structural unit contained in the above nylon resin are as follows: １３ It can be calculated from the integral value of the signals attributed to each structural unit that appear in the spectrum obtained by C-NMR measurement.

[0023] Specifically, the measurement can be carried out by the following procedure: 10 mg of a nylon resin sample is dissolved in 1 ml of trifluoroethanol (TFE) / d2 chloroform (CDCl ３ The compound is dissolved in a mixed solvent of tetramethylsilane (TMS) and tetramethylsilane (TMS) in a volume ratio of 1:1. Then, the compound is analyzed by a nuclear magnetic resonance spectrometer (for example, JNM-ECZ600R / S1 manufactured by JASCO Corporation) using tetramethylsilane (TMS) as a standard. １３C-NMR measurement is performed. Of the signals originating from methylene carbons adjacent to carbonyl groups appearing between 35.0 ppm and 37.0 ppm in the obtained spectrum, the integral value of the signal originating from nylon 6 structural units appearing on the low magnetic field side (for example, near 37.00 ppm) and the integral value of the signal originating from nylon 66 units appearing on the high magnetic field side (for example, near 36.00 ppm) are calculated. The ratio of the integral values ​​of these signals is taken as the mass ratio of nylon 6 structural units to nylon 66 structural units.

[0024] The nylon resin may be a random copolymer or a block copolymer, but from the viewpoint of enhancing biodegradability, it is preferably a random copolymer.

[0025] The weight-average molecular weight (Mw) of the nylon resin is not particularly limited. For example, from the viewpoint of maintaining biodegradability while further maintaining strength and toughness during use, the Mw of the nylon resin may be 10,000 or more, 30,000 or more, or 50,000 or more. The Mw of the nylon resin may be 1,000,000 or less, 500,000 or less, 300,000 or less, 200,000 or less, or 100,000 or less.

[0026] The Mw of the nylon resin can be measured using a gel permeation chromatography (GPC) analyzer (e.g., HLC-8420GPC, manufactured by Tosoh Corporation). Specifically, 10 mg of sample for each test filament is dissolved in hexafluoroisopropanol (HFIP) containing 5 mM sodium trifluoroacetate to obtain 10 mL of solution, which is then filtered through a membrane filter to obtain a sample solution. 100 μL of this sample solution is injected into the analyzer, and measurement is performed under the following conditions. Apparatus: HLC-8420GPC manufactured by Tosoh Corporation Column: HFIP 806M x 2 in series, 40°C Eluent: 5mM CF3COONa / HFIP Flow rate: 1.0 mL / min Detector: Differential refractometer (RI) From the chromatogram obtained by measurement, the weight average molecular weight (Mw) of the resin contained in the filament is calculated using a calibration curve obtained from polymethyl methacrylate resin (PMMA) of known molecular weight.

[0027] 1-2. Other Components In addition to the nylon resin described above, the filament may further contain known additives such as other resins, plasticizers, nucleating agents, antioxidants, ultraviolet absorbers, dyes, pigments, heat stabilizers, light stabilizers, fillers, internal mold release agents, matting agents, conductivity-imparting agents, charge control agents, antistatic agents, lubricants, and other processing aids.

[0028] However, from the viewpoint of further enhancing the biodegradability of the filaments, it is preferable that the content of additives that affect biodegradability, such as antioxidants, is small. That is, the content of antioxidants in the filaments is preferably less than 0.1% by mass. The lower limit of the antioxidant content is not particularly limited, but can be, for example, 0.01% by mass or more.

[0029] 1-3. Physical Properties As described above, the end temperature of the melting peak (endothermic peak) of the filament measured by differential scanning calorimetry (DSC) is 190°C or higher and lower than the melting point of nylon 6 resin (homopolymer) (approximately 225°C), specifically 220°C or lower. Such filaments contain the nylon resin as the main component, in which the hydrogen bonds between the molecular chains of the nylon 6 structural moieties are weakened due to the appropriate mixture of nylon 66 structural moieties and nylon 6 structural moieties, thereby achieving enhanced biodegradability. The end temperature of the melting peak is defined as the temperature at the intersection of a straight line extending the high-temperature baseline toward the low-temperature side and a tangent drawn to the curve on the high-temperature side of the melting peak at the point where the slope is greatest.

[0030] Furthermore, the heat of fusion of the filament in the DSC curve is 80 J / g or less. When the heat of fusion is 80 J / g or less, the hydrogen bonds between the molecular chains of the nylon 6 structural portion of the filament containing the nylon resin are appropriately weak, thereby sufficiently enhancing biodegradability. From the same perspective, the heat of fusion of the filament is preferably 60 J / g or less. The lower limit of the heat of fusion of the filament is not particularly limited, but can be 30 J / g or more. The crystallinity is preferably, for example, 45% or less, and more preferably 35% or less. The lower limit of the crystallinity is not particularly limited, but can be, for example, 20% or more.

[0031] The melting behavior of the filament can be measured by a differential scanning calorimeter (DSC method). Specifically, 2 mg of a sample obtained by cutting the filament is weighed in an aluminum pan and measured using a differential scanning calorimeter (for example, DSC3 manufactured by Mettler Toledo). ＋A DSC curve is obtained by heating the filament at a rate of 20°C / min in a range of 25°C to 280°C using a 1000 kJ / s sieve under a nitrogen atmosphere. The peak area of ​​the endothermic peak (melting peak) based on the melting behavior in the obtained DSC curve is divided by the sample weight to calculate the "heat of fusion" (J / g). The temperature at the intersection of a line extending the high-temperature baseline toward the low-temperature side and a tangent drawn at the point where the slope of the curve on the high-temperature side of the melting peak is maximum is taken as the end temperature of the melting peak. The degree of crystallinity can be calculated as [heat of fusion (J / g) / heat of fusion of fully crystalline nylon 6 (190 J / g)] x 100 (%). To eliminate the influence of structural changes due to moisture absorption and deterioration over time on the physical properties of the filament, the filament should be stored in a cool, dark place after production and measured for heat of fusion within one year.

[0032] The end temperature of the melting peak of the filament can be adjusted, for example, by the content of the nylon resin in the filament. For example, the end temperature of the melting peak of the filament tends to be lower as the content of the nylon resin in the filament increases and the content of nylon 6 resin (homopolymer) decreases.

[0033] The heat of fusion of the filament can be adjusted, for example, by the proportion of nylon 6 structural units in the nylon resin or the filament production conditions (e.g., cooling conditions after melt extrusion and drawing conditions). For example, lowering the cooling temperature after melt extrusion reduces the crystallinity of the resulting filament, and therefore the heat of fusion is likely to be lower. Furthermore, lowering the draw ratio or drawing temperature during drawing tends to reduce the crystallinity of the resulting filament and the heat of fusion.

[0034] From the viewpoint of more easily achieving both biodegradability and strength during use, the melting point of the filament is preferably less than 225°C, more preferably 170°C or higher and 220°C or lower, and even more preferably 180°C or higher and 210°C or lower. The melting point of the filament can be determined as the peak-top temperature of the melting peak in the DSC curve obtained in the above DSC measurement. Note that when there are multiple melting peaks or when one melting peak has multiple peak tops, the peak-top temperature on the highest temperature side is taken as the melting point.

[0035] Such filaments have high strength and good biodegradability.

[0036] For example, the linear strength of the filament measured at 25°C and 50% relative humidity is preferably 600 MPa or more, more preferably 700 MPa or more, and even more preferably 800 MPa or more. When the linear strength is 600 MPa or more, the filament is less likely to break when a load is applied during use. On the other hand, the upper limit of the linear strength is, for example, preferably 1200 MPa or less, more preferably 1100 MPa or less, and even more preferably 1000 MPa or less. When the linear strength is 1200 MPa or less, the flexibility of the filament is less likely to be lost, resulting in better operability. Furthermore, when the filament is immersed in pure water at 25°C for 3 hours and then removed from the pure water and measured at 25°C without drying, the linear strength is preferably 500 MPa or more and 1100 MPa or less, more preferably 600 MPa or more and 1000 MPa or less, and even more preferably 700 MPa or more and 1000 MPa or less.

[0037] The linear strength is a value obtained by dividing the maximum load by the diameter of the filament when a tensile test is conducted based on JIS L1013:2021 using a 300 mm long filament as a test sample, with a grip distance of 150 mm and a crosshead speed of 150 mm / min on the testing machine. For the same reasons as above, the linear strength measurement should be conducted within one year after the filament is produced and stored in a cool, dark place. The filament diameter can be measured using a known technique for measuring fiber diameter. Specifically, the filament diameter is measured using a micrometer at three points: the center of a 150 mm grip distance, a point 50 mm above the center, and a point 50 mm below the center. The arithmetic mean value of each of the three points can be used as the representative value of the fiber diameter.

[0038] For example, the knot strength of the filament measured at 25°C and 50% relative humidity is preferably 500 MPa or more, more preferably 600 MPa or more, and even more preferably 700 MPa or more. A knot strength of 500 MPa or more makes the filament less likely to break when a load is applied during use. On the other hand, the upper limit of the knot strength is preferably 1000 MPa or less, more preferably 900 MPa or less. A knot strength of 1000 MPa or less makes the filament less likely to lose its flexibility, resulting in better operability. Furthermore, the knot strength of the filament measured at 25°C after immersion in pure water at 25°C for 3 hours and then removing it from the pure water without drying is preferably 500 MPa or more and 1100 MPa or less, more preferably 600 MPa or more and 1000 MPa or less, and even more preferably 700 MPa or more and 900 MPa or less.

[0039] The knot strength is a value obtained by dividing the maximum load by the filament diameter when a tensile test is conducted based on JIS L1013:2021 using a 300 mm long filament as a test sample, with a grip distance of 150 mm and a crosshead speed of 150 mm / min. For the same reasons as above, the knot strength measurement should be performed within one year after the filament is produced and stored in a cool, dark place. The filament diameter can be measured using a known technique for measuring fiber diameter. Specifically, the filament diameter is measured by clamping the intended knotting portion with a micrometer before knotting.

[0040] Furthermore, the filament is stored at the interface between seawater and sediment at 25°C for 3 months, washed with water, dried, and then measured at 25°C and a relative humidity of 50%, and the retention of the linear strength relative to the linear strength measured under the same conditions before storage is preferably less than 90%, more preferably 85% or less, and even more preferably 80% or less. On the other hand, from the viewpoint of further suppressing a decrease in strength during use of the filament, the retention is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more.

[0041] The interface between seawater and sediments refers to the environment within 5 cm of the interface between seawater and sediments as defined in ISO 19679. The sediments can be sea sand collected from the ocean. For the same reasons as above, the linear strength retention rate in a biodegradable environment is measured within one year after filament production when stored under the above conditions.

[0042] The linear strength of the filament can be adjusted by the composition of the nylon resin contained in the filament and the manufacturing conditions of the filament. For example, increasing the proportion of nylon 66 structural units in the nylon resin contained in the filament reduces the decrease in filament strength due to water absorption, and therefore tends to increase the linear strength of the filament in water. In addition, increasing the draw ratio or lowering the drawing temperature tends to increase the linear strength of the resulting filament.

[0043] The diameter of the filament is not particularly limited, and may be, for example, 0.05 mm or more and 4.0 mm or less.

[0044] 2. Method for Producing Filaments The filaments can be produced by melt-extruding a resin composition containing the nylon resin described above and spinning the resulting composition into monofilaments under predetermined conditions.

[0045] In this embodiment, the filament can be produced through the steps of: 1) melt-extruding a resin composition containing the nylon resin described above into a fibrous form; 2) cooling the melt-extruded resin composition into a fibrous form in a refrigerant at 5°C or less; and 3) stretching the cooled resin composition.

[0046] In step 1), first, the nylon resin described above is prepared. The nylon resin may be synthesized or may be a commercially available product. For example, when synthesizing a nylon resin, the method for synthesizing the nylon resin described above is not particularly limited. The nylon resin described above can be synthesized, for example, by copolymerizing a first monomer that becomes a nylon 6 structural unit, a second monomer that becomes a nylon 66 structural unit, and, if necessary, a third monomer that becomes a structural unit of other nylon, in the presence of a polymerization initiator.

[0047] As the first monomer, ε-caprolactam can be used. As the second monomer, a salt of adipic acid and hexamethylenediamine (hexamethyleneadipamide) can be used. As the third monomer, a lactam compound other than ε-caprolactam, such as glycine, α-alanine, β-alanine, β-lactam (2-azetidinone), 2-pyrrolidone, ω-octalactam, and ω-laurolactam, can be used. Note that the second monomer may be prepared by reacting adipic acid and hexamethylenediamine in advance before polymerization with the first and third monomers, or by reacting adipic acid and hexamethylenediamine together with the first and third monomers.

[0048] Examples of the polymerization initiator include an ester compound or a derivative thereof, an imide compound, water, and the like.

[0049] Next, the resin composition containing the nylon resin is melt-extruded into a fibrous form. The melt-extrusion is preferably carried out at a temperature higher than the melting point of the nylon resin and lower than its thermal decomposition temperature. For example, the melt-extrusion can be carried out at 180°C or higher and 300°C or lower, preferably 220°C or higher and 300°C or lower. The melt-extrusion temperature refers to the temperature of a resin thermometer installed in a die.

[0050] In step 2), the resin composition melt-extruded into a fiber is cooled in a refrigerant at 5°C or below. Rapidly cooling the resin composition melt-extruded into a fiber at 5°C or below in this manner makes it difficult for the nylon resin to crystallize, thereby appropriately reducing the crystallinity of the filament before drawing. This also appropriately reduces the crystallinity of the final filament, allowing the heat of fusion to be adjusted to a predetermined value or less. The temperature of the refrigerant is preferably 0°C or below, and more preferably -5°C or below. The lower limit of the refrigerant temperature is not particularly limited, but can be, for example, -20°C or above.

[0051] The cooling method is not particularly limited, but it is preferable to pass the resin composition melt-extruded into a fiber form through a bath (cold bath) filled with a refrigerant. The type of refrigerant may be any that can cool to the above temperature, and examples thereof include silicone oil and hydrocarbon solvents. From the viewpoint of being able to cool at a lower temperature, it is preferable to use silicone oil.

[0052] In step 3), the cooled resin composition is further stretched, which allows the nylon resin in the resin composition to be more oriented and provides the higher strength required for, for example, fishing line.

[0053] The conditions for the stretching treatment are not particularly limited. For example, the total stretching ratio can be 4 times or more and 7 times or less, and from the viewpoint of further increasing the knot strength, it is preferably 5 times or more and 6 times or less. When stretching is performed in multiple stages, the total stretching ratio means the product of the stretching ratios in each stage. Note that stretching may be performed in multiple stages. For example, wet heat stretching may be followed by dry heat stretching.

[0054] The wet heat drawing may be performed in warm water or in heated steam. The drawing temperature may be, for example, 80° C. to 100° C., more preferably 90° C. to 100° C., and even more preferably 95° C. to 100° C., from the viewpoint of heating efficiency. In the wet heat drawing, the cooled resin composition (undrawn filaments) can be drawn at a total draw ratio of, for example, 3 to 5 times.

[0055] The hot stretching can be carried out using, for example, an oven, a hot plate, a hot roll, etc. The stretching temperature may be, for example, 140° C. or higher and 270° C. or lower, preferably 160° C. or higher and 230° C. or lower, and more preferably 180° C. or higher and 230° C. or lower. In the hot stretching, the wet heat-stretched resin composition may be stretched so that the total stretch ratio falls within the above range.

[0056] After stretching, a relaxation treatment may be carried out.

[0057] 3. Filaments for Fisheries Materials The filaments described above can be used as filaments for fisheries materials such as fishing lines, fishing nets, etc. Filaments for fisheries materials including the filaments described above have both biodegradability and sufficient strength when used.

[0058] 4. Other Embodiments The above-described embodiments are exemplary embodiments of the present invention, and the present invention is not limited to these.

[0059] For example, in the above embodiment, the melting characteristics of the filaments (the end temperature of the melting peak and the heat of fusion) satisfy a predetermined range, but are not limited to this. The melting characteristics of the filaments can be adjusted as desired depending on the required performance, the composition of the nylon resin contained in the filaments, and the structure of the filaments, and do not necessarily have to satisfy the above-mentioned melting characteristics.

[0060] For example, the filaments may contain, as a main component, a nylon resin containing nylon 6 structural units, nylon 66 structural units, and nylon structural units other than these. For example, the filaments may contain, as a main component, a nylon resin containing nylon 6 structural units, nylon 66 structural units, and nylon structural units 12.

[0061] In this nylon resin, the nylon 6 structural units, which weaken the hydrogen bonds between molecular chains, impart biodegradability to the filaments. Meanwhile, by controlling the proportion of nylon 6 structural units within a predetermined range and including nylon 12 structural units, this nylon resin can reduce the decrease in filament strength due to water absorption and increase the strength during use. In particular, the nylon 12 structural units can impart appropriate hydrophobicity to the filaments, thereby reducing the decrease in filament strength due to water absorption and increasing the strength during use.

[0062] The ratio of nylon 6 structural units to all structural units of the nylon resin can be the same as in the above embodiment. The range of the total amount of nylon 66 structural units and nylon 12 structural units to all structural units of the nylon resin can be the same as the range of the ratio of nylon 66 structural units in the above embodiment. Note that the ratio of nylon 12 structural units to all structural units of the nylon resin can be, for example, 2% by mass or more and 25% by mass or less, from the viewpoint of further increasing strength during use while maintaining the suppleness and flexibility of the filament.

[0063] The composition of the filament may be uniform or may vary from the radial center to the outer periphery. That is, the filament may be composed of a single layer, or may have a core-sheath structure having a core and a sheath. The sheath may have one layer or two or more layers.

[0064] When the filament has a core-sheath structure, the core and sheath may contain biodegradable nylon resins with different biodegradation rates. For example, it is preferable that the core contains a first biodegradable nylon resin and the sheath contains a second biodegradable nylon resin with a different biodegradation rate from that of the first biodegradable nylon resin. The biodegradable nylon resin means a nylon resin with a biodegradability of 10% or more as measured by the BOD test described below.

[0065] Furthermore, it is preferable that the biodegradation rate of the first biodegradable nylon resin is faster than that of the second biodegradable nylon resin. Such a filament can maintain its strength during use because the second biodegradable nylon resin contained in the sheath has a slow biodegradation rate. On the other hand, when the sheath biodegrades, the first biodegradable nylon resin contained in the core biodegrades rapidly, thereby suppressing environmental pollution.

[0066] The biodegradation rate of nylon resin can be measured as biodegradability (%) in the following BOD test. First, a filament is cut to prepare a sample. A BOD test is then performed on this sample. Specifically, 2000 g of sediment collected from the Pacific coast is added to 4000 ml of seawater collected from the Pacific coast, and the microorganisms in the sediment are extracted into the seawater by ultrasonic treatment. The extracted seawater is aerated to prepare extracted seawater. 150 ml of the extracted seawater prepared above is placed in a 250 ml bottle, and approximately 50 mg of the sample is dispersed therein and stirred by turbulence. The pressure change caused by capturing the generated carbon dioxide with sodium hydroxide in a sealed environment is measured using a BOD meter (OxiTop i, manufactured by WTW). The biodegradability of the sample is evaluated using the following formula, where the theoretical value is the amount of oxygen required for 100% decomposition of the sample: Biodegradability (%) = (oxygen consumption from sample / theoretical oxygen demand) x 100

[0067] Examples of the first biodegradable nylon resin and the second biodegradable nylon resin that can be used include a nylon resin containing nylon 4 structural units, a nylon resin containing nylon 4 structural units and nylon 6 structural units, and a nylon resin containing nylon 6 structural units and nylon 66 structural units.

[0068] In particular, from the viewpoint of achieving a better balance between biodegradability and strength, the first biodegradable nylon resin and the second biodegradable nylon resin are preferably nylon resins containing nylon 6 structural units and nylon 66 structural units, respectively. The nylon resins may be the same as the nylon resins described above. Furthermore, the nylon resins may further contain nylon 12 structural units in addition to the nylon 6 structural units and nylon 66 structural units.

[0069] The content ratio of the core to the sheath is not particularly limited and may be set appropriately taking into consideration the balance between biodegradation rate and strength. For example, from the viewpoint of further enhancing biodegradability, the ratio of the mass of the core to the mass of the sheath (mass of the core / mass of the sheath) is preferably 50 / 50 to 95 / 5.

[0070] Filaments having a core-sheath structure can be produced by known methods. For example, filaments having a core-sheath structure can be produced by preparing a core material and a sheath material separately and co-extruding them using a core-sheath composite spinning nozzle. In this case, too, it is preferable to cool or stretch the co-extruded resin composition as needed. However, the cooling conditions and stretching conditions may be the same as or different from those described above.

[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 nylon resins The following nylon resins were used: Nylon resin 1 (nylon 6 / 66 copolymer (86 / 14 mass ratio), Mw 74,000) Nylon resin 2 (nylon 6 / 66 copolymer (10 / 90 mass ratio), Mw 62,000) Nylon resin 3 (nylon 66, Mw 67,000) Nylon resin 4 (nylon 6, Mw 60,000) Nylon resin 5 (a mixture of nylon 6 and nylon 6 / 66 copolymer (86 / 14 mass ratio) in a mass ratio of 67 / 33, Mw 60,000) Nylon resin 6 (a mixture of nylon 6 and nylon 66 in a mass ratio of 70 / 30, Mw 72,000) Nylon resin 7 (nylon 6 / 66 copolymer (94 / 6 mass ratio), Mw 62,000)

[0073] The weight average molecular weight Mw of nylon resins 1 to 7 is a value measured by the following method.

[0074] (Measurement of weight-average molecular weight Mw) Each nylon resin was subjected to GPC analysis using a gel permeation chromatography (GPC) analyzer (HLC-8420GPC, manufactured by Tosoh Corporation). Specifically, 10 mg of sample was dissolved in hexafluoroisopropanol (HFIP) containing sodium trifluoroacetate dissolved at a concentration of 5 mM to obtain 10 mL of solution, which was then filtered through a membrane filter to obtain a sample solution. 100 μL of this sample solution was injected into the analyzer, and measurement was performed under the following conditions. Apparatus: HLC-8420GPC, manufactured by Tosoh Corporation Column: HFIP 806M x 2 in series, 40°C Eluent: 5 mM CF3COONa / HFIP Flow rate: 1.0 mL / min Detector: Differential refractometer (RI) From the chromatogram obtained by measurement, the weight average molecular weight (Mw) of the resin was calculated using a calibration curve obtained from polymethyl methacrylate resin (PMMA) of known molecular weight.

[0075] 2. Filament Production or Preparation (Production of Filament 1) A polymer powder of nylon resin 1 was prepared as a nylon resin. This polymer powder was charged into a small twin-screw extruder, melted at 292°C, and extruded into a fibrous form through a spinning nozzle. The extruded resin was cooled and solidified by passing through a cold bath (refrigerant: silicone oil, cold bath temperature: -10°C) to produce an unstretched monofilament. The produced unstretched monofilament was stretched (wet heat stretched) at a draw ratio of 3.7 times while passing through a steam bath at 100°C. Next, this monofilament was further stretched to a total draw ratio of 5.0 times while passing through an oven (dry heat bath) at 180°C. As a result, filament 1 having a diameter of 189 μm was obtained.

[0076] (Preparation of Filaments 2 to 7) Filaments 2 to 7 were obtained in the same manner as for Filament 1, except that the resins shown in Table 1 were used as nylon resins and spun under the conditions shown in Table 1.

[0077] 3. Measurement and evaluation of filaments For each of the obtained filaments 1 to 7, the following method was used: １３ C-NMR measurement, DSC measurement, measurement of strength (linear strength and knot strength) in a room environment and in a biodegradation environment, and a biodegradability test (BOD test) were performed. Note that, in order to eliminate the influence of aging deterioration and additives on the physical properties of the filaments, the DSC measurement, measurement of strength in a room environment and in a biodegradation environment, and the biodegradation test (BOD test) for filaments 1 to 7 were performed within one year after the filaments were produced and stored in a cool, dark place.

[0078] 3-1. １３ C-NMR Measurement The obtained filament was crushed to prepare a sample. Then, 10 mg of the sample was dissolved in 1 ml of trifluoroethanol (TFE) / d2 chloroform (CDCl ３ The compound was dissolved in a mixed solvent of tetramethylsilane (TMS) and tetramethylsilane (TMS) in a volume ratio of 1:1. The compound was then analyzed using a nuclear magnetic resonance spectrometer (JASCO Corporation, JNM-ECZ600R / S1). １３ C-NMR measurement was performed. Of the signals originating from methylene carbons adjacent to carbonyl groups appearing in the spectrum obtained between 35.0 ppm and 37.0 ppm, the integral value of the signal originating from nylon 6 structural units appearing on the low magnetic field side (near 37.00 ppm) and the integral value of the signal originating from nylon 66 units appearing on the high magnetic field side (near 36.00 ppm) were calculated. The ratio of the integral values ​​of these signals was taken as the mass ratio of nylon 6 structural units to nylon 66 structural units.

[0079] 3-2. DSC Measurement The obtained filaments were cut into samples. Then, DSC measurement was performed to measure the melting point and heat of fusion. Specifically, a differential scanning calorimeter (manufactured by Mettler Toledo, DSC3 ＋DSC curves were obtained by differential scanning calorimetry (DSC) using a 1000-kJ / series calorimeter (Calorimeter). Specifically, 2 mg of sample for each filament was weighed into an aluminum pan and heated at a rate of 20°C / min in a nitrogen atmosphere from 25°C to 280°C. The peak-top temperature of the endothermic peak (melting peak) based on the melting behavior in this DSC curve was taken as the "melting point" of each filament. For samples having melting peaks at multiple positions, the melting points were designated as melting point 1, melting point 2, and so on, starting from the lowest temperature. The peak area of ​​the melting peak was divided by the sample weight to calculate the "heat of fusion" (J / g). The temperature at the intersection of a straight line extending the high-temperature baseline toward the low-temperature side and a tangent drawn to the curve on the high-temperature side of the melting peak at the point where the slope is maximum was taken as the terminal temperature of the peak.

[0080] 3-3. Linear Strength and Knot Strength The strength (linear strength and knot strength) was measured in an indoor environment and a biodegradable environment using a tensile tester (Tensilon RTF-1210, manufactured by A&D Co., Ltd.).

[0081] (Linear strength) Based on JIS L1013:2021, a 300 mm long filament was used as a test sample, the grip interval was 150 mm, and the crosshead speed of the test machine was set to 150 mm / min. The value obtained by dividing the maximum tensile load by the filament diameter was used as the linear strength (tensile strength) in each environment. The filament yarn diameter was measured by pinching the yarn diameter at three points: the center of the grip interval of 150 mm, a point 50 mm above the center, and a point 50 mm below the center, with a micrometer, and the arithmetic mean value was used.

[0082] (Knot Strength) Based on JIS L1013:2021, a 300 mm long filament with a single knot in the center was used as a test sample, with the grip interval set to 150 mm and the crosshead speed of the testing machine set to 150 mm / min. The load at which the knot broke was divided by the filament diameter, and the knot strength in each environment was determined. The filament diameter was measured in the same manner as for the filament sample for linear strength measurement, by clamping the intended knot portion with a micrometer before knotting.

[0083] The environmental conditions were as follows: Indoor environment: Measurements were made at 25°C and a relative humidity of 50%. Biodegradation environment: Storage at the interface between seawater and sediment at 25°C for 3 months, followed by measurements at 25°C and a relative humidity of 50%. Seawater (NaCl concentration: 3.1-3.4%) and sea sand collected from the Pacific coast were used as the seawater and sediment, respectively.

[0084] Furthermore, the ratio of the linear strength in a biodegradable environment to the linear strength in an indoor environment ((linear strength in a biodegradable environment / linear strength in an indoor environment) x 100) was defined as the "linear strength retention rate."

[0085] 3-4. Biodegradability Test (BOD Test) The obtained filaments were cut into samples. A BOD test was conducted on these samples using the following method. 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 the seawater by ultrasonic treatment. The extracted seawater was aerated to produce extracted seawater. 150 ml of the extracted seawater prepared above was placed in a 250 ml bottle, and approximately 50 mg of the sample was dispersed therein and stirred by turbulent rotation. The pressure change caused by capturing the generated carbon dioxide with sodium hydroxide in a sealed environment was measured for 8 weeks using a BOD meter (OxiTop i, manufactured by WTW). The biodegradability of the samples was evaluated using the following formula, where the theoretical value is the amount of oxygen required for 100% decomposition of the sample: Biodegradability (%) = (oxygen consumption from sample / theoretical oxygen demand) x 100

[0086] The materials and manufacturing conditions of filaments 1 to 7 are shown in Table 1, and the evaluation results are shown in Table 2.

[0087]

[0088]

[0089] As shown in Table 2, both filament 4, which uses nylon 6, and filament 3, which uses nylon 66, exhibit high strength retention in a biodegradable environment and low biodegradability in the BOD test. Furthermore, even with nylon 6 / 66 copolymer, filament 2, which has a low nylon 6 copolymerization ratio of 10% by mass, exhibits high strength retention in a biodegradable environment and almost no biodegradability in the BOD test. Furthermore, filaments 5 and 6, which are blends of nylon 6 and nylon 6 / 66 copolymer, have melting peak end temperatures measured by DSC near the melting point of nylon 6 resin (homopolymer) (approximately 225°C), suggesting that they contain a certain amount or more of nylon 6 structural moieties with unweakened hydrogen bonds. Furthermore, filaments 5 and 6 exhibit high strength retention in a biodegradable environment and almost no biodegradability in the BOD test. Similarly, filament 7, which has a high nylon 6 copolymer ratio of 94% by mass and is obtained under specified spinning conditions, has a high terminal temperature of the melting peak near the melting point of nylon 6 resin (homopolymer) (approximately 225°C), has a high strength retention rate in a biodegradable environment, and shows almost no biodegradability in the BOD test.

[0090] In contrast, filament 1, which is mainly composed of a nylon 6 / 66 copolymer in which the copolymerization ratio of nylon 6 is 70% by mass or more but less than 97% by mass and has a heat of fusion of 80 J / g or less, has good linear strength in an indoor environment, but exhibits low linear strength retention in a biodegradable environment, demonstrating biodegradability. Furthermore, the BOD test also shows high biodegradability.

[0091] From these findings, it can be seen that filaments containing a nylon 6 / 66 copolymer in which the copolymerization ratio of nylon 6 is 70% by mass or more but less than 97% by mass, having a melting peak end temperature of 220°C or less as measured by DSC and a heat of fusion of 80 J / g or less, have good strength and exhibit good biodegradability.

[0092] This application claims priority from Japanese Patent Application No. 2024-150779, filed September 2, 2024, the entire contents of which are incorporated herein by reference.

[0093] The filaments for fishery materials according to the present invention have sufficient strength and are biodegradable, and are therefore expected to contribute to reducing environmental pollution caused by broken fishing lines.

Claims

1. A filament for use in fisheries materials, the filament being composed primarily of a nylon resin containing nylon 6 structural units and nylon 66 structural units, wherein the ratio of the nylon 6 structural units to the total structural units of the nylon resin is 70% by mass or more but less than 97% by mass, and the end temperature of the melting peak of the filament measured by differential scanning calorimetry (DSC) is 190°C or more but 220°C or less, and the heat of fusion is 80 J / g or less.

2. The filament for aquatic materials according to claim 1, wherein the filament contains 50% by mass or more of the nylon resin relative to the total mass of the filament.

3. The filament for aquatic materials according to claim 1 or 2, wherein the content of the antioxidant in the filament is less than 0.1% by mass.

4. The filament for use in fisheries materials according to any one of claims 1 to 3, wherein the linear strength of the filament measured at 25°C and a relative humidity of 50% is 700 MPa or more.

5. A filament for use in fisheries materials according to any one of claims 1 to 4, wherein the knot strength of the filament measured at 25°C and a relative humidity of 50% is 500 MPa or more.

6. A filament for use in aquatic materials according to any one of claims 1 to 5, which is stored at the interface between seawater and sediment at 25°C for three months, washed with water, dried, and then measured at 25°C and a relative humidity of 50%, and the retention of the linear strength measured under the same conditions before storage is less than 90%.

7. A method for producing a filament for use in fisheries materials according to any one of claims 1 to 6, comprising the steps of: melt-extruding, into a fibrous form, a resin composition containing a nylon resin that contains nylon 6 structural units and nylon 66 structural units, wherein the proportion of the nylon 6 structural units to all structural units is 70% by mass or more but less than 97% by mass; cooling the melt-extruded resin composition into a fibrous form in a refrigerant at 5°C or less; and stretching the cooled resin composition.

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