Screw element and twin-screw extruder

Abstract

To provide a technology for improving a uniformity of a kneaded material and reducing temperature unevenness in a twin-screw extruder.SOLUTION: A screw element 30 used for kneading a thermoplastic resin composition is provided, a cross section of which is perpendicular to a rotation axis AX is polygonal, the polygon has no recesses, a center of the polygon coincides with the rotation axis AX, and the polygon has an outer shape which is rotated around the rotation axis AX as it progresses in a direction of the rotation axis.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a screw element and a twin-screw extruder. [Background technology]

[0002] The viscosities of materials to be kneaded in an extruder vary widely; for example, the melt viscosity ranges from high to low. Various additives are added to these resins. Various technologies have been proposed to knead such materials with good dispersibility. For example, a twin-screw extruder is one such technology (see, for example, Patent Document 1). A twin-screw extruder melts and kneads a resin (thermoplastic resin composition) using two screws inside a cylinder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-19635 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, twin-screw extruders are used to knead materials with good dispersibility and to uniformly mix different components, but it is extremely difficult to achieve both uniformity in the kneaded thermoplastic resin composition and suppression of temperature unevenness.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a technology for improving the uniformity of a kneaded thermoplastic resin composition and suppressing temperature unevenness in a twin-screw extruder. [Means for solving the problem]

[0006] According to the present invention, the following inventions are provided. 1. A screw element used for kneading a thermoplastic resin composition, The cross section perpendicular to the axis of rotation is polygonal, The polygon has no recesses, the center of the polygon coincides with the axis of rotation, The polygon has an outer shape rotated around the rotation axis as it progresses in the axial direction. Screw element. 2. The screw element according to 1., wherein the corners of the polygon are rounded or chamfered. 3. A screw element according to 1. or 2., wherein the sides of the polygon are bulged outward. 4. A screw element according to 1. or 2., wherein the lead length is 2.0 dl or more and 10.0 dl or less, where dl is the maximum diameter of the polygon. 5. The screw element according to 1. or 2., wherein the polygon is any one of a square, a pentagon, a hexagon, a heptagon, and an octagon. 6. A screw element according to 1. or 2., wherein dl / ds is 1.3 or less, where dl is the maximum diameter of the polygon and ds is the minimum diameter. 7. A cylinder; a first screw and a second screw arranged in parallel inside the cylinder; and the first screw and the second screw each have a kneading section having a screw element attached to a shaft for kneading the thermoplastic resin composition; The screw element The cross section perpendicular to the axis of rotation is polygonal, The polygon has no recesses, the center of the polygon coincides with the axis of rotation, The screw element has an outer shape that rotates around the rotation axis as the polygon advances in the axial direction. 8. The twin-screw extruder according to 7., wherein the corners of the polygon are rounded or chamfered. 9. A twin-screw extruder according to 7. or 8., wherein the sides of the polygon are bulged outward. 10. The twin-screw extruder according to 7. or 8., wherein the lead length is 2.0 dl to 10.0 dl, where dl is the maximum diameter of the polygon. 11. The twin-screw extruder according to 7. or 8., wherein the polygon is any one of a square, a pentagon, a hexagon, a heptagon, and an octagon. 12. The twin-screw extruder according to 7. or 8., wherein dl / ds is 1.3 or less, where dl is the maximum diameter of the polygon and ds is the minimum diameter. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a technology for improving the uniformity of a kneaded material and reducing temperature unevenness in a twin-screw extruder. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing a schematic configuration of the internal structure of a twin-screw extruder according to an embodiment. FIG. [Figure 2] FIG. 2 is a cross-sectional perspective view showing the structure of a cylinder and a screw in a kneading section according to the embodiment. [Figure 3] FIG. 2 is a cross-sectional view showing the structure of a cylinder and a screw in a kneading section according to the embodiment. [Figure 4] FIG. 1 is a perspective view of a portion of a screw element according to an embodiment. [Figure 5] FIG. 2 is a third angle view of a portion of a screw element according to an embodiment. [Figure 6] FIG. 2 is a view showing a developed peripheral surface of a portion of a screw element according to an embodiment. [Figure 7] FIG. 10 is a cross-sectional view showing the structure of a cylinder and a screw of a comparative example according to an embodiment of the present invention. [Figure 8] FIG. 10 is a perspective view showing the structure of a screw of a comparative example according to the embodiment. [Figure 9] FIG. 2 is a diagram showing an example in which the first screw element and the second screw element according to the embodiment are arranged in the same phase. [Figure 10]FIG. 2 is a diagram showing an example in which the first screw element and the second screw element according to the embodiment are arranged out of phase. [Figure 11] FIG. 2 is a diagram showing an example of the arrangement of first screw elements and second screw elements when the cross-sectional shape of the screw elements according to the embodiment is octagonal. [Figure 12] FIG. 2 is a diagram showing an example of the arrangement of first screw elements and second screw elements when the cross-sectional shape of the screw elements according to the embodiment is rectangular. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Summary> An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the general configuration of the internal structure of a twin-screw extruder 1. The right side of FIG. 1 is the upstream side when describing the twin-screw extruder 1, and the left side is the downstream side. The rotation axis direction (also simply referred to as the "axial direction") of the screw 10 provided in the twin-screw extruder 1 coincides with the left-right direction in FIG. 1. FIG. 2 is a cross-sectional perspective view showing the structure of the cylinder 2 and screw 10 in the kneading section 3, taken along the line X1-X1 in FIG. 1. FIG. 3 is a cross-sectional view showing the structure of the cylinder 2 and screw 10 in the kneading section 3, taken along the line X1-X1 in FIG. 1. FIG. 4 is a perspective view of a portion of a screw element 30. The screw element 30 of this embodiment is characterized primarily by its external shape, and the spline shaft 20 and the structure (inner hole) that engages with it are omitted in FIG. 4. FIG. 5 is a third-angle view of a portion of the screw element 30. FIG. 5(a) is a front view, FIG. 5(b) is a side view, and FIG. 5(c) is a rear view. FIG. 6 is a view showing a developed circumferential surface of a portion of the screw element 30. As shown in FIG. In this embodiment, the term "thermoplastic resin composition" will be explained as referring to a material obtained by kneading a thermoplastic resin with other raw materials, such as a kneaded mixture of a "thermoplastic resin and a filler," a kneaded mixture of a "thermoplastic resin and an additive," or a kneaded mixture of a "thermoplastic resin, a filler, and an additive."

[0010] As shown in FIG. 1, the twin-screw extruder 1 includes a cylinder 2 (also called a barrel), a screw 10, a hopper 6, and a heating device 8. The screw 10 is provided so as to pass through the hollow cylinder 2 along the direction of its rotation axis. As the screw 10 rotates relative to the cylinder 2, material is supplied from a hopper 6, which is a material supply port, to the twin-screw extruder 1, and the material supplied into the cylinder 2 is kneaded and sent downstream.

[0011] <Cylinder> The interior of the cylinder 2 is formed as a long hollow along the rotation axis direction, and a pair of screws 10 (first screw 11, second screw 12) arranged in parallel along the rotation axis direction are rotatably inserted through the cylinder 2. The cylinder 2 may be made up of a single cylindrical member, or may be made up of multiple cylindrical members connected in the rotation axis direction.

[0012] A hopper 6, which is the material supply port, is provided at one end (the right end in Fig. 1) of the cylinder 2, and a die 9, which is the material discharge port, is provided at the other end (the left end in Fig. 1). A heating device 8 such as an electric heater is provided around the cylinder 2, and the material supplied from the hopper 6 is heated by this heating device 8, and the material is heated by this heating and by shear heat from the screw 10, the cylinder 2, and the material, to become semi-molten or molten.

[0013] <Screw> The screw 10 (first screw 11, second screw 12) is configured to include a splined shaft 20 (also referred to as a "shaft") extending in the direction of the rotation axis and a plurality of screw elements 30 (also referred to as "segments") fixed in a skewer-like manner by the splined shaft 20. The screw 10 is driven in the rotation direction by a drive unit 7 attached to the end on the upstream side (the right side in FIG. 1). The first screw 11 and the second screw 12 rotate at a rotational speed ratio of 1:1. The rotation directions of the first screw 11 and the second screw 12 can be either "same direction" or "counter direction." The screw elements 30 attached to the splined shaft 20 can be used in both a same-rotation twin-screw extruder 1 and a counter-rotation twin-screw extruder 1.

[0014] The screws 10 are housed inside the cylinder 2. Specifically, as shown in FIG. 2, the screws 10 are provided as a pair inside the cylinder 2 and rotate around two parallel first and second rotation axes AX1 and AX2. That is, the screw 10 has a first screw 11 and a second screw 12. The first screw 11 and the second screw 12 are arranged in parallel. The first screw 11 rotates around the first rotation axis AX1. The second screw 12 rotates around the second rotation axis AX2. When the first screw 11 and the second screw 12 are not distinguished from each other, they are simply referred to as "screws 10." When the first and second rotation axes AX1 and AX2 are not distinguished from each other, they are referred to as "rotation axes AX."

[0015] There are various types of elements, and in the screw 10, by combining multiple types of segments in different patterns, the part that feeds the material (feed section 5) and the part that kneads the material (kneading section 3) are formed over a certain range in the direction of the rotation axis.

[0016] The twin-screw extruder 1 has a feeding section 5 that melts the supplied material and feeds it downstream (from the upstream side (the right side in FIG. 1) to the downstream side (the left side in FIG. 1), a kneading section 3 that kneads the material fed from the feeding section 5, and an extrusion section 4 that feeds the material kneaded in the kneading section 3 downstream.

[0017] In the kneading section 3, the extrusion section 4 and the feeding section 5, elements according to the functions to be performed in each section are attached to a spline shaft 20 (shaft).

[0018] <Feed section> The feeding section 5 includes, for example, an element such as a screw flight (not shown) that is twisted spirally in the direction of the rotation axis. The spirally twisted screw flight rotates to melt the material and feed it from the upstream side to the downstream side.

[0019] <Kneading section> The kneading section 3 has screw elements 30 for kneading the thermoplastic resin composition as elements. When the screw 10 is rotated, the screw elements 30 can guide the material between themselves and the inner wall of the cylinder 2, thereby kneading the material.

[0020] Although details will be described later, in this embodiment, the screw elements 30 of the kneading section 3 have a polygonal cross section perpendicular to the rotation axis AX, the center of the polygon coincides with the rotation axis AX, and the polygon does not have any recesses (grooves), and the polygon has an outer shape that is rotated around the rotation axis AX as it progresses in the direction of the rotation axis AX. This configuration can achieve the following effects. (1) By making the outer shape of the screw element 30 polygonal, it is possible to design a small "maximum diameter (long diameter) / minimum diameter (short diameter)" and reduce the clearance between the screw element 30 and the cylinder 2. In addition, by making the screw element 30 polygonal and twisted in the lead direction, it is possible to exert a stretching effect on the material in the lead direction and knead the material uniformly. (2) As a polygon, the "maximum diameter (long diameter) / minimum diameter (short diameter)" can be made small, and the fluctuation in the clearance between the screw element 30 and the cylinder 2 can be reduced, so that uneven temperature of the material can be prevented during kneading. In the following, an example of a hexagonal cross-sectional shape of the screw element 30 will be shown, followed by a description of examples of an octagonal shape and a quadrilateral shape as modified examples.

[0021] <Extrusion section> The extrusion section 4 is equipped with spirally twisted screw flights, similar to the feed section 5. The screw segments of the extrusion section 4 are formed, for example, so that the clearance between the screw 10 and the cylinder 2 is smaller than that of the kneading section 3, allowing the material sent from the kneading section 3 to be pressurized and stable metering (i.e., stable discharge) to be achieved.

[0022] <Material> The materials fed from the hopper 6 include, for example, thermoplastic resin, filler, and additives. Specifically, for example, a material in which a filler or additive is added to a thermoplastic resin, or even a material in which a different type of thermoplastic resin is combined, is fed. Examples of thermoplastic resins include polyphenylene ether resins (polyphenylene ether, blends of polyphenylene ether and polystyrene resin), polystyrene resins (general-purpose polystyrene, high-impact polystyrene, acrylonitrile / styrene copolymer, acrylonitrile / butadiene / styrene copolymer, etc.), polycarbonate resins, polyolefin resins (polypropylene resin, polyethylene resin, etc.), polyester resins, homopolymer polyoxymethylene, copolymer polyoxymethylene, polyphenylene sulfide, polyamide resins, polyamideimide, polyarylate, polyarylsulfone, polyethersulfone, polyetherimide, polytetrafluoroethylene, polyetherketone, etc., with polyphenylene ether resins, polycarbonate resins, polyamide resins, homopolymer polyoxymethylene, copolymer polyoxymethylene, acrylonitrile / butadiene / styrene copolymer, etc. being particularly preferred. These thermoplastic resins may be used alone or in combination of two or more.

[0023] The filler is not particularly limited, and examples thereof include glass fiber, carbon fiber, metal fiber, potassium titanate whisker, magnesium sulfate whisker, aluminum borate whisker, calcium carbonate whisker, silicon carbide whisker, zinc oxide whisker, calcium silicate (wollastonite), mica, talc, glass flake, calcium carbonate, clay, kaolin, barium sulfate, silica, alumina, magnesium oxide, magnesium sulfate, copper iodide, potassium iodide, (flame-retardant) magnesium hydroxide, and the like, with glass fiber, carbon fiber, calcium silicate, mica, talc, glass flake, calcium carbonate, kaolin, silica, copper iodide, and potassium iodide being particularly preferred. The additives are not particularly limited, and examples thereof include lubricants, antiblocking agents, antistatic agents, pigments, dyes, colorants, heat stabilizers, ultraviolet absorbers, weathering stabilizers, antioxidants, anti-emulsion agents, nucleating agents, and plasticizers.

[0024] The material supplied from the hopper 6 is heated to a molten or semi-molten state by shear heat generated between the heater 8, the raw material during kneading, the screw 10, and the cylinder 2.

[0025] The cylinder 2 has a hole 2a that connects to a hopper 6. Thermoplastic resin, filler, and additives can be supplied into the cylinder 2 via the hopper 6. If necessary, a gate (not shown) that blocks the material to adjust the degree of mixing and an opening (not shown) that discharges gas volatilized from the mixed material to the outside of the cylinder 2 are provided downstream of the hopper 6.

[0026] <Screw elements in the kneading section> The screw elements 30 of the kneading section 3 will be outlined with reference to FIGS.

[0027] 2 and 3, the cylinder 2 has a first cylinder 21 and a second cylinder 22. The first cylinder 21 and the second cylinder 22 each have a shape in which two cylindrical cavities are connected together. The first cylinder 21 has a first screw 11 disposed therein, and the second cylinder 22 has a second screw 12 disposed therein.

[0028] The first screw 11 has a first spline shaft 20a and a first screw element 31 mounted on the first spline shaft 20a in the kneading section 3. The second screw 12 has a second spline shaft 20b and a second screw element 32 mounted on the second spline shaft 20b in the kneading section 3.

[0029] The first screw element 31 and the second screw element 32 may be arranged in phase or out of phase. "In phase" means that the two screw elements 30 are in a positional relationship that is line-symmetric with respect to a perpendicular line drawn to the midpoint of a line connecting the centers of the two screw elements 30 (the first screw element 31 and the second screw element 32), while "out of phase" means that the screw elements 30 are not in a positional relationship that is line-symmetric. In this embodiment, as will be described later, the ratio dl / ds of the maximum diameter dl to the minimum diameter ds of the screw elements 30 is small, making it possible to arrange them out of phase.

[0030] As shown in FIG. 4, the first screw element 31 has no recesses and has an outer shape obtained by rotating a regular hexagon about the first rotation axis AX1 as it advances in the direction of the first rotation axis AX1. The first screw element 31 has a shape in which the outer shape is a hexagon and is twisted about the first rotation axis AX1. In other words, the outer peripheral surface of the first screw element 31 has a shape in which the vertices of the hexagon advance in a spiral shape. The spiral is formed in a feed screw (forward lead direction). In other words, the shape of the screw element 30, i.e., the shape in which the vertices of the hexagon advance in a spiral shape, is set to match the screw rotation direction so that the spiral lead of the screw element 30 can feed material in accordance with the drive rotation direction of the screw 10.

[0031] Like the first screw element 31, the second screw element 32 has no recesses and has an outer shape that is formed by rotating a regular hexagon about the second rotation axis AX2 as it progresses in the direction of the second rotation axis AX2. The second screw element 32 has a shape in which the outer diameter of the second screw element 32 is hexagonal and twisted about the second rotation axis AX2. In other words, the outer peripheral surface of the second screw element 32 has a shape in which the vertices of the hexagon progress in a spiral. The spiral is formed in the form of a feed screw (forward lead direction).

[0032] A more specific shape of the screw element 30 will be described. 5 and 6, both ends of the screw element 30 are twisted by 90°. Hereinafter, the first screw element 31 and the second screw element 32 have the same shape, and when there is no need to distinguish between them, they will be described as "screw element 30."

[0033] In the examples shown in Figures 4 and 5, the six corners (first to sixth vertices 41 to 46) of the regular hexagon of the screw element 30 are rounded. The first vertex 41 is located at the 0 o'clock position clockwise, and the second to sixth vertices 42 to 46 are located in order clockwise. The first to sixth vertices 41 to 46 each form a ridgeline on the circumferential surface of the screw element 30. Therefore, the ridgelines formed by the first to sixth vertices 41 to 46 are curved lines twisted around the rotation axis AX. In addition, when the first to sixth vertices 41 to 46 are rounded or chamfered as in the embodiment, the ridge lines have a constant width corresponding to the width of the rounded or chamfered shape. Here, the region between the first vertex 41 and the second vertex 42 is referred to as the first surface 51, the region between the second vertex 42 and the third vertex 43 is referred to as the second surface 52, the region between the third vertex 43 and the fourth vertex 44 is referred to as the third surface 53, the region between the fourth vertex 44 and the fifth vertex 45 is referred to as the fourth surface 54, the region between the fifth vertex 45 and the sixth vertex 46 is referred to as the fifth surface 55, and the region between the sixth vertex 46 and the first vertex 41 is referred to as the sixth surface 56. The first to sixth surfaces 51 to 56 have curved surfaces that are similarly twisted along the twist of the first to sixth vertices 41 to 46.

[0034] <Polygon type> The polygonal cross-sectional shape of the screw element 30 is preferably one of a square, pentagon, hexagon, heptagon, and octagon, with the center of the polygon coinciding with the axis of rotation AX. By making the polygon square or larger and having the center of the polygon coinciding with the axis of rotation AX, when the maximum diameter of the polygon is dl and the minimum diameter is ds, the difference between the maximum diameter dl and the minimum diameter ds can be reduced (in other words, the ratio dl / ds can be reduced), improving the elongation effect of the material. On the other hand, if the polygon is larger than an octagon, the cross-section approaches a circle, and the difference between the maximum and minimum diameters becomes too small, resulting in insufficient mixing. In the case of a regular 2n-polygon (n is a natural number), the maximum diameter is the distance between two opposing corners, and the minimum diameter is the distance between two opposing sides.In the case of a regular (2n+1)-polygon (n is a natural number), the maximum diameter is twice the distance from the center to a corner, and the minimum diameter is twice the distance from the center to a side.

[0035] <Relationship between maximum diameter dl and minimum diameter ds> The specific relationship between the maximum diameter dl and the minimum diameter ds is as follows: When the maximum diameter of the polygon is dl and the minimum diameter is ds, the ratio dl / ds is 1.3 or less. The ratio dl / ds is preferably 1.2 or less, more preferably 1.1 or less. The lower limit is, for example, 1.05 or more, preferably 1.07 or more, more preferably 1.09 or more. By setting the ratio dl / ds within the above range, the material can be effectively elongated. Furthermore, by reducing the ratio dl / ds, fluctuations in the clearance between the cylinder 2 and the screw element 30 are reduced, and temperature unevenness in the material can be suppressed.

[0036] <Polygon corner shape (rounded, chamfered)> The polygonal cross-sectional shape of the screw element 30 may be a so-called perfect regular polygon, or may have rounded or chamfered corners. A rounded shape refers to a shape in which the corners are rounded to form a curved surface (curve). A chamfered shape refers to a shape in which the corners are removed, and may be a curved surface or a shape in which multiple flat surfaces are gradually shifted. By rounding or chamfering the corners of the polygon, the maximum diameter dl is reduced, and the ratio dl / ds of the maximum diameter dl to the minimum diameter ds can be further reduced. As a result, the elongation effect of the material can be enhanced. Furthermore, the polygon may have curved sides that bulge outward. By using such a shape, the minimum diameter ds can be increased, and the ratio dl / ds of the maximum diameter dl to the minimum diameter ds can be reduced. As a result, the elongation effect of the material can be enhanced.

[0037] Furthermore, by reducing the ratio dl / ds, it is possible to reduce the change in the clearance between the screw element 30 and the inner wall surface of the cylinder 2. This makes it less likely that temperature variations will occur. Furthermore, by forming the screw element 30 into a feed screw shape, it is possible to send the material downstream even with a small clearance, and also to obtain an elongation effect in the lead direction.

[0038] <Relationship between maximum diameter and lead length> When the maximum diameter of the polygon is dl, the lead length is 2.0 dl to 10.0 dl. The lead length is the distance traveled in the direction of the rotation axis when the screw 10 makes one rotation. In other words, the lead length can be said to be the length in the direction of the rotation axis until a corner of a polygon returns to the same position, and can be understood as the distance in the direction of the rotation axis until, for example, the first apex 41 (corner) at the 0 o'clock position clockwise returns to the same 0 o'clock position clockwise.

[0039] By setting the lead length to 2 to 10 times the maximum diameter of the polygon (i.e., the maximum diameter of the screw element 30), it is possible to improve the degree of mixing (i.e., uniformity) while suppressing temperature unevenness of the material over a long distance. trainingMore specifically, the gel is a high molecular weight component of a polymer (resin), and in this embodiment, the effect of stretching and grinding the gel is exhibited by the extension.

[0040] <Configurations of screws and screw elements in comparative examples> Fig. 7 shows a comparative example in which the cross sections of the screws (first screw 111, second screw 112) are made substantially elliptical, which is an example of a commonly used shape and corresponds to Fig. 3. Fig. 8 is a perspective view of the comparative example screws (first screw 111, second screw 112).

[0041] The first screw 111 has five screw elements 131 (screw elements 131a to 131e) that are approximately elliptical when viewed in the direction of the rotation axis, attached to a spline shaft 120a, with the major axes of the ellipses offset by 90 degrees between adjacent elements. Similarly, the second screw 112 has five screw elements 132 (screw elements 132a to 132e) that are approximately elliptical when viewed in the direction of the rotation axis, attached to a second spline shaft 120b, with the major axes of the ellipses rotated by 90 degrees between adjacent elements. The screw elements 131 of the first screw 111 and the screw elements 132 of the second screw 112 are arranged out of phase. When there is no need to distinguish between the screw elements 131 and 132, they are referred to as "screw elements 130."

[0042] Here, in screw elements 131 and 132, if the shape of the end of the long axis of the ellipse is the peak and the shape of the end of the short axis of the ellipse is the valley, there is a large difference between the distance d01 between the outer periphery of screw elements 131 and 132 at the peak and cylinder 102 (wall surface 121a of the first cylinder 121, wall surface 122a of the second cylinder 122) and the distance d02 between the outer periphery of screw elements 131 and 132 and the cylinder at the valley.

[0043] 7 shows an example where the ratio dl / ds is 1.31 or greater. By increasing the ratio dl / ds and rotating the screw element 130, the thermoplastic resin composition is subjected to strong shear at distance d01. The sheared thermoplastic resin composition moves to the resin pool at distance d02, where it is mixed and kneaded. However, because the structure of the system, in which the ratio dl / ds is increased and the thermoplastic resin composition is subjected to strong shear and heat generation at distance d01, is transferred to the resin pool, kneading the thermoplastic resin composition is easy to cause localized heat unevenness in the resin pool. Heat unevenness leads to viscosity and flow unevenness, hindering the improvement of material uniformity.

[0044] Furthermore, because the material contains a thermoplastic resin, the gel, which is an elastic body, is stretched by strong shear at the distance d01, but because the shear is intermittent, the gel is not crushed and tends to escape into the resin pool. However, the screw element 30 of this embodiment can solve these problems.

[0045] <Example of arrangement of the first and second screw elements> 9 and 10, the relationship between the phase of the screw elements 30 (first screw element 31, second screw element 32) and the maximum diameter dl and minimum diameter ds will be described based on simulation results. The ratio of the maximum diameter dl to the minimum diameter ds of the screw elements 30 is dl / ds=1.272.

[0046] FIG. 9 shows an example in which the first screw element 31 and the second screw element 32 are arranged in phase. FIG. 9(a) shows a state in which the clearance between the first screw element 31 and the second screw element 32 is largest. FIG. 9(b) shows a state rotated 30° from the state in FIG. 9(a) in which the clearance between the first screw element 31 and the second screw element 32 is smallest. FIG. 10 shows an example in which the first screw element 31 and the second screw element 32 are arranged out of phase (90° offset). When they are out of phase, the clearance between the first screw element 31 and the second screw element 32 can be made smaller than when they are in phase.

[0047] Figure 11 shows an example of the arrangement of the first screw 11A (first screw element 31A) and the second screw 12A (second screw element 32A) when the cross-sectional shape of the screw element 30A is octagonal (eight-thread type). Figure 11(a) shows the case where they are in phase, and Figure 11(b) shows the case where they are out of phase (22.5° offset). In addition, the ratio of the maximum diameter dl to the minimum diameter ds is dl / ds = 1.055.

[0048] Figure 12 shows an example of the arrangement of the first screw 11B (first screw element 31B) and the second screw 12B (second screw element 32B) when the cross-sectional shape of the screw element 30B is square (four-thread type). Figure 12(a) shows the case where they are in phase, and Figure 12(b) shows the case where they are out of phase (45° offset). In addition, the ratio of the maximum diameter dl to the minimum diameter ds is dl / ds = 1.232.

[0049] The features of this embodiment can be summarized as follows. Since there are no recesses on the outer circumferential surface of the screw element 30, there is little change in the clearance between the cylinder 2 and the screw element 30. Therefore, the input materials (thermoplastic resin, filler, and additives) can be uniformly mixed. Furthermore, the absence of recesses prevents so-called resin accumulation, which helps to eliminate temperature unevenness. Furthermore, the difference between the maximum diameter dl and the minimum diameter ds of the screw elements 30 can be reduced. More specifically, the ratio dl / ds can be reduced. This results in excellent elongational flow kneading and effectively crushing the gel of the material.

[0050] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted. [Explanation of symbols]

[0051] 1 Twin-screw extruder 2 cylinders 2a hole 3. Mixing section 4. Extrusion section 5 Feeding section 6 Hopper 7 Drive unit 8 Heating device 9 Material outlet 10 screws 11 First screw 12 Second screw 20 spline shaft 21 No. 1 cylinder 22 No. 2 cylinder 30 screw elements 31 First screw element 32 Second screw element

Claims

1. A screw element used for kneading a thermoplastic resin composition, The cross section perpendicular to the axis of rotation is polygonal, The polygon has no recesses, the center of the polygon coincides with the axis of rotation, The polygon has an outer shape rotated around the rotation axis as it progresses in the axial direction. Screw element.

2. 2. The screw element according to claim 1, wherein the corners of the polygon are rounded or chamfered.

3. 3. A screw element according to claim 1 or 2, wherein the sides of the polygon are outwardly bulging.

4. 3. The screw element according to claim 1, wherein the lead length is 2.0 dl or more and 10.0 dl or less, where dl is the maximum diameter of the polygon.

5. 3. The screw element according to claim 1, wherein the polygon is any one of a square, a pentagon, a hexagon, a heptagon, and an octagon.

6. 3. The screw element according to claim 1, wherein dl / ds is 1.3 or less, where dl is the maximum diameter of the polygon and ds is the minimum diameter of the polygon.

7. A cylinder and a first screw and a second screw arranged in parallel inside the cylinder; and the first screw and the second screw each have a kneading section having a screw element attached to a shaft for kneading a thermoplastic resin; The screw element The cross section perpendicular to the axis of rotation is polygonal, The polygon has no recesses, the center of the polygon coincides with the axis of rotation, The screw element has an outer shape obtained by rotating the polygonal shape around the rotation axis as it progresses in the axial direction. Twin-screw extruder.

8. 8. The twin-screw extruder according to claim 7, wherein corners of the polygon are rounded or chamfered.

9. 9. The twin-screw extruder according to claim 7 or 8, wherein the sides of the polygon are bulged outward.

10. 9. The twin-screw extruder according to claim 7 or 8, wherein the lead length is 2.0 dl or more and 10.0 dl or less, where dl is the maximum diameter of the polygon.

11. 9. The twin-screw extruder according to claim 7 or 8, wherein the polygon is any one of a square, a pentagon, a hexagon, a heptagon, and an octagon.

12. 9. The twin-screw extruder according to claim 7 or 8, wherein dl / ds is 1.3 or less, where dl is the maximum diameter of the polygon and ds is the minimum diameter of the polygon.

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