Manufacturing method of resin-foamed yarn and ram extruder

Abstract

To provide a manufacturing method for a resin-foamed yarn, which is capable of easily manufacturing a resin-foamed yarn containing bubbles.SOLUTION: There is provided a manufacturing method for a resin-foamed yarn, comprising: a step (S1) of preparing a ram extruder 100; a step (S2) of feeding pellets P1 into a cylinder 101; a step (S3) of melting the pellets P1; a step (S4) of extruding a molten resin P2 by the ram extruder 100 to obtain a primary foamed filament F1; and a step (S6) of subjecting the primary foamed filament F1 to secondary foaming by a laser electrospinning method to obtain a secondary foamed filament F2. When the pellets P1 are fed, spaces are formed between the pellets P1, and the molten resin P2 is extruded by the ram extruder 100 so as to incorporate air contained in those spaces, thereby allowing the primary foamed filament F1 to be easily formed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a foamed resin yarn made of a thermoplastic resin using a ram extrusion molding method, and a ram extruder used for producing the foamed resin yarn. [Background technology]

[0002] BACKGROUND ART Conventionally, foamed yarns made of thermoplastic resins have been used in various fields from the viewpoint of achieving weight reduction.

[0003] Japanese Patent Laid-Open Publication No. 57-193513 (Patent Document 1) discloses a method for producing a filament. The method is characterized by dielectrically heating and stretching the crystalline portion of a polymer. This allows for the production of a filament with a low linear expansion coefficient and a high elastic modulus.

[0004] Japanese Patent Laid-Open Publication No. 58-109617 (Patent Document 2) discloses a method for stretching a polyoxymethylene rod. In this method, the polyoxymethylene rod is continuously stretched while being heated dielectrically in combination with external heating. This allows the production of polyoxymethylene filaments with a high tensile modulus.

[0005] Japanese Patent Laid-Open No. 63-50545 (Patent Document 3) discloses a method for producing a thermoplastic polymer foamed yarn. In the method, an undrawn fiber of a thermoplastic polymer having a moisture content of 0.3 to 1% by weight is heated in a microwave oven at a temperature of 2 kg / mm 2 The yarn is stretched at a tension of 100% or more, which causes foaming and makes the yarn less likely to break. [Prior art documents] [Non-patent literature]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 57-193513 [Patent Document 2] Japanese Unexamined Patent Publication No. 58-109617 [Patent Document 3] Japanese Unexamined Patent Publication No. 63-50545 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the filament manufacturing method of Patent Document 1 and the polyoxymethylene rod drawing method of Patent Document 2 do not propose a method for manufacturing a resin foamed yarn, but rather aim to obtain a filament with high strength and high elastic modulus.

[0008] Furthermore, the method for producing a thermoplastic polymer foamed yarn in Patent Document 3 proposes a method for producing a resin foamed yarn, but in order to adjust the moisture content of the undrawn yarn to 0.3 to 1% by weight, the undrawn yarn must go through steps such as leaving it in the air, drying it, or humidifying it. Furthermore, since it is difficult to maintain the moisture content within the range of 0.3 to 1% by weight, the process of drawing the undrawn yarn is burdensome.

[0009] Therefore, an object of the present disclosure is to provide a method for producing a resin foamed yarn that can easily produce a resin foamed yarn containing bubbles. [Means for solving the problem]

[0010] In order to solve the above problems, the present disclosure is configured as follows: That is, a method for producing a resin foamed yarn according to the present disclosure includes the steps of preparing a ram extruder having a cylinder, a ram, and a die, charging thermoplastic resin pellets into the cylinder, leaving a space inside the cylinder, so that the filling rate is 20% by volume to 80% by volume of the total volume inside the cylinder, heating and melting the pellets to produce a molten resin, inserting the ram into the cylinder, pressurizing the molten resin containing gas contained in the space inside the cylinder with the ram, and extruding rod-shaped primary foamed filaments containing gas bubbles from the die, and irradiating the primary foamed filaments with laser light by laser electrospinning to form thread-like secondary foamed filaments containing gas bubbles that are stretched in the longitudinal direction.

[0011] The ram extrusion molding machine according to the present disclosure is a ram extrusion molding machine used for producing resin foamed yarn, and includes a cylindrical cylinder having one opening and another opening opposite the first opening, a columnar ram inserted through one opening of the cylinder, and a die having a through-hole communicating with the other opening of the cylinder. The ram has an O-ring fixed to its outer peripheral surface. The O-ring has an outer diameter 0.25 to 2.0 mm larger than the inner diameter of the cylinder. [Effects of the Invention]

[0012] According to the method for producing a resin foam yarn and the ram extrusion molding machine of the present disclosure, a resin foam yarn containing bubbles can be easily produced. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a flowchart of the method for producing resin foam yarn according to this embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the pellet charging step of FIG. [Figure 3] FIG. 3 is a cross-sectional view showing the melting step, the primary foaming filament forming step, and the stretching step in FIG. [Figure 4]FIG. 4 is a cross-sectional view showing the primary foamed filament of FIG. [Figure 5] FIG. 5 is a cross-sectional view showing a state in which the primary foamed filament of FIG. 4 is stretched. [Figure 6] FIG. 6 is a schematic diagram showing the step of forming the secondary foamed filament of FIG. [Figure 7] FIG. 7 is an enlarged view showing the step of forming the secondary foamed filament in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] In view of the problems of Patent Document 3, the present inventors conducted extensive research and found that a resin foam yarn containing gas bubbles can be produced by pressurizing and extruding thermoplastic resin pellets mixed with air, and then irradiating the extruded pellets with laser light using a laser electrospinning method. The present inventors have completed the method for producing a resin foam yarn according to the present disclosure based on this finding.

[0015] (Configuration 1) A method for producing a resin foamed yarn according to an embodiment of the present disclosure includes the steps of preparing a ram extruder having a cylinder, a ram, and a die; charging pellets made of a thermoplastic resin into the cylinder, leaving a space inside the cylinder so that the filling rate is 20% by volume to 80% by volume of the total volume inside the cylinder; heating and melting the pellets to produce a molten resin; inserting the ram into the cylinder, pressurizing the molten resin containing gas contained in the space inside the cylinder with the ram, and extruding rod-shaped primary foamed filaments containing gas bubbles from the die; and irradiating the primary foamed filaments with laser light by a laser electrospinning method to form thread-shaped secondary foamed filaments containing gas bubbles that are stretched in the longitudinal direction.

[0016] This makes it possible to easily produce foamed resin yarn containing good bubbles.

[0017] (Configuration 2) The method for producing a resin foamed yarn according to Configuration 1 may include a step of stretching the primary foamed filaments after the step of molding the primary foamed filaments and before the step of forming the secondary foamed filaments, thereby enabling a more stable production of thinner resin foamed yarns.

[0018] (Configuration 3) In the method for producing a resin foamed yarn according to Configuration 1 or 2, the molten resin may be pressurized with a load of 100 N to 1500 N, and may have a melt viscosity of 1000 Pa s to 2500 Pa s when pressurized. This makes it possible to more reliably form primary foamed filaments having bubbles, and to produce a resin foamed yarn having better bubbles.

[0019] (Configuration 4) The method for producing a resin foamed yarn according to any one of configurations 1 to 3, wherein the shear rate when the molten resin passes through the die is 20 sec -1 ~900sec -1 This makes it possible to more reliably form a primary foamed filament having bubbles, and to produce a resin foamed yarn having better bubbles.

[0020] (Configuration 5) In the method for producing a resin foamed yarn according to any one of Configurations 1 to 4, in the step of forming a secondary foamed filament, the temperature of the irradiated portion of the primary foamed filament irradiated with the laser light may be 300° C. to 400° C. This allows the primary foamed filament to be appropriately secondary foamed when irradiated with the laser light.

[0021] (Configuration 6) In the method for producing a resin foamed yarn according to any one of Configurations 1 to 5, the ram may have an O-ring on its outer peripheral surface. The O-ring may have an outer diameter 0.25 to 2.0 mm larger than the inner diameter of the cylinder. This allows the molten resin to be appropriately compressed, making it easier to form a primary foamed filament having bubbles.

[0022] (Configuration 7) A ram extrusion molding machine according to an embodiment of the present disclosure is a ram extrusion molding machine used to produce resin foamed yarn, and includes a cylindrical cylinder having one opening and another opening opposite the first opening, a columnar ram inserted through one opening of the cylinder, and a die having a through-hole communicating with the other opening of the cylinder. The ram has an O-ring fixed to its outer peripheral surface. The O-ring has an outer diameter 0.25 to 2.0 mm larger than the inner diameter of the cylinder. Use of the ram extrusion molding machine makes it possible to appropriately mold a primary foamed filament having bubbles, and then, by secondary foaming the primary foamed filament, resin foamed yarn can be easily produced.

[0023] Hereinafter, an embodiment of the method for producing a resin foamed yarn according to the present disclosure will be specifically described with reference to Figures 1 to 7. Note that the same or corresponding components in the figures are denoted by the same reference numerals, and the same description will not be repeated. To facilitate understanding of the description, the drawings referred to below show simplified or schematic configurations, and some components are omitted.

[0024] As shown in FIG. 1, the method for producing resin foamed yarn according to the present disclosure includes a preparation step S1, a pellet introduction step S2, a melting step S3, a primary foamed filament molding step S4, a drawing step S5, and a secondary foamed filament formation step S6.

[0025] [Preparation process S1] First, in a preparation step S1, a ram extruder 100 is prepared. As shown in FIG.

[0026] Cylinder 101 has a cylindrical shape and has one opening (upper in the figure) and another opening (lower in the figure) formed on the opposite side of the one opening. Cylinder 101 has an internal space with an internal diameter D1. The total internal volume of cylinder 101, which will be described later, is calculated from the internal diameter d1 and the height h of the internal space of cylinder 101.

[0027] The ram 102 has a cylindrical shape and is a push rod that is inserted from one opening of the cylinder 101 and pressurizes the pellets P that have been placed inside the cylinder 101.

[0028] As shown in Fig. 2, the ram 102 may be provided with an O-ring 102a on the outer peripheral surface of the tip end in the insertion direction of the ram 102. The O-ring 102a may be made of, for example, fluororesin (PTFE) and may be fixed to the outer peripheral surface of the ram 102 by fitting into an annular groove formed in the outer peripheral surface of the cylinder 101. The O-ring 102a may have an outer diameter d2 that is 0.25 mm to 2.0 mm larger than the inner diameter d1 of the cylinder 101. As an example, the inner diameter d1 of the cylinder 101 may be 20 mm. If the outer diameter d2 of the O-ring 102a is too small compared to the inner diameter d1 of the cylinder 101, air may escape in the direction opposite to the insertion direction of the ram 102 when the molten resin P2 (see Fig. 3) is pressurized by the ram 102 in the molding step S4 of the primary-foamed filament F1 described below. On the other hand, if the outer diameter d2 of the O-ring 102a is too large relative to the inner diameter d1 of the cylinder 101, the O-ring 102a may be damaged, etc., because it is too tightly fastened to the inner peripheral surface of the cylinder 101 when the ram 102 pressurizes the molten resin P2. Therefore, in order to appropriately compress the molten resin P2 and form a primary-foamed filament F1 having bubbles, it is preferable that the outer diameter d2 of the O-ring 102a be larger than the inner diameter d1 of the cylinder 101 by 0.25 mm to 2.0 mm.

[0029] The die 103 has a through-hole 103a that communicates with the interior of the cylinder 101 at the other opening of the cylinder 101 and penetrates toward the opposite side of the cylinder 101 (downward in the figure). The through-hole 103a of the die 103 is located at the tip of the die 103 and has a land 103b with a constant diameter, and a tapered portion 103c that is located between the land 103b and the interior of the cylinder 101 and is formed so that its diameter decreases in the extrusion direction of the molten resin P2. That is, the inner peripheral surface of the die 103 at the tapered portion 103c is configured as a tapered surface in the shape of an inverted truncated cone that decreases in diameter in the extrusion direction of the molten resin P2. The land 103b may have, for example, a height of 5 mm (in the vertical direction in the figure) and a diameter of 1 mm.

[0030] [Pellet charging process S2] Next, in the pellet charging step S2, as shown in FIG. 2, pellets P1 made of a thermoplastic resin are charged into the cylinder 101 from one opening of the cylinder 101. At this time, the pellets P1 are charged with space so that the filling rate is 20% to 80% by volume with respect to the total volume of the interior of the cylinder 101. In other words, the interior of the cylinder 101 contains the pellets P1 and 20% to 80% by volume of air with respect to the total volume of the interior of the cylinder 101. If the filling rate of the pellets P1 is too low, that is, if there is too much air, the air will not be able to dissolve completely in the molten resin P2 in the melting step S3 described below. When the molten resin P2 is compressed under high pressure in the molding step S4 of the primary foamed filament F1 described below, the air will remain as bubbles even under high pressure, and when the molten resin P2 is extruded from the die 103 and released to atmospheric pressure, the bubbles will expand and break, making it difficult to mold a primary foamed filament F1 containing good bubbles. On the other hand, if the filling rate of the pellets P1 is too high, that is, if there is too little air, bubbles are unlikely to form in the primary foamed filaments F1. From this viewpoint, the pellets P1 are preferably added to the cylinder 101 so that the filling rate is 20% by volume or more, preferably 30% by volume or more, more preferably 40% by volume or more, and 80% by volume or less, preferably 70% by volume or less, and more preferably 60% by volume or less, relative to the total volume inside the cylinder 101. In other words, the pellets P1 are preferably added to the cylinder 101 so that the filling rate is 20% by volume to 80% by volume, preferably 30% by volume to 70% by volume, and more preferably 40% by volume to 60% by volume, relative to the total volume inside the cylinder 101.

[0031] The filling rate of the pellets P1 can be adjusted by changing the size or shape of the pellets P1. That is, if the size of the pellets P1 is large, gaps are more likely to form inside the cylinder 101, and the filling rate of the pellets P1 decreases. On the other hand, if the size of the pellets P1 is small, gaps are less likely to form inside the cylinder 101, and the filling rate of the pellets P1 increases. In this embodiment, the pellets P1 may have a cylindrical shape. However, the shape of the pellets P1 is not limited to this and may be changed in various ways to adjust the filling rate of the pellets P1.

[0032] The pellets P1 may be introduced through an introduction hole (not shown) provided on the side of the cylinder 101 with one opening of the cylinder 101 closed by the tip of the ram 102. The introduction hole connects the inside of the cylinder 101 with the outside of the cylinder 101, and the pellets P1 can be introduced from, for example, a hopper provided outside the cylinder 101. At this time, air can be introduced into the cylinder 101 together with the pellets P1. The gas introduced into the cylinder 101 is not limited to air, and can be, for example, an inert gas such as nitrogen, argon, or carbon dioxide. An inert gas having the same density as or a density higher than that of air is preferred. However, when the pellets P1 are introduced as described above, air is usually also introduced into the cylinder 101, or air is already introduced into the cylinder 101 when the pellets P1 are introduced. Therefore, air is an efficient gas for forming bubbles in the primary foaming filament forming step S4 described below. Therefore, in this disclosure, the gas that is supplied or being supplied inside the cylinder 101 will be described as air.

[0033] The resin material of the pellet P1 is preferably a thermoplastic resin having a melt viscosity in the range of 1000 Pa·s to 2500 Pa·s, such as high-density polyethylene (HDPE), polypropylene (PP), acrylonitrile-butadiene-styrene resin (ABS), perfluoroalkoxyalkane (PFA), polyphenylene sulfide (PPS), etc. In particular, from the viewpoints of cost reduction and improved moldability and strength, polycarbonate is preferably used as the resin material.

[0034] [Melting process S3] Next, the pellets P1 are melted by a heater (not shown) to generate a molten resin P2 as shown in Fig. 3. At this time, the temperature of the molten resin P2 is preferably set to 240°C to 260°C when the resin material of the pellets P is polycarbonate, for example, from the viewpoint of appropriately extruding the primary foaming filament F1 in the next primary foaming filament molding step S4.

[0035] [Primary foaming filament molding process S4] Next, a ram 102 is inserted into the cylinder 101 from one opening thereof, or alternatively, the ram 102 is inserted into the cylinder 101 in advance before the melting step S3, and the molten resin P2 is pressurized together with the air. As a result, the inside of the cylinder 101 is compressed and pressurized, and the air is dissolved in the molten resin P2. Therefore, although not particularly shown, an opening / closing part is provided at the opening of the land 103b of the through hole 103a in the die 103 to pressurize the inside of the cylinder 101, and the opening / closing part is closed until the pressure is increased to a level that enables extrusion foaming.

[0036] The molten resin P2 is pressurized by the ram 102 with a load of 100N to 1500N. This allows the molten resin P2 to have an appropriate melt viscosity, thereby more reliably forming a primary foamed filament F1 having cells. If the load is less than 100N or more than 1500N, the molten resin P2 cannot have an appropriate melt viscosity, which may result in a reduced number of cells or the cells being more susceptible to breakage. From this perspective, the load applied when pressurizing the molten resin P2 is 100N or more, preferably 600N or more, and more preferably 800N or more, and is 1500N or less, preferably 1300N or less, and more preferably 1100N or less. In other words, the load applied when pressurizing the molten resin P2 is 100N to 1500N, preferably 300N to 1300N, and more preferably 500N to 110N. If the molten resin P2 can be pressurized with a load in the above range, the through-hole 103a may be covered with the molten resin P2 without providing an opening / closing portion at the opening of the land 103b of the through-hole 103a in the die 103. In this case, by pressurizing the molten resin P2 with a load in the above range, the molten resin P2 may be extruded from the through-hole within an appropriate melt viscosity range.

[0037] Furthermore, when the molten resin P2 is pressurized, the melt viscosity of the molten resin P2 is preferably 1000 Pa·s to 2500 Pa·s. From the viewpoint of forming a primary-foamed filament F1 containing good bubbles, the melt viscosity of the molten resin P2 is preferably 1000 Pa·s or more, preferably 1200 Pa·s or more, and 2500 Pa·s or less, preferably 1400 Pa·s or less. In other words, the melt viscosity of the molten resin P2 is preferably 1000 Pa·s to 2500 Pa·s, preferably 1200 Pa·s to 1400 Pa·s.

[0038] After the melt viscosity of the molten resin P2 reaches the predetermined value, the opening and closing portion of the die 103 is opened. Then, the molten resin P2 passes through the inside of the die 103, is extruded from the opening of the land 103b of the die 103, and is released to atmospheric pressure, and the air dissolved in the molten resin P2 foams. As a result, as shown in FIG. 4, a rod-shaped primary foamed filament F1 containing bubbles B can be formed. As shown in FIG. 4, the bubbles B contained in the primary foamed filament F1 have a slightly oval spherical shape in cross section. The primary foamed filament F1 thus ram-extrusion molded can have a diameter of, for example, 1 to 2 mm.

[0039] The shear rate when the molten resin P2 passes through the inside of the die is 20 sec -1 ~900sec -1 If the shear rate is too slow, the extrusion of the molten resin P2 will be slow, and the pressure on the molten resin P2 will decrease and the release time will be prolonged, which may cause the bubbles to become coarse. On the other hand, if the shear rate is too fast, the pressure on the molten resin P2 will become too high, which may cause bubbles to break when released. Therefore, from the viewpoint of molding a primary foamed filament F1 containing good bubbles, the shear rate should be set to 20 sec -1 More than 50 seconds, preferably -1 More than 100 seconds, preferably -1 It is better to set it to 900 seconds or more. -1 Less than 700 seconds, preferably -1 Less than 500 seconds, preferably -1In other words, the shear rate should be 20 sec -1 ~900sec -1 , preferably 50 seconds -1 ~700sec -1 , more preferably 100 seconds -1 ~500sec -1 It is better to

[0040] [Stretching process S5] Next, the primary foamed filament F1 is stretched. More specifically, as shown in FIG. 3, the primary foamed filament F1 extruded from the die 103 is stretched while being conveyed by a pulley 110 and a take-up pulley 120. By this stretching step S5, the primary foamed filament F1 can be stretched, for example, to 5 to 10 times the length of the primary foamed filament F before stretching, for example, to a diameter of 0.1 mm to 0.3 mm. At this time, the bubbles B contained in the stretched primary foamed filament F1 are stretched in the longitudinal direction, as shown in FIG. 5. This allows for the stable production of thinner resin foamed yarn. However, the stretching step S5 is not necessarily required. That is, if necessary, the process can proceed from the forming step S4 of the primary foamed filament F1 to the forming step S6 of the secondary foamed filament F2, which will be described later, without passing through the stretching step S5.

[0041] [Secondary foaming filament formation step S6] Next, a high voltage is applied to the primary foamed filament F1 and laser light L is irradiated thereto by a laser electrospinning method, thereby forming a thread-like secondary foamed filament F2.

[0042] As shown in FIG. 6, the laser electrospinning method involves applying a high voltage (e.g., a voltage of 15 to 20 kV) between a needle 202 and a target electrode 203 by a high-voltage application unit 201 in a dry air atmosphere, and irradiating the tip of the primary foamed filament F1 with a carbon dioxide laser beam L at an output of 15 to 20 kV x 9 to 20 W to heat and melt the filament and cause secondary foaming. The filament is then stretched toward the target electrode 203 by electrostatic force, forming a thinner, thread-like secondary foamed filament F2. In this embodiment, the target electrode 203 can function as a take-up device that winds up the secondary foamed filament F2. When the process proceeds from the molding step S4 of the primary foamed filament F1 to the formation step of the secondary foamed filament F2 without passing through the stretching step S5, a high voltage may be applied between the die 103 and the target electrode 203 instead of the needle 202, and the primary foamed filament F1 extruded from the die 103 may be irradiated with the laser beam L.

[0043] Here, secondary foaming refers to the following: When the primary foam filament F1 is irradiated with laser light L in the laser electrospinning method, the temperature of the primary foam filament F1 rises, causing it to melt and a sudden drop in resin viscosity. As a result, as shown in FIG. 7, the bubbles B in the primary foam filament F1 coalesce and expand. Furthermore, the solubility of the air dissolved in the still semi-molten primary foam filament F1 also decreases as the temperature rises, so that the air bubbles B are present in the primary foam filament F1. Thus, in the secondary foam filament formation step S6, following foaming using the ram extruder 100 described above, the primary foam filament F1 is stretched while being secondarily foamed, thereby forming an even finer, thread-like secondary foam filament F2 containing bubbles B extending in the longitudinal direction.

[0044] The temperature of the irradiated portion F11 of the primary foaming filament F1, where the laser light is irradiated, can be set to 300°C to 400°C. If the temperature of the irradiated portion F11 is too low, it becomes difficult to cause the secondary foaming described above. On the other hand, if the temperature of the irradiated portion F11 is too high, the bubbles contained in the primary foaming filament F1 may break, making it difficult to properly form a resin foam yarn. Therefore, the temperature of the irradiated portion F11 is set to 300°C or higher, preferably 320°C or higher, and more preferably 340°C or higher, and is set to 400°C or lower, preferably 380°C or lower, and more preferably 360°C or lower. In other words, the temperature of the irradiated portion F11 is set to 300°C to 400°C, preferably 320°C to 380°C, and more preferably 340°C to 360°C.

[0045] By cooling this secondary foamed filament F2, a resin foamed yarn containing bubbles extending in the longitudinal direction can be easily produced.

[0046] The resin foam yarn produced by the production method according to this embodiment is foam-molded, which reduces the amount of resin used. As a result, the resin foam yarn 1 can contribute to improving resource utilization efficiency, easing transportation burdens, reducing energy consumption, and reducing CO2 emissions. By providing the resin foam yarn 1 to society, we can contribute to achieving Goal 7 (Affordable and Clean Energy), Goal 9 (Industry, Innovation and Infrastructure), and Goal 11 (Sustainable Cities and Communities) of the 17 Sustainable Development Goals (SDGs) established by the United Nations. Furthermore, because the resin foam yarn 1 according to this embodiment can be melted and reused, we can contribute to achieving Goal 12 (Responsible Consumption and Production).

[0047] Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0048] [Example] Test specimens of Examples 1 to 15 and Comparative Examples 1 and 2 were prepared by the above-described manufacturing method under the conditions shown in Table 1, and tests were conducted to determine whether or not foamed resin yarns could be formed. The test results were as follows: "A" indicates that good bubbles were formed; "B" indicates that the size of the bubbles stretched in the longitudinal direction was similar to that of the "A" rating but the number of bubbles was small; "C" indicates that the bubbles stretched in the longitudinal direction were large and the number of bubbles was small; and "D" indicates that no bubbles were formed or that the bubbles broke during ram extrusion and the shape of the bubbles could not be maintained. In Table 1, the "L / D" of the die refers to the ratio of the land height L to the diameter D.

[0049] [Table 1]

[0050] (Examples 1 to 3) Tests were conducted by changing the MFR (melt flow rate) conditions for each resin material for the specimens of Examples 1 to 3. For each specimen, the extrusion temperature was changed to set the melt viscosity of the molten resin during extrusion to 1200 to 1400 Pa s, and as a result, foamed resin yarns with good bubbles could be produced.

[0051] Examples 4 to 6 For the specimens of Examples 4 to 6, tests were conducted by varying the size of the pellets inserted into each cylinder. The pellets had a cylindrical shape. In Table 1, the pellet diameter is the diameter of the top and bottom surfaces of the pellet, and the pellet length is the length (height) between the top and bottom surfaces. It was found that the filling rate and air content of the resin material inside the cylinder could be adjusted by changing the pellet size. That is, in Example 4, where the pellet size was large, gaps were more likely to form inside the cylinder, resulting in a smaller filling rate of the pellets and a larger air content. On the other hand, in Example 6, where the pellet size was small, the pellet filling rate was higher and the air content was lower. In this way, the pellet filling rate could be adjusted by changing the shape or size of the pellets.

[0052] Examples 7 to 9 In Examples 7 to 9, the tests were conducted by changing the outer diameter of each O-ring. In each Example, the inner diameter of the cylinder was 20 mm. A foamed resin yarn with good bubbles was produced in all of the test specimens in Examples 7 to 9. In other words, it was found that a foamed resin yarn with good bubbles could be produced by making the outer diameter of the O-ring larger than the inner diameter of the cylinder, with the difference being 0.25 to 2.0 mm.

[0053] (Examples 10 to 16) Comparing the specimens of Examples 10, 11, 12, 14, 15, and 16, Example 14, in which the melt viscosity during extrusion was slightly greater than 2500 Pa·s, and Example 16, in which the load during extrusion was slightly less than 100 N, had a relatively small shear rate, and the size of the cells stretched in the longitudinal direction was good, but the number of cells was small. Furthermore, in Examples 12 and 15, the load during extrusion was greater than 1500 N, which increased the extrusion shear rate and reduced the melt viscosity during extrusion, resulting in large cells stretched in the longitudinal direction and a small number of cells. From these results, it can be seen that to obtain a foamed resin yarn with better cells, the load during extrusion should be set to 100 N to 1500 N, the melt viscosity of the molten resin should be set to 1000 Pa·s to 2500 Pa·s, or the shear rate when the molten resin passes through the die should be set to 20 sec -1 ~900sec -1 It was found that relatively good results such as an evaluation of "A" or "B" could be obtained by using the above method. -1 If the thickness is less than 100 mm, the bubbles stretched in the longitudinal direction will be relatively large and the number of bubbles will be small, which is presumably why the evaluation will be "C".

[0054] (Comparative Examples 1 and 2) In the specimen of Comparative Example 1, the pellet size was significantly reduced to adjust the pellet filling rate to 90% by volume. In the specimen of Comparative Example 2, the pellet size was significantly increased to adjust the pellet filling rate to 10% by volume. In the specimen of Comparative Example 1, no bubbles were formed, and in the specimen of Comparative Example 2, bubbles were formed but broke during extrusion molding, and the bubble shape could not be maintained. Comparing these results with the pellet filling rates in Examples 1 to 15, it was found that resin foam yarns with good or relatively good bubbles could be produced if the pellet filling rate was 20% to 80% by volume relative to the total volume inside the cylinder. [Explanation of symbols]

[0055] S1 preparation process, S2 pellet input process, S3 melting process, S4 primary foam filament molding process, S5 drawing process, S6 secondary foam filament forming process, 100 ram extruder, 101 cylinder, 102 ram, 103 die, 201 high voltage application unit, 202 needle, 203 target electrode, P1 pellet, P2 molten resin, F1 primary foam filament, F2 secondary foam filament

Claims

1. providing a ram extruder having a cylinder, a ram, and a die; a step of introducing thermoplastic resin pellets into the cylinder, leaving a space therein, so that the filling rate of the pellets is 20% by volume to 80% by volume relative to the total volume of the cylinder; heating and melting the pellets to produce a molten resin; inserting the ram into the cylinder, pressurizing the molten resin containing gas contained in the space inside the cylinder with the ram, and extruding rod-shaped primary foamed filaments containing gas bubbles from the die; and a step of irradiating the primary foamed filaments with laser light by a laser electrospinning method to form thread-like secondary foamed filaments containing the bubbles and stretched in the longitudinal direction.

2. The method for producing the resin foam yarn according to claim 1, A method for producing a resin foamed yarn, comprising a step of stretching the primary foamed filaments after the step of molding the primary foamed filaments and before the step of forming the secondary foamed filaments.

3. The method for producing the resin foam yarn according to claim 1, The molten resin is pressurized with a load of 100 N to 1500 N, and when pressurized, the molten resin has a melt viscosity of 1000 Pa·s to 2500 Pa·s.

4. The method for producing the resin foam yarn according to claim 1, The shear rate when the molten resin passes through the die is 20 sec －１ ~900sec －１ This is a method for producing resin foam yarn.

5. The method for producing the resin foam yarn according to claim 1, In the step of forming the secondary foamed filament, the temperature of the irradiated portion of the primary foamed filament irradiated with the laser light is 300°C to 400°C.

6. The method for producing the resin foam yarn according to claim 1, The ram has an O-ring on its outer circumferential surface, The method for manufacturing a resin foam yarn, wherein the O-ring has an outer diameter that is 0.25 to 2.0 mm larger than the inner diameter of the cylinder.

7. A ram extrusion molding machine used to manufacture foamed resin yarn, a cylinder having a cylindrical shape and having one opening and another opening opposite to the one opening; a ram having a cylindrical shape and inserted from one opening of the cylinder; a die having a through hole communicating with the other opening of the cylinder, The ram has an O-ring fixed to its outer circumferential surface, the O-ring has an outer diameter that is 0.25 to 2.0 mm larger than the inner diameter of the cylinder.

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