JP2025072006A - Injection molding machine for foam molding and foam molding method - Google Patents

Abstract

To provide a foam molding injection molding machine capable of reducing costs during foam molding.SOLUTION: A foam molding injection molding machine comprises: a screw 60 rotatably disposed in a heating barrel 50 and movable in a longitudinal direction of the heating barrel 50; a compressor 110 that supplies compressed gas to the heating barrel 50; and a control unit 100 that controls an operation of the screw 60, wherein the heating barrel 50 has a nozzle 52 for injecting molten resin and a gas injection port 53 for injecting compressed gas supplied from the compressor 110 into the heating barrel 50, and after measuring the molten resin to be injected from the nozzle 52 by rotating the screw 60 while moving it toward a side opposite to the nozzle 52, the control unit 100 reverses a rotation direction of the screw 60 relative to the rotation direction during the measurement of the molten resin, thereby diffusing the compressed gas injected into the heating barrel 50 from the gas injection port 53 into the molten resin in the heating barrel 50.SELECTED DRAWING: Figure 7

Description

The present invention relates to an injection molding machine for foam molding and a foam molding method.

Traditionally, foam molding is a method of molding resin using an injection molding machine, in which the resin is mixed with a gas to form the resin. This type of foam molding is classified into chemical foaming, in which a foaming agent is mixed with the resin to form the resin, and physical foaming, in which a gas such as nitrogen or carbon dioxide is injected into the gas inlet of the heating barrel of the injection molding machine to form the resin.

In recent years, as there is a demand to reduce the environmental impact, foam molding has been attracting attention as a means of reducing the amount of resin used, with physical foaming being particularly promising as it is suitable for recycling. As a method of foam molding using physical foaming, for example, as shown in Patent Documents 1 and 2, a method has been proposed in which a starvation zone is provided in a plasticizing cylinder, and gas such as nitrogen or carbon dioxide is injected from a cylinder storing the gas into the starvation zone in the plasticizing cylinder via an introduction rate adjustment vessel.

Patent No. 6522701 Patent No. 7128015

However, when foam molding is performed by providing a starvation zone in the plasticizing cylinder of an injection molding machine and injecting high-pressure gas from a cylinder into the plasticizing cylinder, a large initial investment is required, and the cylinder needs to be replaced during operation, which can easily increase running costs. For this reason, there is room for improvement in terms of cost when performing foam molding using an injection molding machine.

The present invention has been made in consideration of the above, and aims to provide an injection molding machine for foam molding and a foam molding method that can reduce costs when performing foam molding.

In order to solve the above-mentioned problems and achieve the object, the injection molding machine for foam molding according to the present invention comprises a heating barrel in which a resin material is melted to form a molten resin, a screw rotatably arranged within the heating barrel and movable in the longitudinal direction of the heating barrel within the heating barrel, a compression device that supplies compressed gas to the heating barrel, and a control unit that controls the operation of the screw, and the heating barrel comprises a nozzle that is arranged at one end in the longitudinal direction of the heating barrel and injects the molten resin, and a nozzle that is arranged on a wall surface within the range in the longitudinal direction of the heating barrel where the screw is arranged and supplies the molten resin from the compression device. and a gas inlet for injecting the compressed gas into the heated barrel, and the control unit rotates the screw in the heated barrel while moving it to the side opposite the nozzle in the longitudinal direction of the heated barrel, thereby feeding the molten resin to the nozzle side of the screw in the heated barrel and measuring the molten resin to be injected from the nozzle, and then rotates the screw in the opposite direction to the rotation direction of the screw when measuring the molten resin, thereby diffusing the compressed gas injected into the heated barrel from the gas inlet into the molten resin in the heated barrel.

In order to solve the above-mentioned problems and achieve the object, the foam molding method according to the present invention is a foam molding method in which a foam molding injection molding machine is provided with a heated barrel that melts a resin material inside to form a molten resin, and a screw that is rotatably arranged inside the heated barrel and can move in the longitudinal direction of the heated barrel, and in which a foam molding product is molded from the molten resin to which the compressed gas has been supplied by supplying compressed gas to the heated barrel, and the method includes the steps of: rotating the screw inside the heated barrel, moving the screw to the opposite side of the nozzle of the heated barrel in the longitudinal direction of the heated barrel, while rotating the screw inside the heated barrel, to send the molten resin to a portion of the heated barrel that is closer to the nozzle than the screw, thereby measuring the molten resin to be injected from the nozzle; and, after measuring the molten resin, rotating the screw in the opposite direction to the rotational direction of the screw when measuring the molten resin, thereby diffusing the compressed gas supplied to the heated barrel into the molten resin inside the heated barrel.

The foam molding injection molding machine and foam molding method according to the present invention have the effect of reducing costs when performing foam molding.

FIG. 1 is a perspective view of a foam molding injection molding machine according to an embodiment. FIG. 2 is a cross-sectional view of a main part showing the device configuration of the foam molding injection molding machine according to the embodiment. FIG. 3 is a plan view of the essential parts showing the device configuration of the foam molding injection molding machine according to the embodiment. FIG. 4 is a detailed view of the heating barrel shown in FIG. FIG. 5 is a detailed view of the check ring shown in FIG. FIG. 6 is an explanatory diagram of the steps performed in one cycle of injection and molding operations by a foam injection molding machine. FIG. 7 is an explanatory diagram showing a change in pressure of the molten resin when the screw is rotated in the reverse direction with respect to the rotation direction of the screw in the metering process. FIG. 8 is an explanatory diagram showing the state of the check ring when the molten resin is injected.

Below, an embodiment of the foam molding injection molding machine and foam molding method according to the present disclosure will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. Furthermore, the components in the following embodiments include those that are replaceable and easily conceivable by a person skilled in the art, or those that are substantially the same.

[Embodiment]
FIG. 1 is a perspective view of a foam injection molding machine 1 according to an embodiment. FIG. 2 is a cross-sectional view of a main part showing the device configuration of the foam injection molding machine 1 according to an embodiment. FIG. 3 is a plan view of a main part showing the device configuration of the foam injection molding machine 1 according to an embodiment. In the following description, the up-down direction of the foam injection molding machine 1 in a normal use state is described as the up-down direction Z of the foam injection molding machine 1, the upper side of the foam injection molding machine 1 in a normal use state is described as the upper side of the foam injection molding machine 1, and the lower side of the foam injection molding machine 1 in a normal use state is described as the lower side of the foam injection molding machine 1. In the following description, the longitudinal direction Y of the foam injection molding machine 1 is also described as the longitudinal direction Y of each part having the foam injection molding machine 1, and the direction perpendicular to both the up-down direction Z and the longitudinal direction Y of the foam injection molding machine 1 is described as the width direction X of the foam injection molding machine 1.

<Foam molding injection machine 1>
The foam molding injection molding machine 1 according to this embodiment is configured to include a base 5, and an injection device 10 and a mold clamping device 15 that are arranged on the base 5. The foam molding injection molding machine 1 is further provided, near the center in the longitudinal direction Y, with a display unit 101 that displays various information about the foam molding injection molding machine 1, and an input unit 102 that an operator uses to input information to the foam molding injection molding machine 1.

The base 5 is formed in a generally rectangular parallelepiped shape whose longitudinal direction corresponds to the longitudinal direction Y of the foam injection molding machine 1, and a first rail 6 is disposed on the upper surface of the base 5. Two first rails 6 are disposed on the base 5, spaced apart in the width direction X, and both first rails 6 are formed to extend along the longitudinal direction of the base 5. The injection device 10 is placed on the first rail 6 so as to be freely movable along the extension direction of the first rail 6, and thus the injection device 10 is disposed so as to be freely movable in the longitudinal direction Y.

The clamping device 15 is disposed on one side of the injection device 10 in the longitudinal direction Y on the base 5. The clamping device 15 has a clamping mechanism and opens and closes a mold 16 (see FIG. 4) assembled to the clamping mechanism. The clamping device 15 is preferably driven by a servo motor, but may also be driven by a hydraulic system. The foam molding injection molding machine 1 according to this embodiment has covers on the outside of the injection device 10 and the clamping device 15, and FIG. 1 shows the injection device 10 and the clamping device 15 covered with their covers.

<Injection device 10>
In the following description, the side on which the mold clamping device 15 is located relative to the injection device 10 in the longitudinal direction Y will be referred to as the front or front side, and the side opposite the side on which the mold clamping device 15 is located relative to the injection device 10 in the longitudinal direction Y will be referred to as the rear or rear side.

The injection device 10 includes a frame 20, a heating barrel 50, a screw 60, a rotation mechanism 70 for rotating the screw 60, a forward/backward mechanism 80 for moving the screw 60 forward/backward, and a propulsion mechanism 40 of the injection device 10. The frame 20 is formed with a base 21 and an upper frame 30 attached to the base 21. The base 21 is a flat frame body in the vertical direction Z, and legs 24 are arranged at four locations on both sides in the longitudinal direction Y and both sides in the width direction X. The four legs 24 are placed on two first rails 6 arranged on the base 5 so as to be freely movable along the extension direction of the first rails 6. As a result, the base 21 is supported so as to be freely slidable in the longitudinal direction Y relative to the base 5.

The propulsion mechanism 40 has a drive motor 41 and a ball screw mechanism 43. The drive motor 41 is attached to the rear wall 23 located on the rear side of the base 21 in the longitudinal direction Y. The drive motor 41 is arranged with its drive shaft extending in the longitudinal direction Y, and the drive shaft of the drive motor 41 penetrates the rear wall 23 of the base 21 and is connected to the screw portion 44 of the ball screw mechanism 43 by a connecting mechanism 42. As a result, when the drive motor 41 is driven, the driving force of the drive motor 41 is transmitted from the drive shaft via the connecting mechanism 42, and the ball screw mechanism 43 can rotate by the transmitted driving force.

The screw portion 44 of the ball screw mechanism 43 is arranged to extend in the longitudinal direction Y and penetrates almost the center of the base 21 in the width direction X, and the front end side in the longitudinal direction Y is supported rotatably on the front wall 22 located at the front side of the base 21 in the longitudinal direction Y. The nut portion 45 of the ball screw mechanism 43 is fixed to the upper surface of the base 5 inside the base 21. As a result, when the driving motor 41 is driven, the screw portion 44 of the ball screw mechanism 43 rotates due to the driving force transmitted from the driving motor 41, and the screw portion 44 can move relative to the nut portion 45 fixed to the base 5 in the extension direction of the screw portion 44. Therefore, the driving mechanism 40 can move the base 21 on which the screw portion 44 is supported relative to the base 5 on which the nut portion 45 is fixed in the longitudinal direction Y, and the frame 20 having the base 21 can be moved in the longitudinal direction Y on the first rail 6 arranged on the base 5. This allows the propulsion mechanism 40 to move the injection device 10 in the longitudinal direction Y.

The upper frame 30 is formed in a square frame shape and is rotatably attached to the base 21 at a position near the front end in the longitudinal direction Y by a support pin 33. The upper frame 30 is fixed in a non-rotatable state at a position other than where the support pin 33 is located by a fixing screw 34 that fixes the upper frame 30 to the base 21. Therefore, when the fixing screw 34 is removed and released from the fixation by the fixing screw 34, the upper frame 30 is configured to be rotatable relative to the base 21 around the support pin 33.

The upper frame 30 has a front wall 31 erected upward in the vertical direction Z from the attachment portion to the base 21, and the heating barrel 50 is attached to the front wall 31 of the upper frame 30. The heating barrel 50 extends forward in the longitudinal direction Y from the front wall 31, and a nozzle 52 is disposed at its tip, i.e., the front end of the heating barrel 50, which is in close contact with the mold 16 (see FIG. 4). Therefore, the heating barrel 50 is disposed above the frame 20 in the vertical direction Z and in front of the frame 20 in the longitudinal direction Y.

More specifically, the heating barrel 50 is formed in a substantially cylindrical shape and is arranged such that the axial direction is aligned with the longitudinal direction Y. That is, the heating barrel 50 is arranged such that the longitudinal direction of the heating barrel 50 coincides with the longitudinal direction Y of the foam molding injection molding machine 1. The heating barrel 50 is also provided with a heater 51 (see FIG. 4), such as a band heater, which allows the heating barrel 50 to melt the resin material inside. That is, the heating barrel 50 can increase the temperature of the heating barrel 50 by the heater 51, and the resin material inside can be heated and melted to become molten resin, which is a plasticized material.

The screw 60 is disposed inside the heating barrel 50 and has a helical shape whose axial direction is along the axial direction of the heating barrel 50, that is, the screw 60 has a helical groove on the outer circumferential surface. In this way, the screw 60 formed with a helical shape is rotatable around the axial center in the heating barrel 50. The screw 60 is also movable in the axial direction of the rotation in the heating barrel 50. In other words, the screw 60 is disposed in the heating barrel 50 so that the central axis of the cylinder, which is the shape of the heating barrel 50, and the rotation axis of the screw 60 are approximately aligned, and the screw 60 is disposed so as to be movable in the axial direction of the heating barrel 50 or in the longitudinal direction Y of the heating barrel 50. The screw 60 rotatably disposed in the heating barrel 50 is capable of kneading the molten resin by rotating inside the heating barrel 50, and therefore the heating barrel 50 is a barrel capable of kneading the molten resin inside.

A hopper 55 is disposed near the side of the heating barrel 50 that is attached to the upper frame 30. The hopper 55 is connected to the inside of the heating barrel 50, and is capable of supplying pellets (not shown), which are the resin material that will become the raw resin, to the heating barrel 50.

Furthermore, second rails 35 are arranged on the side walls 32 located on both sides of the upper frame 30 in the width direction X. The second rails 35 extend in the longitudinal direction Y, i.e., they are formed to extend approximately parallel to the heating barrel 50.

The rotation mechanism 70 is disposed behind the heating barrel 50 in the longitudinal direction Y, and is capable of rotating the screw 60 disposed inside the heating barrel 50 around the central axis. The rotation mechanism 70 that rotates the screw 60 has a rotation mechanism main body 71, a driving motor 73, a transmission belt 75, and a pulley 76. Of these, the rotation mechanism main body 71 has a stay 72 that extends in the width direction X, and the stay 72 is slidably mounted on the second rail 35 at two locations in the width direction X. As a result, the rotation mechanism main body 71 is movably mounted on the second rail 35 via the stay 72.

The driving motor 73 is disposed above the rotating mechanism main body 71. The driving motor 73 has an encoder 74 that detects the rotational position of the driving motor 73. The pulley 76 is disposed in front of the rotating mechanism main body 71 and is rotatable relative to the rotating mechanism main body 71 via a bearing 77. The pulley 76 is connected to the driving shaft of the driving motor 73 via a transmission belt 75, so that the pulley 76 can rotate by the driving force of the driving motor 73 transmitted via the transmission belt 75. In this way, the pulley 76, which can rotate by the driving force transmitted from the driving motor 73, is fixed coaxially and integrally to the screw 60. In other words, the rear end side of the screw 60 in the longitudinal direction Y is connected to the pulley 76. As a result, the screw 60 disposed in the heating barrel 50 can rotate integrally with the pulley 76 by the driving force transmitted from the driving motor 73 to the pulley 76.

The forward/reverse mechanism 80 is disposed behind the rotation mechanism main body 71 in the longitudinal direction Y. The forward/reverse mechanism 80 is capable of moving the screw 60 disposed in the heating barrel 50 in the axial direction of the screw 60. That is, the forward/reverse mechanism 80 is capable of moving the screw 60 in the longitudinal direction Y of the heating barrel 50 and the foam molding injection molding machine 1, and is capable of moving the screw 60 forward and backward in the longitudinal direction Y. In detail, the forward/reverse mechanism 80 has a driving motor 81, a transmission belt 83, a pulley 84, and a ball screw mechanism 86. Of these, the driving motor 81 is disposed on the side of the upper frame 30 in the width direction X. The driving motor 81 also has an encoder 82 that detects the rotational position of the driving motor 81, and the drive shaft of the driving motor 81 is connected to the pulley 84 via the transmission belt 83.

The pulley 84 is rotatably supported on the upper frame 30 by a bearing 85. A screw portion 87 of a ball screw mechanism 86 is integrally connected to the pulley 84. The screw portion 87 of the ball screw mechanism 86 is arranged coaxially with the screw 60, and is also arranged coaxially with the pulley 76 of the rotation mechanism main body 71. The nut portion 88 of the ball screw mechanism 86 of the forward/reverse mechanism 80 is formed in a substantially cylindrical shape, and the screw portion 87 of the ball screw mechanism 86 is screwed into the nut portion 88.

A load cell 90 is disposed between the nut portion 88 of the ball screw mechanism 86 of the forward/reverse mechanism 80 and the rotation mechanism main body portion 71 of the rotation mechanism 70 in the longitudinal direction Y. The load cell 90 is disposed behind the rotation mechanism main body portion 71 of the rotation mechanism 70 and in front of the nut portion 88 of the ball screw mechanism 86 of the forward/reverse mechanism 80.

The load cell 90 is a load measuring device that measures the load applied in the axial direction, and is composed of a strain body and a strain sensor (both not shown) attached to the strain body. In this embodiment, the load cell 90 is arranged so that the axial direction is the longitudinal direction Y, and is formed in a substantially cylindrical shape that is flat in the longitudinal direction Y, and the inner diameter of the cylinder is larger than the outer diameter of the screw portion 87 of the ball screw mechanism 86 of the forward/reverse mechanism 80. The load cell 90 thus formed has a front surface in the longitudinal direction Y integrally fixed to the rotation mechanism main body 71 of the rotation mechanism 70, and a rear surface in the longitudinal direction Y integrally fixed to the nut portion 88 of the ball screw mechanism 86 of the forward/reverse mechanism 80. The load cell 90 arranged between the rotation mechanism main body 71 of the rotation mechanism 70 and the nut portion 88 of the ball screw mechanism 86 of the forward/reverse mechanism 80 is capable of detecting the load acting in the longitudinal direction Y between the rotation mechanism main body 71 and the nut portion 88.

Figure 4 is a detailed view of the heating barrel 50 shown in Figure 2. As shown in Figure 4, the heating barrel 50 is formed in a substantially cylindrical shape, and a heater 51 such as a band heater is disposed on the outer circumferential surface. A nozzle 52 is provided at one end in the longitudinal direction Y of the heating barrel 50, i.e., at the front end in the longitudinal direction Y of the heating barrel 50. The nozzle 52 is formed in a substantially cylindrical shape with an inner diameter smaller than the inner diameter of the heating barrel 50, and is disposed so as to open to the front side in the longitudinal direction Y of the heating barrel 50. In this way, the nozzle 52 provided at the front end of the heating barrel 50 is capable of injecting the molten resin R in the heating barrel 50 into the cavity 17 formed by the mold 16 of the mold clamping device 15.

Now, regarding the mold 16, the mold 16 has a fixed mold 16f and a movable mold 16m, and the fixed mold 16f and the movable mold 16m are combined to form one mold 16 that molds the molten resin R into a molded product. Of the fixed mold 16f and the movable mold 16m, the fixed mold 16f is disposed on the side where the heated barrel 50 is located in the longitudinal direction Y, and faces the nozzle 52. The movable mold 16m is disposed on the opposite side of the fixed mold 16f from the side where the heated barrel 50 is located in the longitudinal direction Y. The mold clamping device 15 can move the movable mold 16m in the longitudinal direction Y to separate the movable mold 16m from the fixed mold 16f or to bring the movable mold 16m into contact with the fixed mold 16f.

The mold 16, which has a fixed mold 16f and a movable mold 16m, has a space between the fixed mold 16f and the movable mold 16m when the fixed mold 16f and the movable mold 16m are in contact with each other and are combined. When the fixed mold 16f and the movable mold 16m are combined, the space formed between them becomes the cavity 17 in which the molded product is molded from the molten resin R in the mold 16. The fixed mold 16f has a through hole 18 that penetrates the surface facing the nozzle 52 and the cavity 17, and the heated barrel 50 can inject the molten resin R from the nozzle 52 into the through hole 18, thereby injecting the molten resin R from the heated barrel 50 into the cavity 17.

The screw 60 disposed within the heating barrel 50 has a flight 61 that protrudes outward in the radial direction of the screw 60 and is formed in a spiral shape centered on the axis of the screw 60. As a result, the screw 60 has a screw groove 62, which is a spiral groove-like portion, between adjacent orbital portions of the flight 61 that is formed in a spiral shape.

The screw 60 is also provided with a dam portion 67 that divides the screw 60 into a portion on the side where the nozzle 52 is located and a portion on the opposite side of the side where the nozzle 52 is located in the longitudinal direction Y of the heating barrel 50. The dam portion 67 is formed in an annular shape with an outer diameter that is equal to or larger than the outer diameter of the flight 61. Therefore, the distance between the inner circumferential surface of the heating barrel 50 and the outer circumferential surface of the dam portion 67 is smaller than the distance between the inner circumferential surface of the heating barrel 50 and the outer circumferential surface of the flight 61.

In this embodiment, the dam portion 67 is disposed near the center of the screw 60 in the longitudinal direction Y. In this embodiment, the portion of the screw 60 divided in the longitudinal direction Y by the dam portion 67 on the side where the nozzle 52 is located in the longitudinal direction Y is referred to as the second stage STG2, and the portion opposite the side where the nozzle 52 is located in the longitudinal direction Y is referred to as the first stage STG1. In this way, the screw 60 divided by the dam portion 67 has a diameter including the flight 61 that increases in diameter from the side where the hopper 55 is located in the longitudinal direction Y to the side where the dam portion 67 is located in the first stage STG1, and increases in diameter from the side where the dam portion 67 is located in the longitudinal direction Y to the side where the nozzle 52 is located in the second stage STG2. For this reason, the diameter of the screw 60 in the vicinity of the dam portion 67 in the second stage STG2 is smaller than the diameter of the portion in the vicinity of the dam portion 67 in the first stage STG1.

A check ring 66 is disposed on the screw 60 formed in this manner near the front end in the longitudinal direction Y. The check ring 66 is disposed closer to the nozzle 52 than the second stage STG2, and is disposed in a groove portion 63 formed on the screw 60 near the front end in the longitudinal direction Y. The groove portion 63 is a groove whose groove width direction is the axial direction of the screw 60, and is formed around one circumference of the screw 60 in the circumferential direction.

Figure 5 is a detailed view of the check ring 66 shown in Figure 4. The check ring 66 is formed in a substantially cylindrical shape and is arranged in the groove portion 63 of the screw 60 with its axis substantially coinciding with the axis of the screw 60. The check ring 66 formed in a substantially cylindrical shape has an outer diameter that is approximately the same as the inner diameter of the heating barrel 50 and is slightly smaller than the inner diameter of the heating barrel 50. The inner diameter of the check ring 66 is also larger than the diameter of the groove bottom of the groove portion 63 of the screw 60, and a gap is formed between the inner peripheral surface of the check ring 66 and the groove bottom of the groove portion 63 of the screw 60. The width of the check ring 66 in the axial direction is also smaller than the groove width of the groove portion 63 of the screw 60. Therefore, the check ring 66 is able to move in the groove width direction within the groove portion 63.

The screw 60 also has a communication section 65 that connects the portion of the screw 60 that is forward of the groove section 63 in the longitudinal direction Y with the inside of the groove section 63. The communication section 65 opens into the groove wall 64 on the forward side in the groove width direction of the groove section 63.

The foam injection molding machine 1 also has a compressor 110, which is a compression device that supplies compressed gas to the heated barrel 50. The heated barrel 50 is provided with a gas inlet 53 that injects the compressed gas supplied from the compressor 110 into the heated barrel 50. In detail, the compressor 110 is capable of sucking in the surrounding air, compressing it, and discharging it as compressed gas. The gas inlet 53 is provided on the wall surface of the heated barrel 50 in the longitudinal direction Y in the range in which the screw 60 is disposed. The compressor 110 and the gas inlet 53 are connected by a supply pipe 105 that supplies the compressed gas compressed by the compressor 110 to the heated barrel 50. Therefore, the compressed gas compressed by the compressor 110 is supplied to the gas inlet 53 by the supply pipe 105, and is injected from the gas inlet 53 into the heated barrel 50.

In this way, the compressor 110 that supplies the compressed gas to the heating barrel 50 compresses the compressed gas to a pressure at which the compressed gas becomes a supercritical fluid and supplies it to the heating barrel 50. It is preferable that the compressor 110 supplies the compressed gas to the heating barrel 50 at a pressure of 5 MPa or less while keeping the compressed gas in a supercritical fluid state. In other words, since the critical pressure of air is 3.7 MPa, it is preferable that the compressor 110 converts the air into compressed gas with a pressure in the range of 3.7 MPa or more and 5 MPa or less and supplies it to the heating barrel 50.

The screw 60 is movable in the longitudinal direction Y within the heating barrel 50, but the gas inlet 53 is located on the side where the nozzle 52 is located, relative to any position of the dam section 67, within the range of movement of the dam section 67 when the screw 60 moves in the longitudinal direction Y of the heating barrel 50. In other words, the gas inlet 53 is located within the range of the second stage STG2 in the longitudinal direction Y, regardless of the movement position of the screw 60 in the longitudinal direction Y.

Furthermore, the foam injection molding machine 1 according to this embodiment has an air separation device 120 that separates the compressed gas compressed by the compressor 110. The air separation device 120 is disposed on the compressed gas supply path between the compressor 110 and the gas inlet 53, and is connected to the compressor 110 and the gas inlet 53 by a supply pipe 105. The air separation device 120 disposed between the compressor 110 and the gas inlet 53 in this manner is capable of separating the components of the compressed gas compressed by the compressor 110 and supplying a portion of the compressed gas to the gas inlet 53. That is, the air separation device 120 is capable of separating the components of the compressed gas compressed by the compressor 110 while the compressed gas remains in a supercritical fluid state, and supplying a portion of the compressed gas in a supercritical fluid state to the gas inlet 53.

In this embodiment, the air separation unit 120 is capable of separating nitrogen from the compressed gas compressed by the compressor 110 and supplying the separated compressed nitrogen gas to the gas inlet 53. Therefore, the gas inlet 53 is capable of supplying the nitrogen compressed by the compressor 110 and separated by the air separation unit 120 into the heated barrel 50. Since the critical pressure of nitrogen is 3.4 MPa, it is preferable that the compressor 110 and the air separation unit 120 convert the nitrogen into compressed gas with a pressure in the range of 3.4 MPa to 5 MPa and supply it into the heated barrel 50.

The foam injection molding machine 1 also has a control unit 100 that performs various controls of the foam injection molding machine 1. The control unit 100 has a CPU (Central Processing Unit) that performs arithmetic processing, and a RAM (Random Access Memory) and a ROM (Read Only Memory) that function as memory for storing various information. All or part of the functions of the control unit 100 are realized by loading an application program stored in the ROM into the RAM and executing it on the CPU, thereby reading and writing data in the RAM and ROM.

The display unit 101 and the input unit 102 are both connected to the control unit 100, and the display unit 101 displays information transmitted from the control unit 100. The input unit 102 transmits information input to the control unit 100. The encoder 74 disposed on the driving motor 73 of the rotation mechanism 70, the encoder 82 disposed on the driving motor 81 of the forward/reverse mechanism 80, and the load cell 90 disposed between the forward/reverse mechanism 80 and the rotation mechanism 70 are also connected to the control unit 100, and are capable of transmitting detection results to the control unit 100.

Furthermore, the heater 51 of the injection device 10, the driving motor 73 of the rotation mechanism 70, the driving motor 81 of the forward/reverse mechanism 80, and the driving motor 41 of the propulsion mechanism 40 are connected to the control unit 100 and are operated by control signals from the control unit 100. That is, the control unit 100 is capable of controlling the operation of the heating barrel 50 and the screw 60. Therefore, the control unit 100 is capable of controlling the temperature of the heating barrel 50 heated by the heater 51, controlling the rotation of the screw 60 by the rotation mechanism 70, and controlling the movement of the screw 60 in the longitudinal direction Y by the forward/reverse mechanism 80.

<Action of foam injection molding machine 1>
The foam injection molding machine 1 according to this embodiment includes the above-mentioned configuration, and its operation will be described below. The foam injection molding machine 1 repeats a cycle of injection and molding operations, with one injection and molding operation being one cycle. Fig. 6 is an explanatory diagram of the steps performed in one cycle of injection and molding operations by the foam injection molding machine 1. Each cycle of injection and molding operations by the foam injection molding machine 1 includes a plurality of steps for injecting the resin material used in molding and molding the product. Each cycle includes, for example, a filling step P1, a pressure holding step P2, a cooling step P3, a mold opening step P4, a product removal step P5, and a mold closing step P6.

The filling process P1 is a process in which the nozzle 52 provided on the heated barrel 50 of the injection device 10 is pressed against the through hole 18 of the fixed mold 16f of the mold clamping device 15, and the molten resin R, which is the resin material melted by the heated barrel 50, is injected into the cavity 17 formed by the movable mold 16m and the fixed mold 16f to fill it.

The pressure holding process P2 is a process in which the screw 60 of the injection device 10, which has filled the cavity 17 formed by the movable mold 16m and the fixed mold 16f attached to the mold clamping device 15 with resin material, waits while maintaining the pressure of the resin material injected into the cavity 17 without rotating within the heated barrel 50.

The cooling process P3 is a process in which the temperature of the molding resin, which is the resin material injected into the cavity 17 formed by the fixed mold 16f and movable mold 16m of the mold clamping device 15, drops and solidifies, and the molding resin waits for a certain period of time until it becomes a molded product.

The mold opening process P4 is a process of separating the movable mold 16m from the fixed mold 16f in order to remove the molded product formed by the fixed mold 16f and movable mold 16m of the mold clamping device 15.

The product removal process P5 is a process in which the molded product is pushed out of the movable die 16m by an extrusion member (not shown) provided in the mold clamping device 15, and the molded product, which is the product, is removed from the movable die 16m.

The mold closing process P6 is a process of combining the movable mold 16m and the fixed mold 16f of the mold clamping device 15 to form a cavity 17, which is a space corresponding to the product shape, between the movable mold 16m and the fixed mold 16f.

The cooling process P3 performed by the foam injection molding machine 1 includes a metering process P3a, a screw reverse rotation process P3b, and a screw rotation stop process P3c.

The metering process P3a is a process of sending the molten resin R to be injected in the next cycle to the end side where the nozzle 52 is located in the heated barrel 50 of the injection device 10, and preparing the resin material to be used in the next cycle. That is, the metering process P3a is a process of moving the screw 60 to the side opposite the nozzle 52 in the longitudinal direction Y while rotating the screw 60 in the heated barrel 50 in a direction that sends the molten resin R in the screw groove 62 formed in the screw 60 in a spiral shape to the side where the nozzle 52 is located.

The screw reverse rotation process P3b is a process in which the screw 60 is rotated in the opposite direction to the rotation direction of the screw 60 rotated in the metering process P3a.

The screw rotation stopping process P3c is a process for stopping the rotation of the screw 60 that was rotated in reverse in the screw reverse rotation process P3b.

When a molded product is formed using the foam injection molding machine 1, these injection and molding operation cycles are repeatedly executed. In order to smoothly inject the resin material in the heated barrel 50 during the repeatedly executed cycle, the control unit 100 continuously heats the inside of the heated barrel 50 using the heater 51. As a result, the heated barrel 50 holds in a molten state the resin material that is fed into the hopper 55 in the form of pellets and then supplied from the hopper 55 to the heated barrel 50.

In addition, the compressor 110 continuously compresses air and supplies the compressed gas to the heating barrel 50, and the compressed nitrogen gas compressed by the compressor 110 and separated by the air separation unit 120 is continuously injected into the heating barrel 50 through the gas inlet 53.

The control unit 100 performs control while determining the start or end of each process within the cycle of injection and molding operations. In order to determine the start or end of each process, for example, a flag is defined in advance for the first or last step of each process in a program for operating the foam injection molding machine 1 by the control unit 100. This allows the control unit 100 to determine the start or end of each process while executing a program for operating the foam injection molding machine 1. In other words, by defining the flag, the control unit 100 can determine that processing has progressed to the next process when the flag is executed before or after processing each step.

In addition, when a process transition occurs, the control unit 100 causes the display unit 101 to display the process transition. That is, the display unit 101 displays the current process of the foam molding injection molding machine 1. This allows the operator to recognize the current operating state of the foam molding injection molding machine 1 by visually checking the display unit 101.

The foam injection molding machine 1 has the above-mentioned steps as its basic steps, and by repeating these steps, it is possible to mold a molded product from molten resin R. However, the foam injection molding machine 1 according to this embodiment is capable of molding a foam molded product from molten resin R that contains gas bubbles. Next, we will explain the foam molding method for molding a foam molded product.

<Foam molding method>
In the foam molding method according to this embodiment, compressed gas supplied from the compressor 110 into the heated barrel 50 is diffused into the molten resin R in the heated barrel 50, thereby dispersing the compressed gas in a supercritical fluid state into the molten resin R. Thereafter, the molten resin R containing the compressed gas in a supercritical fluid state is injected into the cavity 17 of the mold 16, and the pressure of the molten resin R is reduced, causing the compressed gas to grow as bubbles, thereby performing foam molding and forming a foam-molded product.

When foam molding using this type of foam molding method is performed using the foam molding injection molding machine 1, the operation of the screw 60 is controlled by the control unit 100 while the compressed gas in a supercritical fluid state compressed by the compressor 110 is supplied into the heated barrel 50. Specifically, foam molding using the foam molding injection molding machine 1 according to the embodiment is performed by metering the molten resin R in the metering process P3a, and then rotating the screw 60 in the opposite direction to the rotation direction in the metering process P3a, thereby diffusing the compressed gas into the molten resin R in the heated barrel 50.

To explain the metering process P3a in detail in the foam molding injection molding machine 1 that performs foam molding in this manner, the resin material to be metered in the metering process P3a is fed into a hopper 55 in the form of pellets, and is then supplied from the hopper 55 into the heated barrel 50. The heated barrel 50 is heated by a heater 51, causing the temperature inside the heated barrel 50 to rise, and the resin material supplied into the heated barrel 50 in the form of pellets melts in the heated barrel 50, becoming molten resin R.

In the metering process P3a, the screw 60 is moved backward in the longitudinal direction Y while rotating inside the heating barrel 50 where the resin material is melted. The rotation of the screw 60 is performed by controlling the rotation mechanism 70 with the control unit 100. That is, the control unit 100 controls the rotation mechanism 70 to drive the driving motor 73 of the rotation mechanism 70. As a result, the driving force generated by the driving motor 73 is transmitted to the pulley 76 by the transmission belt 75, and then transmitted from the pulley 76 to the screw 60, causing the screw 60 to rotate.

The rotation direction of the screw 60 here is a direction in which the molten resin R located in the screw groove 62 formed in the screw 60 in a spiral shape can be sent to the front end side in the longitudinal direction Y, that is, to the side where the nozzle 52 is located, by the rotation of the screw 60. In the following explanation, the direction in which the screw 60 rotates that can send the molten resin R to the side where the nozzle 52 is located in the longitudinal direction Y is described as forward rotation, and the opposite direction to the forward rotation is described as reverse rotation.

In addition, the movement of the screw 60 backward in the longitudinal direction Y, that is, the retreat of the screw 60, is performed by controlling the forward/reverse mechanism 80 with the control unit 100. When the forward/reverse mechanism 80 retreats the screw 60, the control unit 100 controls the forward/reverse mechanism 80 to drive the driving motor 81 of the forward/reverse mechanism 80. The driving force generated by the driving motor 81 is transmitted to the pulley 84 by the transmission belt 83, and is transmitted from the pulley 84 to the screw portion 87 of the ball screw mechanism 86, causing the screw portion 87 to rotate. As a result, the nut portion 88 of the ball screw mechanism 86 moves in the longitudinal direction Y, and together with the nut portion 88, the load cell 90 and the entire rotation mechanism 70 move in the longitudinal direction Y while being supported by the second rail 35. Therefore, the screw 60 connected to the pulley 76 of the rotation mechanism 70 also moves in the longitudinal direction Y together with the pulley 76 of the rotation mechanism 70, and the screw 60 retreats.

In the metering process P3a, the screw 60 is rotated in the forward direction as described above, and the screw 60 is retracted, so that the molten resin R in the heating barrel 50 is sent by the screw 60 to the portion of the heating barrel 50 closer to the nozzle 52 than the screw 60. At this time, the screw 60 is provided with a dam portion 67, and the screw 60 is divided into a first stage STG1 and a second stage STG2 by the dam portion 67. When the screw 60 rotates in the forward direction, the resin material located in the first stage STG1 moves to the second stage STG2 through the portion between the inner circumferential surface of the heating barrel 50 and the dam portion 67.

At that time, the diameter of the screw 60 in the vicinity of the dam portion 67 in the second stage STG2 is smaller than the diameter of the portion in the vicinity of the dam portion 67 in the first stage STG1, so the volume of the space formed by the inner surface of the heating barrel 50 and the screw 60 is large in the portion in the vicinity of the dam portion 67 in the second stage STG2. Therefore, as the screw 60 rotates forward, the pressure of the resin material is relatively small in the portion where the resin material that has passed over the dam portion 67 and been sent from the first stage STG1 to the second stage STG2 is located, i.e., in the portion in the vicinity of the dam portion 67 in the second stage STG2.

In addition, the diameter of the second stage STG2 of the screw 60 increases from the side where the dam portion 67 is located to the side where the nozzle 52 is located in the longitudinal direction Y, so the volume of the space formed by the inner surface of the heating barrel 50 and the screw 60 decreases from the side where the dam portion 67 is located to the front side. Therefore, the pressure of the molten resin R sent to the side where the nozzle 52 is located in the longitudinal direction Y in the metering process P3a increases from the side where the dam portion 67 is located to the front side.

In the metering process P3a, the control unit 100 controls the rotation and movement of the screw 60 as described above, thereby extruding the molten resin R in the heating barrel 50 to the front end side of the heating barrel 50. At that time, the control unit 100 measures the molten resin R using the amount of movement of the screw 60 when extruding the molten resin R to the front end side portion of the heating barrel 50 while retracting the screw 60, and the pressure of the molten resin R sent to the front end side portion of the heating barrel 50.

In this case, the metering of the molten resin R means storing the amount of molten resin R to be injected into the mold 16 of the clamping device 15 in one filling step P1 in a portion of the heated barrel 50 that is located forward of the check ring 66 in the longitudinal direction Y, thereby ensuring the amount of molten resin R to be used in one filling step P1.

Here, when the molten resin R is sent to the front end side in the metering process P3a, the check ring 66 arranged on the screw 60 is pushed forward by the molten resin R sent to the front end side and is pressed against the front groove wall 64 of the groove portion 63 formed in the screw 60 (see FIG. 5). Therefore, a gap is formed between the rear groove wall 64 of the groove portion 63 formed in the screw 60 and the check ring 66, so that the molten resin R located behind the check ring 66 passes through the gap and further passes between the inner surface of the check ring 66 and the groove bottom of the groove portion 63 and is extruded into the communication portion 65. As a result, when the molten resin R is extruded to the front side of the check ring 66 by the screw 60 in the metering process, the molten resin R located behind the check ring 66 is extruded to the front side of the check ring 66.

In the control of the metering process P3a, the amount of movement of the screw 60 is obtained based on the detection result of the encoder 82 of the drive motor 81 of the forward/reverse mechanism 80. In other words, the forward/reverse mechanism 80 moves the screw 60 in the longitudinal direction Y by transmitting the driving force generated by the drive motor 81 to the screw 60, and the encoder 82 is capable of detecting the rotational position of the rotating body (not shown) of the drive motor 81. Therefore, the control unit 100 obtains the position of the screw 60 in the longitudinal direction Y by obtaining the rotational position of the rotating body of the drive motor 81 detected by the encoder 82.

The encoder 82 of the driving motor 81 of the forward/reverse mechanism 80 serves as a screw position detection unit that detects the position of the screw 60 in the longitudinal direction Y within the heating barrel 50. In the metering process P3a, the control unit 100 obtains the amount of retreat of the screw 60 by obtaining the position of the screw 60 in the longitudinal direction Y based on the detection result of the encoder 82 of the driving motor 81 of the forward/reverse mechanism 80.

The pressure of the molten resin R sent to the front end of the heating barrel 50 is detected using the detection results of the load cell 90. The load cell 90 is used as a back pressure detection unit that detects the back pressure, which is the pressure of the molten resin R extruded to the front end by the screw 60 inside the heating barrel 50.

Regarding the detection of the back pressure of the molten resin R by the load cell 90, when the screw 60 pushes the molten resin R in the heating barrel 50 toward the front end of the heating barrel 50, a force acts on the screw 60 toward the rear in the longitudinal direction Y due to a reaction when pushing the molten resin R forward. The force in the longitudinal direction Y acting on the screw 60 is transmitted from the screw 60 to the pulley 76 of the rotation mechanism 70, and from the pulley 76 to the rotation mechanism main body 71, and is then transmitted to the load cell 90 fixed to the rotation mechanism main body 71.

The surface of the load cell 90 opposite to the surface fixed to the rotation mechanism main body 71 is fixed to the nut portion 88 of the ball screw mechanism 86 of the forward/reverse mechanism 80, so that the force from the rotation mechanism main body 71 of the rotation mechanism 70 to the rear in the longitudinal direction Y acts on the load cell 90 as a force compressing the load cell 90 in the longitudinal direction Y. The load cell 90 detects the magnitude of the force acting on the load cell 90 in this manner and transmits it to the control unit 100. The control unit 100 obtains the magnitude of the force transmitted from the load cell 90 as a force acting on the screw 60 in the longitudinal direction Y.

In the metering process P3a, the control unit 100 obtains the magnitude of the force acting on the screw 60 in the longitudinal direction Y based on the detection result of the load cell 90, thereby obtaining the back pressure of the molten resin R extruded forward by the screw 60. That is, in the metering process P3a, the control unit 100 obtains the position of the screw 60 in the longitudinal direction Y based on the detection result of the encoder 82, and obtains the back pressure of the molten resin R based on the detection result of the load cell 90, thereby obtaining the amount of molten resin R extruded to the tip side of the heating barrel 50, which is the side where the nozzle 52 is located, and then measures the molten resin R.

In this way, in the metering process P3a, the control unit 100 rotates the screw 60 within the heating barrel 50 while moving the screw 60 to the side opposite the nozzle 52 in the longitudinal direction Y of the heating barrel 50.

As a result, in the metering process P3a, the molten resin R is extruded toward the tip side within the heated barrel 50, and the molten resin R extruded by the screw 60 is metered based on the position of the screw 60 detected by the encoder 82 and the back pressure detected by the load cell 90. By metering the molten resin R in this manner, in the metering process P3a, the amount of molten resin R to be injected from the heated barrel 50 into the mold 16 of the mold clamping device 15 is metered in one filling process P1. That is, in the metering process P3a, the amount of molten resin R to be injected from the nozzle 52 into the mold 16 in the filling process P1 of the next cycle is metered.

In this manner, the control unit 100 rotates the screw 60 in the forward direction while moving it backward in the longitudinal direction Y to measure the molten resin R in the metering process P3a, and then in the screw reverse rotation process P3b, stops the movement of the screw 60 in the longitudinal direction Y and reverses the rotation of the screw 60. In the screw reverse rotation process P3b, the foam injection molding machine 1 rotates the screw 60 in the reverse direction relative to the rotation direction of the screw 60 when metering the molten resin R, thereby diffusing the compressed gas injected into the heating barrel 50 from the gas inlet 53 into the molten resin R in the heating barrel 50.

In other words, compressed gas supplied from the compressor 110 is continuously injected into the heated barrel 50 through the gas inlet 53, but in the metering process P3a, the molten resin R is sent to the side where the nozzle 52 is located by the forward rotating screw 60, so the pressure of the molten resin R is high. For this reason, the compressed gas supplied into the heated barrel 50 is less likely to diffuse into the molten resin R, which is under high pressure.

Therefore, in this embodiment, when the metering process P3a is completed in the foam injection molding machine 1, the control unit 100 controls the rotation of the driving motor 73 of the rotation mechanism 70, and the screw 60 is rotated in reverse to reduce the pressure of the molten resin R in the heated barrel 50, and the compressed gas supplied into the heated barrel 50 is diffused into the molten resin R. After the molten resin R is metered in the metering process P3a, when the control unit 100 controls the rotation mechanism 70 to rotate the screw 60 in reverse in the screw reverse rotation process P3b, it is preferable to rotate the screw 60 in reverse within a range of 45° or more and 720° or less.

Figure 7 is an explanatory diagram showing the change in pressure of the molten resin R when the screw 60 is rotated in the reverse direction relative to the rotation direction of the screw 60 in the metering process P3a. Note that Figure 7 is a diagram showing the pressure of the molten resin R for each position in the longitudinal direction Y of the heating barrel 50, and the pressure of the molten resin R shown by the graph on the upper side of Figure 7 shows the change in pressure due to the screw 60 being rotated in the reverse direction for each position in the longitudinal direction Y of the heating barrel 50 shown on the lower side.

At the completion of the metering process P3a, the pressure of the molten resin R in the screw groove 62 is high, and in particular, the pressure of the molten resin R in the screw groove 62 located in the second stage STG2, which is located closer to the nozzle 52 than the first stage STG1, is higher than the pressure of the molten resin R in the screw groove 62 located in the first stage STG1. Therefore, at the completion of the metering process P3a, the pressure of the molten resin R in the screw groove 62 located in the second stage STG2 is higher than the pressure of the compressed gas injected into the heating barrel 50 from the gas injection port 53.

In the screw reverse rotation process P3b performed after the completion of the metering process P3a, the movement of the screw 60 in the longitudinal direction Y is stopped and the screw 60 is rotated in reverse, so that the pressure of the molten resin R in the screw groove 62 located in the second stage STG2 decreases, and the pressure of the molten resin R in the screw groove 62 located in the second stage STG2 becomes lower than the pressure of the compressed gas injected into the heating barrel 50. In other words, when the movement of the screw 60 in the longitudinal direction Y is stopped and the screw 60 is rotated in reverse, the molten resin R located in the screw groove 62 moves to the rear side in the longitudinal direction Y. Therefore, a part of the molten resin R located in the second stage STG2 moves to the side located in the first stage STG1 through the part between the inner surface of the heating barrel 50 and the weir portion 67. As a result, the pressure of the molten resin R in the screw groove 62 in the second stage STG2 gradually decreases as the screw 60 rotates in reverse.

In the screw reverse rotation process P3b, the pressure of the molten resin R in the screw groove 62 in the second stage STG2 gradually decreases as the screw 60 rotates in the reverse direction, and by rotating the screw in the reverse direction at a predetermined rotation angle, the pressure of the molten resin R in the screw groove 62 in every part of the second stage STG2 becomes lower than the pressure of the compressed gas injected into the heating barrel 50. In other words, the pressure of the compressed gas in the heating barrel 50 becomes higher than the pressure of the molten resin R in the screw groove 62 in the second stage STG2.

As a result, the compressed gas in the heating barrel 50 spreads over a wide area of the molten resin R, which has a relatively low pressure in the second stage STG2, and is diffused into the molten resin R located in the second stage STG2. That is, in the second stage STG2, the molten resin R comes into contact with the compressed gas over the entire area of the screw groove 62 located in the second stage STG2, and the compressed gas in the heating barrel 50 is diffused into the molten resin R in the second stage STG2. The compressed gas in the heating barrel 50 is thus diffused into the molten resin R in the second stage STG2 and comes into contact with the molten resin R over a wide contact area, so that it permeates the molten resin R even at a relatively low pressure. Furthermore, the compressed gas diffused into the molten resin R is in a supercritical fluid state, so it easily permeates the molten resin R with which it comes into contact.

In this way, once the screw 60 has been rotated in reverse at a predetermined rotation angle in the screw reverse rotation process P3b, the reverse rotation of the screw 60 is stopped in the screw rotation stopping process P3c. For example, once the screw 60 has been rotated in reverse within a range of 45° or more and 720° or less in the screw reverse rotation process P3b, the reverse rotation of the screw 60 is stopped in the screw rotation stopping process P3c.

The screw 60, which has stopped rotating in the screw rotation stopping process P3c, stops rotating until the start of the next weighing process P3a after going through the mold opening process P4, product removal process P5, mold closing process P6, filling process P1, and pressure holding process P2. That is, the screw 60, which has stopped rotating in the screw rotation stopping process P3c, continues to stop rotating during the period between the screw rotation stopping process P3c, mold opening process P4, product removal process P5, mold closing process P6, filling process P1, and pressure holding process P2, which is designated as the stop period RS (see FIG. 6).

As a result, the pressure of the molten resin R located in the second stage STG2 does not change, so the molten resin R located in the second stage STG2 continues to be in contact with the compressed gas at a low pressure. Therefore, the compressed gas in the heating barrel 50 is diffused into the molten resin R throughout the stop period RS when the rotation of the screw 60 stops, and comes into contact with the molten resin R over a wide contact area. Therefore, the compressed gas in the heating barrel 50 penetrates the molten resin R even at a relatively low pressure.

After the reverse rotation of the screw 60 is stopped in the screw rotation stopping process P3c, the foam injection molding machine 1 goes through the mold opening process P4, the product removal process P5, and the mold closing process P6, and then in the filling process P1, the molten resin R in the heated barrel 50 is injected from the nozzle 52 into the cavity 17 formed in the mold 16.

When the molten resin R in the heated barrel 50 is injected in the filling process P1, the screw 60 is advanced by operating the forward/backward mechanism 80 while the rotation of the screw 60 is stopped. As a result, the molten resin R located in front of the screw 60 in the heated barrel 50, which has been metered in the metering process P3a, is pushed out of the nozzle 52 by the screw 60 and injected into the cavity 17 formed in the mold 16.

Here, a check ring 66 with an outer diameter approximately the same as the inner diameter of the heating barrel 50 is disposed on the screw 60, but there is a gap between the inner peripheral surface of the check ring 66 and the screw 60. Therefore, when the screw 60 is rotated in the metering process P3a, the molten resin R located behind the check ring 66 passes through this gap and is pushed out to the front side of the check ring 66.

In contrast, when the molten resin R metered in the metering process P3a is injected, the check ring 66 is in a state in which the molten resin R cannot move between both sides in the longitudinal direction Y. FIG. 8 is an explanatory diagram showing the state of the check ring 66 when the molten resin R is injected. When the molten resin R in the heating barrel 50 is injected from the nozzle 52 in the filling process P1, the control unit 100 operates the forward/backward mechanism 80 to advance the screw 60. As a result, a pressing force is applied from the screw 60 to the molten resin R located in front of the check ring 66 in the heating barrel 50 in the longitudinal direction Y. The check ring 66 arranged in the groove portion 63 of the screw 60 has a width in the longitudinal direction Y that is smaller than the groove width of the groove portion 63 of the screw 60, so that the check ring 66 can move in the groove width direction within the groove portion 63.

In addition, when a forward pressing force is applied to the molten resin R located forward of the check ring 66 as the screw 60 advances, a backward pressing force acts as a reaction force from the molten resin R on the check ring 66. As a result, the check ring 66 moves backward relative to the groove portion 63 within the range in which the groove portion 63 is formed in the screw 60, and the check ring 66 abuts against the groove wall 64 located rearward of the groove portion 63 in the groove width direction.

Therefore, there is no gap between the groove wall 64 located on the rear side of the groove portion 63 in the groove width direction and the check ring 66, and the molten resin R cannot pass through. In other words, even if the molten resin R located in front of the check ring 66 flows into the gap between the inner surface of the check ring 66 and the groove bottom of the groove portion 63 through the communication portion 65 formed in the screw 60, it cannot flow rearward from that position. Therefore, when the molten resin R metered in the metering process P3a is injected in the filling process P1 by moving the screw 60 forward, the molten resin R located in front of the check ring 66 is extruded from the nozzle 52 without flowing behind the check ring 66.

At this time, the compressed gas in a supercritical fluid state is permeated into the molten resin R, so in the filling process P1, the molten resin R permeated with the compressed gas in a supercritical fluid state is injected from the nozzle 52 through the through hole 18 of the fixed mold 16f into the cavity 17 formed in the mold 16. This fills the cavity 17 of the mold 16 with the molten resin R permeated with the compressed gas in a supercritical fluid state.

When the cavity 17 of the mold 16 is filled with molten resin R, the pressure of the molten resin R becomes lower than the back pressure of the molten resin R measured at a position forward of the check ring 66 in the measuring process P3a. As a result, the compressed gas that has permeated the molten resin R turns into bubbles and grows in the cavity 17 as the pressure of the molten resin R decreases. Therefore, foam molding is performed in the cavity 17 into which the molten resin R has been injected, and the molten resin R into which the compressed gas has diffused and permeated is molded into a foam molded product.

Effects of the embodiment
In the injection molding machine 1 for foam molding and the foam molding method according to the above embodiment, the screw 60 is rotated in the metering step P3a while supplying compressed gas to the heated barrel 50 to measure the molten resin R, and then the screw 60 is rotated in the opposite direction to the rotation direction of the screw 60 when measuring the molten resin R, thereby diffusing the compressed gas into the molten resin R in the heated barrel 50. This allows the compressed gas in the heated barrel 50 to be efficiently diffused into the molten resin R by using a compressed gas of a relatively low pressure as the gas to be supplied to the heated barrel 50 without using a cylinder to supply high-pressure gas to the heated barrel 50. Therefore, since foam molding can be performed without using a cylinder containing high-pressure gas, the initial investment cost when performing foam molding can be reduced. In addition, since no cylinder is used, it is not necessary to replace the cylinder during operation, so the running cost when performing foam molding can also be reduced. As a result, the cost when performing foam molding can be reduced.

After the control unit 100 measures the molten resin R in the metering process P3a, the screw 60 is rotated in the reverse direction within a range of 45° to 720° in the screw reverse rotation process P3b, so that the compressed gas can be diffused into the molten resin R while suppressing defects such as clogging of the resin material in the heating barrel 50. In other words, if the reverse rotation of the screw 60 is less than 45°, the reverse rotation of the screw 60 is too little, so even if the screw 60 is rotated in reverse, the pressure of the molten resin R in the screw groove 62 located in the second stage STG2 may not be effectively reduced. In this case, the compressed gas in the heating barrel 50 may not be effectively diffused into the molten resin R. In addition, if the reverse rotation of the screw 60 exceeds 720°, the reverse rotation of the screw 60 is too much, so there is a risk that the amount of movement when the resin material of the heating barrel 50 moves backward in the longitudinal direction Y due to the reverse rotation becomes too large. In this case, the resin material located in the first stage STG1 may move too far behind the position of the hopper 55 in the longitudinal direction Y, which may cause problems such as clogging of the resin material.

In contrast, when the reverse rotation of the screw 60 in the screw reverse rotation process P3b is within the range of 45° or more and 720° or less, the pressure of the molten resin R in the screw groove 62 located in the second stage STG2 can be reduced while suppressing clogging of the resin material at a position behind the hopper 55 in the first stage STG1. Therefore, the compressed gas can be diffused into the molten resin R while suppressing problems such as clogging of the resin material in the heating barrel 50. As a result, foam molding can be performed more reliably while suppressing increases in costs.

In addition, because the compressor 110 supplies compressed air at a pressure of 5 MPa or less, a relatively general-purpose compressor 110 can be used, and the cost of the device that supplies compressed gas to the heating barrel 50 can be reduced. This makes it possible to more reliably reduce the cost of foam molding, and as a result, it is possible to more reliably reduce the cost of foam molding.

In addition, since the air separation unit 120 is disposed between the compressor 110 and the gas inlet 53, gas that easily becomes a supercritical fluid can be separated by the air separation unit 120 and supplied to the heated barrel 50 as the compressed gas to be supplied into the heated barrel 50. This allows the compressed gas at a relatively low pressure to be more reliably diffused into the molten resin R in the heated barrel 50, and the compressed gas can be permeated into the molten resin R. As a result, foam molding can be performed more reliably while suppressing increases in costs.

In addition, the screw 60 is provided with a dam section 67, and the gas inlet 53 is located on the side where the nozzle 52 is located, relative to any position of the dam section 67 in the range of movement of the dam section 67 when the screw 60 moves in the longitudinal direction Y of the heated barrel 50. This allows compressed gas to be supplied to the portion of the heated barrel 50 that is closer to the nozzle 52 than the dam section 67. This allows compressed gas to be supplied more reliably to the molten resin R located in the portion of the heated barrel 50 closer to the nozzle 52, regardless of the position of the screw 60 in the longitudinal direction Y. Therefore, the resin material is sufficiently melted, and the compressed gas can be diffused to the molten resin R that is close to the timing of injection from the nozzle 52. As a result, foam molding can be performed more reliably while suppressing increases in cost.

[Modification]
In the above embodiment, compressed gas is supplied from the compressor 110 to the heating barrel 50 via the air separation unit 120, but compressed air may be supplied directly from the compressor 110 to the heating barrel 50 without using the air separation unit 120. If compressed air in a supercritical fluid state can be supplied from the compressor 110 to the heating barrel 50 without separating the compressed air with the air separation unit 120, the air separation unit 120 may not be used. Regardless of the presence or absence of the air separation unit 120, by supplying compressed air in a supercritical fluid state to the heating barrel 50, the compressed air can be diffused into the molten resin R, and foam molding can be performed more reliably. In addition, if the air separation unit 120 is not used, the cost of foam molding can be further reduced.

In addition, by supplying compressed air from a compressor 110 of 5 MPa or less without using an air separation unit 120, foam molding can be performed without going through the procedures required for equipment applications when using high-pressure gas. This makes it possible to more reliably reduce the costs involved in foam molding, and as a result, it is possible to more reliably reduce the costs involved in foam molding.

In the above embodiment, in the screw reverse rotation process P3b, the movement of the screw 60 in the longitudinal direction Y is stopped and the screw 60 is rotated in reverse. However, when rotating the screw 60 in reverse, the screw 60 may be moved in the longitudinal direction Y. For example, after the metering process P3a, the screw 60 may be rotated in reverse while performing a so-called suck back, which is an operation of the screw 60 for relieving the back pressure of the molten resin R. If the pressure of the molten resin R in the heating barrel 50, particularly the pressure of the molten resin R located in the second stage STG2, can be reduced by rotating the screw 60 in reverse, the screw 60 may be moved slightly in the longitudinal direction Y in the screw reverse rotation process P3b.

1...injection molding machine for foam molding, 5...base, 6...first rail, 10...injection device, 15...mold clamping device, 16...mold, 16f...fixed mold, 16m...movable mold, 17...cavity, 18...through hole, 20...frame, 21...base, 22...front wall, 23...rear wall, 24...legs, 30...upper frame, 31...front wall, 32...side wall, 33...support pin, 34...fixing screw, 35...second rail, 40...propulsion mechanism, 41...driving motor, 42...connecting mechanism, 43...ball screw mechanism, 44...screw portion, 45...nut portion, 50...heating barrel, 51...heater, 52...nozzle, 53...gas inlet, 55...hopper, 60...screw, 61... Flight, 62...screw groove, 63...groove portion, 64...groove wall, 65...connection portion, 66...check ring, 67...dam portion, 70...rotation mechanism, 71...rotation mechanism main body, 72...stay, 73...driving motor, 74...encoder, 75...transmission belt, 76...pulley, 77...bearing, 80...forward/reverse mechanism, 81...driving motor, 82...encoder, 83...transmission belt, 84...pulley, 85...bearing, 86...ball screw mechanism, 87...screw portion, 88...nut portion, 90...load cell, 100...control portion, 101...display portion, 102...input portion, 110...compressor, 105...supply pipe, 120...air separation device, R...molten resin

Claims (6)

a heating barrel for melting the resin material therein to form molten resin;
a screw rotatably disposed within the heating barrel and movable within the heating barrel in a longitudinal direction of the heating barrel;
a compressor for supplying compressed gas to the heated barrel;
A control unit for controlling the operation of the screw;
Equipped with
The heating barrel comprises:
a nozzle disposed at one end in a longitudinal direction of the heating barrel and configured to inject the molten resin;
a gas inlet that is disposed on a wall surface of the heating barrel in a range in which the screw is disposed in the longitudinal direction thereof and that injects the compressed gas supplied from the compression device into the heating barrel;
having
The control unit rotates the screw within the heated barrel while moving it to the opposite side of the nozzle in the longitudinal direction of the heated barrel, thereby sending the molten resin to the portion of the heated barrel that is closer to the nozzle than the screw, thereby metering the molten resin to be injected from the nozzle, and then rotates the screw in the opposite direction to the rotation direction of the screw when metering the molten resin, thereby diffusing the compressed gas injected into the heated barrel from the gas injection port into the molten resin in the heated barrel. The foam injection molding machine according to claim 1, wherein the control unit reverses rotation of the screw within a range of 45° to 720° after metering the molten resin. The foam injection molding machine according to claim 1 or 2, wherein the compression device supplies the compressed gas to the heating barrel at a pressure of 5 MPa or less. The foam injection molding machine according to claim 1 or 2, wherein an air separation device is disposed between the compression device and the gas inlet, which separates the components of the compressed gas compressed by the compression device and supplies a portion of the compressed gas to the gas inlet. A dam portion is disposed on the screw to divide the screw into a portion on a side where the nozzle is located in the longitudinal direction of the heating barrel and a portion on the opposite side to the side where the nozzle is located;
3. The foam molding injection molding machine according to claim 1, wherein the gas inlet is positioned on the side where the nozzle is located relative to any position of the dam part within the range of movement of the dam part when the screw moves in the longitudinal direction of the heating barrel. a heating barrel for melting the resin material therein to form molten resin;
a screw rotatably disposed within the heating barrel and movable within the heating barrel in a longitudinal direction of the heating barrel;
A foam molding method for molding a foam-molded product from the molten resin to which the compressed gas has been supplied by supplying compressed gas to the heated barrel in a foam molding injection molding machine comprising:
a step of rotating the screw in the heating barrel, while moving the screw in the longitudinal direction of the heating barrel to a side opposite to a side where a nozzle of the heating barrel is located, thereby feeding the molten resin to a portion of the heating barrel on the nozzle side relative to the screw, and measuring the amount of the molten resin to be injected from the nozzle;
a step of diffusing the compressed gas supplied to the heating barrel into the molten resin in the heating barrel by rotating the screw in a reverse direction to a rotation direction of the screw when the molten resin is metered after the molten resin is metered;
A foam molding method comprising the steps of:

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