Method and apparatus for manufacturing a foamed molded body

Abstract

The present invention provides a method for manufacturing a foam molded body, which can omit or simplify a complex control device for a physical foaming agent and can stabilize the amount of the physical foaming agent dissolved in a molten resin by a simple mechanism. The method for manufacturing a foam molded body uses a plasticizing cylinder having a plasticizing region for plasticizing and melting a thermoplastic resin to form a molten resin and a starving region in which the molten resin becomes starved, and having an inlet for introducing the physical foaming agent into the starving region. The manufacturing method includes the following steps: plasticizing and melting the thermoplastic resin to form the molten resin; making the molten resin starved in the starving region; introducing a pressurized fluid including the physical foaming agent at a constant pressure into the starving region and maintaining the starving region at the constant pressure; in the case of maintaining the starving region at the constant pressure, bringing the starved molten resin in the starving region into contact with the pressurized fluid including the physical foaming agent at the constant pressure; and forming the molten resin, which has been brought into contact with the pressurized fluid including the physical foaming agent, into a foam molded body.

Description

[0001] This application is a divisional application; the application number of its parent application is "2016800330418", and the invention title is "Method and apparatus for manufacturing a foamed molded body". Technical Field

[0002] The present invention relates to a method and an apparatus for manufacturing a foamed molded body. Background Art

[0003] In recent years, an injection foaming method (Patent Documents 1 to 3) using nitrogen or carbon dioxide in a supercritical state as a physical foaming agent has been studied and applied. According to these Patent Documents 1 to 3, the injection foaming method using a physical foaming agent is carried out as follows. First, a physical foaming agent is introduced into a closed plasticizing cylinder and dispersed in contact with the plasticized and molten resin. The plasticizing cylinder is maintained at a high pressure to the extent that the physical foaming agent becomes a supercritical state, and the molten resin in which the physical foaming agent is dispersed is metered and injected into a mold. The supercritical fluid that is soluble in the molten resin rapidly decompresses and gasifies during injection filling, and bubbles (foaming units) are formed inside the molded body as the molten resin solidifies. In these injection foaming methods, the physical foaming agent is metered at a pressure slightly higher than the resin internal pressure, and after metering, it is introduced into the plasticizing cylinder. Thus, the amount of the physical foaming agent dissolved in the molten resin is determined by the introduced amount of the physical foaming agent (introduced amount control).

[0004] In addition, Patent Document 4 discloses that, in an injection foaming method using a physical foaming agent, a part of the physical foaming agent contained in the molten resin is separated during molding and exhausted outside the plasticizing cylinder (mixing device). In Patent Document 4, a mixing device is disclosed that forms an opening for discharging the physical foaming agent and has a mechanism for maintaining the pressure in the region where the opening is formed (decompression region) constant. According to this method, the amount of the physical foaming agent dissolved in the molten resin is determined by the pressure of a back pressure valve in the decompression region (pressure control). Therefore, as disclosed in the above Patent Documents 1 to 3, it is not necessary to accurately control the injection amount of the physical foaming agent into the plasticizing cylinder.

[0005] Patent Documents 5 and 6 also disclose a method of introducing a physical foaming agent into a plasticizing cylinder by pressure control in an injection foaming method using a physical foaming agent. In Patent Documents 5 and 6, a starving region where the molten resin is not filled is provided in the plasticizing cylinder, and the physical foaming agent is introduced into the starving region.

[0006] The manufacturing apparatuses disclosed in Patent Documents 5 and 6 are the same as existing general manufacturing apparatuses, having a structure in which the inner diameter of the introduction port of the physical foaming agent is small, and the introduction port is intermittently opened by a check valve or the like. The reason for the existing manufacturing apparatus using a physical foaming agent having such a structure is as follows. First, when the physical foaming agent is introduced into the plasticizing cylinder, due to contact with the high-temperature molten resin, the temperature of the physical foaming agent rises rapidly, resulting in the drawback of unstable introduction amount of the physical foaming agent. Therefore, in the existing manufacturing apparatus, it is desired to throttle the flow path of the physical foaming agent to be thin, control the flow rate of the physical foaming agent, and stabilize the introduction amount. Second, if the molten resin flows back into such a thin flow path, there is a possibility that the flow path will be blocked soon and the function cannot be exerted. Therefore, a structure is provided in which the introduction port of the physical foaming agent is not always open, and a check valve or the like is provided to be intermittently opened.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent No. 2625576 Gazette

[0010] Patent Document 2: Japanese Patent No. 3788750 Gazette

[0011] Patent Document 3: Japanese Patent No. 4144916 Gazette

[0012] Patent Document 4: Japanese Unexamined Patent Application Publication No. 2013 - 107402

[0013] Patent Document 5: Japanese Unexamined Patent Application Publication No. 2001 - 341152

[0014] Patent Document 6: Japanese Unexamined Patent Application Publication No. 2004 - 237522 Summary of the Invention

[0015] Problems to be Solved by the Invention

[0016] In the injection foam molding method using a physical foaming agent in Patent Documents 1 to 3, if the concentration of the physical foaming agent in the molten resin is high, there is a possibility of phase separation between the molten resin and the physical foaming agent. Therefore, it is necessary to reduce the concentration of the physical foaming agent to about 1 / 5 to 1 / 10 of the saturation solubility. And in order to form more foaming nuclei during injection filling into the mold while keeping the concentration of the physical foaming agent in the molten resin at a low ratio relative to the saturation solubility, it is necessary to set the physical foaming agent introduced into the plasticizing cylinder at a high pressure and accurately measure the introduction amount. This becomes the main reason for complicating the supply mechanism of the physical foaming agent and increasing the initial cost of the apparatus.

[0017] On the other hand, in the injection foam molding method using a physical foaming agent in Patent Document 4, by adopting the above-described mixing device, after discharging a part of the physical foaming agent, the concentration of the physical foaming agent in the molten resin can be increased to near the saturation solubility (saturation concentration), and more foam nuclei can be formed using a physical foaming agent at a relatively low pressure. However, in the injection foam molding method of Patent Document 4, in order to keep the pressure in the decompression region constant, there is a sealing mechanism that shuts off the decompression region from other regions by reversing the screw. Therefore, there are problems such as the screw becoming longer and the plasticizing and metering time becoming longer due to the reverse rotation of the screw.

[0018] In the injection foam molding methods of Patent Document 5 and Patent Document 6, the physical foaming agent is introduced into the plasticizing cylinder by pressure control. Therefore, it is not necessary to accurately measure the introduction amount of the physical foaming agent. In addition, it is not necessarily required to provide the sealing mechanism disclosed in Comparative Document 4. However, according to the research of the present inventors, as disclosed in Patent Documents 5 and 6, when the introduction of the physical foaming agent into the starving region in the plasticizing cylinder is performed intermittently, the pressure in the starving region fluctuates. As a result, it may not be possible to precisely control the dissolution amount (penetration amount) of the molten resin with respect to the physical foaming agent.

[0019] The main reason is presumably that the introduction amount of the physical foaming agent is insufficient because the physical foaming agent is introduced into the plasticizing cylinder intermittently. However, as described above, there are problems such as the temperature difference between the introduced physical foaming agent and the molten resin and the backflow of the molten resin. Therefore, it is difficult to increase the introduction amount of the physical foaming agent and achieve stabilization using the devices having the structures disclosed in Patent Documents 5 and 6.

[0020] The present invention is a solution to the above problems, and provides a method for manufacturing a foam molded body that can omit or simplify a complex control device for a physical foaming agent and can stabilize the dissolution amount (penetration amount) of the physical foaming agent with respect to the molten resin by a simple mechanism.

[0021] Method for solving the problems

[0022] According to a first aspect of the present invention, there is provided a manufacturing method, which is a manufacturing method of a foamed molded body. A plasticizing cylinder is used, which has a plasticizing region for plasticizing and melting a thermoplastic resin to form a molten resin and a starving region where the molten resin becomes starved. An inlet for introducing a physical foaming agent into the starving region is formed. The manufacturing method includes the following steps: plasticizing and melting the thermoplastic resin to form the molten resin; in the starving region, making the molten resin in a starved state; introducing a pressurized fluid including the physical foaming agent at a constant pressure into the starving region, and maintaining the starving region at the constant pressure; in a state where the starving region is maintained at the constant pressure, in the starving region, bringing the starved molten resin into contact with the pressurized fluid including the physical foaming agent at the constant pressure; and forming the molten resin into a foamed molded body, where the molten resin is brought into contact with the pressurized fluid including the physical foaming agent.

[0023] In this aspect, in the starving region, the molten resin can be pressurized by the pressurized fluid including the physical foaming agent. During the manufacture of the foamed molded body, the starving region is always maintained at the constant pressure, and the physical foaming agent in contact with the molten resin penetrates into the molten resin. Additionally, the constant pressure can be 1 MPa to 15 MPa.

[0024] On the plasticizing cylinder, a compression region and the starving region are arranged adjacent to each other in this order from the upstream side in the flow direction of the molten resin. By providing a mechanism in the compression region to increase the flow resistance of the molten resin, the pressure of the molten resin in the compression region is increased, and in the starving region, the molten resin is made in a starved state. The inner diameter of the inlet can be 20% to 100% of the inner diameter of the plasticizing cylinder, and the inlet is always kept open.

[0025] The plasticizing cylinder has an introduction speed adjustment container connected to the inlet. The manufacturing method further includes a step of supplying a pressurized fluid including the physical foaming agent to the introduction speed adjustment container, and a pressurized fluid including the physical foaming agent at a constant pressure can be introduced from the introduction speed adjustment container into the starving region. The volume of the introduction speed adjustment container can be 5 mL to 10 L. Additionally, the manufacturing method of this embodiment further includes the following steps: detecting the situation where the molten resin bulges out from the inlet; and when it is detected that the molten resin bulges out from the inlet, stopping the drive of the plasticizing cylinder.

[0026] According to the second aspect of the present invention, there is provided a manufacturing apparatus for manufacturing a foamed molded body, which has a plasticizing region for plasticizing and melting a thermoplastic resin to form a molten resin and a starving region where the molten resin becomes in a starving state, a plasticizing cylinder formed with an inlet for introducing a physical foaming agent into the starving region, an introduction speed adjustment container connected to the inlet, and a physical foaming agent supply mechanism connected to the introduction speed adjustment container and supplying the physical foaming agent to the plasticizing cylinder through the introduction speed adjustment container. A pressurized fluid including the physical foaming agent at a constant pressure is introduced into the starving region, and the starving region is maintained at the constant pressure. In the case of maintaining the starving region at the constant pressure, in the starving region, the molten resin in the starving state is brought into contact with the pressurized fluid including the physical foaming agent at the constant pressure, and the molten resin is formed into a foamed molded body, and the molten resin is brought into contact with the pressurized fluid including the physical foaming agent.

[0027] In this aspect, the inner diameter of the inlet is 20% to 100% of the inner diameter of the plasticizing cylinder, and the volume of the introduction speed adjustment container can be 5 mL to 10 L. In addition, the introduction speed adjustment container may be provided with a bulging detection mechanism for detecting the bulging of the molten resin from the inlet.

[0028] Advantages of the Invention

[0029] The manufacturing method of the foamed molded body of the present invention does not require controlling the introduction amount, introduction time, etc. of the physical foaming agent into the molten resin. Therefore, the manufacturing method of the present invention can omit or simplify a complicated control device, and can reduce the device cost. In addition, the manufacturing method of the foamed molded body of the present invention can stabilize the dissolution amount (penetration amount) of the physical foaming agent with respect to the molten resin through a simple mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flowchart showing the manufacturing method of the foamed molded body of the embodiment.

[0031] Figure 2 is a schematic diagram showing the manufacturing apparatus of the foamed molded body used in the embodiment.

[0032] Figure 3 is a schematic diagram showing the manufacturing apparatus of the foamed molded body used in Example 4.

[0033] Figure 4 is a schematic diagram showing the introduction speed adjustment container used in the embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] While referring to Figure 1 the flow shown Figure 1Next, a method for manufacturing the foamed molded article of the present embodiment will be described.

[0035] (1) Manufacturing apparatus for foamed molded article

[0036] First, a manufacturing apparatus for manufacturing the foamed molded article used in the present embodiment will be described. In the present embodiment, the manufacturing apparatus (injection molding apparatus) 1000 shown in Figure 2 is used to manufacture the foamed molded article. The manufacturing apparatus 1000 mainly includes a plasticizing cylinder 210 provided with a screw 20, a gas cylinder 100 as a physical foaming agent supply mechanism for supplying a physical foaming agent to the plasticizing cylinder 210, a mold clamping unit 250 provided with a mold 251, and a control device (not shown) for controlling the operation of the plasticizing cylinder 210 and the mold clamping unit 250. The molten resin plasticized and melted in the plasticizing cylinder 210 flows from Figure 2 the right hand to the left hand in Figure 2 Thus, in the plasticizing cylinder 210 of the present embodiment, the right hand in

[0037] is defined as "upstream" or "rear", and the left hand is defined as "downstream" or "front". The plasticizing cylinder has a plasticizing region 21 for plasticizing and melting the thermoplastic resin into molten resin, and a starving region 23 on the downstream side of the plasticizing region 21 where the molten resin becomes in a starving state. The "starving state" is a state where the molten resin does not fill the starving region and is in an unfilled state. Thus, there is a space other than the occupied portion of the molten resin in the starving region 23. In addition, an inlet 202 for introducing the physical foaming agent into the starving region 23 is formed, and an inlet speed adjustment container 300 is connected to the inlet 202. The gas cylinder 100 supplies the physical foaming agent to the plasticizing cylinder 210 through the inlet speed adjustment container 300.

[0038] In addition, the manufacturing apparatus 1000 has only one starving region 23, but the manufacturing apparatus used in the present embodiment is not limited thereto. For example, in order to promote the penetration of the physical foaming agent into the molten resin, it may be a structure having a plurality of starving regions 23 and inlets 202 formed in the starving regions 23, and introducing the physical foaming agent into the plasticizing cylinder 210 from the plurality of inlets 202. In addition, the manufacturing apparatus 1000 is an injection molding apparatus, but the manufacturing apparatus used in the present embodiment is not limited thereto. For example, it may be an extrusion molding apparatus 2000 as shown in Figure 3 The details of the extrusion molding apparatus 200 will be described later in Example 4.

[0039] (2) Manufacturing method for foamed molded article

[0040] First, in the plasticizing region 21 of the plasticizing cylinder 210, the thermoplastic resin is plasticized and melted into molten resin (Figure 1 Step S1). As the thermoplastic resin, various resins can be used according to the type of the molded article as the purpose. Specifically, for example, polypropylene, polymethyl methacrylate, polyamide, polycarbonate, amorphous polyolefin, polyetherimide, polyethylene terephthalate, polyetheretherketone, ABS resin (acrylonitrile, butadiene, styrene copolymer resin), polyamideamide, polylactic acid, polycaprolactone and other thermoplastic resins and composites thereof can be used. These thermoplastic resins can be used alone or in combination of two or more. In addition, materials in which various inorganic fillers such as glass fiber, talc, and carbon fiber are mixed in these thermoplastic resins can be used. It is preferable to mix an inorganic filler that acts as a foaming nucleating agent and an additive that improves the melt tension in the thermoplastic resin. By mixing these, the foaming cells can be made finer. The thermoplastic of the present embodiment may also include various other general additives as needed.

[0041] In the present embodiment, the plasticization and melting of the thermoplastic resin are carried out in the plasticizing cylinder 210 provided with the screw 20 as shown in Figure 2 . A zone heater (not shown) is disposed on the outer wall surface of the plasticizing cylinder 210, whereby the plasticizing cylinder 210 is heated, and shearing heat caused by the rotation of the screw 20 is also applied to plasticize and melt the thermoplastic resin.

[0042] Next, a physical foaming agent at a constant pressure is introduced into the starving region 23, and the starving region 23 is maintained at the above constant pressure ( Figure 1 Step S2).

[0043] As the physical foaming agent, a pressurized fluid is used. In the present embodiment, the "fluid" means any of a liquid, a gas, and a supercritical fluid. In addition, from the viewpoints of cost and environmental load, the physical foaming agent is preferably carbon dioxide, nitrogen, or the like. Since the pressure of the physical foaming agent in the present embodiment is relatively low, for example, a fluid stored in a gas cylinder such as a nitrogen gas cylinder, a carbon dioxide gas cylinder, or an air gas cylinder can be used, and the fluid is decompressed to a constant pressure by a pressure reducing valve and taken out. In this case, since a pressure boosting device is not required, the cost of the entire manufacturing apparatus can be reduced. In addition, if necessary, a fluid pressurized to a predetermined pressure can be used as the physical foaming agent. For example, when nitrogen is used as the physical foaming agent, the physical foaming agent can be generated by the following method. First, while compressing the air in the atmosphere with a compressor, nitrogen is refined through a nitrogen separation membrane. Then, the refined nitrogen is pressurized to a predetermined pressure using a pressure boosting pump, a cylinder pump, or the like, and the physical foaming agent is generated.

[0044] The pressure of the physical foaming agent introduced into the starving zone 23 is constant, and the pressure in the starving zone 23 is maintained at the same constant pressure as the introduced physical foaming agent. The pressure of the physical foaming agent is preferably 1 MPa to 15 MPa, more preferably 2 MPa to 10 MPa, and even more preferably 2 MPa to 8 MPa. Depending on the type of molten resin, the optimum pressure is different, but by setting the pressure of the physical foaming agent to 1 MPa or more, an amount of the physical foaming agent necessary for foaming can penetrate into the molten resin, and by setting it to 15 MPa or less, the equipment load can be reduced. In addition, the "constant" pressure of the physical foaming agent that pressurizes the molten resin means that the pressure variation range relative to the predetermined pressure is preferably within ±10%, more preferably within ±5%. The pressure in the starving zone is measured, for example, by a pressure sensor (not shown) provided at a position of the plasticizing cylinder 210 opposite to the inlet 202.

[0045] In the present embodiment, as Figure 2 shown, the physical foaming agent is supplied from the gas cylinder 100 through the introduction speed adjustment container 300 and into the starving zone 23 from the inlet 202. After the physical foaming agent is decompressed to a predetermined pressure using the pressure reducing valve 151, it is introduced into the starving zone 23 from the inlet 202 without passing through a pressure increasing device or the like. In the present embodiment, the introduction amount, introduction time, etc. of the physical foaming agent introduced into the plasticizing cylinder 210 are not controlled. Therefore, a mechanism for controlling these, such as a drive valve using a check valve, solenoid valve, etc., is not required. The inlet 202 does not have a drive valve and is always open. In the present embodiment, the pressure of the physical foaming agent is maintained constant from the pressure reducing valve 151 through the introduction speed adjustment container 300 to the starving zone 23 in the plasticizing cylinder 210 by the physical foaming agent supplied from the gas cylinder 100.

[0046] The inner diameter of the inlet 202 of the physical foaming agent is larger than that of the inlet of the physical foaming agent of the existing manufacturing equipment. Therefore, even a physical foaming agent at a relatively low pressure can be effectively introduced into the plasticizing cylinder 210. In addition, even when a part of the molten resin comes into contact with the inlet 202 and solidifies, since the inner diameter is large, it will not be completely blocked and can function as an inlet. On the other hand, if the inner diameter of the inlet 202 is too large, retention of the molten resin will occur and cause poor molding, and in addition, the introduction speed adjustment container 300 connected to the inlet 202 will be enlarged, resulting in an increase in the overall cost of the equipment. Specifically, the inner diameter of the inlet 202 is preferably 20% to 100% of the inner diameter of the plasticizing cylinder 210, more preferably 30% to 80%. In addition, preferably regardless of the inner diameter of the plasticizing cylinder 210, the inner diameter of the inlet 202 is 3 mm to 100 mm, more preferably 5 mm to 50 mm.

[0047] The introduction speed adjustment container 300 connected to the introduction port 202 has a volume equal to or greater than a certain value, which can slow down the flow rate of the physical foaming agent introduced into the plasticizing cylinder 210 and ensure the residence time of the physical foaming agent in the introduction speed adjustment container 300. By staying near the heated plasticizing cylinder 210, the physical foaming agent is heated, and the temperature difference between the physical foaming agent and the molten resin becomes smaller, which can stabilize the dissolution amount (penetration amount) of the physical foaming agent into the molten resin. That is, the introduction speed adjustment container 300 functions as a buffer container. On the other hand, if the volume of the introduction speed adjustment container 300 is large, the cost of the entire device increases. The volume of the introduction speed adjustment container 300 also depends on the amount of molten resin in the starving region 23, but is preferably 5 mL to 10 L, more preferably 10 mL to 1 L. By setting the volume of the introduction speed adjustment container 300 within this range, both cost and the residence time of the physical foaming agent can be considered.

[0048] In addition, as described later, the physical foaming agent is consumed in the plasticizing cylinder 210 due to contact with and penetration into the molten resin. In order to keep the pressure in the starving region 23 constant, the consumed amount of the physical foaming agent is introduced from the introduction speed adjustment container 300 into the starving region 23. If the volume of the introduction speed adjustment container 300 is too small, the replacement frequency of the physical foaming agent becomes high. Therefore, the temperature of the physical foaming agent is unstable, and as a result, the supply of the physical foaming agent may be unstable. Therefore, the introduction speed adjustment container 300 preferably has a volume capable of retaining the amount of the physical foaming agent consumed in the plasticizing cylinder during a period of 1 to 10 minutes.

[0049] In addition, the introduction speed adjustment container 300 may be a different container from the plasticizing cylinder 210 or may be integrally formed with the plasticizing cylinder 210 to form a part of the plasticizing cylinder 210. In addition, in the present embodiment, only the physical foaming agent is introduced into the starving region 23, but other pressurized fluids other than the physical foaming agent may be introduced into the starving region 23 simultaneously to the extent that the effects of the present invention are not affected. In this case, the pressurized fluid including the physical foaming agent introduced into the starving region 23 has the above-mentioned constant pressure.

[0050] Next, the molten resin is made to flow into the starving region 23 to make the molten resin in a starving state ( Figure 1 step S3). The starving state is determined by the balance between the amount of molten resin transported from the upstream of the starving region 23 to the starving region 23 and the amount of molten resin transported from the starving region 23 to its downstream. If the former is less, it is in a starving state.

[0051] In the present embodiment, the molten resin is brought into a starved state by the method described below. The plasticizing cylinder 210 used in the present embodiment has, upstream of the starved region 23, a compression region 22 that is disposed adjacent to the starved region 23 and compresses the molten resin to increase the molten resin pressure. A large-diameter portion 20A is provided in the compression region 22, where the diameter of the shaft of the screw 20 is larger (thicker) than that of the upstream plasticizing region 21 and the screw flights gradually become shallower. In addition, a ring 26 is provided at the boundary with the starved region 23. The ring 26 has a structure cut in half, and these two parts are covered and provided on the screw 20. If the diameter of the shaft of the screw is increased, the gap between the inner wall of the plasticizing cylinder 210 and the screw 20 is reduced, and the resin supply amount transported downstream can be reduced. Therefore, the flow resistance of the molten resin is increased. In addition, even by providing the ring 26 on the screw 20, the flow resistance of the molten resin can be increased in the same manner. Therefore, in the present embodiment, the large-diameter portion 20A and the ring 26 are mechanisms for increasing the flow resistance of the molten resin.

[0052] Due to the presence of the large-diameter portion 20A and the ring 26, the resin flow rate supplied from the compression region 22 to the starved region 23 decreases. In the upstream compression region 22, the molten resin is compressed and the pressure rises. In the downstream starved region 23, the molten resin is not filled (starved state). To promote the starved state of the molten resin, the screw 20 has a structure in which the diameter of the shaft of the portion located in the starved region 23, that is, the downstream side of the ring 26, is smaller (thinner) and the screw flights are deeper than the portion located in the compression region 22. In addition, compared with the portion located in the compression region 22, the screw 20 preferably has a structure in which the diameter of the shaft of the portion located in the entire starved region 23 is smaller (thinner) and the screw flights are deeper. In addition, preferably, throughout the starved region 23, the diameter of the shaft of the screw 20 and the depth of the screw flights are substantially constant. Thereby, the pressure in the starved region 23 can be maintained substantially constant, and the starved state of the molten resin can be stabilized. In the present embodiment, as shown in Figure 2 the starved region 23 is formed in the screw 20 as a portion downstream of the ring 26 where the diameter of the shaft of the screw 20 and the depth of the screw flights are constant.

[0053] The mechanism for increasing the flow resistance of the molten resin provided in the compression region 22 is not particularly limited as long as it is a mechanism for restricting the resin flow rate supplied from the compression region 22 to the starved region 23 and temporarily reducing the flow passage area through which the molten resin passes. In the present embodiment, both the large-diameter portion 20A of the screw 20 and the ring 26 are used, but only one of them may be used. As mechanisms for increasing the flow resistance other than the large-diameter portion 20A and the ring 26 of the screw 20, structures in which the screw is provided reversely to other parts, labyrinth seal ring structures provided on the screw, etc. are cited.

[0054] The mechanism for increasing the flow resistance of the molten resin can be provided on the screw as a ring or the like that is a different component from the screw, or can be provided integrally with the screw as part of the screw structure. If the mechanism for increasing the flow resistance of the molten resin is a ring or the like that is a different component from the screw, the size of the clearance portion, which is the flow path for the molten resin, can be changed by changing the ring. Therefore, it has the advantage of being able to easily change the magnitude of the flow resistance of the molten resin.

[0055] In addition, in addition to the mechanism for increasing the flow resistance of the molten resin, even by providing a backflow prevention mechanism (sealing mechanism) that prevents the molten resin from flowing back from the starvation region 23 to the upstream compression region 22 at the boundary between the compression region 22 and the starvation region 23, the molten resin can be made in a starvation state in the starvation region 23. For example, a sealing mechanism such as a ring or a steel ball that can move upstream by the pressure of the physical foaming agent is cited. However, since the backflow prevention mechanism requires a driving part, resin may stay. Therefore, a flow resistance increasing mechanism without a driving part is preferred.

[0056] In the present embodiment, in order to stabilize the starvation state of the molten resin in the starvation region 23, the supply amount of the thermoplastic resin supplied to the plasticizing cylinder 210 can be controlled. This is because if the supply amount of the thermoplastic resin is too large, it is difficult to maintain the starvation state. For example, a general feeding screw is used to control the supply amount of the thermoplastic resin.

[0057] In addition, the manufacturing method of the present embodiment may further include a step of detecting that the molten resin bulges from the inlet 202 and stopping the driving of the manufacturing apparatus 1000 including the plasticizing cylinder 210 when it is detected that the molten resin bulges from the inlet 202. Since the step of the screw 20 in the starvation region 23 is deep and the amount of resin accumulated is small, even if the inner diameter of the inlet 202 is large, the molten resin does not bulge from the inlet 202. However, for the following reasons, the molding apparatus 1000 of the present embodiment preferably includes a bulge detection mechanism for detecting the case where the molten resin bulges from the inlet 202. In the starvation region 23, in order to maintain the starvation state of the molten resin, there needs to be a difference of a certain level or more between the fluidity (ease of flow) of the resin in the compression region 22 and the fluidity in the starvation region 23. In order to obtain this difference in fluidity, the amount of molten resin supplied to the compression region 22, the outer diameter of the ring 26 that becomes the flow resistance, the metering conditions, etc. need to be optimized. Once stable molding conditions are found, stable molding is performed, but until the optimum molding conditions are reached, the molten resin may bulge from the inlet 202. Therefore, especially in the case of mass-producing a foamed molded body, it is preferable to optimize the manufacturing conditions using a molding machine equipped with a bulge detection mechanism before mass production.

[0058] In the present embodiment, a bulge detection mechanism 310 that can stably and mechanically detect the bulge of the resin even in a pressurized environment is provided on the introduction speed adjustment container 300. As Figure 4 shown, the introduction speed adjustment container 300 has a cylindrical main body 30 whose lower part is connected to the introduction port 202 and has a space 38 where the physical foaming agent stays inside, and a lid 31 that is connected to the main body 30, seals the space 38, and is formed with a through hole 37 communicating with the space 38. A gas cylinder 100 is connected to the space 38 through a pipe 154, and the physical foaming agent is supplied through the pipe 154. In order for the physical foaming agent to stay, the space 38 is always in a pressurized state. In order to reliably seal the pressurized space 38, the lid 31 has a seal 36. The bulge detection mechanism 310 included in the introduction speed adjustment mechanism 300 has a detection rod 32 (moving part) disposed in the space 38 and the through hole 37, whose position is displaced upward by contact with the molten resin bulging from the port, and a magnetic sensor 33 (detection part) disposed on the lid 31 so as to block the through hole 37 and detecting the position displacement of the detection rod 32 with non-contact high precision. The magnetic sensor 33 is connected to a control device (not shown) of the molding device 1000 through a signal line 34.

[0059] The detection rod 32 holds the upper part in the through hole 37, the lower part extends from the through hole 37 into the space 38, and the lower end 32a is inserted into the introduction port 202. In addition, the detection rod 32 has a permanent magnet 35 at the upper end. Since the detection rod 32 is held in the through hole 37 without load without interfering with the surrounding components, it can easily move upward (toward the magnetic sensor 33) even in a pressurized environment.

[0060] When the molten resin is about to bulge from the introduction port 202, the molten resin contacts the lower end 32a of the rod 32 and pushes the detection rod 32 upward. Along with this, the position of the permanent magnet 35 is also displaced upward. The magnetic sensor 33 detects the slight position displacement of the permanent magnet 35 with non-contact high precision and sends a signal to the control device (not shown) of the manufacturing device 1000 through the signal line 34. Thereby, the control device detects the bulge of the resin. And the control device sends an error signal to stop the drive of the manufacturing device 1000 including the plasticizing cylinder 210. Thereby, the space 38 of the introduction speed adjustment container 300 is filled with the molten resin, preventing failures such as the inability to remove the lid 31 from the main body 30.

[0061] In the present embodiment, the length of the starving region 23 in the flow direction of the molten resin is preferably as long as possible in order to ensure the contact area and contact time between the molten resin and the physical foaming agent. However, if it is too long, there will be disadvantages such as an increase in the molding cycle and the length of the screw. Therefore, the length of the starving region is preferably 2 to 12 times the inner diameter of the plasticizing cylinder 210, more preferably 4 to 10 times. In addition, the length of the starving region 23 preferably covers the entire range of the metering stroke for injection molding. That is, the length of the starving region 23 in the flow direction of the molten resin is preferably equal to or greater than the length of the metering stroke in injection molding. As the molten resin is plasticized, metered, and injected, the screw 20 moves forward and backward. However, by making the length of the starving region 23 equal to or greater than the length of the metering stroke, the inlet 202 can always be arranged (formed) within the starving region 23 during the manufacture of the foamed molded body. In other words, even when the screw 20 moves forward and backward during the manufacture of the foamed molded body, the region outside the starving region 23 will not reach the position of the inlet 202. Thus, the physical foaming agent introduced from the inlet 202 is always introduced into the starving region 23 during the manufacture of the foamed molded body. By providing a starving region with a sufficient and appropriate size (length) and introducing the physical foaming agent at a constant pressure therein, the starving region 23 can be easily maintained at a constant pressure. In the present embodiment, the length of the starving region 23 is as Figure 2 shown, downstream of the ring 26 in the screw 20, and is substantially the same as the length of the portion where the diameter of the axis of the screw 20 and the depth of the screw step are constant.

[0062] Next, in a state where the starving region 23 is maintained at a constant pressure, the starved molten resin is brought into contact with the physical foaming agent at a constant pressure in the starving region 23 ( Figure 1 step S4). That is, in the starving region 23, the molten resin is pressurized by the physical foaming agent at a constant pressure. Since the starving region 23 has a space that is not filled with the molten resin (starved state) and where the physical foaming agent can exist, the physical foaming agent can effectively come into contact with the molten resin. The physical foaming agent that has come into contact with the molten resin penetrates into the molten resin and is consumed. When the physical foaming agent is consumed, the physical foaming agent remaining in the introduction speed adjustment container 300 is supplied to the starving region 23. Thereby, the pressure in the starving region 23 is maintained at a constant pressure, and the molten resin continuously comes into contact with the physical foaming agent at a constant pressure.

[0063] In the existing foam molding using a physical foaming agent, a predetermined amount of high-pressure physical foaming agent is forcibly introduced into the plasticizing cylinder within a predetermined time. Therefore, it is necessary to boost the pressure of the physical foaming agent to a high pressure and correctly control the introduction amount, introduction time, etc. of the physical foaming agent into the molten resin. The contact between the physical foaming agent and the molten resin is only for a short introduction time. In contrast, in the present embodiment, the physical foaming agent is not forcibly introduced into the plasticizing cylinder 210, and the physical foaming agent at a constant pressure is continuously supplied into the plasticizing cylinder in such a manner that the pressure in the starving region 23 is kept constant, so that the physical foaming agent continuously contacts the molten resin. As a result, the dissolution amount (penetration amount) of the physical foaming agent into the molten resin determined by the temperature and pressure is stabilized. In addition, since the physical foaming agent in the present embodiment is always in contact with the molten resin, a necessary and sufficient amount of the physical foaming agent can penetrate into the molten resin. Therefore, compared with the existing forming method using a physical foaming agent, the foam molded body manufactured in the present embodiment has finer foam cells even when a low-pressure physical foaming agent is used.

[0064] In addition, the manufacturing method of the present embodiment does not require control of the introduction amount, introduction time, etc. of the physical foaming agent. Therefore, it does not require drive valves such as check valves and solenoid valves, nor a control mechanism for controlling these, and the device cost can be suppressed. In addition, the physical foaming agent used in the present embodiment has a lower pressure compared with the existing physical foaming agent, so the device load is also small.

[0065] In the present embodiment, in the manufacture of the foam molded body, the starving region 23 is always maintained at a constant pressure. That is, in order to replenish the physical foaming agent consumed in the plasticizing cylinder, all the processes of the manufacturing method of the foam molded body are carried out while continuously supplying the physical foaming agent at the above constant pressure. In addition, in the present embodiment, for example, in the case of injection molding in which multiple injections are continuously performed, during the injection process, the cooling process of the molded body, and the process of taking out the molded body, the molten resin for the next injection amount is also prepared in the plasticizing cylinder, and the molten resin for the next injection amount is pressurized by the physical foaming agent at a constant pressure. That is, in the injection molding with multiple continuous injections, in the plasticizing cylinder, in a state where the molten resin and the physical foaming agent at a constant pressure always exist and are in contact, that is, in a state where the molten resin is always pressurized by the physical foaming agent at a constant pressure in the plasticizing cylinder, one cycle of injection molding including a plasticizing metering process, an injection process, a cooling process of the molded body, a taking-out process, etc. is carried out. Similarly, in the case of continuous molding such as extrusion molding, the molding is also carried out in a state where the molten resin and the physical foaming agent at a constant pressure always exist and are in contact, that is, in a state where the molten resin is always pressurized by the physical foaming agent at a constant pressure in the plasticizing cylinder.

[0066] Next, the molten resin in contact with the physical foaming agent is formed into a foam molded body ( Figure 1Step S5). The plasticizing cylinder 210 used in this embodiment has a recompression region 24 that is disposed adjacent to the starvation region 23 downstream of the starvation region 23 and compresses the molten resin, and the pressure is increased. First, by the rotation of the plasticizing screw 20, the molten resin in the starvation region 23 flows toward the recompression region 24. The molten resin including the physical foaming agent is pressure-adjusted in the recompression region 24, extruded forward of the plasticizing screw 20, and metered. At this time, the internal pressure of the molten resin extruded forward of the plasticizing screw 20 is controlled as the screw back pressure by a hydraulic motor or an electric motor (not shown) connected to the rear of the plasticizing screw 20. In this embodiment, in order to uniformly dissolve the physical foaming agent without separating from the molten resin and stabilize the resin density, the internal pressure of the molten resin extruded forward of the plasticizing screw 20, that is, the screw back pressure, is preferably controlled to be about 1 to 4 MPa higher than the pressure of the starvation region 23 that is kept constant. In addition, in this embodiment, a check ring 50 is provided at the front end of the screw 20 so that the compressed resin in front of the screw 20 does not flow backward to the upstream side. Thus, during metering, the pressure in the starvation region 23 does not affect the resin pressure in front of the screw 20.

[0067] The method for forming the foamed molded body is not particularly limited. For example, a molded body can be formed by injection foam molding, extrusion foam molding, foam blowing molding, etc. In this embodiment, Figure 2 the metered molten resin is injected and filled into the cavity 253 in the mold 251 from the plasticizing cylinder 210 shown, and injection foam molding is performed. As the injection foam molding, a short shot method in which molten resin with a filling capacity of 75% to 95% of the volume of the mold cavity is used and the bubbles expand while filling the mold cavity can be used. In addition, a core back method in which, after filling the molten resin with a filling amount of 100% of the mold cavity container, the cavity volume is expanded and foamed can also be used. Since the obtained foamed molded body has foaming units inside, shrinkage during cooling of the thermoplastic resin can be suppressed, charring and warping can be reduced, and a molded body with a low specific gravity can be obtained.

[0068] In the manufacturing method of the present embodiment described above, it is not necessary to control the introduction amount, introduction time, etc. of the physical foaming agent into the molten resin. Therefore, a complicated control device can be omitted or simplified, and the device cost can be reduced. In addition, in the manufacturing method of the foamed molded body of the present embodiment, in a state where the starvation region 23 is kept at a constant pressure, the molten resin in a starvation state in the starvation region 23 is brought into contact with the physical foaming agent at the above constant pressure. Thus, the dissolution amount (penetration amount) of the physical foaming agent with respect to the molten resin can be stabilized by a simple mechanism.

[0069] Examples

[0070] Hereinafter, the present invention will be further described using examples and comparative examples. However, the present invention is not limited to the examples and comparative examples described below.

[0071] [Example 1]

[0072] In this example, mineral-reinforced polyamide 6 (PA6) is used as the thermoplastic resin, and nitrogen is used as the physical foaming agent to manufacture a foamed molded body.

[0073] (1) Manufacturing apparatus

[0074] In this example, the manufacturing apparatus 1000 shown in the above-described embodiment is used. A detailed description of the manufacturing apparatus 1000 will be given. As described above, the manufacturing apparatus 1000 is an injection molding apparatus, and includes a plasticizing cylinder 210, a gas cylinder 100 as a physical foaming agent supply mechanism for supplying a physical foaming agent to the plasticizing cylinder 210, a mold clamping unit 250 provided with a mold 251, and a control device (not shown) for controlling the operation of the plasticizing cylinder 210 and the mold clamping unit 250. Figure 2

[0075] A closed-circuit valve 28 that opens and closes by the drive of a cylinder is provided at the nozzle tip 29 of the plasticizing cylinder 210, and the inside of the plasticizing cylinder 210 can be maintained at a high pressure. The mold 251 is in close contact with the nozzle tip 29, and the molten resin is injected and filled into the cavity 253 formed by the mold 251 from the nozzle tip 29. On the upper side surface of the plasticizing cylinder 210, a resin supply port 201 for supplying a thermoplastic resin to the plasticizing cylinder 210 and an introduction port 202 for introducing a physical foaming agent into the plasticizing cylinder 210 are formed in order from the upstream side. A resin supply funnel 211 and an introduction speed adjustment container 300 are respectively provided at these resin supply port 201 and introduction port 202. The introduction speed adjustment container 300 is connected by a pipe 154 through a buffer tank 153, a pressure reducing valve 151, and a pressure gauge 152. In addition, a sensor (not shown) for monitoring the pressure is provided at a position of the plasticizing cylinder 210 opposite to the introduction port 202.

[0076] The screw 20 is rotatably and reciprocally disposed in the plasticizing cylinder 210 in order to promote the plasticizing and melting of the thermoplastic resin and to meter and inject the molten resin. As described above, a ring 26 cut into two and a large-diameter portion 20A of the screw 20 are provided on the screw 20 as mechanisms for increasing the flow resistance of the molten resin.

[0077] In the plasticizing cylinder 210, a thermoplastic resin is supplied into the plasticizing cylinder 210 from a resin supply port 201. The thermoplastic resin is plasticized by a zone heater (not shown) and becomes a molten resin, and is conveyed downstream by the forward rotation of a screw 20. Due to the presence of a ring 26 and a large-diameter portion 20A provided on the screw 20, on the upstream side of the ring 26, the molten resin is compressed and the pressure increases, and on the downstream side of the ring 26, the molten resin is not filled (starved state). The molten resin conveyed downstream is compressed again near the front end of the plasticizing cylinder 210 before injection and is metered.

[0078] Thus, in the plasticizing cylinder 210, a plasticizing zone 21 for plasticizing and melting the thermoplastic resin, a compression zone 22 for compressing the molten resin and increasing the pressure, a starved zone 23 where the molten resin is not filled, and a recompression zone 24 for recompressing the molten resin decompressed in the starved zone are sequentially formed from the upstream side. The ring 26 provided on the screw 20 is located at the boundary between the compression zone 22 and the starved zone 23. In addition, an inlet 202 for introducing a physical foaming agent is provided in the starved zone 23.

[0079] In the manufacturing apparatus 1000, the inner diameter of the plasticizing cylinder 210 is 35 mm, and the inner diameter of the inlet 202 is 8 mm. Therefore, the inner diameter of the inlet 202 is approximately 23% of the inner diameter of the plasticizing cylinder 210. The volume of the introduction speed adjustment container 300 is approximately 80 mL. In addition, in this embodiment, a mold with a cavity 253 sized 100 mm × 200 mm × 3 mm is used.

[0080] (2) Manufacturing of the foamed molded body

[0081] In this embodiment, as the gas cylinder 100, a nitrogen gas cylinder with a volume of 47 L filled with nitrogen at 14.5 MPa is used. First, the value of a pressure reducing valve 151 is set to 4 MPa, the gas cylinder 100 is opened, and nitrogen at 4 MPa is supplied from the inlet 202 of the plasticizing cylinder 210 to the starved zone 23 through a buffer container 153 with a volume of 0.99 L, the pressure reducing valve 151, a pressure gauge 152, and the introduction speed adjustment container 300. During the manufacturing of the molded body, the gas cylinder 100 is always in an open state.

[0082] In the plasticizing cylinder 210, the plasticizing zone 21 is adjusted to 220°C, the compression zone 22 is adjusted to 240°C, the starving zone 23 is adjusted to 220°C, and the recompression zone is adjusted to 240°C by a zone heater (not shown). Further, resin pellets (manufactured by Toyobo, T777-02) of a thermoplastic resin are supplied from the resin supply hopper 211, and the screw 20 is rotated forward. Thus, in the plasticizing zone 21, the thermoplastic resin is heated and mixed to become a molten resin. By rotating the screw 20 at a back pressure of 6 MPa and a rotational speed of 100 rpm, the molten resin flows from the plasticizing zone 21 to the compression zone 22 and also to the starving zone 23.

[0083] The molten resin flows from the clearance between the large-diameter portion 20A of the screw and the ring 26 and the inner wall of the plasticizing cylinder 210 to the starving zone 23. Therefore, the supply amount of the molten resin to the starving zone 23 is restricted. As a result, in the compression zone 22 on the upstream side of the ring 26, the molten resin is compressed and the pressure increases, and in the starving zone 23 on the downstream side, the molten resin is not filled (starved state). In the starved state 23, since the molten resin is not filled (starved state), a physical foaming agent (nitrogen gas) introduced from the inlet 202 exists in the space where there is no molten resin, and the molten resin is pressurized by this physical foaming agent.

[0084] In addition, the molten resin is conveyed to the recompression zone 24 and recompressed, and at the front end of the plasticizing cylinder 210, a shot amount of the molten resin is metered. Thereafter, the shut-off valve 28 is opened, and the molten resin is filled in the cavity 253 in a pattern with a filling rate of 90% of the volume of the cavity 253 to form a flat-shaped foamed molded article (short-shot method). After molding, the foamed molded article is allowed to cool, and then taken out of the mold. The cooling time is 10 seconds. The molding cycle is 18 seconds, which is the same value as that of a solid molded article (a non-foamed molded article).

[0085] The injection molding of the molded body described above was continuously carried out 100 times of injection, and 100 foamed molded bodies were obtained. In the production of 100 foamed molded bodies, the pressure in the starving region 23 in the plasticizing cylinder 210 was always measured by a pressure sensor (not shown). As a result, the pressure in the starving region 23 was always 4 MPa and was constant. In addition, the value of the pressure gauge 152 indicating the pressure of the nitrogen gas supplied to the starving region 23 was also always 4 MPa during the production of the foamed molded body. Based on the above, in one cycle of the entire injection molding including the plasticizing metering process, the injection process, the cooling process of the molded body, the take-out process, etc., it was confirmed that the molten resin was always pressurized by nitrogen gas at 4 MPa in the starving region 23, and during the continuous molding of 100 molded bodies, the molten resin was always pressurized by nitrogen gas in the starving region 23. In addition, in the production of 100 foamed molded bodies, it was confirmed that the bulging detection mechanism 310 did not detect the bulging of the molten resin, and the state of the starving region 23 was stable.

[0086] The weight non-uniformity of the obtained 100 foamed molded bodies was evaluated by the value (σ / ave. (%)) obtained by dividing the standard deviation (σ) by the weight average (ave.). As a result, (σ / ave.) = 0.21%. As a result of the same evaluation for a solid molded body (a non-foamed molded body), (σ / ave.) = 0.22%, which is the same value as in this embodiment. Based on this result, it was clear that the weight stability of the foamed molded body in this embodiment was the same as that of the solid molded body.

[0087] In this embodiment, compared with the solid molded body, the specific gravity was approximately 10% lighter, and a foamed molded body with warpage corrected could be continuously and stably manufactured. The specific gravity reduction rate affects the dissolution amount (penetration amount) of the physical foaming agent. As a result, it was understood that the dissolution amount (penetration amount) of the physical foaming agent with respect to the molten resin was stabilized. In addition, spiral marks that transfer on the surface of the molded body and deteriorate the surface property by the separated gas slightly remained. In addition, the state of the foaming cells in the cross-section of the obtained foamed molded body was observed. As a result, the average cell diameter of the foaming cells was 20 μm, which was fine.

[0088] [Example 2]

[0089] In this embodiment, carbon dioxide was used as the physical foaming agent. Therefore, as the physical foaming agent supply device, i.e., the gas cylinder 100, a liquid carbon dioxide gas cylinder with a pressure of 6 MPa was used. And the value of the pressure reducing valve 151 was set to 4.5 MPa. Otherwise, 100 foamed molded bodies were continuously manufactured by the same method as in Example 1.

[0090] In the manufacture of the foamed molded body, the pressure in the starving region 23 within the plasticizing cylinder 210 is always measured by a pressure sensor (not shown). As a result, the pressure in the starving region 23 is always 4.5 MPa and is constant. Additionally, the value of the pressure gauge 152 indicating the pressure of the carbon dioxide supplied to the starving region 23 is also always 4.5 MPa during the manufacture of the foamed molded body. Based on the above, it is possible to confirm that throughout one cycle of injection molding including the plasticizing metering process, injection process, cooling process of the molded body, take-out process, etc., in the starving region 23, the molten resin is always pressurized with 4.5 MPa of carbon dioxide, and during the continuous molding of 100 molded bodies, in the starving region 23, the molten resin is always pressurized with carbon dioxide. Additionally, it was confirmed that during the manufacture of 100 foamed molded bodies, the bulging detection mechanism 310 did not detect bulging of the molten resin, and the state of the starving state 23 was stable.

[0091] The weight non-uniformity of the obtained 100 foamed molded bodies was evaluated using the value obtained by dividing the standard deviation (σ) by the weight average (ave.) (σ / ave. (%)). As a result, (σ / ave.) = 0.24%. The same evaluation was carried out for a molded body (non-foamed molded body), and the result was (σ / ave.) = 0.22%, which is the same value as in this example. Based on this result, it is clear that the weight stability of the foamed molded body in this example is the same as that of a solid molded body.

[0092] In this example, compared to the solid molded body, the specific gravity is approximately 10% lighter, and a foamed molded body with corrected warping can be continuously and stably manufactured. As a result, it can be understood that the dissolution amount (penetration amount) of the physical foaming agent with respect to the molten resin is stabilized. Additionally, the state of the foaming cells in the cross-section of the obtained foamed molded body was observed. As a result, compared to Example 1, the average cell diameter of the foaming cells is 80 μm, which is larger. The difference in the size of the foaming cells between this example and Example 1 is presumably due to the different types of physical foaming agents.

[0093] Based on the results of this example, even when carbon dioxide is used as the physical foaming agent, the pressure in the starving region 23 can be maintained by a simple method, and the same effect as in Example 1 where nitrogen was used as the physical foaming agent can be obtained.

[0094] [Example 3]

[0095] In this example, as the thermoplastic resin, polypropylene (PP) resin containing an inorganic filler was used. Additionally, the value of the pressure reducing valve 151 was set to 8 MPa, and the center reverse method was used as the foamed body forming method. The foamed molded body was manufactured by the same method as in Example 1 for the rest.

[0096] PP resin particles (primary polymer, primary polypropylene, J105G) without reinforcing materials such as inorganic fillers were mixed in a weight ratio of 80:20, and 80% by weight of calibration batch particles (masterbatch pellets) (manufactured by Idemitsu Kosan Co., Ltd., MP480) were included as inorganic fillers. Similar to Example 1, the mixed resin material was supplied from the resin supply hopper 211 into the plasticizing cylinder 210, and the plasticizing and metering of the resin material were carried out in the plasticizing cylinder 210. The closed-loop valve 36 was opened, and the molten resin was injection-molded into the cavity 253 in a pattern with a filling rate of 100% of the volume of the cavity 253. After 3 seconds, the mold clamping unit 250 was retracted, and the mold was opened in such a way that the cavity volume expanded from 100% to 200% to form a foam molded body (central reverse method). After molding, the foam molded body was allowed to cool, and the foam molded body was taken out of the mold. The cooling time was 30 seconds. In addition, in this embodiment, since the central reverse method was used, compared with Example 1 using the short injection method, the wall thickness of the molded body increased and the heat insulation effect became higher. Therefore, the cooling time was made longer than that in Example 1.

[0097] The injection molding of the molded body described above was continuously carried out 30 times to obtain 30 foam molded bodies. During the manufacture of the foam molded body, the pressure in the starvation region 23 in the plasticizing cylinder 210 was always measured by a pressure sensor (not shown). As a result, the pressure in the starvation region 23 was always 8 MPa and was constant. In addition, the value of the pressure gauge 152 indicating the pressure of the nitrogen gas supplied to the starvation region 23 was also always 8 MPa during the manufacture of the foam molded body. It was confirmed that throughout one cycle of injection molding including the plasticizing and metering process, the injection process, the cooling process of the molded body, the taking-out process, etc., the molten resin was always pressurized with 8 MPa of nitrogen gas in the starvation region 23, and during the continuous molding of 30 molded bodies, the molten resin was always pressurized with nitrogen gas in the starvation region 23.

[0098] In this embodiment, compared with the solid molded body, the specific gravity was approximately 48% lighter, and a foam molded body with corrected warping could be continuously and stably manufactured. As a result, it was found that the dissolution amount (penetration amount) of the physical foaming agent with respect to the molten resin was stabilized. In addition, the surface state of the obtained foam molded body was observed. The spiral marks in which the separated gas was transferred to the surface of the molded body and deteriorated the surface properties were limited to slightly generated. In addition, the state of the foam cells in the cross-section of the obtained foam molded body was observed. The average cell diameter of the foam cells was 35 μm, which was fine.

[0099] [Example 4]

[0100] In this embodiment, use Figure 3The manufacturing apparatus 2000 shown continuously manufactures a thin plate-shaped foamed molded body by extrusion molding. In the present embodiment, as the thermoplastic resin, unreinforced polyamide 6 (PA6) (Toyobo's Amilan CM1021FS) was used. In addition, as the physical foaming agent, nitrogen in the air was refined, compressed, and used.

[0101] (1) Manufacturing apparatus

[0102] The manufacturing apparatus 2000 is an extrusion molding apparatus, and includes a plasticizing cylinder 410 having a screw 40 therein, a physical foaming agent supply mechanism 500 for supplying a physical foaming agent to the plasticizing cylinder 410, and a control device (not shown) for controlling the operation of the plasticizing cylinder 410. Similar to the Figure 2 shown plasticizing cylinder 210 used in the first embodiment, the molten resin plasticized and melted in the plasticizing cylinder 410 flows from Figure 3 the right hand to the left hand in Figure 3 this. Therefore, inside the plasticizing cylinder 410 of the present embodiment, the

[0103] “right hand” in Figure 4 this is defined as “upstream” or “rear”, and the left hand is defined as “downstream” or “front”.

[0104] A mold 420 is provided at the front end of the plasticizing cylinder 410, and the molten resin is extrusion molded by extruding the molten resin from the mold 420 into the atmosphere. On the upper side surface of the plasticizing cylinder 410, a resin supply port 401 for supplying a thermoplastic resin to the plasticizing cylinder 410 and two inlets 402A, 402B for introducing a physical foaming agent into the plasticizing cylinder 410 are formed in order from the upstream side. A resin supply funnel 411 and a feed screw 412 are disposed on the resin supply port 401, and introduction speed adjustment containers 300A, 300B are respectively disposed on the inlets 402A, 402B. The introduction speed adjustment containers 300A, 300B have the same structure as the

[0105] In the plasticizing cylinder 410, a thermoplastic resin is supplied into the plasticizing cylinder 410 from the resin supply port 401. The thermoplastic resin is plasticized by a zone heater (not shown) and becomes molten resin, and is conveyed downstream by the forward rotation of the screw 40. Due to the presence of the large-diameter portion 40A of the screw 40 and the ring 46, on the upstream side of the ring 46, the molten resin is compressed and the pressure increases, and on the downstream side of the ring 46, the molten resin is not filled (starved state). The molten resin conveyed downstream is compressed and the pressure increases due to the presence of the large-diameter portion 40B of the screw 40, and on the downstream side of the large-diameter portion 40B, the molten resin becomes unfilled again (starved state). The resin conveyed further downstream is compressed again near the front end of the plasticizing cylinder 410 before extrusion, and then extruded from the mold 420.

[0106] Accordingly, in the plasticizing cylinder 410, a plasticizing region 41 for plasticizing and melting the thermoplastic resin, a first compression region 42A for compressing the molten resin and increasing the pressure, a first starved region 43A where the molten resin is not filled, a second compression region 42B where the molten resin is extruded again, a second starved region 43B where the molten resin is unfilled again, and a recompression region 44 where the molten resin decompressed in the starved region is compressed again are sequentially formed from the upstream side. The ring 46 provided on the screw 40 is located at the boundary between the first compression region 42A and the first starved region 43A, and the large-diameter portions 40A and 40B of the screw 40 are respectively disposed in the first compression region 42A and the second compression region 42B. In addition, the introduction ports 402A and 402B for introducing the physical foaming agent are respectively provided in the first starved region 43A and the second starved region 43B. Thus, in the plasticizing cylinder 410, there are two starved regions and introduction ports, and the physical foaming agent is introduced into the plasticizing cylinder from the two introduction ports.

[0107] The physical foaming agent supply mechanism 500 includes a nitrogen generation device 51 that purifies nitrogen through a nitrogen separation membrane while compressing air in the atmosphere using a compressor, and an air-driven booster pump 52 that boosts the purified nitrogen to a predetermined pressure.

[0108] In the manufacturing apparatus 2000, the inner diameter of the plasticizing cylinder 410 is 35 mm, and the inner diameters of the first and second introduction ports 402A and 402B are both 8 mm. Therefore, the inner diameters of the first and second introduction ports 402 are both 23% of the inner diameter of the plasticizing cylinder 410. The volumes of the introduction speed adjustment containers 300A and 300B are both approximately 80 mL. In addition, in this embodiment, in order to obtain a sheet-shaped molded article, a mold 420 with a linear (linear) extrusion port is used. The size of the gap of the extrusion port corresponding to the thickness of the sheet is 0.2 mm.

[0109] (2) Manufacture of the foamed molded article

[0110] First, in the nitrogen gas generation device 51 of the physical foaming agent supply mechanism 500, while compressing the air in the atmosphere using a compressor, nitrogen gas at a pressure of 0.8 MPa is refined through a nitrogen separation membrane. Next, the refined nitrogen gas is boosted to 10 MPa by a booster pump 52 and stored in a buffer tank 153. The value of the pressure reducing valve 151 is set to 6 MPa, and nitrogen gas is distributed from the buffer tank 153 through the pressure reducing valve 151 and a pressure gauge 152 to two introduction speed adjustment containers 300A and 300B. Additionally, nitrogen gas at 6 MPa is supplied from the introduction speed adjustment containers 300A and 300B to the first and second starving regions 43A and 43B of the plasticizing cylinder 410, respectively.

[0111] In the plasticizing cylinder 410, the plasticizing region 41 is adjusted to 240 °C, the first and second compression regions 42A and 42B are adjusted to 250 °C, the first and second starving regions 43A and 43B are adjusted to 220 °C, and the recompression region 44 is adjusted to 240 °C by a region heater (not shown). Then, resin particles of the thermoplastic resin are supplied from a resin supply funnel 411, and the screw 40 is rotated forward. As a result, in the plasticizing region 41, the thermoplastic resin is heated and mixed to become molten resin. In this embodiment, in order to stably maintain the starving state of the first and second starving regions 43A and 43B, a feed screw 412 is used to limit the supply amount of resin particles from the funnel 411 to the plasticizing cylinder 410. By reducing the conveyance amount of resin particles, the molten resin in the plasticizing and melting region 41 can be reduced. As a result, the starving state in the downstream first and second starving regions 43A and 43B is stabilized. By continuously rotating the screw 40 forward at a rotational speed of 150 rpm, the molten resin flows from the plasticizing region 41 to the first compression region 42A and then to the first starving region 43A.

[0112] Since the molten resin flows from the clearance between the large diameter portion 40A of the screw and the ring 46 and the inner wall of the plasticizing cylinder 410 to the first starving region 43, the supply amount of the molten resin to the first starving region 43 is restricted. As a result, in the first compression region 42A on the upstream side of the ring 46, the molten resin is compressed and the pressure increases, and in the downstream first starving region 43A, the molten resin is not filled (starving state). In the first starving region 43A, since the molten resin is not filled (starving state), nitrogen gas introduced from an inlet 402A exists in the space where there is no molten resin, and the molten resin is pressurized using this nitrogen gas. Additionally, the molten resin is conveyed downstream. Similarly, it is compressed in the second compression region 42B and becomes a starving state again in the second starving region 43B, and is pressurized using nitrogen gas. Thus, in this embodiment, in the first and second starving regions 43A and 43B, the molten resin is pressurized twice using nitrogen gas as a physical foaming agent. As a result, the amount of the physical foaming agent infiltrated into the molten resin increases.

[0113] In addition, after delivering the molten resin to the recompression area and recompressing it, it was continuously extruded from the mold 420 into the atmosphere, obtaining a sheet-like foam-formed body with a length of 10 m. In this embodiment, the molten resin was foamed to 5 times the size of the extrusion port of the mold 420, obtaining a sheet with a thickness of 1.0 mm.

[0114] In the production of the foam-formed body, the pressures in the first and second starving areas 43A and 43B in the plasticizing cylinder 410 were always measured by a pressure sensor (not shown). As a result, the pressures in the first and second starving areas 43A and 43B were always 6 MPa and were constant. In addition, the value of the pressure gauge 152 indicating the pressure of the nitrogen gas supplied to the first and second starving areas 43A and 43B was also always 6 MPa during the production of the foam-formed body. Through the above, it was confirmed that in the first and second starving areas 43A and 43B, the molten resin was always pressurized with 6 MPa of nitrogen gas during the extrusion molding. In addition, during the production of the foam-formed body, it was confirmed that the bulging detection mechanism 310 did not detect the bulging of the molten resin, and the states of the first and second starving areas 43A and 43B were stable.

[0115] In this embodiment, the foam-formed body can be continuously and stably produced. Based on this result, it was found that the dissolution amount (penetration amount) of the physical foaming agent with respect to the molten resin was stabilized. In addition, the state of the foam cells in the cross-section of the obtained foam-formed body was observed. The average cell diameter of the foam cells was 20 μm, which was fine.

[0116] [Example Five]

[0117] In this embodiment, in the manufacturing apparatus 1000 used in Example One, except that the inner diameter of the introduction port 202 of the physical foaming agent was made 1 mm, the same injection molding as in Example One was continuously performed 100 times. Therefore, the inner diameter of the introduction port 202 in this embodiment was approximately 2.9% of the inner diameter (35 mm) of the plasticizing cylinder 210.

[0118] In this embodiment, until 50 injections, a foam-formed body having the same characteristics as in Example One could be produced. In the production of 50 foam-formed bodies, as in Example One, it was possible to confirm that during the entire cycle of injection molding including the plasticizing metering process, the injection process, the cooling process of the formed body, the taking-out process, etc., the molten resin was always pressurized with 4 MPa of nitrogen gas in the starving area 23, and during the continuous forming of 50 formed bodies, the molten resin was always pressurized with nitrogen gas in the starving area 23.

[0119] However, after exceeding 50, the foaming property of the molded body gradually decreases. After injection at 80, it is impossible to produce a molded body with foaming cells. After injection molding at 100, the introduction speed adjustment container 300 was removed and the introduction port 202 was confirmed. The introduction port 202 was blocked by resin. Due to the blockage of the introduction port 202, the introduction of the physical foaming agent into the plasticizing cylinder body was hindered. After injection exceeding 50, it is speculated that the foaming property of the molded body decreases. From the results of this embodiment, it can be understood that when continuously manufacturing a foamed molded body, it is preferable that the inner diameter of the introduction port 202 is large.

[0120] [Comparative Example 1]

[0121] In this comparative example, in the manufacturing apparatus 1000 used in Example 1, except that there is a metal blockage in the introduction speed adjustment container 300 and its volume is 1 ml, the same injection molding as in Example 1 was continuously carried out 100 times.

[0122] During the manufacture of 100 foamed molded bodies, the pressure in the starving area 23 in the plasticizing cylinder 210 was always measured using a pressure sensor (not shown). As a result, the pressure in the starving area 23 varied in the range of 4 MPa ± 1 MPa. The variation range (2 MPa) of the pressure in the starving area 23 with respect to the introduction pressure (4 MPa) of the physical foaming agent is 50%. In this comparative example, it is impossible to maintain the starving area 23 at a constant pressure of the physical foaming agent. The reason for this is speculated to be that the volume of the introduction speed adjustment container 300 is small.

[0123] The weight unevenness of the obtained 100 foamed molded bodies was evaluated using the value (σ / ave. (%)) obtained by dividing the standard deviation (σ) by the weight average value (ave.). As a result, (σ / ave.) = 0.82%. Compared with Example 1, the unevenness of the weight became larger. In addition, the surface state of the obtained foamed molded body was observed. As a result, from the appearance of the molded body, it can be seen that the foaming state of the molded body is unstable.

[0124] [Example 6]

[0125] In this embodiment, in the manufacturing apparatus 1000 used in Example 1, except that the inner diameter of the introduction port 202 for the physical foaming agent is 33 mm, the same injection molding as in Example 1 was continuously carried out 2100 times. Therefore, the inner diameter of the introduction port 202 in this embodiment is approximately 94% of the inner diameter (35 mm) of the plasticizing cylinder 210.

[0126] In the initial 100 injection moldings, that is, in the production of the first 100 foam-molded articles, the pressure in the starving region 23 within the plasticizing cylinder 210 is always measured by a pressure sensor (not shown). As a result, the pressure in the starving region 23 is always 4 MPa and is constant. Additionally, the value of the pressure gauge 152 indicating the pressure of the nitrogen gas supplied to the starving region 23 is also always 4 MPa during the production of the foam-molded articles. Based on the above, during one cycle of injection molding including the plasticizing metering process, the injection process, the cooling process of the molded article, the ejection process, etc., it can be confirmed that in the starving region 23, the molten resin is always pressurized with nitrogen gas at 4 MPa, and during the continuous molding of 100 molded articles, the molten resin is always pressurized with nitrogen gas in the starving region 23. Additionally, during the production of 100 foam-molded articles, it can be confirmed that the bulging detection mechanism 310 does not detect the bulging of the molten resin, and the state of the starving region 23 is stable.

[0127] The weight non-uniformity of the obtained 100 foam-molded articles is evaluated using the value obtained by dividing the standard deviation (σ) by the weight average value (ave.) (σ / ave. (%)). As a result, (σ / ave.) = 0.21%. When the same evaluation was performed on a solid molded article (a non-foamed molded article), the result was (σ / ave.) = 0.18%, which is the same value as in this example. Based on this result, it is clear that the weight stability of the foam-molded articles in this example is the same as that of the solid molded articles.

[0128] In this example, compared with the solid molded article, the specific gravity is approximately 10% lighter, and a foam-molded article with corrected warping can be continuously and stably manufactured. The specific gravity reduction rate affects the dissolved amount (penetration amount) of the physical foaming agent. As a result, it can be understood that the dissolved amount (penetration amount) of the physical foaming agent with respect to the molten resin is stabilized. Additionally, the spiral marks in which the separated gas transfers on the surface of the molded article and deteriorates the surface properties are limited to slightly generated. Additionally, the state of the foam cells in the cross-section of the obtained foam-molded article was observed. As a result, the average cell diameter of the foam cells is 20 μm, which is fine.

[0129] Additionally, in this example, even after exceeding 2000 injections, it can be confirmed that a molded article having the same characteristics as the previously evaluated 100 molded articles can be stably formed.

[0130] [Example VII]

[0131] In the manufacturing apparatus 1000 used in Example I, except that the inner diameter of the physical foaming agent inlet 202 is made 37 mm, the same injection molding as in Example I is continuously performed 1100 times. Therefore, the inner diameter of the inlet 202 in this example is approximately 106% of the inner diameter (35 mm) of the plasticizing cylinder 210.

[0132] In the initial 50 injections, i.e., in the production of the first 50 foam-formed bodies, the pressure in the starving region 23 within the plasticizing cylinder 210 was always measured by a pressure sensor (not shown). As a result, in the production of 50 foam-formed bodies, as in the first embodiment, it was confirmed that in the entire cycle of injection molding including the plasticizing metering process, the injection process, the cooling process of the formed body, the take-out process, etc., in the starving region 23, the molten resin was always pressurized with nitrogen at 4 MPa, and during the continuous forming of 50 formed bodies, the molten resin was always pressurized with nitrogen in the starving region 23.

[0133] In addition, in this embodiment, even when more than 50 injections were made, formed bodies could be stably formed. However, around 1000 injections, charring started to occur on the formed bodies. "Charring" is a phenomenon in which black combustion products are generated on the surface of the formed body. After injection molding at 1100 injections, the introduction speed adjustment container 300 was removed and the introduction port 202 was confirmed, and discolored resin adhered around the introduction port 202. In this embodiment, the inner diameter of the introduction port 202 was approximately 106% of the inner diameter of the plasticizing cylinder 210, which was slightly larger. Therefore, retention of the molten resin occurred near the introduction port 202, which is presumed to be the cause of the charring of the formed body.

[0134] [Eighth Embodiment]

[0135] In this embodiment, in the manufacturing apparatus 1000 used in the first embodiment, the inner diameter of the physical foaming agent introduction port 202 was made other than 5 mm, and the same injection molding as in the first embodiment was continuously performed 400 times. Therefore, the inner diameter of the introduction port 202 in this embodiment was approximately 14% of the inner diameter (35 mm) of the plasticizing cylinder 210.

[0136] In the initial 50 injections, i.e., in the production of the first 50 foam-formed bodies, the pressure in the starving region 23 within the plasticizing cylinder 210 was always measured by a pressure sensor (not shown). As a result, in the production of 50 foam-formed bodies, as in the first embodiment, it was confirmed that in the entire cycle of injection molding including the plasticizing metering process, the injection process, the cooling process of the formed body, the take-out process, etc., in the starving region 23, the molten resin was always pressurized with nitrogen at 4 MPa, and during the continuous forming of 50 formed bodies, the molten resin was always pressurized with nitrogen in the starving region 23.

[0137] In this embodiment, even when it exceeds 50, a molded body can be stably formed. However, after injection beyond 200, the foaming property of the molded body gradually decreases, and a molded body having foaming cells cannot be manufactured after injection at 300 or more. After injection molding at 400, the introduction speed adjustment container 300 was removed and the result of the introduction port 202 was confirmed. The introduction port 202 was clogged with resin. Since the introduction port 202 was clogged, the introduction of the physical foaming agent into the plasticizing cylinder was hindered, and it was presumed that the foaming property of the molded body decreased after injection beyond 200. According to the results of this embodiment, when continuously manufacturing a foamed molded body, it is preferable that the inner diameter of the introduction port 202 is relatively large to some extent.

[0138] Industrial applicability is as follows

[0139] The manufacturing method of the present invention can simplify the device mechanism related to the physical foaming agent. In addition, a foamed molded body having excellent foaming properties can be manufactured at low cost and effectively.

[0140] Reference signs

[0141] 20, 40 - screws, 21, 41 - plasticizing regions, 22, 42A, 42B - compression regions, 23, 43A, 43B - starved regions, 24, 44 - recompression regions, 26, 46 - rings, 100 - gas cylinder, 210, 410 - plasticizing cylinders, 250 - clamping unit, 300, 300A, 300B - introduction speed adjustment containers, 420 - mold, 500 - physical foaming agent supply mechanism, 1000, 2000 - manufacturing devices.

Claims

1. A manufacturing method, which is a manufacturing method of a foamed molded body, and the manufacturing method is characterized in that a plasticizing cylinder is used. The plasticizing cylinder has a plasticizing region for plasticizing and melting a thermoplastic resin to form a molten resin and at least one starvation region where the molten resin becomes in a starvation state. An inlet for introducing a physical foaming agent into the starvation region is formed, and the inlet is connected to an introduction speed adjustment container with a volume of 5 mL to 10 L. The manufacturing method includes the following steps: In the plasticizing region, a step of plasticizing and melting the thermoplastic resin to form the molten resin; In the starvation region, a step of making the molten resin in a starvation state; A step of supplying a pressurized fluid including the physical foaming agent to the introduction speed adjustment container; A step of introducing a pressurized fluid including the physical foaming agent at a constant pressure from the introduction speed adjustment container through the inlet into the starvation region, so that the molten resin in the starvation state contacts the pressurized fluid including the physical foaming agent at the constant pressure; and A step of extruding the molten resin from a mold provided at the downstream end of the plasticizing cylinder into the atmosphere to form a foamed molded body, and the molten resin contacts the pressurized fluid including the physical foaming agent. The inlet is always open in all the above steps, and the pressurized fluid including the physical foaming agent at the constant pressure can be introduced into the starvation region.

2. The manufacturing method according to claim 1, characterized in that by introducing a pressurized fluid including the physical foaming agent at the constant pressure into the starvation region through the inlet, the starvation region is maintained at the constant pressure.

3. The manufacturing method according to claim 1, characterized in that the constant pressure is 1 MPa to 15 MPa.

4. The manufacturing method according to claim 1, characterized in that on the plasticizing cylinder, a compression region is provided on the upstream side of the starvation region, by providing a mechanism for increasing the flow resistance of the molten resin in the compression region, the pressure of the molten resin in the compression region is increased, and the molten resin in the starvation region is made in a starvation state.

5. The manufacturing method according to claim 1, characterized in that the inner diameter of the inlet is 20% to 100% of the inner diameter of the plasticizing cylinder.

6. The manufacturing method according to claim 1, characterized in that it further includes a step of detecting the bulging of the molten resin from the inlet, when it is detected that the molten resin bulges from the inlet, the driving of the plasticizing cylinder is stopped.

7. A manufacturing apparatus, which is a manufacturing apparatus for manufacturing a foamed molded body, and the manufacturing apparatus is characterized in that it has: a plasticizing cylinder, which has a plasticizing region for plasticizing and melting a thermoplastic resin to form a molten resin and at least one starvation region where the molten resin becomes in a starvation state, and an inlet for introducing a physical foaming agent into the starvation region is formed; an introduction speed adjustment container connected to the inlet and having a volume of 5 mL to 10 L; and A physical foaming agent supply mechanism that supplies a pressurized fluid including a physical foaming agent to the plasticizing cylinder through the above-mentioned introduction speed adjustment container. The above-mentioned inlet is always open during the manufacture of the above-mentioned foamed molded body, and a pressurized fluid including a physical foaming agent at a constant pressure can be introduced into the above-mentioned starving region. The molten resin that has come into contact with the pressurized fluid including the above-mentioned physical foaming agent is extruded from a mold provided at the downstream end of the above-mentioned plasticizing cylinder into the atmosphere to form a foamed molded body.

8. The manufacturing apparatus according to claim 7, characterized in that By introducing a pressurized fluid including the above-mentioned physical foaming agent at a constant pressure into the above-mentioned starving region through the above-mentioned inlet, the above-mentioned starving region is maintained at the above-mentioned constant pressure.

9. The manufacturing apparatus according to claim 7, characterized in that The above-mentioned constant pressure is 1 MPa to 15 MPa.

10. The manufacturing apparatus according to claim 7, characterized in that On the above-mentioned plasticizing cylinder, a compression region is provided on the upstream side of the above-mentioned starving region. By providing a mechanism for increasing the flow resistance of the above-mentioned molten resin in the above-mentioned compression region, the pressure of the above-mentioned molten resin in the above-mentioned compression region is increased, and the above-mentioned molten resin is in a starving state in the above-mentioned starving region.

11. The manufacturing apparatus according to claim 7, characterized in that The inner diameter of the above-mentioned inlet is 20% to 100% of the inner diameter of the above-mentioned plasticizing cylinder.

12. The manufacturing apparatus according to claim 7, characterized in that The above-mentioned introduction speed adjustment container is provided with a bulging detection mechanism for detecting the bulging of the above-mentioned molten resin from the above-mentioned inlet.

13. The manufacturing apparatus according to claim 7, characterized in that A screw is rotatably disposed in the above-mentioned plasticizing cylinder.

14. The manufacturing apparatus according to claim 7, characterized in that The above-mentioned manufacturing apparatus is an injection molding apparatus, and the length of the above-mentioned starving region is not less than the length of the metering stroke in injection molding.

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