Screws for single-screw extruders and single-screw extruders

Abstract

The present invention provides a screw for a single-screw extruder and a single-screw extruder that, when kneading and extruding a thermoplastic resin composition, suppresses local temperature increases in the raw materials to suppress the resin temperature, and that are excellent in kneading properties, distribution, and diffusion during kneading. [Solution] A screw for a single-screw extruder having a kneading element in a kneading section, wherein the kneading element has a spiral flight, a groove, and a plurality of convex portions provided within the groove, wherein the groove has a curved surface shaped like a cutout of a portion of an ellipsoid, the curved surface being connected in a continuous manner with the major axis of the ellipsoid oriented in the direction of the twist angle of the flight, and the convex portions are formed as ridgelines of the connecting portions between the curved surfaces of the groove, the ridgelines of the convex portions having a height lower than that of the flight, and the curve where the flight and the curved surface of the groove intersect has a shape where a concave arc is connected in a continuous manner when viewed from the flight.

Description

[Technical Field]

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

[0002] When kneading two or more raw materials to form a thermoplastic resin composition, such as kneading thermoplastic resins (hereinafter also referred to as resins) with each other, kneading a resin with additives, or kneading a resin with powder particles, particularly when continuously producing a kneaded product using a thermoplastic resin as the resin, kneading is performed using an extruder equipped with a screw from the viewpoint of mass productivity. In kneading using an extruder, it is required that the raw materials heated and melted in the extruder are sufficiently kneaded so that the thermoplastic resin composition after kneading is discharged in a uniform state. If the kneading is insufficient and the material 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 concentrations of the components and separation of additives from the kneaded product occur.

[0003] A single-screw extruder is one example of a screw-based kneading device. A single-screw extruder has a single screw inside a cylinder, and by rotating the screw, the raw materials fed into the feed section upstream of the extruder are forcibly transported along the flow path in the screw's spiral direction, where they are melted and plasticized by the heat from the cylinder in the kneading section of the extruder and kneaded. The molten mixture is then measured under pressure in the metering section downstream of the extruder, and the molten mixture is then discharged from the mold / die at the tip to obtain the kneaded product. However, although single-screw extruders are excellent for continuous production, unlike other kneading machines, the screw's spiral direction is fixed, so a high kneading effect cannot be obtained. Furthermore, because the kneading is performed under high pressure with all of the flow paths in the screw filled with raw materials, high-temperature shear heat caused by localized shearing causes the resin temperature of the kneaded material to rise excessively, and unevenness in the resin temperature within the kneaded material prevents uniform shearing. There is also the problem of localized heat generation causing the resin and powder particles to burn. To address these issues, various modifications have been made to improve the kneading performance of the parts in the kneading section of the screw.

[0004] Patent Document 1, filed by the present applicant, is one example of a process that can suppress excessive increases in resin temperature and achieve high mixing performance. Patent Document 1 discloses a screw for a single-screw extruder that has multiple spiral flights and grooves, and that includes a convex portion as a mixing element, which extends across the width of the spiral groove and has a wide peak. Patent Document 1 discovered that using this single-screw extruder screw can achieve high mixing performance while suppressing increases in resin temperature. However, while Patent Document 1 achieves excellent mixing due to the characteristic shape of the convex portion, the flow path of the kneaded material outside the convex portion is parallel to the spiral flight. Therefore, although mixing in the flow direction is excellent, in applications requiring greater uniformity and reduced temperature unevenness in the final kneaded material, further performance is required to diffuse and mix the kneaded material.

[0005] Patent Document 2 discloses an extruder having a plurality of grooves with a bottom surface having continuous irregularities, and a plurality of recessed grooves straddling the grooves on the inner peripheral surface of a cylinder located on the lateral side of the zone. Patent Document 2 discloses that the screw groove 7 in the main part of the screw shown in Figure 2 forms an inclination angle β with respect to the axis, a so-called helix angle, and that a large number of oblong groove-like recessed portions 9 are formed adjacent to each other within the groove, and each recessed portion forms an inclination angle γ with respect to the axis that is larger than the inclination angle β. Patent Document 2 discloses that a rolling effect of the resin is generated by interaction with the grooves of the cylinder, which will be described later, and that by arranging the oblong shapes with a large inclination angle γ, good self-cleaning properties and a large pushing effect can be obtained. Patent Document 2 also discloses that zone B disclosed in FIG. 1 has the structure shown in FIG. 2, with the inclination angle β set to a small angle, and that the cylinder 3 of the extruder is provided with a plurality of grooves 10 arranged in the axial direction so as to straddle the grooves of the screw, so that as shown in FIG. 2, a sufficient pushing effect is imparted from groove-like recess 9a of the screw, causing the resin material to move forward to second groove-like recess 9b, and the resin material in groove-like recess 9a flows from the contact area between groove-like recess 9a and groove-like recess 9b, where the groove bottom becomes shallow, into groove 10 of the cylinder, and then flows into groove-like recess 9b, so that the resin material is subjected to a rolling and rotating action, causing the additives to be rapidly enveloped in the resin and promoting kneading. However, in Patent Document 2, local mixing is achieved by the rolling rotation action of the resin material in the groove-like recesses of the screw and the grooves provided in the cylinder, which results in high shear heat being locally generated in the resin material, resulting in the problem of the resin material burning and deteriorating due to high temperatures. Furthermore, because a special groove needs to be provided in the cylinder, a special extruder is required, such as connecting cylinder 3 between cylinders 2 and 4 in Figure 1. In addition, a slight step is created on the resin material flow path side of the connecting cylinders, which creates the problem of resin burning and resin deterioration being prone to occur depending on the resin material that convects into the step part.

[0006] Patent Document 3 discloses, in FIGS. 1 and 2, a screw in which a discharge-side main part 2c having the same shape as the main part of the screw described in Patent Document 2 is provided together with a main part 2b having a different characteristic shape, and details of the main part 2c in FIGS. 1 and 2 are disclosed in FIG. 4. It should be noted that the torsion angles β and γ shown in Figure 4 of Patent Document 3 are shown in the opposite order to the inclination angles β and γ in Figure 2 of Patent Document 2, and the angle reference in Patent Document 2 is based not on the axial direction of the screw but on a right angle to said axial direction. However, paragraph

[0025] of Patent Document 3 reveals that the uneven bottom surfaces are aligned at a torsion angle γ, and that each of the numerous grooves having said uneven bottom surfaces is inclined in a direction perpendicular to the axis of the screw, and it can be seen that what is shown in Figure 4 of Patent Document 3 is the same shape as Figure 2 of Patent Document 2. Patent Document 3 states that uniform kneading can be achieved by providing a main part of the above shape together with other main parts 2b. However, the discharge side of the screw where main part 2c is provided, the so-called metering section of the screw, is different from the kneading section provided in the middle of the screw as in Patent Documents 1 and 2, in that it is a section through which resin material that has completely melted flows, and therefore it is not possible to obtain sufficient kneading power for resin material whose viscosity has decreased due to melting and heating.

[0007] [Patent Document 1] Patent No. 6473098 [Patent Document 2] Japanese Patent Application Publication No. 4-62131 [Patent Document 3] Japanese Patent Application Publication No. 5-2289020 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a screw for a single-screw extruder and a single-screw extruder that, when kneading and extruding a thermoplastic resin composition, suppresses local temperature increases in the raw materials, thereby suppressing the resin temperature, and that are excellent in kneading properties, distribution, and diffusion during kneading. [Means for solving the problem]

[0009] In order to solve the problems, the present inventors conducted extensive research into the structure of kneading parts of screws for single-screw extruders, and as a result, found that the problems could be solved by using a screw for single-screw extruders having kneading parts with the following shapes, thereby completing the present invention.

[0010] That is, the screw for a single-screw extruder of the present invention is (1) A screw used in a single-screw extruder having a kneading element in a kneading section, the kneading element having a spiral flight, a groove, and a plurality of convex portions provided within the groove, the groove having a curved surface shaped to cut out a part of an ellipsoid shape, the major axis of the ellipsoid shape being arranged in the direction of the twist angle of the flight, and a shape in which a large number of convex portions are connected continuously, the groove having a plurality of convex portions formed as ridge lines of the connecting portions between the curved surfaces of the groove, the convex portions being arc-shaped ridge lines formed across the adjacent flights, the ridge lines of the convex portions having a height lower than that of the flights, In a plan view of the kneading parts in the circumferential direction of the screw, The curve where the flight and the curved surface of the groove intersect is concave to the side a screw for a single-screw extruder, characterized in that the screw has a shape in which arcs are continuously connected; (2) A screw for a single-screw extruder, characterized in that the ridge lines of the convex portions according to (1) are ridge lines formed between the flights so as to extend in a direction perpendicular to the helix angle, or a tangent line of the ridge line at the center of the groove in the width direction is a ridge line perpendicular to the helix angle. is. 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]

[0011] The present invention provides a screw for a single-screw extruder and a single-screw extruder that, when kneading and extruding a thermoplastic resin composition, suppresses local temperature increases in the raw materials, thereby suppressing the resin temperature, and that are excellent in kneading properties, distribution, and diffusion during kneading. [Brief explanation of the drawings]

[0012] [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] 1 is a projection view of a kneading part of a screw for a single-screw extruder according to a first embodiment of the present invention. [Figure 3] 1 is a development view of a kneading part of a screw for a single-screw extruder according to a first embodiment of the present invention in the circumferential direction of the screw, and a conceptual diagram of a cross section. [Figure 4] 1 is a conceptual diagram showing an example of processing a kneading part of a screw for a single-screw extruder according to a first embodiment of the present invention. [Figure 5] 1 is a development view and a cross-sectional conceptual diagram showing the flow of raw materials in the screw circumferential direction of the kneading part of the screw for a single-screw extruder according to the first embodiment of the present invention; [Figure 6] 1 is a development view of a kneading part of a screw for a single-screw extruder according to a second embodiment of the present invention in the screw circumferential direction and a cross-sectional conceptual diagram. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in this specification, the expression "a to b" in the description of a range of numerical values ​​means not less than a and not more than b, unless otherwise specified.

[0014] [Single-screw extruder] A cross-sectional view of a single-screw extruder equipped with a screw for a single-screw extruder (hereinafter also referred to as "screw") of the present invention is shown in Figure 1. 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 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 spiral flight 5 and a valley 6. By rotating the screw in the forward direction using rotational power, a raw material containing a thermoplastic resin (hereinafter also referred to as "raw material") supplied in a fixed amount from a hopper 4 is sent in the forward spiral direction through a flow path between a cylinder 2 heated by a heater 8 wrapped around the cylinder and the valley 6, and transferred downstream 94 in the screw axial direction. As the raw material transferred between the cylinder 2 and the valley 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 be mixed. The mixed material passes through a die 10 installed downstream and is discharged as a thermoplastic resin composition.

[0015] The screw 3 is divided into three zones: a supply section 11 that conveys and supplies the raw material supplied from the hopper 4; a kneading section 12 that melts and plasticizes the resin in the raw material and kneads the raw material; and a metering section 13 that meters the plasticized raw material. The kneading section 12 is equipped with a kneading component 7 described below.

[0016] [Screw for single-screw extruder equipped with kneading part of first embodiment] FIG. 2 shows a projection view of the kneading member 7 provided in the screw for a single-screw extruder of the first embodiment, and FIG. 3(a) shows a planar development of the kneading member 7 in the circumferential direction of the screw. In addition, a conceptual diagram of a cross section of the imaginary line L-L' shown in the direction of the torsion angle 80 in the unfolded view of Figure 3(a) is shown in Figure 3(b), and a conceptual diagram of a cross section of the imaginary line M-M' shown in the direction perpendicular to the torsion angle 80 in the unfolded view of Figure 3(a) is shown in Figure 3(c). Note that Figure 3(a) is an exploded view showing the kneading part 7, which is a single spiral flight, and in Figure 3(a) the upper and lower parts of the figure are connected in the circumferential direction, and the imaginary line L-L' is a line passing through the center of the width of the groove 21 when viewed in the direction of the twist angle 80. Fig. 3(b) is a cross-sectional view taken along line L-L' in Fig. 3(a), and the flight 20 is also shown by a virtual line. In Fig. 3(b), the protrusion 22 leading to the flight 20 is also shown by a virtual line. In Figures 3(b) and (c), the top shows the direction toward the cylinder side of the extruder screw, and the bottom shows the direction toward the axial center of the screw. Figures 3(b) and (c) are conceptual diagrams that correspond to Figure 3(a) expanded in the circumferential direction of the screw. FIG. 3(c) is a cross-sectional view of the M-M' cross section shown along the central convex portion 22 in FIG. 3(a), and the deepest cross section of the curved surface 23 is also shown by an imaginary line. In addition, in this embodiment, as shown in Figures 3(a) and (c), an example is given in which the distance between the convex portions is adjusted so that the convex portion 22 and the widest and deepest part of the curved surface 23 are aligned on the virtual line M-M'.

[0017] As shown in Figures 2 and 3(a), the kneading part 7 has a forward spiral flight 20, a groove 21, and a plurality of protrusions 22 provided within the groove 21, and the flight 20 is a forward spiral flight having a twist angle 80 that is provided to block the resin. As shown in Figure 3(a), the groove 21 has a shape in which a number of curved surfaces 23, each of which is a cut-out portion of an ellipsoid whose major axis 34 is aligned in the direction of the twist angle 80 of the spiral flight, are connected in succession so that the major axis 34 of each curved surface 23 is aligned in the direction of the twist angle 80 of the spiral flight, and the connecting portions between each curved surface 23 have the protrusions 22 provided as ridges of the connecting portions. The helix angle 80 is defined as the angle at which the spiral flight is inclined relative to the screw axial direction, and in Figure 3, 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. In addition, in this specification, the term "ellipsoid shape" refers to a shape that has a major axis, and in which a vertical cross section including the major axis and a vertical cross section including the center and perpendicular to the major axis are elliptical or circular, and the surface is composed of a curved surface, and specific examples include a spheroid and a distorted ellipsoid. Each curved surface 23 in the groove 21 is a curved surface having a shape obtained by cutting out a part of the lower surface of an ellipsoid.

[0018] In the groove 21, the plurality of ellipsoid shapes are arranged so that their major axes 34 are parallel to the helix angle 80, and furthermore, in this embodiment, the curved surfaces are connected so as to be equally spaced apart, so that in a vertical cross section taken along the direction of the helix angle 80 as shown in Fig. 3(b), the curved surfaces 23 form symmetrical arcs that convex toward the axial center of the screw, and convex portions 22 are formed as ridgelines at the connections of the curved surfaces 23. Furthermore, as shown in Fig. 3(c), in a vertical cross section taken along a direction perpendicular to the helix angle 80, the curved surfaces 23 form symmetrical arcs that convex toward the axial center of the screw. In addition, each curved surface 23 disclosed in the first embodiment is a curved surface having the same shape in terms of depth, width, and length in the torsion angle direction, and the deepest point of the curved surface is the center when viewed from the direction of torsion angle 80 and the direction perpendicular to torsion angle 80. Furthermore, since the curved surface 23 is an ellipsoidal curved surface with the major axis 34 oriented in the direction of the torsion angle 80, when comparing the change in curvature in the direction of the torsion angle 80 from the center of the curved surface, i.e., the deepest part of the curved surface, with the change in curvature in the direction perpendicular to the torsion angle 80, the change in curvature in the direction of the torsion angle 80 changes gradually.

[0019] As shown in Figures 3(a) and 3(c), the convex portions 22 formed as ridges at the connecting portions of the curved surfaces 23 are ridges formed between two adjacent flights 20, and a plurality of convex portions 22 are provided in the groove 21. As shown in the development view of Figure 3(a), the convex portions 22 are formed between the flights 20 so that the ridges extend in a direction perpendicular to the twist angle 80. Furthermore, as shown in Figure 3(c), in a vertical cross section (cross section of virtual line M-M') along a direction perpendicular to the twist angle 80, the convex portion 22 exhibits a symmetrical arc shape that is convex toward the axial center of the screw. 3(b), the convex portion 22 is provided inside the groove 21 as a connecting portion between two curved surfaces 23 that rise from the center, i.e., as an apex, so that the convex portion 22 has a height lower than that of the flight 20 when viewed from the axial center of the screw. Also, as shown in FIG. 3(c), the groove depth from the flight 20 to the convex portion 22 is shallower than the groove depth of the curved surfaces 23.

[0020] As shown in Figure 3(a), the curve 24 where the flight 20 intersects with each curved surface 23 of the groove 21 has a shape in which concave arcs are connected continuously when viewed from the flight, and the groove 21 provided between the curves 24 has the narrowest width at the convex portion 22 and the widest width midway between the two convex portions 22 when viewed as a flow path flowing in the direction of the torsion angle 80. In this specification, the width of the groove and the width of the curved surface refer to the width in the direction perpendicular to the twist angle.

[0021] A conceptual diagram of an example of a method for processing a kneading part of a single-screw extruder screw according to the present invention is shown in Figure 4. Figures 4(a) and (b) are conceptual diagrams of the kneading part 7 expanded in a planar view in the circumferential direction of the screw, corresponding to Figures 3(a) and (b), and a conceptual diagram of a cross section taken along imaginary line L-L' in Figure 3(a), which is drawn to pass through the center of the width of the groove 21 as viewed in the direction of the helix angle 80, with the processing line added as a solid line. Also, Figure 4(b), like Figure 3(b), also shows the flight 20 located at the back of the L-L' cross section and the protrusion 22 extending onto the flight 20 as imaginary lines. The kneading part 7 is produced by cutting a cylindrical screw base material with a cutting tool having an arc-shaped R-shaped blade at the tip, aligning the major axes 34 of the ellipsoid shapes in the direction of a torsion angle of 80 as shown in Figure 4(a) and cutting each ellipsoid shape so that they overlap. Specifically, a cutting tool having an arc-shaped R-shaped blade at its tip is set so that the blade is parallel to the direction perpendicular to the helix angle 80, and cutting is performed in the direction of the helix angle 80 while changing the cutting depth of the cutting tool in the direction of the helix angle 80 so that an arc-shaped cutting curved surface 81(a) is formed, the deepest at the middle of the convex portion 22 when viewed from the direction of the helix angle 80, as shown in Figure 4(b). As a result, the major axis 34 of the ellipsoid shape is aligned in the direction of the helix angle 80, and the cutting width changes as the cutting depth changes, forming a cutting curved surface 81(a) shaped to cut away a portion of the lower surface of the ellipsoid shape as shown in Figures 4(a) and (b). In this case, by adjusting the R-shape of the cutting tool and the cutting length, it is possible to cut the ellipsoid shape shown in Figure 4(a). 4(a) and 4(b), cutting is then started from the position where the ellipses overlap, and cutting curved surface 81(b) is also excavated using the same procedure, thereby creating convex portions 22 between each of cutting curved surfaces 81(a) and 81(b) as ridge lines perpendicular to the torsion angle 80. By similarly providing cutting curved surfaces thereafter, portions of the lower surface of the ellipsoid shape are cut away, forming grooves 21 in which a large number of curved surfaces having ridge lines perpendicular to the torsion angle 80 are connected in succession, and the portions that were not cut form flights 20.

[0022] <Actions and Effects of the Kneaded Part in the First Embodiment> The function and effect of the kneading element 7 provided in the screw for a single-screw extruder of the first embodiment will be described below with reference to Fig. 5. Figs. 5(a) and 5(b) are diagrams illustrating the flow of raw material using arrows in Figs. 3(a) and 3(b), and Fig. 5(c) is a diagram illustrating the same in Fig. 3(c). Figs. 5(b) and 5(c) also show the cylinder 2 located on the outer periphery of the kneading element 7, and Fig. 5(b) also shows the flight 20 and the protrusion 22 extending to the flight 20 using imaginary lines. Note that Figure 5(a) shows a planar view of the kneading part 7 of the first embodiment in the circumferential direction of the screw, Figure 5(b) is a cross-sectional view taken along the imaginary line L-L' drawn at a position passing through the center of the width of the groove 21 as viewed in the direction of the twist angle 80 shown in Figure 3(a), and Figure 5(c) is a conceptual diagram of the M-M' cross section shown in Figure 3(a) in a direction perpendicular to the twist angle 80.

[0023] The raw material flows from the upstream 95 side in the screw axis direction through the supply section 11 of the cylinder 2 and screw 3 of the single-screw extruder into the kneading element 7, and then flows in a forward spiral direction along flights 20 having a helix angle of 80 in the flow path between the cylinder 2 and the grooves 21 formed in the kneading element 7, as shown by arrow A in Figure 5(a). Of the raw material flowing in the spiral direction through the grooves, the flow of raw material at the center as seen from the width direction of the grooves indicated by arrow A passes over the curved surface 23 of the groove, then climbs over the center 22(a) of the convex portion 22, and flows to the adjacent curved surface 23 on the downstream side. As shown in Figure 5(b), the center 22(a) of the convex portion is lower than the flight 20, but is a ridge between curved surfaces that rise and fall to narrow the flow path for the raw material. As shown by the arrows indicating the flow of raw material before and after the convex portion in Figure 5(b), the raw material flowing downstream between the cylinder 2 and the bottom of the curved surface 23 flows along the rising curved surface in front of the convex portion and into the narrow flow path between the center 22(a) of the convex portion and the cylinder 2, as the raw material is compressed and agitated in front of the convex portion, the raw material exchanges position, and then the compressed raw material is released into the adjacent flow path immediately after passing the convex portion 22.

[0024] The curved surface 23 located downstream of the convex portion is a curved surface that changes continuously in both the width and depth directions, widening the flow path for the raw material between the curved surface and the cylinder. As a result, the flow of raw material that passes over the convex portion 22 and opens into the adjacent flow path becomes a flow in which the raw material diffuses in the width direction with a change in flow velocity as the flow path for the raw material widens, as shown by the hatched arrow A in Figure 5(a), and similar diffusion also occurs in the depth direction, as shown in Figure 5(b), allowing the raw material to be diffused efficiently.

[0025] As shown in Figure 5(a), the curve 24 where the flight and the curved surface of the groove intersect is a gentle curve such that the width of the flow channel of the groove 21 is narrow around the convex portion 22 and widens between the convex portion and the downstream convex portion, causing the raw material to flow in a meandering pattern, changing its flow direction as the flow channel width changes, as indicated by arrows B and B' in Figure 5(a). As the flow changes in the flow channel width and direction, the raw material exchanges its position in the planar direction.

[0026] Furthermore, as shown by arrows B and B' in Figure 5(a), when the raw material flowing near the curve 24 where the flight and the curved surface of the groove intersect flows into the convex portion 22, the raw material is compressed in the depth direction at the convex portion and then released, exchanging positions, as shown by the arrows in Figure 5(b). However, as shown in Figure 5(c), the flow path formed by the arc-shaped cross section of the convex portion 22 and the flight 20 is compressed at the end of the flow path near the curve 24 where the flight and the curved surface of the groove intersect because the flow path is narrower than near the center 22(a) of the convex portion. As shown by the thicker arrows B and B' in Figure 5(a) around the convex portion, the raw material also spreads in the width direction of the groove during compression, exchanging positions.

[0027] The kneading part 7 passes through the convex parts 22 provided between the flights 20 many times, and each time the distribution and diffusion are carried out by the complex position exchanges, so that the raw material is kneaded uniformly, and as a result, the raw material that has passed through the kneading part becomes uniform. Furthermore, the raw material flowing in the spiral direction along the twist angle 80 also spreads in the width direction of the groove as it is compressed and released at the convex portion 22, and as a result, the raw material undergoes a three-dimensional position exchange and diffusion through multiple repeated gentle compressions and releases. This prevents localized high shear heat generation in the raw material as occurs with conventional screws, and ultimately enables the production of a uniform thermoplastic resin composition.

[0028] Furthermore, the flow paths of the raw material seen from the direction of the torsion angle 80 are all composed of curved surfaces, and the curved surfaces 23, the convex portions 22 with ridges extending perpendicular to the flights 20, and the curves 24 where the flights and the curved surfaces of the grooves intersect all form flow paths that are symmetrical in the width direction. As a result, the flow of the raw material is also symmetrical, as shown by arrows B and B' in Figure 5(a), and the raw material flows without accumulating locally and generating heat, thereby suppressing an increase in the resin temperature.

[0029] [Screw for single-screw extruder equipped with kneading part of second embodiment] FIG. 6(a) shows a kneading member 7 provided in the screw for a single-screw extruder of the second embodiment, developed on a plane in the circumferential direction of the screw. FIG. 6(b) shows a conceptual diagram of a cross section of the imaginary line L-L' in the direction of the torsion angle 80 in the developed view of FIG. 6(a), and FIG. 6(c) shows a conceptual diagram of a cross section of the imaginary line M-M' in the direction perpendicular to the torsion angle 80 in the developed view of FIG. 6(a). FIG. 6(a) is a development view showing the kneading part 7, which is a single spiral flight, and in FIG. 6(a) the upper and lower parts of the figure are connected in the circumferential direction. 6(b) is a cross-sectional view taken along imaginary line L-L', which passes through the center of the width of groove 21 shown in FIG. 6(a) when viewed in the direction of twist angle 80, and flight 20 is also shown by imaginary line. In FIG. 6(b), protrusion 32 up to flight 20 is also shown by imaginary line. In Figures 6(b) and (c), the top shows the direction toward the cylinder side of the extruder screw, and the bottom shows the direction toward the screw axis. Figures 6(b) and (c) are conceptual diagrams that correspond to Figure 6(a) expanded in the circumferential direction of the screw. Figure 6(c) is a cross-sectional view taken along the imaginary line M-M' in Figure 6(a) along the point where the convex portion 32(b) and the flights 20 on its left and right sides intersect, and also shows the ridge line of the convex portion 32(b) located at the back of the M-M' cross section, and also shows two curved surfaces 33(a) and 33(b) of different depths by imaginary lines.

[0030] As shown in Figure 6(a), the kneading part 7 in the second embodiment has the same width and length in the twist angle direction of each curved surface 33 that makes up the groove 21, but differs from the first embodiment in that, as shown in Figures 6(b) and 6(c), the curved surfaces 33 are alternately combined, with the curved surfaces 33 having two different depths, i.e., deep curved surfaces 33(a) and shallow curved surfaces 33(b), each having a shape that cuts out a portion of an ellipsoid shape. In FIG. 6(b), the deepest part of the deep curved surface 33(a) is indicated by an imaginary line N, and in FIG. 6(c), the deepest part is indicated by an imaginary line N'.

[0031] The kneading part 7 of the second embodiment is formed by alternately combining the deep curved surfaces 33(a) and the shallow curved surfaces 33(b) in the direction of the twist angle 80, and therefore, as shown in Figure 6(a), the ridge line of each curved surface, i.e., the shape of the convex portion 32, is an arc that is convex from the deep curved surface 33(a) to the shallow curved surface 33(b). On the other hand, although the curved surfaces 33 in the second embodiment have different depths, all of the curved surfaces 33, like the first embodiment, are formed as a cut-out portion of an ellipsoid whose major axis is aligned in the direction of the twist angle 80 of the flight, and each curved surface is connected in a series so that the major axis 34 is aligned in the direction of the twist angle 80 of the spiral flight, and the connection points of each curved surface form the convex portion 32.Therefore, as shown in Figure 6(a), the tangents 82(a) and 82(b) of the ridge line of the convex portion 32 at the center of the width direction of the groove 21 when viewed in the direction of the twist angle 80 are both perpendicular to the twist angle 80. Furthermore, as shown in Figures 6(a) and 6(c), each curved surface 33 in the groove 21, the convex portion 32 which is the ridge line, and the curve 24 where the flight 20 intersects with the curved surface 33 have a bilaterally symmetrical shape, as in the first embodiment, and as shown in Figure 6(c), the shape of the convex portion 32 when viewed from a vertical cross section along a direction perpendicular to the twist angle 80 is a bilaterally symmetrical arc shape convex toward the axial center of the screw.

[0032] <Actions and Effects of the Kneaded Part in the Second Embodiment> As in the first embodiment, the kneading part 7 in the second embodiment also changes position in the raw material flow path provided between the cylinder and the groove of the kneading part as the raw material is compressed in front of the convex part, and the curved surface 33 downstream of the adjacent convex part also changes continuously in both the width direction and the depth direction, so that the raw material that passes over the convex part 32 and is released into the adjacent flow path becomes a flow that diffuses with changes in flow rate in both the width direction and the depth direction, allowing the raw material to be diffused efficiently. Furthermore, as in the first embodiment, the curve 24 where the flight of the groove and the curved surface intersect is formed as a gentle curve so that the width of the flow path of the groove 21 is narrow around the convex portion 32 and widens in the middle between the convex portions and adjacent convex portions. As a result, the raw material flows in a meandering manner, changing its flow path direction as the width of the flow path changes. As a result, the raw material exchanges positions due to changes in the flow path width and flow path direction in the flow. In addition, the flow path between the arc-shaped convex portion 32 and the flight 20 shown in Figure 6(c) becomes a flow path that is narrow on the left and right, allowing for three-dimensional position exchange of the raw material. In the kneading part 7 of the second embodiment, as in the first embodiment, the raw material flowing in a spiral direction along the twist angle 80 passes through the convex portion 32 multiple times, and each time is distributed and diffused by complex position exchanges, resulting in uniform kneading.As a result, the raw material that passes through the kneading part becomes uniform, and multiple gentle compressions and releases are repeated to exchange and diffuse the raw material in three dimensions, so a uniform thermoplastic resin composition can be obtained without generating localized high shear heat in the raw material as occurs with conventional screws.

[0033] Furthermore, unlike the first embodiment, the kneading part 7 in the second embodiment has different depths for each curved surface 33(a) and 33(b) in the groove 21, so that the compression and release of the raw material flowing continuously between each convex portion 32 and the cylinder 2, as well as the diffusion due to the change in the curved surface, change continuously.Furthermore, the ridge shape of the convex portion 32 continuously changes the direction in which it becomes convex relative to the flow of raw material in the direction of the twist angle 80, so that the raw material is subjected to complex compression and release even when flowing in the direction of the twist angle 80, resulting in three-dimensional positional exchange of the raw material, and ultimately resulting in a more uniform thermoplastic resin composition compared to the first embodiment.

[0034] Furthermore, as in the first embodiment, the flow paths of the raw material viewed from the direction of the torsion angle 80 are all composed of curved surfaces, and further, the curved surface 33, the convex portion 32 whose tangent at the center of the groove width is perpendicular to the torsion angle 80, and the curve 24 where the groove flight intersects with the curved surface all form flow paths that are symmetrical in the width direction, so the flow of the raw material is also symmetrical, and the raw material flows without stagnating locally and generating heat, thereby suppressing an increase in resin temperature.

[0035] [Variations] 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.

[0036] The number of flights in the kneading element 7 of the screw 3 of the present invention may be a single flight as disclosed in the first and second embodiments, or, from the viewpoint of improving kneading and diffusibility, may be a multi-flight spiral flight with grooves provided between each flight so that the raw material is branched from upstream and flows into the kneading element. In the case of a multi-flight configuration, the number of flights is preferably 12 or less, which allows for better kneading and diffusibility while suppressing an increase in resin temperature. The helix angle of the flights of the kneading parts is preferably 25 to 80°. By making it 25° or more, a flow that stably pushes out the raw materials necessary for kneading in the spiral direction can be obtained, and by making it 80° or less, the flights can efficiently transport the raw materials downstream.

[0037] The curved surface of the groove of the kneading element 7 of the screw 3 of the present invention is preferably a curved surface shaped like a cutout of an ellipsoid, with the major axis of the ellipsoid oriented in the direction of the helix angle of the flight, and the major axis may be oriented in the direction of the helix angle within the range of machining accuracy for cutting the screw. By using a curved surface with this shape, the raw material flows evenly from side to side, which suppresses an increase in resin temperature and allows for the production of a uniform thermoplastic resin composition.

[0038] The grooves preferably have curved surfaces with a maximum groove width between the flights of 1.0 to 50.0 mm. A width of 1.0 mm or more allows for stable flow in the spiral direction, thereby suppressing an increase in resin temperature, while a width of 50.0 mm or less allows for positional changes due to flow changes at the curves where the flights and curved surfaces intersect, and provides excellent kneading and diffusibility due to the effects of compression and release at the convex portions. The width of the convex portions provided across the flight in the groove is the minimum width of the groove, and the ratio of the maximum width to the minimum width is preferably 1.1 to 3.0. By setting the ratio to 1.1 or more, it is possible to suppress an increase in resin temperature, while by setting the ratio to 3.0 or less, it is possible to obtain flow changes along the curve where the flight intersects the curved surface, position exchanges due to width changes, and kneading and diffusion by the convex portions.

[0039] The depth of each curved surface provided in the groove may all be the same depth as in the first embodiment, or two types of curved surfaces of different depths may be combined and connected and arranged continuously as in the second embodiment to improve kneading and diffusibility, but any combination may also be used as long as it does not increase the resin temperature. Furthermore, as shown in the first and second embodiments, it is preferable that the curved surfaces be connected with curved surfaces having the same width perpendicular to the twist angle of the curved surfaces, but it is also possible to combine curved surfaces with widths that vary in the range of 1:1 to 1:3 within the range of the maximum width of the groove described above.

[0040] As shown in the first and second embodiments, the deepest part of the groove is preferably a curved surface that is deepest at a position midway between the convex portions as viewed from the direction of the helix angle, from the viewpoint of generating a stable flow accompanied by compression and release of the raw material. However, by adjusting the cutting position of the elliptical shape in the processing example shown in Figure 4(a), it is also possible to adjust the ratio of (distance from the upstream convex portion in the helix angle direction to the deepest part of the groove): (distance from the deepest part of the groove to the downstream convex portion) within one curved surface to be in the range of 1:10 to 1:1. By setting this ratio, the raw material can be efficiently dispersed and compressed efficiently from the deepest part of the groove to the downstream convex portion, and therefore distribution by position exchange of the raw material at the convex portions can also be efficiently performed.

[0041] The curved surfaces of the grooves are made up of 6 to 150 curved surfaces connected in succession, so that the flowing raw material is kneaded while gently compressing and releasing repeatedly, exchanging its position three-dimensionally. This suppresses the rise in resin temperature and makes it possible to obtain a uniformly kneaded product.

[0042] The convex portions of the kneading element 7 of the screw 3 of the present invention are provided at the connecting portions of the curved surfaces, and the length from one convex portion to the adjacent convex portion in the helix angle direction is preferably 10 to 100 mm. By making the length 10 mm or more, local shear heating in the flow path can be suppressed, a thermoplastic resin composition that is not burned can be obtained, and an increase in resin temperature can be suppressed. By making the length 100 mm or less, the raw material that has passed through the convex portion and is released can be sufficiently kneaded and diffused in the flow path between the curved surface and the cylinder until it reaches the adjacent downstream convex portion, and a uniform thermoplastic resin composition can be obtained.

[0043] The cross-sectional shape of the convex portion is a downwardly convex, bilaterally symmetrical arc, as shown in Figure 3(c) of the first embodiment and Figure 6(c) of the second embodiment. The height of the lower surface of the convex portion is preferably 0.1 to 0.9 times the flight height from the deepest part of the curved groove provided in the kneading part, based on the deepest part of the groove. By setting the height of the lower surface of the convex portion to 0.1 times or more, the raw material is sufficiently compressed and released in the flow path between the convex portion and the cylinder, allowing it to be kneaded and dispersed, resulting in a uniform thermoplastic resin composition. By setting the height of the lower surface of the convex portion to 0.9 times or less, shear heating in the flow path can be suppressed, resulting in a thermoplastic resin composition that is free of resin burn, and the rise in resin temperature can be suppressed.

[0044] The height of the flight can be set arbitrarily depending on the diameter of the cylinder and screw of the single-screw extruder and the desired resin discharge rate, but it is preferable that the flight diameter is about -0.5 to -0.1 mm relative to the cylinder diameter.

[0045] The screw 3 of the present invention may have the kneading parts disclosed in the kneading section of the screw. The screw parts upstream and downstream of the kneading section may be parts such as full flights that allow the raw material to flow stably in the kneading section, and other kneading parts may be provided before and after them as long as the effects of the present invention are not impaired.

[0046] 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 flight of the kneading part of the screw is clockwise, and counterclockwise if the forward direction of the spiral is counterclockwise. As shown in FIG. 1, the single-screw extruder of the present invention may be any extruder provided with a cylindrical cylinder and a vertical hole connecting the upstream hopper 4 and the cylinder 2. Alternatively, as shown in FIG. 1, a vertical hole connecting to the cylinder 2 may be provided to provide a vacuum vent 92 for degassing the raw material and removing moisture. The cross-sectional shape of the cylindrical cylinder is preferably circular in order to improve kneading and diffusibility without localized shear heating by providing a unidirectional flow to the raw material in the grooves of the kneading parts, but may also be polygonal. The inner wall of the cylinder 2 in the kneading section 12 is preferably smooth, but may also be grooved.

[0047] By having the above-described configuration, the screw 3 for a single-screw extruder and the single-screw extruder 1 of the present invention can suppress local temperature increases in the raw materials and keep the resin temperature down when kneading and extruding a thermoplastic resin composition, and can provide a screw and single-screw extruder that are excellent in kneading, distribution, and diffusion properties. In particular, the screw 3 and single-screw extruder 1 of the present invention have a mechanism for kneading by gradually compressing and releasing the material, distributing and diffusing the kneaded thermoplastic resin composition to make it uniform. Therefore, suitable kneading can be performed even in applications where multiple materials are kneaded and diffused to form a thermoplastic resin. Furthermore, because no local temperature rise occurs, additives such as surfactants can be suitably kneaded together with the pigment and resin. Furthermore, the single-screw extruder 1 of the present invention can perform suitable kneading while suppressing heat generation in the raw materials due to the structure of the kneading parts, even when kneading is performed at a high screw rotation speed in order to perform kneading at a high output rate. [Explanation of symbols]

[0048] 1 Single-screw extruder 2 cylinders 3 screws 4 Hopper 5 screw flights 6 screw grooves 7 Mixing parts 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 Curved surface 24. Curve where the flight intersects with the surface 32 Convex part 33 Curved surface 34 Long axis 80 twist angle 81 Cutting curved surface 82 Tangent to a ridge 91 Screw connection 92 Vacuum Vent 94 Downstream of the screw axis 95 Upstream in the screw axis direction

Claims

1. A screw used in a single-screw extruder equipped with a kneading element in the kneading section, The kneading part has a spiral flight, a groove, and a plurality of protrusions provided in the groove, the groove has a shape in which a large number of curved surfaces, each of which is a cutout of an ellipsoid, are connected in series with the major axis of the ellipsoid oriented in the direction of the torsion angle of the flight; 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, In a plan view of the kneading part in the circumferential direction of the screw, the curve where the flight and the curved surface of the groove intersect has a shape in which an arc concave toward the flight side is continuously connected. A screw for a single-screw extruder characterized by:

2. The ridge line of the protrusion according to claim 1 is A ridge formed between the flights so as to extend in a direction perpendicular to the twist angle. Alternatively, a tangent to the ridge line at the center in the width direction of the groove is a ridge line that is perpendicular to the twist angle. A screw for a single-screw extruder characterized by:

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

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