Screws for single-screw extruders and single-screw extruders

Abstract

Provided are a screw for a single-screw extruder and a single-screw extruder that, when kneading and extruding a thermoplastic resin composition, suppresses local temperature increases in the raw materials, thereby suppressing the resin temperature, and has kneading properties with excellent distribution and diffusion, making it possible to obtain a uniform thermoplastic resin composition. [Solution] A screw for a single-screw extruder equipped with kneading parts in the kneading section, characterized in that the kneading parts are composed of an upstream kneading element and a downstream kneading element in the direction from upstream to downstream in the screw axial direction, the upstream kneading element having a spiral flight, a plurality of grooves, and a plurality of convex portions that form ridges formed at the connections of adjacent grooves, and the downstream kneading element having a spiral flight, a plurality of connecting circular holes formed parallel to the twist angle direction of the flight, and convex portions that form ridges formed at each connection of the circular holes.

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 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 concentrations of the components and separation of additives from the kneaded product and insufficient effect can 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, extending across the width of the spiral groove and having a width at its apex. Patent Document 1 discovered that using the above-described 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 always 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 4 discloses a rotating screw for kneading used to knead thermosetting resins. In response to the problem of the raw material remaining in a low-pressure portion during kneading and gradually hardening, thereby obstructing the flow of the raw material, Patent Document 4 discloses that, as shown in Fig. 2, a large number of kneading recesses are formed along the spiral direction with progressively shallower groove depths to temporarily increase the flow rate, and narrow flow passages with a fixed flow path length are formed between the spiral kneading recesses, with the ratio of the raw material flow cross-sectional area of ​​the kneading recesses to the cross-sectional area of ​​the flow passages being set to about 2:1. However, Patent Document 4 describes a screw for suppressing hardening due to heating during retention, which is a characteristic of thermosetting resins, and when the screw of Patent Document 4 is used for a thermoplastic resin composition, there is a problem that heat is generated by strong shear when the thermoplastic resin passes through a narrow flow path of a fixed length, resulting in resin burning and resin deterioration. Furthermore, Patent Document 4 only kneads the mixed raw material of the thermosetting resin by changing the flow speed when it passes through a flow path with a narrow cross-sectional area, so it is not possible to achieve sufficient kneading of the thermoplastic resin composition.

[0008] Patent Document 5 discloses a kneading screw used to mix synthetic resins and other raw materials. It discloses, along with Fig. 1, that shallow, narrow grooves and deep, wide grooves are alternately provided along the spiral direction on the outer circumferential surface of the kneading section of a rotating screw, and that adjacent kneading grooves on the rear side in the spiral width direction are connected by flow passages. It states that, with this structure, the flow rate in the shallow, narrow grooves is restricted to rapidly compress the raw material, and the raw material that passes through the shallow, narrow grooves is suddenly released into the deep, wide grooves, accelerating the flow rate and generating turbulence, resulting in high mixing. At the same time, the flow passages provided in the rear parts of the shallow, narrow grooves allow the raw material to be diverted back to the adjacent rear kneading grooves, thereby achieving optimal kneading. However, the structure disclosed in Patent Document 5, particularly when used with thermoplastic resins, has a narrow flow path of a certain length to obtain high pressure in the shallow, narrow groove portion so that the flow is diverted to the flow path, and therefore has the problem of resin burning and resin deterioration occurring in raw materials passing through the shallow, narrow groove portion for a certain period of time. Furthermore, because the spirally flowing raw material is returned to the upstream side through the flow path, the time required for heating and shearing the raw material is long. Furthermore, as shown in Figure 1, the flow of the raw material passing through the flow path and flowing into the shallow, narrow groove on the upstream side changes direction at a nearly right angle, and the wall surface at the outlet of the flow path is convex. As a result, the resin is likely to heat up due to the raw material changing direction and the high shear caused by the convex wall surface, which can cause problems such as resin burning and deterioration of the raw material.

[0009] [Patent Document 1] JP 2017-193096 A [Patent Document 2] Japanese Patent Application Publication No. 4-62131 [Patent Document 3] Japanese Patent Application Publication No. 5-228920 [Patent Document 4] Official Gazette of Jitsuzenhei 4-30030 [Patent Document 5] Jitsuzenhei 2-82514 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a screw for a single-screw extruder and a single-screw extruder that, when kneading and extruding a thermoplastic resin composition, can suppress local temperature increases in the raw materials, thereby suppressing the resin temperature, and that has kneading properties with excellent distribution and diffusion, thereby enabling the production of a uniform thermoplastic resin composition. [Means for solving the problem]

[0011] 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.

[0012] That is, the screw for a single-screw extruder of the present invention is a screw used in a single-screw extruder equipped with kneading parts in a kneading section, wherein the kneading parts are composed of at least one upstream kneading element and at least one downstream kneading element in a direction from the upstream side to the downstream side in the screw axial direction, and the upstream kneading element has a spiral flight, a plurality of grooves formed parallel to the twist angle direction of the flight, and a plurality of convex portions that serve as ridgelines formed at the connection points of the adjacent grooves, the convex portions being ridgelines formed at each connection point of two grooves that cut upward, the convex portions having a height lower than the face height of the flight, and being arc-shaped ridgelines formed across the connection points between the adjacent flights, In a plan view of the kneading parts in the circumferential direction of the screw,The boundary line formed by the surface of the flight and the groove is To narrow the width of the groove the kneading elements are boundary lines curved toward the center between the flights, and the downstream kneading elements have spiral flights, a plurality of connecting circular holes formed parallel to the twist angle direction of the flights, and convex portions serving as ridge lines formed at each connection between the adjacent circular holes, the plurality of connecting circular holes being circular holes shaped as if cutting out a portion of the surface of a true sphere, or circular holes shaped as if cutting out a portion of the surface of an ellipsoid whose major axis is positioned in the twist angle direction of the flights, and the convex portions have a height lower than the surface height of the flights and are arc-shaped ridge lines formed across the space between adjacent flights, In a plan view of the kneading parts in the circumferential direction of the screw, The boundary line formed by the surface of the flight and the circular hole is Depression on the flight side The screw for a single-screw extruder is characterized in that the kneading element has an arc shape. The single-screw extruder of the present invention is characterized by comprising the above-mentioned screw for a single-screw extruder. [Effects of the Invention]

[0013] 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 has kneading properties with excellent distribution and diffusion, making it possible to obtain a uniform thermoplastic resin composition. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a single-screw extruder equipped with a screw for a single-screw extruder of the present invention. [Figure 2] Projection diagram of kneading parts in the screw for a single-screw extruder of the first embodiment [Figure 3] 1 is a development view of a kneading part of a screw for a single-screw extruder according to a first embodiment in the circumferential direction of the screw; [Figure 4]1A and 1B are schematic diagrams of the L-L′ cross section and the M-M′ cross section of the upstream kneading element of the kneading part of the screw for a single-screw extruder according to the first embodiment; [Figure 5] 1A and 1B are schematic diagrams of the N-N' cross section and the O-O' cross section of the kneading element downstream of the kneading part of the screw for a single-screw extruder according to the first embodiment; [Figure 6] 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. [Figure 7] 1 is a conceptual diagram of the LL' cross section and the MM' cross section of the upstream kneading element of the screw for a single-screw extruder of the first embodiment, showing the flow of raw materials. [Figure 8] 1 is a conceptual diagram of the N-N' cross section and the O-O' cross section of the kneading element downstream of the kneading part of the screw for a single-screw extruder of the first embodiment, showing the flow of raw materials. [Figure 9] 2 is a development view of the kneading part of the screw for a single-screw extruder in the screw circumferential direction, and a conceptual diagram of the P-P' cross section and the Q-Q' cross section of the downstream kneading element. [Figure 10] Processing example of kneading parts of the screw for a single-screw extruder according to the second embodiment DETAILED DESCRIPTION OF THE INVENTION

[0015] 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.

[0016] [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 95 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.

[0017] 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.

[0018] [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 shows a planar development view of the kneading member 7 in the circumferential direction of the screw.

[0019] 2 and 3, the kneading part 7 is composed of two or more kneading elements arranged in a direction from upstream 94 to downstream 95 in the screw axial direction. The most upstream kneading element 27, the most downstream kneading element 28, and, as an example, the kneading element 79 located between them, shown in FIGS. 2 and 3, will be described below in order. 2 and 3 show an example of a kneading part 7 having two spiral flights, and FIG. 3 is a developed view in which the upper and lower parts of the figure are connected in the circumferential direction, and the imaginary lines L-L' and N-N' are lines passing through the center of the width of the groove and the round hole when viewed in the direction of the flight twist angle of 80. 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 right side of the figure is the upstream 94 in the screw axial direction, and the left side is the downstream 95 in the screw axial direction.

[0020] (Upstream mixing element) The upstream kneading element 27 in the kneading part 7 is shown in a projection of the kneading part in FIG. 2 and in a development in FIG. The upstream kneading element 27 comprises a spiral flight 20, a plurality of grooves 21 formed parallel to the direction of the twist angle 80 of the flight, and a plurality of convex portions 22 which serve as ridge lines formed at each connection point of adjacent grooves, the convex portions 22 being ridge lines formed at the connection points of two grooves 21 that are cut upward, the convex portions 22 having a height lower than the surface height of the flight 20, and being arc-shaped ridge lines formed between adjacent flights, and the boundary line 24 formed by the surface of the flight 20 and the groove 21 is a kneading element which is a boundary line shaped to curve toward the center between the flights around the convex portions.

[0021] In the kneading element 27 on the upstream side of the developed view of Figure 3, a conceptual diagram of a cross section of the imaginary line L-L' shown in the direction of the torsion angle 80 is shown in Figure 4(a), and a conceptual diagram of a cross section of the imaginary line M-M' shown in the direction perpendicular to the torsion angle 80 is shown in Figure 4(b). FIG. 4(a) is a cross-sectional view taken along line LL' in FIG. 3, and also shows the flight 20 and the protrusion 22 extending to the flight 20 as imaginary lines. In Figures 4(a) and (b), 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 4(a) and (b) are conceptual diagrams that correspond to Figure 3, which is expanded in the circumferential direction of the screw. FIG. 4(b) is a cross-sectional view of the M-M' cross section shown along the convex portion 22 in the drawing of FIG. 3, and the cross section of the groove 21 is also shown by an imaginary line in the cross-sectional view.

[0022] As shown in Figures 2 and 3, the upstream kneading element 27 has a forward spiral flight 20, a plurality of grooves 21, and a plurality of protrusions 22, and the flight 20 is a forward spiral flight having a helix angle 80 configured to dam the resin. The groove 21 is a spiral groove having a certain width provided between two flights 20 aligned in the direction of a torsion angle of 80. In this embodiment, the cross-sectional shape of the flow path of the groove 21 is exemplified as a rectangular cross-section, as shown in FIG. 4(b). As shown in Figure 4(a), groove 21 has a bottom surface of a constant depth, and the end of the groove in the direction of the helix angle of 80 has a cross section that rises from the bottom surface. Each groove 21 is arranged parallel to the helix angle direction of the flight, and the ends of the grooves are connected. At each connecting portion of the groove ends, the protrusion 22 is provided as a ridge line of the connecting portion of the two groove ends that rises. In this embodiment, the convex portions 22 are formed across the flights 20 so that their ridge lines extend in a direction perpendicular to the twist angle 80, as shown in the development view of FIG.

[0023] The convex portion 22 formed as the ridge of the connection of each of the grooves 21 is a ridge that forms a downwardly convex semicircular arc shape extending between two adjacent flights 20, as shown in Figures 3 and 4(b). As shown in Figure 4(a), the convex portion 22 is provided as a ridgeline at the connection between the ends of two grooves 21 that are cut in an arc shape that convexly rises toward the axial center of the screw, and the convex portion 22 is provided so as to have a height lower than the upper surface of the flight 20 when viewed from the axial center of the screw. Furthermore, as shown in Figure 4(b), the convex portion 22 is formed between the flights 20 in the shape of a downwardly convex semicircular arc, so that the groove depth from the surface of the flight 20 to the convex portion 22 is shallower than the groove depth of the groove 21.

[0024] As shown in Figure 3, the boundary line 24 between the surface of the flight 20 and the groove 21, as viewed from the side of the screw, is a line parallel to the direction of the flight twist angle 80, where the width of the flow path of the groove 21 is constant away from the convex portion 22, but around the convex portion 22, the boundary line is a curved line that curves toward the center between the flights so as to narrow the width of the groove 21, which serves as the flow path. In the upstream kneading element 27, the boundary lines 24 are continuously connected, so that the grooves 21 formed between the boundary lines 24 have the narrowest width at the convex portions 22 when viewed as a flow path flowing in the direction of the torsion angle 80, and the middle of the grooves 21 have a shape with a wide width. The end of the groove 21 around the protrusion 22 is formed of a curved surface, including the cross section of the end that is cut up as described above.

[0025] (Downstream mixing element) The downstream kneading element 28 of the kneading part 7 is shown in the projection of the kneading part in FIG. 2 and in the development in FIG. The downstream kneading element 28 comprises a spiral flight 20, a plurality of connecting circular holes 23 formed parallel to the twist angle direction 80 of the flight, and a convex portion 26 which forms a ridge line formed at each connection point of adjacent circular holes, and the plurality of connecting circular holes 23 are circular holes shaped like a portion of the surface of a true sphere, connected in a row in the twist angle 80 direction of the flight 20, the convex portion 26 has a height lower than the face height of the flight 20 and is an arc-shaped ridge line formed between adjacent flights, and the boundary line 25 formed by the face of the flight 20 and the circular hole 23 is a kneading element which has a concave arc shape when viewed from the flight.

[0026] In the kneading element 28 downstream of the unfolded view of Figure 3, a conceptual diagram of a cross section of the imaginary line N-N' shown in the direction of the torsion angle 80 is shown in Figure 5(a), and a conceptual diagram of a cross section of the imaginary line O-O' shown in the direction perpendicular to the torsion angle 80 is shown in Figure 5(b). Figure 5(a) is a cross-sectional view taken along line N-N' in Figure 3, and also shows the flight 20 and the protrusion 26 extending to the flight 20 as imaginary lines. In Figures 5(a) and (b), the top is toward the cylinder side of the extruder screw, and the bottom is toward the axial center of the screw. Figures 5(a) and (b) are conceptual diagrams that correspond to Figure 3, which is expanded in the circumferential direction of the screw. FIG. 5(b) is a cross-sectional view of the O-O' cross section shown along the protrusion 26 in FIG. 3, and the cross section of the deepest circular hole 23 is also shown by an imaginary line in the cross-sectional view.

[0027] 2 and 3, the downstream kneading element 28 includes a forward spiral flight 20, a plurality of round holes 23, and a plurality of protrusions 26, and the flight 20 is a forward spiral flight having a helix angle 80 that is provided to block the resin. Note that, like the flight in the upstream kneading element 27, a two-edge flight 20 is exemplified. As shown in Figure 3, the round holes 23 have a curved surface shaped like a portion of the lower surface of a true sphere, and are arranged in the same direction as the twist angle 80 of the spiral flight, forming a shape in which multiple round holes 23 are connected in series, and at each connection between the round holes 23, the protrusions 26 are provided as ridges of the connection parts.

[0028] The round holes 23 are arranged parallel to the helix angle 80 of the flight so that the multiple spherical curved surfaces overlap, and furthermore, in this embodiment, the curved surfaces are arranged at equal intervals, so that in a vertical cross section taken along the direction of the helix angle 80 as shown in Figure 5(a), one round hole 23 forms a symmetrical arc convex toward the axial center of the screw, and a convex portion 26 is formed as a ridgeline at the connection between the two round holes 23. Furthermore, as shown in Figure 5(b), in a vertical cross section taken along a direction perpendicular to the helix angle 80, the round holes 23 form a symmetrical arc convex toward the axial center of the screw. In addition, each of the round holes 23 disclosed in the first embodiment is a curved surface having the same shape in terms of depth, width, and length in the twist angle direction, and the deepest point of the curved surface is the center of the curved surface when viewed from the direction of twist angle 80 and the direction perpendicular to twist angle 80. Furthermore, since the circular hole 23 is a curved surface shaped by cutting out a portion of the lower surface of a true sphere, when comparing the change in curvature from the center of the curved surface, i.e., the deepest part of the circular hole 23, in the direction of the torsion angle 80 with the change in curvature in the direction perpendicular to the torsion angle 80, the curvature is the same.

[0029] The protrusions 26 formed as ridges at the connection points of the circular holes 23 are ridges that extend between two adjacent flights 20, as shown in Figures 3 and 5(b). The protrusions 26 are formed between the flights 20 so that their ridges extend perpendicular to the twist angle 80, as shown in the development view of Figure 3. Furthermore, as shown in Figure 5(b), in a vertical cross section (cross section of imaginary line O-O') along a direction perpendicular to the torsion angle 80, the convex portion 26 is a ridge line provided at the connection between two curved surfaces that have a symmetrical arc-shaped cross section that is convex toward the axial center of the screw. 5(a), the convex portion 26 is provided as a ridgeline of the connection between the two round holes 23 that rises from the center so that it has a height lower than the upper surface of the flight 20 when viewed from the axial center of the screw. Also, as shown in FIG. 5(b), the groove depth from the flight 20 to the convex portion 26 is shallower than the groove depth of the round holes 23.

[0030] As shown in Figure 3, the boundary line 25 between the surface of the flight 20 and the round holes 23, as viewed from the side of the screw, is a concave arc when viewed from the flight, and the boundary line between each connecting round hole 23 and the surface of the flight 20 has a shape in which the concave arc is continuously connected.Therefore, when viewed as a flow path for flow in the direction of the torsion angle 80, the round holes 23 provided between the boundary lines 25 have the narrowest width at the convex portions 26 and the widest width midway between the two convex portions 26. In this specification, the width of the flow channel means the width in the direction perpendicular to the torsion angle.

[0031] (Intermediate kneading element) In the first embodiment, an intermediate kneading element 79 positioned between the upstream kneading element 27 and the downstream kneading element 28 is illustrated in FIGS. 2 and 3 as an example of the kneading part 7. FIG.

[0032] 2 and 3 has a flight 20, a round hole 73, a groove 71, and a protrusion 72 provided at the connection between the round hole 73 and the groove 71. Here, the round hole 73 has the same shape as the round hole 23 in the downstream kneading element, and the groove 71 has the same shape as the groove 21 in the upstream kneading element except that the length in the helix angle direction is shorter. The illustrated intermediate kneading element 79, as shown in Figure 3, is configured such that grooves 71 and round holes 73 are repeatedly connected in this order downstream in the twist angle direction, and the intermediate kneading element 79 is connected upstream to the groove of the upstream kneading element 27 and downstream to the round hole of the downstream kneading element 28. In addition, the flight 20 illustrated in this embodiment has the same shape as the flight on the upstream kneading element 27 around the groove 71, and the same shape as the flight around the convex portion of the upstream kneading element 27 and the downstream kneading element 28 around the round hole 73, and the width of the flow path is narrowest at the convex portion. The convex portion 72, like the convex portion 22 of the upstream kneading element 27 and the convex portion 26 of the downstream kneading element 28, is provided as a ridge at the connection portion, and the convex portion 72 is an arc-shaped ridge that convex toward the center of the screw axis across the flight 20, and the ridge is at a height lower than the surface of the flight 20.

[0033] <Actions and Effects of the Kneaded Part in the First Embodiment> The effects of the kneading elements 7 included in the screw for a single-screw extruder of the first embodiment will be described below in the order of the upstream kneading elements and the downstream kneading elements.

[0034] The function and effect of the upstream kneading element 27 will be described below with reference to FIGS. Figures 6 and 7(a) are diagrams showing the upstream kneading element 27 in Figures 3 and 4(a) with the flow of raw material indicated by arrows, and Figure 7(b) is a diagram shown in Figure 4(b). In addition, Figures 7(a) and 7(b) additionally show a cylinder 2 located on the outer periphery of the kneading part 7, and Figure 7(a) also shows the flight 20 and the protrusion 22 extending to the flight 20 as virtual lines in the cross-sectional view. Note that Figure 6 shows a planar view of the kneading part 7 of the first embodiment in the circumferential direction of the screw, Figure 7(a) 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 shown in Figure 3 when viewed in the direction of the twist angle 80, and Figure 7(b) is a conceptual diagram of the M-M' cross-section shown in Figure 3 in a direction perpendicular to the twist angle 80.

[0035] The raw material flows from the upstream 94 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 part 7. After being diverted by the two flights 20 of the kneading element 27 on the upstream side of the kneading part 7, the raw material flows into the flow path between the grooves 21, as shown by the arrows in Figure 6, and flows in a spiral direction with a helix angle of 80 along the flights 20 through the resin passage between the groove 21 arranged in the spiral direction, the two flights 20 adjacent to the groove, and the cylinder 2.

[0036] Of the raw material flowing in the spiral direction, the raw material flowing in the center of the groove as viewed in the width direction indicated by arrow A passes over groove 21, then climbs over center 22(a) of convex portion 22 and flows into adjacent groove 21 downstream. As shown in Figure 7(a), the center 22(a) of the convex portion is lower than the flight 20, but is a ridge line formed between curved surfaces that have an upward and downward cut-off shape so that the flow path for the raw material narrows in the vertical direction. Therefore, as shown by the arrows indicating the flow of raw material before and after the convex portion in Figure 7(a), the raw material flowing downstream between the cylinder 2 and the bottom of the groove 21 flows along the upward cut-off 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, the raw material is compressed and agitated in front of the convex portion, causing the raw material to exchange positions. After that, the compressed raw material is immediately released into the adjacent flow path as it passes over the convex portion 22(a), and the raw material is then exchanged positions.

[0037] 6, the boundary line 24 between the flight and the groove is formed as a gentle curve such that the width of the channel in the groove 21 is narrow around the convex portion 22 and wide in the groove 21 away from the convex portion, so that the raw material flows in a flow path that changes both in flow rate and flow velocity as the channel width and channel direction change, as indicated by arrows B and B' in FIG. 6. As the channel width and channel direction change in the flow, the raw material exchanges positions in the planar direction. Furthermore, as shown by arrows B and B', the raw material flowing near the boundary 24 between the flight and the groove is compressed and released in the height direction at the protrusion 22 as it flows into the protrusion 22, similar to the arrows shown in Figure 7(a), and exchanges position.However, as shown in Figure 7(b), the flow path consisting of the arc-shaped cross section of the protrusion 22 and the flight 20 is narrower in the height direction at the end of the flow path near the boundary 24 between the flight and the circular hole than near the center 22(a) of the protrusion, so the raw material is strongly compressed, and as shown by arrows B and B' in Figure 6 that are thicker around the protrusion 22, the raw material also spreads in the width direction of the groove during compression and exchanges position. The upstream kneading element 27 has a shape in which the grooves 21 are continuously connected, and the boundary line 24 between the flight and the groove immediately after the convex portion 22 is arranged to widen in the width direction. Therefore, the raw material that passes through the convex portion 22 and is released into the next groove 21 is released while diffusing, changing its flow direction, as shown by arrows B and B' in Figure 6, further advancing the position exchange of the raw material.

[0038] As described above, in the convex portions 22, the raw material is kneaded while being distributed by the complex positional exchange of the raw material due to compression and release in the width and depth directions and changes in the flow path, and the kneaded raw material flows in the direction of the twist angle, and then is further distributed and kneaded in the same way by the next convex portion 22. Below, in the upstream kneading element 27, repeated distribution and kneading are promoted at the numerous convex portions 22 provided, but since the convex portions 22 are provided as ridges that have no length in the flow direction of the raw material, the raw material at the convex portions 22 is released immediately after compression, and further, since each convex portion 22 is provided with a gap between them, the raw material can be kneaded without generating heat, and since the raw material flows without being locally retained and generating heat, an increase in resin temperature can be suppressed.

[0039] The raw material that has passed through the grooves and convex portions of the upstream kneading element 27 then flows into the grooves 71 and round holes 73 provided in the intermediate kneading element 79 exemplified in the first embodiment. In the round holes 73 in the intermediate kneading element 79 and the convex portions 72 provided before and after the round holes 73, the raw material is kneaded in the same manner as the flow of the raw material in the upstream kneading element 27 and the downstream kneading element 28 described above and below, and the kneaded raw material flows in a spiral direction through the grooves and then flows into the grooves of the downstream kneading element 28.

[0040] The function and effect of the downstream kneading elements 28 will be described with reference to FIGS. Figure 8(a) is a diagram in which the flow of raw material is shown by arrows in Figure 5(a), and Figure 8(b) is a diagram in which the flow of raw material is shown in Figure 5(b). In Figures 8(a) and 8(b), the cylinder 2 located on the outer periphery of the kneading part 7 is additionally shown, and Figure 8(a) also shows the protrusion 26 extending to the flight 20 as a virtual line. 8(a) is a cross-sectional view taken along the imaginary line N-N' drawn at a position passing through the center of the width of the round hole 23 shown in FIG. 3 when viewed in the direction of the twist angle 80, and FIG. 8(b) is a conceptual diagram of the O-O' cross-section shown in FIG. 3 in a direction perpendicular to the twist angle 80.

[0041] The raw material that flows from the intermediate kneading element 79 into the downstream kneading element 28 flows into the round hole 23 in the downstream kneading element 28, and flows in the spiral direction through the round hole 23 arranged in the spiral direction and the resin passage arranged between the two flights 20 adjacent to the round hole and the cylinder 2. Of the raw material flowing in the spiral direction, the flow of raw material at the center as viewed from the width direction of the groove indicated by arrow C passes over the round hole 23, then climbs over the center 26(a) of the convex portion 26 and flows into the adjacent round hole 23 downstream. As shown in Figure 8(a), the center 26(a) of the convex portion is lower than the flight 20, but is a ridge line formed between curved surfaces that have an upward and downward cut-off shape so that the flow path for the raw material narrows in the vertical direction. Therefore, as shown by the arrows indicating the flow of raw material before and after the convex portion in Figure 8(a), the raw material flowing downstream between the cylinder 2 and the bottom of the round hole 23 flows along the upward cut-off curved surface in front of the convex portion and into the narrow flow path between the center 26(a) of the convex portion and the cylinder 2, the raw material is compressed and agitated in front of the convex portion, causing the raw material to exchange positions, and then the compressed raw material is released into the adjacent flow path immediately after passing the convex portion 26.

[0042] The circular hole 23 located downstream of the convex portion has a curved surface that changes continuously in both the width and depth directions, and the flow path for the raw material between the curved surface and the cylinder widens toward the center of the circular hole. Therefore, the flow of raw material that passes over the convex portion 26 and opens into the adjacent downstream 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 arrows C immediately after the convex portion 26 in Figure 6, which indicate that the width of the tip of the arrow C widens on both sides. Similarly, diffusion also occurs in the depth direction toward the center of the circular hole, as shown in Figure 8(a). Furthermore, after the raw material passes near the center of the circular hole 23, the width and height of the flow path for the raw material narrows along the curved surface of the circular hole, and the diffused raw material changes flow direction and flows into the convex portion 26 while being compressed, as shown by the hatched arrow in front of the convex portion 26 in Figure 6. As a result, the positional exchange of the raw material further progresses due to the flow that is accompanied by changes in the flow rate and flow velocity due to the change in flow path direction.

[0043] As shown in Figure 6, boundary line 25 between the flight and the circular hole is formed as a gentle curve such that the width of the flow path of circular hole 23 is narrow around convex portion 26 and widens midway between the convex portion and the adjacent convex portion downstream. As a result, the raw material flows with varying flow rate and velocity, changing the flow path direction as the flow path width changes, as indicated by arrows D and D' in Figure 6. This change in flow promotes the exchange of the raw material's position.

[0044] Furthermore, as shown by the flow of arrows D and D' in Figure 6, when the raw material flowing near the boundary line 25 between the flight and the circular hole flows into the convex portion 26, the raw material is compressed and released in the depth direction at the convex portion, similar to the arrows shown in Figure 8(a), and exchanges position.However, as shown in Figure 8(b), the flow path consisting of the arc-shaped cross section of the convex portion 26 and the flight 20 is compressed at the end of the flow path near the boundary line 25 between the flight and the circular hole because the flow path is narrower than near the center 26(a) of the convex portion.As shown by the thicker arrows D and D' in Figure 6 around the convex portion, the raw material also spreads in the width direction of the groove during compression, and exchanges position.

[0045] The downstream kneading element 28 passes through the convex portion 26 provided between the round hole 23 and the flight 20 many times, and each time it distributes and kneads the raw material through the complex position exchange described above, and also diffuses the raw material in the round hole 23.Therefore, the raw material distributed and kneaded in the upstream kneading element 27 is further distributed, diffused and kneaded in the downstream kneading element 28, thereby enhancing the effect, and as a result, the raw material that has passed through the kneading section 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 26, and as a result, the raw material undergoes a three-dimensional position exchange and diffusion as a result of repeated gentle compression and release multiple times. This prevents the raw material from generating high localized shear heat as occurs with conventional screws, and ultimately enables the production of a uniform thermoplastic resin composition.

[0046] Furthermore, the flow paths of the raw material viewed from the direction of the torsion angle 80 are all composed of curved surfaces, and the convex portions 26 having ridges extending perpendicular to the flights 20 in the downstream kneading element 28, the round holes 23, and the boundary lines 25 between the flights and the round holes all form flow paths that are symmetrical in the width direction, so the flow of the raw material is also symmetrical as shown by arrows D and D' in Figure 6, and the raw material flows without stagnating locally and generating heat.As a result, even if the raw material is repeatedly kneaded by the convex portions, which are spaced closer together than the upstream kneading element 27, the rise in resin temperature can be suppressed.

[0047] As described above, the kneading part 7 of the present invention first kneads the unmixed raw material by distributing it multiple times using the spaced convex portions 22 in the upstream kneading element 27, and then further diffuses and distributes it evenly using the downstream kneading element 28, which has round holes with curved surfaces and convex portions, thereby kneading and diffusing the raw material evenly.Since the raw material is kneaded without flowing back to the upstream side or generating heat due to localized flow, the raw material flows without stagnating locally and generating heat, and the rise in resin temperature can be suppressed.

[0048] Furthermore, the intermediate kneading elements exemplified in the first embodiment described above can perform more uniform kneading by performing two kneading processes in the middle of the kneading section: the grooves of the upstream kneading element 27, which stabilize the flow, and the round holes of the downstream kneading element 28, which are excellent at kneading.

[0049] [Screw for single-screw extruder equipped with kneading part of second embodiment] FIG. 9(a) shows a view of the 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. Figure 9(b) shows a conceptual diagram of a cross section of the imaginary line P-P' in the direction of torsion angle 80 in the unfolded view of Figure 9(a), and Figure 9(c) shows a conceptual diagram of a cross section of the imaginary line Q-Q' in the direction perpendicular to torsion angle 80 in the unfolded view of Figure 9(a). FIG. 9(a) is a development view showing the kneading part 7, which is a two-strip spiral flight, and in FIG. 9(a) the upper and lower parts of the figure are connected in the circumferential direction. Figure 9(b) is a cross-sectional view of the circular hole 33 of the downstream kneading element 38 shown in Figure 9(a) along the imaginary line P-P', which is drawn to pass through the center of the width of the circular hole 33 when viewed in the direction of the torsion angle 80, and the flight 20 and the protrusion 32 extending to the flight 20 are also shown as imaginary lines. In Figures 9(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 9(b) and (c) are conceptual diagrams that correspond to Figure 9(a), which is expanded circumferentially around the screw. FIG. 9(c) is a cross-sectional view taken along the imaginary line Q-Q' drawn along the intersection of the convex portion 32 and the flights 20 on either side of it in FIG. 9(a), and the cross-section of the deepest circular hole 33 is also shown by an imaginary line in the cross-sectional view.

[0050] As shown in Figure 9(a), the kneading part 7 in the second embodiment differs from the first embodiment in that the shape of the round hole 33 when viewed from the side of the screw in the downstream kneading element 38 is not a shape that cuts out a part of the surface of a perfect sphere like the round hole 23 in the first embodiment, but a shape that cuts out a part of the surface of an ellipsoid whose major axis 31 is aligned in the twist angle direction of the flight.The upstream kneading element 27 and the intermediate kneading element 79 are exemplified as having the same shape as in the first embodiment. In this specification, the term "ellipsoid shape" refers to a shape having a major axis, 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 curved; specific examples include a spheroid and a distorted ellipsoid. Each of the circular holes 33 has a curved surface formed by cutting out a part of the lower surface of an ellipsoid.

[0051] In order to explain the long shaft 31, a conceptual diagram of an example of the method of processing the kneading parts of the screw of a single-screw extruder of the present invention will be shown in FIG. 10 and explained below. 10(a) and (b) are conceptual diagrams of the kneading part 7 developed on a plane in the circumferential direction of the screw corresponding to FIGS. 9(a) and (b), and a conceptual diagram of a cross section taken along imaginary line P-P' in FIG. 9(a), which is drawn to pass through the center of the width as viewed in the direction of the helix angle 80, with the lines to be processed added as solid lines. Also, in FIG. 10(b), like FIG. 9(b), the flight 20 and the protrusion 32 extending to the flight 20 are also illustrated as imaginary lines. The circular holes 33 in the kneading part 7 can be created by cutting elliptical holes, as shown by the cutting curved surfaces 81(a) and 82(b), into a cylindrical screw base material. As shown in Figure 10(a), during cutting, the cutting curved surfaces are oriented with the major axis 31 of the ellipsoidal shape aligned in the direction of the helix angle 80, and the ellipsoidal shapes are cut so that they overlap, thereby creating multiple connected circular holes and the convex portions disclosed in the present invention. The circular holes carved by the above-described processing method are shaped by cutting out a portion of the lower surface of an ellipsoidal shape whose major axis is aligned in the direction of the helix angle 80 of the flight 20. At the connection points of the multiple connected circular holes 81(a) and 81(b), convex portions 32 are formed as ridges perpendicular to the helix angle 80, and the uncut portions form the flight 20.

[0052] As shown in FIG. 9( a), one of the circular holes 33 has a shape in which the major axis 31 is oriented in the direction of the helix angle 80 of the flight 20, and the multiple circular holes 33 are connected so that their major axes 31 are aligned along the helix angle direction. The connected circular holes 33 are arranged so that ellipses overlap when viewed from the side of the screw. Therefore, as shown in FIG. 9( b), in a vertical cross section taken along the direction of the helix angle 80, the cross-sectional shape of the circular holes 33 is an arc that convex toward the axial center of the screw. A convex portion 32 is formed as a ridgeline at the connecting portion of the circular holes 33. As shown in FIG. 9( c), in a vertical cross section taken along a direction perpendicular to the helix angle 80, the cross-sectional shape of the circular holes 33 is a symmetrical arc that convex toward the axial center of the screw. In the second embodiment, the circular holes 23 are arranged at equal intervals, so the circular holes 33 in FIG. 9( b) are symmetrical arcs. Furthermore, unlike the first embodiment, the round hole 33 has an ellipsoidal curved surface with the major axis 31 oriented in the direction of the torsion angle 80. Therefore, when comparing the change in curvature from the center of the curved surface, i.e., the deepest part of the curved surface, in the direction of the torsion angle 80 with the change in curvature in the direction perpendicular to the torsion angle 80, the curved surface has a gradual change in curvature in the direction of the torsion angle 80.

[0053] The protrusions 32 formed as ridges at the connection points of the circular holes 33 are ridges that extend between two adjacent flights 20, as in the first embodiment, as shown in Figures 9(a) and 9(c). As shown in the developed view of Figure 9(a), the convex portion 32 is a ridge provided at the connection portion of the round hole 33 whose major axis is oriented in the direction of the helix angle 80, and therefore the ridge is formed across the flights 20 so as to extend in a direction perpendicular to the helix angle 80. Also, as shown in Figure 9(b), the convex portion 32 is a ridge having a bilaterally symmetrical arc shape that is convex toward the axial center of the screw, and the ridge has a height lower than that of the flights 20 when viewed from the axial center of the screw.

[0054] Furthermore, as shown in Figure 9(a), the boundary line 35 formed by the flight 20 and the circular holes 33 has a shape in which concave arcs are connected continuously when viewed from the flight, and when the connected circular holes 33 provided between the boundary lines 35 are viewed as a flow path that flows in the direction of the torsion angle 80, the width is narrowest at the convex portion 32 and widest midway between the two convex portions 32.

[0055] <Actions and Effects of the Kneaded Part in the Second Embodiment> The kneading part of the second embodiment has the same effect as the first embodiment, and when kneading and extruding a thermoplastic resin composition, it suppresses local temperature increases in the raw materials, thereby suppressing the resin temperature, and can perform kneading with excellent distribution and diffusion, ultimately resulting in a uniform thermoplastic resin composition. Furthermore, in the second embodiment, the shape of the round hole 33 of the downstream kneading element is a long round hole in the direction of the twist angle 80, shaped like a cut-out portion of the surface of an ellipsoid whose major axis 31 is aligned in the direction of the twist angle 80 of the flight, and the curvature of the curved surface of the round hole 33 is the gentlest in the direction parallel to the direction of the twist angle 80 of the flight, so the shear heat applied to the raw material flowing spirally in the direction of the twist angle can be reduced more than in the first embodiment.

[0056] [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.

[0057] The number of flights in the kneading element 7 of the screw 3 of the present invention may be two, as disclosed in the first and second embodiments, to separate the raw material flow path into two, or one, from the viewpoint of widening the raw material flow path to suppress a rise in resin temperature due to shear. Furthermore, from the viewpoint of improving kneading performance, the number of flights may be three or more, but is preferably 12 or less. By having 12 or less flights, excellent distribution can be achieved while suppressing a rise in resin temperature, and a uniform thermoplastic resin composition can be obtained. In addition, the number of grooves in the upstream kneading element 27 and the downstream kneading element 28 in the kneading part 7 may be different within the above range, and may be changed so that the flows split or merge before and after the kneading part or within the kneading part 7. The helix angle of the flights of the kneading parts is preferably 25 to 80°. A helix angle of 25° or more ensures a stable flow that pushes the raw material necessary for kneading in the spiral direction, while a helix angle of 80° or less allows the flights to efficiently transport the raw material downstream. The flights around the grooves may also be provided with notches to act as subleads that direct the raw material downstream.

[0058] The intermediate kneading element 79 in the kneading part 7 is not limited to the shapes disclosed in the first and second embodiments, and may have any shape. For example, the intermediate kneading element may have the same shape as the upstream kneading element 27 with the convex portions spaced apart, or the kneading part 7 may be configured with only the upstream kneading element 27 and the downstream kneading element 28 without the intermediate kneading element.

[0059] The maximum width of the grooves between the flights of the round holes and grooves of the kneading elements 7 of the screw 3 of the present invention is preferably 1.0 to 50.0 mm. A width of 1.0 mm or more allows for stable flow in the spiral direction, suppressing an increase in resin temperature, while a width of 50.0 mm or less allows for excellent kneading and diffusibility due to the effects of position exchange and compression and release at the convex portions associated with flow changes at the boundary between the flights and grooves. The width of the convex portion of the kneading part 7 is the minimum value of the width of the adjacent round holes or grooves, and the ratio of the maximum width to the minimum width is preferably 1.1 to 3.0. By making the ratio 1.1 or more, it is possible to suppress an increase in resin temperature, and by making it 3.0 or less, it is possible to obtain flow changes along the boundary between the flight and the groove, position exchanges due to width changes, distribution by the convex portions, and diffusion in the round holes.

[0060] The circular holes in the downstream kneading elements 28 shown in the second embodiment are preferably arranged so that the curved surface, which is a cutout of an ellipsoid, is shaped so that the major axis of the ellipsoid is in the direction of the helix angle of the flight, but it is sufficient to arrange the major axis in the direction of the helix angle within the range of machining accuracy for cutting the screw. By using such a curved surface, the raw material flows evenly to the left and right, which suppresses an increase in resin temperature and allows for the production of a uniform thermoplastic resin composition.

[0061] The depth of each round hole of the downstream kneading element 28 may all be the same depth, as shown in the first and second embodiments, or may be a series of connected curved surfaces of different depths arranged in order to enhance kneading and diffusibility. Furthermore, as shown in the first and second embodiments, it is preferable to connect circular holes having the same width perpendicular to the twist angle, but circular holes having different widths in the range of 1:1 to 1:3 within the maximum width range may also be combined.

[0062] As shown in the first and second embodiments, the circular holes in the downstream kneading elements 28 are preferably connected at equal intervals to form a curved surface with the deepest point midway between the convex portions as viewed from the direction of the twist angle, from the viewpoint of generating a stable flow accompanied by compression and release of the raw material. However, the spacing between the circular holes may also be adjusted so that the ratio of (the distance from the convex portion in the twist angle direction to the deepest part of the circular hole):(the distance from the deepest part of the circular hole to the downstream convex portion) within one curved surface is in the range of 1:10 to 1:1. By setting this ratio, the raw material is efficiently dispersed and can be efficiently compressed from the deepest part of the groove to the downstream convex portion, allowing for efficient distribution by exchanging the position of the raw material.

[0063] The round holes in the downstream kneading element 28 are connected in a series of 3 to 50 round holes, so that the flowing raw material is kneaded while gently compressing and releasing multiple times, exchanging the position of the raw material in three dimensions, thereby suppressing the rise in resin temperature and enabling the production of a uniform thermoplastic resin composition.

[0064] In the downstream kneading element 28, 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 diffused in the flow path between the round holes, flights, and cylinders before reaching the adjacent convex portion, and a uniform thermoplastic resin composition can be obtained.

[0065] The cross-sectional shape of the convex portion of the downstream kneading element 28 is a downwardly convex, symmetrical arc, as shown in FIG. 4(b) of the first embodiment and FIG. 8(b) of the second embodiment. The height of the underside of the convex portion is preferably 0.1 to 0.9 times the flight height from the deepest part of the groove to the underside of the convex portion, based on the deepest part of the circular hole provided in the kneading element. By setting the height of the underside 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, resulting in a uniform thermoplastic resin composition. Setting the height of the underside of the convex portion to 0.9 times or less suppresses shear heating in the flow path, resulting in a thermoplastic resin composition without resin burn, and suppresses an increase in resin temperature.

[0066] The length of the grooves in the upstream kneading elements 27 is preferably 5 to 80 mm, measured from one convex portion to the adjacent convex portion in the helix angle direction. A length of 5 mm or more can suppress local shear heating in the flow path, resulting in a thermoplastic resin composition that is not burned, and can also suppress an increase in resin temperature. A length of 80 mm or less can efficiently distribute the raw materials at each convex portion, resulting in a uniform thermoplastic resin composition. The grooves may also be a combination of grooves with lengths within the above numerical ranges. Furthermore, the cross-sectional shape of the groove may be rectangular as disclosed in the first and second embodiments in order to stabilize the flow of raw material, or may be semicircular in order to prevent resin from burning at the corners formed by the flight side and the groove bottom, and may be any shape.

[0067] As disclosed in the first and second embodiments, the cross-sectional shape of the convex portions of the upstream kneading elements 27 is a downwardly convex, bilaterally symmetrical arc, and the height of the lower surface of the arc of the convex portion is preferably 0.1 to 0.9 times the flight height from the deepest part of the groove to the lower surface of the arc of the convex portion, based on the deepest part of the groove. By setting the height of the lower surface of the arc 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, resulting in a uniform thermoplastic resin composition. By setting the height of the lower surface of the arc 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 an increase in resin temperature can be suppressed.

[0068] The upstream kneading element 27 is provided with 2 to 30 convex portions, which gently compress and release the flowing raw material multiple times, kneading the raw material while exchanging its position three-dimensionally, thereby making it possible to obtain a uniform thermoplastic resin composition while suppressing an increase in resin temperature. Furthermore, as disclosed in the first and second embodiments, the direction of the ridge line of the convex portion formed as a ridge line spanning between the flights is preferably perpendicular to the twist angle when viewed from the side of the screw. However, since the raw material at the convex portion of the upstream kneading element is a mixture of raw materials before melting and raw materials after melting, which have poor fluidity, from the viewpoint of improving fluidity, the convex portion of the upstream kneading element may have a ridge line inclined at an angle of -30 to +30° to the perpendicular direction of the twist angle. If this range is met, shear heating in the flow path can be suppressed, a thermoplastic resin composition can be obtained that is free of resin burn, and an increase in resin temperature can be suppressed.

[0069] The height of the flights in the kneading part 7 can be set arbitrarily depending on the diameters 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.

[0070] The screw 3 of the present invention may have the kneading element 7 disclosed in the kneading section of the screw. The screw parts upstream and downstream of the kneading element 7 may be parts such as full flights that allow the raw material to flow stably in the kneading section, and other kneading elements may be provided before and after them as long as the effects of the present invention are not impaired.

[0071] 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 gases and removing moisture from the raw materials. 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.

[0072] 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 gradually compressing and releasing the material and repeatedly kneading it to distribute and diffuse the thermoplastic resin composition to make it uniform. Therefore, even in applications where multiple materials are kneaded together to form a thermoplastic resin composition, a uniform thermoplastic resin composition can be obtained. 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]

[0073] 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 portion (upstream kneading element) 23 Round hole (downstream mixing element) 24 Boundary line formed by the flight and groove in the upstream mixing element 25 Boundary line formed by the flight and round hole in the downstream mixing element 26 Convex portion (downstream kneading element) 27 Upstream mixing element 28 Downstream mixing element 30 flights 31 Long axis 32 Convex portion (downstream kneading element) 33 Round hole (downstream mixing element) 35 Boundary line formed by flight and round hole in downstream kneading element 38 Downstream mixing element 71 Groove (intermediate kneading element) 72 Convex part (intermediate kneading element) 73 Round hole (intermediate kneading element) 79 Intermediate kneading element 80 twist angle 81 Cutting curved surface 91 Screw connection 92 Vacuum Vent 94 Upstream of the screw axis 95 Downstream 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 parts are arranged in a direction from the upstream side to the downstream side in the screw axial direction. At least one upstream kneading element; At least one downstream mixing element is configured, The upstream kneading element is The gear has a spiral flight, a plurality of grooves formed parallel to the twist angle direction of the flight, and a plurality of convex portions that form ridges formed at connecting portions of the adjacent grooves, The convex portion is a ridge formed at each connection portion of two grooves, the convex portion has a height lower than the surface height of the flight and is an arc-shaped ridgeline formed between adjacent flights, In a plan view of the kneading parts in the circumferential direction of the screw, the boundary line formed by the surface of the flight and the groove is a boundary line that curves toward the center between the flights so as to narrow the width of the groove around the convex portion. is a kneading element, The downstream kneading element is The rotor comprises a spiral flight, a plurality of connecting circular holes formed parallel to the twist angle direction of the flight, and a convex portion serving as a ridge line formed at each connecting portion of the adjacent circular holes, The plurality of connecting circular holes are circular holes shaped like a part of a surface of a perfect sphere being cut away, Alternatively, a circular hole having a shape of cutting out a part of the surface of an ellipsoid whose major axis is arranged in the twist angle direction of the flight is A plurality of the flights are connected and arranged at positions in the torsion angle direction of the flights, the convex portion has a height lower than the surface height of the flight and is an arc-shaped ridgeline formed between adjacent flights, In a plan view of the kneading parts in the circumferential direction of the screw, the boundary line formed by the surface of the flight and the round hole is a kneading element having an arc shape recessed toward the flight side. A screw for a single-screw extruder characterized by:

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

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