Screw for single-screw extruder, and single-screw extruder

Abstract

The present invention provides a screw for a single-screw extruder and a single-screw extruder that suppresses localized temperature rises of raw materials during kneading and extrusion, thereby controlling the resin temperature, while also achieving excellent kneadability and diffusion during kneading. [Solution] A screw for a single-screw extruder equipped with a kneading component in the kneading section, wherein the kneading component comprises a helical flight and a groove, the groove having a shape in which a large number of round holes are connected in succession, the round holes forming a row of round holes in the direction of the twist angle, and within one groove there are three or more rows of round holes in the direction of the screw's axial direction, and each connection of the round holes is provided with a protrusion formed as a ridge of the connection, the protrusion is an arc-shaped ridge and has a height lower than the flight, and the round holes in the intermediate row of round holes among the three or more rows of round holes in the direction of the screw's axial direction have a shape in which each round hole has six protrusions.

Description

Technical Field

[0001] The present invention relates to a screw for a single-screw extruder for kneading a thermoplastic resin composition and a single-screw extruder.

Background Art

[0002] When kneading two or more types of raw materials such as kneading thermoplastic resins (hereinafter also referred to as resins) with each other, kneading a resin with an additive, or kneading a resin with powder particles to form a thermoplastic resin composition, especially when continuously producing a kneaded product using a thermoplastic resin as the resin, from the viewpoint of mass productivity, kneading is performed using an extruder equipped with a screw. In kneading by an extruder, there is a requirement for performance such that the raw materials heated and melted in the extruder are sufficiently kneaded and the kneaded thermoplastic resin composition is discharged in a uniform state. If the kneading is insufficient and the kneaded product is extruded from the extruder in a non-uniform state, problems such as a decrease in the physical properties of the kneaded product due to uneven concentration of each component, separation of the additive from the kneaded product, and insufficient发挥 of its effect occur.

[0003] One example of a screw-type kneading device is the single-screw extruder. A single-screw extruder has a single screw inside a cylinder, and by rotating the screw, the raw material supplied in the supply section upstream of the extruder is forcibly transferred into the helical flow path of the screw. In the kneading section of the extruder, the material is kneaded while being melted and plasticized by the heat from the cylinder, and then the molten kneaded material is measured under pressure in the metering section downstream of the extruder, and the molten kneaded material is discharged from the mold / die at the tip to obtain the kneaded product. However, while single-screw extruders excel in continuous manufacturing, unlike other kneaders, the screw's helical direction is constant, resulting in a lack of high kneading efficiency. Furthermore, because the structure involves kneading under high pressure with raw materials filling all the flow paths within the screw, localized shearing causes high-temperature shearing heat, leading to an excessive rise in the resin temperature of the kneaded material. This also results in uneven resin temperature within the kneaded material, preventing uniform shearing. Additionally, localized heat generation can cause the resin or powder particles to burn. To address these issues, various modifications have been conventionally made to improve the kneading performance of the screw's kneading components.

[0004] Patent Document 1 discloses a screw having a helical flight and a shaft, in which multiple grooves are discontinuously cut parallel to each other in a helical pattern. As disclosed in Figures 4 and 5 of Patent Document 1, the cross-section of each groove is semicircular when perpendicular to the helical direction, and the cross-section in the helical direction is circular at both ends and has a constant or tapered groove diameter. It is stated that when the raw resin passes through the groove, it is subjected to low shear, and when it moves from groove to groove, it is subjected to high shear, thereby forcibly melting the unmelted raw resin and completely removing the unmelted solid. However, although it was possible to remove unmelted solids, when raw materials of different viscosities were used, or when resin and particles were used as raw materials, one of the materials would remain in the groove before mixing, resulting in a problem where the raw materials could not be mixed sufficiently.

[0005] Patent Document 2 discloses an extruder characterized in that, on the circumferential surface of the spiral groove formed on the outer surface of the rotating screw of the extruder, arc-shaped kneading recesses are carved in a staggered pattern in the spiral direction, with gradually different depths in the spiral direction, being deepest in the center and gradually becoming shallower as they move away from the spiral direction, and adjacent parts of each kneading recess are partially overlapped to form a flow passage for the resin. Patent Document 2 states that when kneading a resin raw material such as cured polyvinyl chloride resin with a kneading material such as calcium carbonate or talc, it is possible to achieve high kneading capacity without causing stagnation in the resin raw material. However, as described in Figures 3 and 4 of Patent Document 2, the flow grooves are set at the same height as the spiral flanges that form the flights, allowing the resin to pass only through two narrow flow grooves, and the resin flows into adjacent kneading recesses to create a turbulent pulsation phenomenon. As a result, with resins other than heat-resistant polyvinyl chloride resin, there was a problem in that the resin raw material was subjected to strong shear when passing through the very narrow flow grooves, generating heat and degrading the resin raw material.

[0006] Patent Document 3 discloses a screw for a resin molding machine in which the bottom surface of the grooves between screw flights is divided in the axial direction of the screw to form several strip-shaped portions along the screw flights, and adjacent strip-shaped portions are alternately displaced so that there are interlocking points where the end faces of adjacent strip-shaped portions between the screw flights are in tolerance. In Figures 3, 4, and 8, a screw for a molding machine is disclosed in which two strip-shaped portions with polygonal cross-sections are alternately provided between the screw flights. Patent Document 3 states that by providing the interlocking points, as disclosed in Figure 6, the melting of the solid bed formed by the unmelted resin due to heat and the destruction of the solid bed due to shear are promoted, reducing the power required to melt the resin and obtaining a homogeneous melted state. Furthermore, Patent Document 4, like Patent Document 3, is a patent relating to a screw shaft of an injection molding machine or the like having two valleys with an n-gon cross-section, and states that by setting the phase of the push-side and pull-side valleys to π / n, as shown in Figures 2 and 3, it acts on the solid bed to rapidly promote breakup and melting, resulting in a uniform plasticized state. However, these structures, such as the interlocking point in Patent Document 3 and the shear action indicated by arrow l and the dispersion action indicated by arrow k in Figure 7 of Patent Document 4, are designed to melt the resin quickly, and are not designed to homogenize the resin after melting.

[0007] Furthermore, Patent Document 5 discloses an extruder screw in which the screw groove is further divided into three or more sections in the groove width direction, with each section being a band, and each band having alternating peaks and valleys, with the peaks having lands, and each band being arranged with respect to adjacent bands at a rotational phase difference of 360° / N·n. Patent Document 5 states that by using a screw with the above structure, a kneading effect can be obtained when a resin containing solid resin pieces is flowed through it, similar to Patent Documents 3 and 4, and the resin can be sufficiently melted. However, Patent Document 5, like Patent Documents 3 and 4, is a structure for early melting of the resin, not a structure for homogenizing the resin after melting. Furthermore, because the land portion in the peaks forms a narrow flow path between it and the cylinder of the extruder, the resin that passes through the land portion is prone to generating heat, which leads to the problem of the resin degrading easily.

[0008] Patent Document 6 is an invention that specifies the configuration of a material supply zone, a plasticizing zone, and a metering zone in an extruder screw. As disclosed in Figures 3, 4, and 5, the single-flight portion of the plasticizing zone is made into a wave-shaped groove, the cross-section of the wave-shaped groove has a continuously changing uneven shape, and the bottom of the wave-shaped groove is divided into three sections. Patent Document 6 states that by using the specified zones and the wave-shaped groove structure, as disclosed in Figure 6, the resin flows from the convex groove bottom to the adjacent concave groove bottom, suppressing the resin temperature in the non-halogen flame-retardant extruded material and allowing the material to be thoroughly mixed. However, while Patent Document 6 was suitable for melting, stirring, and mixing the resin with foaming particles such as inorganic flame retardants, it was not suitable for uniformly distributing the mixed components within the resin. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent Registration No. 4639143 [Patent Document 2] Publication No. 2-23394 [Patent Document 3] Japanese Patent Publication No. 52-85256 [Patent Document 4] Japanese Patent Application Publication No. 59-38041 [Patent Document 5] Japanese Patent Publication No. 2000-176995 [Patent Document 6] Japanese Patent Publication No. 2002-154148 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The present invention aims to provide a screw for a single-screw extruder and a single-screw extruder that suppresses local temperature rises of raw materials and thus suppresses resin temperature when a thermoplastic resin composition is kneaded and extruded, while also achieving excellent kneadability and diffusion during kneading. [Means for solving the problem]

[0011] In order to solve the problem, the inventors diligently studied the structure of the kneading component of a screw for a single-screw extruder and, as a result, found that the problem could be solved by a single-screw extruder screw having a kneading component of the following shape, thus completing the present invention.

[0012] In other words, the present invention is (1) A screw used in a single-screw extruder equipped with kneading parts in a kneading section, wherein the kneading parts include a spiral flight and a groove, the groove has a shape in which a plurality of round holes are continuously connected, the round holes are round holes having a shape obtained by cutting off a part of a spherical shape or an ellipsoidal shape, the round holes form a row of round holes in the torsional angle direction that are continuously connected in the torsional angle direction, and the groove has 3 or more rows of the row of round holes in the axial direction of the screw within one groove, the rows of round holes have a shape in which each row is connected to an adjacent row, a convex portion is provided at the connection portion of each of the round holes as a ridge line of the connection portion, the convex portion is a ridge line having a height lower than that of the flight, and among the rows of round holes that form 3 or more rows in the axial direction of the screw, the round holes in the middle row of round holes have a shape having 6 convex portions per round hole. A screw for a single-screw extruder, characterized in that (2) The convex portion is a ridge line in the shape of a convex arc toward the axial center of the screw (1) A screw for a single-screw extruder, which relates to Further, the single-screw extruder of the present invention is a single-screw extruder characterized by including the screw for a single-screw extruder.

Effect of the Invention

[0013] According to the present invention, when kneading and extruding a thermoplastic resin composition, it is possible to provide a screw for a single-screw extruder and a single-screw extruder that suppress a local temperature rise of the raw material to suppress the resin temperature and that are excellent in both kneading property and diffusibility during kneading.

Brief Description of the Drawings

[0014] [Figure 1] A cross-sectional view of a single-screw extruder equipped with the screw for a single-screw extruder of the present invention [Figure 2] A projection view of the kneading parts in the screw for a single-screw extruder of the first embodiment [Figure 3] A developed view and a conceptual cross-sectional view in the circumferential direction of the screw of the kneading parts of the screw for a single-screw extruder of the first embodiment [Figure 4] Development view in the screw circumferential direction and conceptual diagram of the cross-section of the kneading component of the screw for the single-screw extruder according to the first embodiment [Figure 5] In the development view in the screw circumferential direction and conceptual diagram of the cross-section of the kneading component of the screw for the single-screw extruder according to the first embodiment, a diagram showing the flow of the raw material [Figure 6] Processing examples and modified examples of the kneading component of the screw for the single-screw extruder [Figure 7] Development view in the screw circumferential direction and conceptual diagram of the cross-section of the kneading component of the screw for the single-screw extruder in the modified example

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that this embodiment is merely one form for carrying out the present invention, and the present invention is not limited by this embodiment, and various changes and embodiments are possible without departing from the gist of the present invention. In this specification, the notation "a~b" in the description of the numerical range represents a or more and b or less unless otherwise specified. In addition, the reference numerals of the members and parts described in this specification are shown with parentheses as necessary. In addition, in each figure in this specification, the right side of the figure is shown as the upstream 95 where the raw material is supplied, and the left side is shown as the downstream 94 where the raw material is discharged from the single-screw extruder.

[0016] [Single-screw extruder] FIG. 1 shows a cross-sectional view of a single-screw extruder 1 equipped with a screw for a single-screw extruder of the present invention (hereinafter also referred to as "screw"). As shown in FIG. 1, the single-screw extruder 1 has a cylinder 2 with a hollow interior and a screw 3 housed inside the cylinder. The rotational power of the motor and the speed reducer 9 provided in the single-screw extruder 1 is transmitted to the screw 3 by connecting the output shaft of the speed reducer and the screw 3 at the screw connection portion 91, and the screw 3 rotates. The screw 3 has forward-facing helical screw flights 5 and screw grooves 6. By rotating the screw 3 in the forward direction using rotational power, the raw material containing thermoplastic resin (hereinafter also referred to as "raw material") supplied in a fixed amount from the hopper 4 is transported downstream 94 in the screw axial direction, while being sent in the forward direction of the helix through the flow path between the cylinder 2, which is heated by a heater 8 wound around the cylinder, and the screw grooves 6. As the raw material is transported downstream between the cylinder 2 and the screw grooves 6, it is heated by the heat from the heater 8 wound around the cylinder, as well as by shear heat between the raw material and the cylinder 2 and between the raw material and the screw 3. The thermoplastic resin (hereinafter also referred to as "resin") in the raw material melts, the raw material becomes plasticized and moves, is kneaded, and the kneaded material is discharged as a thermoplastic resin composition by passing through a die 10 installed downstream.

[0017] The screw 3 is divided into three zones: a supply section 11 for transporting and supplying raw materials supplied from the hopper 4, a kneading section 12 for melting and plasticizing the resin in the raw materials, and a weighing section 13 for weighing the plasticized raw materials. The kneading section 12 is equipped with the kneading components 7 described below.

[0018] [Screw for a single-screw extruder equipped with a kneading component according to the first embodiment] Figure 2 shows a projection view of the kneading component 7 provided in the screw for a single-screw extruder of the first embodiment, and Figure 3(a) shows a view of the kneading component 7 in the circumferential direction of the screw unfolded on a plane. Furthermore, Figure 3(b) shows a conceptual diagram of the cross-section of the imaginary line L-L', which is shown in the direction of the twist angle 80 of flight 20 in the unfolded view of Figure 3(a); Figure 3(c) shows a conceptual diagram of the cross-section of the imaginary line M-M', which is shown in the direction perpendicular to the twist angle 80 in the unfolded view of Figure 3(a); and Figure 3(d) shows a conceptual diagram of the cross-section of the imaginary line N-N'. Figure 3(c) also shows a cross-section of the convex portion 22 perpendicular to the twist angle in the intermediate row of circular holes 25(b) in the first embodiment described later, and Figure 3(d) also shows a cross-section of the convex portion 22 in the row of circular holes 25(a) and the circular hole 25(c) adjacent to the flight 20. Figure 3(a) is an unfolded view showing the kneading component 7, which is a single spiral flight. In Figure 3(a), the upper and lower parts of the figure are connected in the circumferential direction, and the dashed line L-L' is a line that passes through the center of the width when viewed in the direction of the twist angle 80 in the row of round holes 25(b). Also in Figure 3(a), the left-right direction is the screw axis direction, with the left side of the figure being the downstream 94 in the screw axis direction and the right side being the upstream 95 in the screw axis direction. Figure 3(b) is a cross-sectional view of L-L' in Figure 3(a), and flight 20 is also shown with dashed lines. Figures 3(b), (c), and (d) show the direction of the extruder screw toward the cylinder at the top and the direction toward the screw's axis at the bottom. Also, Figures 3(b), (c), and (d) are conceptual diagrams and correspond to Figure 3(a), which is an unfolded view of the screw in the circumferential direction.

[0019] As shown in Figures 2 and 3(a), the kneading component 7 comprises forward-facing spiral flights 20 and grooves 21 between the flights 20, the flights 20 being forward-facing spiral flights having a twist angle 80 provided to block the resin. As shown in Figures 2 and 3(a), the groove 21 has a structure in which a number of circular holes 23 are connected. The aforementioned round holes 23 are arranged in a row 25 in the direction of the twist angle 80 of the helical flight, with a large number of round holes 23 connected in a continuous manner. Furthermore, as shown in Figure 3(a) where each row of round holes is denoted by reference numerals 25(a), 25(b), and 25(c), each of the rows of round holes 25 connected in the direction of the twist angle is aligned in the direction of the screw axis and is connected to adjacent rows of round holes. The twist angle 80 is defined as the angle at which the helical flight is tilted with respect to the screw axis direction, and in this embodiment, an example is shown where there are three rows of the circular holes 25.

[0020] Each of the aforementioned circular holes 23 is a curved surface shaped like a part of the lower surface of an ellipsoid, and the convex portion 22 is provided as a ridge of the connection portion at the connection portion between a circular hole 23 and an adjacent circular hole 23 in the direction of the twist angle 80, and at the connection portion between a circular hole 23 and a row of adjacent circular holes 23. In this embodiment, we illustrate a case where all the round holes 23 in the groove 21 are of the same depth, and the rows of round holes 25 are arranged in such a way that each row is connected at equal intervals so that the center of each round hole 23 is the deepest point, midway between the two protrusions in each round hole 23. Furthermore, in this embodiment, as shown in Figure 3(a), we illustrate a case where the major axis of the elliptical shape of each round hole 23 is parallel to the twist angle 80, and as a result, the protrusions 22 provided at the connection point between a round hole and an adjacent round hole in the direction of the twist angle 80 are shaped to be perpendicular to the twist angle. Furthermore, in this specification, an ellipsoid shape refers to a shape having a major axis, in which the vertical cross-section containing the major axis and the vertical cross-section containing the center and perpendicular to the major axis are elliptical or circular, and the surface is composed of curved surfaces. Specifically, examples include spheroids and distorted ellipsoids.

[0021] In the row of circular holes 25, the circular holes 23 are arranged parallel to the twist angle 80, and as shown in Figure 3(b), the row of circular holes 25 connects the circular holes 23 that have the deepest groove depth within the curved surface, so a protrusion 22 is formed as a ridge at the connection point of each circular hole 23. As shown in Figures 3(c) and (d), the convex portion 22 is a ridge line in the shape of a convex arc toward the axial center of the screw, having a height lower than the flight 20 and higher than the deepest part of the round hole 23. As shown in Figures 3(b), (c), and (d), the groove 21 has a structure in which the round hole 23 and the convex portion 22, whose cross-sectional shape is a convex arc toward the axial center of the screw, are connected across the groove 21.

[0022] In the present invention, the intermediate row of circular holes that is not adjacent to the flight 20, i.e., the row indicated by reference numeral 25(b) in this embodiment, is connected to adjacent rows of circular holes 25(a) and 25(c) on the downstream and upstream sides in the screw axial direction. As shown in Figure 3(a), the circular holes 23 in the intermediate row of circular holes 25(b) have a shape in which each circular hole has six protrusions 22 that serve as connecting parts. Figure 4(a) shows an enlarged view of Figure 3(a), and Figures 4(b), 4(c), and 4(d) show cross-sectional views along the imaginary lines O-O', P-P', and Q-Q' drawn along the protrusions 22(b), (c), and (d) of the circular hole 23 in Figure 4(a). Although only three protrusions 22 are shown in Figures 4(b), (c), and (d), in this embodiment the remaining three protrusions located diagonally opposite the center of the circular hole 23 of the illustrated protrusions have a similar shape. The protrusion 22(b) in Figure 4(b) is an enlarged view of the protrusion 22 in Figure 3(c), and is a convex arc-shaped ridge that is lower than the flight 20 and higher than the deepest part of the circular hole 23, directed toward the axial center of the screw. Similarly, the protrusions 22 formed at the connection points with adjacent rows of circular holes, as shown in Figures 4(c) and (d), are convex arc-shaped ridges that are lower than the flight 20 and higher than the deepest part of the circular hole 23, directed toward the axial center of the screw.

[0023] In the intermediate row of circular holes 25(b), each row of circular holes 25 is arranged with a displacement in the direction of a twist angle of 80 such that there are six protrusions 22 for each circular hole 23, and the intermediate row of circular holes 25(b) becomes a circular hole surrounded by six protrusions 22. In this embodiment, as shown in Figure 3(a), if the distance from the center of one circular hole 23 to the protrusion 22 is X, the row of circular holes 25(b) is positioned at a location displaced by X downstream relative to the row of circular holes 25(a) when viewed in the direction of the twist angle 80, and the row of circular holes 25(c) is positioned at a location displaced by a further X downstream relative to the row of circular holes 25(b) when viewed in the direction of the twist angle 80.

[0024] An example of a method for processing the kneading component of the single-screw extruder screw of the present invention is shown and explained in Figure 6(A). Figure 6(A) is an enlarged version of Figure 3(a), and dashed lines have been added to show the elliptical cutting surface 81 whose outer circumference is cut when processing into a curved shape. In this embodiment, each ellipse of the cutting surface 81 is exemplified as having a shape in which the major axis is parallel to the direction of the helix angle 80. The round hole 23 in the kneading part 7 can be created by cutting an elliptical hole shown on the cutting surface 81 into the cylindrical screw base material. As shown in Figure 6(A), during cutting, each ellipsoidal shape is arranged in the direction of the twist angle 80 and overlaps to form a cutting surface 81. Furthermore, each row of adjacent cutting surfaces 81 is displaced as described above so that a row of cutting surfaces 81 overlaps with a row of adjacent cutting surfaces 81. This forms an arc-shaped convex portion 22 between two or more overlapping cutting surfaces 81, a round hole 23 is formed at the center of the cutting surface 81, a groove 21 is formed where it is cut, and a flight 20 is formed where it is not cut. As shown in Figure 6(A), by arranging the cutting surfaces 81 such that there are six overlapping locations for each cutting surface 81 in the row of intermediate cutting surfaces 81, it is possible to form six protrusions 22 for each round hole. Furthermore, in this embodiment, as shown in Figure 6(A), by overlapping three cut surfaces 81, a convex portion 22 is formed between them, with the point where the three cut surfaces 81 intersect as the vertex. Since the point of intersection is lower than the flight 20, the convex portion 22 is lower than the flight 20, and both the round holes 23 in the groove 21 and the convex portion 22 are lower than the flight 20.

[0025] As shown in Figure 3(a), the boundary line 24 where the flight 20 intersects with the rows of circular holes 25(a) and (b) adjacent to the flight 20 in the groove 21 has a shape in which arcs that are recessed toward the flight 20 are continuously connected, and the flow path width of the groove 21 provided between the boundary line 24, when viewed in the direction of the twist angle 80, changes in accordance with the shape of the continuous arcs.

[0026] <Effects of the kneaded component in the first embodiment> The effects of the kneading component 7 provided in the screw for the single-screw extruder of the first embodiment will be explained below with reference to Figure 5. Figures 5(a) and 5(b) are diagrams of Figures 3(a) and 3(b) with arrows illustrating the flow of raw materials, and Figures 5(c) and 5(d) are the same diagrams as those shown in Figures 3(c) and 3(d). However, in Figures 5(b), 5(c), and 5(d), the cylinder 2 located on the outer circumference of the mixing component 7 is added, and in Figure 5(b), the cross-section of the flight 20 is also shown with dashed lines.

[0027] The raw material that flows into the mixing component 7 from upstream of the mixing component 7 flows into the groove 21 and flows in a spiral direction through the spiral groove 21 and the resin passage provided between the groove 21 and the two adjacent flights 20 and cylinder 2. Of the raw material flowing spirally along the twist angle 80, the flow of raw material that flows through the center of each circular hole 23 in the groove 21, as viewed from the width direction, passes over the circular hole 23, crosses over the protrusion 22, and flows to the adjacent circular hole 23 downstream, as shown by arrow A in Figure 5(a). As shown in Figure 5(b), the center of the aforementioned protrusion is lower than the flight 20, but it is a ridge line provided between curved surfaces that have an upward and downward shape so that the height direction of the raw material flow path becomes narrower. Therefore, as shown by the arrows in Figure 5(b) indicating the flow of raw material before and after the protrusion 22, the raw material flowing downstream between the cylinder 2 and the bottom of the round hole 23 flows along the upward curved surface before the protrusion 22 and flows into the narrow flow path between the protrusion 22 and the cylinder 2. Before reaching the protrusion 22, the raw material is compressed and stirred, causing the raw material to exchange positions. After that, the compressed raw material is released into the adjacent flow path as soon as it passes the protrusion 22, where the raw material exchanges positions again and is kneaded. Furthermore, as shown by the flow indicated by arrow B in Figure 5(a), the raw material flowing at both ends of the protrusion 22 is compressed and released in the depth direction at the protrusion 22, causing it to exchange positions and be kneaded, similar to Figure 5(b). However, as shown in Figures 5(c) and 5(d), the flow path consisting of the cross-section of the arc-shaped protrusion 22 and the cylinder 2 is more compressed at both ends of the protrusion 22 because the height of the flow path is higher at both ends compared to the central part of the protrusion 22. As indicated by the thicker arrow B around the protrusion 22, the raw material also spreads in the width direction of the groove during compression, causing it to exchange positions and be kneaded.

[0028] The circular hole 23 located downstream of the protrusion 22 is a curved surface that changes continuously in both the width and depth directions, and the raw material spreads out on the curved surface at the center of the circular hole 23. Therefore, the flow of the raw material that is opened to the adjacent flow channel downstream beyond the protrusion 22 becomes a flow in which the raw material diffuses with a change in flow velocity in the width direction as the flow channel of the raw material widens, as shown by the hatched arrows in Figure 5(a) which show the width of the tip widening to the left and right of arrow A immediately after the protrusion 22, and similarly, diffusion in the depth direction toward the center of the circular hole 23 also occurs, as shown in Figure 5(b).

[0029] In the present invention, each circular hole 23 in the intermediate row of circular holes has six protrusions 22. Therefore, the raw material diffused near the center of the circular hole 23 not only flows into the protrusions 22 in the direction of the twist angle 80, but also flows out and diffuses into the downstream circular hole 23 of the adjacent row of circular holes via the protrusions 22, as shown by arrow D in Figure 5(a). Furthermore, as shown by arrows B and C in Figure 5(a), the raw material flowing into the circular hole 23 flows not only from upstream in the direction of the twist angle 80 (arrow B), but also from the upstream circular hole 23 of the row of adjacent circular holes via the convex portion 22 (arrow C), and the flow from arrows B and C merges in the circular hole 23, thus further promoting diffusion. At arrows C and D, the raw material passes through the arc-shaped convex portion 22, which is lower than the flight height, and a positional exchange occurs due to the compression and release of the raw material at the convex portion 22, thus efficiently diffusing the raw material.

[0030] Furthermore, as shown in Figure 5(a), the rows of circular holes 25(a) and 25(c) adjacent to the flight 20 also have a structure that connects the circular holes 23. Therefore, the boundary line 24 where the flight and the groove intersect is formed as a curve to change the width of the groove 21, and the circular holes 23 near the boundary line are shallower than the center of the circular holes 23. As a result, the raw material promotes the exchange of positions of the raw material through a flow that involves changes in flow rate and flow velocity that change the direction of the flow path, as shown by arrow E in Figure 5(a), and diffuses the raw material that has been stressed by the flight 20 back to the center of the groove.

[0031] The kneading component 7 passes through the protrusions 22, which are provided between the round holes 23, multiple times. Each time, the raw material is kneaded through the complex positional changes described above, and diffusion occurs before and after each round hole 23, the protrusions 22 that connect each round hole 23, and between the grooves 21 and the flights 20. As a result, the raw material that passes through the kneading component 7 becomes uniform. Furthermore, as the raw material flowing spirally along the twist angle 80 is compressed and released at the protrusions 22, it also spreads in the width direction of the groove. This allows for multiple gradual compressions and releases, resulting in three-dimensional repositioning and diffusion of the raw material. This avoids the localized high shear heat generation of the raw material seen in conventional screws, and because the circular holes are also curved, it is possible to obtain a uniform thermoplastic resin composition while suppressing the rise in resin temperature.

[0032] <Variation> The embodiments of the present invention have been described above, but these are merely examples, and various other configurations can also be adopted.

[0033] The kneading component 7 of the single-screw extruder screw of the present invention may, as in the first embodiment, have three rows of circular holes 25 within a single groove 21, connecting the circular holes 23 of the intermediate row of circular holes 25(b) with the left and right rows of circular holes 25(a) and (c). Alternatively, the number of rows of circular holes may be increased to four rows of circular holes 25, as shown in Figure 7, with two intermediate rows of circular holes as indicated by reference numerals 25(b) and 25(c), so that each circular hole 23 in the intermediate rows of circular holes 25(b) and 25(c) has six protrusions 22. From the viewpoint of improving the diffusibility of the raw material, it is preferable that the number of rows of circular holes 25 be 3 to 12.

[0034] Figure 6(A) is an enlarged version of Figure 3(a) in the first embodiment, showing an example of machining. Further modifications are shown in Figures 6(B) and (C) with the cutting surface 81 during machining indicated by dashed lines, and will be explained below. Figure 6(A), shown as an example of processing in the first embodiment, shows rows 25 of round holes connected in the twist angle direction, with each row connected such that the protrusions 22 in each row are positioned alternately. The distance between each row is adjusted so that the cutting surfaces 81 of each row overlap in places where two cutting surfaces overlap and places where three cutting surfaces overlap. By adopting the shape of the first embodiment, both the protrusions 22 and the vertices 26 where the three protrusions intersect are lower than the flight 20, and every part within the groove 21 is at a height lower than the flight 20, which is a desirable shape from the viewpoint of suppressing the resin temperature and diffusing the raw material.

[0035] The circular hole 23 may be a curved surface with a shape that cuts out a part of an ellipsoid, as in the first embodiment, or, as shown in Figure 6(C), the circular hole 23 may be a curved surface with a shape that cuts out a part of a sphere. By making it a curved surface, the raw material flowing from the deepest part of the circular hole 23 in each direction downstream flows on a curved surface with uniform curvature, thereby improving the diffusivity of the raw material. Furthermore, if the circular hole 23 is a curved surface that cuts out a part of the ellipsoid shape, the orientation of one circular hole 23 may be directed in the direction of the twist angle relative to the major axis of the ellipsoid, as shown in the first embodiment, but the circular holes 23 in the intermediate row of circular holes 25 can also be directed in any direction within the range where there are six protrusions 22.

[0036] In the grooves 21 of the kneading component 7, each row of circular holes 25 is positioned at a displaced location to connect the rows. However, as shown by the distance X from the center of the circular hole to the protrusion 22 in Figure 3(a) of the first embodiment, they may be positioned with a displacement of X in the twist angle direction. Alternatively, they can be positioned so that each circular hole 23 has six protrusions 22. For example, in Figure 6(B), the displacement distance Y is set to Y = X * 0.6, and the displacement distance can be set arbitrarily.

[0037] Preferably, the maximum width of the grooves 21 between flights is 1.0 to 25.0 mm. A width of 1.0 mm or more allows for stable flow in the helical direction, resulting in excellent metering performance and suppression of the rise in raw material temperature. A width of 25.0 mm or less allows for excellent kneading performance due to the diffusion effect of each round hole 23 and the compression and release effects of the convex portions. Furthermore, the width of the protrusion 22 that connects to the round hole 23 is preferably set to a ratio of (maximum width of the round hole perpendicular to the twist angle 80) / (width of the protrusion 22) of 1.50 to 3.50. By setting this ratio, positional exchange of the protrusion 22 and excellent kneading properties due to the protrusion can be obtained.

[0038] The length from one protrusion 22(b) to the adjacent protrusion 22(a) in the direction of the 80-degree twist angle is preferably 10 to 80 mm. A length of 10 mm or more suppresses localized shear heat generation in the flow path, allowing for the production of a thermoplastic resin composition that does not burn, and also suppresses the rise in resin temperature. A length of 80 mm or less allows the raw material that has passed through the protrusion 22(b) and been released to be sufficiently kneaded and diffused in the flow path between the round hole 23 and the cylinder 2 until it reaches the adjacent downstream protrusion 22(a), resulting in a uniform thermoplastic resin composition. In the groove 21, each circular hole 23 is connected in a continuous manner, with 3 to 12 circular holes per row in the direction of the twist angle 80 within a single groove 21. This allows the flowing raw material to be gently compressed and released multiple times, resulting in a three-dimensional exchange of raw material positions during kneading. This suppresses the rise in temperature of the raw material and makes it possible to obtain a uniform thermoplastic resin composition.

[0039] The depth of each circular hole 23 in the groove 21 may be the same, as shown in the first embodiment, or it may be a combination of circular holes of different depths connected together and arranged in a continuous pattern to enhance diffusion.

[0040] The cross-sectional shape of the protrusion 22 in the groove 21 is preferably a downwardly convex arc toward the center of the screw shaft, as disclosed in Figures 3(c) and (d) of the first embodiment, but any shape is acceptable as long as it is a flow path shape that compresses the raw material flowing from the round hole 23 into the protrusion 22. From the viewpoint of compressing the raw material and releasing the compressed raw material after it passes through the protrusion 22, the height of the deepest part of the protrusion is preferably 0.1 to 0.9 times the height of the deepest part of the round hole 23 relative to the height of the flight 20 from the deepest part of the round hole 23, with the deepest part of the round hole 23 as the reference. By setting the height of the deepest part of the protrusion 22 to 0.1 times or more, the raw material is sufficiently compressed and released and kneaded in the flow path between the protrusion 22 and the cylinder 2, so that a uniform thermoplastic resin composition can be obtained. By setting it to 0.9 times or less, shear heat generation in the flow path is suppressed, so that a thermoplastic resin composition without resin burning can be obtained, and the temperature rise of the raw material can be suppressed.

[0041] The number of flights 20 may be one flight as disclosed in the first embodiment, or, from the viewpoint of improving kneadability and diffusion, a multi-flight spiral configuration with grooves 21 between each flight 20 may be used to branch the raw material from upstream and allow it to flow into the kneading component. When there are multiple flights, the number of flights is preferably four or less, as this allows for better kneadability and diffusion while suppressing the rise in resin temperature. Furthermore, it is preferable that the twist angle 80 of the flight 20 be 25 to 80°. Setting it to 25° or more provides a stable flow that pushes the raw materials necessary for kneading in a helical direction, while setting it to 80° or less allows the flight 20 to efficiently transport the raw materials downstream.

[0042] The height of the flight 20 can be arbitrarily set depending on the diameter of the cylinder and screw of the single-screw extruder and the desired resin discharge volume, but it is preferable that the diameter of the flight 20 be approximately -0.5 to -0.1 mm relative to the diameter of the cylinder 2.

[0043] The direction of the spiral of flight 20 should be aligned with the forward direction of the flight of the upstream screw on screw 3, and can be set arbitrarily in accordance with the rotation of the extruder.

[0044] The kneading component 7 may have the flight 20 and groove 21 as disclosed herein, and may have additional parts that allow the raw materials to flow stably, such as full flights, upstream and downstream of the groove 21, or may have other structures as long as they do not impair the effects of the present invention. Furthermore, as disclosed in Figures 2 and 3(a) of the first embodiment, the connection between the groove 21 of the kneading component 7 and the screw grooves 6 upstream and downstream of the kneading component 7 may be such that the bottom surface of the groove 21 is cut up and connected to the full-flight screw grooves 6, but any shape is acceptable as long as it allows the raw material to be fed to the kneading component 7.

[0045] (Variations of screw and single-screw extruders) The screw 3 only needs to have the kneading component 7 of the disclosed shape in the kneading portion 12 of the screw 3, and can have any structure as long as it does not impair the effects of the present invention.

[0046] The single-screw extruder 1 of the present invention may be any single-screw extruder having the screw for single-screw extruder of the present invention. The rotation direction of the screw by the rotational power of the single-screw extruder is such that if the forward direction of the helix of the screw 3 and the flights of the kneading component 7 is clockwise, it rotates clockwise, and if the forward direction of the helix is ​​counterclockwise, it rotates counterclockwise. Furthermore, the single-screw extruder of the present invention may be provided with a cylindrical cylinder 2 as shown in Figure 1, and a vertical hole connecting the upstream hopper 4 and the cylinder 2. Alternatively, as shown in Figure 1, a vacuum vent 92 may be provided, which is further connected to the cylinder 2 and used for degassing gases and removing moisture from the raw material. In addition, a breaker plate or polymer filter may be provided between the screw 3 and the die 10 to remove foreign matter, or a molding die or the like may be used instead of the die 10. The cross-sectional shape of the cylindrical cylinder is preferably circular from the viewpoint of efficiently mixing and diffusing with the mixing component 7, but it may be arbitrarily polygonal. Furthermore, the inner wall of the cylinder 2 is preferably smooth, but it may be arbitrarily provided with a groove shape.

[0047] The screw 3 and single-screw extruder 1 of the present invention, by having the above configuration, can suppress local temperature rise of the raw material when extruding a thermoplastic resin composition, and provide a screw and single-screw extruder with excellent kneadability and diffusivity. In particular, the screw 3 and single-screw extruder 1 of the present invention are designed to homogenize the thermoplastic resin composition by gradually compressing and releasing it repeatedly while diffusing it through each connected round hole 23. Therefore, even when mixing resin and fillers, or raw materials with significantly different melt viscosities, a uniform thermoplastic resin composition can be obtained. Furthermore, it offers good metering capabilities and does not cause localized temperature increases, making it suitable for mixing. [Explanation of Symbols]

[0048] 1. Single-screw extruder 2 cylinders 3 Screws 4 Hopper 5 Screw Flight 6 Screw grooves 7 Mixing components 8 Heater 9. Motors and reducers 10 dice 11 Supply section 12 Mixing section 13 Measuring part 20 flights 21 Groove 22 Convex part 23 round holes 24 The boundary where flights and trenches intersect 25 Rows of round holes connected in the direction of the twist angle 26 The vertex where the three convex parts intersect 80 degrees of twist 81 Cutting curved surface 91 Screw connection 92 Vacuum vent 94 Downstream in the screw axial direction 95 Upstream in the screw axial direction

Claims

1. A screw used in a single-screw extruder equipped with a mixing component in the mixing section, The aforementioned kneading component comprises a spiral flight and a groove, The groove has a shape in which a large number of circular holes are connected in a continuous sequence. The aforementioned circular hole is a circular hole that cuts out a part of a spherical or ellipsoidal shape, The aforementioned circular holes form a row of circular holes in the direction of the twist angle, which are connected in a large number of consecutive connections in the direction of the twist angle. The groove has three or more rows of the circular holes arranged in the axial direction of the screw within a single groove. The rows of circular holes are arranged so that each row is connected to the adjacent row. Each of the aforementioned round holes is provided with a protrusion that forms as the ridge of the connection, The aforementioned protrusion is a ridge having a height lower than the aforementioned flight. In the rows of circular holes, which form three or more rows in the axial direction of the screw, the circular holes in the intermediate rows have a shape in which each circular hole has six protrusions. A screw for a single-screw extruder characterized by the following features.

2. The screw for a single-screw extruder according to claim 1, wherein the convex portion is a ridge line in the shape of a convex arc toward the axis center of the screw.

3. A single-screw extruder comprising the screw for a single-screw extruder described in claim 1.

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