Screw, injection molding machine, and injection molding method

There is provided a screw of an injection molding machine that can eliminate uneven distribution of reinforcing fibers without giving an excessive shear force to the reinforcing fibers. A screw is provided inside a heating cylinder of an injection molding machine to which a resin pellet is fed on an upstream side in a conveyance direction of resin and to which reinforcing fibers are fed on a downstream side therein, and includes: a first stage at which the resin pellet which is fed is melted; and a second stage that continues to the first stage, and at which molten resin and the reinforcing fibers are mixed with each other. A second flight provided at the second stage includes: a large-diameter flight with a relatively large outer diameter; and a small-diameter flight with a relatively small outer diameter.

RELATED APPLICATIONS

The present application is a National Phase entry of International Application No. PCT/JP2014/003066, filed Jun. 9, 2014.

TECHNICAL FIELD

The present invention relates to injection molding of resin containing reinforcing fibers.

BACKGROUND ART

There have been used for various applications molded products of fiber reinforced resin in which strength have been enhanced by making them contain reinforcing fibers. As a technique to obtain the molded product by injection molding, a technique has been known in which thermoplastic resin is melted by rotation of a screw in a cylinder serving as a plasticizing device, fibers are mixed in or kneaded with the melted thermoplastic resin, and subsequently, the thermoplastic resin is injected into a mold of an injection molding machine.

In order to obtain an effect of improved strength by reinforcing fibers, the reinforcing fibers are desired to be uniformly dispersed in resin. Although mixing conditions may just be made severe to strengthen a shear force given to reinforcing fibers in order to achieve uniform dispersion, an excessively strong shear force causes cutting of the reinforcing fibers. In that case, a fiber length after molding might be significantly shorter than an original fiber length, and obtained molded products cannot possibly satisfy desired characteristics (Patent Literature 1). Accordingly, it becomes necessary to select conditions of injection molding in which the shear force is weakened so that breakage of the fibers does not occur at the time of mixing. In that case, the reinforcing fibers cannot be uniformly dispersed in fiber reinforced resin, and are unevenly distributed. Although a mechanism (a feeder) that forcibly feeds the reinforcing fibers inside the cylinder is also provided in order to contribute to uniform dispersion of the reinforcing fibers (for example, Patent Literature 2), a mass of the reinforcing fibers has not been eliminated yet. Particularly, in a case where a contained amount of the reinforcing fibers is high, i.e. not less than 10%, it is difficult to uniformly disperse the reinforcing fibers in the resin.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

The present invention aims to provide a screw of an injection molding machine that can eliminate uneven distribution of reinforcing fibers without giving an excessive shear force to the reinforcing fibers.

In addition, the present invention aims to provide an injection molding machine including such an injection screw.

Further, the present invention aims to provide a method of injection-molding resin containing reinforcing fibers using such an injection screw.

Solution to Problem

The present inventors examined a cause of uneven distribution of reinforcing fibers, and obtained one conclusion. That is, during a plasticizing process of injection molding, as shown inFIGS. 8A to 8C, a fiber mass, which is a set of a number of reinforcing fibers F, and molten resin M are present in a screw groove301between flights306of a screw300for injection molding arranged inside a cylinder310, the fiber mass and the molten resin M being separated into a pull side303and a push side305of the flight. Since a viscosity of the molten resin M is relatively high, and the molten resin M cannot get into the fiber mass, a shear force by rotation of the screw300through a medium of the molten resin M is not transmitted to an inside of the fiber mass, and opening of the fiber mass does not proceed. Accordingly, since the reinforcing fibers F are injection-molded while remaining as the fiber mass, they are unevenly distributed in a molded product. Note that a white arrow ofFIG. 8Ashows a direction in which the screw300rotates, and that white arrows ofFIG. 8Cshow relative moving directions of the screw300and the cylinder310in an axial direction or in a peripheral direction along with the rotation of the screw300. The same applies to an embodiment, which will be mentioned later.

Consequently, the present inventors have conceived of an idea in which a part of the molten resin M present on the push side305of the flight of the screw groove301is made to flow backward to the adjacent pull side303of the screw groove301over a top portion T of the flight306. That is, it is the idea that opening of a fiber mass is promoted by making the molten resin M having flowed backward act on the fiber mass.

The screw of the present invention based on the above knowledge is provided inside a cylinder of an injection molding machine to which a resin raw material is fed on an upstream side and to which reinforcing fibers are fed on a downstream side, and includes: a first stage at which the resin raw material which is fed is melted; and a second stage that continues to the first stage, and at which the melted resin raw material and the reinforcing fibers which are fed are mixed with each other.

In the screw of the present invention, a flight provided at the second stage includes a resin passage in which a backflow of the melted resin raw material is generated from a screw groove of the downstream side toward a screw groove of the upstream side of the screw. The screw of the present invention is intended so that the backflow is generated in the molten resin M by providing the resin passage.

Note that a term of the upstream or the downstream used in the present application shall be used on the basis of a direction in which the resin is conveyed by the screw.

A mode of the resin passage in the screw of the present invention can be selected from a mode A in which the resin passage is continuously provided in a predetermined range in a winding direction of the flight, and a mode B in which the resin passage is provided at a part of the flight in the winding direction.

In the mode A, both of a first mode in which the second stage includes a single-thread flight and a second mode in which the second stage includes a two-thread flight can be selected.

In the first mode in the mode A, in the second stage, a large-diameter flight, and a small-diameter flight with a relatively small outer diameter are continuous with each other to thereby form the single-thread flight. A backflow passage in the mode is formed with a gap between a top portion of the small-diameter flight and the cylinder.

In addition, in the second mode, the second stage is formed with the two-thread flight including a main flight, and a sub-flight provided in a screw groove formed by the main flight, the main flight serves as the large-diameter flight, and the sub-flight serves as the small-diameter flight. Also in the mode, a backflow passage is formed with a gap between a top portion of the small-diameter flight and the cylinder.

In the second mode, the sub-flight can be provided at a part or a plurality of points of the screw in an axial direction.

In addition, in the second mode, the sub-flight can be provided corresponding to a portion to which the reinforcing fibers are fed. As a matter of course, it can also be provided at a position away from the portion to which the reinforcing fibers are fed.

In addition, in the second mode, either one or both of a start end and a terminal end of the sub-flight is (are) preferably blocked to the main flight.

In addition, the mode B includes an intermittent flight in which a notch has been provided at a part of the flight so that continuity is lacked in the winding direction of the flight, and the resin passage can be achieved by a third mode including the notch.

The present invention provides an injection molding machine of fiber reinforced resin, the injection molding machine including: a cylinder at which a discharge nozzle has been formed; a screw provided rotatable and movable in a rotation axis direction inside the cylinder; a resin feed portion that feeds a resin raw material in the cylinder; and a fiber feed portion that is provided closer to a downstream side than the resin feed portion, and feeds reinforcing fibers in the cylinder, in which the above-mentioned screw is applied.

In addition, the present invention provides an injection molding method of fiber reinforced resin, the injection molding method being for feeding a resin raw material to a cylinder inside which a screw rotatable and movable in a rotation axis direction has been provided, also feeding reinforcing fibers closer to a downstream side than the resin raw material, and injection-molding the reinforcing fibers, in which the above-mentioned screw is applied.

Advantageous Effects of Invention

According to the present invention, there can be provided the screw of the injection molding machine that can eliminate uneven distribution of the reinforcing fibers without giving an excessive shear force to the reinforcing fibers.

DESCRIPTION OF EMBODIMENT

Hereinafter, the present invention will be explained in detail based on an embodiment shown in accompanying drawings.

An injection molding machine1according to the embodiment, as shown inFIG. 1, includes: a mold clamping unit100; a plasticizing unit200; and a control unit50that controls operations of the units.

Hereinafter, outlines of a configuration and an operation of the mold clamping unit100, and a configuration and an operation of the plasticizing unit200will be explained, and next, procedures of injection molding by the injection molding machine1will be explained.

The mold clamping unit100includes: a fixed die plate105that has been fixed on a base frame101and to which a fixed mold103has been attached; a movable die plate111that moves on a slide member107, such as a rail and a slide plate in a left and right direction inFIG. 1by actuating a hydraulic cylinder113, and to which a movable mold109has been attached; and a plurality of tie bars115that couple the fixed die plate105with the movable die plate111. At the fixed die plate105, a hydraulic cylinder117for mold clamping is provided coaxially with each tie bar115, and one end of the each tie bar115is connected to a ram119of the hydraulic cylinder117.

Each of the components performs a necessary operation in accordance with an instruction of the control unit50.

An operation of the mold clamping unit100is outlined as follows.

First, the movable die plate111is moved to a position of a chain double-dashed line inFIG. 1by actuation of the hydraulic cylinder113for mold opening and closing to thereby make the movable mold109abut against the fixed mold103. Next, a male screw portion121of each tie bar115and a half nut123provided at the movable die plate111are engaged with each other to thereby fix the movable die plate111to the tie bars115. Subsequently, a pressure of hydraulic oil of an oil chamber of a movable die plate111side in the hydraulic cylinder117is increased to thereby clamp the fixed mold103and the movable mold109. After mold clamping is performed in a manner as described above, molten resin M is injected from the plasticizing unit200into a cavity of the mold to then form a molded product.

Since the screw10of the embodiment, as will be mentioned later, has a system that individually feeds a thermoplastic resin pellet P and reinforcing fibers F in a longitudinal direction of the screw, an entire length of the screw10or an entire length of the plasticizing unit200tends to be long. For this reason, in the embodiment, combining the mold clamping unit100having the above-mentioned configuration that can save a space is effective for suppressing an entire length of the injection molding machine1to be short, the mold clamping unit100being able to be installed even in a narrow space in which a mold clamping apparatus of a toggle link system or a system including a mold clamping cylinder at a back surface of a movable die plate cannot be installed. However, the configuration of the mold clamping unit100shown here is merely one example, and it does not prevent application of or replacement with the other configuration. For example, although the hydraulic cylinder113is shown as an actuator for mold opening and closing in the embodiment, it may be replaced with a combination of a mechanism that converts a rotational motion into a linear motion, and an electric motor, such as a servomotor and an induction motor. As the conversion mechanism, a ball screw and a rack and pinion can be used. In addition, it is needless to say that the mold clamping unit100may be replaced with a toggle link type mold clamping unit by electric drive or hydraulic drive.

The plasticizing unit200includes: a cylindrical heating cylinder201; a discharge nozzle203provided at a downstream end of the heating cylinder201; the screw10provided inside the heating cylinder201; a fiber feed device213to which the reinforcing fibers F are fed; and a resin feed hopper207to which the resin pellet P is fed. The fiber feed device213is coupled with a vent hole206provided closer to the downstream side than the resin feed hopper207.

The plasticizing unit200includes: a first electric motor209that advances or retreats the screw10; a second electric motor211that rotates the screw10in a normal or a reverse direction; and a pellet feed device215that feeds the resin pellet P to the resin feed hopper207. Each of the components performs a necessary operation in accordance with an instruction of the control unit50.

The screw10has a two-stage type design similar to a so-called gas vent type screw. Specifically, the screw10has a first stage21provided on an upstream side, and a second stage22that continues to the first stage21and is provided on the downstream side, the first stage21includes a feed portion23, a compression portion24, and a measurement portion70in that order from the upstream side, and the second stage22includes a feed portion25, a compression portion26, and a measurement portion71in that order from the upstream side. Note that a right side inFIG. 1is the upstream side, and that a left side therein is the downstream side. The same applies to an embodiment, which will be mentioned later.

In the screw10, a first flight27is provided at the first stage21, and a second flight28is provided at the second stage22.

In both of the first stage21and the second stage22, relatively, screw grooves between the flights in the feed portions23and25are set to be deep, screw grooves between the flights of the compression portions24and26are set to gradually decrease from the upstream side toward the downstream side, and screw grooves in the measurement portions70and71are set to be the most shallow. Here, since the screw groove of the feed portion25of the second stage22is deeper than that of the measurement portion70of the first stage21, the molten resin M discharged from the first stage21to the feed portion25cannot fill the screw groove of the feed portion25. Hereby, the molten resin M is pushed against the push side305by rotation of the screw10, and is unevenly distributed. Hereby, a space is generated on the pull side303of the feed portion25of the second stage22. For this reason, it is understood that the reinforcing fibers F fed from the fiber feed device213through the vent hole206are distributed to the pull side303serving as the space, and that thereby the molten resin M and the reinforcing fibers F are divided as shown inFIG. 8.

Since the first stage21conveys the generated molten resin M toward the second stage22in addition to melting a resin raw material to thereby generate the molten resin M, it may just include a function to secure a conveyance velocity and plasticizing capacity of the molten resin M.

In order to obtain the function, as shown inFIG. 1, it is preferable that a flight lead (L1) of the first flight27of the first stage21is not more than a flight lead (L2) of the second flight28of the second stage22, i.e. L1≤L2is established. Note that the flight lead (hereinafter simply referred to as a lead) means an interval between flights at the front and rear. As one index, the lead L1of the first flight27is preferably set to be 0.4 to 1.0 times of the lead L2, and is more preferably set to be 0.5 to 0.9 times thereof.

Next, in the second stage22, the second flight28includes a large-diameter flight28A with a large outer diameter, and a small-diameter flight28B with a small outer diameter as shown inFIG. 3A. A size of an outer diameter here is a relative matter, and the outer diameter (a radius) of the small-diameter flight28B is set to be smaller than that of the large-diameter flight28A by δ.

An outer diameter of a flight of a screw is usually set so that a top portion thereof can slide to an inner surface of a heating cylinder. As shown inFIGS. 3B and 3C, the large-diameter flight28A of the embodiment corresponds to the flight slidable to the inner surface of the heating cylinder, and the small-diameter flight28B is formed so that a top portion T thereof is separated from an inner surface of the heating cylinder201. A gap generated between the top portion T and the inner surface forms a resin passage in the present invention in which a backflow of the molten resin M is generated.

In the screw10, the large-diameter flight28A, the small-diameter flight28B, and the large-diameter flight28A are arranged in that order from the upstream side on which the reinforcing fibers F are put in.

Effects by providing the small-diameter flight28B at the second stage22will be mentioned after procedures of injection molding are explained.

According to the above-mentioned preferred mode in which L1≤L2is established, the lead L2of the second flight28of the second stage22is larger than the lead L1of the first flight27. The reinforcing fibers F are fed to a rear end side of the second stage22during the plasticizing process. When the lead L2is large, a groove width between the second flights28is large, thereby making a large space, the space in which the reinforcing fibers F drop and fill. In addition to that, the number of times decreases that the vent hole206is blocked by the second flight28at the time of retreat of the screw10in the plasticizing process, and at the time of advance of the screw10in an injection process. Accordingly, even during the retreat or the advance of the screw10, the drop of the reinforcing fibers F is not stopped at the second flight28, and the reinforcing fibers F easily continuously drop in the groove. Specifically, in a region of the second flight28in which the reinforcing fibers F fed through the vent hole206are received, the lead L2is preferably set to be not less than 1.0×D, and is more preferably set to be not less than 1.2×D. Thereby, the reinforcing fibers F can be stably dropped in the groove of the screw10during the injection process. Note that D is an inner diameter of the heating cylinder201.

However, when the lead L2becomes too large, a force of conveying the molten resin M becomes weak, conveyance of the molten resin M becomes unstable even at an extent of a back pressure (5 to 10 MPa) required for usual plasticization, the molten resin M due to the back pressure flows backward to the vent hole206, and vent-up easily occurs. Accordingly, the lead L2is preferably set to be not more than 2.0×D, and is more preferably set to be not more than 1.7×D. That is, the lead L2of the second flight28is preferably set to be 1.0×D to 2.0×D, and is more preferably set to be 1.2×D to 1.7×D.

In addition, a width of the flight of the second flight28is preferably set to be 0.01 to 0.3 times (0.01×L2to 0.3×L2) of the lead L2. This is because when the width of the flight is smaller than 0.01 times of the lead L2, strength of the second flight28becomes insufficient, and because when the width of the flight exceeds 0.3 times of the lead L2, a screw groove width becomes small, and the fibers are caught in a flight top to thereby be hard to drop in the groove.

In addition, besides the above-mentioned preferred mode in which L1≤L2is established, a part or all of the second flights28particularly of the feed portion25of the second stage22may be a plural-thread flight (plural-thread flights) instead of a single-thread flight (single-thread flights). In this case, since the molten resin M discharged from the first stage21is divided and distributed into the screw grooves partitioned by the plural-thread flights, respectively, and thus a fiber mass and the molten resin M are brought into contact with and are mixed with each other in each screw groove, respectively, the plural-threaded flights are effective for impregnation of the molten resin M into the fiber mass. Further, since the number of times of passes of the flights under the vent hole206per one rotation of the screw10is increased by the plural-threaded flights by employing the plural-threaded flights for the region to which the reinforcing fibers F are fed from the fiber feed device213, capability to scrape the reinforcing fibers F from the vent hole206is improved, and efficiency of taking the reinforcing fibers F in the screw10groove is improved.

In the fiber feed device213of the embodiment, a biaxial type screw feeder214is provided at the heating cylinder201as shown inFIG. 1, and the reinforcing fibers F are forcibly fed in the groove of the screw10. Note that it is needless to say that there is no problem if a uniaxial type screw feeder is used.

As a method of feeding the reinforcing fibers F to the biaxial type screw feeder214, continuous fibers, so-called fibers in a roving state (hereinafter referred to as roving fibers) may be directly put in the biaxial type screw feeder214, or fibers in a chopped strand state (hereinafter referred to as chopped fibers) may be put therein, the fibers being previously cut to have a predetermined length. Alternatively, the roving fibers and the chopped fibers may be mixed and put in the biaxial type screw feeder214at a predetermined ratio.

In a case where the chopped fibers are put in the biaxial type screw feeder214, the roving fibers may be conveyed near a fiber inlet of a measurement feeder as they are, and may be put in the above-described measurement feeder immediately after being cut near the fiber inlet. Hereby, since the chopped fibers likely to be scattered are not exposed before being put in the molding machine, workability can be improved.

In the embodiment, a roving cutter218is provided near the fiber inlet of the biaxial type screw feeder214. The roving fibers are cut by the roving cutter218to thereby be made into the chopped fibers, and then, they are fed to the biaxial type screw feeder214.

An operation of the plasticizing unit200is outlined as follows. Please refer toFIG. 1.

When the screw10provided inside the heating cylinder201is rotated, the reinforcing fibers F fed from the fiber feed device213through the vent hole206, and a pellet (the resin pellet P) comprising thermoplastic resin fed from the resin feed hopper207is sent out toward the discharge nozzle203of the downstream end of the heating cylinder201. Note that timing to start the feed of the reinforcing fibers F is preferably set to be a timing after the resin pellet P (the molten resin M) fed from the resin feed hopper207reaches the vent hole206through which the reinforcing fibers F are fed. When the reinforcing fibers F are started to be put in before the molten resin M reaches the vent hole206, the reinforcing fibers F poor in flowability, and conveyability by the screw10block the inside of the screw groove, thereby the molten resin M might be prevented from being conveyed to overflow the vent hole206, or abnormal wear and breakage of the screw10might occur. After the molten resin M is mixed with the reinforcing fibers F, only a predetermined amount of the molten resin M is injected to the cavity formed between the fixed mold103and the movable mold109of the mold clamping unit100. Note that it is needless to say that a basic operation of the screw10in which injection is performed by advance of the screw10follows after the screw10retreats while receiving the back pressure along with melting of the resin pellet P. In addition, the present invention does not prevent applying or being replaced with the other configuration, such as providing a heater outside the heating cylinder201in order to melt the resin pellet P.

The injection molding machine1including the above components performs injection molding in the following procedures.

Injection molding, as is known well, includes: a mold clamping process of closing the movable mold109and the fixed mold103, and clamping them with a high pressure; a plasticizing process of heating, melting, and plasticizing the resin pellet P in the heating cylinder201; an injection process of injecting the plasticized molten resin M to the cavity formed by the movable mold109and the fixed mold103, and filling the cavity with the plasticized molten resin M; a holding process of cooling the molten resin M with which the cavity has been filled until it is solidified; a mold opening process of opening the mold; and a taking-out process of taking out a molded product cooled and solidified in the cavity. The above-mentioned respective processes are sequentially carried out, or a part of them is concurrently carried out, and the one-cycle injection molding is completed.

Subsequently, the plasticizing process and the injection process to which the embodiment is related will be explained in that order with reference toFIGS. 2A to 2CandFIGS. 3A to 3F.

In the plasticizing process, the resin pellet P is fed through a feed hole208corresponding to the resin feed hopper207of the upstream side of the heating cylinder201. The screw10at the time of plasticization start is located on the downstream of the heating cylinder201, and it is retreated from an initial position while being rotated (“plasticization start” inFIG. 2A). By rotating the screw10, the resin pellet P fed between the screw10and the heating cylinder201is gradually melted while being heated by receiving a shear force, and is conveyed toward the downstream. Note that rotation (a direction) of the screw10in the plasticizing process is set to be a normal rotation in the present invention. If the molten resin M is conveyed to the fiber feed device213, the reinforcing fibers F are fed from the fiber feed device213. Along with the rotation of the screw10, the reinforcing fibers F are kneaded with and dispersed in the molten resin M, and are conveyed to the downstream together with the molten resin M. When feed of the resin pellet P and the reinforcing fibers F is continued, and the screw10is continued to be rotated, they are conveyed on the downstream side of the heating cylinder201, and the molten resin M is accumulated closer to the downstream side than the screw10together with the reinforcing fibers F. The screw10is retreated by balance between a resin pressure of the molten resin M accumulated on the downstream of the screw10and the back pressure that suppresses the retreat of the screw10. After that, the rotation and the retreat of the screw10are stopped at the time when an amount of the molten resin M required for one shot is accumulated (“plasticization completion” inFIG. 2B).

FIGS. 2A to 2Cshow states of the resin (the resin pellet P or the molten resin M) and the reinforcing fibers F by dividing the states into four stages of “unmolten resin”, “resin melting”, “fiber dispersion”, and “fiber dispersion completion”. In the stage of “plasticization completion”, the “fiber dispersion completion” closer to the downstream than the screw10shows the state where the reinforcing fibers F are dispersed in the molten resin M, and are subjected to injection, and the “fiber dispersion” shows that the fed reinforcing fibers F are dispersed in the molten resin M along with the rotation of the screw10. In addition, the “resin melting” shows that the resin pellet P is gradually melted by receiving the shear force, and the “unmolten resin” shows the state where the insufficiently melted resin remains although the shear force is received, and shows that not all the resin has been melted. However, the reinforcing fibers F may be unevenly distributed in a region of the “fiber dispersion completion” in some cases.

When the procedures enter the injection process, the screw10is advanced as shown inFIG. 2C. In that case, a not-shown backflow prevention valve included in a tip of the screw10is closed, thereby the pressure (the resin pressure) of the molten resin M accumulated on the downstream of the screw10rises, and the molten resin M is discharged toward the cavity from the discharge nozzle203.

Hereafter, one-cycle injection molding is completed through the holding process, the mold opening process, and the taking-out process, and the mold clamping process and the plasticizing process of a next cycle are performed.

Next, the effects of providing the small-diameter flight28B will be explained in the embodiment.

The second stage22is fed with the reinforcing fibers F in the feed portion25thereof during the plasticizing process. As previously mentioned with reference toFIGS. 8A to 8C, it is understood that the reinforcing fibers F are present on the pull side of the flight in a form of a fiber mass in a conventional screw whose flight has a fixed diameter. The small-diameter flight28B is provided in order to be used for opening the fiber mass and uniformly dispersing the reinforcing fibers F. Hereinafter, the embodiment will be explained with reference toFIGS. 3A to 3F. Note that hereinafter, the screw10is referred to as a screw10A in order to distinguish the embodiment from a second embodiment and a third embodiment.

The screw10A includes the large-diameter flight28A and the small-diameter flight28B in the second stage22. When they are disposed inside the heating cylinder201, as shown inFIGS. 3B and 3C, the gap (δ) is generated between the top portion T of the small-diameter flight28B and an inside surface2011of the heating cylinder201, even if the top portion T of the large-diameter flight28A abuts against the inside surface2011of the heating cylinder201.

Accordingly, as shown inFIG. 3D, a part of the molten resin M staying on the push side35of the flight flows backward over the top portion T, and a backflow400is generated in the screw groove31of the upstream side. Since a region over the top portion T is the pull side33of the screw groove31in which the fiber mass is present, the molten resin M having flowed backward covers the reinforcing fibers F having become the fiber mass from an outside of the heating cylinder201in a radial direction (hereinafter referred to as an upper side). In this way, the fiber mass is brought into contact with the molten resin M also from the upper side in addition to the laterally located molten resin M of the push side35by providing the small-diameter flight28B. Note that flows of the molten resin M are shown by dashed arrows inFIG. 3D.

Note that the backflow400of the molten resin M means that the molten resin M flows in a direction opposite (from a left side to a right side inFIG. 3D) to the molten resin M in the plasticizing process being conveyed from an upstream toward a downstream (from a right side to a left side inFIG. 3D).

Here, in order to open the fiber mass, it is important to make a shear force due to a swirling flow of the molten resin M along with the rotation of the screw10A act not only on an outer periphery of the fiber mass but on an inside thereof.

As mentioned above, by providing the small-diameter flight28B, as shown by arrows e inFIG. 3E, the molten resin M that comes into contact with a fiber mass G (it is shown as a rectangular parallelepiped in a simplified manner) not only from a side surface SS but from an upper surface US gets into an inside of the fiber mass G, and then the fiber mass G is impregnated. Accordingly, the shear force is transmitted to a wider range inside the fiber mass G through the molten resin M as a medium compared with the fiber mass G being impregnated with the molten resin M only from the side surface SS, and as a result, opening of the fiber mass G is promoted. In addition, as shown inFIG. 3F, since a shear force S can be made to act also on the upper surface US of the fiber mass G in addition to the side surface SS thereof through the molten resin with high adherence property as a medium at the time of the rotation of the screw10A without slipping on the inside surface2011of the cylinder, opening of the fiber mass G is more promoted.

In the second stage22, a position at which the small-diameter flight28B is provided is arbitrary as long as the molten resin M can be made to flow backward. Accordingly, although the small-diameter flight28B can be provided at both of the feed portion25and the compression portion26, it is preferably provided at the feed portion25. In doing so, the molten resin M is conveyed to the compression portion26on which a stronger shear force can be made to act than on the feed portion25after opening of the reinforcing fibers F is promoted in the feed portion25, thereby enabling to contribute to uniform dispersion of the reinforcing fibers F in the molten resin M. In addition, since the molten resin M can be conveyed to the compression portion26in which a groove depth is gradually decreased after the opening of the reinforcing fibers F is promoted to reduce a size of the fiber mass G in the feed portion25, the large fiber mass G can be prevented from blocking an inside of the groove of the compression portion26. In addition, the plurality of small-diameter flights28B may be provided at a plurality of points with an interval. In this case, opening of the reinforcing fibers F can be more promoted.

The second stage22includes the large-diameter flight28A.

This is for securing stable rotation of the screw10A. That is, although all the second flights28of the second stage22can also be replaced with the small-diameter flights28B, in that case, a gap is generated between the inside surface2011of the heating cylinder201and the top portion T of the second flight28in an entire region in an axial direction. In this state, when the screw10A is rotated, the second stage22might be swayed, and abnormal wear and abnormal vibration of the screw10A might occur. Consequently, in the embodiment, the large-diameter flight28A is provided at the front and rear (the upstream side and the downstream side) of the small-diameter flight28B, the large-diameter flight28A is made to function as a bearing, and thereby sway of the second stage22is prevented to secure the stable rotation of the screw10A. Note that the first flight27of the first stage21is used as a substitute for the large-diameter flight28A of the upstream side of the small-diameter flight28B, and that thereby the large-diameter flight28A may be provided only on the downstream side of the small-diameter flight28B.

In the embodiment, it is preferable that a lower-limit value of a size of the gap δ is set to be 0.1 mm, and that an upper-limit value thereof is set to be either smaller one of 8 mm and 60% of the groove depth. When the size of the gap δ is smaller than 0.1 mm, the reinforcing fibers F block the gap δ, which may make it difficult to generate the backflow400. When the size of the gap δ is larger than either smaller one of 8 mm and 60% of the groove depth, an amount of the molten resin M that covers the fiber mass G is increased, impregnation of the molten resin M into the fiber mass G is promoted. However, resin conveyance capacity to the downstream side by the screw10might be insufficient to cause the decrease in molding production efficiency. In addition, since the size of the fiber mass G is larger on the upstream side on which the fibers have just been put in than the downstream side on which stirring has proceeded, the reinforcing fibers F easily block the gap δ when δ of the upstream side is small. Accordingly, the gap δ is preferably gradually decreased or reduced in stages from the upstream side toward the downstream side.

Although the screw with a single-thread flight, a so-called single-flight screw, has been explained in the first embodiment, double flight with a two-thread flight including the main flight and the sub-flight can be applied to the second stage22. Hereinafter, a screw to which the double flight is applied will be explained as a second embodiment. The second embodiment includes a second-first mode in which the double flight is applied to a portion to which the reinforcing fibers F are fed, and a second-second mode in which the double flight is applied to a downstream region away from the portion to which the reinforcing fibers F are fed.

Note that regarding the second flight28in the first embodiment to be included in the main flight, hereinafter, the second flight28shall be read as the main flight28, and the sub-flight is represented as a sub-flight29. As for the other components, portions different from the first embodiment will be mainly explained hereinafter, while the same symbols as in the first embodiment are cited for the same components as in the first embodiment.

The screw10B according to the second-first mode includes the main flight28and the sub-flight29as shown inFIGS. 4A, 4B, and 4C. Note thatFIG. 4Bshows a cross section of an arbitrary position of a downstream side, andFIG. 4Cshows a cross section of an arbitrary position of an upstream side.

Although the main flight28is provided in a substantially entire region of the second stage22in an axial direction, an outer diameter specified by the top portion T of the main flight28is set to be equal over an entire length. The main flight28is independently provided without the sub-flight29in the compression portion26. The outer diameter of the main flight28is set to be similar to that of the large-diameter flight28A in the first embodiment. Note that the top portion of the main flight28is represented as a reference character T28, and that a top portion of the sub-flight29as a reference character T29.

The sub-flight29is provided between the main flights28adjacent at the front and rear, and includes the same lead as a lead of the main flight28, or a lead larger than that of the main flight28. As shown inFIGS. 4B and 4C, the sub-flight29divides the screw groove31provided between the adjacent main flights28into a pull-side groove31A of the downstream side and a push-side groove31B of the upstream side. The outer diameter of the sub-flight29is set to be smaller than that of the main flight28, and corresponds to the small-diameter flight28B of the first embodiment.

The sub-flight29is provided in a region X (FIG. 4A) of the upstream side of the second stage22, and the region X includes a projection region of the vent hole206through which the reinforcing fibers F are fed to the inside of the heating cylinder201. That is, the reinforcing fibers F which are fed are dropped or forcibly introduced in a range of the region X in which the sub-flight29has been formed. Particularly, at the time of start of the plasticizing process, as shown inFIG. 4A, a position of the screw10B is set so that both sides of the screw groove31are bridged by the vent hole206with the sub-flight29being set as a boundary.

Next, actions and effects of the screw10B according to the second-first mode will be explained.

The molten resin M originating from the resin pellet P fed from the resin feed hopper207is sent into the second stage22from the first stage21. In that case, the molten resin M gets into the pull-side groove31A between the sub-flight29of the screw10B and the main flight28located closer to the downstream side than the sub-flight29. As shown inFIG. 4E, a part of the molten resin M having got into the pull-side groove31A flows backward to the push-side groove31B over the top portion T29of the sub-flight29along with rotation of the screw10B. The molten resin M that flows backward over the sub-flight29covers the reinforcing fibers F introduced into the push-side groove31B, and an inside of the reinforcing fibers F is impregnated with the molten resin M. Note that a gap between the top portion T29of the sub-flight29and the inside surface201I of the heating cylinder201in the embodiment forms the resin passage in the present invention in which the backflow of the melted resin raw material is generated.

Meanwhile, the reinforcing fibers F are fed to both of the push-side groove31B and the pull-side groove31A. Accordingly, the reinforcing fibers F are caught in the molten resin M having flowed backward in the push-side groove31B, and the reinforcing fibers F are pushed into the molten resin M from an upper side in the pull-side groove31A.

Here, although only the part of the molten resin M sent into the second stage22from the first stage21flows backward over the sub-flight29, most of it stays on the pull-side groove31A, and a width of the pull-side groove31A is narrower compared with that of the screw groove of the first stage21. Consequently, since an empty space in which the fed reinforcing fibers F can be present as the fiber mass G is significantly reduced, a degree of filling of the molten resin M in an inside of the pull-side groove31A is high. Accordingly, since a pushing force by the fiber feed device213effectively acts as a force to push the reinforcing fibers F inside the molten resin M, impregnation of the molten resin M into the fiber mass G is promoted. As a result of it, the molten resin M enters the reinforcing fibers F and the reinforcing fibers F to thereby weaken tangle of the fibers, or a binder agent of the fiber bundle is melted or dissolved by heat of the molten resin M to thereby weaken a binding force, whereby opening of the reinforcing fibers F is promoted.

In addition, although a lead in a start end29S of the sub-flight29coupled to the main flight28may have the same size as a lead of a center of the sub-flight29in the axial direction, it can be set as shown inFIG. 4A. That is, in the present invention, the lead in the start end29S of the sub-flight29is increased more than the lead of the center of the sub-flight29in the axial direction, and the groove width of the pull-side groove31A may be narrowed early. The degree of filling of the molten resin M in the inside of the pull-side groove31A can be more enhanced by early narrowing the groove width of the pull-side groove31A. In that case, in addition to the pushing force by the fiber feed device213effectively acting as the force to push the reinforcing fibers F inside the molten resin M, a pressure of the molten resin M in the pull-side groove31A can be increased to thereby promote the backflow from the pull-side groove31A to the push-side groove31B.

Although the reinforcing fibers F is impregnated with the molten resin M that flows backward from the pull-side groove31A to the push-side groove31B, a proper shear force acts when the molten resin M flows backward passing through the gap between the top portion T29of the sub-flight29and the inside surface of the heating cylinder201, and thus opening of the fiber mass G that flows backward from the pull-side groove31A to the push-side groove31B together with the molten resin M can be more promoted.

The molten resin M reaches an end point of the sub-flight29while impregnation of the molten resin M into the fiber mass G in the pull-side groove31A and an action of the strong shear force at the time of the backflow of the molten resin M are continued along with the rotation of the screw10B. In the process, as shown inFIG. 4D, the width of the pull-side groove31A becomes narrower, and the opened reinforcing fibers F are dispersed in the molten resin M that has flowed backward from the pull-side groove31A to the push-side groove31B whose width has become wider.

In the embodiment, both of the start end29S and a terminal end29E of the sub-flight29are blocked to the main flight28, which is not essential in the embodiment. However, while the molten resin M leaks from gaps of the start end29S and the terminal end29E when the start end29S and the terminal end29E are separated from the main flight28, the molten resin M can flow backward over all the top portions T29of the sub-flights29to give the shear force if the gaps are blocked.

In a screw10C according to the second-second mode, the sub-flight29is provided closer to the downstream than a put-in portion for the reinforcing fibers F as shown inFIGS. 5A, 5B, and 5C. Since except for the point, the screw10C has the same configuration as the screw10B of the second-first mode, differences from the screw10B will be mainly explained hereinafter.

In the screw10C, while the sub-flight29is provided substantially from a center portion toward a downstream end of the feed portion25, the main flight28is independently provided closer to the upstream side than a region in which the sub-flight29is provided. Accordingly, similarly to the case shown in the first embodiment, as shown inFIG. 5E, the molten resin M and the reinforcing fibers F are divided into the push-side groove31B and the pull-side groove31A until the reinforcing fibers F are fed and reach the sub-flight29.

Along with rotation of the screw10C, the molten resin M and the reinforcing fibers F are conveyed downstream, and reach a double-flight zone in which the sub-flight29is provided. In that case, the molten resin M is guided to the pull-side groove31A together with the reinforcing fibers F. When the molten resin M and the reinforcing fibers F are further conveyed to the downstream side, the molten resin M, as shown inFIG. 5D, flows backward to the push-side groove31B over the top portion T29of the sub-flight29together with the reinforcing fibers F as the width of the pull-side groove31A becomes gradually narrower. Since a strong shear force acts when the molten resin M passes through the gap between the top portion T29of the sub-flight29and the inside surface2011of the heating cylinder201, opening of the reinforcing fibers F transferred to the push-side groove31B is promoted. However, it is also assumed that the fiber mass G with insufficient opening remains even though the molten resin M flows backward over the top portion T29of the sub-flight29. However, with respect to the fiber mass G unevenly distributed on a pull-side side surface of the sub-flight29, similarly to the second-first mode, the backflow of the molten resin M together with the reinforcing fibers F from the pull-side groove31A to the push-side groove31B is continued to the terminal end of the sub-flight29. As a result of the above, the molten resin M that has flowed backward over the top portion T29of the sub-flight29covers the fiber mass G unevenly distributed on the pull-side side surface of the sub-flight29, whereby impregnation of the molten resin M is promoted into the fiber mass G, opening of the reinforcing fibers F in the molten resin M in the push-side groove31B are more promoted, and they are uniformly dispersed.

Although widening of each of the push-side groove31B and the pull-side groove31A is gradual since the screw10C has a long range in which the sub-flight29is provided, the range in which the sub-flight29is provided can also be made shorter to make the widening sharp as shown inFIG. 6A. In this case, a shear force per unit time acting on the fiber mass G when the molten resin M flows backward over the sub-flight29can be strengthened.

The short sub-flight29is provided at a plurality of points (two points here) with an interval as shown inFIG. 6B, and thereby opening of the reinforcing fibers F can be more promoted.

In addition, in a case of providing the sub-flight29at the plurality of points, a combination of the flights to be combined is arbitrary. For example, the sub-flights29each having a region X with the same length may be combined with each other as shown inFIG. 6B, or the sub-flights29each having the region X with a different length may be combined with each other. In a former case, the sub-flights29each having the long region X as shown inFIG. 4A or 5Amay be combined with each other. In addition, in a latter case, the sub-flight29with the long region X as shown inFIG. 4A or 5A, and the sub-flight29with the short region X as shown inFIG. 6Amay be combined with each other.

In addition, the gap δ, which is a difference in height between the main flight28and the sub-flight29in the second-first mode and the second-second mode, is preferably set to be similar to an example 1. That is, it is preferable that the lower-limit value of the gap δ is set to be 0.1 mm, and that the upper-limit value thereof is set to be either smaller one of 8 mm and 60% of the groove depth. Additionally, it is preferable that the gap δ is reduced in stages from the upstream side toward the downstream side, or is gradually decreased over an entire length or in a part of the region X. Particularly, in a case of including the sub-flight29in the plurality of points, the gap δ in the sub-flight29in each point may be gradually decreased from the downstream side to the upstream side, or the gap δ between the sub-flights29provided on the downstream side may be relatively reduced to the gap δ between the sub-flights29provided on the upstream side with the gap δ in the sub-flight29in each point being set to be constant, respectively. In this case, an appropriate shear force can be added to the fiber mass G in which stirring has proceeded by reducing δ of the downstream side similarly to the case shown in the first embodiment, which is effective for opening the fiber mass G. Particularly by setting the gap δ on the upstream side to be large, there can be prevented breakage of the reinforcing fibers F due to generation of an excessive shear force caused by the large fiber mass G being rapidly deformed when the large fiber mass G enters the gap δ between the top portions T29of the sub-flights29, opening of the large fiber mass G not having proceeded.

In addition, the length of the region X of the sub-flight29is preferably set to be 1.5×D to 12×D (D is an inner diameter of the heating cylinder201).

When the region X is shorter than 1.5×D, breakage of the reinforcing fibers F easily occurs due to an excessive compressive force and shear force generated by rapid deformation of the fiber mass G due to rapid reduction of a groove cross section area of the pull-side groove31A. In addition, the large fiber mass G must flow into the small gap δ in a short distance, and thus the gap δ might be blocked by the fiber mass G. In that case, the backflow of the molten resin M from the downstream side to the upstream side is not generated.

When the region X is longer than 12×D, a region in which the molten resin M covers the fiber mass G becomes large, and thus impregnation of the molten resin M into the fiber mass G is promoted. However, most of the molten resin M flows backward over the sub-flight29by the time when the molten resin M reaches the terminal end29E of the sub-flight29. In that case, only the fiber mass G with poor flowability and conveyability by the screw10remains near the terminal end29E, and the fiber mass G cannot flow backward over the sub-flight29, and might stay in the pull-side groove31A.

In addition, the groove depth of the pull-side groove31A may be constant (the feed portion25or the measurement portion71) over the entire length of the region X. However, the present invention is not limited to this, and the groove depth of the pull-side groove31A is preferably gradually decreased from the upstream side toward the downstream side with the vicinity of the terminal end29E of the sub-flight29being set as the compression portion26, in order to prevent the molten resin M or the fiber mass G from staying at the terminal end29E of the sub-flight29. As for a switching position from the feed portion25to the compression portion26, the feed portion25may be switched to the compression portion26on the position closer to the upstream side than the region X, or may be switched inside the region X. Particularly, in the terminal end29E of the sub-flight29, the groove depth is preferably gradually decreased from a groove bottom of the pull-side groove31A to the top portion T29of the sub-flight29so that the pull-side groove31A disappears. In this case, an inclination at which the groove depth of the pull-side groove31A is gradually decreased in the terminal end29E may be the same as an inclination of the compression portion26, or may be set to be larger or smaller than the inclination of the compression portion26by switching the inclination near the terminal end29E.

Although in the first embodiment and the second embodiment, examples have been explained where the resin passage in which the backflow of the melted resin raw material is generated is continuously provided in the predetermined range in the winding direction of the flight, the resin passage can be provided at a part of the winding direction of the flight in the present invention. Hereinafter, a screw in which the resin passage is applied to the part of the winding direction of the flight will be explained as a third embodiment.

Note that hereinafter, portions different from the first embodiment will be mainly explained, while citing the same symbols as in the first embodiment for the same components as in the first embodiment.

In a screw10F according to the third embodiment, as shown inFIG. 7A, a notch75is provided in a part of the second flight28, and a flight28C of the upstream side and a flight28D of the downstream side that are divided by the notch75are included in the intermittent second flight28. In the second flight28, the part of the second flight28continuous in the winding direction is notched to make a terminal end of the flight28C of the upstream side, and a screw groove of the upstream side and a screw groove of the downstream side are coupled with each other in a groove bottom with the notch75being set as a boundary. The gap (δ) is provided between a terminal end of the flight28C of the upstream side and a start end of the flight28D of the downstream side, and the gap (δ) corresponds to a resin passage in the present invention in which a backflow is generated in the molten resin M.

Next, actions and effects of the screw10F according to the third embodiment will be explained.

In the screw10F, the intermittent flight in which the gap (δ) has been provided is included by providing the notch75in the part of the second flight28of the second stage, and the screw groove of the upstream side and the screw groove of the downstream side are coupled with each other in the groove bottom.

Accordingly, as shown inFIG. 7A, a part of the molten resin M staying on the push side35of the flight passes through the notch75that forms the gap (δ) between the terminal end28E of the upstream-side flight28C and the start end28S of the downstream-side flight28D, and flows backward to the screw groove31of the upstream side. Since a region located through the gap (δ) is the pull side33of the screw groove31in which the fiber mass G is present, the molten resin M having flowed backward covers the reinforcing fibers F having become the fiber mass G mainly from a side from the pull side33. In this way, the fiber mass G is brought into contact with the molten resin M also from the pull side33in addition to the laterally located molten resin M of the push side35by providing the notch75. Note that a flow of the molten resin M is shown by a dashed arrow inFIG. 7A.

A position at which the notch75of the flight is provided, a size, and the number of the notch75of the flight in the second stage22are arbitrary as long as the molten resin M can be made to flow backward.

In addition, the number of threads of the second flight28having the notch75is not limited to one, and the plural threads of the second flights28and28each having a different phase in a peripheral direction may be provided as shown inFIG. 7B. In a case of the plural threads of the second flights28and28, only a part of the respective second flights28and28may be overlapped, or all of them may be overlapped. In this case, since the notch75is provided in the respective second flights28and28, the plurality of gaps δ are formed.

In addition, as shown inFIG. 8C, as for the number of flight threads, the number of flight threads of the upstream side is preferably more reduced than that of the downstream side so that opening of the reinforcing fibers F is promoted, the fiber mass G is sequentially subdivided into smaller ones, surfaces of the smaller fiber masses G are covered with the resin, the smaller fiber masses G are impregnated with the resin, and so that the resin containing the smaller fiber masses G can be conveyed to the compression portion26in which a groove depth is gradually decreased.FIG. 8Cshows an example where a two-thread flight is employed on the upstream side, and where a three-thread flight on the downstream side.

In addition, in a case of providing the plurality of gaps δ, all the gaps δ may have the same width, but they can have different widths. Since the size of the fiber mass G is larger on the upstream side on which the fibers have just been put in than the downstream side on which stirring has proceeded, the reinforcing fibers F easily block the gap δ when δ of the upstream side is small. Consequently, the gap δ is preferably gradually decreased or reduced in stages from the upstream side toward the downstream side. In addition, since the molten resin M can be conveyed to the compression portion26in which the groove depth is gradually decreased after the opening of the reinforcing fibers F is promoted to reduce a size of the fiber mass G in the feed portion25, the large fiber mass G can be prevented from blocking the inside of the groove of the compression portion26.

In addition, in the intermittent second flight28, the flight28D of the downstream side may be provided with a phase thereof being displaced to an extension in the winding direction of the flight28C of the upstream side as shown inFIG. 7D. In this case, since a contact area of the fiber mass G with the molten resin M flowing backward in the terminal end of the flight is increased, impregnation of the molten resin M into the fiber mass G is promoted.

Hereinbefore, although the present invention has been explained based on the embodiment, it is possible to select a configuration exemplified in the above-described embodiment or to appropriately change the configuration to the other configuration, unless the configuration departs from the spirit of the present invention,

In addition, the small-diameter flight28B of the first mode and the sub-flight29of the second mode may be combined and provided with an interval, or the sub-flight29may be provided in the screw groove31of the small-diameter flight28B. In addition, the flights of the first to third embodiments may be arbitrarily combined and provided.

In addition, the screw10is not limited to a two-stage type design shown in the embodiment, and it can be a three-stage type design further including a third stage on a downstream side of the second stage, the third stage including a feed portion, a compression portion, and a measurement portion. In this case, such a function that adds a function member to the molten resin or deairs a volatile substance may be added to the third stage.

In the plasticizing unit200of the present invention, although the fiber feed device213and the resin feed hopper207are fixed to the heating cylinder201, a movable hopper that moves in the axial direction of the screw10can be employed. Particularly in a case where a multiaxial type measurement feeder is used for the fiber feed device213, a plurality of feeders may be parallelly coupled and arranged in the longitudinal direction of the screw10, and the feeders that feed the reinforcing fibers F in the plasticizing process may be switched and used. Specifically, the reinforcing fibers F are fed from the feeder arranged at the tip side of the screw10at the time of start of the plasticizing process, and along with the retreat of the screw10in the plasticizing process, the feeder that feeds the reinforcing fibers F may be switched to the feeders of the back side one after the other so that a relative position of the screw10and a feeder screw from which the fibers are discharged is not changed. Hereby, a feed position of the reinforcing fibers F to the screw10can be set to be constant regardless of the change of the relative position of the heating cylinder201and the screw10due to the retreat of the screw10and the advance of the screw10at the time of injection.

Specifically, since a position of the fiber feed feeder screw at the time of plasticization completion, i.e. a position of the backmost screw groove filled with the reinforcing fibers F, can be made coincide with a position of the fiber feed feeder screw at the time of next plasticization start in a position of the screw advanced by the injection, the reinforcing fibers F can be continuously fed to the screw groove located closer to the downstream than the fiber feed device213, and it is effective for preventing or suppressing generation of a region not filled with the reinforcing fibers F, the region being located in the groove of the screw10closer to the downstream than the fiber feed device213.

In addition, as a way of switching the feeder screws, mere ON/OFF control may be performed, or the number of rotation of adjacent screw feeders may be changed in cooperation. Specifically, the number of rotation of the screw feeders of the downstream side is gradually reduced along with the retreat of the screw, and the number of rotation of the screw feeders of the back side may be increased gradually.

In addition, feed of the reinforcing fibers F to the heating cylinder201may be performed not only in the injection process and the plasticizing process, but may also be, for example, performed in a dwelling process and an injection standby process (a period from completion of the plasticizing process to start of the injection process). Since the screw10does not perform rotation, and advance or retreat during the dwelling process and the injection standby process, the vent hole is not intermittently blocked by movement of the flights. For this reason, the reinforcing fibers can be stably fed in the groove of the screw10.

In addition, not only the reinforcing fibers F but the reinforcing fibers F with which powdery or pellet-type raw resin has been mixed may be fed to the fiber feed device213. In this case, even though the molten resin M cannot easily infiltrate between the reinforcing fibers F, the mixed raw resin is melted in the mass of the reinforcing fibers F, enters the inside of the fiber bundle, and can promote loosening of the fiber bundle.

In addition, resin and reinforcing fibers applied to the present invention are not particularly limited, and well-known materials are widely encompassed, such as: general-purpose resin, such as polypropylene and polyethylene; well-known resin such as engineering plastics, such as polyamide and polycarbonate; and well-known reinforcing fibers, such as glass fibers, carbon fibers, bamboo fibers, and hemp fibers. Note that in order to remarkably obtain the effects of the present invention, fiber reinforced resin with a high content rate of reinforcing fibers, i.e. a content rate not less than 10%, is preferably employed as a target. However, since conveyance resistance of the reinforcing fibers in the screw groove becomes large when the content rate of the reinforcing fibers exceeds 70%, it becomes difficult to convey the reinforcing fibers in the present invention using the small-diameter flights with relatively low conveyance capacity of resin, and the reinforcing fibers might block the inside of the screw groove to generate vent-up in the vent hole portion. For this reason, the content rate of the reinforcing fibers applied to the present invention is preferably 10 to 70%, and is more preferably 15 to 50%.

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