Foam injection molding method and foam injection molding device

Abstract

The invention provides a foam injection molding method and a foam injection molding device, even if a motor (an electric or hydraulic plasticizing measuring motor) without a brake is used in physical foam molding, the screw rod can be prevented from retreating when a safety door is opened (when the power supply of the motor is cut off), and the revision of JIS B6711 can be coped with. In this foam injection molding method, in a state in which a molten resin containing a foaming agent is plasticized and measured under the condition that the back pressure of a screw (20) is 8 MPa or less in a measurement step, after opening a safety door of a mold clamping part (250) for taking out a molded article and cutting off a power supply of a plasticization measurement motor, the molded article is subjected to plasticization measurement; before the safety door is closed for injection filling of the next injection cycle, the position of the screw (20) is confirmed, and the screw (20) is returned to the metering completion position.

Description

Technical Field

[0001] This invention relates to a foam injection molding method and a foam injection molding apparatus. Background Technology

[0002] Foam injection molding has been widely used to reduce resin content and improve dimensional accuracy, such as warpage and shrinkage. Foam molding agents are broadly classified into chemical and physical foaming agents, primarily using nitrogen, carbon dioxide, carbon monoxide, ammonia, and water vapor. Among these, methods using physical foaming agents composed of inert gases like carbon dioxide or nitrogen are increasingly being implemented due to their lower environmental impact. Examples include molding methods using high-pressure supercritical fluids and low-pressure gases (Patent Document 1). In particular, the method in Patent Document 1 does not require special high-pressure equipment and can achieve low-environmental-impact foam molding by changing the plasticizing screw and barrel.

[0003] On the other hand, on March 25, 2021, the safety standard for injection molding machines, "JIS B6711," was revised to comply with ISO 20430. The standard's requirements included changes to the safety standards for semi-automatic molding (override, manual intervention). Therefore, manual operations such as opening safety doors and removing molded parts from the mold during molding condition adjustments or production cycles need to be replaced with mechanical devices that can be performed without opening safety doors, or additional special safety devices are required.

[0004] Generally, injection molding equipment closes the mold by moving the movable mold side relative to the fixed mold side through a clamping section. After resin is injected into the mold, the clamping section is driven to open the mold and remove the molded part. Because this action is required, it is necessary to be able to reach into the clamping section from the outside when installing the mold, performing maintenance on the clamping section, or manually removing the molded part. However, since the clamping section is the component that opens and closes the mold, there is a risk of the mold trapping the operator's hand. Therefore, the conventional safety measure is to install a safety door in the clamping section, allowing the clamping section to operate only when the safety door is closed. The revision of "JIS B6711" can be considered as adding requirements related to this safety door.

[0005] Previously, when adjusting molding conditions, the safety door was opened and the product was removed during semi-automatic operation. This disconnected the power to the motor, which was the drive source. In foam molding, the high pressure at the tip of the plasticizing screw in the barrel used to flow the resin caused the screw to retract, making it impossible to adjust molding conditions. To avoid this problem, a motor with a braking mechanism was installed.

[0006] For example, Patent Documents 2 and 3 disclose examples of electric motors with braking mechanisms. In particular, Patent Document 3 discloses an electric vertical injection molding machine in which a brake is installed in the electric motor of the mold clamping device, constituting a safety device. That is, when the power supply to the motor is cut off, the brake operates, using the frictional force of the brake to limit the rotation of the motor. Regarding the braking function of the electric motor, electromagnetic brakes, which apply voltage to the excitation coil when energized, thus putting the brake into a released state, are commonly used.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent No. 6139038

[0010] Patent Document 2: Japanese Patent No. 3201304

[0011] Patent Document 3: Japanese Patent Application Publication No. 2005-199449 Summary of the Invention

[0012] The technical problem that the invention aims to solve

[0013] When the molded part is taken out through the safety door in semi-automatic operation, the power supply to the motor is cut off. When the mold closing device is set horizontally, the power supply to the motor on the mold closing side is cut off while the mold is open. Therefore, even without a braking function, the moving platen and the moving mold will not move, and there will be no problems with safety and the next cycle.

[0014] On the other hand, on the plasticizing side, the screw stops at the metering completion position after metering is completed. In this state, the plasticizing metering motor applies screw back pressure to the resin in front of the screw. However, in typical solid molding, the screw back pressure is low, below 4 MPa. When the power to the plasticizing metering motor is cut off in this state, the resin pressure at the front end, i.e., the pressure pushing the screw backward, is low. Therefore, due to the weight of the screw and the frictional force of the molten resin, the screw is difficult to retract even without a braking function from the motor. This minimizes the risk of adverse effects on safety and the next cycle.

[0015] In contrast, in the case of physical foaming molding, when the pressure of the introduced physical foaming agent is high, the pressure at the front end of the screw increases, and as mentioned above, the screw will retract, making it difficult to adjust the molding conditions.

[0016] The present invention was made in view of the above circumstances, and its object is to provide a foam injection molding method and a foam injection molding apparatus that, even when using a motor (electric or hydraulic plastic metering motor) without a brake in the case of physical foam molding, can limit the screw from retracting when the safety door is opened (when the motor power is cut off), and can comply with the revision of "JIS B6711".

[0017] Technical means to solve the problem

[0018] To address the aforementioned problems, this invention provides a foam injection molding method. This method utilizes a semi-automatic operation of a foam injection molding apparatus to perform metering and injection processes. In the metering process, a plasticizing metering motor without a brake is driven to retract the screw to the plasticizing metering completion position, thereby accumulating the supplied molten resin in front of the screw for metering. In the injection process, an injection motor is driven to advance the screw, thereby filling the accumulated molten resin from the injection nozzle into the mold cavity of the mold closing section. The foam injection molding method is characterized in that: in the metering process, when the molten resin containing the foaming agent is plasticized and metered under a screw back pressure of 8 MPa or less, after opening the safety door of the mold closing section for removing the molded article and cutting off the power to the plasticizing metering motor, before closing the safety door and proceeding to the next injection cycle, the position of the screw is checked, and the screw is returned to the metering completion position.

[0019] According to the above-described structure of the present invention, during the metering process, the molten resin containing the foaming agent is plasticized and metered under a screw back pressure of 8 MPa or less. Therefore, even when using a motor without a brake (electric or hydraulic plasticizing and metering motor) in physical foaming molding, the screw retraction can be restricted after the safety door is opened and the power to the plasticizing and metering motor is cut off. Furthermore, this structure can adequately comply with the revisions to "JIS B6711". Additionally, by checking the screw position before closing the safety door and proceeding with the next injection cycle, the screw is returned to the metering completion position, thus enabling reliable molding condition adjustment.

[0020] Furthermore, the present invention provides a foaming injection molding apparatus, comprising: a plasticizing barrel internally provided with a screw for flowing molten resin; a physical foaming agent supply mechanism for supplying a physical foaming agent to the plasticizing barrel; a mold closing part provided with a mold and having a safety door for removing the molded article; and a control part for controlling the movement of the screw. The foaming injection molding apparatus is capable of performing a metering process and an injection process in semi-automatic operation. In the metering process, a plasticizing metering motor without a brake is driven to retract the screw to the plasticizing metering completion position, thereby accumulating the molten resin supplied from the physical foaming agent supply mechanism on the screw. In front of the screw, molten resin is metered. During the injection process, the injection motor is driven to advance the screw, thereby filling the molten resin accumulated in front of the screw from the injection nozzle of the plasticizing barrel into the mold cavity of the mold closing part. The foaming injection molding device is characterized in that: when the control unit operates in semi-automatic mode, the power supply to the plasticizing metering motor is cut off when the safety door is opened. When it is detected that the screw has further retreated from the plasticizing metering completion position, the screw is returned to the metering completion position with arbitrary back pressure before the safety door is closed and the next injection cycle is started.

[0021] According to the above-described structure of the present invention, when the control unit opens the safety door during semi-automatic operation, it cuts off the power supply to the plasticizing metering motor. If it is detected at this time that the screw has moved further back from the plasticizing metering completion position, the screw is returned to the metering completion position with arbitrary back pressure before the safety door is closed and the next injection cycle is started. Therefore, the molding conditions can be reliably adjusted.

[0022] Furthermore, in the aforementioned structure, it is preferable that the control unit drives the screw backward during the metering process under a screw back pressure of 8 MPa or less to plasticize and meter the molten resin containing the foaming agent. Therefore, since the molten resin containing the foaming agent is plasticized and metered under a screw back pressure of 8 MPa or less, even when using a motor without a brake (electric or hydraulic plasticizing metering motor) in physical foaming molding, screw backward retraction can be restricted after the safety door is opened and the power to the plasticizing metering motor is cut off. Additionally, this structure can adequately comply with the revisions to "JIS B6711".

[0023] In addition, in the above structure, "semi-automatic operation" refers to automatic operation with partial human intervention, such as operations such as workers taking out the molded products through safety doors.

[0024] Invention Effects

[0025] According to the foam injection molding method and foam injection molding apparatus of the present invention, even when a motor without a brake (electric or hydraulic plastic metering motor) is used in the case of physical foam molding, the screw retraction can be limited when the safety door is opened (when the motor power is cut off), and the revision of "JIS B6711" can be met. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a foam injection molding method according to one embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of a foam injection molding apparatus according to one embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of the screw's operating mechanism. Detailed Implementation

[0029] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. These embodiments can contribute to the United Nations Sustainable Development Goals (SDGs) "9. Industry, Innovation and Infrastructure" "9.1 Developing high-quality, reliable, sustainable and resilient infrastructure, including regional and transboundary infrastructure, to support economic development and improve human well-being, with an emphasis on affordability and equitable access to such infrastructure for all."

[0030] Reference Figure 1 The flowchart shown illustrates the foam injection molding method of this embodiment for manufacturing foamed molded articles.

[0031] (1) Foaming injection molding device

[0032] First, the foam injection molding apparatus used to manufacture foamed molded articles will be described. In this embodiment, a foam injection molding apparatus is used. Figure 2 The foam injection molding apparatus 1000 shown manufactures foamed molded articles. The apparatus 1000 mainly includes a plasticizing cylinder 210 with an internal screw 20, a physical foaming agent supply mechanism (i.e., a gas cylinder 100) for supplying physical foaming agent to the plasticizing cylinder 210, a mold closing unit (mold closing section) 250 with a mold 251, and a control unit (not shown) for controlling the movement of the plasticizing cylinder 210 and the mold closing unit 250. Inside the plasticizing cylinder 210, molten resin after plasticization and melting flows from... Figure 2 The material flows from the right side to the left. Therefore, inside the plasticizing cylinder 210 of this embodiment, the material... Figure 2 The right side is defined as "upstream" or "rear", and the left side is defined as "downstream" or "front".

[0033] The plasticizing barrel 210 has a plasticizing zone 21 where heated plastic resin undergoes plasticizing and melting to become molten resin, and a starved zone 23 downstream of the plasticizing zone 21 where the molten resin is in a starved state.

[0034] "Starved state" refers to a state where the molten resin does not completely fill the starved zone 23. Therefore, the starved zone 23 contains space beyond the portion occupied by the molten resin. Furthermore, an inlet 202 for introducing physical foaming agent is formed in the starved zone 23, and the inlet 202 is connected to the inlet speed adjustment container 300. The gas cylinder 100 supplies physical foaming agent to the plasticizing cylinder 210 via the inlet speed adjustment container 300.

[0035] Furthermore, the device 1000 has only one starved zone 23, but the device 1000 used in this embodiment is not limited to this. For example, in order to promote the penetration of the physical foaming agent into the molten resin, it may also have multiple starved zones 23 and inlet ports 202 formed therein, from which the physical foaming agent is introduced into the plasticizing cylinder 210.

[0036] (2) Foaming injection molding method

[0037] First, in the plasticizing zone 21 of the plasticizing barrel 210, the thermoplastic resin is plasticized and melted to become molten resin. Figure 1 Step S1). Various resins can be used as thermoplastic resins depending on the type of the target molded article. Specifically, for example, thermoplastic resins such as polypropylene, polymethyl methacrylate, polyamide, polycarbonate, amorphous polyolefin, polyetherimide, polyethylene terephthalate, polyetheretherketone, ABS resin (acrylonitrile-butadiene-styrene copolymer), polyphenylene sulfide, polyamide-imide, polylactic acid, and polycaprolactone, and their composites, can be used. These thermoplastic resins can be used alone or in combination of two or more. Additionally, products obtained by blending various inorganic fillers such as glass fiber, talc, and carbon fiber into these thermoplastic resins can also be used. Inorganic fillers that act as foaming nucleating agents and additives that increase melt tension are preferred when blending the thermoplastic resin. By blending them, the cell size can be reduced. Furthermore, the thermoplastic resin of this embodiment can contain various other general-purpose additives as needed.

[0038] In this embodiment, Figure 2 The plasticizing barrel 210, which is shown to have a screw 20 inside, is used for the plasticizing and melting of thermoplastic resin. A ring-type heater (not shown) is arranged on the outer wall of the plasticizing barrel 210, thereby heating the plasticizing barrel 210. In addition, the shear heat generated by the rotation of the screw 20 causes the thermoplastic resin to plasticize and melt.

[0039] Next, a physical foaming agent at a certain pressure is introduced into the starvation zone 23 to maintain the starvation zone 23 at the aforementioned certain pressure. Figure 1 Step S2). A pressurized fluid is used as a physical blowing agent. In this embodiment, "fluid" refers to one of liquid, gas, or supercritical fluid. Furthermore, from the perspective of cost and environmental impact, carbon dioxide, nitrogen, etc., are preferred as physical blowing agents. The pressure of the physical blowing agent in this embodiment is relatively low, so, for example, fluid can be taken from a gas cylinder containing fluid, such as a nitrogen cylinder, carbon dioxide cylinder, or air cylinder, after being depressurized to a certain pressure by a pressure reducing valve. In this case, a pressurization device is not required, thus reducing the overall cost of the manufacturing apparatus. Alternatively, if necessary, a fluid pressurized to a specified pressure can also be used as a physical blowing agent. For example, when using nitrogen as a physical blowing agent, the physical blowing agent is generated by the following method: First, atmospheric air is compressed using a compressor and purified by passing it through a nitrogen separation membrane. Then, the purified nitrogen is pressurized to a specified pressure using a booster pump or injection pump to generate the physical blowing agent.

[0040] The pressure of the physical foaming agent introduced into the starved zone 23 is constant, and the pressure of the starved zone 23 is maintained at the same constant pressure as the introduced physical foaming agent. The pressure of this 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. The optimal pressure varies depending on the type of molten resin, but by using a pressure of 1 MPa or higher for the physical foaming agent, the amount of physical foaming agent required for foaming can penetrate into the molten resin; by using a pressure of 15 MPa or lower, the load on the equipment can be reduced. Furthermore, the term "constant" (constant) for the pressure of the physical foaming agent pressurizing the molten resin means that the pressure variation relative to the specified pressure is preferably within ±10%, and more preferably within ±5%. The pressure of the starved zone is measured, for example, by a pressure sensor (not shown) located at a position on the plasticizing cylinder 210 opposite to the inlet 202.

[0041] In this embodiment, such as Figure 2As shown, physical foaming agent is supplied from gas cylinder 100 to starved zone 23 via inlet 202 through inlet speed adjustment container 300. After the physical foaming agent is depressurized to a predetermined pressure using pressure reducing valve 151, it is introduced into starved zone 23 from inlet 202 without passing through a pressure boosting device or the like. In this embodiment, the amount and timing of the physical foaming agent introduced into plasticizing cylinder 210 are not controlled. Therefore, there is no need to provide mechanisms for controlling these, such as a drive valve composed of a check valve or solenoid valve; inlet 202 does not have a drive valve and is always open. In this embodiment, under the action of the physical foaming agent supplied from gas cylinder 100, the pressure of the physical foaming agent is maintained at a constant level from pressure reducing valve 151 through inlet speed adjustment container 300 to starved zone 23 within plasticizing cylinder 210.

[0042] The inlet 202 of the physical foaming agent has a larger inner diameter than that of the physical foaming agent inlet in existing devices. Therefore, even physical foaming agents with relatively low pressure can be efficiently introduced into the plasticizing cylinder 210. Furthermore, even if a portion of the molten resin comes into contact with and solidifies at the inlet 202, the larger inner diameter prevents complete blockage, allowing the inlet to function effectively. On the other hand, if the inner diameter of the inlet 202 is too large, molten resin retention can occur, leading to poor molding. Additionally, the inlet speed adjustment container 300 connected to the inlet 202 becomes larger, increasing the overall cost of the device. Specifically, the inner diameter of the inlet 202 is preferably 20% to 100% of the inner diameter of the plasticizing cylinder 210, and more preferably 30% to 80%. Alternatively, regardless of the inner diameter of the plasticizing cylinder 210, the inner diameter of the inlet 202 is preferably 3 mm to 100 mm, and more preferably 5 mm to 50 mm.

[0043] The inlet speed adjustment container 300, connected to the inlet port 202, has a certain or greater volume, thereby slowing down the flow rate of the physical foaming agent to be introduced into the plasticizing cylinder 210 and ensuring the residence time of the physical foaming agent within the inlet speed adjustment container 300. By residing near the heated plasticizing cylinder 210, the physical foaming agent is heated, reducing the temperature difference between the physical foaming agent and the molten resin, thus stabilizing the amount of physical foaming agent dissolved (penetrated) in the molten resin. In other words, the inlet speed adjustment container 300 functions as a buffer container. On the other hand, if the volume of the inlet speed adjustment container 300 is too large, the overall cost of the device will increase. The volume of the inlet speed adjustment container 300 also depends on the amount of molten resin present in the starvation zone 23, but is preferably 5 mL to 10 L, and more preferably 10 mL to 1 L. By setting the volume of the inlet speed adjustment container 300 within this range, the residence time of the physical foaming agent can be ensured while taking cost into account.

[0044] Furthermore, as described later, the physical foaming agent is consumed within the plasticizing cylinder 210 by contacting and penetrating the molten resin. To maintain a constant pressure in the starved zone 23, an amount of physical foaming agent equivalent to the consumed amount is introduced into the starved zone 23 from the introduction speed adjustment container 300. When the volume of the introduction speed adjustment container 300 is too small, the replacement frequency of the physical foaming agent increases, thus the temperature of the physical foaming agent becomes unstable, resulting in a risk of unstable supply of the physical foaming agent. Therefore, the introduction speed adjustment container 300 preferably has a volume capable of retaining the amount of physical foaming agent consumed in the plasticizing cylinder 210 within 1 to 10 minutes.

[0045] Furthermore, the inlet speed adjustment container 300 can be a separate container from the plasticizing cylinder 210, or it can be integrally formed with the plasticizing cylinder 210, constituting a part of the plasticizing cylinder 210. In this embodiment, only a physical foaming agent is introduced into the starved zone 23, but it is also possible to simultaneously introduce other pressurized fluids besides the physical foaming agent into the starved zone 23 without affecting the effects of the present invention. In this case, the pressurized fluid containing the physical foaming agent introduced into the starved zone 23 has the aforementioned pressure.

[0046] Next, the molten resin is allowed to flow into the starved zone 23, where the molten resin is made into a starved state. Figure 1 (Step S3). The starved state is determined by the balance between the amount of molten resin transported from upstream of the starved zone 23 to the starved zone 23 and the amount of molten resin transported from the starved zone 23 to its downstream. When the former is less, it is a starved state.

[0047] In this embodiment, the molten resin is brought into a starved state by the method described below. The plasticizing barrel 210 used in this embodiment has a compression zone 22 upstream of the starved zone 23, which is disposed adjacent to the starved zone 23, where the molten resin is compressed and the pressure increases. In the compression zone 22, a coarse-diameter portion 20A is provided, which has a larger diameter (thicker) of the screw 20 shaft compared to the upstream plasticizing zone 21, and a shallower, stepped screw ridge. A ring 26 is then provided at the boundary between this portion and the starved zone 23. The ring 26 has a semi-split structure, consisting of two halves fitted onto the screw 20. Increasing the diameter of the screw shaft reduces the gap between the inner wall of the plasticizing barrel 210 and the screw 20, reducing the amount of resin supplied downstream and thus increasing the flow resistance of the molten resin. Similarly, providing the ring 26 on the screw 20 also increases the flow resistance of the molten resin. Therefore, in this embodiment, the coarse-diameter portion 20A and the ring 26 are mechanisms for increasing the flow resistance of the molten resin.

[0048] Due to the presence of the coarse-diameter portion 20A and the ring 26, the resin flow rate supplied from the compression zone 22 to the starved zone 23 is reduced. In the upstream compression zone 22, the molten resin is compressed, causing a pressure increase, while in the downstream starved zone 23, the molten resin is not fully filled (is in a starved state). To promote the starved state of the molten resin, the screw 20 is configured such that, compared to the portion located in the compression zone 22 (i.e., the upstream portion of the ring 26), the portion located in the starved zone 23 (i.e., the downstream portion of the ring 26) has a smaller shaft diameter and deeper screw threads. Furthermore, the screw 20 is preferably configured such that, compared to the portion located in the compression zone 22, the portion located in that portion of the starved zone 23 has a smaller shaft diameter and deeper screw threads throughout the entire starved zone 23. Furthermore, it is preferable that the shaft diameter and screw thread depth of the screw 20 are approximately constant throughout the entire starved zone 23. This allows the pressure in the starved zone 23 to be kept approximately constant, stabilizing the starved state of the molten resin. In this embodiment, the starved zone 23 is as follows... Figure 2 As shown, a portion of the screw 20 downstream of the ring 26 is formed, with a fixed diameter of the screw 20 shaft and a fixed depth of the screw ridge.

[0049] Regarding the mechanism provided in the compression zone 22 for increasing the flow resistance of the molten resin, there are no particular limitations as long as it is a mechanism that temporarily reduces the flow path area through which the molten resin passes in order to limit the flow rate of resin supplied from the compression zone 22 to the starvation zone 23. In this embodiment, both the coarse diameter portion 20A of the screw and the ring 26 are used, but only one may be used. As a mechanism other than the coarse diameter portion 20A of the screw and the ring 26 that can increase the flow resistance, examples include a structure in which the screw ridges are reversed compared to other parts, or a labyrinth structure provided on the screw.

[0050] As a mechanism for increasing the flow resistance of molten resin, a component such as a ring, which is separate from the screw and installed on the screw, can be used, or it can be integrally installed with the screw as part of the screw structure. When a component such as a ring, which is separate from the screw, is used as a mechanism for increasing the flow resistance of molten resin, the size of the flow path, i.e., the gap, of the molten resin can be changed by replacing the ring, thus having the advantage of being able to easily change the magnitude of the flow resistance of the molten resin.

[0051] In addition to mechanisms that increase the flow resistance of the molten resin, a backflow prevention mechanism (sealing mechanism) can be provided between the compression zone 22 and the starved zone 23 to prevent the molten resin from flowing back from the starved zone 23 to the upstream compression zone 22, thus starving the molten resin in the starved zone 23. For example, sealing mechanisms such as rings or steel balls that can move upstream under the pressure of a physical foaming agent can be used. However, since the backflow prevention mechanism requires a drive unit, there is a risk of resin retention. Therefore, it is preferable to use a mechanism that does not have a drive unit and can increase the flow resistance.

[0052] In this embodiment, in order to stabilize the starved state of the molten resin in the starved zone 23, the supply amount of thermoplastic resin to the plasticizing barrel 210 can be controlled. This is because it is difficult to maintain the starved state when the supply amount of thermoplastic resin is too large. For example, the supply amount of thermoplastic resin can be controlled using a general-purpose feed screw.

[0053] In this embodiment, to ensure sufficient contact area and contact time between the molten resin and the physical foaming agent, the length of the starved zone 23 in the flow direction of the molten resin is preferably relatively long. However, excessive length can lead to problems such as increased molding cycle time and screw length. Therefore, the length of the starved zone 23 is preferably 2 to 12 times the inner diameter of the plasticizing barrel 210, and more preferably 4 to 10 times. Furthermore, the length of the starved zone 23 preferably covers the entire range of the metering stroke in injection molding. That is, the length of the starved zone 23 in the flow direction of the molten resin is preferably greater than or equal to 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. By ensuring that the length of the starved zone 23 is greater than or equal to the length of the metering stroke, the inlet 202 can always be positioned (formed) within the starved zone 23 during the manufacturing process of the foamed molded article. In other words, even if the screw 20 moves forward and backward during the manufacturing process of the foamed molded article, areas outside the starved zone 23 will not reach the position of the inlet 202. Therefore, the physical foaming agent introduced through the inlet 202 is consistently introduced into the starved zone 23 during the manufacturing process of the foamed molded article. By setting a starved zone of sufficient and appropriate size (length) and introducing a physical foaming agent at a certain pressure therein, it is easier to maintain a certain pressure in the starved zone 23. In this embodiment, the length of the starved zone 23 is as follows: Figure 2 As shown, the length of the portion of the screw 20 downstream of the ring 26, where the diameter of the screw 20 shaft and the depth of the screw ridges are fixed, is approximately the same.

[0054] Next, while maintaining the starved zone 23 at a certain pressure, the starved molten resin in the starved zone 23 is brought into contact with the aforementioned physical foaming agent at a certain pressure. Figure 1 Step S4). That is, in the starved zone 23, the molten resin is pressurized at a certain pressure using a physical foaming agent. The molten resin in the starved zone 23 is not completely filled (it is in a starved state), providing space for the physical foaming agent to exist, thus enabling efficient contact between the physical foaming agent and the molten resin. The physical foaming agent, after contacting the molten resin, permeates into the molten resin and is consumed. When the physical foaming agent is consumed, the physical foaming agent retained in the introduction speed adjustment container 300 is supplied to the starved zone 23. Therefore, the pressure in the starved zone 23 is maintained at a certain pressure, and the molten resin continues to be in contact with the physical foaming agent at a certain pressure.

[0055] In existing foaming molding technologies using physical foaming agents, a predetermined amount of high-pressure physical foaming agent is forcibly introduced into the plasticizing cylinder within a specified time. This requires pressurizing the physical foaming agent to a high pressure and correctly controlling the amount and duration of the foaming agent introduced into the molten resin, ensuring that the physical foaming agent and molten resin only come into contact for a short period. In contrast, this embodiment does not forcibly introduce the physical foaming agent into the plasticizing cylinder 210. Instead, it continuously supplies a certain pressure of physical foaming agent into the plasticizing cylinder while maintaining a constant pressure in the starved zone 23, ensuring continuous contact between the physical foaming agent and the molten resin. This stabilizes the amount of physical foaming agent dissolved (penetrated) in the molten resin, which is determined by temperature and pressure. Furthermore, because the physical foaming agent in this embodiment is always in contact with the molten resin, a sufficient amount of physical foaming agent can penetrate into the molten resin. Therefore, compared to existing molding methods using physical foaming agents, the foamed molded body produced in this embodiment uses a low-pressure physical foaming agent, yet exhibits finer cell structure.

[0056] Furthermore, the manufacturing method of this embodiment does not require controlling the amount and timing of the physical foaming agent, thus eliminating the need for check valves, solenoid valves, and other drive valves, as well as control mechanisms for them, thereby reducing equipment costs. Additionally, the physical foaming agent used in this embodiment has a lower pressure compared to existing physical foaming agents, resulting in a smaller equipment load.

[0057] In this embodiment, the starved zone 23 is maintained at a constant pressure throughout the manufacturing process of the foamed molded article. That is, while continuously supplying the aforementioned physical foaming agent at a constant pressure to replenish the physical foaming agent consumed in the plasticizer barrel, all steps of the foamed molded article manufacturing method are performed. Furthermore, in this embodiment, for example, when performing injection molding for multiple consecutive injection cycles, during the injection step, the molded article cooling step, and the molded article removal step, the amount of molten resin for the next injection cycle is prepared in the plasticizer barrel, and the amount of molten resin for the next injection cycle is pressurized at a constant pressure using the physical foaming agent. That is, in the continuous injection molding for multiple injection cycles, one cycle of injection molding, including the plasticizing metering step, the injection step, the molded article cooling step, and the removal step, is performed while the molten resin and the physical foaming agent at a constant pressure are always present and in contact within the plasticizer barrel—that is, while the molten resin is always pressurized at a constant pressure using the physical foaming agent within the plasticizer barrel. Similarly, in continuous molding processes such as extrusion molding, molding is also carried out in a state where the molten resin and a physical foaming agent under a certain pressure are always present and in contact within the plasticizing barrel, that is, in a state where the physical foaming agent applies pressure to the molten resin within the plasticizing barrel.

[0058] Next, the molten resin that has come into contact with the physical foaming agent is molded into a foamed molded body. Figure 1 (Step S5). In this embodiment, the plasticizing cylinder 210 has a recompression zone 24 downstream of the starved zone 23, which is arranged adjacent to the starved zone 23, in which the molten resin is compressed and the pressure is increased. First, by rotating the plasticizing screw 20, the molten resin in the starved zone 23 flows to the recompression zone 24. The molten resin containing the physical foaming agent is pressure-adjusted in the recompression zone 24, and is extruded and metered in front of the plasticizing screw 20. At this time, the internal pressure of the molten resin extruded in front of the plasticizing screw 20 is controlled as the screw back pressure by a hydraulic motor or electric motor (not shown) connected to the rear of the plasticizing screw 20. In this embodiment, in order to prevent the physical foaming agent from separating from the molten resin but to make it uniformly soluble and to stabilize the resin density, the internal pressure of the molten resin extruded in front of the plasticizing screw 20, i.e., the screw back pressure, is preferably controlled to be about 1 to 4 MPa higher than the pressure of the starved zone 23 that maintains a certain pressure. Furthermore, in this embodiment, a check ring 50 is provided at the front end of the screw 20 to prevent the compressed resin in front of the screw 20 from flowing upstream. Therefore, the pressure in the starved zone 23 during metering is not affected by the resin pressure in front of the screw 20.

[0059] In this embodiment, from Figure 2 The plasticizing cylinder 210 shown injects metered molten resin into the cavity 253 of the mold 251 for injection foaming molding. As injection foaming molding, a short-shot method can be used, filling the mold cavity 253 with molten resin to 75% to 95% of its volume, allowing the cavity to fill as the bubbles expand. Alternatively, a core retraction method can be used, where the cavity volume expands and foams after 100% of the molten resin has been filled. The resulting foamed molded body has internal pores, thus suppressing shrinkage of the thermoplastic resin during cooling, reducing shrinkage marks and warpage, and resulting in a low-density molded body.

[0060] Next, the operating mechanism of the screw 20, which moves forward and backward in conjunction with the plasticizing, metering, and injection of molten resin, will be described.

[0061] In injection molding, molten resin is conveyed forward by the forward rotation of the screw 20, increasing the resin pressure (density). The screw 20 then retracts to the position where plasticizing and metering are completed, thereby metering the molten resin. Specifically, as... Figure 3As shown, the ball screw shaft 121 is rotatably supported by the frame 114, and one end of the ball screw shaft 121 is connected to the plasticizing moving motor 122. Furthermore, the ball screw shaft 121 is screwed into the ball screw nut 123, which is connected to the actuation mechanism 11 via a spring 124 and a bracket 125. Thus, when the motor 122 is driven in either the forward or reverse direction, the rotational motion of the plasticizing moving motor 122 is converted into linear motion by the combination of the ball screw shaft 121 and the ball screw nut 123, i.e., the screw assembly 91, and this linear motion is transmitted to the bracket 125. The bracket 125 then moves along the guide portion 81 in the direction of arrow A, causing the actuation mechanism 11 to move forward and backward.

[0062] Here, the operation of the actuation mechanism 11 will be explained. First, in the aforementioned plasticizing metering process, the metering servo motor 83, which serves as the plasticizing metering motor, is driven to rotate the screw 20 via the synchronous belt 84, causing the screw 20 to retract (move to the right in the figure) to a predetermined position. At this time, the resin supplied from the hopper 211 is heated and melted inside the barrel 210, and accumulates in front of the screw 20 as it retracts.

[0063] Next, in the injection process, the nozzle tip 29 is pressed against the mold 251, and the injection motor (servo motor) 86 is driven to rotate the ball screw shaft 85 via the timing belt 87. At this time, the support member 82 moves along with the rotation of the ball screw shaft 85, causing the screw 20 to advance (to the left in the figure), so that the resin accumulated in front of the screw 20 is injected from the nozzle tip 29 and filled into the cavity 253 of the mold 251.

[0064] Furthermore, the above actions are performed under the control of the aforementioned control unit of the device 1000.

[0065] [Example]

[0066] The present invention will now be further described using embodiments and comparative examples. However, the present invention is not limited to the embodiments and comparative examples described below.

[0067] In the foaming molding process of this invention, any method using a foaming agent gas that can set the screw back pressure to below 8 MPa can be used, including chemical foaming, physical foaming using foaming beads, and physical foaming using inactive gases. However, if a high-pressure gas physical foaming method is used, the pressure of the introduced foaming agent and the back pressure setting can be as high as 10-15 MPa or more. Therefore, the risk of the screw 20 retracting again after metering increases, which is unsuitable from the perspectives of safety and mechanical wear.

[0068] (1) Foaming injection molding device

[0069] In this embodiment, the method used in the above embodiments is employed. Figure 2 The apparatus 1000 is shown. Details of the apparatus 1000 will be described below. As described above, the apparatus 1000 is an injection molding apparatus, including a plasticizing barrel 210, a physical foaming agent supply mechanism (i.e., a gas cylinder 100) for supplying physical foaming agent to the plasticizing barrel 210, a mold closing unit (mold closing section) 250 on which a mold 251 is provided, and a control unit (not shown) for controlling the operation of the plasticizing barrel 210 and the mold closing unit 250.

[0070] A shut-off valve 28, which is opened and closed by a cylinder, is provided at the nozzle tip 29 of the plasticizing cylinder 210 to maintain high pressure inside the plasticizing cylinder 210. The mold 251 is in close contact with the nozzle tip 29, and molten resin is injected from the nozzle tip 29 into the cavity 253 formed by the mold 251. On the upper side of the plasticizing cylinder 210, starting from the upstream side, a resin supply port 201 for supplying thermoplastic resin to the plasticizing cylinder 210 and an inlet port 202 for introducing physical foaming agent into the plasticizing cylinder 210 are formed sequentially. A resin supply hopper 211 and an inlet speed adjustment container 300 are respectively provided at the resin supply port 201 and the inlet port 202. The gas cylinder 100 and the inlet speed adjustment container 300 are connected by a pipe 154 via a buffer tank 153, a pressure reducing valve 151, and a pressure gauge 152. In addition, a pressure monitoring sensor (not shown) is provided at a position on the plasticizing barrel 210 opposite to the inlet 202.

[0071] The screw 20 is rotatably and retractably disposed within the plasticizing barrel 210 to facilitate the plasticizing and melting of the thermoplastic resin, and to meter and inject the molten resin. As described above, the screw 20 is provided with a semi-split ring 26 and a coarse-diameter portion 20A of the screw 20 as a mechanism to increase the flow resistance of the molten resin.

[0072] In the plasticizing barrel 210, thermoplastic resin is supplied from the resin supply port 201. The thermoplastic resin is plasticized by a belt heater (not shown) into molten resin, which is then conveyed downstream by the forward rotation of the screw 20. Due to the presence of the ring 26 and the coarse-diameter portion 20A on the screw 20, the molten resin is compressed and the pressure increases on the upstream side of the ring 26, while the molten resin is not fully filled (is in a starved state) on the downstream side of the ring 26. The molten resin further conveyed downstream is compressed again and metered near the front end of the plasticizing barrel 210 before injection.

[0073] Thus, within the plasticizing barrel 210, from the upstream side, a plasticizing zone 21 is sequentially formed where the heated plastic resin undergoes plasticizing and melting; a compression zone 22 where the molten resin is compressed and the pressure increases; a starved zone 23 where the molten resin is not fully filled; and a recompression zone 24 where the molten resin, after being depressurized in the starved zone, is compressed again. The ring 26, located on the screw 20, is situated at the boundary between the compression zone 22 and the starved zone 23. Furthermore, an inlet 202 for introducing the physical foaming agent is located in the starved zone 23.

[0074] In this embodiment, the metering and injection processes are performed using the semi-automatic operation of the foam injection molding apparatus 1000. In the metering process, the aforementioned plasticizing metering motor 83 (without a brake) is driven to retract the screw 20 to the plasticizing metering completion position, thereby accumulating the supplied molten resin in front of the screw 20 for metering. In the injection process, the injection motor 86 is driven to advance the screw 20, thereby filling the molten resin accumulated in front of the screw 20 from the nozzle tip (injection nozzle) 29 into the cavity 253 of the mold 251 of the mold closing section 250. Furthermore, in the metering process, when the molten resin containing the foaming agent is plasticized and metered under a back pressure of 8 MPa or less on the screw 20, after opening the safety door (not shown) of the mold closing section 250 for removing the molded article and cutting off the power to the plasticizing metering motor 83, before closing the safety door and proceeding with the next injection cycle, the position of the screw 20 is checked, and the screw 20 is returned to the aforementioned metering completion position. Specifically, during semi-automatic operation, when the safety door is opened, the control unit of device 1000 cuts off the power to the plasticizing metering motor 83. At this time, if a position detection sensor (not shown) detects that the screw 20 has further retreated from the plasticizing metering completion position, the screw 20 is returned to the metering completion position with arbitrary back pressure before the safety door is closed and the next injection cycle is started. Furthermore, during the metering process, the control unit drives the screw 20 backward under a back pressure of 8 MPa or less to plasticize and meter the molten resin containing the foaming agent.

[0075] (2) Example 1

[0076] In this embodiment, foaming molding is performed via the semi-automatic operation of device 1000 as described below. Specifically, 4700G PP resin (containing 20% ​​talc) manufactured by Idemitsu Lion Composites is used as the resin, and a 100×200×2mm flat molded product with a center direct gate is used as the mold 251. The temperature of mold 251 is set to 40°C, and the resin temperature is set to 200°C.

[0077] First, during plasticizing and metering, the screw 20, built into the barrel 210, plasticizes the resin particles fed from the hopper 211 at any rotation speed. Then, in the starvation zone 23, nitrogen, acting as a physical foaming agent, dissolves in the molten resin. Upon completion of metering, the dissolved foaming agent accumulates at the front end of the screw 20. The foaming agent is introduced by depressurizing nitrogen gas from a nitrogen cylinder to a certain pressure and continuously pressurizing the barrel 210 containing the screw 20. Thus, the foaming agent mixes and dissolves with the molten resin simultaneously on the screw 20 in the starvation zone 23, completing the metering process. In this embodiment, the metering speed is set to 100 rpm, the gas pressure introduced from the nitrogen cylinder is 4 MPa, and the back pressure of the screw 20 is 6 MPa.

[0078] Next, injection filling was performed without holding pressure, resulting in a foamed molded product with a 10% weight reduction. After cooling, the mold was opened and the product was ejected. The metering process for the next injection cycle was performed after injection filling and completed before cooling was finished.

[0079] Only in the first injection cycle is the metering completion position shortened to reduce the injection volume; from the second injection cycle onwards, the metering conditions are set. After cooling, the safety door is opened and the product (molded part) is manually removed. With the safety door open, the power supply to all drive motors, including the metering motor 83, is cut off.

[0080] As a result, during the 10-15 seconds before the filling process of the next injection cycle, the position of the screw 20 is retracted by 0.3-0.5 mm.

[0081] After the safety door is closed, the power to all drive motors is turned on. The screw 20 advances to the set position of metering completion under the back pressure of the plasticizing metering motor 83. The back pressure at this time is set to 8 MPa, which is 2 MPa higher than the back pressure during metering. Because the screw 20 retracts when the safety door opens, and the pressure at the front end of the screw 20 is reduced, the foaming agent dissolved at 4 MPa will separate. To allow the foaming agent to dissolve again in a short time, the screw back pressure when the screw 20 is reset can be increased.

[0082] Through this semi-automatic operation, qualified products were obtained starting from the 8th injection cycle. Continuous molding continued until the 55th injection cycle. The warpage decreased from an average of 1 mm during solid molding to an average of approximately 0.2 mm, and no fluctuation in warpage was detected.

[0083] Starting from injection cycle 10, samples were taken every 5 injection cycles for a total of 10 injection cycles. The standard deviation σ divided by the average weight ave., σ / ave., was 0.25, which is approximately equal to 0.23 in the case of continuous sample collection in automatic operation mode using an extraction machine without opening the safety gate. The average pore diameter was 80–100 μm, and the fluctuation in pore diameter between samples was the same as in automatic operation.

[0084] (3) Example 2

[0085] In this embodiment, the pressure of the nitrogen-based physical foaming agent is set to 6 MPa, the back pressure during metering is set to 8 MPa, and the back pressure of the screw 20 after the safety door is closed again is set to 10 MPa. Otherwise, molding is performed semi-automatically, similar to Embodiment 1. The retraction amount of the screw 20 when the safety door is open is 1.0~1.5 mm.

[0086] Similar to Example 1, qualified products were obtained starting from the 8th injection cycle. Continuous molding continued until the 55th injection cycle. The warpage decreased from an average of 1 mm during solid molding to an average of approximately 0.15 mm, and no fluctuation in warpage was detected.

[0087] Starting from injection cycle 10, 10 injection cycles were sampled every 5 injection cycles. The standard deviation σ divided by the average weight ave., σ / ave., was 0.32, which, compared to 0.25 when samples were continuously collected in automatic operation mode without opening the safety gate and using the extraction machine without changing the metrological conditions, showed no significant deterioration. The average pore diameter was 60–80 μm, and the variation between samples was the same as in automatic operation.

[0088] (4) Comparative examples

[0089] In this comparative example, the back pressure during measurement was set to 10 MPa, and molding was performed using the same semi-automatic operation as in Examples 1 and 2. When the safety door opened, accompanied by a loud noise, the screw retracted more than 30 mm again.

[0090] According to this comparative example, semi-automatic operation cannot be safely performed when the back pressure of screw 20 is higher than 8 MPa. Furthermore, by returning the screw to the metering completion position under a back pressure of 12 MPa, similar to Examples 1 and 2, continuous molding can be performed, but the warpage fluctuates significantly, ranging from 0.1 to 0.2 mm. This can be attributed to insufficient redissolution of the separated foaming agent.

[0091] Starting from the 10th injection cycle, samples were taken every 5 injection cycles for a total of 10 injection cycles. The standard deviation σ divided by the average weight ave., σ / ave., was 0.60, which was significantly worse than 0.27 when samples were continuously collected in automatic operation mode without opening the safety gate and using the extraction machine without changing the metrological conditions. The average pore diameter was 100–250 μm, compared to 30–60 μm in continuous operation, indicating an increase in pore diameter and greater fluctuation.

[0092] As can be seen from the above, if the back pressure of screw 20 is below 8 MPa, the screw 20 can be prevented from retracting after the safety gate is opened and the power to the plasticizing metering motor is cut off. Furthermore, before closing the safety gate and proceeding with the next injection cycle, the molding conditions can be reliably adjusted by confirming the position of screw 20 and returning it to the metering completion position.

[0093] Furthermore, the present invention is not limited to the above-described embodiments and can be implemented in various modifications without departing from its spirit. Within the scope of the present invention, some or all of the above embodiments can be combined, or a portion of the structure of one of the above embodiments can be omitted.

[0094] Explanation of reference numerals in the attached figures

[0095] 20: Screw; 83: Plasticizing metering motor; 86: Injection motor; 100: Gas storage bottle (physical foaming agent supply mechanism); 210: Plasticizing barrel; 250: Mold closing unit (mold closing section); 1000: Foaming injection molding device.

Claims

1. A foam injection molding method, which uses a semi-automatic operation of a foam injection molding device to perform metering and injection processes. In the metering process, a plasticizing metering motor without a brake is driven to retract the screw to the plasticizing metering completion position, thereby accumulating the supplied molten resin in front of the screw for metering. In the injection process, an injection motor is driven to advance the screw, thereby filling the mold cavity of the mold closing section with molten resin accumulated in front of the screw from the injection nozzle. The foam injection molding method is characterized by the following: In the metering process, when the molten resin containing the foaming agent is plasticized and metered under the condition that the back pressure of the screw is less than 8 MPa, after the safety door of the mold closing part for taking out the molded article is opened and the power of the plasticizing and metering motor is cut off, before closing the safety door and starting the injection filling for the next injection cycle, the position of the screw is checked and the screw is returned to the metering completion position.

2. A foam injection molding apparatus, comprising: The device includes a plasticizing barrel with an internal screw for flowing molten resin, a physical foaming agent supply mechanism for supplying physical foaming agent to the plasticizing barrel, a mold closing part with a safety door for removing the molded product, and a control part for controlling the movement of the screw. The foam injection molding device can perform metering and injection processes in a semi-automatic operation. In the metering process, a plasticizing metering motor without a brake is driven to retract the screw to the plasticizing metering completion position, thereby accumulating the molten resin supplied from the physical foaming agent supply mechanism in front of the screw for metering of the molten resin. In the injection process, an injection motor is driven to advance the screw, thereby filling the mold cavity of the mold part with molten resin accumulated in front of the screw from the injection nozzle of the plasticizer barrel. The foaming injection molding apparatus is characterized in that: When the control unit operates in semi-automatic mode, it cuts off the power supply to the plasticizing metering motor when the safety door is opened. When it detects that the screw has moved further back from the plasticizing metering completion position, it uses arbitrary back pressure to return the screw to the metering completion position before closing the safety door and starting the injection filling for the next injection cycle.

3. The foaming injection molding apparatus as described in claim 2, characterized in that: The control unit drives the screw backward under a back pressure of 8 MPa or less during the metering process to plasticize and meter the molten resin containing the foaming agent.

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