JP7128015B2 - Manufacturing method and manufacturing apparatus for foam molded product - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and apparatus for manufacturing a foam molded article.

In recent years, an injection foam molding method using supercritical nitrogen or carbon dioxide as a physical foaming agent has been researched and put into practical use (Patent Documents 1 to 3). According to these Patent Documents 1 to 3, the injection foam molding method using a physical foaming agent is carried out as follows. First, a physical blowing agent is introduced into a closed plasticizing cylinder and contacted and dispersed in the plasticized molten resin. While maintaining the inside of the plasticizing cylinder at a high pressure to the extent that the physical foaming agent is in a supercritical state, the molten resin in which the physical foaming agent is dispersed is weighed and injected into the mold. The supercritical fluid that is compatible with the molten resin is rapidly depressurized and gasified at the time of injection filling, and the molten resin solidifies to form bubbles (foamed cells) inside the molded body. In these injection foam molding methods, the physical blowing agent is metered at a pressure slightly higher than the internal pressure of the resin and introduced into the plasticizing cylinder after metering. Therefore, the amount of the physical blowing agent dissolved in the molten resin is determined by the introduction amount of the physical blowing agent (introduction amount control).

Further, Patent Document 4 discloses a method of introducing a physical foaming agent into a plasticizing cylinder by pressure control instead of controlling the amount of introduction in an injection foam molding method using a physical foaming agent. In Patent Document 4, a starvation zone in which the molten resin is not filled is provided in the plasticizing cylinder, and a physical blowing agent is introduced into the starvation zone at a constant pressure. In the starvation zone, the starved molten resin is brought into contact with a physical blowing agent under a constant pressure to allow the physical blowing agent to permeate the molten resin. The starvation zone is then always kept at a constant pressure of the introduced physical blowing agent.

Japanese Patent No. 2625576 Japanese Patent No. 3788750 Japanese Patent No. 4144916 Japanese Patent No. 6139038

In the injection foam molding methods of Patent Documents 1 to 3, it was necessary to set the physical foaming agent to be introduced into the plasticizing cylinder at a high pressure and to accurately measure the introduction amount. This complicates the supply mechanism of the physical foaming agent and increases the initial cost of the device.

On the other hand, in the injection foam molding method of Patent Document 4, since the physical foaming agent is introduced into the plasticizing cylinder under pressure control, there is no need to control the introduction amount, introduction time, etc. of the physical foaming agent into the molten resin. Therefore, the injection foam molding method of Patent Document 4 can omit or simplify a complicated control device, and can reduce the cost of the device. In addition, the amount of physical foaming agent dissolved in the molten resin (permeation amount) can be stabilized by a simple mechanism.

Injection foam molding methods in which a physical foaming agent is introduced into a plasticizing cylinder under pressure control are being further improved so that high-quality foam molded articles can be stably produced. For example, it is preferable to further suppress the separation of the physical foaming agent from the molten resin, which causes enlargement and unevenness of foam cell diameter.

The present invention is intended to solve the above problems, and provides a method for suppressing separation of a physical foaming agent from a molten resin and stably producing a high-quality foam-molded product.

According to the first aspect of the present invention, there is provided a method for producing a foam molded article, comprising a screw provided inside so as to be rotatable and advanceable and retractable, and a thermoplastic resin being plasticized and melted to become a molten resin. and a starvation zone in which the molten resin is in a starvation state. , plasticizing and melting the thermoplastic resin into the molten resin in the plasticization zone; and pressurizing the physical blowing agent in the starvation zone with a first pressure that is a constant pressure. introducing a fluid; starving the molten resin in the starvation zone; and contacting the starved molten resin with a pressurized fluid at the first pressure in the starvation zone. and weighing a predetermined amount of the molten resin brought into contact with the pressurized fluid of the first pressure, and injecting the weighed molten resin from the plasticizing cylinder to form the foam molded body. holding the screw back pressure at a second pressure higher than the first pressure until the completion of the metering of the molten resin, and maintaining the screw back pressure from the completion of the metering of the molten resin to the start of injection A method for producing a foam molded article is provided, characterized in that the pressure is maintained at a third pressure equal to or higher than the second pressure .

From the completion of metering of the molten resin to the start of injection, the pressure of the metered molten resin may be maintained at a pressure higher by 0.5 MPa to 10 MPa than the first pressure.

The second pressure and the third pressure may be the same.

The screw is provided in the plasticizing cylinder so as to move forward and backward from the plasticization zone to the starvation zone and rearward from the starvation zone to the plasticization zone. Inside, there is a tip sealing mechanism that suppresses the molten resin from flowing back from the front to the rear, and the tip sealing mechanism includes a screw head positioned at the front end of the screw, and a screw head located at the front end of the screw. a back-positioned abutment ring, a shaft connecting the screw head and the abutment ring, and a shaft loosely fitted to the shaft so as to be movable forward and backward between the screw head and the abutment ring. check ring.

The ratio (S1/S2) of the pressure-receiving area S1 on the front side of the check ring to the pressure-receiving area S2 on the rear side is 0.6 to 0.95 when the check ring is positioned at the most forward position. may The check ring is formed with a through-hole through which the shaft passes, and a part of the inner wall defining the through-hole of the check ring is formed from the rear end of the through-hole and the inner diameter of the rear end. forming a first tapered surface connecting a small inner diameter portion having a small inner diameter, the shaft connecting the connection portion with the impingement ring and the small diameter portion having a diameter smaller than the diameter of the connection portion; The taper ratio of the first tapered surface and the taper ratio of the second tapered surface are substantially the same, and as the check ring moves forward and backward, the first tapered surface and the second tapered surface may be spaced apart and in contact with each other. A groove may be formed in the outer surface of the check ring, and the groove may form a labyrinth structure in the outer surface of the check ring. In the plasticizing cylinder, the screw is capable of forward rotation for sending the molten resin forward and reverse rotation opposite to the forward rotation, and the tip seal mechanism rotates the screw in the reverse direction. has a lock mechanism for maintaining the state in which the check ring abuts against the abutment ring, and the method for manufacturing the foam molded article comprises rotating the screw in the reverse direction after completion of weighing the molten resin, and The check ring may maintain contact with the abutment ring.

According to the second aspect of the present invention, there is provided a manufacturing apparatus for manufacturing a foamed molded article, which includes a screw provided therein so as to be rotatable and forward/backward, and a thermoplastic resin is plasticized and melted to become a molten resin. It has a plasticization zone and a starvation zone in which the molten resin is in a starvation state, an introduction port for introducing a physical blowing agent is formed in the starvation zone, and a certain amount of the molten resin is measured and discharged to the outside. a plasticizing cylinder for injection; a physical blowing agent supply mechanism for supplying a physical blowing agent at a first pressure, which is a constant pressure, to the plasticizing cylinder ; 1, and the screw back pressure is maintained at a third pressure higher than the second pressure from the completion of metering of the molten resin to the start of injection. A manufacturing apparatus is provided, comprising: a pressure holding mechanism;

The pressure holding mechanism may be a mechanism that holds the pressure of the metered molten resin at a pressure higher by 0.5 MPa to 10 MPa than the first pressure from the completion of metering of the molten resin to the start of injection. . The pressure holding mechanism may be a screw driving mechanism that controls screw back pressure. Further, the screw is provided so as to move forward and backward from the plasticization zone to the starvation zone and rearward from the starvation zone to the plasticization zone in the plasticization cylinder. A front end sealing mechanism may be provided to prevent the molten resin from flowing back from the front to the rear in the curing cylinder, and the pressure holding mechanism may be the front end sealing mechanism. In the plasticizing cylinder, the screw is capable of forward rotation for sending the molten resin forward and reverse rotation opposite to the forward rotation. an abutment ring positioned behind the screw head; a shaft connecting the screw head and the abutment ring; A check ring that can move forward and backward between the ring and a lock mechanism that maintains a state in which the check ring is in contact with the abutment ring by rotating the screw in the reverse direction. .

The method for producing a foam-molded article of the present invention suppresses the separation of the physical foaming agent from the molten resin, and provides a production method for stably producing a high-quality foam-molded article.

4 is a flow chart showing a method for manufacturing a foam molded article according to the first embodiment. 1 is a schematic diagram of an apparatus for manufacturing a foam molded article used in the first embodiment; FIG. FIG. 3(a) is a diagram showing a state in the middle of measuring the molten resin in the first embodiment, and FIG. 3(b) is a diagram showing a state at the completion of the measurement of the molten resin. FIG. 4(a) is a diagram showing the pressure detected by the pressure sensor (load cell) of the screw drive mechanism and the pressure in the starvation zone when screw back pressure is applied after the completion of weighing of the molten resin in the first embodiment. FIG. 4(b) is a diagram showing the pressure detected by the pressure sensor (load cell) and the pressure in the starvation zone when screw back pressure is not applied after the completion of metering of the molten resin. FIG. 5(a) is a diagram showing a state in which the check ring is positioned forwardmost in the tip seal mechanism used in the second embodiment, and FIG. FIG. 5C is a diagram showing a state in which neither the head nor the abutment ring are in contact with each other, and FIG. 5(d) is a cross-sectional view of the DD' cross section in FIG. 5(a), and FIG. 5(e) is a cross-sectional view of the EE' cross section in FIG. 5(a). (f) is a cross-sectional view taken along the line FF' in FIG. 5(c). FIG. 6(a) is a cross-sectional view of the DD′ cross section of the tip seal mechanism used in the second embodiment shown in FIG. 5(a), and FIG. 6(b) is a tip of another example. FIG. 4 is a cross-sectional view of a partial sealing mechanism; FIG. 7(a) is a diagram showing a state in which the check ring is positioned furthest forward in the tip seal mechanism used in Modification 1 of the second embodiment, and FIG. It is a figure which shows the state located behind. FIG. 7(c) is a diagram showing only the check ring, and FIG. 7(d) is a diagram showing the components (screw head, shaft and abutment ring) of the tip seal mechanism other than the check ring. FIG. 8(a) is a diagram showing a state in which the check ring is positioned most forward in the tip sealing mechanism used in Modification 2 of the second embodiment, and FIG. 8(b) is a main body of the check ring. Fig. 8(c) is a diagram showing a state in which the ring is not in contact with both the screw head and the abutment ring, and Fig. 8(c) is a diagram showing a state in which the check ring is positioned at the rearmost position; FIG. 9(a) is a diagram showing a state in which the check ring is positioned most forward in the distal end sealing mechanism used in Modification 3 of the second embodiment, and FIG. 9(b) is a main body of the check ring. Fig. 9(c) shows a state where the ring is not in contact with both the screw head and the abutment ring, and Fig. 9(c) shows a state where the check ring is positioned at the rearmost position;

[First Embodiment]
A method for producing a foam molded article according to the present embodiment will be described with reference to the flowchart shown in FIG. The method for producing a foam molded article of the present embodiment can be carried out using, for example, a production apparatus 1000 shown in FIG. First, the manufacturing apparatus 1000 will be described.

<Production equipment for foam molding>
A manufacturing apparatus (injection molding machine) 1000 mainly includes a plasticizing cylinder 210 in which a screw 20 is installed, a screw drive mechanism 260 that drives the screw 20, and a physical foaming agent that supplies a physical foaming agent to the plasticizing cylinder 210. Equipped with a cylinder 100 as an agent supply mechanism, a mold clamping unit 250 provided with a mold 251, and a control device (not shown) for controlling the operations of the plasticizing cylinder 210, the screw drive mechanism 260, and the mold clamping unit 250. .

The molten resin that is plasticized and melted in the plasticizing cylinder 210 flows from right to left in FIG. Therefore, inside the plasticizing cylinder 210 of this embodiment, the right hand in FIG. 2 is defined as "upstream" or "rear", and the left hand is defined as "downstream" or "forward". The direction in which the plasticizing cylinder 210 and the screw 20 extend (the axial direction of the screw 20 and the flow direction of the molten resin) is defined as the "front-rear direction". Further, in the plasticizing cylinder 210 of the present embodiment, similarly to the configuration of a conventionally known plasticizing cylinder, when viewed from the rear side of the plasticizing cylinder 210, when the screw 20 is rotated counterclockwise, the molten resin is expelled. It is configured to rotate in the forward direction and rotate in the reverse direction when rotated clockwise.

The plasticizing cylinder 210 has a plasticizing zone 21 in which the thermoplastic resin is plasticized and melted to become molten resin, and a starvation zone 23 downstream of the plasticizing zone 21 in which the molten resin starves. The “starvation state” is a state in which the molten resin does not fill the starvation zone 23 but does not fill the starvation zone 23 . Therefore, in the starvation zone 23, there exists a space other than the portion occupied by the molten resin. Also, an inlet 202 for introducing the physical foaming agent is formed in the starvation zone 23 , and the inlet 202 is connected to an introduction speed adjusting container 300 . The cylinder 100 supplies the physical blowing agent to the plasticizing cylinder 210 through the introduction speed adjusting container 300 .

The screw drive mechanism 260 is connected to the upstream rear end of the plasticizing cylinder 210 and includes a screw rotation drive mechanism including a screw rotation motor M2 and a transmission means 262, a screw forward/backward movement motor M1 and a transmission means 263. It has a screw moving mechanism and a pressure sensor 261 such as a load cell that detects the pressure applied to the screw 20 . The screw rotating motor M2 rotates the screw 20 forward and backward through a transmission means 262 composed of a pulley, a belt, and the like. The screw forward/backward motor M1 moves the screw 20 forward/backward via a transmission means 263 that converts rotary motion of a pulley, belt, ball screw/nut mechanism, or the like into linear motion. This allows the screw 20 to advance forward from the plasticization zone 21 to the starvation zone 23 and to retract backwards from the starvation zone 23 to the plasticization zone 21 .

The magnitude of the pressure applied to the screw 20 detected by the pressure sensor 261 is the magnitude of the pressure of the molten resin positioned in front of the screw 20. When the screw back pressure is applied to the screw 20, , is also the magnitude of the screw back pressure. The “screw back pressure” is the force that pushes the screw 20 forward from the rear. For example, when the resin is plasticized and weighed, that is, when the screw 20 rotates forward, the molten resin is sent to the front of the plasticizing cylinder 210, and the screw 20 is retracted by the resin pressure. Apply a pushing force (screw back pressure) from the rear to the front. At this time, the screw back pressure and the pressure of the molten resin positioned in front of the screw 20 are equal. The pressure detected by the pressure sensor 26 is the pressure of the molten resin positioned in front of the screw 20 and also the screw back pressure. In this embodiment, screw back pressure is controlled by screw drive mechanism 260 .

On the other hand, when no screw back pressure is applied, that is, when the screw back pressure is 0 (zero), the pressure sensor 261 detects only the pressure of the molten resin positioned in front of the screw 20 . For example, when the screw back pressure is set to 0 (zero) after a predetermined amount of molten resin has been measured, the pressure detected by the pressure sensor 261 is the pressure of the measured molten resin located in front of the screw 20. be.

The screw 20 has a tip sealing mechanism 50 including a check ring 52 at its forward end. The tip seal mechanism 50 prevents the compressed resin in front of the screw 20 from flowing backward.

Although the manufacturing apparatus 1000 has only one starvation zone 23, the manufacturing apparatus used in this embodiment is not limited to this. For example, in order to promote penetration of the physical foaming agent into the molten resin, the starvation zone 23 and a plurality of inlets 202 formed therein are provided, and the physical foaming agent is introduced into the plasticizing cylinder 210 from the plurality of inlets 202. It may be a structure that

<Method for producing foam molded product>
(1) Plasticization and Melting of Thermoplastic Resin First, in the plasticizing zone 21 of the plasticizing cylinder 210, the thermoplastic resin is plasticized and melted to form a molten resin (step S1 in FIG. 1). Various resins can be used as the thermoplastic resin depending on the type of the desired molded article. Specifically, for example, polypropylene, polymethyl methacrylate, polyamide, polycarbonate, amorphous polyolefin, polyetherimide, polyethylene terephthalate, polyether ether ketone, ABS resin (acrylonitrile-butadiene-styrene copolymer resin), polyphenylene sulfide, polyamide Thermoplastic resins such as imide, polylactic acid, polycaprolactone, and composite materials thereof can be used. These thermoplastic resins may be used alone or in combination of two or more.

In addition, it is also possible to use those obtained by kneading various inorganic fillers such as glass fiber, talc, and carbon fiber with these thermoplastic resins. The thermoplastic resin is preferably mixed with an inorganic filler that functions as a foam nucleating agent or an additive that increases melt tension. By mixing these, foamed cells can be made finer. The thermoplastic resin of the present embodiment may contain various general-purpose additives as needed. Further, the thermoplastic resin of this embodiment may contain a general-purpose chemical blowing agent. Foaming performance can be complemented by the addition of small amounts of chemical blowing agents.

In this embodiment, the thermoplastic resin is plasticized and melted in a plasticizing cylinder 210 in which the screw 20 shown in FIG. 2 is installed. A band heater (not shown) is provided on the outer wall surface of the plasticizing cylinder 210, which heats the plasticizing cylinder 210 and further heats sheared by rotation of the screw 20, thereby plasticizing the thermoplastic resin. melted.

(2) Introduction of Physical Foaming Agent Next, a physical foaming agent is introduced into the starvation zone 23 at a constant pressure (first pressure) (step S2 in FIG. 1).

A pressurized fluid is used as the physical blowing agent. In this embodiment, "fluid" means any one of liquid, gas, and supercritical fluid. Moreover, the physical blowing agent is preferably carbon dioxide, nitrogen, or the like from the viewpoint of cost and environmental load. Since the pressure of the physical foaming agent of the present embodiment is relatively low, for example, from a cylinder storing fluid such as a nitrogen cylinder, a carbon dioxide cylinder, an air cylinder, etc., the fluid taken out after being decompressed to a certain pressure by a pressure reducing valve can be used. In this case, the cost of the entire manufacturing apparatus can be reduced because the booster is not required. Also, if necessary, a fluid pressurized to a predetermined pressure may be used as a physical foaming agent. For example, when nitrogen is used as the physical blowing agent, the physical blowing agent can be produced by the following method. First, nitrogen is purified through a nitrogen separation membrane while compressing atmospheric air with a compressor. Next, the purified nitrogen is pressurized to a predetermined pressure using a booster pump, a syringe pump, or the like to generate a physical blowing agent. Compressed air may also be used as a physical foaming agent. In this embodiment, the physical blowing agent and the molten resin are not subjected to forced shear kneading. Therefore, even if compressed air is used as a physical blowing agent, oxygen, which has a low solubility in the molten resin, is difficult to dissolve in the molten resin, and oxidative deterioration of the molten resin can be suppressed.

The pressure (first pressure) of the physical foaming agent introduced into starvation zone 23 is constant. The pressure of this foaming agent (first pressure) is preferably 1 MPa to 15 MPa, more preferably 1 MPa to 10 MPa, and even more preferably 2 MPa to 8 MPa. The optimum pressure varies depending on the type of molten resin, but by setting the pressure of the physical foaming agent to 1 MPa or more, the amount of physical foaming agent necessary for foaming can be penetrated into the molten resin, and the pressure is 15 MPa or less. By doing so, the device load can be reduced.

Further, in the present embodiment, only the physical blowing agent is introduced into the starvation zone 23, but other pressurized fluids other than the physical blowing agent are simultaneously introduced into the starvation zone 23 to the extent that the effect of the present embodiment is not affected. You may In this case, the pressurized fluid containing the physical blowing agent introduced into the starvation zone 23 has the constant pressure mentioned above.

In this embodiment, as shown in FIG. 2 , the physical foaming agent is supplied from the cylinder 100 to the starvation zone 23 through the introduction port 202 via the introduction speed adjusting container 300 . The physical foaming agent is decompressed to a predetermined pressure using the decompression valve 151, and then introduced into the starvation zone 23 from the inlet 202 without passing through a booster or the like. In this embodiment, the introduction amount of the physical foaming agent introduced into the plasticizing cylinder 210, introduction time, etc. are not controlled. Therefore, a mechanism for controlling them, for example, a driven valve using a check valve, an electromagnetic valve, or the like, is unnecessary in the section from the pressure reducing valve 151 to the introduction port 202 . Also in this embodiment, the section from the pressure reducing valve 151 to the introduction port 202 does not have a driven valve and is always open. A check valve or an electromagnetic valve may be provided in the section from the pressure reducing valve 151 to the introduction port 202, but it shall always be open during the period of the continuous molding cycle. The starvation zone 23 moves back and forth in the plasticizing cylinder 210 as the screw 20 advances and retreats, but the introduction port 202 is provided so as to always be positioned in the starvation zone 23 .

The physical foaming agent introduction port 202 has a larger inner diameter than the physical foaming agent introduction port of the conventional manufacturing apparatus. Therefore, even a relatively low-pressure physical foaming agent can be efficiently introduced into the plasticizing cylinder 210 . Further, even if a part of the molten resin contacts the inlet 202 and solidifies, it can function as an inlet without being completely blocked due to the large inner diameter. For example, when the inner diameter of the plasticizing cylinder 210 is large, that is, when the outer diameter of the plasticizing cylinder is large, it is easy to increase the inner diameter of the introduction port 202 . On the other hand, if the inner diameter of the introduction port 202 is too large, the molten resin will stagnate and cause molding defects, and the size of the introduction speed adjusting container 300 connected to the introduction port 202 will increase, increasing the cost of the entire apparatus. . Specifically, the inner diameter of the introduction port 202 is preferably 20% to 100%, more preferably 30% to 80%, of the inner diameter of the plasticizing cylinder 210 . Alternatively, regardless of the inner diameter of the plasticizing cylinder 210, the inner diameter of the introduction port 202 is preferably 3 mm to 100 mm, more preferably 5 mm to 50 mm. Here, the inner diameter of the introduction port 202 means the inner diameter of the opening on the inner wall of the plasticizing cylinder 210 . Moreover, the shape of the inlet 202, that is, the shape of the opening on the inner wall of the plasticizing cylinder 210 is not limited to a perfect circle, and may be an ellipse or a polygon. When the shape of the introduction port 202 is elliptical or polygonal, the diameter of a perfect circle having the same area as the area of the introduction port 202 is defined as the "inner diameter of the introduction port 202".

The introduction speed adjusting container 300 connected to the introduction port 202 has a volume equal to or greater than a certain value, thereby slowing down the flow rate of the physical foaming agent introduced into the plasticizing cylinder 210, so that the physical foaming agent is introduced into the introduction speed adjusting container 300. You can secure the time you can stay. By staying in the vicinity of the heated plasticizing cylinder 210, the physical blowing agent is heated, the temperature difference between the physical blowing agent and the molten resin becomes small, and the amount of dissolution (permeation amount) of the physical blowing agent into the molten resin ) can be stabilized. That is, the introduction speed adjusting container 300 functions as a buffer container. On the other hand, if the volume of the introduction speed adjusting container 300 is too large, the cost of the entire device increases. The volume of the introduction speed adjusting container 300 depends on the amount of molten resin present in the starvation zone 23, but is preferably 5 mL to 10 L, more preferably 10 mL to 1 L. By setting the volume of the introduction speed adjusting container 300 within this range, it is possible to secure a time during which the physical foaming agent can stay while considering the cost.

As will be described later, the physical foaming agent is consumed in the plasticizing cylinder 210 by contacting and permeating the molten resin. In order to keep the pressure in the starvation zone 23 constant, the consumed physical blowing agent is introduced into the starvation zone 23 from the introduction rate adjusting vessel 300 . If the volume of the introduction speed adjusting container 300 is too small, the replacement frequency of the physical blowing agent becomes high, so the temperature of the physical blowing agent becomes unstable, and as a result, there is a possibility that the supply of the physical blowing agent becomes unstable. Therefore, the introduction speed adjusting container 300 preferably has a volume capable of retaining the amount of physical foaming agent consumed in the plasticizing cylinder for 1 to 10 minutes.

The introduction speed adjusting container 300 may be a separate container from the plasticizing cylinder 210 , or may be integrally formed with the plasticizing cylinder 210 and constitute a part of the plasticizing cylinder 210 .

(3) Starvation of Molten Resin Next, the molten resin is made to flow into the starvation zone 23, and the molten resin is starved in the starvation zone 23 (step S3 in FIG. 1). The starvation state is determined by the balance between the amount of molten resin sent from the upstream of the starvation zone 23 to the starvation zone 23 and the amount of molten resin sent from the starvation zone 23 to the downstream thereof. becomes.

In this embodiment, the molten resin is starved in the starvation zone 23 by providing the compression zone 22 in which the molten resin is compressed and the pressure increases upstream of the starvation zone 23 . The compression zone 22 is provided with a large-diameter portion 20A in which the diameter of the shaft of the screw 20 is made larger (thicker) than that of the plasticizing zone 21 located on the upstream side, and the screw flights are gradually shallowed. A ring 26 is provided on the border with the starvation zone 23 adjacent to the downstream side of 20A. The ring 26 has a half-split structure, and is split into two and placed over the screw 20 . By increasing the diameter of the shaft of the screw 20, the large-diameter portion 20A and the ring 26 reduce the clearance between the inner wall of the plasticizing cylinder 210 and the screw 20, thereby reducing the amount of resin to be supplied downstream. Increases flow resistance. Therefore, in the present embodiment, the large-diameter portion 20A and the ring 26 are mechanisms that increase the flow resistance of the molten resin. The ring 26 also has the effect of suppressing the reverse flow of the physical foaming agent, that is, the movement of the physical foaming agent from the downstream side to the upstream side of the seal portion 26 .

Due to the presence of the large diameter portion 20A and the ring 26, the resin flow rate supplied from the compression zone 22 to the starvation zone 23 is reduced, the molten resin is compressed in the compression zone 22 on the upstream side, the pressure increases, and the starvation zone on the downstream side At 23, the molten resin becomes insufficient (starved state). In order to promote the starvation state of the molten resin, the screw 20 has a structure in which the shaft diameter of the portion located in the starvation zone 23 is smaller (thinner) and the screw flight is deeper than the portion located in the compression zone 22. have

The mechanism for increasing the flow resistance of the molten resin provided in the compression zone 22 is a mechanism for temporarily reducing the flow area through which the molten resin passes in order to limit the flow rate of the resin supplied from the compression zone 22 to the starvation zone 23. If there is, it is not particularly limited. Although both the large-diameter portion 20A of the screw and the ring 26 are used in this embodiment, only one of them may be used. Mechanisms for increasing the flow resistance other than the large-diameter portion 20A of the screw and the ring 26 include a structure in which screw flights are provided in the opposite direction to other portions, a labyrinth structure provided on the screw, and the like.

The mechanism for increasing the flow resistance of the molten resin may be provided on the screw as a separate member such as a ring from the screw, or may be provided integrally with the screw as a part of the structure of the screw. If the mechanism for increasing the flow resistance of the molten resin is provided as a ring or the like, which is a separate member from the screw, the size of the clearance, which is the flow path of the molten resin, can be changed by changing the ring, so the flow of the molten resin can be easily controlled. It has the advantage of being able to change the magnitude of the resistance.

In addition to the mechanism that increases the flow resistance of the molten resin, a backflow prevention mechanism (sealing mechanism) that prevents the molten resin from flowing back from the starvation zone 23 to the compression zone 22 upstream is provided between the compression zone 22 and the starvation zone 23. This also allows the molten resin to be starved in the starvation zone 23 . For example, a seal mechanism such as a ring or steel ball that can be moved upstream by the pressure of the physical foaming agent can be used. However, since the backflow prevention mechanism requires a drive unit, there is a risk of resin stagnation. Therefore, a mechanism that does not have a drive unit and increases flow resistance is preferable.

In this embodiment, in order to stabilize the starvation state of the molten resin in the starvation zone 23, the amount of thermoplastic resin supplied to the plasticizing cylinder 210 may be controlled. This is because if the amount of thermoplastic resin supplied is too large, it will be difficult to maintain the starvation state. In this embodiment, a general-purpose feeder screw 212 is used to control the amount of thermoplastic resin supplied. The rate of molten resin metering in the starvation zone 23 is greater than the plasticization rate in the compression zone 22 due to the limited supply of thermoplastic resin. As a result, the density of the molten resin in the starvation zone 23 is stably lowered, promoting the permeation of the physical foaming agent into the molten resin.

In this embodiment, the length of the starvation zone 23 in the front-rear direction is preferably long in order to secure the contact area and contact time between the molten resin and the physical blowing agent, but if it is too long, the molding cycle and screws become long. occur. Therefore, the length of the starvation zone 23 is preferably 2 to 12 times the inner diameter of the plasticizing cylinder 210, more preferably 4 to 10 times. Also, the length of starvation zone 23 preferably covers the full range of metering strokes in injection molding. That is, the length of the starvation zone 23 in the flow direction of the molten resin is preferably equal to or longer than the length of the metering stroke in injection molding. The screw 20 moves forward and backward as the resin is plasticized, metered, and injected. 202 can be placed (formed) within the starvation zone 23 . In other words, no zone other than the starvation zone 23 will come to the position of the inlet 202 even if the screw 20 moves forward and backward during the production of the foam molding. Thereby, the physical foaming agent introduced from the introduction port 202 is always introduced into the starvation zone 23 during the production of the foam molded product. The length of the starvation zone 23 of this embodiment, as shown in FIG. 2, is the length from the downstream of the ring 26 in the screw 20 to the upstream of the recompression zone 24 where the molten resin is compressed and the pressure increases, which will be described later. be. In the starvation zone 23 of this embodiment, the shaft diameter of the screw 20 and the depth of the screw flight are constant.

(4) Contact between Molten Resin and Physical Foaming Agent Next, the starved molten resin is brought into contact with a physical foaming agent at a constant pressure (first pressure) in the starvation zone 23 (step S4 in FIG. 1). That is, in the starvation zone 23, the molten resin is pressurized with a constant pressure by a physical foaming agent. Since the starvation zone 23 is not filled with the molten resin (starved state) and has a space in which the physical foaming agent can exist, the physical foaming agent and the molten resin can be efficiently brought into contact with each other. The physical blowing agent that comes into contact with the molten resin permeates the molten resin and is consumed. When the physical blowing agent is consumed, the physical blowing agent remaining in the introduction rate adjusting container 300 is supplied to the starvation zone 23, and the molten resin continues to contact the physical blowing agent at constant pressure. Starvation zone 23 is always kept at a constant pressure (first pressure).

In addition, the pressure (first pressure) of the starvation zone 23 is "constant" means that the fluctuation width of the pressure with respect to the predetermined pressure is preferably within ±10%, more preferably within ±5%. do. The pressure in the starvation zone 23 is measured by a pressure sensor (not shown) provided within the starvation zone 23 , eg at a position opposite the inlet 202 of the plasticizing cylinder 210 .

In conventional foam molding using a physical foaming agent, a predetermined amount of high-pressure physical foaming agent is forcibly introduced into a plasticizing cylinder within a predetermined time. Therefore, it is necessary to pressurize the physical blowing agent to a high pressure and accurately control the amount of introduction into the molten resin, the introduction time, etc., and the physical blowing agent is in contact with the molten resin only for a short introduction time. . In contrast, in the present embodiment, instead of forcibly introducing the physical foaming agent into the plasticizing cylinder 210, the physical foaming agent is continuously supplied into the plasticizing cylinder 210 at a constant pressure, and the physical foaming agent is continuously supplied to the plasticizing cylinder. The agent is brought into contact with the molten resin. This stabilizes the amount of physical foaming agent dissolved in the molten resin (permeation amount), which is determined by temperature and pressure. Moreover, since the physical foaming agent of this embodiment is always in contact with the molten resin, a necessary and sufficient amount of the physical foaming agent can penetrate into the molten resin. As a result, the foamed molded article produced in the present embodiment has finer foam cells despite the fact that the physical foaming agent is used at a lower pressure than in the conventional molding method using a physical foaming agent.

In addition, since the production method of the present embodiment does not require control of the introduction amount of the physical foaming agent, the introduction time, etc., drive valves such as check valves and electromagnetic valves, and control mechanisms for controlling these are unnecessary. Equipment costs can be reduced. Moreover, since the physical foaming agent used in this embodiment has a lower pressure than the conventional physical foaming agent, the load on the apparatus is also small.

In this embodiment, all the steps of the method for producing a foam molded product are carried out while continuously supplying the physical blowing agent at a constant pressure in order to compensate for the consumed physical blowing agent in the plasticizing cylinder. . In addition, in the present embodiment, for example, when injection molding is continuously performed for a plurality of shots, the molten resin for the next shot is supplied during the injection process, the cooling process for the molded body, and the process for taking out the molded body. Prepared in a plasticizing cylinder, the next shot of molten resin is pressurized at a constant pressure by a physical foaming agent. In other words, in the continuous injection molding of multiple shots, the molten resin and the physical foaming agent at a constant pressure are always present and in contact with each other in the plasticizing cylinder. One cycle of injection molding including a plasticizing and weighing process, an injection process, a cooling process of the molded body, a taking-out process, etc. is carried out in a state of being constantly pressurized at a constant pressure by the agent.

(5) Weighing of Molten Resin Next, a predetermined amount of the molten resin brought into contact with the physical foaming agent is weighed (step S5 in FIG. 1). FIG. 3(a) shows a state in the middle of weighing the molten resin, and FIG. 3(b) shows a state after the completion of weighing the molten resin. The plasticizing cylinder 210 used in this embodiment has a recompression zone 24 located downstream of the starvation zone 23 and adjacent to the starvation zone 23 where the molten resin is compressed to increase pressure. First, the screw 20 rotates forward to flow the molten resin in the starvation zone 23 to the recompression zone 24 . The molten resin containing the physical blowing agent is pressure adjusted in the recompression zone 24 . By further rotating the screw 20 in the forward direction, the molten resin is sent to the front of the plasticizing cylinder 210, and the screw 20 is retracted by the resin pressure. As shown in FIGS. 3(a) and 3(b), by retracting the screw 20, a metering zone 25 is formed in front of the screw 20, and a predetermined amount of molten resin (one shot of molten resin) is placed in the metering zone 25. ) is weighed.

In the present embodiment, from the start of plasticization of the thermoplastic resin to the completion of metering of the molten resin (during the plasticization and metering of the resin), the screw 20 is provided with a screw back pressure higher than the constant pressure (first pressure) in the starvation zone 23. (second pressure) is applied. When applying screw back pressure, the pressure in the metering zone 25 (the pressure of the molten resin in front of the screw 20) is equal to the screw back pressure. Therefore, the pressure in the metering zone 25 is maintained at a pressure higher than the constant pressure in the starvation zone 23 (second pressure) until the metering of the molten resin is completed. This suppresses separation of the physical blowing agent from the molten resin and promotes homogeneous compatibility. On the other hand, if the screw back pressure during plasticizing metering is too high, the pressure in the metering zone 25 will be too high. As a result, it becomes difficult to feed the molten resin to the front of the tip seal mechanism 50 , and there is a risk that the molten resin may vent up from the inlet 203 of the starvation zone 23 . From these points of view, the screw back pressure (second pressure) until the completion of metering of the molten resin is, for example, 0.4 MPa to 4 MPa higher than the constant pressure (first pressure) in the starvation zone 23, and 0.5 MPa to 3 MPa higher is preferred.

(6) Maintaining the pressure of the metered molten resin In this embodiment, the pressure of the metered molten resin (the pressure in the metering zone 25) is constantly maintained at a constant pressure in the starvation zone 23 (the first pressure) is maintained at a higher pressure (step S6). Thereby, separation of the physical blowing agent from the molten resin after weighing is suppressed, and uniform compatibility is promoted.

If the measured pressure of the molten resin is sufficiently higher than the first pressure, separation of the physical blowing agent from the molten resin can be sufficiently suppressed. On the other hand, if the pressure of the metered molten resin (the pressure in the metering zone 25) is too high, the position of the screw 20 may fluctuate greatly before injection. From these points of view, from the completion of metering of the molten resin to the start of injection, the pressure of the metered molten resin (pressure in the metering zone 25) is 0.5 MPa than the constant pressure in the starvation zone 23 (first pressure). ~10 MPa higher is preferred, 1 MPa to 10 MPa higher is more preferred, and 2 MPa to 5 MPa higher is even more preferred.

Any method can be used to maintain the metered pressure of the molten resin (the pressure of the metering zone 25) higher than the constant pressure (the first pressure) of the starvation zone 23, but in the present embodiment, the metering of the molten resin The screw back pressure is maintained above a constant pressure (first pressure) in the starvation zone 23 from completion to the start of injection. The screw back pressure is controlled by screw drive mechanism 260 . Therefore, in this embodiment, the screw driving mechanism 260 keeps the pressure of the metered molten resin higher than the constant pressure (first pressure) of the starvation zone 23 from the completion of metering of the molten resin to the start of injection. It is a pressure holding mechanism that

The screw back pressure (third pressure) from the completion of metering of the molten resin to the start of injection is preferably equal to or higher than the screw back pressure (second pressure) until the completion of metering of the molten resin. That is, the third pressure may be the same as the second pressure or may be higher than the second pressure. As described above, if the screw back pressure (second pressure) until the completion of the measurement of the molten resin is too high, the molten resin cannot be sent to the front of the tip seal mechanism 50, and the molten resin cannot be fed from the inlet 203 of the starvation zone 23. may vent up. On the other hand, since there is no need to feed the molten resin to the front of the tip seal mechanism 50 after the molten resin has been measured, even if the screw back pressure (third pressure) is increased, such a problem does not occur. Rather, by increasing the screw back pressure (third pressure), it is possible to further promote the dissolution of the physical foaming agent into the molten resin, improve the sealing performance of the tip sealing mechanism 50, and increase the pressure in front of the tip sealing mechanism 50. It is possible to suppress the backflow of the molten resin from the .

(7) Foam molding Next, a physical foaming agent is brought into contact, and the measured molten resin is molded into a foam molding (step S7 in FIG. 1). In injection foam molding, the mold cavity is filled with molten resin with a filling capacity of 75% to 95% of the mold cavity volume, and the short shot method is used to fill the mold cavity while the bubbles expand. Alternatively, a core-back method may be used in which the mold cavity is filled with molten resin in a filling amount of 100% of the mold cavity volume, and then the cavity volume is expanded to cause foaming. Since the resulting foamed molded article has foamed cells inside, shrinkage of the thermoplastic resin during cooling is suppressed, sink marks and warpage are reduced, and a molded article with a low specific gravity can be obtained.

In the manufacturing method of the present embodiment described above, since it is not necessary to control the introduction amount of the physical foaming agent into the molten resin, the introduction time, etc., a complicated control device can be omitted or simplified, and the device cost can be reduced. Further, in the method for producing a foam molded article of the present embodiment, in the starvation zone 23, the starved molten resin and the physical foaming agent under constant pressure are brought into contact with each other. This makes it possible to stabilize the amount of physical foaming agent dissolved in the molten resin (permeation amount) by a simple mechanism.

In addition, in the manufacturing method of the present embodiment, the pressure of the measured molten resin (the pressure of the metering zone 25) is set to a pressure higher than the constant pressure (the first pressure) of the starvation zone 23 from the completion of metering of the molten resin to the start of injection. to hold. As a result, separation of the physical foaming agent from the molten resin can be suppressed, and enlargement and unevenness of foam cells in the foam molded product can be suppressed. This effect will be further explained.

For example, in the method of manufacturing a foam molded product (injection foam molding method) using the molding apparatus 1000 shown in FIG. We discovered a phenomenon in which the pressure of the molten resin decreases.

FIG. 4(b) shows an example of pressure change in the metering zone 25 when this phenomenon occurs. FIG. 4(b) shows the injection process (0 to 7.5S) of the previous shot, detected by the pressure sensor 261 (load cell) of the screw drive mechanism 260, and the following from the start of plasticization to the start of injection of the next shot. The pressure M in the metering zone 25 from (7.5S to 35S) is shown. FIG. 4(b) also shows the pressure S in the starvation zone 23. FIG.

In the example shown in FIG. 4B, the pressure S (first pressure) in the starvation zone 23 is kept constant at 6 MPa, and from the start of plasticization of the thermoplastic resin to the completion of weighing of the molten resin (7.5S to 27S), 9 MPa. of screw back pressure is applied. Therefore, the pressure M in the metering zone 25 is 9 MPa during this time. After the completion of weighing the molten resin, the screw back pressure is set to 0 (zero) as in general injection molding. Immediately after the completion of metering of the molten resin, i.e., immediately after setting the screw back pressure to 0 (zero), the pressure M in the metering zone 25 was reduced from 9 MPa to 7 MPa, and further decreased gradually until the pressure in the starvation zone 23 (6 MPa ) is almost identical to

The reason for this is presumed to be that the molten resin located in front of the screw 20 or the physical foaming agent molten therein flows backward in the direction of the starvation zone 20 (rearward).

In the conventional method for molding a non-foamed molded article, even if the molten resin in the metering zone 25 flows backward to some extent, the resin density of the molten resin in the metering zone 25 changes, but does not significantly affect the quality of the molded article. Since the pressure in the plasticizing cylinder is the same, the pressure in the metering zone 25 does not change. Further, for example, in the conventional foam molding method using a physical foaming agent such as a supercritical fluid as described in Patent Documents 1 to 3, the pressure inside the plasticizing cylinder is the same. Therefore, even if the molten resin in the metering zone 25 flows backward to some extent, neither the pressure in the metering zone 25 nor the separation of the physical foaming agent from the molten resin occurs. Therefore, it is presumed that the quality of the foam molded product is not greatly affected. In other words, in conventional molding methods for non-foamed molded articles and foamed molded articles, the backflow of the molten resin in the metering zone 25 to some extent is not a big problem. On the other hand, in the molding method of this embodiment, the pressure in the metering zone 25 is higher than the constant pressure in the starvation zone 23 . Thus, in this embodiment, the pressure within the plasticizing cylinder 210 is not uniform. Therefore, when the molten resin backflows in the metering zone 25, the pressure in the metering zone 25 decreases even if the backflow amount is not a problem in the conventional molding method, and finally the pressure in the metering zone 25 is reduced. The same pressure as the starvation zone 23 is reached as shown in b). This promotes the separation of the physical foaming agent from the molten resin, and can cause enlargement and non-uniformity of foam cells in the foam molded article.

Usually, the tip of the screw 20 is provided with a tip seal mechanism 50 to suppress backflow of molten resin from the metering zone 25 . However, as described above, a small amount of backflow of molten resin is not a big problem in the conventional molding method. may not have Moreover, even if the tip portion sealing mechanism 50 can prevent backflow of the molten resin, it may not be possible to prevent backflow of the physical foaming agent, which is a fluid. In this case as well, the physical blowing agent separated from the molten resin flows backward from the metering zone 25, thereby reducing the pressure in the metering zone 25. FIG. Thus, it has been found that the tip sealing mechanism 50 may not function sufficiently to separate the pressure between the starvation zone 23 and the metering zone 25 .

As described above, the problem that the pressure in the metering zone 25 drops after the completion of metering of the molten resin is a problem peculiar to this embodiment, which requires separation of the pressure between the starvation zone 23 and the metering zone 25. In order to solve this problem, in this embodiment, as described above, a screw back pressure higher than the constant pressure (first pressure) of the starvation zone 23 is applied from the completion of metering of the molten resin to the start of injection. For example, as shown in FIG. 4( a ), the screw back pressure (third pressure, 9 MPa) of the same magnitude as the screw back pressure (second pressure, 9 MPa) until the completion of metering of the molten resin is applied to the molten resin. Continue to add even after weighing is complete. This prevents a decrease in pressure in the metering zone 25, suppresses separation of the physical blowing agent from the molten resin, and promotes uniform compatibility.

As described above, the magnitude of the screw back pressure (third pressure) applied after the completion of the measurement of the molten resin is not limited to the same pressure as the screw back pressure (the second pressure) until the completion of the measurement of the molten resin. , may be at high pressure. In the case of the example shown in FIG. 4(a), the screw back pressure may be set to 9 MPa until the completion of the measurement of the molten resin, and after the completion of the measurement of the molten resin, the screw back pressure may be set to a pressure higher than 9 MPa.

[Second embodiment]
In the above-described first embodiment, the pressure of the metered molten resin (the pressure in the metering zone 25) is adjusted to the constant pressure (the first pressure) in the starvation zone 23 by applying the screw back pressure after the metering of the molten resin is completed. Hold at higher pressure. In this embodiment, instead of applying the screw back pressure after the completion of the metering of the molten resin, by using the tip seal mechanism 60 having a specific structure shown in FIGS. 25 pressure is maintained above the first pressure. In this embodiment, the tip seal mechanism 60 is a pressure holding mechanism that maintains the pressure of the metered molten resin higher than the constant pressure of the starvation zone 23 from the completion of metering of the molten resin to the start of injection.

<Production equipment for foam molding>
The manufacturing apparatus used in the present embodiment has the same structure as the manufacturing apparatus 1000 shown in FIG. 2 except that the tip seal mechanism 60 shown in FIGS. manufacturing equipment. The tip seal mechanism 60 will be described below.

The tip seal mechanism 60 mainly connects a screw head 61 positioned at the front end of the screw 20 , an abutment ring 63 positioned behind the screw head 61 , and the screw head 61 and the abutment ring 63 . and a check ring 62 loosely fitted on the shaft 64 and movable forward and backward between the screw head 61 and the abutment ring 63 . The check ring 62 has a body ring 62a loosely fitted on the shaft 64 and two claws 62b projecting forward from the body ring 62a. A side surface of the screw head 61 is formed with two recesses 61a with which claws 62b of the check ring are engaged. The check ring 62 moves in the front-rear direction with the body ring 62 a loosely fitted on the shaft 64 and the claws 62 b engaged with the recesses 61 a of the screw head 61 . When the check ring 62 moves in the front-rear direction, the claws 62b of the check ring 62 slide in the recesses 61a of the screw head 61 in the front-rear direction. Between the shaft 64 and the body ring 62a loosely fitted thereon, a gap G1 is formed through which the molten resin can pass. Further, as shown in FIG. 5(d), a gap G2 through which the molten resin can pass is also formed between the surface of the screw head 61 defining the groove 61a and the pawl 62b of the check ring that engages with the groove 61a. It is

FIG. 5(a) shows a state in which the check ring 62 is positioned at the forwardmost position. At this time, the rear end face of the screw head 61 and the front end face of the body ring 62a of the check ring 62 come into contact with each other. FIG. 5(c) shows a state in which the check ring 62 is positioned at the rearmost position. At this time, the rear end face 62c of the body ring 62a of the check ring 62 and the front end face 63a of the abutment ring 63 come into contact. FIG. 5(b) shows a state in which the body ring 62a of the check ring 62 is not in contact with both the screw head 61 and the abutment ring 63, that is, the intermediate state between FIGS. 5(a) and 5(c). .

When the molten resin tries to flow from the rear (upstream) to the front (downstream) of the tip sealing mechanism 60, the check ring 62 is pushed forward by the forward-moving molten resin, and is shown in FIG. 5(a). state shown. The molten resin can pass through the gaps G1 and G2, pass through the tip sealing mechanism 60, and flow to the metering zone 25 in front of the screw 20, as indicated by the arrows in FIG. 5(a). Conversely, when the molten resin tries to flow back from the front (downstream) to the rear (upstream) of the tip sealing mechanism 60, the check ring 62 is pushed rearward and enters the state shown in FIG. 5(c). At this time, the rear end face 62c of the body ring 62a and the front end face 63a of the abutment ring 62 come into contact. The abutment ring 62 closes the gap G<b>1 and suppresses backflow of the molten resin from the front to the rear of the leading end sealing mechanism 60 .

From the start of plasticization of the thermoplastic resin to the completion of weighing of the molten resin, that is, during the plasticization and weighing of the resin, the tip seal mechanism 60 is preferably in the state shown in FIG. 5(a). Since the molten resin can be easily fed to the front of the tip portion sealing mechanism 60, the starvation state of the molten resin can be stabilized in the starvation zone 23, and the foamability of the foam molded product can be improved. Therefore, from the viewpoint of stabilizing the starvation state of the starvation zone 23, it is desirable to design the check ring 62 so that it can easily move forward so that the tip seal mechanism 60 is in the state shown in FIG. 5(a). preferable. On the other hand, after the completion of weighing of the molten resin, it is preferable that the check ring 62 quickly moves rearward and enters the state shown in FIG. 5(c). When the movement of the check ring 62 backward is slow and the state of FIG. 5B is long, or when the check ring 62 cannot move sufficiently backward and stops in the state of FIG. 5B Since the gap G1 is open, the molten resin flows back from the front to the rear of the tip portion sealing mechanism 60 . In this embodiment, since there is a difference between the pressure in the metering zone 25 and the pressure in the starvation zone 23, these pressures cannot be separated and the pressure in the metering zone 25 decreases. Therefore, from the viewpoint of maintaining the pressure in the metering zone 25, it is preferable that the check ring 62 be designed so that it can be easily moved rearward so that the tip seal mechanism 60 is in the state shown in FIG. 5(c). .

The easiness of movement of the check ring 62 in the front-rear direction is determined by the ratio (S1/ S2). The present inventors stabilize the starvation state of the molten resin in the starvation zone 23 by setting the ratio (S1/S2) to, for example, 0.6 to 0.95, preferably 0.7 to 0.9. However, it was found that the pressure of the metered molten resin (the pressure in the metering zone 25) can be kept higher than the constant pressure in the starvation zone 23 from the completion of metering of the molten resin to the start of injection.

The pressure receiving area S1 on the front side of the check ring 62 is the hatched area in FIG. 5(d). The pressure receiving area S1 is the sum of the area of the front end face of the pawl 62b and the area of the region not in contact with the screw head 61 on the front end face of the body ring 62a in the state shown in FIG. 5(a). be. The pressure receiving area S1 is the area of the surface (pressure receiving surface) that receives the pressure in front of the tip seal mechanism 60, that is, the pressure in the measurement zone 25 in front of the screw. The pressure receiving area S2 on the rear side of the check ring 62 is the hatched area in FIG. 5(e). The pressure receiving area S2 is the area of the rear end face 62c of the body ring 62a in the state shown in FIG. 5(a). The pressure-receiving area S2 is the area of the surface (pressure-receiving surface) that receives the pressure behind the tip seal mechanism 60 . As can be seen from the comparison between the pressure receiving area S1 shown in FIG. 5(d) and the pressure receiving area S2 shown in FIG. 5(e), the pressure receiving area S1 is normally smaller than the pressure receiving area S2 (S1<S2).

If the ratio (S1/S2) is small, the check ring 62 tends to move forward, and if the ratio (S1/S2) is large, the check ring 62 tends to move backward. If the ratio (S1/S2) is smaller than the above range, the sealing performance of the tip portion sealing mechanism 60 is deteriorated. As a result, there is a risk that the pressure of the molten resin in front of the screw 20 will decrease and the physical foaming agent will separate, or the molten resin will flow back and vent up from the introduction port 202 . On the other hand, if the ratio (S1/S2) is larger than the above range, the sealing performance of the tip sealing mechanism 60 is improved, but it becomes difficult for the check ring 62 to move forward from the state shown in FIG. 5(c). In the state shown in FIG. 5(c), the pressure receiving area S3 on the rear side of the check ring 62 is indicated by the shaded area in FIG. 5(f). The pressure receiving area S3 is smaller than the pressure receiving area S2. Therefore, if the pressure receiving area S1 is large, that is, if the ratio (S1/S2) is large, it becomes difficult to push back the check ring 62 forward. Since it becomes difficult to feed the molten resin forward, there is a possibility that the plasticizing ability is lowered and the time for measuring the molten resin becomes long. Moreover, the starvation state of the molten resin in the starvation zone 23 may become unstable, and the foaming performance may deteriorate. As described above, in the present embodiment, by balancing the pressure receiving areas S1 and S2, that is, by setting the ratio (S1/S2) within the range described above, the movement of the check ring 62 in the front-rear direction is smoothed. While stabilizing the starvation state of the molten resin in the starvation zone 23, the pressure of the metered molten resin (pressure in the metering zone 25) is higher than the constant pressure in the starvation zone 23 from the completion of metering of the molten resin to the start of injection. to hold. As a result, the foamability of the foam-molded product is improved, the separation of the physical foaming agent from the molten resin is suppressed, and enlargement and unevenness of foam cells in the foam-molded product can be suppressed.

The magnitude of the ratio (S1/S2) can be adjusted by changing the magnitudes of the pressure receiving areas S1 and S2. Regarding the pressure receiving area S1, for example, as can be seen from a comparison of FIGS. On the contrary, S1 can be reduced by reducing the front end surface of the claw 62b. As for the receiving area S2, for example, in the body ring 62a of the check ring 61, S2 can be increased by reducing the inner diameter of the hole through which the shaft 64 penetrates. Conversely, S2 can be reduced by increasing the inner diameter of the hole.

In this embodiment, the pressure receiving areas S1 to S3 shown as shaded areas in FIGS. 5(d) to (f) and FIGS. is. However, the pressure receiving surface is not limited to a plane perpendicular to the front-rear direction. For example, the pressure-receiving surface may be a flat surface (inclined surface) inclined with respect to the front-rear direction, or may be a tapered surface. However, if the pressure-receiving surface is not a plane perpendicular to the front-rear direction such as a slope or tapered surface, the pressure-receiving areas S1 to S3 are not the areas of the slope or tapered surface, but the surfaces that are perpendicular to the front-rear direction. It is the area of the projection plane projected onto the surface (projected area).

<Method for producing foam molded product>
In this embodiment, the same foam molding method as in the first embodiment is used except that the apparatus for manufacturing a foam molded body having the tip seal mechanism 60 described above is used, and the screw back pressure is not applied after the molten resin is weighed. manufacture the body. By using the tip sealing mechanism 60 with the ratio (S1/S2) set within a specific range, the pressure of the metered molten resin (the pressure in the metering zone 25) is maintained in the starvation zone 23 from the completion of metering of the molten resin to the start of injection. It can be held at a pressure higher than a certain pressure. As a result, separation of the physical foaming agent from the molten resin can be suppressed, and enlargement and unevenness of foam cells in the foam molded product can be suppressed.

In this embodiment, it is not necessary to apply the screw back pressure after the molten resin is weighed. A screw back pressure higher than the pressure (first pressure) may be applied. For example, by applying a screw back pressure (third pressure) greater than or equal to the screw back pressure (second pressure) until the completion of the measurement of the molten resin after the completion of the measurement of the molten resin, the check ring 62 becomes more difficult to return forward. Therefore, the sealing performance of the tip portion sealing mechanism 60 is further improved, and uniform compatibility of the physical foaming agent with the molten resin can be further promoted.

[Modification 1]
In the tip seal mechanism 60 of the second embodiment, when the check ring 62 is positioned at the rearmost position shown in FIG. By contacting the front end face 63a of 63, the gap G1, which is a path for the molten resin, is closed. At this time, the end face 62c and the end face 63a, which are the faces (contact faces) that contact each other, are planes perpendicular to the front-rear direction. However, in the second embodiment, the contact surface is not limited to a plane perpendicular to the front-rear direction. For example, the contact surface may be a tapered surface.

In this modified example, instead of the tip seal mechanism 60 of the second embodiment, a tip seal mechanism 70 having a tapered abutment surface shown in FIGS. 7(a) to 7(d) is used. In this modified example, the same manufacturing apparatus as in the second embodiment is used, except that the tip seal mechanism 70 is used, and the foam molded body is manufactured by the same manufacturing method. Further, the value of the ratio (S1/S2) of the tip seal mechanism 70 is within the specific range described above, like the tip seal mechanism 60 used in the second embodiment.

The tip seal mechanism 70 will be described below. FIG. 7(a) shows a state in which the check ring 72 is positioned at the forwardmost position in the distal end sealing mechanism 70. FIG. FIG. 7(b) shows a state in which the check ring 72 is positioned at the rearmost position. FIG. 7(c) shows only the check ring 72. FIG. FIG. 7( d ) shows components of the tip seal mechanism 70 other than the check ring 72 , that is, the screw head 71 , the shaft 74 and the abutment ring 73 .

As shown in FIG. 7C, the check ring 72 is formed with a through hole 75 through which the shaft 74 passes. A part of the inner wall defining the through-hole 75 has a first tapered surface 75c that connects the rear end 75a of the through-hole 75 and a small inner diameter portion 75b having an inner diameter d75 smaller than the inner diameter D75 of the rear end 75a. Form.

In this modification, an end surface 72c perpendicular to the front-rear direction and a tapered surface 75c continuous with the end surface 72c shown in FIG. 7A are surfaces that receive pressure from the rear. Therefore, in this modified example, the end surface 72c and the tapered surface 75c are pressure receiving surfaces on the rear side of the check ring 72 . The pressure receiving area S2 in this modified example is the sum of the area of the end surface 72c and the projected area of the tapered surface 75c projected onto a plane perpendicular to the axial direction of the screw 20. As shown in FIG.

As shown in FIG. 7(d), the shaft 74 has a second tapered surface that connects a connection portion 74a with the abutment ring 73 and a small diameter portion 74b having a diameter d74 smaller than the diameter D74 of the connection portion 74a. 74c. The taper ratio of the first tapered surface 75c and the taper ratio of the second tapered surface 74c are substantially the same. As the check ring 72 moves forward and backward, the first tapered surface 75c and the second tapered surface 74c are separated from each other and come into contact with each other. As shown in FIG. 7A, when the first tapered surface 75c and the second tapered surface 74c are separated from each other, a gap G1 is formed between them through which the molten resin can pass. When the check ring 72 moves rearward and the first tapered surface 75c and the second tapered surface 74c come into contact with each other, the gap G1 disappears as shown in FIG. Reverse flow from the front to the rear of the mechanism 70 is prevented.

In this modified example, the same manufacturing apparatus as in the second embodiment is used, except that the tip seal mechanism 70 is used, and the foam molded body is manufactured by the same manufacturing method. Therefore, the same effects as those of the above-described second embodiment are obtained.

Further, in the tip portion seal mechanism 70 of this modified example, the gap G1, which is the passage of the molten resin, is eliminated by the contact between the first tapered surface 75c and the second tapered surface 74c, thereby preventing the molten resin from flowing back. Suppress. The contact area is larger when the tapered surfaces are brought into contact with each other than when the flat surfaces are brought into contact with each other. As a result, the sealing performance can be further enhanced in the tip portion sealing mechanism 70 of this modified example, and the pressure of the measured molten resin (the pressure in the measuring zone 25) can be easily maintained.

[Modifications 2 and 3]
Modification 2 uses a tip seal mechanism 80 having a check ring 82 with a groove 82d formed on the outer surface, as shown in FIGS. 8(a) to 8(c). FIG. 8(a) shows a state in which the check ring 82 is positioned at the forwardmost position. FIG. 8(c) shows a state in which the check ring 82 is located at the rearmost position. FIG. 8(b) shows a state in which the body ring 82a of the check ring 82 is not in contact with both the screw head 81 and the abutment ring 83, that is, a state intermediate between FIGS. 8(a) and 8(c). .

In Modified Example 2, the same manufacturing apparatus as in the second embodiment is used, except that the tip seal mechanism 80 is used, and the foam molded body is manufactured by the same manufacturing method. Further, the value of the ratio (S1/S2) of the tip seal mechanism 80 is within the specific range described above, like the tip seal mechanism 60 used in the second embodiment.

Modification 2 has the same effect as the above-described second embodiment. Further, in the tip seal mechanism 70 of Modification 2, a groove 82d is formed in the outer surface of the check ring 82 facing the inner wall of the plasticizing cylinder 210 (see FIG. 1). Molten resin that has entered between the outer surface of the check ring 82 and the inner wall of the plasticizing cylinder 210 is trapped in the groove 82d. This enhances the seal between the outer surface of check ring 82 and the inner wall of plasticizing cylinder 210 . For example, when the pressure difference between the starvation zone 23 and the screw back pressure is large, or when the viscosity of the molten resin is low, the molten resin passes between the outer surface of the check ring 82 and the inner wall of the plasticizing cylinder 210. Therefore, the check ring 82 tends to flow backward from the front to the rear. Even in such a case, the check ring 82 of Modification 2 can suppress backflow of the molten resin. As a result, in this modified example, the pressure of the metered molten resin (the pressure in the metering zone 25 ) can be easily maintained higher than the constant pressure in the starvation zone 23 .

From the viewpoint of improving the sealing performance between the outer surface of the check ring 82 and the inner wall of the plasticizing cylinder 210, the number of the grooves 82d is preferably large, and the grooves 82d form a labyrinth structure on the outer surface of the check ring 82. preferably. Therefore, it is preferable that the length L82a of the body ring 82a in the front-rear direction is long. On the other hand, when the length L82a of the body ring 82a is long, the movement distance of the check ring 82 in the front-rear direction is long, and the time during which the gap G1 formed between the shaft 84 and the check ring 82 is open is long. Become. Therefore, the sealing performance of the gap G1 is deteriorated. As a configuration for improving the sealing performance of the gap G1, for example, a configuration in which the abutment surface between the shaft 84 and the check ring 82 is a tapered surface can be mentioned. This configuration will be described in Modification 3 below.

In Modification 3, a distal end sealing mechanism 90 having a check ring 92 having a groove 92d formed on the outer surface thereof, as in Modification 2, shown in FIGS. 9A to 9C, is used. FIG. 9(a) shows a state in which the check ring 92 is positioned at the forwardmost position. FIG. 9(c) shows a state in which the check ring 92 is positioned at the rearmost position. FIG. 9(b) shows a state in which the body ring 92a of the check ring 92 is not in contact with both the screw head 91 and the abutment ring 93, that is, the intermediate state between FIGS. 9(a) and 9(c). .

In the tip seal mechanism 90, the contact surface between the shaft 94 and the check ring 92 is tapered. In Modified Example 3, as shown in FIG. 9(c), the gap G1, which is the path for the molten resin, is eliminated by the contact between the first tapered surface 95c and the second tapered surface 94c, thereby allowing the molten resin to flow. Suppresses reflux. In Modified Example 3, the same manufacturing apparatus as in the second embodiment is used, except that the tip seal mechanism 90 is used, and the foam molded body is manufactured by the same manufacturing method. Further, the value of the ratio (S1/S2) of the tip seal mechanism 90 is within the specific range described above, like the tip seal mechanism 60 used in the second embodiment.

FIG. 9B, in which the check ring 92 in Modification 3 is moving from the front to the rear, is compared with FIG. 8B, in which the check ring 82 in Modification 2 is moving from the front to the rear. The gap G in the tip sealing mechanism 90 shown in FIG. 9(b) is narrower than the gap G in the tip sealing mechanism 80 shown in FIG. 8(b). From this, the tip seal mechanism 90 in which the abutment surface between the shaft 94 and the check ring 92 is tapered is compared with the tip seal mechanism 80 in which the abutment surface is flat, and the check ring 92 is in the process of returning to the rear. , the molten resin is less likely to flow back from the front to the rear, and the sealing performance of the gap G1 is high.

Modification 3 has the same effect as the above-described second embodiment. Furthermore, the tip portion seal mechanism 90 of this modified example forms a groove 92d in the outer surface of the check ring 92 to improve the seal between the outer surface of the check ring 92 and the inner wall of the plasticizing cylinder 210, thereby By making the contact surface between 94 and check ring 92 a tapered surface, the sealing performance of gap G1 can be improved.

[Third Embodiment]
In the second embodiment, in the tip seal mechanism 60, the ratio (S1/S2) of the pressure receiving area S1 on the front side of the check ring 62 to the pressure receiving area S2 on the rear side is set within a specific range. The pressure of the molten resin (the pressure in the metering zone 25) is kept higher than the constant pressure in the starvation zone 23 (the first pressure). In this embodiment, instead of setting the ratio (S1/S2) to a specific range, the check ring is kept in contact with the abutment ring by rotating the screw in the tip seal mechanism in the reverse direction. A locking mechanism is provided to maintain the pressure in the metering zone 25 above the first pressure. In this embodiment, the tip seal mechanism having a locking mechanism maintains the pressure of the metered molten resin at a pressure higher than the constant pressure of the starvation zone 23 from the completion of metering of the molten resin to the start of injection. is.

The locking mechanism of the tip sealing mechanism may be any mechanism as long as it maintains the state in which the check ring is in contact with the abutment ring by reverse rotation of the screw. Mechanisms disclosed in JP-A-2003-201055 and the like can be used.

This embodiment uses a manufacturing apparatus having the same structure as the manufacturing apparatus 1000 used in the first embodiment shown in FIG. Then, a foam molded article is produced in the same manner as in the first embodiment, except that the screw 20 is reversely rotated after the completion of the measurement of the molten resin instead of applying the screw back pressure after the measurement of the molten resin. . By rotating the screw 20 in the reverse direction, the check ring is maintained in contact with the abutment ring, and the pressure of the measured molten resin (pressure in the metering zone 25) is maintained in the starvation zone from the completion of metering of the molten resin to the opening of injection. It can be held at a pressure higher than the constant pressure of 23. As a result, separation of the physical foaming agent from the molten resin can be suppressed, and enlargement and unevenness of foam cells in the foam molded product can be suppressed.

In this embodiment, it is not necessary to apply the screw back pressure after the molten resin is weighed. A screw back pressure higher than the pressure (first pressure) may be applied. For example, after the completion of the measurement of the molten resin, by applying a screw back pressure (third pressure) higher than the screw back pressure (second pressure) until the completion of the measurement of the molten resin, the physical foaming agent to the molten resin is uniformly distributed. The compatibility can be further promoted.

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

[Example 1]
In this example, a reinforced polypropylene (PP) (manufactured by Idemitsu Lion Composites, 4700G) containing 20% by weight of talc was used as the thermoplastic resin, and nitrogen was used as the physical blowing agent to produce a foam molded product.

(1) Manufacturing Apparatus In this example, the manufacturing apparatus used in the above-described second embodiment was used. That is, in this example, the manufacturing apparatus 1000 shown in FIG. 2, which is provided with the tip seal mechanism 60 shown in FIGS. 5(a) to 5(e), was used. Details of the manufacturing apparatus 1000 will be described. As described above, the manufacturing apparatus (injection molding machine) 1000 mainly includes a plasticizing cylinder 210 in which the screw 20 is installed, a screw driving mechanism 260 for driving the screw 20, and a physical foaming agent in the plasticizing cylinder 210. Cylinder 100 which is a physical foaming agent supply mechanism to supply to, a mold clamping unit 250 provided with a mold 251, a plasticizing cylinder 210, a screw drive mechanism 260 and a control device for controlling the operation of the mold clamping unit 250 ( not shown).

The nozzle tip 29 of the plasticizing cylinder 210 is provided with a shut-off valve 28 that is opened and closed by driving the air cylinder, so that the inside of the plasticizing cylinder 210 can be maintained at a high pressure. A mold 251 is in close contact with the nozzle tip 29 , and molten resin is injected and filled from the nozzle tip 29 into a cavity 253 formed by the mold 251 . On the upper side surface of the plasticizing cylinder 210, a resin supply port 201 for supplying the thermoplastic resin to the plasticizing cylinder 210 and an introduction port 202 for introducing the physical foaming agent into the plasticizing cylinder 210 are arranged in order from the upstream side. is formed. A resin supply hopper 211, a feeder screw 212, and an introduction speed adjusting container 300 are arranged in the resin supply port 201 and the introduction port 202, respectively. The cylinder 100 is connected to the introduction speed adjusting container 300 by a pipe 154 via a pressure reducing valve 151 and a pressure gauge 152 . A sensor (not shown) is also provided in the starvation zone 23 of the plasticizing cylinder 210 to monitor the pressure in the starvation zone 23 .

In the plasticizing cylinder 210, thermoplastic resin is supplied from the resin supply port 201 into the plasticizing cylinder 210, and the thermoplastic resin is plasticized by a band heater (not shown) to become molten resin, and the screw 20 rotates forward. sent downstream by Due to the presence of the ring 26 and the large diameter portion 20A provided in the screw 20, the molten resin is compressed and the pressure increases on the upstream side of the ring 26, and the molten resin is not filled ( starvation). The molten resin sent further downstream is recompressed and weighed near the tip of the plasticizing cylinder 210 before injection.

As a result, in the plasticizing cylinder 210, in order from the upstream side, there are a plasticizing zone 21 in which the thermoplastic resin is plasticized and melted, a compression zone 22 in which the molten resin is compressed and the pressure increases, and a starvation zone in which the molten resin is not filled. A zone 23 and a recompression zone 24 are formed in which the molten resin decompressed in the starvation zone is recompressed.

In the manufacturing apparatus 1000, the inner diameter of the plasticizing cylinder 210 was 35 mm, and the inner diameter of the inlet 202 was 8 mm. Thus, the inner diameter of inlet 202 was about 23% of the inner diameter of plasticizing cylinder 210 . The volume of the introduction rate control container 300 was approximately 80 mL. Further, in the tip seal mechanism 60, the ratio (S1/S2) of the pressure receiving area S1 on the front side of the check ring 62 to the pressure receiving area S2 on the rear side was set to 0.75. Moreover, in this embodiment, a mold 251 having a cavity 253 with a size of 100 mm×200 mm×3 mm is used.

(2) Manufacture of Foam Molded Body In this example, as the plurality of cylinders 100, nitrogen cylinders with a volume of 47 L filled with nitrogen at 14.5 MPa were used. First, the value of the pressure reducing valve 151 is set to 6 MPa, the cylinder 100 is opened, and through the pressure reducing valve 151, the pressure gauge 152, and the introduction speed adjusting container 300, from the introduction port 202 of the plasticizing cylinder 210, the starvation zone 23 was supplied with 6 MPa of nitrogen. The cylinder 100 was kept open at all times during the production of the compact.

In the plasticizing cylinder 210, band heaters (not shown) were used to adjust the plasticizing zone 21 to 210°C, the compression zone 22 to 200°C, the starvation zone 23 to 200°C, and the recompression zone 24 to 210°C. Then, while rotating the feeder screw 212 at a rotation speed of 30 rpm from the resin supply hopper 211, resin pellets of thermoplastic resin were supplied to the plasticizing cylinder 210, and the screw 20 was rotated forward. As a result, the thermoplastic resin is heated and kneaded in the plasticizing zone 21 to form a molten resin.

The number of rotations of the feeder screw 212 was set to the number of rotations at which the resin pellets were starved and supplied by setting the molding conditions (conditioning) in this example by molding a solid molded body (unfoamed molded body) in advance. . Here, the starvation supply of resin pellets means that in the plasticizing zone 21, during the supply of resin pellets, the state in which the plasticizing cylinder is not filled with the resin pellets or the molten resin is maintained, and the supplied resin pellets or the molten resin is maintained. , means that the flight of the screw 20 is exposed. Confirmation of the starvation supply of the resin pellets includes, for example, a method of confirming the presence or absence of resin pellets or molten resin on the screw 20 with an infrared sensor or a visualization camera. In this example, the feeder screw 212 used was provided with a transparent window, and the state of the plasticizing zone 21 immediately below the resin supply port 201 was visually confirmed through the transparent window.

The screw 20 was forwardly rotated at a screw back pressure of 9 MPa and a rotational speed of 100 rpm to flow the molten resin from the plasticization zone 21 to the compression zone 22 and further to the starvation zone 23 .

Since the molten resin flows into the starvation zone 23 through the gap between the screw large diameter portion 20A and the ring 26 and the inner wall of the plasticizing cylinder 210, the amount of molten resin supplied to the starvation zone 23 is limited. As a result, the molten resin was compressed in the compression zone 22 to increase the pressure, and the starvation zone 23 on the downstream side was filled with the molten resin (starvation state). In the starvation zone 23, the molten resin is not filled (starved state), so there is a physical blowing agent (nitrogen) introduced from the inlet 202 in the space where the molten resin does not exist, and the physical blowing agent causes the molten resin to pressurized.

Further, the molten resin is sent to the recompression zone 24 and recompressed, the screw 20 is retracted and stopped at a predetermined position (measurement completion position), and one shot of the molten resin is transferred to the tip of the plasticizing cylinder 210. Weighed. The metering time was 10 seconds. After completion of metering, the screw back pressure was increased from 9 MPa to 10 MPa. As a result, the screw 20 moved forward from the metering completion position by 0.3 mm to 0.4 mm.

After that, the shut-off valve 28 was opened, and the molten resin was injection-filled into the cavity 253 so that the filling rate was 90% of the volume of the cavity, thereby forming a flat plate-shaped foam-molded body (short-shot method). . In this embodiment, since the screw back pressure is applied after the completion of the metering of the molten resin, the screw position at the start of injection deviates from the metering completion position. Since the deviation amount differs for each shot, the injection amount is controlled based on the stroke (movement amount) of the screw 20 rather than the position of the screw 20 before and after injection. After molding, the foam-molded article was taken out from the mold after waiting for the foam-molded article to cool. The cooling time was 10 seconds. The molding cycle was 23 seconds, which was equivalent to the molding cycle for a solid molded article (unfoamed molded article).

100 shots of injection molding of the molded article described above were continuously performed to obtain 100 foam molded articles. During the production of 100 foamed moldings, the pressure in the starvation zone 23 inside the plasticizing cylinder 210 was constantly measured by a pressure sensor (not shown). As a result, the pressure in starvation zone 23 was always constant at 6 MPa. Moreover, the value of the pressure gauge 152, which indicates the pressure of nitrogen supplied to the starvation zone 23, was always 6 MPa during the production of the foam molded product. From the above, the molten resin was constantly pressurized by 6 MPa of nitrogen in the starvation zone 23 through one cycle of injection molding including the plasticization weighing process, the injection process, the cooling process of the molded body, the take-out process, etc. , and during continuous molding of 100 molded bodies, it was confirmed that the molten resin was always pressurized by nitrogen in the starvation zone 23 .

In addition, the resin pressure in front of the screw 20 detected by the pressure sensor 261 (load cell) of the screw drive mechanism 260 was 10 MPa, which is higher than the pressure 6 MPa in the starvation zone 23, from the completion of metering of the molten resin to the start of injection. From this result, in this embodiment, the pressure in the starvation zone 23 and the resin pressure in front of the screw 20 (the pressure in the metering zone 25) are separated, and the metering is performed from the completion of metering of the molten resin to the start of injection. It was confirmed that the pressure of the molten resin could be kept higher than the pressure of the starvation zone.

The variation in weight of 100 foam molded articles was evaluated by dividing the standard deviation (σ) by the weight average value (ave.) (relative standard deviation value: σ/ave. (%)). As a result, (σ/ave.) was 0.19%. When the same evaluation was performed on a solid molded body (unfoamed molded body), (σ/ave.) was 0.18%, which was the same value as in this example. From this result, it was found that the weight stability of the foam molded article of this example was equivalent to that of the solid molded article.

In this example, a foamed molded article having a specific gravity about 10% lighter than that of a solid molded article and having warpage corrected could be continuously and stably produced. It is considered that the specific gravity reduction rate is affected by the amount of physical blowing agent dissolved (permeation amount). From this result, it was found that the dissolution amount (permeation amount) of the physical foaming agent in the molten resin was stable. Furthermore, foam cells in the cross section of the obtained foam molded product were observed. No large bubble breakage was observed at the ends of the molded article, and the average cell diameter of the foamed cells was as fine as 20 to 30 µm. Enlargement and non-uniformity of foam cell diameter were not confirmed.

[Example 2]
In this example, after the completion of weighing of the molten resin, a foam molded article was produced by the same method using the same production apparatus as in Example 1, except that the screw back pressure was not applied.

In this example, the screw back pressure was set to 9 MPa until the completion of the measurement of the molten resin, and was set to 0 (zero) after the completion of the measurement of the molten resin. Two seconds after the completion of metering, the resin pressure in front of the screw 20 detected by the pressure sensor 261 (load cell) of the screw drive mechanism 260 decreased from 9 MPa by 2 MPa to 7 MPa, and the pressure of the starvation zone 23 (6 MPa). The difference was 1 MPa. Immediately after that, the molten resin was injected into the mold to obtain a foam molded product. The molten resin metering time was the same as in Example 1.

100 shots of injection molding of the molded article described above were continuously performed to obtain 100 foam molded articles. As in Example 1, the pressure in starvation zone 23 was always constant at 6 MPa during the production of 100 foamed moldings.

The foamed cells in the cross section of the obtained foamed molded product were observed. The average cell diameter of the foamed cells was 30 to 40 μm, which was larger than that of Example 1, but fine. Enlargement and non-uniformity of foam cell diameter were not confirmed.

[Example 3]
In the present embodiment, as shown in FIG. 6(b), in the tip seal mechanism 60, the front end surface of the claw 62b of the check ring 62 is made large to increase S1 and the ratio (S1/S2). was set to 0.9. Further, after the completion of weighing the molten resin, no screw back pressure was applied. A foam molded article was produced in the same manner as in Example 1 using the same production apparatus as in Example 1 except for this.

In this example, as in Example 2, the screw back pressure was set to 9 MPa until the completion of the measurement of the molten resin, and was set to 0 (zero) after the completion of the measurement of the molten resin. From the completion of metering to the start of injection, the resin pressure in front of the screw 20 detected by the pressure sensor 261 (load cell) of the screw driving mechanism 260 was 8.5 MPa, and remained at a decrease of 0.5 MPa. On the other hand, in this embodiment, since the ratio (S1/S2) is larger than that in the first embodiment, it is difficult to feed the molten resin to the front of the tip sealing mechanism 60, and the plasticizing ability is low. The molten resin weighing time was 1.5 times longer than the weighing time of Example 1.

100 shots of injection molding of the molded article described above were continuously performed to obtain 100 foam molded articles. As in Example 1, the pressure in starvation zone 23 was always constant at 6 MPa during the production of 100 foamed moldings.

The foamed cells in the cross section of the obtained foamed molded product were observed. The average cell diameter of the foamed cells was 20 to 30 μm, which was the same as in Example 1 and fine. Enlargement and non-uniformity of foam cell diameter were not confirmed.

[Example 4]
In this example, a manufacturing apparatus similar to that of Example 1 was used except that it had a tip sealing mechanism 90 shown in FIGS. 9(a) to 9(c). In the tip sealing mechanism 90, the contact surfaces between the shaft 94 and the check ring 92 are tapered surfaces 95c and 94c, and the outer surface of the check ring 92 is formed with a groove 92d. Further, after the completion of weighing the molten resin, no screw back pressure was applied. Except for this, a foam molded article was produced in the same manner as in Example 1.

In this example, as in Example 2, the screw back pressure was set to 9 MPa until the completion of the measurement of the molten resin, and was set to 0 (zero) after the completion of the measurement of the molten resin. From the completion of metering to the start of injection, the resin pressure in front of the screw 20 detected by the pressure sensor 261 (load cell) of the screw drive mechanism 260 was 8.6 MPa, and remained at a decrease of 0.4 MPa. The molten resin metering time was the same as in Example 1.

100 shots of injection molding of the molded article described above were continuously performed to obtain 100 foam molded articles. As in Example 1, the pressure in starvation zone 23 was always constant at 6 MPa during the production of 100 foamed moldings.

The foamed cells in the cross section of the obtained foamed molded product were observed. The average cell diameter of the foamed cells was 20 to 30 μm, which was the same as in Example 1 and fine. Enlargement and non-uniformity of foam cell diameter were not confirmed.

[Example 5]
In this embodiment, except that the tip seal mechanism has a known locking mechanism disclosed in Japanese Patent No. 3432776, which keeps the check ring in contact with the abutment ring by rotating the screw in reverse. used the same manufacturing apparatus as in Example 1. Further, after the completion of weighing of the molten resin, the screw back pressure was not applied, and instead the screw 20 was reversely rotated. Except for this, a foam molded article was produced in the same manner as in Example 1.

In this example, as in Example 2, the screw back pressure was set to 9 MPa until the completion of the measurement of the molten resin, and was set to 0 (zero) after the completion of the measurement of the molten resin. Then, the screw 20 was reversely rotated by 180°, and the check ring was maintained in contact with the abutment ring. From the completion of metering to the start of injection, the resin pressure in front of the screw 20 detected by the pressure sensor 261 (load cell) of the screw drive mechanism 260 remained at 9.0 MPa and did not decrease. The molten resin metering time was the same as in Example 1.

100 shots of injection molding of the molded article described above were continuously performed to obtain 100 foam molded articles. As in Example 1, the pressure in starvation zone 23 was always constant at 6 MPa during the production of 100 foamed moldings.

The foamed cells in the cross section of the obtained foamed molded product were observed. The average cell diameter of the foamed cells was 20 to 30 μm, which was the same as in Example 1 and fine. Enlargement and non-uniformity of foam cell diameter were not confirmed.

[Comparative Example 1]
In this comparative example, the ratio (S1/S2) was set to 0.5 in the tip portion sealing mechanism 60 . Further, after the completion of weighing the molten resin, no screw back pressure was applied. A foam molded article was produced in the same manner as in Example 1 using the same production apparatus as in Example 1 except for this.

In this comparative example, as in Example 2, the screw back pressure was set to 9 MPa until the completion of the measurement of the molten resin, and was set to 0 (zero) after the completion of the measurement of the molten resin. After completion of metering, the resin pressure in front of the screw 20 detected by the pressure sensor 261 (load cell) of the screw drive mechanism 260 was 6.0 MPa, and decreased to the starvation zone 23 pressure. The molten resin weighing time was the same as in Example 1.

100 shots of injection molding of the molded article described above were continuously performed to obtain 100 foam molded articles. As in Example 1, the pressure in starvation zone 23 was always constant at 6 MPa during the production of 100 foamed moldings.

The foamed cells in the cross section of the obtained foamed molded product were observed. The average cell diameter of the foamed cells was 50 to 100 μm, and compared with Example 1, an increase in the diameter of the foamed cells was confirmed.

[Comparative Example 2]
In this comparative example, the ratio (S1/S2) was set to 0.96 in the tip seal mechanism 60 . Further, after the completion of weighing the molten resin, no screw back pressure was applied. A foam molded article was produced in the same manner as in Example 1 using the same production apparatus as in Example 1 except for this.

In this comparative example, similarly to Example 2, the thermoplastic resin was plasticized and the molten resin was weighed while applying a screw back pressure of 9 MPa. However, in this comparative example, since the ratio (S1/S2) is large, it is difficult to feed the molten resin to the front of the tip sealing mechanism 60, and the plasticizing ability is low. It took a very long time to weigh the molten resin. Therefore, it was determined that it was impossible to measure a predetermined amount of molten resin while applying a screw back pressure of 9 MPa, and production of the molded body was stopped during the measurement of the molten resin.

The manufacturing method of the present invention can simplify the device mechanism related to the physical foaming agent. In addition, a foam molded article having excellent foamability can be produced efficiently at low cost. Moreover, the method for producing a foam-molded article of the present invention suppresses the separation of the physical foaming agent from the molten resin, and can stably produce a high-quality foam-molded article.

20 screw 21 plasticization zone 22 compression zone 23 starvation zone 24 recompression zone 60, 70, 80, 90 tip seal mechanism 100 cylinder 210 plasticization cylinder 300 introduction speed adjustment container 1000 manufacturing apparatus

Claims (13)

A method for producing a foam molded article,
Equipped with a screw provided inside to rotate and move back and forth, a plasticization zone in which a thermoplastic resin is plasticized and melted to become a molten resin, and a starvation zone in which the molten resin is in a starvation state,
Using a manufacturing device comprising a plasticizing cylinder formed with an inlet for introducing a physical blowing agent into the starvation zone,
The manufacturing method is
plasticizing and melting the thermoplastic resin into the molten resin in the plasticizing zone;
introducing into the starvation zone a pressurized fluid comprising the physical blowing agent having a first pressure that is a constant pressure;
Starving the molten resin in the starvation zone;
contacting the starved molten resin with a pressurized fluid at the first pressure in the starvation zone;
weighing a predetermined amount of the molten resin brought into contact with the pressurized fluid at the first pressure;
Injecting the weighed molten resin from the plasticizing cylinder and molding it into the foam molded body,
maintaining the screw back pressure at a second pressure higher than the first pressure until the metering of the molten resin is completed;
A method for producing a foam molded article, wherein the screw back pressure is maintained at a third pressure higher than the second pressure from the completion of metering of the molten resin to the start of injection. The foaming according to claim 1, wherein the pressure of the measured molten resin is maintained at a pressure higher by 0.5 MPa to 10 MPa than the first pressure from the completion of measuring the molten resin to the start of injection. A method for producing a molded article. The screw is provided in the plasticizing cylinder so as to move forward and backward from the plasticization zone to the starvation zone and backward from the starvation zone to the plasticization zone,
The screw has a tip sealing mechanism that prevents the molten resin from flowing back from the front to the rear in the plasticizing cylinder,
The tip seal mechanism is
a screw head positioned at the front end of the screw;
an abutment ring positioned behind the screw head;
a shaft that connects the screw head and the abutment ring;
3. The production of the foam molded article according to claim 1, further comprising a check ring loosely fitted on the shaft and movable forward and backward between the screw head and the abutment ring. Method. The ratio (S1/S2) of the pressure-receiving area S1 on the front side of the check ring to the pressure-receiving area S2 on the rear side is 0.6 to 0.95 when the check ring is positioned at the most forward position. The method for producing a foam molded article according to claim 3 , characterized in that: A through hole through which the shaft passes is formed in the check ring,
A portion of the inner wall defining the through hole of the check ring forms a first tapered surface connecting the rear end of the through hole and a small inner diameter portion having an inner diameter smaller than the inner diameter of the rear end. ,
the shaft has a second tapered surface connecting a connecting portion with the butt ring and a small diameter portion having a diameter smaller than that of the connecting portion;
The taper ratio of the first tapered surface and the taper ratio of the second tapered surface are substantially the same,
5. The method of manufacturing a foam molded article according to claim 3 , wherein the first tapered surface and the second tapered surface are separated from each other and come into contact with each other as the check ring moves forward and backward. 6. The method for producing a foam molded article according to any one of claims 3 to 5 , wherein grooves are formed on the outer surface of the check ring. 7. The method of manufacturing a foam molded article according to claim 6 , wherein the groove forms a labyrinth structure on the outer surface of the check ring. The screw is provided in the plasticizing cylinder so as to move forward and backward from the plasticization zone to the starvation zone and to the rearward from the starvation zone to the plasticization zone. Rotation and reverse rotation opposite to forward rotation are possible,
The screw has a tip sealing mechanism that suppresses the molten resin from flowing back from the front to the rear in the plasticizing cylinder,
The tip seal mechanism is
a screw head positioned at the front end of the screw;
an abutment ring positioned behind the screw head;
a shaft that connects the screw head and the abutment ring;
a check ring loosely fitted on the shaft and movable forward and backward between the screw head and the abutment ring;
a lock mechanism that maintains a state in which the check ring is in contact with the abutment ring by rotating the screw in the reverse direction;
3. The method of manufacturing the foam molded article further comprising rotating the screw in reverse after the completion of metering of the molten resin to maintain a state in which the check ring is in contact with the abutment ring. A method for producing the described foamed molded article. A manufacturing apparatus for manufacturing a foam molded body,
Equipped with a screw provided inside to rotate and move back and forth, a plasticization zone in which a thermoplastic resin is plasticized and melted to become a molten resin, and a starvation zone in which the molten resin is in a starvation state,
a plasticizing cylinder that is formed with an inlet for introducing a physical foaming agent into the starvation zone and that measures a certain amount of the molten resin and injects it to the outside;
a physical foaming agent supply mechanism that supplies a physical foaming agent at a first pressure, which is a constant pressure, to the plasticizing cylinder;
The screw back pressure is maintained at a second pressure higher than the first pressure until the measurement of the molten resin is completed, and the screw back pressure is maintained at the second pressure from the completion of the measurement of the molten resin to the start of injection. and a pressure holding mechanism configured to hold a third pressure higher than the pressure. The pressure holding mechanism is a mechanism that holds the pressure of the measured molten resin at a pressure higher by 0.5 MPa to 10 MPa than the first pressure from the completion of weighing of the molten resin to the start of injection. The manufacturing apparatus according to claim 9 . 11. The manufacturing apparatus according to claim 9 , wherein the pressure holding mechanism is a screw driving mechanism that controls screw back pressure. The screw is provided in the plasticizing cylinder so as to move forward and backward from the plasticization zone to the starvation zone and backward from the starvation zone to the plasticization zone,
The screw has a tip sealing mechanism that prevents the molten resin from flowing back from the front to the rear in the plasticizing cylinder,
11. The manufacturing apparatus according to claim 9 , wherein the pressure holding mechanism is the tip sealing mechanism. The screw is capable of forward rotation for sending the molten resin forward and reverse rotation opposite to the forward rotation in the plasticizing cylinder,
The tip seal mechanism is
a screw head positioned at the front end of the screw;
an abutment ring positioned behind the screw head;
a shaft that connects the screw head and the abutment ring;
a check ring loosely fitted on the shaft and movable forward and backward between the screw head and the abutment ring;
13. The manufacturing apparatus according to claim 12 , further comprising a lock mechanism that keeps the check ring in contact with the abutment ring by rotating the screw in the reverse direction.

Images