Extruder screw including conveyance portions and paths within the conveyance portions, extruder, and extrusion method

At a part of the screw main body at which the kneading portion is provided, conveyance portions, a barrier portion and a path are provided at a plurality of places. At least one of the places, the path is provided inside the screw main body, and includes an entrance and an exit. The entrance is opened in such a manner that the raw material whose pressure is enhanced by being restricted in conveyance by the barrier portion flows into the entrance. The path is formed in such a manner that the raw material flowing into the path from the entrance flows toward the exit in a direction opposite to the direction of conveyance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an extrusion technique capable of improving the degree of kneading without lengthening an extruder (screw).

2. Description of the Related Art

Heretofore, an extrusion technique for improving the degree of kneading by utilizing “stretching action” imparted to the raw material when the raw material passes from a large part through a small part is known. For example, in Patent Literature 1 and Patent Literature 2, an extrusion technique in which a stretch imparting mechanism configured to impart stretching action to the raw material is added to a leading end of the extruder (screw) is disclosed. Furthermore, in Patent Literature 3, an extrusion technique in which a stretch imparting region configured to augment a flow having a high degree of stretch is secured between a pair of screws provided with spiral flights is disclosed.

CITATION LIST

Patent Literature

Patent Literature 1: JP H07-227836 A

Patent Literature 2: JP 2010-137405 A

Patent Literature 3: JP 2013-123841 A

BRIEF SUMMARY OF THE INVENTION

However, in the extrusion technique disclosed in Patent Literature 1 and Patent Literature 2, the whole of the extruder is lengthened by a length corresponding to the addition of the stretch imparting mechanism. Particularly, in the paragraph “0027” of Patent Literature 2, a description “the raw material is made to pass through a gap between surfaces opposed parallel to each other a plurality of times, whereby stretching action is imparted to the raw material” is given. Accordingly, in order to realize such description content, further lengthening of the whole extruder is inevitable.

Further, in the extrusion technique of Patent Literature 3, as the raw material to be conveyed by a pair of screws, part of the raw material flowing along the spiral flight while avoiding the stretch imparting region exists besides the part of the raw material passing through the stretch imparting region. Accordingly, in the extrusion technique of Patent Literature 3, there is some question as to whether or not all of the raw material conveyed by the pair of screws passes through the stretch imparting region without any omission. In this case, in order to make all of the raw material pass through the stretch imparting region without any omission, it is necessary to secure the stretch imparting region sufficiently long. However, if the stretch imparting region is secured sufficiently long, the extruder (screw) is lengthened by a length corresponding to the elongation of the stretch imparting region.

Thus, an object of the present invention is to provide an extrusion technique for imparting stretching action to all of the raw material to be conveyed by a screw without any omission, and improving the degree of kneading of the raw material without lengthening the extruder (screw) by making the screw itself possess a function of imparting stretching action to the raw material.

In order to achieve the object of the invention, an extruder screw comprises a transfer portion configured to continuously convey supplied materials; a melting and mixing portion configured to continuously melt and mix the conveyed materials; and a kneading portion configured to continuously knead a raw material obtained by melting and mixing the materials, wherein the transfer portion, the melting and mixing portion, and the kneading portion are provided on a screw main body rotating around a linear axis line, at a part of the screw main body at which the kneading portion is provided, a conveyance portion configured to convey the raw material, a barrier portion configured to restrict conveyance of the raw material, and a path through which the raw material flows are provided at each of a plurality of places, at least one of the places, the path is provided inside the screw main body, and includes an entrance and an exit, the entrance is opened at an outer circumferential surface of the screw main body at the conveyance portion in such a manner that the raw material pressure of which is enhanced by being restricted in conveyance by the barrier portion flows into the entrance, the path is formed in such a manner that the raw material flowing into the path from the entrance flows toward the exit in a direction opposite to the direction of conveyance carried out by the conveyance portion, and the exit is opened at a position in the conveyance portion in which the entrance is opened on the upstream side of the entrance in the conveyance direction on the circumferential surface of the screw main body.

Further, an extruder comprising the above-described extruder screw, comprises a barrel including a cylinder in which the extruder screw is rotatably inserted; a supply port provided on the barrel, and configured to supply materials to the inside of the cylinder; and a discharge port which is provided on the barrel, and from which kneaded stuff created by the screw is continuously extruded.

Furthermore, an extrusion method comprises: kneading a raw material by using the above-described extruder screw; the method comprising continuously creating kneaded stuff of the raw material; and extruding the kneaded stuff, wherein in a kneading portion, while the kneaded stuff is continuously extruded, the raw material conveyed along an outer circumferential surface of a screw main body flows through a path, and thereafter returns to the outer circumferential surface of the screw.

According to the present invention, a screw itself is made to possess a function of imparting stretching action to the raw material, whereby it is possible to realize an extrusion technique for imparting stretching action to all of the raw material to be conveyed by the screw without any omission, and improving the degree of kneading of the raw material without lengthening the extruder (screw).

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1andFIG. 2, the configuration of a single-screw extruder1according to this embodiment is shown. The single-screw extruder1is provided with one extruder screw2, and barrel4including a cylinder3in which the screw2is rotatably inserted.

The barrel4is provided with a supply port5configured to supply a plurality of types of materials6such as a thermoplastic resin and the like at one end thereof. The supply port5penetrates the barrel4to communicate with the cylinder3. Further, the barrel4is provided with a discharge port7at the other end thereof. The discharge port7is formed in a lid body8to be coupled to the barrel4to cover the opening of the other end of the barrel4. From the discharge port7, the kneaded stuff created by the extruder screw2is continuously extruded.

Furthermore, the barrel4is provided with a coolant passage through which cooling water is made to flow, heater, temperature sensor, and the like (all of which are not shown). By controlling the heater to heat the barrel4to a set temperature, it is possible to heat the inside of the cylinder3. When the temperature of the barrel4exceeds the set temperature, cooling water is made to flow through the coolant passage to cool the barrel4, whereby the inside of the cylinder3can be cooled to the set temperature.

The extruder screw2extends straight from the base end thereof to the leading end thereof, and the total length thereof is set to a length corresponding to the total length of the cylinder3of the barrel4. Thereby, the extruder screw2can be arranged in such a manner that the screw2is rotatably inserted in the cylinder3of the barrel4. In a state where the extruder screw2is rotatably inserted in the cylinder3of the barrel4, the base end of the extruder screw2is positioned on one end side of the barrel4on which the supply port5is provided, and leading end of the extruder screw2is positioned on the other end side of the barrel4on which the discharge port7is provided.

At the base end of the extruder screw2, a stopper portion9is coaxially provided. The stopper portion9is configured to close the opening of the cylinder3on the base end side of extruder screw2in a state where the extruder screw2is rotatably inserted/arranged in the cylinder3of the barrel4. Thereby, it is possible to prevent the plurality of types of materials6to be supplied to the inside of the cylinder3from leaking to the outside of the extruder. The stopper portion9is configured to be able to be coupled to a rotating device such as a motor or the like through a coupling not shown. When the torque from the rotating device is transmitted to the stopper portion9, the extruder screw2is rotated around a linear axis line10extending from the base end thereof to the leading end thereof.

Furthermore, the extruder screw2is provided with a screw main body11rotating together with the extruder screw2in an integrated manner. In the description to be given hereinafter, the rotational direction (left rotation, right rotation) of the screw main body11implies the rotational direction (left rotation, right rotation) of a case where the screw main body11is viewed from the base end side thereof, in other words, of a case where the discharge port7is viewed from the supply port5of the barrel4. Likewise, the twisting direction (clockwise, counterclockwise) of each of flights12,25a,25b,25c,26, and41implies the twisting direction (clockwise, counterclockwise) of each of the flights12,25a,25b,25c,26, and41of a case where each of them is viewed from the base end side of the screw main body11.

The screw main body11includes, in the order from the base end of the screw main body11to the leading end thereof, a transfer portion11a, melting and mixing portion11b, and kneading portion11c. The transfer portion11acontinuously conveys the plurality of types of materials6supplied from the supply port5to the inside of the cylinder3toward the melting and mixing portion11b. The melting and mixing portion11bcontinuously melts and mixes the plurality of types of materials6. Then, the resultant obtained by melting and mixing the plurality of types of materials6is continuously introduced into the kneading portion11cas a raw material for kneading. In the kneading portion11c, desired kneaded stuff is continuously created.

The part of the screw main body11at which the kneading portion11cis provided is formed not only by arranging an area (shearing action region) for imparting shearing action to the raw material, but also by particularly arranging an area (stretching action region) for imparting stretching action to the raw material at each of a plurality of positions in the axial direction. Thereby, the degree of dispersing the raw material is improved, and as a result, it is possible to create kneaded stuff excellent in the degree of kneading. Then, the kneaded stuff created inside the cylinder3is continuously extruded through the discharge port7.

On the outer circumferential surfaces M1and M2of the screw main body11from the transfer portion11ato the melting and mixing portion11b, a spirally twisted flight12is continuously formed. The flight12is configured to continuously convey the materials6to be supplied from the supply port5to the inside of the cylinder3from the transfer portion11ato the melting and mixing portion11b. For this reason, the flight12is twisted in a direction opposite to the rotational direction of the screw main body11.

In the drawing, a flight12of a case where the materials6are conveyed by the left rotation of the screw main body11is shown. In this case, the twisting direction of the flight12is set to the clockwise direction as in the case of the right-handed screw. It should be noted that when the materials6are conveyed by the right rotation of the screw main body11, it is sufficient if the twisting direction of the flight12is set to the counterclockwise direction as in the case of the left-handed screw.

The outer circumferential surface M1of the screw main body11at the transfer portion11ahas a cylindrical shape, and the gap between the outer circumferential surface M1thereof and inner surface3sof the cylinder3is set wide. The outer circumferential surface M2of the screw main body11at the melting and mixing portion11bhas a shape widen from the transfer portion11atoward the kneading portion11c, and the gap between the outer circumferential surface M2thereof and inner surface3sof the cylinder3is set in such a manner that the gap continuously becomes less from the transfer portion11atoward the kneading portion11c.

Here, in a state where the extruder screw2is caused to make left rotation, the materials6supplied from the supply port5to the cylinder3are conveyed by the flight12from the transfer portion11ato the melting and mixing portion11b. In the melting and mixing portion11b, the materials6receive compression mainly from the gap continuously made less while being heated by the heater, whereby a molten and mixed raw material for kneading is formed. The raw material is continuously conveyed from the melting and mixing portion11bto the kneading portion11c.

The part of the screw main body11at which the kneading portion11cis provided is constituted of a plurality of cylinder bodies13each of which has a cylindrical shape, and one rotating shaft14(seeFIG. 2) configured to support thereon these cylinder bodies13. Furthermore, the kneading portion11cincludes an introduction portion15configured to introduce the raw material conveyed from the melting and mixing portion11binto the kneading portion11c. The introduction portion15is configured to be adjacent to the end face16of the melting and mixing portion11b. Details of the introduction portion15will be described later.

The rotating shaft14is provided in an area from the leading end of the screw main body11to the end face16of the melting and mixing portion11b. The rotating shaft14extends straight from the base end to the leading end, and the base end thereof is coaxially connected to the end face16of the melting and mixing portion11b. The rotating shaft14has a columnar shape, and the external profile thereof is set smaller than the external profile of the end face16of the melting and mixing portion11b.

It should be noted that regarding the method of connecting the base end of the rotating shaft14and end face16of the melting and mixing portion11bto each other, it is sufficient if one of already-existing methods such as a method of coaxially and integrally forming the rotating shaft14together with the screw main body11from the transfer portion11ato the melting and mixing portion11b, method of separately forming the screw main body11from the transfer portion11ato the melting and mixing portion11band rotating shaft14, and thereafter coaxially coupling the base end of the rotating shaft14to the end face16of the melting and mixing portion11b, and the like is appropriately selected.

As shown inFIG. 3andFIG. 4, as an example of the supporting structure in which the plurality of cylinder bodies13are supported on the rotating shaft14, the rotating shaft14is provided with a pair of keys17in the outer circumferential surface thereof. The keys17are fitted into a pair of groove parts18formed at positions shifted from each other by 180° along the outer circumferential surface of the rotating shaft14. Each groove part18is formed by partially cutting away the outer circumferential surface of the rotating shaft14in the axial direction.

Furthermore, each cylinder body13is formed in such a manner that the rotating shaft14can be made to coaxially penetrate the cylinder body13along the inner circumferential surface thereof. In the inner circumferential surface of each cylinder body13, key groves19are formed at positions shifted from each other by 180° in the circumferential direction. The pair of key grooves19is formed by partially cutting away the inner circumferential surface of the cylinder body13in the axial direction.

As shown inFIG. 1throughFIG. 4, the rotating shaft14is made to penetrate all the cylinder bodies13along the inner circumferential surfaces of the cylinder bodies13while positional alignment of each key17with each key groove19is carried out. Thereafter, a fixing screw21is screwed into the leading end of the rotating shaft14through a collar20. At this time, all the cylinder bodies13are clamped between the leading end collar20and end face16of the melting and mixing portion11b, and are held by the clamping force in a state where the cylinder bodies13are in close contact with each other without any gaps between them.

By the supporting structure described above, all the cylinder bodies13are coaxially coupled to each other on the rotating shaft14, whereby each cylinder body13and rotating shaft14are integrally assembled. Each cylinder body13and rotating shaft14are integrally assembled, whereby the screw main body11is formed as a rod-like member extending from the base end to the leading end in the axial direction (longitudinal direction).

Thereby, it becomes possible to rotate each cylinder body13together with the rotating shaft14around the axis line10, i.e., to rotate the screw main body11around the axis line10. Furthermore, the base end of the screw main body11coincides with the base end of the rotating shaft14, and the leading end of the screw main body11coincides with the leading end of the rotating shaft14. In other words, the base end of the screw main body11coincides with the base end of the extruder screw2corresponding to one end of the barrel4, and the leading end of the screw main body11coincides with the leading end of the extruder screw2corresponding to the other end of the barrel4.

At this time, at the part of the screw main body11at which the kneading portion11cis provided, each cylinder body13becomes a constituent element defining the outer diameter D1(seeFIG. 3) of the screw main body11. In the kneading portion11c, regarding the cylinder bodies13coaxially coupled to each other along the rotating shaft14, their outer diameters D1are set identical to each other. The outer diameter D1of the screw main body11(each cylinder body13) is a diameter to be defined coaxially with the axis line10which is a rotational center of the rotating shaft14.

Thereby, a segment type screw2in which the outer diameter D1of the screw main body11(each cylinder body13) at the kneading portion11chas a fixed value is formed. The segment type screw2can hold a plurality of screw elements in an arbitrary order and combination along the rotating shaft14. Regarding the screw element, for example, a cylinder body13on which at least part of each of the flights12,25a,25b,25c,26, and41to be described later is formed can be defined as one screw element.

By segmenting the screw2, it is possible to, with respect to, for example, a change or adjustment in the specification of the screw2or service and maintenance thereof, remarkably improve the convenience thereof.

It should be noted that in this embodiment, the structure for whirl-stop and fixation of the plurality of cylinder bodies13and rotating shaft14is not limited to the structure associated with the combination of the key17and groove19, and a spline structure (not shown) may be used instead.

Furthermore, the segment type screw2is coaxially accommodated in the cylinder3of the barrel4. More specifically, the screw main body11in which the plurality of screw elements are held along the rotating shaft14is rotatably accommodated in the cylinder3. In this state, between the outer circumferential surface of the screw main body11(cylinder bodies13) and inner surface3sof the cylinder3, a conveyance path29configured to convey the raw material is formed. The conveyance path29has an annular cross-sectional shape in the radial direction of the cylinder3, and extends in the axial direction along the cylinder3.

In this embodiment, at the part of the screw main body11at which the kneading portion11cis provided, the aforementioned introduction portion15, first to third conveyance portions22a,22b, and22cconfigured to convey the raw material introduced by the introduction portion15, and barrier portion23configured to restrict the flow of the raw material are provided. The first to third conveyance portions22a,22b, and22c, and barrier portion23are arranged at each of a plurality of positions in the axial direction (longitudinal direction) of the screw main body11at the kneading portion11c.

That is, on the base end side of the screw main body11at the kneading portion11c, the first conveyance portion22ais arranged. The first conveyance portion22ais also used as a constituent of the introduction portion15. In the direction from the first conveyance portion22ato the leading end of the screw main body11, the second conveyance portion22band third conveyance portion22care arranged adjacent to each other. Here, assuming that the first to third conveyance portions22a,22b, and22cconstitute one group, the groups concerned and barrier portions23are alternately arranged in the axial direction (longitudinal direction) of the screw main body11.

In one group, the first to third conveyance portions22a,22b, and22care arranged adjacent to each other. In the direction from the base end of the screw main body11to the leading end thereof, the first conveyance portion22a, second conveyance portion22b, and third conveyance portion22care arranged in the order mentioned. The third conveyance portion22cis adjacent to the barrier portion23.

On the other hand, on the leading end side of the screw main body11at the kneading portion, a discharge conveyance portion24is arranged. The discharge conveyance portion24is configured to convey the kneaded stuff kneaded in the cylinder3in a direction identical to the direction of conveyance carried out by the other conveyance portions22a,22b, and22c.

The first to third conveyance portions22a,22b, and22care respectively provided with spirally twisted first to third flights25a,25b, and25c. The first to third flights25a,25b, and25cjut out from the outer circumferential surface of the cylinder body13in the circumferential direction thereof toward the conveyance path29. These flights25a,25b, and25care twisted in a direction opposite to the rotational direction of the screw main body11from the base end of the screw main body11to the leading end thereof. In this case, the twist pitch of the second flight25bis set to a value identical to or smaller than those of the first and third flights25aand25c.

The discharge conveyance portion24is provided with a spirally twisted flight26. The flight26juts out from the outer circumferential surface of the cylinder body13in the circumferential direction thereof toward the conveyance path29. The flight26is twisted in a direction opposite to the rotational direction of the screw main body11.

It should be noted that when a function of a backflow prevention portion to be described later, i.e., a function of preventing backflow of the raw material is imparted to the second conveyance portion22b, it is desirable that the twist pitch of the second flight25bin the second conveyance portion22bbe set smaller than the twist pitch of the third flight25cin the third conveyance portion22c.

Here, when the raw material is kneaded by rotating the screw main body11in the leftward direction, the flights25a,25b, and25cof the conveyance portions22a,22b, and22care twisted in such a manner that the raw material is conveyed from the base end of the screw main body11toward the leading end thereof. That is, the twisting direction of the flights25a,25b, and25cis set to the clockwise direction as in the case of the right-handed screw.

Furthermore, when the raw material is kneaded by rotating the screw main body11in the leftward direction, the flight26of the discharge conveyance portion24is twisted in such a manner that the raw material is conveyed from the base end of the screw main body11toward the leading end thereof. That is, the twisting direction of the flight26is set to the clockwise direction as in the case of the right-handed screw.

Conversely, when the raw material is kneaded by rotating the screw main body11in the rightward direction, the flights25a,25b, and25cof the conveyance portions22a,22b, and22care twisted in such a manner that the raw material is conveyed from the base end of the screw main body11toward the leading end thereof. That is, the twisting direction of the flights25a,25b, and25cis set to the counterclockwise direction as in the case of the left-handed screw.

Furthermore, when the raw material is kneaded by rotating the screw main body11in the rightward direction, the flight26of the discharge conveyance portion24is twisted in such a manner that the raw material is conveyed from the base end of the screw main body11toward the leading end thereof. That is, the twisting direction of the flight26is set to the counterclockwise direction as in the case of the left-handed screw.

Each barrier portion23includes a spirally twisted flight41. The flight41juts out from the outer circumferential surface of the cylinder body13in the circumferential direction thereof toward the conveyance path29. The flight41is twisted in a direction identical to the rotational direction of the screw main body11.

Here, when the raw material is kneaded by rotating the screw main body11in the leftward direction, the flight41of each barrier portion23is twisted in such a manner that the raw material is conveyed from the leading end of the screw main body11toward the base end thereof. That is, the twisting direction of the flight41is set to the counterclockwise direction as in the case of the left-handed screw.

Conversely, when the raw material is kneaded by rotating the screw main body11in the rightward direction, the flight41of each barrier portion23is twisted in such a manner that the raw material is conveyed from the leading end of the screw main body11toward the base end thereof. That is, the twisting direction of the flight41is set to the clockwise direction as in the case of the right-handed screw.

In each barrier portion23, the twist pitch of the flight41is set to a value identical to or smaller than those of the flights25a,25b,25c, and26in the aforementioned conveyance portions22a,22b,22c, and24. Furthermore, between the top parts of the flights25a,25b,25c,26, and41and inner surface3sof the cylinder3, a small clearance is secured.

Each barrier portion23according to this embodiment is designed to enable the raw material to flow over each barrier portion23. In other words, each barrier portion23according to this embodiment is designed in such a manner that the raw material can pass through the gap between each barrier portion23and cylinder3in a state where the extruder screw2is rotatably inserted in the cylinder3of the barrel4. In this case, it is desirable that a gap27(seeFIG. 8) between an outer diameter portion23sof each barrier portion23and inner surface3sof the cylinder3be set within a range greater than or equal to 0.05 mm and smaller than or equal to 2 mm. Furthermore, more desirably, the gap27is set within a range greater than or equal to 0.05 mm and smaller than or equal to 0.7 mm.

It should be noted that in each barrier portion23, instead of providing the flight41, a barrier annular body28(seeFIG. 20andFIG. 21) continuous in the circumferential direction along the outer circumferential surface of the screw main body11may be provided. The barrier annular body28includes a cylindrical surface28scoaxially continuous in the circumferential direction around the axis line10. The cylindrical surface28sjuts out from the outer circumferential surface of the cylinder body13in the circumferential direction thereof toward the conveyance path29. The gap between the cylindrical surface28sand inner surface3sof the cylinder3is set within the range of the aforementioned gap27.

Incidentally, the length of each of the conveyance portions22a,22b,22c, and24in the axial direction of the screw main body11is appropriately set according to, for example, the type of the raw material, degree of kneading of the raw material, amount of production of the kneaded stuff per unit time, and the like. Although each of the conveyance portions22a,22b,22c, and24is at least an area in which each of the flights25a,25b,25c, and26is formed on the outer circumferential surface of the cylinder body13, the area is not particularly limited to an area between the starting point and ending point of each of the flights25a,25b,25c, and26.

That is, at the outer circumferential surface of the cylinder body13, the part of the surface outside the extent of each of the flights25a,25b,25c, and26is also regarded as the part of each of the conveyance portions22a,22b,22c, and24in some cases. For example, when a cylindrical spacer or cylindrical collar is arranged at a position adjacent to the cylinder body13including each of the flights25a,25b,25c, and26, there can be a case where the spacer or collar is included in each of the conveyance portions22a,22b,22c, and24.

Further, the length of the barrier portion23in the axial direction of the screw main body11is appropriately set according to, for example, the type of the raw material, degree of kneading of the raw material, amount of production of the kneaded stuff per unit time, and the like. The barrier portion23functions in such a manner that the flow of the raw material conveyed by the conveyance portions22a,22b, and22cis temporarily dammed up. That is, the barrier portion23is configured to be adjacent to the third conveyance portion22con the downstream side in the conveyance direction of the raw material, and restrict the passage of the raw material conveyed by the conveyance portions22a,22b, and22cthrough the aforementioned gap27.

At the part of the screw2(screw main body11) at which the kneading portion11cis provided, the flights25a,25b,25c,26, and41, and barrier annular body28(cylindrical surface28s) jut out from the outer circumferential surfaces of the plurality of cylinder bodies13each having the identical outer diameter D1toward the conveyance path29. Accordingly, the outer circumferential surface of each cylinder body13in the circumferential direction thereof defines the root diameter of the screw2at the kneading portion11c. The root diameter coincides with the aforementioned outer diameter D1, and is held at a fixed value throughout the total length of the screw main body11at the part thereof at which the kneading portion11cis provided.

In this case, in order that the depth of the root may become smaller, the root diameter of the kneading portion11cmay be made larger. According to such a configuration, it is possible to stably discharge the kneaded stuff created by the screw2from the discharge port7. It should be noted that the depth of the root can be defined as a height dimension from the outer circumferential surface of the screw main body11(cylinder body13) to the outer diameter of each of the flights25a,25b,25c,26, and41, and barrier annular body28(cylindrical surface28s) in the radial direction.

Furthermore, at the part of the screw main body11at which the kneading portion11cis provided, a plurality of paths37extending in the axial direction are provided inside the part. The plurality of paths37may be formed in such a manner that the paths37are arranged in the circumferential direction of the screw main body11with intervals held between them or may be arranged in the axial direction with intervals held between them. In the drawing, as an example, a configuration in which a plurality of paths37are arranged at regular intervals in the axial direction of the screw main body11(kneading portion11c) is shown.

Each path37is provided at a position deviated from the axis line10which is the rotational center of the screw2. That is the path37is off the axis line10. Accordingly, the path37revolves around the axis line10with the rotation of the screw main body11.

Regarding the shape of the path37, as the cross-sectional shape thereof, for example, a circular shape, rectangular shape, elliptical shape, and the like can be set if the shapes are passable for the raw material. In the drawing, as an example, a path37which is a hole having a circular cross-sectional shape is shown. In this case, it is desirable that the inner diameter (bore) of the hole be set to a value greater than or equal to 1 mm and smaller than 6 mm. More desirably, the inner diameter (bore) of the hole is set to a value greater than or equal to 1 mm and smaller than 5 mm.

Hereinafter, the specific configuration of the aforementioned path37will be described.

As shown inFIG. 2throughFIG. 5, in the extruder screw2according to this embodiment, inside the screw main body11(kneading portion11c) on which the aforementioned groups (each of which is constituted of the first to third conveyance portions22a,22b, and22c), and plurality of barrier portions23are alternately arranged in the axial direction (longitudinal direction), the plurality of paths37are arranged in the axial direction (longitudinal direction) with intervals held between them. By virtue of such a screw structure, a screw2provided with a screw main body11(kneading portion11c) having a function of continuously imparting shearing action and stretching action to the raw material is realized.

In this embodiment, the path37is formed in the cylinder body13of the third conveyance portion22cin the aforementioned group. That is, inside the screw main body11(kneading portion11c), the cylinder body13of the third conveyance portion22cincludes a cylindrical wall surface30defining the path37which is a hole. In this case, the path37is a hole constituted of only hollow space. The wall surface30continuously surrounds the hollow path37in the circumferential direction. Thereby, the path37is formed as hollow space allowing passage of only the raw material. In other words, inside the path37, any elements constituting the screw main body11do not exist at all. In this case, the wall surface30revolves around the axis line10without rotating around the axis line10when the screw main body11is rotated.

According to such a path37, when the raw material conveyed through the conveyance path29by the conveyance portions22a,22b, and22cflows through the path37, the “stretching action” happening to the raw material when the raw material passes through the narrow area (path37) from the wide area (conveyance path29) can be made to effectively happen. Accordingly, the path37is defined as an area (stretching action region) configured to impart stretching action to the raw material.

Here, in the aforementioned screw structure, when attention is given to the third conveyance portion22cin which the path37is formed, and second conveyance portion22band barrier portion23which are adjacent to the third conveyance portion22con both sides thereof, such a configuration can be grasped as one unit which is structurally unified. The one unit has a structure as an axial direction circulation portion configured to circulate the raw material in the axial direction.

The screw main body11according to this embodiment is formed in such a manner that the plurality of units concerned are arranged in the axial direction (longitudinal direction), and each of the first conveyance portions22ais adjacently arranged between the units. Thereby, a screw structure in which the aforementioned axial direction circulation portion is provided at each of a plurality of positions is realized.

In other words, the aforementioned one unit can be grasped as one functionally unified module. As functions of the one module, besides the function of circulating the raw material in the axial direction, for example, a function of imparting shearing action to the raw material, function of imparting stretching action to the raw material, function of restricting conveyance of the raw material by means of the barrier portion23, function of guiding the raw material the pressure of which is enhanced by the barrier portion23to the path37, function of forming a raw material basin R in which the saturation factor of the raw material is 100% immediately before the barrier portion23, and the like are conceived.

Furthermore, in the above-mentioned screw structure, the path37includes an entrance38, exit40, and path main body39connecting the entrance38and exit40to each other. The entrance38and exit40are provided within a range of one third conveyance portion22cin the one unit (axial direction circulation portion). Within the range of the third conveyance portion22c, the entrance38is provided on one side (position closer to the leading end of the screw main body11) of the path main body39, and exit40is provided on the other side (position closer to the base end of the screw main body11) of the path main body39.

The formation positions of the entrance38and exit40can freely be set within the range of the third conveyance portion22c. For example, when the circulation cycle at the third conveyance portion22cis made larger, the entrance38is made closer to the barrier portion23, and exit40is made closer to the second conveyance portion22b. In other words, the entrance38and exit40are made away from each other. Conversely, when the circulation cycle at the third conveyance portion22cis made smaller, the entrance is made separate from the barrier portion23, and exit40is made separate from the second conveyance portion22b. In other words, the entrance38and exit40are made closer to each other. In the drawing, as an example, the configuration in which the circulation cycle is made larger is shown.

The entrance is a hole bored from the outer circumferential surface of the cylinder body13(screw main body11) in the radial direction within the range of the third conveyance portion22c. The entrance38can be formed by, for example, machining using a drill. As a result, the bottom part38aof the entrance38is an inclined surface shaved off into a conical shape by the tip of the drill. In other words, the conical bottom part38ais an inclined surface widen toward the outer circumferential surface of the screw main body11.

The exit40is a hole bored from the outer circumferential surface of the cylinder body13(screw main body11) in the radial direction within the range of the third conveyance portion22c. The exit40can be formed by, for example, machining using a drill. As a result, the bottom part40aof the exit40is an inclined surface shaved off into a conical shape by the tip of the drill. In other words, the conical bottom part40ais an inclined surface widen toward the outer circumferential surface of the screw main body11.

In this embodiment, the third conveyance portion22cis formed along outer circumferential surfaces of two cylinder bodies13adjacent to each other in the axial direction. The path main body39is formed to extend through the insides of both the cylinder bodies13. The path main body39is constituted of first and second parts39aand39b. The first part39ais formed in the inside of one cylinder body13. The second part39bis formed in the inside of the other cylinder body13.

In the one cylinder body13, the first part39aextends along the axis line10in parallel with the axis line10. One end of the first part39ais opened at an end face13aof the cylinder body13. The other end of the first part39ais closed by an end wall13bof the cylinder body13. Furthermore, the other end of the first part39ais connected to the entrance38described above to communicate with the entrance38.

In the other cylinder body13, the second part39bextends along the axis line10in parallel with the axis line10. One end of the second part39bis opened at an end face13aof the cylinder body13. The other end of the second part39bis closed by an end wall13bof the cylinder body13. Furthermore, the other end of the second part39bis connected to the exit40described above to communicate with the exit40.

The path main body39can be formed by constricting the cylinder body13in which the first part39ais formed, and the cylinder body13in which the second part39bis formed in the axial direction to thereby bring their end faces13ainto close contact with each other. In this state, the path39linearly and continuously extends in the axial direction of the screw main body11without branching halfway. Further, both sides of the path main body39are connected to the entrance38and exit40to communicate with the entrance38and exit40.

In this case, the bore of the path main body39may be set smaller than the bores of the entrance38and exit40or may be set identical to the bores. In either case, the path cross-sectional area defined by the bore of the path main body39is set far smaller than the annular cross-sectional area of the aforementioned conveyance path29in the radial direction.

In this embodiment, each cylinder body13on which at least part of each of the flights25a,25b,25c,26, and41is formed can be grasped as a screw element corresponding to each of the conveyance portions22a,22b,22c, and24, and barrier portion23. InFIG. 4, as an example of the screw element, the cylinder body13of the third conveyance portion22cprovided with the aforementioned path37(entrance38, path main body39, and exit40) is shown. In the third conveyance portion22c, the entrance38and exit40are formed in the outer circumferential surface of the cylinder body13.

It should be noted that as another configuration of the path37, as shown in, for example,FIG. 6, the path main body39may be formed by penetrating the cylinder body13in the axial direction. In this case, the entrance38and exit40are formed by partially cutting away both end faces of the cylinder body13in the axial direction to thereby form concave parts. According to such a configuration, it is possible to form a complete path main body39by only forming a perforated horizontal hole in the cylinder body13.

According to such an element structure, it is possible to form the kneading portion11cof the screw main body11by arranging a plurality of screw elements (cylinder bodies13) in sequence along the rotating shaft14. Accordingly, it is possible to, for example, exchange or rearrange the conveyance portions22a,22b,22c, and24, and barrier portion23according to the degree of kneading of the raw material, and easily carry out the work for the exchange and rearrangement.

Furthermore, the plurality of cylinder bodies13serving as the screw elements are constricted in the axial direction to be brought into close contact with each other, whereby the path main body39of each path37is formed, and the part from the entrance38of the path37to the exit40thereof is made integrally continuous through the path main body39. Accordingly, in forming the path37in the screw main body11, it is advisable to subject each of the cylinder bodies13each having lengths sufficiently shorter than the total length of the screw main body11(kneading portion11c) to machining for forming the path37. Accordingly, it becomes easy to carry out machining, and carry out handling at the time of forming the path37.

Furthermore, in the screw structure of the extruder screw2, the aforementioned introduction portion15has a structure configured to continuously introduce the raw material conveyed from the melting and mixing portion11binto the kneading portion11c. InFIG. 1andFIG. 2, an example of such an introduction structure is shown. That is, the introduction portion15is formed by utilizing the first conveyance portion22aarranged on the upstream side in the conveyance direction in the aforementioned group (first to third conveyance portions22a,22b, and22c). In the introduction portion15, on the outer circumferential surface of the cylinder body13, a spirally twisted first flight25ais provided. The first flight25ais twisted in a direction opposite to the rotational direction of the screw main body11.

According to such an introduction structure, it is possible to continuously introduce the raw material conveyed from the melting and mixing portion11binto the kneading portion11cby means of the first flight25aof the introduction15(first conveyance portion22a).

In the kneading portion11c, the aforementioned axial direction circulation portion (second conveyance portion22b, third conveyance portion22c, barrier portion23, and path37) is provided at each of a plurality of positions. In each axial direction circulation portion, the raw material conveyed by the third conveyance portion22cin the axial direction is restricted in the conveyance thereof by the barrier portion23, whereby the pressure of the raw material is enhanced. At this time, part of the pressure-enhanced raw material flows into the entrance38, and thereafter flows through the path main body39toward the exit40. Then, the raw material flowing out of the exit40is guided by the second conveyance portion22bto the outer circumferential surface of the third conveyance portion22cextending in the circumferential direction thereof. The raw material guided to the outer circumferential surface is conveyed in the axial direction by the third conveyance portion22c, and thereafter the same operation is repeated.

According to the axial direction circulation portion, to the raw material conveyed by the third conveyance portion22cin the axial direction, the “shearing action” created by the speed difference between the third flight25cof the third conveyance portion22crotating along the conveyance path29and inner surface3sof the cylinder3is imparted, and stirring action incidental to the rotation of the spiral flight25citself is also imparted. Furthermore, to the raw material flowing through the path main body39from the entrance38toward the exit40, the aforementioned “stretching action” is imparted. Thereby, the degree of kneading for the raw material is enhanced.

Accordingly, a plurality of axial direction circulation portions are provided in the axial direction of the screw main body11with interval held between them (for example, at regular intervals), whereby it is possible to realize a screw structure in which shearing action regions and stretching action regions are alternately and consecutively arranged in the axial direction. In the drawing, as an example, an extruder screw2having a screw structure in which a plurality of axial direction circulation portions and a plurality of first conveyance portions22aare alternately arranged in the axial direction is shown.

Furthermore, in the axial direction circulation portion, the twist pitch of the second flight25bin the second conveyance portion22bis set smaller than the twist pitch of the third flight25cin the third conveyance portion22c, whereby it is possible to impart a function of a backflow prevention portion to the second conveyance portion22b. In this case, in the second flight25bof the second conveyance portion22b, the conveyance capability thereof for conveying the raw material in the conveyance direction is enhanced by an amount corresponding to the reduced amount of the twist pitch. In other words, in the second flight25bof the second conveyance portion22b, prevention capability thereof for preventing the raw material from flowing in a direction opposite to the conveyance direction is improved by an amount corresponding to the reduced amount of the twist pitch.

Thereby, the raw material flowing out of the exit40of the third conveyance portion22cis prevented by the second conveyance portion22bfrom flowing in a direction opposite to the conveyance direction. At the same time, flow of the raw material flowing out of the exit40in the conveyance direction is promoted by the second conveyance portion22b. As a result, it is possible to efficiently and exhaustively spread the raw material over the entire third conveyance portion22cin the circumferential direction.

Next, the operation of kneading the raw material by using a single-screw extruder screw2will be described below. In this operation description, the “outer circumferential surface of the screw main body11” implies the outer circumferential surface of the screw main body11in the circumferential direction excluding both end faces thereof in the longitudinal direction. Furthermore, in the operation description, a case where kneading is carried out while rotating the extruder screw2at a rotational speed of, for example, 50 rpm to 100 rpm counterclockwise in the leftward direction is assumed.

As shown inFIG. 7andFIG. 8, materials6(seeFIG. 1) are supplied from the supply port5to the cylinder3in a state where the extruder screw2is rotated in the leftward direction.

The pellet-like resin supplied to the cylinder3is conveyed from the transfer portion11ato the melting and mixing portion11bby the flight12. In the melting and mixing portion11b, the resin receives compression mainly from the continuously narrowed gap while being heated by the heater. As a result, the raw material formed by melting and mixing two types of resins is conveyed from the melting and mixing portion11b.

The raw material conveyed from the melting and mixing portion11bis continuously introduced into the kneading portion11cby the introduction portion15(first conveyance portion22a). At this time, the raw material is continuously supplied to the outer circumferential surface of the screw main body11at the kneading portion11c. The supplied raw material is conveyed from the base end of the screw main body11toward the leading end thereof in the direction S1by the first to third flights25a,25b, and25cof the first to third conveyance portions22a,22b, and22c.

While the raw material is conveyed in the direction S1, the “shearing action” created by the speed difference between the flights25a,25b, and25cof the conveyance portions22a,22b, and22crotating along the conveyance path29and inner surface3sof the cylinder3is imparted to the raw material, and stirring action incidental to the rotation of the spiral flights25a,25b, and25cthemselves is also imparted to the raw material. Thereby, the degree of kneading for the raw material is enhanced.

The raw material conveyed in the direction S1is restricted in the conveyance thereof by the barrier portion23. That is, the flight41of the barrier portion23acts to convey the raw material in the direction opposite to the direction S1, i.e., to convey the raw material from the leading end of the screw main body11toward the base end thereof. As a result, the raw material is restricted in the flow thereof by the barrier portion23.

The flow of the raw material is restricted, whereby the pressure applied to the raw material is enhanced. More specifically, inFIG. 8, the saturation factor of the raw material of the part corresponding to the third conveyance portion22cof the screw main body11in the conveyance path29is expressed by gradation. That is, in the conveyance path29, the thicker the tone, the higher the saturation factor of the raw material is. As is evident fromFIG. 8, in the conveyance path29corresponding to the third conveyance portion22c, the saturation factor of the raw material becomes higher from an off position to the barrier portion23. The saturation factor of the raw material is 100% immediately before the barrier portion23.

Accordingly, a “raw material basin R” in which the saturation factor of the raw material becomes 100% is formed immediately before the barrier portion23. In the raw material basin R, the flow of the raw material is restricted, whereby the pressure of the raw material is raised. The raw material the pressure of which is raised continuously flows into the path main body39from the entrance38opened at the outer circumferential surface of the third conveyance portion22c(cylinder body13) and, then flows through the inside of the path main body39in a direction S2from the leading end of the screw main body11toward the base end thereof, the direction S2being opposite to the direction S1.

As described above, the path cross-sectional area defined by the bore of the path main body39is far smaller than the annular cross-sectional area of the conveyance path29in the radial direction of the cylinder3. According to another grasping method, the spread area based on the bore of the path main body39is far smaller than the spread area of the annular conveyance path29. Accordingly, when flowing into the path main body39from the entrance38, the raw material is abruptly narrowed, whereby “stretching action” is imparted to the raw material.

Furthermore, the path cross-sectional area is sufficiently smaller than the annular cross-sectional area, and hence the raw material collected in the raw material basin R is never exhausted. That is, part of the raw material collected in the raw material basin R continuously flows into the entrance38. During this time, the new raw material is fed to the barrier portion23by the third flight25cof the third conveyance portion22c. As a result, the saturation factor in the raw material basin R immediately before the barrier portion23is kept at 100% at all times. At this time, even when some variation in the amount of conveyance by the third flight25coccurs, the variation state is absorbed by the raw material remaining in the raw material basin R. Thereby, it is possible to continuously and stably supply the raw material to the path main body39. Accordingly, in the path main body39, it is possible to incessantly and continuously impart stretching action to the raw material.

The raw material passing through the path main body39flows out of the exit40to the outer circumferential surface of the screw main body11. The raw material flowing out of the exit40is guided to the outer circumferential surface of the third conveyance portion22cextending in the circumferential direction thereof by the second conveyance portion22bhaving the function of a backflow prevention portion.

The raw material guided to the outer circumferential surface is conveyed in the direction S1by the third conveyance portion22c. The raw material conveyed in the direction S1is restricted in the conveyance thereof by the barrier portion23, whereby the raw material flows into the entrance38, and thereafter the operation identical to the above operation is repeated.

While such an operation is repeated, part of the raw material the flow of which is restricted by the barrier portion23passes through a gap27between the outer diameter portion23sof the barrier portion23and inner surface3sof the cylinder3and is fed to the first conveyance portion22aadjacent to the barrier portion23on the downstream side of the barrier portion23.

In the screw main body11(kneading portion11c), the aforementioned conveyance portions22a, conveyance portions22b, conveyance portions22c, and barrier portions23are alternately arranged in the axial direction. In other words, the aforementioned axial direction circulation portions and first conveyance portions22aare alternately arranged in the axial direction. Accordingly, the aforementioned series of shearing/stretching action is repeated. Thereby, the raw material in the cylinder3is continuously conveyed from the base end of the screw main body11(kneading portion11c) toward the leading end thereof in a state where the shearing flow and stretching flow are repeated. As a result, the degree of kneading of the raw material is enhanced.

Further, the conveyed kneaded stuff is conveyed in the direction S1by the flight26of the discharge conveyance portion24, and is thereafter continuously extruded from the discharge port7(seeFIG. 1andFIG. 2).

As described above, according to this embodiment, the function of imparting stretching action to the raw material is given to the extruder screw2itself, whereby it is possible to enhance the degree of kneading of the raw material without lengthening the screw2or single-screw extruder.

According to this embodiment, it is possible to continuously impart shearing action and stretching action to the raw material a plurality of times. Accordingly, it is possible to increase the number of times and length of time of imparting the shearing action and stretching action to the raw material. As a result, it is possible to more accurately control the degree of kneading than in the case of using the conventional method.

According to this embodiment, in an already-existing extruder screw provided with a supply portion, compression portion, and measuring portion from the base end thereof toward the leading end thereof in the order mentioned, and having no paths through which the raw material flows inside the screw, the supply portion is replaced with a transfer portion11a, compression portion is replaced with a melting and mixing portion11b, and measuring portion is replaced with a kneading portion11cin which a combination of a conveyance portion22, barrier portion23, and path37is arranged. Thereby, it is possible to make the already-existing extruder screw possess both a function of imparting shearing action to the raw material, and function of imparting stretching action to the raw material. As a result, it is possible to realize an extruder screw in which handling facility is maintained and improved.

According to this embodiment, at the part at which the kneading portion11cis provided, the outer diameter D1of the screw main body11(each cylinder body13) is set to a fixed value, i.e., the root diameter of the screw2is set to a fixed value, whereby it is possible to realize a segment type screw2in which a plurality of screw elements can be held in an arbitrary order and combination. By segmenting the screw2, it is possible to remarkably improve the convenience thereof with respect to, for example, a change or adjustment in the specification of the screw2or service and maintenance thereof.

Furthermore, according to this embodiment, the cross-sectional area of the path37(path main body39) is set far smaller than the cross-sectional area of the conveyance path29configured to convey the raw material, whereby it is possible to uniformly, stably, and efficiently impart stretching action to the raw material passing through the path37(path main body39).

Up to this point, although an embodiment of the present invention has been described, the present invention is not limited to the one embodiment, and the following modification examples are also included in the technical scope of the present invention.

In the embodiment described above, inFIG. 2andFIG. 5, the path37joined to the entrance38and exit40at positions off the bottom parts38aand40aof the entrance38and exit40is shown. However, the joining relationship between the path main body39and entrance38or exit40is not limited to the one embodiment described above, and the following joining relationships are also included in the technical scope of the present invention.

In each ofFIG. 9throughFIG. 14, as an example, the path37joined to the bottom parts38aand40aof the entrance38and exit40at both ends of the path main body39is shown. More specifically, one side of the path main body39, i.e., the other end of the first part39ais joined to the bottom part38aof the entrance38. Furthermore, the other side of the path main body39, i.e., the other end of the second part39bis joined to the bottom part40aof the exit40.

In each ofFIG. 9(A) andFIG. 9(B), andFIG. 10(A) andFIG. 10(B), the path37according to a first modification example is shown. In the path37, an end face of one side (the other end of the first part39a) of the path main body39is joined to the bottom part38aof the entrance38. In the bottom part38a, one opening38bcommunicating with the path main body39(first part39a) is formed. On the other hand, an end face of the other side (the other end of the second part39b) of the path main body39is joined to the bottom part40aof the exit40. In the bottom part40a, one opening40bcommunicating with the path main body39(second part39b) is formed.

The one opening38bof the entrance38is formed in an area opposed to the bottom part38ahaving a shape widen toward the outer circumferential surface of the screw main body11. On the other hand, the one opening40bof the exit40is formed in an area opposed to the bottom part40ahaving a shape widen toward the outer circumferential surface of the screw main body11.

In this case, the raw material flowing into the entrance38is guided to the opening38balong the inclined surface of the bottom part38a. As a result, all of the raw material continuously and smoothly flows into the path main body39without stagnating inside the entrance38. The raw material passing through the path main body39subsequently flows into the exit40. The raw material flowing into the exit40is guided to the outer circumferential surface of the screw main body11along the inclined surface of the bottom part40a. As a result, all of the raw material continuously and smoothly flows out to the outer circumferential surface of the screw main body11without stagnating inside the exit40.

Thereby, it is possible to impart stretching action to the raw material passing through the path37without any omission, uniformly, and continuously while preventing the raw material from locally stagnating inside the path37.

In each ofFIG. 11(A) andFIG. 11(B), andFIG. 12(A) andFIG. 12(B), the path37according to a second modification example is shown. In the path37, the part of the path main body39closer to an end face39sof one side (the other end of the first part39a) of the path main body39, i.e., the part just this side of the end face39sis joined to the bottom part38aof the entrance38. In the bottom part38a, two openings38bcommunicating with the path main body39(first part39a) are formed. On the other hand, the part of the path main body39closer to an end face39sof the other side (the other end of the second part39b) of the path main body39, i.e., the part just this side of the end face39sis joined to the bottom part40aof the exit40. In the bottom part40a, two openings40bcommunicating with the path main body39(second part39b) are formed.

The two openings38bof the entrance38are formed in an area opposed to the bottom part38ahaving a shape widen toward the outer circumferential surface of the screw main body11. On the other hand, the two openings40bof the exit40are formed in an area opposed to the bottom part40ahaving a shape widen toward the outer circumferential surface of the screw main body11. It should be noted that the function and advantage of the path37according to the second modification example are identical to the path37according to the first modification example, and hence descriptions of them are omitted.

In the one embodiment, and modification examples described above, as the opening direction of the entrance38and exit40, although the direction perpendicular to the axis line10is assumed, the direction is not limited to this. As shown in, for example,FIG. 13(A) andFIG. 13(B), andFIG. 14(A) andFIG. 14(B), the opening directions of the entrance38and exit40may be set to the directions (directions indicated by dotted lines) intersecting the axis line10. In this case, openings may be formed in a plurality of directions from both sides of the path main body39to thereby provide a plurality of entrances38and38-1, and a plurality of exits40and40-1.

Furthermore, regarding the entrance38, it is desirable that the entrance38be formed in such a manner that the entrance38is made sunken below the outer circumferential surface of the screw main body11. Thereby, it is possible to make the raw material flow into the entrance38more easily.

Furthermore, in the embodiment and modification examples described above, although a path37provided with a path main body39parallel to the axis line10is assumed, the path37is not limited to this, and a path37provided with a path main body39intersecting the axis line10is also included in the technical scope of the present invention. For example, the exit40is eliminated, whereby the other side of the path main body39one side of which is joined to the entrance38is directly opened to the outer circumferential surface of the screw main body11(cylinder body13). In this case, the path main body39having a gradient rising from one side to the other side is formed.

According to such a configuration, the raw material flowing into the path main body39from the entrance38receives centrifugal action at the time of the rotation of the screw main body11, whereby the raw material flows through the path main body39more smoothly, and flows out to the outer circumferential surface of the screw main body11(cylinder body13). At this time, stretching action is imparted to the raw material more efficiently and continuously. As a result, it is possible to further enhance the degree of kneading of the raw material.

Further, in the one embodiment described above, although a case where the path37(specifically, path main body39) is formed inside the screw main body11(cylinder body13) at the kneading portion11cis assumed, in place of this, when the rotating shaft14is made to penetrate each cylinder body13constituting the screw main body11(kneading portion11c) along the inner circumferential surface of each cylinder body13, the path37(path main body39) may be formed at the boundary part between each cylinder body13and rotating shaft14. It should be noted that as the configuration of this modification example, the configuration of the part corresponding toFIG. 3is shown inFIG. 15throughFIG. 18.

The path37shown inFIG. 15is constituted of a wall surface30aformed by depressing part of the inner circumferential surface of the cylinder body13in the axial direction to form a concave shape. In this case, the rotating shaft14is made to penetrate the cylinder body13along the inner circumferential surface of the cylinder body13, whereby it is possible to define the path37surrounded by the wall surface30aand outer circumferential surface of the rotating shaft14.

The path37shown inFIG. 16is constituted of a wall surface30bformed by depressing part of the outer circumferential surface of the rotating shaft14in the axial direction to form a concave shape. In this case, the rotating shaft14is made to penetrate the cylinder body13along the inner circumferential surface of the cylinder body13, whereby it is possible to define the path37surrounded by the wall surface30band inner circumferential surface of the cylinder body13.

The path37shown inFIG. 17is constituted of a wall surface30cformed by depressing part of the outer circumferential surface of the key17in the axial direction to form a concave shape. In this case, the rotating shaft14is made to penetrate the cylinder body13along the inner circumferential surface of the cylinder body13, whereby it is possible to define the path37surrounded by the wall surface30cand groove bottom surface of the key groove19.

In any one of the paths37described above, by only processing a part exposed to the outside into a concave shape, each of the wall surfaces30a,30b, and30ccan be formed, and hence the formation work can easily be carried out. In this case, as the shape of the concave wall surfaces30a,30b, and30c, for example, various shapes such as a semicircular shape, triangular shape, elliptical shape, rectangular shape, and the like can be employed.

Further, in the one embodiment described above, although the part of the screw main body11at which the kneading portion11cis provided is constituted of a plurality of cylinder bodies13and rotating shaft14, in place of this, as shown inFIG. 18, the screw main body11(kneading portion11c) may be constituted of one straight shaft-like member2t. In this case, the aforementioned conveyance portions and barrier portions are provided on the outer circumferential surface of the solid screw main body11(kneading portion11c), and the aforementioned paths37are provided inside the screw main body11(kneading portion11c). It should be noted that in the drawing, as an example, although one of a pair of paths37provided at a position deviated from the axis line10and defined by a cylindrical wall surface30dis shown, this does not limit the arrangement of each path37.

Further, in the one embodiment described above, although a case where a single-screw extruder1in which one extruder screw2is rotatably inserted in the cylinder3of the barrel4is assumed, in place of this, to also a twin-screw extruder34in which two extruder screws31are rotatably inserted in the cylinder33of the barrel32, the technical idea of the present invention is applicable, and the identical advantage can be realized.

InFIG. 19, an example of a twin-screw extruder34is shown. InFIG. 19, only one extruder screw31of the two extruder screws31is shown. The other extruder screw is hidden behind the one extruder screw31, and hence is not shown.

In the twin-screw extruder34, the two extruder screws31can be rotated in the same direction in a state where the screws31are engaged with each other. As in the case of the aforementioned one embodiment, each of the two extruder screws31is provided with a screw main body11rotating together with the screw31in an integrated state. In a state where the extruder screws31are engaged with each other, between the screw main bodies11, a transfer portion11a, melting and mixing portion11b, and kneading portion11care formed in the order mentioned from the base end of the screw main body11toward the leading end thereof.

The transfer portion11acontinuously conveys the plurality of types of materials6supplied from the supply port5to the inside of the cylinder3toward the melting and mixing portion11b. On the outer circumferential surface of each screw main body11at the transfer portion11a, a spiral flight35is continuously formed. The flight35is configured to continuously convey the materials6supplied from the supply port5to the inside of the cylinder3from the transfer portion11atoward the melting and mixing portion11b. Accordingly, the flight35is twisted in a direction opposite to the rotational direction of the screw main body11.

The melting and mixing portion11bcontinuously melts and mixes the materials6conveyed thereto from the transfer portion11a. Each screw main body11at the melting and mixing portion11bis configured to include a plurality of disks36adjacent to each other in the axial direction. The plurality of disks36are arranged in a state where phase differences are given to disks adjacent to each other.

At the kneading portion11c, in each screw main body11, as in the case of the aforementioned one embodiment, the conveyance portions22a, conveyance portions22b, conveyance portions22c, and barrier portions23are alternately arranged in line in the axial direction. It should be noted that at the barrel32, the inner surface33sof the cylinder33is configured to have a shape making it possible to accommodate therein both the two extruder screws31in a state where the screws31are engaged with each other, and cause the extruder screws31to simultaneously rotate in the same direction. Other configurations are identical to the aforementioned one embodiment, and hence descriptions of them are omitted.

According to such a twin-screw extruder34, in a state where the two extruder screws31are rotated in the same direction at a rotational speed of, for example, 100 rpm to 300 rpm, a plurality of types of materials6supplied from the supply port5to the inside of the cylinder33are continuously conveyed from the transfer portion11ato the melting and mixing portion11b. In the melting and mixing portion11b, the materials6are continuously melted and mixed. At this time, the melted and mixed materials6are turned into a kneading raw material, and the raw material is conveyed from the melting and mixing portion11bto the kneading portion11c. Then, the conveyed raw material is introduced into the kneading portion11cthrough the aforementioned introduction portion15, and is thereafter turned into kneaded stuff having an enhanced degree of kneading to thereby be continuously extruded from the discharge port7.

It should be noted that in the embodiment described above, although the technical idea (extrusion technique for enhancing the degree of kneading) of the present invention is applied to the case where a plurality of materials6are to be kneaded, the application is not limited to this, and the technique is also applied to a case where a minute unmelted part is to be prevented from occurring when one type of material is melted, and case where a minute part of a resin in which the resin temperature is non-uniform is to be prevented from occurring.

REFERENCE SIGNS LIST