JP7806535B2 - Injection device and injection foam molding method - Google Patents

Description

The present invention relates to an injection device that injects an inert gas as a foaming agent into molten resin to perform injection molding to obtain a foam-molded product.

Molded foam products containing many fine bubbles are in high demand because they are lightweight yet strong. The blowing agents used to obtain molded foam products through injection molding are divided into chemical and physical blowing agents. Chemical blowing agents are substances such as azodicarboxylic acid amide that decompose when heated to generate gas. Physical blowing agents are inert gases such as nitrogen and carbon dioxide. Physical blowing agents made from inert gases are injected into the resin at high pressure and temperature, resulting in strong penetration and less chance of uneven foaming in the resulting molded foam.

In foam molding using an inert gas as a physical foaming agent, Patent Document 1 discloses a screw for an injection molding machine that is formed with a first compression zone in which the resin is compressed, a starvation zone in which the resin pressure is reduced, and a second compression zone in which the resin is compressed, and in which gas is injected into the starvation zone. The screw disclosed in Patent Document 1 has a barrier flight formed in the section corresponding to the first compression zone, consisting of a main flight and a sub-flight with a larger lead angle than the main flight, as well as a ring-shaped dam flight of a predetermined width formed in front of the barrier flight. The screw in Patent Document 1 is said to eliminate the risk of gas flowing or leaking upstream of the screw within the heating cylinder, even during the molding cycle or when the screw is stopped for maintenance, etc.

Japanese Patent Application Laid-Open No. 2020-032547

The screw in Patent Document 1 has barrier flights and dam flights redundantly arranged (in series) in the flow direction (conveying direction) of the molten resin. Because the sealing function of the barrier flights and dam flights is a clearance seal, the molten resin passes through narrow gaps between the barrier flight and dam flight sections during the conveying process. In other words, with the screw of the above-mentioned prior art, the barrier flight and dam flight sections encounter significant flow resistance, resulting in reduced plasticizing capacity.

Based on the above, the present invention aims to provide an injection device for foam molding that can prevent a decrease in plasticizing capacity.

The foam molding injection device of the present invention comprises a heating cylinder equipped with an injection nozzle, a screw mounted inside the heating cylinder that is rotatable about its central axis and capable of moving forward downstream and backward upstream along the central axis, a first gas supply passage that supplies foaming gas to be injected into the molten resin inside the heating cylinder, and a second gas supply passage that supplies counter gas to the heating cylinder that opposes the backflow of the molten resin upstream.

The foam molding injection device of the present invention preferably includes a raw material hopper that holds the resin raw material and supplies the resin raw material to the inside of the heating cylinder through a raw material passage, and a shutoff mechanism that opens or closes the raw material passage.

The foam molding injection device of the present invention preferably includes a sealing mechanism that airtightly seals the upstream end of the heating cylinder.

In the foam molding injection device of the present invention, the counter gas supply port through the second gas supply path is preferably provided in the raw material passage between the cutoff mechanism and the heating cylinder.

In the foam molding injection device of the present invention, the counter gas supply port through the second gas supply path is preferably provided in the sealing mechanism.

In the foam molding injection device of the present invention, the counter gas supply port through the second gas supply path is preferably located downstream of the sealing mechanism.

The foam molding injection device of the present invention preferably includes a third gas supply passage for supplying a shielding gas that prevents leakage of counter gas from the sealed portion of the sealing mechanism.

In the foam molding injection device of the present invention, the shutoff mechanism preferably has a function for measuring the amount of resin raw material supplied to the heating cylinder through the shutoff mechanism.

In the foam molding injection device of the present invention, the foaming gas from the first gas supply line and the counter gas from the second gas supply line are preferably controlled independently of each other.

In the foam molding injection device of the present invention, the counter gas from the second gas supply passage is preferably supplied based on the screw rotation speed.

This invention proposes an injection foam molding method in which raw resin material supplied to the inside of a heating cylinder is heated and melted into a molten resin while being transported from upstream to downstream by the rotational driving force of a screw, and foaming gas is injected into and dissolved in the molten resin during this transport process. This proposal involves supplying a counter gas into the heating cylinder to counter the reverse flow of the molten resin upstream.

This invention provides a two-stage injection device that can prevent a decrease in plasticizing capacity by supplying a counter gas into the heating cylinder to counter the backflow of molten resin upstream.

FIG. 2 is a front cross-sectional view of the injection device according to the first embodiment. FIG. 3 is a diagram illustrating the specifications of a screw of the injection device according to the first embodiment. 3A to 3C are diagrams illustrating a plasticization process to an injection process using the injection device according to the first embodiment. 5A to 5C are diagrams illustrating the operation of the injection device according to the first embodiment. 5 is a diagram showing a supply pattern of a foaming gas G1 and a counter gas G2 of the injection device according to the first embodiment. FIG. 10A and 10B are diagrams illustrating a modified example of the injection device according to the first embodiment. FIG. 10 is a front cross-sectional view of an injection device according to a second embodiment. FIG. 10 is a diagram showing supply patterns of a foaming gas G1, a counter gas G2, and a shielding gas G3 of an injection device according to a second embodiment. FIG. 10 is a diagram showing a modified example of the injection device according to the second embodiment. FIG. 10 is a diagram showing another screw used in the injection device according to the embodiment.

Embodiments of the present invention will be described below with reference to the accompanying drawings. This embodiment includes a first and second embodiment, both of which are intended to produce foam-molded products, and provides an injection device with two stages that can prevent a decrease in plasticizing capacity.

[First embodiment: FIGS. 1 to 6]
The schematic configuration of an injection device 1 according to a first embodiment will be described with reference to FIGS. 1, 2 and 3. FIG.
1, an injection device 1 for foam molding includes a hollow heating cylinder 10 and a screw 20 that is capable of rotational movement around a central axis C and reciprocal movement along the central axis C in a processing region 11, which is the space between the inner peripheral surface of the heating cylinder 10 and the outer surface of the screw 20. In addition, the injection device 1 includes a gas supply mechanism 50 that supplies, for example, an inert gas for foam molding into the interior of the heating cylinder 10.
In the injection device 1, a downstream side L and an upstream side U are specified according to the direction of resin flow as shown in Fig. 1. The downstream side L and the upstream side U have relative meanings.

A raw material hopper 13 is provided on the upstream side U of the heating cylinder 10. Resin pellets P, which are the resin raw material for injection molding, are stored in the raw material hopper 13, and the resin pellets P are supplied from the raw material hopper 13 to the processing area 11 through a raw material passage 14 that passes through the inside and outside of the heating cylinder 10.
A first nozzle 53B of a first gas supply path 53 is provided in the heating cylinder 10 on the downstream side L of the position where the raw material hopper 13 is provided. The first nozzle 53B penetrates the inside and outside of the heating cylinder 10, and the foaming gas G1 made of, for example, an inert gas IG supplied from the gas supply source 51 passes through the first gas supply path 53 and reaches the processing region 11.
An injection nozzle 18 is provided on the most downstream side L of the heating cylinder 10. The molten resin plasticized inside the heating cylinder 10 passes through this injection nozzle 18 and fills the cavity of a mold (not shown).
A plurality of heaters 19 for melting the resin pellets P are provided on the outer periphery of the heating cylinder 10. The heaters 19 may be configured in a different way or may be replaced with other heaters on the outside of the heating cylinder 10.

[Screw 20: Figures 1 and 2]
Next, the screw 20 will be described with reference to FIGS.
The screw 20 conveys the resin pellets P from the upstream side U to the downstream side L by its rotational driving force.
The screw 20 has a first stage 30 provided on the upstream side U and a second stage 40 connected to the first stage 30 and provided on the downstream side L. The first stage 30 melts the resin pellets P to generate the molten resin M, and also transports the generated molten resin M toward the second stage 40. The second stage 40 injects and disperses a foaming gas G1 into the molten resin M supplied from the first stage 30.

[First stage 30: Figure 1]
1, the first stage 30 is divided into three regions, namely, a first region 30A, a second region 30B, and a third region 30C, in this order from the upstream side U. The resin pellets P are turned into molten resin M by passing through the first region 30A, the second region 30B, and the third region 30C in this order inside the heating cylinder 10.

In the first region 30A, a single flight 31 is formed so as to form a screw groove with a constant groove depth D _30A , and the resin pellets P supplied from the raw material hopper 13 are transported toward the second region 30B. The groove depth in the first region 30A is greater than the groove depths in the second region 30B and the third region 30C. The first region 30A is a portion referred to as the supply section. In the first region 30A, the resin pellets P are transported in a solid state toward the second region 30B. The first region 30A is positioned corresponding to the raw material hopper 13 at the start of plasticization ( FIG. 3( a) ).

Next, the second region 30B, as an example, includes a main flight 33 continuing from the flight 31 of the first region 30A and a sub-flight 35 having a smaller outer diameter than the main flight 33. The sub-flight 35 has a larger lead angle than the main flight 33. The second region 30B is configured so that the groove depth D _30B becomes shallower from the upstream side U to the downstream side L. Note that the groove depths D _30A and D _30B at the boundary between the second region 30B and the first region 30A are equal. The resin pellets P, which are solid on the upstream side U of the second region 30B, become molten resin M on the downstream side L. The second region 30B is a portion referred to as a compression section.

It is preferable that both ends of the secondary flight 35 are closed off from the main flight 33. If either or both ends of the secondary flight 35 are separated from the main flight 33, solid resin will leak from the gap and mix with the molten resin M, whereas if the secondary flight 35 is closed off, the solid resin will not be able to get over the secondary flight 35 and only the molten resin M will be able to get over the secondary flight 35. This allows the molten resin M to get over the tops of the secondary flights 35 without exception, so that a shear force is applied to the molten resin M, allowing it to be transported downstream.
By providing a secondary flight 35 in the second region 30B of the first stage 30, it is assumed that the solid resin and the molten resin are separated and compressed gently with a relatively weak force. This prevents the solid resin pellets P from clogging the screw groove of the first stage 30, forming wedges against the heating cylinder 10 and causing uneven load, eccentricity, and runout of the screw 20.

If the outer diameter (diameter) of the top of the main flight 33 is D, the secondary flight 35 is preferably provided so that its length (L35) in the direction of the central axis C falls within the range of 7D to 12D. A more preferred length (L35) is 8D to 11D, and an even more preferred length (L35) is 9D to 10D.

Next, in the third region 30C, as an example, a single flight 37 is formed that continues to the main flight 33 of the second region 30B. The third region 30C is formed with a constant groove depth D _30C . This is intended to make the density of the molten resin M conveyed from the second region 30B constant. The third region 30C is a portion called a metering section.

[Second stage 40: Figures 1 and 2]
1 and 2, the second stage 40 is divided into three regions, namely, a first region 40A, a second region 40B, and a third region 40C, in order from the upstream side U. Inside the heating cylinder 10, the foaming gas G1 is injected into the molten resin M and dispersed therein by passing through the first region 40A, the second region 40B, and the third region 40C in that order.

The first region 40A is provided corresponding to the first nozzle 53B through which the foaming gas G1 is supplied to the processing region 11 inside the heating cylinder 10. "Corresponding" here means that the first nozzle 53B is provided so as not to leave the range of the first region 40A even when the screw 20 moves forward or backward. As an example, the first region 40A is formed with multiple flights 41. In a preferred embodiment, the first region 40A is formed so that its groove depth D _40A increases from the upstream side U to the downstream side L. By forming the first region 40A so that the groove depth D _40A increases from the upstream side U to the downstream side L, variation in the amount of foaming gas G1 dissolved within the molten resin M can be reduced. It is a preferred embodiment that the groove depth D _40A becomes deeper from the upstream side U toward the downstream side L, but in the present invention, the groove depth D _40A of the first region 40A may become shallower from the upstream side U toward the downstream side L, or the groove depth D _40A may be constant from the upstream side U toward the downstream side L.

The first region 40A, which is made up of multiple flights, preferably has a length (L41) in the direction of the central axis C in the range of 2D to 5D. A more preferred length (L41) is 2.5D to 4.5D, and an even more preferred length (L41) is 2D to 4D.

Furthermore, in order to increase the number of divisions of the molten resin M, it is preferable to have a large number of flights 41 in the first region 40A. However, if the number of flights 41 is too large, the cross-sectional area of the grooves in the multi-flight section becomes too small. This increases the degree of filling of the grooves in the gas injection section region, reducing the voids into which the foaming gas G1 can enter and potentially reducing the amount of foaming gas G1 injected. For this reason, based on the inventor's experience and extensive research, in order to obtain a sufficient amount of foaming gas G1 injected and to ensure good dispersion into the molten resin M, it is preferable to have 6 to 10 flights 41, and it is preferable that each flight 41 have 1 to 2 turns. It is also preferable that each flight 41 have the same outer diameter and the same lead angle.

If the overall groove depth _D40A from the upstream side U to the downstream side L is deeper than the groove depth D30C of the third region 30C of the first stage ₃₀ , the degree of filling with molten resin M will be low, and the first region 40A can be called a starvation region.

Next, in the second region 40B, as an example, a single flight 43 is formed. The groove depth D _40B of the second region 40B becomes shallower from the upstream side U to the downstream side L. This compresses the molten resin M conveyed from the first region 40A. The second region 40B is a portion called a compression section, similar to the second region 30B.

Next, in the third region 40C, as an example, a flight 43 is formed that continues to the flight 43 of the second region 40B. The groove depth D _40c of the third region 40C is formed to be constant, similar to the most downstream side L of the first region 40A. This is intended to keep the density of the molten resin M constant. The third region 40C, like the third region 30C, is a portion called a metering section.

[Gas supply mechanism 50: FIG. 1]
Next, the gas supply mechanism 50 will be described with reference to FIG.
The gas supply mechanism 50 includes a gas supply source 51 in which, for example, an inert gas IG is stored, a first gas supply path 53 that supplies a foaming gas G1, which is a gas for foam generation, and a second gas supply path 55 that supplies a counter gas G2 that suppresses backflow in opposition to the backflow of the molten resin M toward the upstream side U, and the first gas supply path 53 and the second gas supply path 55 are branched off from a basic gas supply path 52 that is directly connected to the gas supply source 51.

The first gas supply path 53 connects the gas supply source 51 to the first region 40A of the second stage 40, and includes a first supply pipe 53A that supplies the foaming gas G1 from the gas supply source 51 to the interior of the heating cylinder 10, and a first nozzle 53B located at the tip of the first supply pipe 53A. The first gas supply path 53 also includes a first valve 53C located midway along the first supply pipe 53A that controls the supply of the foaming gas G1 toward the first nozzle 53B. The first valve 53C is opened and closed (ON/OFF) in response to instructions from the control unit 60. When the first valve 53C is turned ON, the foaming gas G1 is supplied to the heating cylinder 10, and foam molding is performed.

The second gas supply path 55 connects the gas supply source 51 and the raw material passage 14 and includes a second supply pipe 55A that supplies counter gas G2 from the gas supply source 51 into the raw material passage 14, and a second nozzle 55B located at the end of the second supply pipe 55A. The second gas supply path 55 also includes a second valve 55C located midway along the second supply pipe 55A that controls the supply of counter gas G2 toward the second nozzle 55B. The second nozzle 55B is located in the raw material passage 14 downstream of the shutoff mechanism 70, which will be described below, in the direction of flow of the resin pellets P. In other words, the counter gas G2 supply port of the second nozzle 55B is located in the raw material passage 14 between the shutoff mechanism 70 and the heating cylinder 10. The second valve 55C is opened and closed (ON/OFF) by instructions from the control unit 60. When the second valve 55C is turned ON, counter gas G2 is supplied into the raw material passage 14. The second valve 55C and the first valve 53C are independently controlled to open and close under the control of the control unit 60, and can maintain any intermediate opening between fully open and fully closed to control the flow rate or pressure of the foaming gas G1 and counter gas G2 supplied to the first nozzle 53B and second nozzle 55B.

[Shut-off mechanism 70: Figure 1]
The shutoff mechanism 70 opens or closes the raw material passage 14 between the interior of the heating cylinder 10 and the raw material hopper 13 in connection with the plasticization process. Specifically, the shutoff mechanism 70 opens the raw material passage 14 during the plasticization process but closes it when the process is completed. The shutoff mechanism 70 closes the raw material passage 14 when counter gas G2 is supplied from the second gas supply path 55. This allows the shutoff mechanism 70 to improve the counter gas G2 supply effectiveness in the second gas supply path 55. Here, "open" means fully opening the raw material passage 14, and "close" means fully closing the raw material passage 14. Alternatively, the shutoff mechanism 70 may close the raw material passage 14 when the screw rotation speed slows to a predetermined speed near the end of the plasticization process, and then open it after the screw rotation speed reaches the predetermined speed after the start of the plasticization process. This allows counter gas G2 to be supplied when gas backflow is likely to occur due to a low screw rotation speed and low pump capacity, as described below.

The shutoff mechanism 70, for example, includes a valve element 71 that moves back and forth relative to the raw material passage 14 to open and close the raw material passage 14, and a valve seat 73 that supports the valve element 71. The shutoff mechanism 70 also includes a drive source 75, such as a piston-cylinder device, that drives the valve element 71 to move back and forth. The drive source 75 causes the valve element 71 to move back and forth linearly in response to instructions from the control unit 60. In the shutoff mechanism 70, when the valve element 71 closes the raw material passage 14, the raw material passage 14 is hermetically sealed. Therefore, the counter gas G2 supplied from the second gas supply path 55 to the inside of the raw material passage 14 cannot leak beyond the shutoff mechanism 70 into the raw material hopper 13.
Although an example in which one set of blocking mechanisms 70 is provided is shown here, a plurality of sets of blocking mechanisms 70, for example, two sets of blocking mechanisms 70, can also be provided in the direction in which the resin pellets P flow.

[Sealing mechanism 80: Figure 1]
Next, in a preferred embodiment, the injection device 1 is provided with a sealing mechanism 80 at the end of the upstream side U, which airtightly seals the space between the heating cylinder 10 and the screw 20. The sealing mechanism 80 prevents the counter gas G2 supplied from the second gas supply path 55 from leaking from the upstream side U of the heating cylinder 10 to the outside.
As an example, the sealing mechanism 80 includes a packing 81 provided between the heating cylinder 10 and the screw 20, and a packing support 83 that supports the packing 81. The packing 81 is a ring-shaped member made of, for example, a resin material or a metal material and arranged between the inner periphery of the heating cylinder 10 and the outer periphery of the screw 20. The packing support 83 is a member made of, for example, a metal material, to whose end on the downstream side L the packing 81 is fixed. The packing support 83 includes a cylindrical fixed tube 83A inserted between the heating cylinder 10 and the screw 20, and a fixed flange 83B connected to the end on the upstream side U of the fixed tube 83A. The fixed flange 83B is fixed to the end on the upstream side U of the heating cylinder 10 by a fastening means (not shown).

[Operation of injection device 1: Figure 1]
The operation of the injection device 1 is outlined below (see FIG. 1).
When the screw 20 installed inside the heating cylinder 10 rotates, resin pellets P made of thermoplastic resin supplied from the raw material hopper 13 are sent toward the injection nozzle 18 at the downstream end of the heating cylinder 10, and during this process, the resin pellets P become molten resin M. The molten resin M is mixed with foaming gas G1 supplied from a gas supply source 51 and then injected in a predetermined amount into a cavity formed between the fixed mold and movable mold of a mold clamping device (not shown). The basic operation of the screw 20 involves the screw 20 retreating while receiving back pressure as the resin pellets P melt, and then moving forward to perform injection. Furthermore, it is not prohibited to apply or replace other configurations of the heater 19 outside the heating cylinder 10 for melting the resin pellets P.

[Injection molding procedure: Figure 3]
The injection device 1 having the above elements performs injection molding in the following procedure.
As is well known, injection molding comprises the following steps: a mold clamping process in which a movable mold and a fixed mold (not shown) are closed and clamped under high pressure; a plasticization process in which resin pellets P are heated, melted, and plasticized inside a heating cylinder 10; an injection process in which the plasticized molten resin M is injected and filled into a cavity formed by the movable mold and the fixed mold; a holding and cooling process in which the molten resin M filled in the cavity is cooled until it solidifies; a mold opening process in which the molds are opened; and an ejection process in which the molded product that has been cooled and solidified in the cavity is ejected. One cycle of injection molding is completed by performing each of the above steps sequentially or partially in parallel.

Among the above-described series of steps in injection molding, the plasticizing step and the injection step to which this embodiment relates will be outlined with reference to FIG.
[Plasticization process]
In the plasticization process, resin pellets P are supplied from a raw material hopper 13 on the upstream side U of the heating cylinder 10. At the start of plasticization, the screw 20 is positioned downstream of the heating cylinder 10 and is then rotated and retracted from its initial position ( FIG. 3( a) “Plasticization Start”). By rotating the screw 20, the resin pellets P supplied between the screw 20 and the heating cylinder 10 are heated by shear force, gradually melted, and transported downstream. In this embodiment, the rotation (direction) of the screw 20 during the plasticization process is defined as forward rotation. As the supply of resin pellets P continues and the screw 20 continues to rotate, molten resin M is transported downstream of the heating cylinder 10, discharged from the screw 20, and accumulated downstream of the screw 20. The screw 20 is retracted by balancing the resin pressure of the molten resin M accumulated downstream of the screw 20 with the back pressure that prevents the screw 20 from retracting. Thereafter, when the amount of molten resin M required for one shot has been measured and accumulated, the rotation and retraction of the screw 20 is stopped (FIG. 3(b) "Plasticization completed").

The state of the resin (resin pellets P, molten resin M) and the foaming gas G1 is roughly classified into four stages: "α" when the resin is not yet melted, "β" when the resin is melted, "γ" when the foaming gas G1 is dispersed in the molten resin M, and "γ'" when the dispersion of the foaming gas G1 is complete.
"Unmelted resin α" indicates that the resin is subjected to shearing force, but some resin remains insufficiently melted, and not all of the resin is melted. "Melted resin β" indicates that the resin pellets P are gradually melted by being subjected to shearing force. "Gas dispersion γ" indicates that the supplied foaming gas G1 is dispersed into the molten resin M as the screw 20 rotates, and "gas dispersion completed γ'" indicates that the foaming gas G1 is sufficiently dispersed in the molten resin M and is ready for injection. However, the foaming gas G1 may be unevenly distributed in the "gas dispersion completed" region.

[Injection process]
3(c), the screw 20 is advanced, which closes a check valve (not shown) provided at the tip of the screw 20, increasing the pressure (resin pressure) of the molten resin M accumulated downstream of the screw 20, and the molten resin M is ejected from the injection nozzle 18 toward the cavity described above.
Thereafter, one cycle of injection molding is completed through the holding step, mold opening step, and removal step, and then the next cycle of mold clamping step and plasticizing step is carried out.

[Effect of supplying counter gas G2: Figure 4]
Next, the effect of supplying the counter gas G2 in addition to the foaming gas G1 will be described with reference to FIG.
When the foaming gas G1 is supplied, a gas pressure P1 due to the foaming gas G1 acts on the molten resin M from the downstream side L to the upstream side U, as shown in Figure 4. In principle, the injected molten resin M moves from the upstream side U to the downstream side L, but the gas pressure P1 causes the molten resin M to backflow, moving from the downstream side L to the upstream side U. However, in this embodiment, a gas pressure P2 due to the counter gas G2 supplied to the raw material passage 14 acts on the molten resin M from the upstream side U to the downstream side L. Therefore, the backflow of the molten resin M due to the foaming gas G1 is suppressed.
In a preferred embodiment, the supply of the foaming gas G1 through the first gas supply path 53 and the supply of the counter gas G2 through the second gas supply path 55 are controlled independently of each other in terms of supply amount and supply pressure.

[Foaming gas G1 and counter gas G2 supply pattern: Figure 5]
Next, the supply pattern of the foaming gas G1 and the counter gas G2 will be described with reference to FIG.
In the first embodiment, there are two supply patterns of the foaming gas G1 and the counter gas G2, 1-1 and 1-2.
In pattern 1-1, counter gas G2 is not supplied from the start to the middle of the plasticization process (G2 OFF), but is supplied from the middle to the end of the plasticization process (G2 ON). The factor that determines whether or not counter gas G2 needs to be supplied is the rotation speed of the screw 20. In other words, counter gas G2 is not supplied while the rotation speed is high, but is supplied when the rotation speed decreases. This is for the following reason.

While the screw 20 is rotating, the pumping action of the screw 20 can increase the pressure inside the screw groove (molten resin pressure). In particular, while the screw rotation speed is high, the pumping action of the screw 20 can prevent backflow of the molten resin M due to the gas pressure of the foaming gas G1 from the first gas supply path 53, even without the pressure of the counter gas G2. However, as the rotation speed of the screw 20 decreases, the pumping action of the screw 20 decreases, making it impossible to completely prevent backflow of the molten resin M due to the gas pressure of the foaming gas G1 from the first gas supply path 53. Therefore, when the rotation speed of the screw 20 decreases and the pumping action of the screw 20 is small, counter gas G2 is supplied from the second gas supply path 55. This effectively reduces the supply of counter gas G2 because counter gas G2 is not supplied while the rotation speed of the screw 20 is high, thereby keeping the supply amount of counter gas G2 low, which is effective in reducing injection molding costs.

However, even when the screw rotation speed changes from high to low, it is possible to continue supplying counter gas G2 from the start to the end of the plasticization process. This is pattern 1-2 shown in Figure 4.

[effect]
The effects of this embodiment will be described below.
As described above, according to the injection device 1, the counter gas G2 suppresses the backflow of the molten resin M caused by the foaming gas G1. This eliminates the need to provide an obstacle such as a dam flight that would cause flow resistance and conveyance resistance to the molten resin M in the screw groove, or even if an obstacle is provided, the height of the dam flight need not be increased to prevent the backflow of the molten resin M, thereby reducing the degree of flow resistance and conveyance resistance and suppressing a decrease in plasticizing capacity.

The injection device 1 is equipped with a shutoff mechanism 70 in the raw material passage 14, through which the counter gas G2 is supplied. This shutoff mechanism 70 prevents the counter gas G2 supplied from the first gas supply path 53 from escaping into the raw material hopper 13 in the raw material passage 14. Therefore, the shutoff mechanism 70 can prevent the counter gas G2 from being consumed unnecessarily. This effectively prevents a decrease in plasticizing capacity.

For example, if the first embodiment is applied to a two-stage screw with a dam flight or barrier flight in the first stage, as in Patent Document 1, the gas pressure P2 from the counter gas G2 can suppress the above-mentioned backflow of the molten resin M, even if the height of the dam flight or barrier flight is lowered to increase plasticization capacity.

The injection device 1 also has a sealing mechanism 80 at the very end of the upstream side U of the heating cylinder 10, which seals the gap between the heating cylinder 10 and the screw 20. Therefore, the sealing mechanism 80 also prevents unnecessary consumption of counter gas G2. This effectively prevents a decrease in plasticizing capacity.

In the injection device 1, the destination of the counter gas G2 supplied by the second gas supply path 55 is located between the raw material passage 14 and the screw 20. This allows the counter gas G2 to come into contact with the molten resin M from the time the raw material is introduced, so the counter gas G2 supplied from the second gas supply path 55 not only prevents the molten resin M from flowing back from the tip of the screw 20, but also allows the counter gas G2 to be impregnated into the molten resin M.

Furthermore, at the base of the upstream side U of the screw 20, the counter gas G2 supplied from the second gas supply passage 55 comes into contact with the resin pellets P, which are raw resin. Therefore, the counter gas G2 can penetrate the resin pellets P in this region, increasing the amount of inert gas IG dissolved in the resin pellets P. Furthermore, since the inert gas IG penetrates more easily the lower the temperature of the resin pellets P, contacting the resin pellets P with the inert gas IG at the base of the screw 20, where the resin pellets P are in a low-temperature state before melting, is effective in increasing the amount of gas dissolved in the resin pellets P. This increases the amount of foaming gas G1 impregnated into the molten resin M, allowing for the production of a foam-molded product with a high expansion ratio.

[Modification of the first embodiment: FIGS. 6(a) and 6(b)]
A modification of the first embodiment will be described with reference to FIGS. 6(a) and 6(b).
This modification relates to the destination of the counter gas G2 supplied from the second gas supply path 55.
As shown in FIG. 6( a), counter gas G2 can be supplied into the heating cylinder 10 through the sealing mechanism 80. Also, as shown in FIG. 6( b), counter gas G2 can be supplied into the heating cylinder 10 through the gap between the blocking mechanism 70 and the sealing mechanism 80. In foam molding using foaming gas G1, a core material serving as a nucleus for bubble generation is often added along with the raw resin pellets P. This core material is often in the form of fine particles or powder. Therefore, there is a risk that the core material may leak out through a gap between the outer periphery of the screw 20 and the inner periphery of the heating cylinder 10 on the upstream side U of the screw 20. To address this issue, injecting counter gas G2 as shown in FIGS. 6( a) and 6(b) not only prevents backflow of molten resin from the tip of the screw 20, but also pushes back any core material attempting to leak out by the gas pressure of the counter gas G2. Note that the screw 20 is not shown in FIG. 6.

[Second embodiment: Figs. 7 and 8]
Next, an injection device 3 according to a second embodiment will be described with reference to FIGS.
The injection device 3 includes a third gas supply path 57 in addition to the first gas supply path 53 and the second gas supply path 55. The third gas supply path 57 is adjacent to the end (left end in the drawing) of the downstream side L of the packing 81, and supplies a shielding gas G3 made of an inert gas to the processing region 11 of the heating cylinder 10. Furthermore, except for the third gas supply path 57, the configuration of the injection device 3 follows that of the injection device 1.

The third gas supply line 57 connects the gas supply source 51 to the first region 30A of the first stage 30 and includes a third supply pipe 57A that supplies the shielding gas G3 from the gas supply source 51 to the interior of the heating cylinder 10, and a third nozzle 57B located at the tip of the third supply pipe 57A. The third gas supply line 57 also includes a third valve 57C located midway along the third supply pipe 57A and controlling the supply of the shielding gas G3 toward the third nozzle 57B. The third valve 57C is opened and closed (ON/OFF) in response to instructions from the control unit 60. When the third valve 57C is turned ON, the shielding gas G3 is supplied to the processing region 11 of the heating cylinder 10, near the downstream side L of the gasket 81. Similar to the second valve 55C and the first valve 53C, the third valve 57C is independently controlled to open and close under instructions from the control unit 60, and can maintain any intermediate opening between fully open and fully closed to control the flow rate or pressure of the shielding gas G3 supplied to the third valve 57C.

The effect of supplying the shielding gas G3 from the third gas supply line 57 is as follows.
By supplying the shielding gas G3 from the third nozzle 57B, the air pressure at the end of the downstream side L of the packing 81 can be increased, or a barrier made of the shielding gas G3, i.e., an air curtain, can be generated on the downstream side L. This prevents the counter gas G2 supplied from the second gas supply passage 55 from leaking to the outside from the end of the upstream side U of the injection device 3, and suppresses a decrease in the groove pressure on the screw base side, which has been increased by the pressure of the counter gas G2 supplied from the second gas supply passage 55.
Furthermore, the third gas supply path 57 may be supplied near the end of the upstream side U of the packing 81, rather than the end of the downstream side L of the packing 81. Specifically, as shown in FIG. 9 , a packing 82 may be provided on the upstream side U of the packing 81 at a distance from the packing 81 in the direction of the central axis C, and a shielding gas G3 may be supplied between the packings 81 and 82. In this way, in addition to the air curtain effect, the shielding gas G3 supplied between the packings 81 and 82 increases the pressure between the packings 81 and 82, further crushing the packing 81 and more tightly sealing the gap between the heating cylinder 10 and the screw 20 by the packing 81. Furthermore, the shielding gas G3 supplied between the packings 81 and 82 may also function as a back pressure against the counter gas G2 supplied from the second gas supply path 55 passing through the packing 81 and leaking to the outside from the end of the upstream side U of the injection device 3.

Figure 8 shows the supply pattern of the foaming gas G1 and counter gas G2, including the shielding gas G3 supplied by the third gas supply path 57. The foaming gas G1 and counter gas G2 in Figure 8 are the same as the foaming gas G1 and counter gas G2 in Figure 5 shown for the injection device 1 of the first embodiment. While Figure 8 shows an example in which the shielding gas G3 is supplied at the same time as the counter gas G2, the shielding gas G3 may be supplied before or after the counter gas G2.

In addition to the above, the configurations given in the above embodiments can be selected or changed as appropriate to other configurations without departing from the spirit of the present invention.
For example, the second nozzle 55B of the second gas supply path 55 of the injection device 3 may be provided in the body of the heating cylinder 10, between the first nozzle 53B of the first gas supply path 53 and the raw material passage 14. In this way, the counter gas G2 can be added to the molten resin M that is about to flow back toward the upstream side U at a position close to the first nozzle 53B. In addition, the distance from the second nozzle 55B to the molten resin M that is about to flow back is short. Therefore, there is little pressure loss of the counter gas G2 from the second nozzle 55B between the second nozzle 55B and the molten resin M that is about to flow back, and gas pressure can be more reliably applied to the molten resin M, which is expected to have a significant effect of preventing backflow.

Furthermore, in the screw 20 described above, the second region 40B and the third region 40C of the second stage 40 are single-flighted flights 37, but the present invention is not limited to this. For example, as shown in Figure 9, a fin kneading section 40D as the second region can be provided downstream L of the first region 40A, which is made up of multiple flights.

As shown in Figure 10, the fin kneading section 40D is of a multi-fin type and has a plurality of fin groups 45 consisting of a plurality of plate-shaped fins 44 spaced apart in the circumferential direction, spaced apart in the direction of the central axis C.
In this way, on the downstream side L of the first region 40A consisting of multiple flights, there are provided fins 44 with relatively short length, and a region where the flow path cross-sectional area is large and flow resistance is low, where no fins 44 are provided. This region of low flow resistance includes both the spacing in the direction of the central axis C and the spacing in the circumferential direction of adjacent fins 44. By providing this fin kneading section 40D, the agitation effect and flow resistance reduction effect of the fins 44 are alternately applied to the mixture of molten resin M and foaming gas G1, thereby suppressing uneven dissolution of the gas into the molten resin M, even if the pressure of the injected foaming gas G1 is low and the amount of injected gas is small.

In the fin kneading section 40D, it is preferable that the length L44 of each fin 44 in the direction of the central axis C is 0.05D to 0.2D, and the distance L46 between adjacent fins 44 in the direction of the central axis C is 0.1D to 0.2D. Furthermore, it is preferable that the number of stages in the fin group 45 is 5 to 10.

The shutoff mechanism 70 shown in the above embodiment is an example in which the valve element 71 moves back and forth in a linear fashion. However, in the present invention, a wide range of shutoff mechanisms can be applied, such as those equipped with a rotary valve element, which can open and close the raw material passage 14 to allow and stop the flow of resin pellets P.

Furthermore, in order to prevent the groove of the screw 20 from becoming filled up, it is generally known to provide a metering type raw material supply device that measures the amount of resin pellets P supplied toward the processing region 11 and reduces the amount of resin pellets P supplied. The above-mentioned shutoff mechanism 70 can have a function of measuring the amount of resin pellets P supplied toward the processing region 11 and controlling the opening amount of the raw material passage 14, in addition to opening (fully opening) and closing (fully closing) the raw material passage 14.
By providing a gap inside the screw groove near the first nozzle 53B of the first gas supply path 53, it becomes easy to supply the foaming gas G1 into the screw groove from the first nozzle 53B. Therefore, the supply amount of the resin pellets P passing through the blocking mechanism 70 is measured to determine the supply amount of the resin pellets P per unit time to be supplied to the screw 20 inside the processing region 11. The opening of the valve body 71 is adjusted based on the supply amount per unit time to reduce the supply amount of the resin pellets P, thereby preventing the inside of the screw groove from being filled with the resin pellets P.
In this way, in addition to preventing the counter gas G2 supplied from the second gas supply path 55 from leaking into the raw material hopper 13, the blocking mechanism 70 also serves the function of adjusting the supply amount of resin pellets P, thereby eliminating the need to separately provide a measuring type raw material supply device that adjusts the supply amount of resin pellets P and a blocking mechanism, making it possible to make the device smaller.

1, 3 Injection device 10 Heating cylinder 11 Processing area 13 Raw material hopper 14 Raw material passage 18 Injection nozzle 19 Heater 20 Screw 30 First stage 30A First area 30B Second area 30C Third area 31 Flight 33 Main flight 35 Sub-flight 37 Flight 40 Second stage 40A First area 40B Second area 40C Third area 40D Fin kneading section 41, 43 Flight 44 Fin 45 Fin group 50 Gas supply mechanism 51 Gas supply source 53 First gas supply path 53A First supply pipe 53B First nozzle 53C First valve 55 Second gas supply path 55A Second supply pipe 55B Second nozzle 55C Second valve 57 Third gas supply path 57A Third supply pipe 57B Third nozzle 57C Third valve 60 Control unit 70 Shutoff mechanism 71 Valve body 73 Valve seat 75 Driving source 80 Sealing mechanisms 81, 82 Packing 83 Packing support 83A Fixed cylinder 83B Fixed flange C Central axis G1 Foaming gas G2 Counter gas G3 Shielding gas IG Inert gas M Molten resin P Resin pellets P1, P2 Gas pressure U Upstream side L Downstream side

Claims (11)

a heating cylinder provided with an injection nozzle;
a screw provided inside the heating cylinder, the screw being rotatable about a central axis and being capable of advancing downstream and retracting upstream along the central axis;
a first gas supply passage for supplying a foaming gas to be injected into the molten resin inside the heating cylinder into the heating cylinder;
a second gas supply passage for supplying a counter gas into the heating cylinder, the counter gas flowing in opposition to the backflow of the molten resin toward the upstream side;
a raw material hopper for holding a resin raw material and supplying the resin raw material to the inside of the heating cylinder through a raw material passage;
a shutoff mechanism for opening or closing the ingredient passage;
An injection device for foam molding, comprising:
a sealing mechanism that airtightly seals the upstream end of the heating cylinder;
2. The injection device for foam molding according to claim 1.
The counter gas supply port of the second gas supply path is
provided in the raw material passage between the blocking mechanism and the heating cylinder;
3. The foam molding injection device according to claim 1 or 2.
The counter gas supply port of the second gas supply path is
The sealing mechanism is provided with:
3. The injection device for foam molding according to claim 2 .
The counter gas supply port of the second gas supply path is
provided downstream of the sealing mechanism;
5. The foam molding injection device according to claim 2 or 4.
a third gas supply path for supplying a shielding gas that suppresses leakage of the counter gas from a portion sealed by the sealing mechanism;
3. The injection device for foam molding according to claim 2.
The blocking mechanism includes:
a function of measuring the amount of the resin raw material supplied to the heating cylinder through the blocking mechanism;
4. The foam molding injection device according to claim 1 or 3.
The foaming gas from the first gas supply line and the counter gas from the second gas supply line are controlled independently of each other.
8. The injection device for foam molding according to claim 1.
a heating cylinder provided with an injection nozzle;
a screw provided inside the heating cylinder, the screw being rotatable about a central axis and being capable of advancing downstream and retracting upstream along the central axis;
a first gas supply passage for supplying a foaming gas to be injected into the molten resin inside the heating cylinder into the heating cylinder;
a second gas supply passage that supplies a counter gas into the heating cylinder that flows in opposition to the backflow of the molten resin toward the upstream side,
The counter gas from the second gas supply line
Supplied based on the rotation speed of the screw.
1. An injection device for foam molding, comprising:
The resin raw material supplied to the inside of the heating cylinder is heated and melted into molten resin, and is transported from the upstream side to the downstream side by the rotational driving force of the screw.
In the process of conveying, a foaming gas is injected into the molten resin and dissolved therein,
supplying a counter gas into the heating cylinder in a direction opposite to the backflow of the molten resin toward the upstream side;
a raw material passage for supplying the resin raw material from the raw material hopper to the inside of the heating cylinder is opened during the plasticizing process and closed when the plasticizing process is completed;
An injection foam molding method characterized by:
The resin raw material supplied to the inside of the heating cylinder is heated and melted into molten resin, and is transported from the upstream side to the downstream side by the rotational driving force of the screw.
In the process of conveying, a foaming gas is injected into the molten resin and dissolved therein,
a counter gas that opposes the backflow of the molten resin toward the upstream side is supplied into the heating cylinder based on the rotation speed of the screw;
An injection foam molding method characterized by: