JP7570514B2 - Undrawn monofilament yarn and method for producing monofilament - Google Patents

Description

The present invention relates to polyamide 4 monofilament and a method for producing the same.

Polyamide 4 (hereinafter, also referred to as "PA4") is a bioplastic that is expected to be put to practical use as filaments for use in, for example, fishing lines and fishing nets. For such filaments, linear strength, knot strength, and transparency are important required properties.

A method for producing PA4 monofilaments is known, for example, by melt spinning (see, for example, Patent Document 1).

International Publication No. 2012/157576

To obtain a monofilament that meets the above requirements, the undrawn yarn formed in the extrusion process in melt spinning must be in an amorphous state, i.e., have a low density. Here, since PA4 can undergo thermal decomposition during melt spinning, the spinning temperature must be close to the melting temperature. If spinning is performed near the melting temperature, the amount of residual crystal nuclei increases, and the crystallization rate increases during the cooling process after the extrusion process. For this reason, it is difficult to produce an amorphous monofilament.

In order to complete the cooling process in a short time, other polyamide resins such as nylon 6 and nylon 66 are rapidly cooled using cold water at about 5°C. However, when cooling with cold water, dissolution and hydrolysis occur on the PA4 surface due to the high hydrophilicity of PA4. This results in surface roughness and white powder, and a decrease in the desired physical properties.

One aspect of the present invention aims to provide a low density PA4 monofilament.

In order to solve the above problems, a monofilament according to one aspect of the present invention is a polyamide 4 monofilament having a density of 1.230 g/cm3 ^or less.

In addition, in order to solve the above problems, a method for producing a monofilament according to one embodiment of the present invention includes a melt extrusion process in which polyamide 4 is melt extruded, and a cooling process in which the fibrous molten extrudate of polyamide 4 produced by the melt extrusion process is cooled to -10°C or below using a non-polar solvent.

According to one aspect of the present invention, a low density PA4 monofilament can be provided.

[Monofilament]
[Polyamide 4]
The monofilament according to the embodiment of the present invention is substantially composed of polyamide 4 (PA4). PA4 is a polymer compound having a structural unit represented by the following formula (1): x in the following formula is 4.

In an embodiment of the present invention, the polymer compound that constitutes the fiber structure of the monofilament may be only PA4. In an embodiment of the present invention, other components other than PA4 may be further contained within a range in which the effects of this embodiment can be obtained. The other components may be one or more types, and examples include reinforcing materials, plasticizers, lubricants, and stabilizers. The other components may include polymer compounds other than PA4. The other components are used appropriately in an amount that further exerts the effects of the other components. Thus, the monofilament of the embodiment of the present invention is a PA4 monofilament.

[density]
The density of the monofilament of the embodiment of the present invention is 1.230 g/cm ³ or less. The density of the monofilament is correlated with the crystallinity of the monofilament, and the lower the density, the lower the crystallinity tends to be. For example, the density of the monofilament of 1.230 g/cm ³ corresponds to the crystallinity of the monofilament of about 10%. If the density of the monofilament is high, the tensile strength and elongation of the monofilament at the time of knotting may be insufficient. From the viewpoint of further improving the tensile properties at the time of knotting, the density of the monofilament is preferably 1.225 g/cm ³ or less, and more preferably 1.223 g/cm ³ or less. The density of the monofilament may be within a range that can be realized as a PA4 monofilament, and may be, for example, 1.215 g/cm ³ or more.

The density of the monofilament can be determined by a method also known as the "density gradient method." The density of the monofilament can also be adjusted by the cooling conditions in the production of the undrawn yarn, and can be reduced, for example, by cooling in the cooling step of the production method described below.

[Other physical properties]
The monofilament of the embodiment of the present invention is only required to have the above-mentioned physical properties, and may further have other physical properties in addition to those described above, as long as the effects of the embodiment described above are achieved.

[Thread diameter]
The diameter of the monofilament according to the embodiment of the present invention may be appropriately determined depending on the application of the monofilament, but is preferably 1 mm or less from the viewpoint of sufficiently reducing the density of the monofilament. Note that the diameter of the monofilament referred to here is the diameter of an undrawn yarn.

If the thread diameter exceeds 1 mm, the cooling in the cooling step of the manufacturing method described below may be insufficient, and the density of the monofilament may become high. From the viewpoint of sufficiently lowering the density of the monofilament, the thread diameter of the monofilament is preferably 0.8 mm or less, and more preferably 0.5 mm or less. On the other hand, the thread diameter of the monofilament may be within a range that can be realized with a PA4 monofilament depending on the application of the monofilament, but from the viewpoint of sufficiently performing the above-mentioned cooling, it may be 0.1 mm or more. The thread diameter of the monofilament can be adjusted by the hole diameter of the die.

The thread diameter of the monofilament can be measured by known techniques for measuring fiber diameter, for example, by a known method of measuring the thread diameter of a fiber by pinching the fiber. The thread diameter of the monofilament tends to become smaller by increasing the draw ratio in the manufacturing method described below.

In the case where the monofilament in the embodiment of the present invention is a drawn yarn, the yarn diameter of the monofilament is more preferably 0.4 mm or less, and even more preferably 0.25 mm or less, from the viewpoint of sufficiently reducing the density of the monofilament in the undrawn yarn. The yarn diameter of the monofilament that is a drawn yarn may be, for example, 0.05 mm or more, from the viewpoint of practical use as a monofilament depending on the application. The yarn diameter of the monofilament that is a drawn yarn can be adjusted by the drawing ratio.

[Tensile properties at knots]
The tensile strength of the monofilament after stretching according to the embodiment of the present invention at the time of knotting is preferably 460 MPa or more from the viewpoint of realizing sufficient tensile strength in applications where the monofilament can be used in a knotted state. An example of an application where the monofilament can be used in a knotted state is fishing line. The tensile strength at the time of knotting can be appropriately determined depending on the application of the monofilament. The tensile strength at the time of knotting is preferably high from the viewpoint of preventing the monofilament from breaking at the knotted portion when pulled, and is more preferably, for example, 470 MPa or more, and even more preferably, 480 MPa or more. On the other hand, the tensile strength at the time of knotting may be within a range that can be realized with a PA4 monofilament, and from such a viewpoint, the tensile strength at the time of knotting may be 800 MPa or less.

The tensile strength of a monofilament at a knot can be measured using a known device capable of performing tensile testing of fibers. The tensile strength of a monofilament at a knot can be made sufficiently high by setting the density of the monofilament within the range described above. In addition, the tensile strength of a monofilament at a knot can be increased by stretching during the production of the monofilament.

It is preferable that the tensile elongation at knotting of the stretched monofilament of the embodiment of the present invention is 10% or more from the viewpoint of preventing breakage when used in a knotted state. The tensile elongation at knotting can be appropriately determined depending on the application of the monofilament, and from the above viewpoint, it is more preferable that it is 12% or more, and even more preferable that it is 14% or more. On the other hand, the tensile elongation at knotting may be within the range that can be achieved with PA4 monofilament, and from this viewpoint, the tensile elongation at knotting may be 30% or less.

The tensile elongation of the monofilament at the knot can be measured using a known device capable of performing tensile testing of fibers. The tensile elongation of the monofilament at the knot can be made sufficiently high by setting the density of the monofilament within the range described above. In addition, the tensile elongation of the monofilament at the knot can be increased by stretching during the production of the monofilament.

[Birefringence]
In the drawn monofilament of the embodiment of the present invention, it is preferable that PA4 has a specific orientation from the viewpoint of enhancing the tensile properties of the monofilament. From this viewpoint, the birefringence of the monofilament is preferably 50×10 ⁻³ or more. The birefringence of a fiber material is a measure of the degree of orientation of the polymer chains in the polymer compound constituting the fiber with respect to the fiber axis direction. The larger the absolute value of the birefringence, the greater the degree of orientation in the fiber of the polymer compound. From the above viewpoint, the birefringence of the monofilament is more preferably 55×10 ⁻³ or more, and even more preferably 60×10 ⁻³ or more. The birefringence of the monofilament in the embodiment of the present invention may be within a range that can be realized with a PA4 monofilament, and from this viewpoint, it may be 90×10 ⁻³ or less.

The birefringence of the monofilament can be determined, for example, by retardation measurement using a polarizing microscope equipped with a Berek compensator and a sodium lamp as a light source. The birefringence of the monofilament can also be adjusted by the degree of orientation of the PA4 in the monofilament, and can be increased by increasing the stretch ratio in the manufacturing method described below.

[Method of manufacturing monofilament]
The method for producing a monofilament according to an embodiment of the present invention includes a melt extrusion step of melt extruding polyamide 4, and a cooling step of cooling the fibrous molten extrudate of polyamide 4 produced by the melt extrusion step to −10° C. or lower with a non-polar solvent. These steps can be carried out by a known melt spinning technique that produces an undrawn yarn by liquid cooling, within a range that satisfies the conditions described below.

[Melt extrusion process]
In the melt extrusion process, the melt kneaded product of PA4 is extruded by extrusion molding to produce a fibrous melt extrudate of PA4. The spinning temperature in the melt extrusion process is preferably high from the viewpoint of reducing the crystal nuclei of PA4 in the melt extrudate. From this viewpoint, the spinning temperature is preferably 255°C or higher, more preferably 260°C or higher, and even more preferably 262°C or higher, in terms of the resin temperature. On the other hand, the spinning temperature is preferably low from the viewpoint of suppressing thermal decomposition of PA4. From this viewpoint, the spinning temperature is preferably 275°C or lower, more preferably 270°C or lower, and even more preferably 267°C or lower, in terms of the resin temperature.

[Cooling process]
The cooling temperature of the molten extrudate using a non-polar solvent in the cooling step is −10° C. or lower. If the cooling temperature is too high, the density of the undrawn yarn may become too high. From the viewpoint of sufficiently lowering the density of the undrawn yarn, the cooling temperature is preferably −15° C. or lower, and more preferably −20° C. or lower. The cooling temperature can be appropriately determined according to the type of refrigerant liquid and the production cost within a range in which the effects of this embodiment can be obtained. In this embodiment in which a non-polar solvent is used as the refrigerant liquid, the cooling temperature may be, for example, −60° C. or higher from the viewpoint of cost.

In the above cooling step, the cooling time is preferably long from the viewpoint of reducing the density of the undrawn yarn, and more specifically, it is preferably 0.1 seconds or more, more preferably 0.2 seconds or more, and even more preferably 0.3 seconds or more. From the viewpoint of productivity, the cooling time is preferably short, and from this viewpoint, it is preferably 5 seconds or less, more preferably 3 seconds or less, and even more preferably 2 seconds or less.

<Non-polar solvent>
The non-polar solvent is substantially inert to the molten extrudate of PA4 from the viewpoint of preventing the occurrence of surface roughness or whitening of the undrawn yarn. "Substantially inert" means that it has no substantial effect on the molten extrudate, and more specifically, it means that it is poorly soluble or insoluble in PA4 and has no permeability into the molten extrudate of PA4.

In addition, from the viewpoint of the stability of the cooling liquid medium in the cooling process, the melting point (Tm) of the nonpolar solvent is preferably -20°C or lower, and the boiling point (Tb) of the nonpolar solvent is preferably 100°C or higher. The nonpolar solvent may be one or more types. Examples of nonpolar solvents include silicone oil, hexane, nonane, decane, ethylcyclohexane, isopropylcyclohexane, toluene and p-cymene. Examples of nonpolar solvents and their melting points and boiling points are shown in Table 1.

[Other steps]
The method for producing the monofilament according to the embodiment of the present invention may further include other steps than the melt extrusion step and the cooling step described above, within the scope of the effects of the embodiment of the present invention. For example, the method may further include a step (drawing step) of drawing the monofilament cooled in the cooling step. The drawing step is more effective from the viewpoint of improving the tensile properties of the monofilament.

The stretching process may be dry heat stretching or wet heat stretching. The stretching process may be carried out once or multiple times. The stretching temperature in the stretching process may be set appropriately from a range of 40 to 240°C depending on the mode of the stretching process. The final stretch ratio in the stretching process may be set appropriately from a range of 3.5 to 6 times depending on the mode of the stretching process. In this specification, "to" indicates a range including both the numerical values at both ends.

For example, if the stretching process is a single hot stretch, the stretching temperature may be 150 to 240°C (e.g., 200°C), and the stretch ratio may be 3.5 to 5 times (e.g., 4 times). If the stretching process is a double hot stretch, the stretching temperature in the first hot stretch may be 40 to 80°C (e.g., 60°C), and the stretch ratio may be 2.5 to 3.5 times (e.g., 3 times). And, the stretching temperature in the second hot stretch may be 150 to 240°C (e.g., 200°C), and the stretch ratio may be 1.05 to 2.0 times (e.g., 1.33 times).

In the spinning process, the fibrous molten extrudate is typically cooled while being pulled at a speed faster than the discharge speed of the molten extrudate, and then supplied to a drawing device. In an embodiment of the present invention, the pulling of the molten extrudate from the melt extrusion process to be supplied to the cooling process and the subsequent drawing process is not included in the drawing process, and may be set appropriately within a range in which the effects of this embodiment can be obtained.

[Action and Effect]
The monofilament in the embodiment of the present invention is substantially composed of the above-mentioned PA4 and has a density of 1.230 g/cm3 or ^less . A monofilament with a low density has higher tensile properties when knotted than a monofilament with a high density. Thus, according to the embodiment of the present invention, a monofilament having improved tensile properties when knotted can be realized, more specifically, a monofilament having high tensile strength and tensile elongation when knotted can be realized.

The method for producing a monofilament according to an embodiment of the present invention includes a melt-extrusion step of melt-extruding a monofilament, and a cooling step of cooling the melt-extruded monofilament to −10° C. or lower using a non-polar solvent. According to this configuration, a monofilament having a density of 1.230 g/cm ³ or lower can be produced.

By making the diameter of the undrawn monofilament yarn sufficiently small, it is possible to fully realize the cooling effect in the cooling process, and from this perspective, it is advantageous for the diameter of the monofilament to be, for example, 1 mm or less.

The non-polar solvent in the embodiment of the present invention may be selected from the group consisting of silicone oil, hexane, nonane, decane, ethylcyclohexane, isopropylcyclohexane, toluene and p-. These non-polar solvents are suitable from the viewpoint of stability as a refrigerant liquid in the above-mentioned cooling process.

Furthermore, when the method for producing a monofilament in an embodiment of the present invention further includes a step of stretching the monofilament cooled in the cooling step, it can exhibit sufficient tensile properties applicable to applications such as fishing lines or fishing nets.

In the production of polyamide 6 monofilaments, a method has been reported in which hexane at -10°C to +20°C is used as a coolant (JP Patent Publication 03-27118). If the temperature of the coolant is below -10°C, the cooling rate becomes too rapid, and the stretching in the next step does not proceed smoothly. Polyamide 4 has a higher crystallization rate in the monofilament production process than polyamide 6, and there is a problem that the monofilament will crystallize and not become strong if the cooling process is not performed at a sufficiently low temperature. For this reason, the embodiment of the present invention focuses on preventing crystallization.

In addition, in WO 2018/150835, air cooling and ice cooling are used in the manufacturing process of polyamide particles. These methods do not allow sufficient and uniform cooling in the production of monofilaments, and tend not to prevent crystallization or allow sufficient stretching. Therefore, liquid cooling is adopted in the embodiment of the present invention.

〔summary〕
As is clear from the above description, the monofilament according to the embodiment of the present invention is a polyamide 4 monofilament and has a density of 1.230 g/cm3 ^or less.

In addition, the method for producing monofilament in an embodiment of the present invention includes a melt extrusion process in which polyamide 4 is melt extruded, and a cooling process in which the fibrous molten extrudate of polyamide 4 produced by the melt extrusion process is cooled to -10°C or below using a non-polar solvent.

In an embodiment of the present invention, the diameter of the monofilament may be 1 mm or less. This configuration is even more effective in terms of increasing the tensile properties of the monofilament.

In an embodiment of the present invention, the non-polar solvent may be one or more solvents selected from the group consisting of silicone oil, hexane, nonane, decane, ethylcyclohexane, isopropylcyclohexane, toluene and p-cymene.

The method for producing a monofilament according to an embodiment of the present invention may further include a step of stretching the monofilament cooled in the cooling step. This configuration is even more effective in terms of obtaining a monofilament with excellent tensile properties.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the different embodiments are also included in the technical scope of the present invention.

Example 1
At room temperature, 2 mol% of potassium tert-butoxide was added to α-pyrrolidone in a polymerization vessel and stirred. After dissolving potassium tert-butoxide, 2 mol% of tetramethylammonium chloride was added as a polymerization aid and 0.1 mol% of N,N'-adipyldipyrrolidone was added as an initiator. After the addition, the system became cloudy and stirring soon became difficult. 72 hours after stirring was stopped, the lumps formed in the flask were removed and crushed. Unreacted materials and low molecular weight materials were washed with acetone. The washed crushed material was dried to obtain powdered PA4. The weight average molecular weight (Mw) of the obtained PA4 was 140,000.

The Mw of PA4 was measured by the following procedure, analytical equipment and conditions.
[Measurement procedure]
10 mg of the PA4 sample obtained as described above was dissolved in hexafluoroisopropanol (HFIP) containing 5 mM sodium trifluoroacetate to make 10 ^cm3 , and then filtered through a membrane filter to obtain a sample solution. 10 μL of this sample solution was injected into the analyzer shown below, and the weight average molecular weight of PA4 was measured under the measurement conditions described below.
[Analytical equipment]
GPC device: Tosoh HLC-8420GPC
[Measurement conditions]
A) Column: Shoko Science GPC HFIP806M x 2 (connected in series)
B) Eluent: 5mM _CF3COONa /HFIP
C) MALS: DAWN HELEOS 2 manufactured by Wyatt
D) Sample 10-11 mg/5 mM CF ₃ COONa/HFIP 10 mL
E) Flow rate: 1.0 mL/min
F) dn/dc: 0.240

PA4 was formed into a fiber shape by melt extrusion at a temperature of 265°C, and the obtained fibrous melt extrudate was passed through a volatile silicone oil ("KF-995", Shin-Etsu Silicone Co., Ltd.) bath at -20°C for 0.3 seconds immediately after forming to cool and solidify. In this way, an undrawn monofilament yarn of PA4 having a yarn diameter of 340 μm was produced. The density of the undrawn yarn was measured by the following measurement method. The density of the undrawn yarn was 1.220 g/ ^cm3 .

[Method of measuring density]
The density of the undrawn yarn was determined by the density gradient method. Six types of mixed solvents were used, each of which had a density adjusted in increments of 0.02 between 1.20 and 1.30 g/ ^cm3 by changing the mixture ratio of heptane and carbon tetrachloride.

Next, the undrawn yarn produced was stretched by dry heat drawing at a drawing temperature of 60°C and a draw ratio of 3.0 times. As the second drawing stage, it was stretched by dry heat drawing at a drawing temperature of 200°C and a draw ratio of 1.33 times (total draw ratio of 4.0 times). The humidity of the atmosphere during dry heat drawing was 10% RH or less. In this way, a drawn PA4 monofilament yarn was produced.

Example 2
A monofilament was produced in the same manner as in Example 1, except that the diameter of the undrawn yarn was changed to 480 μm. The density of the undrawn yarn was 1.220 g/cm ³ .

Example 3
A monofilament was produced in the same manner as in Example 1, except that the refrigerant was changed to hexane and the temperature of the refrigerant was changed to -55° C. The density of the undrawn yarn was 1.219 g/cm ³ .

Example 4
A monofilament was produced in the same manner as in Example 1, except that the refrigerant was changed to toluene and the temperature of the refrigerant was changed to -50° C. The density of the undrawn yarn was 1.219 g/cm ³ .

Comparative Example 1
A monofilament was produced in the same manner as in Example 1, except that the refrigerant was changed to water and the temperature of the refrigerant was changed to 4° C. The density of the undrawn yarn could not be measured due to the rough surface of the undrawn yarn. In addition, due to the rough surface of the undrawn yarn, drawing breakage occurred during subsequent drawing, and a drawn yarn could not be obtained.

Comparative Example 2
A monofilament was produced in the same manner as in Example 1, except that the coolant was changed to tetradecane and the temperature of the coolant was changed to 40° C. The density of the undrawn yarn was 1.240 g/cm ³ .

Comparative Example 3
A monofilament was produced in the same manner as in Example 1, except that the temperature of the coolant was changed to 40° C. The density of the undrawn yarn was 1.240 g/cm ³ .

The yarn diameters of the drawn yarns of Examples 1 to 4 and Comparative Examples 1 to 3 were determined in the same manner as the yarn diameter of the undrawn yarn, and were 170 to 240 μm. The densities of the drawn yarns of Examples 1 to 4 and Comparative Examples 1 to 3 were determined in the same manner as the density of the undrawn yarn, and were 1.246 to 1.250 g/cm ^3. The birefringences of the drawn yarns of Examples 1 to 4 and Comparative Examples 1 to 3 were determined in the same manner as the density of the undrawn yarn, and were 58×10 ^-3 to 67×10 ^-3 .

[Method of measuring birefringence]
The birefringence of PA4 in the drawn yarn was determined by retardation measurements using a polarizing microscope equipped with a Berek compensator and a sodium lamp as the light source.

〔evaluation〕
[Tensile properties of monofilament at knot]
For each of the monofilaments in the above Examples and Comparative Examples, the tensile strength and tensile elongation at the knot of the monofilament were measured by the following measuring methods.
<Method of measuring tensile strength and tensile elongation>
The tester was a Tensilon RTF-1210, and the tensile measurements were performed at 23°C, 50% RH, with the chuck distance set to 150 mm and the tensile speed set to 150 mm/min. When knotting, the knot was placed at the center between the chucks.

The manufacturing conditions and density of the undrawn yarn in the above examples and comparative examples, as well as the tensile strength and tensile elongation of the drawn yarn at the knot are shown in Table 2.

[Considerations of Examples 1 to 4 and Comparative Examples 1 to 3]
As is clear from Table 1, the density of the monofilaments of the Examples is 1.230 g/ ^cm3 or less. As a result, the tensile strength and knot elongation at knot of the drawn yarn obtained by drawing the undrawn yarn are higher than those of the drawn yarn of the Comparative Example.

In contrast, in Comparative Example 1, the surface of the unstretched yarn became rough. This is thought to be because water was used as the refrigerant, and the PA4 in the unstretched yarn dissolved in water or became wet during cooling. Also, in Comparative Example 1, it was not possible to draw the unstretched yarn. This is thought to be because the strength of the unstretched yarn decreased due to the above-mentioned surface roughness and the dissolution and moisture absorption of the unstretched yarn.

In Comparative Examples 2 and 3, the density of the undrawn yarn is low. In addition, in Comparative Examples 2 and 3, the tensile strength and tensile elongation at the knot of the drawn yarn are both lower than those of Example 1. This is thought to be because the cooling temperature in the production of the undrawn yarn was too high, promoting the crystallization of PA4 in the undrawn yarn.

The PA4 monofilament of the present invention can be used as a synthetic fiber with excellent tensile properties, and the present invention is expected to further reduce the environmental burden associated with the use of such synthetic fibers.

Claims (5)

An undrawn monofilament yarn of polyamide 4 having a density of 1.230 g/cm3 ^or less. 2. The undrawn monofilament yarn of claim 1, wherein the monofilament has a diameter of 1 mm or less. A melt extrusion step of melt extruding polyamide 4;
A cooling step of cooling the fibrous molten extrudate of polyamide 4 produced by the melt extrusion step to −10° C. or lower using a non-polar solvent. The method for producing monofilaments according to claim 3, wherein the non-polar solvent is one or more solvents selected from the group consisting of silicone oil, hexane, nonane, decane, ethylcyclohexane, isopropylcyclohexane, toluene, and p-cymene. The method for producing a monofilament according to claim 3 or 4, further comprising a step of drawing the fibrous molten extrudate cooled in the cooling step.