Screws for single-screw extruders and single-screw extruders

Abstract

Provided are a screw for a single-screw extruder and a single-screw extruder that can obtain excellent mixability when mixing and extruding a thermoplastic resin composition, suppress heat generation in the thermoplastic resin when mixing raw materials, and have excellent metering properties. [Solution] A screw for a single-screw extruder, characterized in that the mixing element at the tip of the screw is composed of a small diameter screw portion, a cylinder placed on the outer periphery of the small diameter screw portion, and a cylinder holder that holds the cylinder, the small diameter screw portion has a spiral flight with a twist angle, a groove, and multiple convex portions provided within the groove, the groove has a shape in which multiple curved surfaces that are shaped to cut out a portion of a sphere or ellipsoid are arranged in the twist angle direction of the flight and connected in succession, the cylinder is a hollow cylindrical cylinder that can rotate independently of the screw, and has multiple circular holes that penetrate from the outer surface to the inner surface of the cylinder.

Description

[Technical Field]

[0001] The present invention relates to a screw for a single-screw extruder for mixing a thermoplastic resin composition, and to a single-screw extruder. [Background technology]

[0002] When mixing two or more raw materials to form a thermoplastic resin composition, such as mixing thermoplastic resins (hereinafter also referred to as resins), mixing a resin with additives, or mixing a resin with powder particles, particularly when continuously producing a mixture using a thermoplastic resin as the resin, mixing is performed using an extruder equipped with a screw from the viewpoint of mass productivity. Mixing using an extruder requires that the raw materials heated and melted in the extruder be thoroughly mixed so that the thermoplastic resin composition after mixing is discharged in a uniform state. If the mixture is extruded from the extruder in an insufficiently mixed and non-uniform state, problems such as a decrease in the physical properties of the mixture due to uneven concentrations of the components and separation of additives from the mixture, resulting in insufficient effects, can occur.

[0003] One example of a screw-based mixing device is the single-screw extruder. A single-screw extruder has a single screw inside a cylinder. By rotating the screw, raw materials fed into the feed section upstream of the extruder are forcibly transported along the flow path in the screw's helical direction, where they are mixed in the kneading section while being melted and plasticized by the heat from the cylinder. The molten mixture is then metered under pressure in the metering section downstream of the extruder, and discharged as a strand from a die at the tip. However, although single-screw extruders are excellent for continuous production, unlike other mixers, the spiral direction of the screw is fixed, so a high mixing effect cannot be obtained. Furthermore, because the structure is such that all of the flow paths in the screw are filled with raw materials and mixing is performed under high pressure, particularly when the raw materials contain thermoplastic resins, high-temperature shear heat caused by localized shearing can cause the resin temperature of the raw materials to rise excessively, and uneven resin temperatures within the raw materials can occur, preventing uniform shearing. In addition, there are problems with localized heat generation, such as burning of the resin and powder particles.

[0004] Furthermore, a strand made of the molten thermoplastic resin composition discharged from the die of the single-screw extruder is cooled and solidified in a cooling water tank, and after cooling, is taken up by a take-up roll in a strand cutter and cut to a predetermined length by a cutter rotating at a constant speed, thereby producing pellets. The raw materials for the strands are in a molten state when they are discharged from the die, and in a solidified state in the cooling water tank; therefore, the viscosity and melt tension change significantly between the die and the take-up rolls. Therefore, if the molten thermoplastic resin composition is discharged from the die at an unstable flow rate, the strands will move wildly before and after the cooling water tank due to uneven tension, resulting in molding problems such as strand breakage and uneven pellet shape and diameter. Therefore, in an extruder, it is necessary to ensure a sufficiently stable flow rate in the metering section of the extruder before discharging the thermoplastic resin composition from the die. In particular, the produced pellets are used in an extruder such as a molding machine in the next process. If the pellet shape or diameter is non-uniform, the uneven pellet shape will make the metering unstable when the raw material is supplied in the next process, which will result in uneven molding and uneven mixing in the resulting molded product. Therefore, when producing strands, a single-screw extruder is required that has excellent metering properties and discharges at a stable flow rate.

[0005] As described above, single-screw extruders are required to suppress the resin temperature to achieve uniform mixing performance, as well as stable discharge. To address this, various modifications have been made to improve the mixing and metering performance of the screw. Patent Document 1 discloses a uniaxial plasticizing screw used to obtain molded products, which includes an eccentric flight in the metering section, a rotor with multiple cavities as a mixing section at the tip of the metering section, and a ring with multiple cavities on its inner circumferential surface that is rotatably inserted into the rotor. The ring is allowed to slide axially relative to the rotor to the extent that the gap ε is zero. The rotor has independent cavities arranged in a staggered pattern, and the ring has cavities arranged at half the pitch of the rotor cavities. This allows the ring to rotate at a speed significantly slower than the rotation of the screw and rotor. As shown in Figure 4 of Patent Document 1, the cavities of the rotor and ring are arranged perpendicular to the shear direction, resulting in a complex flow of division and orientation in the mixing section, resulting in efficient mixing. However, in Patent Document 1, resins are mixed in the mixing section after being kneaded under sufficiently low temperature conditions using specially shaped concentric and eccentric flights just before the mixing section. As shown in Figure 4(a) of Patent Document 1, the mixing section has a structure in which cavities are provided in both the rotor and the ring so that the resin flow in the screw axis direction is blocked and the resin flows in a direction perpendicular to the screw axis. Therefore, in order to send the resin to the downstream end of the mixing section, a strong shearing force is required to push the resin from the rear of the mixing section, which makes the resin prone to heat generation. Furthermore, because the mixing is performed using a complex flow that blocks the flow in the screw axis direction, residual stress accumulates in the molten resin after passing through the mixing section, resulting in poor metering ability. In applications where the above-mentioned strands are to be obtained, there are problems such as the strands discharging from the die becoming uncontrollable.

[0006] Similar to Patent Document 1, Patent Document 2 discloses an invention relating to a single-screw kneading extruder having a rotor with a plurality of hemispherical cavities carved therein and a cylindrical body with radial through-holes as cavities, which is rotatable relative to the rotor, in a screw, and is characterized in that the cylindrical body is divided in the radial direction. Patent Document 2 discloses that the flowing resin flows are mixed in the rotor and the through-holes of the cylindrical body in the same way as Patent Document 1, and furthermore, because the cylindrical body is a divided cylindrical body, there is a phase shift between them in the axial direction, resulting in even greater mixing. However, because the cavity has the same shape as that of Patent Document 1, the resin is prone to heat generation, and residual stresses that accumulate in the molten resin after passing through the mixing section result in poor metering ability.In addition, because the divided cylinders are out of phase with each other, in applications where strands are to be obtained, there are problems such as the strands dislodging when discharged from the die.

[0007] Patent Documents 3 and 4 relate to inventions in which the screw of a single-screw extruder is provided with a continuous groove in which adjacent recesses are formed, and the recesses form an inclination angle larger than the twist angle of the groove. Figure 1 of Patent Document 3 and Figure 2 of Patent Document 4 disclose that the groove is formed at the tip of the screw. Patent Document 3 also discloses that the screw groove 7 in the main part of the screw forms an inclination angle β with respect to the axis, a so-called twist angle, and that the groove has a large number of adjacent oblong groove-like recesses 9 formed within it, and the inclination angle γ with respect to the axis is larger than the inclination angle β. Furthermore, the torsion angles β and γ shown in Figure 4 of Patent Document 4 are shown opposite to the inclination angles β and γ in Figure 2 of Patent Document 3, and the angle reference in Patent Document 3 is based not on the axial direction of the screw but on a right angle to the axial direction. However, paragraph

[0025] of Patent Document 4 reveals that the uneven bottom surfaces are aligned at a torsion angle γ, and each of the numerous grooves having the uneven bottom surfaces is inclined in a direction perpendicular to the axis of the screw, and it can be seen that the one shown in Figure 4 of Patent Document 4 has the same shape as Figure 2 of Patent Document 3. Figure 1 of Patent Document 3 and Figure 2 of Patent Document 4 further disclose that groove-like recesses (referred to as recessed grooves in Patent Document 4) are provided in the cylinder around the grooves so as to straddle the grooves of the screw, and that by providing a continuous series of oblong grooves in the screw whose oblong grooves have a larger inclination angle in the axial direction in which the grooves are aligned, i.e., the helical twist angle, a pushing effect is obtained, which not only causes the resin material in the grooves to flow into the groove-like recesses of the cylinder, but also transports the resin from the groove-like recesses to grooves adjacent to the oblong grooves, promoting breakup and dispersion, and that the resin material is subjected to a rolling and rotating action in the flow of the resin material, so that the additives are rapidly enveloped in the resin, thereby promoting kneading. However, the flow of the resin material is such that the major axis of the oblong ellipse in the screw groove is inclined at an angle greater than the helix angle, as shown by γ in Figure 2 of Patent Document 3, and much of the material shown as 9a in Figure 2 of Patent Document 3 flows upstream to 9c through a groove-like recess in a fixed cylinder. Although this method is effective in mixing resins and additives with extremely different viscosities due to its rolling rotation action, it is not suitable for efficiently mixing two or more resins with similar viscosities, or resin and particles. Furthermore, as with Patent Documents 1 and 2, the resin material is prone to heat generation, and residual stresses accumulate in the molten resin due to the complex rolling effect, which causes problems such as the strands discharging from the die becoming uncontrollable in applications where strands are to be obtained.

[0008] Furthermore, although different from the mixing extruder, an example of a structure having a rotatable rotor at the tip of the screw as in Patent Documents 1 and 2 is the screw head of an injection molding machine having a check ring for preventing backflow, as disclosed in Patent Document 5. Patent Document 5 discloses a backflow prevention device in which a slidable check ring and a spiral convex portion are provided on the screw head in the small diameter portion inside the check ring, but the spiral convex portion is provided to prevent stagnation of molten resin in the check ring and eliminate color mixing defects and color retention defects in molding that performs intermittent operations such as injection molding, and is not excellent for applications in which resin is continuously extruded, such as extrusion molding. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 7-256717 [Patent Document 2] Japanese Patent Application Publication No. 6-106527 [Patent Document 3] Japanese Patent Application Publication No. 4-62131 [Patent Document 4] Japanese Patent Application Publication No. 5-228920 [Patent Document 5] Japanese Patent Application Publication No. 2023-27789 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a screw for a single-screw extruder and a single-screw extruder that can obtain excellent mixability when mixing and extruding a thermoplastic resin composition, suppress heat generation in the thermoplastic resin when mixing raw materials, and have excellent metering properties. [Means for solving the problem]

[0011] The present inventors have found that the above object can be achieved by using the following screw for a single-screw extruder, and have thus completed the present invention.

[0012] That is, the present invention is A screw for a single-screw extruder equipped with a mixing element at the tip of the screw, the mixing part is composed of a screw small diameter portion, a cylindrical body arranged on the outer periphery of the screw small diameter portion, and a cylindrical body holder that holds the cylindrical body, The screw small diameter portion is The flight has a spiral shape with a helix angle, a groove, and a plurality of protrusions provided in the groove, the grooves have a shape in which a plurality of curved surfaces, each of which is a cutout of a spherical or ellipsoidal shape, are arranged in the twist angle direction of the flight and are connected in series, a plurality of convex portions formed as ridges of connecting portions between the curved surfaces of the groove are provided in the groove; The convex portion is an arc-shaped ridge formed between adjacent flights, The ridge of the convex portion has a height lower than that of the flight, The cylindrical body is A hollow cylindrical body that can rotate independently of the screw, a plurality of circular holes penetrating from the outer peripheral surface to the inner peripheral surface of the cylindrical body; The cylinder holders are provided on the upstream and downstream sides of the cylinder in the screw axial direction so as to limit movement of the cylinder in the screw axial direction. A screw for a single-screw extruder characterized by It is related to. The single-screw extruder of the present invention is characterized by comprising the above-mentioned screw for a single-screw extruder. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a screw for a single-screw extruder and a single-screw extruder that can obtain excellent mixability when mixing and extruding a thermoplastic resin composition, suppress heat generation in the thermoplastic resin when mixing raw materials, and have excellent metering properties. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a single-screw extruder equipped with a screw for a single-screw extruder of the present invention. [Figure 2] Schematic diagram of a cross section of the mixing element in a single-screw extruder screw [Figure 3] Third angle view and cross section of the cylinder in the mixing part [Figure 4] Circumferential development of the small diameter screw part of the mixing part and a cross-sectional view [Figure 5] Third angle view of screw cap in mixing part [Figure 6] A diagram showing the flow of raw materials in the circumferential development of the small diameter part of the screw. [Figure 7] A cross-sectional view of the small diameter screw of the mixing part, showing the flow of raw materials. [Figure 8] A cross-sectional conceptual diagram of the mixing part showing the flow of raw materials [Figure 9] Conceptual diagram showing the cross-sectional structure of the mixed part and the rotation of each part [Figure 10] FIG. 1 is a diagram showing pellet processing using a single-screw extruder equipped with the screw for a single-screw extruder of the present invention. [Figure 11] 1 is a development view of a screw small diameter portion of a mixing part in a modified example in the screw circumferential direction and a cross-sectional conceptual diagram DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that this embodiment is merely one embodiment for carrying out the present invention, and the present invention is not limited to this embodiment, and various modifications and embodiments are possible within the scope of the gist of the present invention. Furthermore, in this specification, the expression "a to b" in the description of a numerical range means not less than a and not more than b, unless otherwise specified. In each drawing in this specification, the right side of the drawing is shown as upstream 95 where raw materials are supplied, and the left side is shown as downstream 94 where the raw materials are discharged from the single screw extruder.

[0016] [Single-screw extruder] Figure 1 shows a cross-sectional view of a single-screw extruder 1 equipped with a screw for a single-screw extruder (hereinafter also referred to as "screw") of the present invention. As shown in Figure 1, the single-screw extruder 1 has a hollow cylinder 2 and a screw 3 housed in the cylinder, and the rotational power of a motor and reducer 9 provided in the single-screw extruder 1 is transmitted to the screw 3 by connecting the reducer output shaft to the screw 3 at a screw connection part 91, causing the screw 3 to rotate. The screw 3 has a forward-direction spiral screw flight 5 and screw groove 6, and by rotating the screw 3 in the forward direction by rotational power, a raw material (hereinafter also referred to as "raw material") containing a thermoplastic resin supplied in a fixed amount from a hopper 4 is sent in the forward direction of the spiral through a flow path between a cylinder 2 heated by a heater 8 wrapped around the cylinder and the screw groove 6, and transferred downstream 94 in the screw axial direction. As the raw material transferred between the cylinder 2 and the screw groove 6 is transferred downstream, it is heated by the heat from the heater 8 wrapped around the cylinder and by shear heat between the raw material and the cylinder and between the raw material and the screw, causing the thermoplastic resin (hereinafter also referred to as "resin") in the raw material to melt, plasticize the raw material, move, and mix, and the mixture passes through a die 10 installed downstream and is discharged as a thermoplastic resin composition.

[0017] The screw 3 is divided into three zones: a supply section 11 that conveys and supplies the raw materials supplied from the hopper 4; a kneading section 12 that melts and plasticizes the resin in the raw materials; and a metering section 13 that mixes and weighs the plasticized raw materials. The tip of the screw 3 in the metering section 13 is equipped with a mixing element 7, which will be described below.

[0018] <Screw for single-screw extruder equipped with the mixing element of the first embodiment> A conceptual diagram of the mixing element 7 provided at the tip of the screw 3 for a single-screw extruder of the first embodiment is shown in Fig. 2. Fig. 2 is an enlarged conceptual cross-sectional view of the mixing element 7 shown in the single-screw extruder 1 of Fig. 1, and further shows a cross-sectional view of only the cylindrical body 22 of the mixing element 7. 3(a) to 3(c) show views of the cylindrical body 22 in third angle projection, and Fig. 3(d) shows a cross-sectional view of the cylindrical body 22. Fig. 3(a) shows a left side view of the cylindrical body 22, Fig. 3(b) shows a front view, Fig. 3(c) shows a right side view, and Fig. 3(d) is a cross-sectional view taken along imaginary line LL' which bisects the cylindrical body 22 in Figs. 3(a) and 3(b).

[0019] The mixing part 7 is composed of a screw small diameter section 21 that is smaller in diameter than the upstream screw, a cylinder 22 that is placed on the outer periphery of the screw small diameter section 21, and a cylinder holder that limits the movement of the cylinder 22 in the axial direction of the screw, and the cylinder holder is further composed of two parts: a ring part 24 and a screw cap 23. Each part will be described in detail below.

[0020] (cylindrical body) The cylindrical body 22 shown in Fig. 3 is a hollow cylindrical body and has a large number of circular holes 51 penetrating from the outer peripheral surface 55 to the inner peripheral surface 54 of the cylindrical body 22. In this embodiment, the circular holes 51 are exemplified by a plurality of circular holes 51 arranged in a checkerboard pattern, with the diameter of the inner peripheral surface 54 being larger than the diameter of the outer peripheral surface 55 of the cylindrical body 22. Note that Figs. 3(b) and (d) show an example in which five rows of circular holes 51 are arranged in the screw axial direction, while Figs. 3(a) and (c) show an example in which twelve rows of circular holes 51 are arranged in a checkerboard pattern at 30° intervals in the circumferential direction. The cylindrical body 22 is a cylinder that can rotate independently of the screw 3, and the outer diameter of the cylindrical body 22 is smaller than the diameter of the cylinder 2 so as to provide a clearance between the cylindrical body 22 and the cylinder 2 of the single-screw extruder, and the inner diameter of the cylindrical body 22 is larger than the diameter of the flight 30 of the small diameter portion 21 of the screw. In addition, in this embodiment, as shown in Figures 2 and 3(d), in order to provide a flow path for the raw material described later, an example is given in which an upstream end face 56 and a downstream end face 57 of the cylindrical shape of the cylindrical body 22 are tapered toward the inner surface 54 of the cylindrical body 22. The cylindrical body 22 is disposed between two cylindrical body holders as viewed in the screw axial direction, as shown in Fig. 2. The length of the cylindrical body 22 as viewed in the screw axial direction is shorter than the distance between the two cylindrical body holders so as to provide a flow path for the raw material to flow between the two cylindrical body holders and the cylindrical body.

[0021] (Cylindrical body holder) The cylinder holder of the mixing part 7 of this embodiment will be described below with reference to FIG. The cylinder holders in the mixing part 7 are arranged on the upstream and downstream sides of the cylinder 22 as viewed in the screw axis direction, respectively, as shown in Figure 2 as a ring portion 24 and a screw cap 23, so as to restrict movement of the cylinder 22 in the screw axis direction via the raw material between the cylinder 22 and the cylinder holders. The distance between the ring portion 24 and the screw cap 23 in the screw axial direction is arranged so that raw material supplied from upstream of the screw flows between the inner surface 54 of the cylindrical body 22 and the groove 31 of the small diameter portion 21 of the screw via the outer periphery of the ring portion 24, and the raw material that passes between the small diameter portion 21 of the screw and the inner surface 54 of the cylindrical body 22 is discharged downstream through the gap between the cylindrical body 22 and the screw cap 23.

[0022] (Ring part) The ring portion 24, which serves as a cylinder holder, is arranged upstream of the cylinder 22 and the small diameter screw portion 21, has a ring shape, and connects with the screw upstream of the ring portion 24 and the small diameter screw portion 21 downstream. 2, the outer diameter of the ring portion 24 is smaller than the inner diameter of the cylinder 2, but larger than the cylindrical inner diameter of the cylinder 22 so as to hold the cylinder 22. Furthermore, in this embodiment, an example is shown in which the outer diameter of the ring portion 24 is smaller than the outer diameter of the cylinder 22, and the downstream surface of the ring portion 24 is tapered to correspond to the cylinder 22, so as to provide a raw material flow path between the ring portion 24 and the cylinder 22. Furthermore, in this embodiment, an example is shown in which the upstream side of the ring portion 24 is also tapered so as to allow raw material from the screw groove 6 of the screw 3 upstream of the ring portion 24 to flow smoothly into the raw material flow path between the ring portion 24 and the cylinder 2.

[0023] (Screw cap) The screw cap 23 in this embodiment will be described with reference to Figures 2 and 5. Figure 5(a) is a left side view of the screw cap 23, Figure 5(b) is a front view, and Figure 5(c) is a right side view. 2, the screw cap 23 is disposed downstream of the cylindrical body 22 and the screw small diameter portion 21, and has a bottom surface 64 perpendicular to the screw axial direction so as to limit downstream movement of the cylindrical body 22 in the screw axial direction. The maximum outer diameter of the screw cap 23 is smaller than the diameter of the cylinder 2, and the diameter of the bottom surface 64 is the same as the outer peripheral surface 55 of the cylindrical body 22. In this embodiment, as shown in FIG. 5, the screw cap 23 has the shape of a cylinder and a hexagonal cylinder with a smaller diameter than the cylinder, and has a structure in which the downstream side is a hexagonal cylinder and the upstream side is a cylinder. In addition, the bottom surface 64 on the upstream side of the screw cap 23 has a cylindrically carved screw small diameter portion contact surface 63 into which the screw small diameter portion 21 is fitted, and an example is shown in which the center of the screw small diameter portion contact surface 63 has a hole with a female thread 62 into which the male thread at the tip of the screw small diameter portion 21 is fitted. By threading the small diameter screw portion 21 into the small diameter screw portion contact surface 63, the small diameter screw portion contact surface 63 acts as a counterbore, connecting the tip of the small diameter screw portion 21 and the screw cap 23.

[0024] (Small diameter part of the screw) As shown in Figure 2, the small screw diameter section 21 of the mixing part 7 has a diameter smaller than the diameter of the screw flight 5 of the screw 3 located upstream of the small screw diameter section 21, has the same rotation axis as the screw 3, and rotates in the same direction and at the same speed as the rotation of the screw 3. Fig. 4(a) shows a planar development of the screw minor diameter portion 21 of this embodiment in the circumferential direction of the screw. Fig. 4(b) shows a conceptual diagram of a cross section taken along imaginary line M-M' in the direction of helix angle 80 in the development of Fig. 4(a), and Fig. 4(c) and Fig. 4(d) show conceptual diagrams of cross sections taken along imaginary lines N-N' and O-O' in the direction perpendicular to helix angle 80 in the development of Fig. 4(a). Note that Figure 4(a) illustrates a six-thread screw small diameter section in which each groove 31 has the same shape, and in Figure 4(a) the upper and lower parts of the figure are connected in the circumferential direction, and the imaginary line M-M' is a line passing through the center of the width of the groove 31 when viewed in the direction of the helix angle of 80. FIG. 4(b) is a cross-sectional view taken along line MM' in FIG. 4(a), and the flight 30 and the protrusion 32 extending to the flight 30 are also shown in imaginary lines. In Figures 4(b), (c), and (d), the top indicates the direction toward the cylinder side of the extruder screw, and the bottom indicates the direction toward the axial center of the screw. Figures 4(b), (c), and (d) are conceptual diagrams that correspond to Figure 4(a), which is expanded circumferentially around the screw. Figure 4(c) is a cross-sectional view of the N-N' section at the widest point of groove 31 in Figure 4(a), and Figure 4(d) is a cross-sectional view of the O-O' section along the convex portion in Figure 4(a). Furthermore, although not shown in the drawings, the screw small diameter portion 21 exemplified in this embodiment has a male screw with a seat at the downstream tip, and the male screw and the female screw 62 of the screw cap 23 described above are tightened and screwed together with a certain torque to form the mixing part 7.

[0025] 2 and 4(a), the screw small diameter portion 21 includes a forward spiral flight 30, a groove 31, and a plurality of protrusions 32 provided within the groove 31. The outer diameter of the flight 30 in the screw small diameter portion 21 is smaller than the outer diameter of the screw flight 5 of the screw 3 upstream of the screw small diameter portion 21, and the flight 30 is a spiral flight with a constant height. As shown in Figure 4(a), the groove 31 has a shape in which a number of curved surfaces 33, each shaped like a cutout of an ellipsoid, are connected in succession so that each curved surface 33 is aligned in the direction of the twist angle 80 of the spiral flight 30, and the connecting portions between each curved surface 33 have the protrusions 32 as ridges of the connecting portions. In this embodiment, the curved surface 33 having a shape obtained by cutting out a part of an ellipsoid is exemplified as an ellipsoid having a shape in which the major axis is oriented in the direction of the twist angle 80 of the spiral flight 30 . The helix angle 80 is defined as the angle at which the spiral flight 30 is inclined relative to the screw axial direction, and in Figure 4(a) the left side of the figure is the downstream side 94 in the screw axial direction, and the right side is the upstream side 95 in the screw axial direction.

[0026] In the groove 31, multiple curved surfaces 33 are arranged parallel to the helix angle 80, and as shown in Figure 4(b), the curved surfaces 33 connect the curved surfaces with the deepest groove shape within the curved surfaces, so that a convex portion 32 is formed as a ridgeline extending between two adjacent flights 30 at the connection between the curved surfaces 33. As shown in Figure 4(d), the convex portion 32 has a ridgeline in the shape of a circular arc convex toward the axial center of the screw, and has a height lower than that of the flights 30. As shown in Figure 4(c) and (d), the cross-sectional shape of the curved surfaces 33 and convex portions 32 across the groove 31 is a circular arc convex toward the axial center of the screw. In this embodiment, the major axis of the ellipsoid is oriented in the direction of the twist angle 80 of the spiral flight 30, and the curved surfaces 33 are arranged at equal intervals, so that the ridge lines of the convex portions 32 are arranged so as to be perpendicular to the twist angle 80, as shown in Figure 4(a). Also, in this embodiment, the curved surfaces 33 of the groove 31 are all of the same depth.

[0027] Since a plurality of curved surfaces 33 are connected within the groove 31, a plurality of the convex portions 32 provided as ridge lines of the connecting portions of the curved surfaces 33 are also provided within the groove 31. Furthermore, as shown in Figure 4(a), the boundary lines 34 where the flight 30 intersects with each of the curved surfaces 33 of the groove 31 have a shape consisting of a series of concave arcs that are recessed toward the flight 30, and the width of the groove 31 between the boundary lines 34 is narrowest at the connection of the curved surfaces 33 when viewed as a flow path flowing in the direction of the torsion angle 80. In this specification, the width of the groove means the width in the direction perpendicular to the twist angle.

[0028] <Actions and Effects of Mixing Part in First Embodiment> The effects of the mixing part 7 in the first embodiment will be described in the order of the effects of the small diameter screw portion 21 and the effects of the cylindrical body 22. The effect of the screw minor diameter portion 21 will be explained with reference to Figures 2, 6, 7, and 8. Figure 6 is a diagram in which the flow of raw material is indicated by arrows in Figure 4(a), and Figures 7(a) and 8 are additions to the diagram in Figure 4(b). Figure 7(a) shows the inner circumferential surface 54 of the cylindrical body 22 when the circular hole 51 of the cylindrical body 22 is not located near the curved surface 33, and Figure 8 shows the case when the circular hole 51 of the cylindrical body 22 is located near the curved surface 33. Figure 7(a) shows the inner circumferential surface 54 of the cylindrical body 22, and Figure 8 shows the inner circumferential surface 54 and outer circumferential surface 55 of the cylindrical body 22, with the cylindrical body 22 added as hatching. Figure 8 also adds as hatching the wall surface of the cylinder 2 to which the outer circumferential surface 55 of the cylindrical body 22 is adjacent. 7(b) is a view shown in FIG. 4(c), and FIG. 7(c) is a view shown in FIG. 4(d), with the inner circumferential surface 54 of the cylindrical body 22 additionally indicated by hatching. 7(a) and 8, the flights 30 and the protrusions 32 extending to the flights 30 are also shown by imaginary lines, as in FIG. 4(b).

[0029] In the mixing element 7 of this embodiment, the raw material flowing into the mixing element 7 from the upstream screw groove 6 passes through the flow path between the outer circumferential surface of the ring portion 24 and the cylinder 2 shown in Figure 2, and flows through the raw material flow path formed between the ring portion 24, which is exemplified as having a tapered shape, and the upstream end face 56 of the cylindrical body 22. The raw material then branches according to the number of grooves 31 in the small diameter screw portion 21, and flows in the spiral direction toward the downstream 94 side through the raw material flow path formed between the grooves 31 provided in the spiral direction and the two flights 30 adjacent to the grooves 31 and the inner circumferential surface 54 of the cylindrical body 22, as shown by arrows A and B in Figure 6. Of the raw material flowing in the spiral direction, the flow of raw material at the center as viewed from the width direction of groove 31 indicated by arrow A passes over curved surface 33 provided in groove 31, then passes over the center of multiple protrusions 32 provided, and flows to the adjacent curved surface 33 downstream. As shown in Figure 7(a), the center of the convex portion 32 is lower than the flight 30, but since it is a ridge line provided between the curved surfaces 33 that have an upward and downward cut-off shape so that the height direction of the raw material flow path narrows, as shown by the arrows indicating the flow of raw material before and after the convex portion 32 in Figure 7(a), the raw material flowing downstream between the inner surface 54 of the cylinder 22 and the bottom of the curved surface 33 flows along the upward cut-off curved surface in front of the convex portion and into the narrow raw material flow path between the center of the convex portion and the inner surface 54 of the cylinder 22, the raw material is compressed and agitated in front of the convex portion, so the raw material exchanges position, and then the compressed raw material is released onto the adjacent curved surface 33 immediately after passing the convex portion 32.

[0030] The curved surface 33 located downstream of the convex portion 32 is a curved surface that changes continuously in both the width direction and the depth direction, and as shown in Figure 7(a), the raw material flow path between the curved surface 33 and the inner peripheral surface 54 of the cylindrical body 22 widens toward the center of the curved surface 33. For this reason, the flow of raw material that has passed over the convex portion 32 and opened to the adjacent curved surface 33 downstream becomes a flow in which the raw material diffuses with a change in flow velocity in the width direction as the raw material flow path widens, as shown by the hatched arrows that indicate that the width of the tip of the arrow A immediately after the convex portion 32 widens on both sides, and similarly, diffusion also occurs in the depth direction toward the center of the curved surface 33, as shown in Figure 7(a). Furthermore, after the raw material passes near the center of curved surface 33, the width and height of the raw material flow path narrows along curved surface 33, and the diffused raw material changes its flow path direction and flows into convex portion 32 while being compressed, as shown by the hatched arrow in front of convex portion 32 in Figure 6.As a result, the positional exchange of the raw material further progresses due to the flow that is accompanied by changes in the flow rate and flow velocity due to the change in flow path direction.

[0031] As shown in Figure 6, boundary line 34 where flight 30 and curved surface 33 intersect is formed as a gentle curve such that the width of the raw material flow path on curved surface 33 is narrow at convex portion 32 where the curved surfaces connect, and widens midway between one convex portion and the adjacent convex portion downstream. As a result, the raw material flows with changes in flow rate and velocity, changing the flow path direction as the width of the raw material flow path changes, as indicated by arrow B in Figure 6. This change in flow promotes the exchange of raw material positions.

[0032] Furthermore, as shown by the flow of arrow B in Figure 6, when the raw material flowing near the boundary line 34 where the flight 30 and the curved surface 33 intersect flows into the convex portion 32, the raw material is compressed and released in the depth direction at the convex portion, similar to the arrows shown in Figure 7(a), and exchanges position.However, as shown in Figure 7(c), the raw material flow path consisting of the arc-shaped curved surface 33, the cross section of the convex portion 32, and the flight 30 is more compressed at the end of the raw material flow path near the boundary line 34 where the flight 30 and the curved surface 33 intersect compared to the center because the flow path is narrower.As shown by the thicker arrow B in Figure 6 around the convex portion 32, the raw material also spreads in the width direction of the groove 31 during compression, and exchanges position.

[0033] Next, the effect of the cylindrical body 22 will be described with reference to Figures 8 and 9. Figure 9 is a front view of the mixing part 7 of this embodiment, with the cylinder 2 of the single-screw extruder also shown. In Figure 9, only the cylindrical body 22 is shown as a partial cross-sectional view to illustrate the rotation direction of the cylindrical body 22 and the small diameter screw portion 21, and the area between the two broken lines is shown as a front view.

[0034] As shown in Figure 8, the cylindrical body 22 has a circular hole 51, and when the curved surface 33 and the convex portion 32 are located near the circular hole 51, part of the raw material flowing above the groove 31 flows into the circular hole 51 as shown by arrow C. The cylindrical body 22 is fitted with a clearance between the outer circumferential surface 55 and the cylinder 2 so that it can rotate independently of the screw 3 and the small diameter screw portion 21. Therefore, part of the raw material that flows into the circular hole 51 passes through the circular hole 51 and flows downstream in the flow path between the cylinder 2 and the outer circumferential surface 55 of the cylindrical body 22, but the rest of the raw material that flows into the circular hole 51 is stirred within the circular hole 51 and then returns to the raw material flow path between the groove 31 and the inner circumferential surface 54 of the cylindrical body 22 and flows downstream. The raw material in the circular holes 51 flows downstream as it flows in the spiral direction in the grooves 31, and near the convex portions 32 of the grooves 31, the convex portions 32 flow so as to push the raw material toward the circular holes 51, so that a stress is applied to the cylindrical body 22 in the downstream direction as shown by arrow D in Fig. 8. The direction of this stress is the direction of the torsion angle 80, which is the flow direction of the raw material, as shown by arrow I in Fig. 9. 9, the movement of the cylindrical body 22 in the screw axial direction is restricted by the ring portion 24 upstream of the cylindrical body 22 and the screw cap 23 downstream thereof, which act as a cylindrical body retainer, so the stress indicated by arrow I acts as a force that rotates the cylindrical body 22 in the screw axial direction, and as indicated by arrow H in Fig. 9, the cylindrical body 22 rotates in the direction opposite to the screw rotation direction (arrow G) and at a slower speed than the screw rotation. As the cylindrical body 22 rotates, the circular holes 51 also move in the direction of arrow H, while the flow of the raw material in the grooves 31 moves in the direction of the helix angle 80 as indicated by arrow I. Therefore, the raw material flowing into the circular holes 51 is subjected to large shear as the circular holes 51 move away from the grooves 31, and position exchange progresses. 8 and flows into the flow path between the outer circumferential surface 55 of the cylindrical body 22 and the cylinder 2, is also subjected to shear as the cylindrical body 22 rotates, and similarly undergoes position exchange.

[0035] As described above, in the raw material flow path above the screw minor diameter section 21, the raw material passes repeatedly through the multiple convex sections 32 provided between the grooves 31 and flights 30, the curved surfaces 33, and the multiple circular holes 51 in the cylindrical body 22, and each time undergoes position exchange at the convex sections, diffusion at the curved surfaces 33, and shearing at the circular holes 51, resulting in mixing and homogenization of the raw material after passing through the screw minor diameter section 21. Furthermore, the raw material flowing in the spiral direction along the helix angle 80 undergoes multiple gentle compression and release at the convex sections 32, resulting in three-dimensional position exchange of the raw material, and the shearing at the circular holes 51 associated with the rotation of the cylindrical body 22 is also gentle due to the flow of the raw material, so there is no localized high shear heat generation in the raw material as occurs with conventional screws. Furthermore, since the flow of the raw material proceeds without impeding the flow in the screw axial direction or the spiral direction of the twist angle 80, a stable flow of a constant amount of raw material with excellent metering properties can be obtained compared to the mixing parts of conventional screws. The raw materials that pass through the grooves 31 join together and flow downstream from the flow path between the downstream end face 57 of the cylindrical body 22 and the screw cap 23, ultimately resulting in a uniform thermoplastic resin composition.

[0036] Furthermore, the raw materials flowing through the flow path between the outer circumferential surface 55 of the cylindrical body 22 and the cylinder 2 are mixed by exchanging positions due to shear caused by the rotation of the cylindrical body 22 and the merging of the raw materials flowing out from the multiple circular holes 51, and flow stably downstream in the screw axial direction while being mixed, and then merge with the raw materials flowing over the small diameter portion of the screw and further exchange positions, and the merged raw materials pass between the outer periphery of the screw cap 23 and the cylinder 2 and are sent further downstream. The raw materials sent downstream then flow to the die 10 installed downstream of the mixing part 7 of the single-screw extruder, and a uniformly mixed thermoplastic resin composition is discharged from the die 10.

[0037] An example of the process for pelletizing a thermoplastic resin composition extruded from a single-screw extruder is shown in Figure 10. In pelletizing, the thermoplastic resin composition is extruded as strand 15 from die 10, which has a cylindrical hole attached to the tip of single-screw extruder 1, and the strand is taken up by take-up roll 18 provided in pelletizer 17, which acts as a pinch roll, while being cooled and solidified in cooling water tank 16. The strand is then cut by strand cutter 19 of pelletizer 17 to produce pellets. In this process, the thermoplastic resin composition is in a molten state when it is discharged from the die 10, and in a solidified state in the cooling water tank, and the viscosity and melt tension change significantly between the die and the take-up roll. Therefore, if the thermoplastic resin composition is not easily measured when it is discharged from the die, the strand will move wildly before and after the cooling water tank due to uneven tension caused by uneven discharge volume, resulting in molding problems such as strand breakage and quality defects such as uneven pellet shape and diameter. However, the mixing part 7 of this embodiment has excellent measuring properties as described above and is capable of stable discharge of the thermoplastic resin composition, so it can prevent these molding problems and quality defects.

[0038] In addition, in this embodiment, the downstream tip of the small diameter screw portion 21 is a male thread, the upstream bottom surface of the screw cap 23 is a female thread 62, and the tip of the screw cap 23 is a hexagonal prism.However, by using these structures, when cleaning the screw 3, the screws of the screw cap 23 can be removed with a tool such as a wrench, and the small diameter screw portion 21, cylindrical body 22, and screw cap 23 can each be disassembled and efficiently cleaned together with the ring portion 24 and screw 3.

[0039] <Modification> 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.

[0040] (Modification of the screw small diameter portion 21) The screw small diameter portion 21 in the mixing part 7 of the screw 3 of the present invention may be engraved at the tip of the screw 3, or may be configured in any way, such as by connecting the upstream side of the screw small diameter portion 21 to the screw tip or ring portion 24 as a separate member from the screw with a mechanism such as a screw.

[0041] The number of flights 30 of the screw small diameter section 21 may be multiple as disclosed in the first embodiment, or may be one flight from the viewpoint of widening the width of the raw material flow path to suppress a rise in the temperature of the raw materials due to shear. Furthermore, from the viewpoint of improving mixability, the number of flights may be two or more, but preferably 12 or less, and more preferably 2 to 6. By setting the number of flights within the above range, excellent mixing can be performed while suppressing a rise in the resin temperature, and a uniform thermoplastic resin composition can be obtained.

[0042] Figure 11 shows a planar development of the screw minor diameter portion 21 in the circumferential direction of the screw as a modified example of the curved surface 33. Note that Figure 11 shows a modified version of the curved surface 33 from Figure 4, with a different shape and different numbers of flights 30 and grooves 31. Note that the number of threads on the screw minor diameter portion 21 in Figure 11 is shown as four. The curved surface 33 of the screw minor diameter section 21 in the mixing part 7 does not have to be a curved surface shaped like a cutout of an ellipsoid as disclosed in the first embodiment, but may be a curved surface shaped like a cutout of a sphere as shown in Fig. 11. The curved surfaces 33 are arranged in the direction of the helix angle 80 of the flights 30 to form grooves 31 shaped like a number of continuously connected grooves, so that the connecting portions of the curved surfaces 33 are provided with a plurality of convex portions 32 formed as ridgelines of the connecting portions between the curved surfaces 33, and the convex portions 32 are arc-shaped ridgelines formed across the spaces between the adjacent flights 30, and the ridgelines of the convex portions 32 have a height lower than that of the flights 30. By configuring the mixing part 7 as the screw small diameter section 21 of the above-mentioned shape, as in the first embodiment, excellent mixability can be obtained when extruding a thermoplastic resin composition, and heat generation of the thermoplastic resin in the raw material during mixing can be suppressed, making it possible to create a screw for a single-screw extruder with excellent metering properties.In particular, if the curved surface 33 is spherical, the curved surface has a uniform curvature compared to an elliptical shape, and therefore diffusion of the raw material is promoted on the curved surface 33, resulting in excellent mixability.

[0043] When the curved surface 33 is a curved surface shaped by cutting out a portion of an ellipsoid, the groove 31 may be arranged by connecting multiple curved surfaces shaped such that the major axis of the ellipsoid is in the direction of the helix angle 80 of the flight 30, as in the first embodiment, or by connecting multiple curved surfaces 33 shaped such that the major axis of the ellipsoid is tilted at an angle of -20 to 20° from the direction of the helix angle 80 toward the direction perpendicular to the screw axis, so that the curved surfaces are parallel to the helix angle 80. By adjusting the major axis of the ellipsoid with respect to the helix angle within the above range, the propulsive force of the raw materials can be changed, and mixing can be adjusted.

[0044] The helix angle of the flights 30 of the screw small diameter portion 21 is preferably 25 to 80°. A helix angle of 25° or more ensures a stable flow that extrudes the raw materials necessary for mixing in the helical direction, while a helix angle of 80° or less allows the raw materials to be efficiently transported downstream by the flights 30. In addition, notches may be provided on the flights 30 around the grooves to serve as sub-leads that direct the raw materials to the adjacent downstream side.

[0045] The maximum groove width between flights of each groove 31 in the screw small diameter section 21 is preferably 1.0 to 50.0 mm. A width of 1.0 mm or more allows for stable flow in the spiral direction, resulting in excellent metering performance and suppressing a rise in the temperature of the raw material. A width of 50.0 mm or less allows for excellent mixing performance due to the effects of position exchange accompanying flow changes at the boundary between the flight 30 and groove 31 and compression and release at the convex portions. The width of the convex portion 32 in the groove 31 is the minimum value of the width of the adjacent curved surface or groove, and the ratio of the maximum width to the minimum width is preferably 1.1 to 3.0. By making the ratio 1.1 or more, excellent metering performance can be obtained and the rise in temperature of the raw material can be suppressed, while by making the ratio 3.0 or less, excellent mixing performance due to the position exchange and convex portion accompanying the flow change and width change along the boundary between the flight 30 and the groove 31 can be obtained.

[0046] The depth of each curved surface 33 in the groove 31 may be the same as in the first embodiment, or may be a combination of curved surfaces of different depths that are connected and arranged in succession to improve mixability. Furthermore, as shown in the first embodiment, it is preferable that the curved surface 33 connects curved surfaces having the same width perpendicular to the torsion angle 80, but it is also possible to combine curved surfaces whose widths vary in the range of 1:1 to 1:3 within the maximum width range.

[0047] As shown in the first embodiment, the curved surfaces 33 in the groove 31 are preferably connected at equal intervals from the viewpoint of generating a stable flow with excellent metering properties accompanied by compression and release of the raw material, but the intervals between the curved surfaces 33 may also be adjusted so that the ratio of (distance from the upstream convex portion in the direction of the torsion angle 80 to the deepest part of the curved surface 33):(distance from the deepest part of the curved surface 33 to the downstream convex portion) within one curved surface is in the range of 1:10 to 1:1. By setting this ratio, the raw material is efficiently diffused and can be efficiently compressed from the deepest part of the curved surface 33 to the downstream convex portion, so that distribution by position exchange of the raw material can also be efficiently performed.

[0048] Each curved surface 33 in the groove 31 is connected in succession with 6 to 150 curved surfaces per groove, so that the flowing raw materials are mixed while gently compressing and releasing repeatedly, exchanging their positions three-dimensionally, thereby suppressing the rise in temperature of the raw materials and making it possible to obtain a uniform thermoplastic resin composition.

[0049] 4(b) of the first embodiment, the cross-sectional shape of the convex portion 32 in the groove 31 is a downwardly convex arc, and the height of the lower surface of the arc of the convex portion is preferably 0.1 to 0.9 times the height from the deepest part of the curved surface 33 provided in the screw small diameter portion 21 to the flight 30. By setting the height to the lower surface of the arc of the convex portion 32 to 0.1 times or more, the raw materials are sufficiently compressed and released in the flow path between the convex portion 32 and the inner circumferential surface 54 of the cylindrical body 22, thereby allowing for mixing and obtaining a uniform thermoplastic resin composition. By setting the height to the lower surface of the arc of the convex portion 32 to 0.9 times or less, shear heating in the flow path can be suppressed, allowing for a thermoplastic resin composition that is free of resin burn, and preventing the temperature rise of the raw materials.

[0050] The height of the flight 30 in the small diameter screw portion 21 can be set according to the diameters of the cylinder 2 and small diameter screw portion 21 of the single screw extruder 1, and the diameter of the inner circumferential surface 54 of the cylindrical body 22, which will be described later. The spiral direction of the flight 30 only needs to be aligned with the forward direction of the flight of the screw upstream of the small diameter screw portion 21 in the screw 3, and can be set arbitrarily according to the rotation of the extruder.

[0051] The screw small diameter section 21 may have grooves 31 having the shape disclosed in this specification, and may have parts such as full flights that stably move the raw material upstream and downstream of the grooves 31, or may have other structures as long as they do not impair the effects of the present invention.

[0052] (Modification of the cylindrical body 22) The cylinder 22 in the mixing part 7 may be a hollow cylindrical cylinder that can rotate independently of the screw 3, the small diameter screw portion 21, and the cylinder holder, and from the viewpoint of rotating the cylinder 22 to stabilize the flow of the raw materials and perform efficient mixing, it is preferable that the cylinder 22 be a cylinder of one-piece structure. The thickness of the cylindrical body 22 from the inner peripheral surface 54 to the outer peripheral surface 55 is preferably 8 to 20 mm. If the thickness is 8 mm or more, the cylindrical body 22 can rotate without being deformed even by the pressure of the raw material, and if the thickness is 20 mm or less, the cylindrical body 22 can rotate by the pressure applied by the raw material in the circular hole 51, thereby obtaining excellent mixability.

[0053] It is preferable that the outer diameter of the cylindrical body 22 has a clearance of 0.1 to 1 mm relative to the inner diameter of the cylinder 2. If the clearance is 0.1 mm or more, the raw material will flow into the clearance, allowing the cylindrical body 22 to rotate smoothly without damaging the cylinder, and if the clearance is 1 mm or less, it is possible to prevent the cylindrical body 22 from galling the cylinder when the extrusion operation starts. It is preferable that the inner diameter of the cylindrical body 22 has a clearance of 0.1 to 0.5 mm relative to the diameter of the flight 30 of the small diameter portion 21 of the screw. By making the clearance 0.1 mm or more, the cylindrical body 22 can rotate smoothly without being damaged by the pressure of the raw material flowing through the groove 31, and by making the clearance 0.5 mm or less, it is possible to prevent the cylindrical body 22 from galling against the cylinder 2 when the extrusion operation starts. Furthermore, it is preferable that the length of the cylindrical body 22, when assembled into the mixing part 7, provides a clearance of 0.1 mm to 0.5 mm in the screw axial direction between the upstream end face 56 of the cylindrical body 22 and the ring portion 24, and between the downstream end face 57 of the cylindrical body 22 and the bottom surface 64 of the screw cap. By making each of the clearances 0.1 mm or more, gaps are created between the cylindrical body 22 and the ring portion 24, and between the cylindrical body 22 and the screw cap 23, allowing the raw materials to flow stably and the cylindrical body 22 to rotate smoothly without contact. By making each of the clearances 0.5 mm or less, the cylindrical body 22 can rotate smoothly without moving wildly in the screw axial direction.

[0054] In order to promote mixing by increasing the rotation speed of the cylindrical body 22 and thereby facilitating stirring within the circular hole 51, the diameter of the circular hole 51 on the outer surface 55 of the cylindrical body 22 may be smaller than the diameter of the circular hole 51 on the inner surface 54 of the cylindrical body 22, as disclosed in the first embodiment, or the diameters of the circular holes 51 on the inner surface 54 and outer surface 55 of the cylindrical body 22 may be the same. Furthermore, the internal shape of the circular hole 51 may be curved so as to receive the pressure of the raw material in the direction of the torsion angle 80, as disclosed in the first embodiment, but it may also be any shape, such as a tapered shape obtained by cutting off a cone. Furthermore, as disclosed in the first embodiment, it is preferable that the circular hole 51 penetrates so that the center line of the circular hole 51 is perpendicular to the screw axial direction, but it may have any shape that promotes stirring in the circular hole 51 and rotation of the cylindrical body 22.

[0055] The diameter of the circular hole 51 in the inner peripheral surface 54 of the cylindrical body 22 is preferably 5 to 15 mm. By setting the diameter within this range, the raw material can be sufficiently agitated in the circular hole 51 and the cylindrical body 22 can be rotated by the pressure of the raw material. Furthermore, the cylindrical body 22 may have the circular holes 51 arranged in a lattice pattern as disclosed in the first embodiment, but they may also be arranged in a staggered pattern or any other pattern as long as the cylindrical body 22 can rotate, sufficient mixing can be achieved, and the strength of the cylindrical body 22 is not impaired. From the viewpoint of smoothly rotating the cylindrical body 22 by the pressure of the raw materials and achieving a shearing effect, the number of circular holes 51 is preferably 5 to 15 in the screw axial direction and 3 to 12 in the circumferential direction.

[0056] The upstream end face 56 and the downstream end face 57 of the cylindrical body 22 preferably have a tapered shape toward the inner circumferential surface to stabilize the flow of the raw material as shown in the first embodiment, but they may also be surfaces perpendicular to the screw axial direction without being tapered. Also, the corners of the cylindrical body 22 may be rounded to prevent resin scorching.

[0057] (Modification of the cylinder holder) The cylinder holder of the mixing part 7 may have any shape as long as it restricts the movement of the cylinder 22 upstream and downstream in the screw axial direction. Below, examples of modifications will be given based on the screw cap 23 and ring portion 24 in the first embodiment.

[0058] The ring portion 24, which serves as a cylinder holder installed upstream of the cylinder 22, can be of any shape as long as it is capable of preventing the cylinder 22 from moving upstream in the screw axial direction. The ring portion 24 may have a diameter smaller than the diameter of the outer peripheral surface 55 of the cylindrical body 22 and larger than the diameter of the inner peripheral surface 54 of the cylindrical body 22 as shown in the first embodiment, so that the raw material flows from the outer periphery of the ring portion 24, but it may also be of any diameter and a through hole may be provided separately in the ring portion 24 to allow the raw material to flow from the screw groove 6 of the screw 3. As shown in the first embodiment, the ring portion 24 may have a cylindrical tapered shape so that the raw material in the screw groove 6 upstream of the ring portion 24 flows stably into the mixing element 7, but it may also have a shape without a tapered shape and having a surface perpendicular to the screw axial direction.

[0059] The ring portion 24 may be previously engraved on the screw 3 together with the screw flights 5 and screw grooves 6, or may be fitted onto the screw with a screw or the like.

[0060] The screw cap 23, which is a cylinder holder installed downstream of the cylinder 22, is not limited to the combination of a hexagonal column and a cylinder shown in the first embodiment, but can have any shape as long as it is a shape that can prevent the cylinder 22 from moving downstream in the screw axial direction, and the diameter of the screw cap 23 is the same as the outer peripheral surface 55 of the cylinder 22.

[0061] As shown in the first embodiment, the screw cap 23 may be removably connected to the small diameter screw portion 21 by a screw in order to efficiently clean the screw, but the screw cap 23 and the small diameter screw portion 21 may also be structured as an integrated unit. Furthermore, the kneading part 7 may be configured to discharge the raw material from between the screw cap 23 and the cylindrical body 22, but the screw cap 23 may be provided with a separate raw material flow hole that passes through the screw cap 23 and allows the raw material to flow from upstream to downstream.

[0062] (Screw and Single Screw Extruder Variants) The screw 3 may have any structure as long as it has the mixing element 7 of the disclosed shape at the tip of the screw 3, and may have any structure as long as the effect of the present invention is not impaired.

[0063] The single-screw extruder 1 of the present invention may be any single-screw extruder having the screw for a single-screw extruder of the present invention. The rotation direction of the screw by the rotational power of the single-screw extruder is clockwise if the forward direction of the spiral of the screw 3 and the flight in the screw small diameter portion 21 is clockwise, and counterclockwise if the forward direction of the spiral is counterclockwise. 1, the single-screw extruder of the present invention may be any extruder provided with a cylindrical cylinder 2 and a vertical hole connecting the upstream hopper 4 and the cylinder 2, but may also be provided with a vertical hole connecting the cylinder 2 so as to provide a vacuum vent 92 for degassing gases in the raw materials and removing moisture, as shown in FIG. 1. The extruder may also have a breaker plate or polymer filter between the screw 3 and the die 10 to remove foreign matter. The cross-sectional shape of the cylindrical cylinder is preferably circular from the viewpoint of smoothly rotating the cylindrical body 22 of the mixing part 7, but may be optionally polygonal. The inner wall of the cylinder 2 is preferably smooth, but may be optionally grooved.

[0064] By configuring the screw 3 for a single-screw extruder and the single-screw extruder 1 of the present invention as described above, it is possible to provide a screw and a single-screw extruder that can suppress local temperature increases in the raw materials when extruding a thermoplastic resin composition and that have excellent mixability and metering properties. In particular, the screw 3 and single-screw extruder 1 of the present invention have a mechanism for gradually compressing and releasing the thermoplastic resin composition and repeatedly mixing it to make it uniform. Therefore, even in applications where resin and particles or raw materials with significantly different melt viscosities are mixed, a uniform thermoplastic resin composition can be obtained, and since there is good metering ability and no local temperature rise, mixing can be performed favorably. [Explanation of symbols]

[0065] 1 Single-screw extruder 2 cylinders 3 screws 4 Hopper 5 screw flights 6 screw grooves 7 Mixed Parts 8. Heater 9 Motors and reducers 10 dice 11 Supply section 12 Mixing section 13 Measuring part 15 strands 16 Cooling water tank 17 Pelletizer 18 Take-off roll 19 Strand Cutter 21 Small diameter screw part 22 Cylinder 23 Screw Cap 24 Ring section 30 flights 31 Groove 32 Convex part 33 Curved surface 34 Boundary where the flight intersects with the curved surface 51 Round hole 54 Inner surface of cylinder 55 Outer surface of cylinder 56 Upstream end face of the cylinder 57 Downstream end face of the cylinder 62 Female thread 63 Screw small diameter contact surface 64 Bottom of screw cap 80 twist angle 91 Screw connection 92 Vacuum Vent 94 Downstream of the screw axis 95 Upstream in the screw axis direction

Claims

1. A screw for a single-screw extruder equipped with a mixing element at the tip of the screw, the mixing part is composed of a screw small diameter portion, a cylindrical body arranged on the outer periphery of the screw small diameter portion, and a cylindrical body holder that holds the cylindrical body, The screw small diameter portion is The flight has a spiral shape with a helix angle, a groove, and a plurality of protrusions provided in the groove, the grooves have a shape in which a plurality of curved surfaces, each of which is a cutout of a spherical or ellipsoidal shape, are arranged in the twist angle direction of the flight and are connected in series, a plurality of convex portions formed as ridges of connecting portions between the curved surfaces of the groove are provided in the groove; The convex portion is an arc-shaped ridge formed between adjacent flights, The ridge of the convex portion has a height lower than that of the flight, The cylindrical body is A hollow cylindrical body that can rotate independently of the screw, a plurality of circular holes penetrating from the outer peripheral surface to the inner peripheral surface of the cylindrical body; The cylinder holders are provided on the upstream and downstream sides of the cylinder in the screw axial direction so as to limit movement of the cylinder in the screw axial direction. A screw for a single-screw extruder characterized by:

2. A single-screw extruder comprising the screw for a single-screw extruder according to claim 1.

Images