Screw elements and twin screw extruders

Abstract

Provided is a technology for improving the uniformity of a kneaded material and reducing temperature unevenness in a twin-screw extruder. [Solution] A screw element 30 is provided which is used for kneading a thermoplastic resin composition, the cross section perpendicular to the rotation axis AX being polygonal, the polygon having no recesses, the center of the polygon coinciding with the rotation axis AX, and the polygon having an outer shape rotated around the rotation axis AX as it progresses in the direction of the rotation axis.

Description

[Technical field]

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

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

[0003] [Patent Document 1] JP 2023-19635 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, a twin-screw extruder is used when kneading objects with good dispersibility and mixing different components uniformly, 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 consideration of the above circumstances, and aims to provide a technique 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, comprising: 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 claim 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 described in 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 of the polygon. 7. A cylinder; a first screw and a second screw arranged in parallel inside the cylinder; having 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 composition, The screw element is 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 claim 7, wherein the corners of the polygonal shape are rounded or chamfered. 9. A twin-screw extruder as described in 7. or 8., wherein the sides of the polygon are bulging 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. A 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. A twin-screw extruder as described in 7. or 8., in which 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. Effect of the Invention

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

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

[0009] <Summary> An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of the internal structure of a twin-screw extruder 1. The right side of FIG. 1 is the upstream side when explaining the twin-screw extruder 1, and the left side is the downstream side. The rotation axis direction (also simply referred to as "axial direction") of the screw 10 included in the twin-screw extruder 1 coincides with the left-right direction of FIG. 1. FIG. 2 is a cross-sectional perspective view showing the structure of the cylinder 2 and the screw 10 in the kneading section 3, and is a cross-sectional perspective view taken along the X1-X1 line in FIG. 1. FIG. 3 is a cross-sectional view showing the structure of the cylinder 2 and the screw 10 in the kneading section 3, and is a cross-sectional view taken along the X1-X1 line in FIG. 1. FIG. 4 is a perspective view of a part of the screw element 30. Note that the screw element 30 of this embodiment is mainly characterized by its outer shape, and in FIG. 4, the spline shaft 20 and the structure (inner hole) that fits therewith are omitted. FIG. 5 is a view showing a part of the screw element 30 by third angle projection. 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 development view of a portion of the circumferential surface of the screw element 30. As shown in FIG. In this embodiment, the term "thermoplastic resin composition" will be described as referring to a material kneaded with a thermoplastic resin and other raw materials, such as a mixture of "thermoplastic resin and filler", a mixture of "thermoplastic resin and additive", or a mixture of "thermoplastic resin, filler, and 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 the 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 inside 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 composed of a single cylindrical member, or may be composed of multiple cylindrical members connected in the rotation axis direction.

[0012] A hopper 6, which is a material supply port, is provided at one end (the right end in Fig. 1) of the cylinder 2, and a die 9, which is a 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 the shear heat of the screw 10, the cylinder 2, and the material, to become in a semi-molten or molten state.

[0013] <Screw> The screw 10 (first screw 11, second screw 12) is configured to have a splined shaft 20 (also called a "shaft") extending in the direction of the rotation axis, and a plurality of screw elements 30 (also called "segments") fixed in a skewered shape 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 rotation speed ratio of 1:1. The first screw 11 and the second screw 12 may rotate in the same direction or in different directions. The screw elements 30 attached to the splined shaft 20 may be used in both a twin screw extruder 1 with the same rotation direction and a twin screw extruder 1 with different rotation directions.

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

[0015] There are various types of elements, and in the screw 10, by combining multiple types of segments in different patterns, the section that feeds the material (feed section 5) and the section 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 material supplied from the upstream side (the right side in FIG. 1) toward the downstream side (the left side in FIG. 1) and feeds it downstream, 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 exerted in each section are attached to a splined shaft 20 (shaft).

[0018] <Feed section> The feeding section 5 includes, for example, an element, a screw flight (not shown), which 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, as an element, a screw element 30 for kneading a thermoplastic resin composition. When the screw 10 is rotated, the screw element 30 can introduce a material between the screw 10 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 in the kneading section 3 are shaped such that the cross section perpendicular to the rotation axis AX is polygonal, the center of the polygon coincides with the rotation axis AX, the polygon does not have a recess (groove), and the polygon has an outer shape rotated around the rotation axis AX as it proceeds in the direction of the rotation axis AX. With this configuration, the following effects can be achieved. (1) By making the outer shape of the screw element 30 polygonal, the "maximum diameter (long diameter) / minimum diameter (short diameter)" can be designed to be small, and the clearance between the screw element 30 and the cylinder 2 can be reduced. In addition, by making the screw element 30 polygonal in shape and twisted in the lead direction, a stretching effect is exerted on the material in the lead direction, and the material can be uniformly kneaded. (2) Since the "maximum diameter (long diameter) / minimum diameter (short diameter)" of the polygon can be made small and the fluctuation in the clearance between the screw element 30 and the cylinder 2 can be reduced, it is possible to prevent uneven temperature of the material during kneading. In the following, an example of a hexagon as a polygonal cross-sectional shape of the screw element 30 will be shown, followed by explanations of examples of an octagon and a rectangle as modified examples.

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

[0022] <Material> The material fed from the hopper 6 may be, for example, a thermoplastic resin, a filler, or an additive. Specifically, for example, a material in which a thermoplastic resin is combined with a filler, an additive, or even a different type of thermoplastic resin may be fed. Examples of thermoplastic resins include polyphenylene ether resins (polyphenylene ether, blends of polyphenylene ether and polystyrene resins), polystyrene resins (general purpose polystyrene, high impact polystyrene, acrylonitrile / styrene copolymers, acrylonitrile / butadiene / styrene copolymers, etc.), polycarbonate resins, polyolefin resins (polypropylene resins, polyethylene resins, etc.), polyester resins, homopolymer polyoxymethylene, copolymer polyoxymethylene, polyphenylene sulfide, polyamide resins, polyamideimides, polyarylates, polyarylsulfones, polyethersulfones, polyetherimides, polytetrafluoroethylenes, polyetherketones, etc., and particularly, polyphenylene ether resins, polycarbonate resins, polyamide resins, homopolymer polyoxymethylene, copolymer polyoxymethylene, acrylonitrile / butadiene / styrene copolymers, etc. are 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 fibers, carbon fibers, metal fibers, potassium titanate whiskers, magnesium sulfate whiskers, aluminum borate whiskers, calcium carbonate whiskers, silicon carbide whiskers, zinc oxide whiskers, calcium silicate (wollastonite), mica, talc, glass flakes, calcium carbonate, clay, kaolin, barium sulfate, silica, alumina, magnesium oxide, magnesium sulfate, copper iodide, potassium iodide, (flame retardant) magnesium hydroxide, and the like. In particular, glass fibers, carbon fibers, calcium silicate, mica, talc, glass flakes, calcium carbonate, kaolin, silica, copper iodide, and potassium iodide are preferred. The additives are not particularly limited, and examples thereof include lubricants, antiblocking agents, antistatic agents, pigments, dyes, colorants, heat stabilizers, ultraviolet absorbers, weather resistance stabilizers, antioxidants, anti-dye agents, crystal 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 heating device 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 portion (not shown) that blocks the material and adjusts the degree of kneading, and an opening portion (not shown) that discharges gas volatilized from the kneaded 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 a cylindrical cavity is connected. The first cylinder 21 has a first screw 11, and the second cylinder 22 has a second screw 12.

[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 line-symmetrical positional relationship with respect to a perpendicular line drawn at 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), and out of phase means that the two screw elements 30 are not in a line-symmetrical positional relationship. In this embodiment, as described later, the ratio dl / ds of the maximum diameter dl to the minimum diameter ds of the screw elements 30 is small, so that out of phase arrangement is possible.

[0030] As shown in FIG. 4, the first screw element 31 has no recess and has an outer shape obtained by rotating a regular hexagon around 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 around the first rotation axis AX1. In other words, the apexes of the hexagon advance in a spiral shape on the outer circumferential surface of the first screw element 31. 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 apexes of the hexagon advance in a spiral shape, is set to match the screw rotation direction so that the material can be fed by the spiral lead of the screw element 30 in accordance with the drive rotation direction of the screw 10.

[0031] The second screw element 32, like the first screw element 31, does not have a recess, and has an outer shape obtained by rotating a regular hexagon about the second rotation axis AX2 as it advances in the direction of the second rotation axis AX2. The second screw element 32 has a shape in which the outer diameter of the hexagon is twisted about the second rotation axis AX2. In other words, the apex of the hexagon advances in a spiral shape on the outer circumferential surface of the second screw element 32. The spiral is formed in a feed screw (forward lead direction).

[0032] A more specific shape of the screw element 30 will now 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 example shown in Fig. 4 and Fig. 5, 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 ridgeline formed by the first to sixth vertices 41 to 46 is a curve 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 line has a certain 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 the first surface 51, the region between the second vertex 42 and the third vertex 43 is the second surface 52, the region between the third vertex 43 and the fourth vertex 44 is the third surface 53, the region between the fourth vertex 44 and the fifth vertex 45 is the fourth surface 54, the region between the fifth vertex 45 and the sixth vertex 46 is the fifth surface 55, and the region between the sixth vertex 46 and the first vertex 41 is 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 any one of a square, pentagon, hexagon, heptagon, and octagon, and the center of the polygon coincides with the rotation axis AX. By making the polygon square or larger and by making the center of the polygon coincide with the rotation axis 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), and the elongation effect of the material is improved. On the other hand, if the polygon is larger than an octagon, the cross section approaches a circle, and the difference between the maximum diameter and the minimum diameter becomes too small, resulting in insufficient kneading. 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 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 in the above range, the material can be effectively elongated. In addition, by reducing the ratio dl / ds, the fluctuation of the clearance between the cylinder 2 and the screw element 30 is small, and the occurrence of temperature unevenness in the material can be suppressed.

[0036] <Polygon corner shape (round shape, chamfer shape)> The polygonal shape of the cross section of the screw element 30 may be not only a so-called perfect regular polygon, but also a shape with rounded or chamfered corners. A rounded shape refers to a shape with rounded corners to form a curved surface (curve). A chamfered shape refers to a shape with corners cut off, and may be a curved surface or a shape with multiple planes gradually shifted. By making the corners of the polygon rounded or chamfered, the maximum diameter dl is reduced, and the ratio dl / ds of the maximum diameter dl and the minimum diameter ds can be further reduced. As a result, the elongation effect of the material can be improved. Furthermore, the polygon may have a curved shape with the sides bulging outward. By making such a shape, the minimum diameter ds is increased, and the ratio dl / ds of the maximum diameter dl and the minimum diameter ds can be reduced. As a result, the elongation effect of the material can be improved.

[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 difficult for temperature unevenness to 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 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 rotational axis direction when the screw 10 rotates once. In other words, the lead length can be said to be the length in the rotational axis direction until a corner of a polygon returns to the same position, and can be understood as the distance in the rotational axis direction until the first apex 41 (corner) at the 0 o'clock position clockwise reaches 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 kneading (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 by elongation is exhibited.

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

[0041] The first screw 111 has five screw elements 131 (screw elements 131a to 131e) that are substantially elliptical when viewed from the direction of the rotation axis, attached to the spline shaft 120a, with the major axis direction of the ellipse shifted by 90 degrees between adjacent elements. Similarly, the second screw 112 has five screw elements 132 (screw elements 132a to 132e) that are substantially elliptical when viewed from the direction of the rotation axis, attached to the second spline shaft 120b, with the major axis direction of the ellipse 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 the screw elements 131 and 132 are not distinguished from each other, they are referred to as "screw elements 130."

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

[0043] Also, as an example, FIG. 7 shows a ratio dl / ds of 1.31 or more, and by increasing the ratio dl / ds and rotating the screw element 130, the thermoplastic resin composition is subjected to strong shear at the location of distance d01, and the sheared thermoplastic resin composition is moved to the resin pool at the location of distance d02 and mixed, thereby kneading. However, since the structure is such that the thermoplastic resin composition that is subjected to strong shear and strong heat generation at the location of distance d01 by increasing the ratio dl / ds is delivered to the resin pool, there is a problem that the thermoplastic resin composition is prone to localized heat unevenness in the resin pool, although it is kneaded. Heat unevenness leads to viscosity unevenness and flow unevenness, which is an obstacle to improving the uniformity of the material.

[0044] In addition, since the material contains a thermoplastic resin, the gel, which is an elastic body, is stretched by strong shear at the distance d01, but since 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 the results of a simulation. 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 the 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 the 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° shifted). In the out of phase case, the clearance between the first screw element 31 and the second screw element 32 can be made smaller than in the in phase case.

[0047] FIG. 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 (8-strand type). FIG. 11(a) shows the case of in-phase, and FIG. 11(b) shows the case of out-of-phase (22.5° shift). In addition, the ratio of the maximum diameter dl to the minimum diameter ds is dl / ds=1.055.

[0048] Fig. 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 a square (four-thread type). Fig. 12(a) shows the case of in-phase, and Fig. 12(b) shows the case of out-of-phase (45° shift). 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 peripheral 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 kneaded. In addition, since there are no recesses, there is no so-called resin pool, and temperature unevenness can be eliminated. In addition, the difference between the maximum diameter dl and the minimum diameter ds of the screw element 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 configurations other than those described above can also be adopted. [Explanation of symbols]

[0051] 1 Twin screw extruder 2 Cylinder 2a hole 3. Mixing section 4. Extrusion section 5 Feeding section 6 Hopper 7 Drive unit 8 Heating device 9 Material outlet 10 Screw 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 about the rotation axis as it progresses in the axial direction, When the maximum diameter of the polygon is dl and the minimum diameter is ds, dl / ds is 1.3 or less; A screw element wherein the corners of the polygon are rounded or chamfered and the sides of the polygon are bulged outward.

2. A screw element as described in claim 1, wherein dl / ds is 1.05 or more.

3. A screw element as described in claim 1 or 2, having a lead length of 2.0 dl or more and 10.0 dl or less.

4. 3. The screw element according to claim 1 or 2, wherein the polygon is any one of a square, a pentagon, a hexagon, a heptagon and an octagon.

5. A cylinder and a first screw and a second screw arranged in parallel inside the cylinder; having The first screw and the second screw each have a screw element attached to a shaft in a kneading section for kneading a thermoplastic resin, The screw element is 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 polygon around the rotation axis as it progresses in the axial direction, When the maximum diameter of the polygon is dl and the minimum diameter is ds, dl / ds is 1.3 or less; A twin screw extruder, wherein the corners of the polygon are rounded or chamfered, and the sides of the polygon are bulged outward.

6. A twin-screw extruder as described in claim 5, wherein the dl / ds is 1.05 or more.

7. A twin-screw extruder as described in claim 5 or 6, wherein the lead length is 2.0 dl or more and 10.0 dl or less.

8. The twin-screw extruder according to claim 5 or 6, wherein the polygon is any one of a square, a pentagon, a hexagon, a heptagon, and an octagon.

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