JP2008260245A - Injection molding die and method of manufacturing foamed molding using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding die capable of rapid and reliable degassing and providing a molding with good surface conditions, and to provide a method of manufacturing a foamed molding by the use of the die. <P>SOLUTION: The on/off valve has a gas through hole which makes the gas supply and discharge passage communicate with the cavity, and, with the mold kept closed, the gas through hole is movable between the supply and discharge position where the gas through hole communicates with the gas supply and discharge passage and the closing position where the gas through hole becomes noncommunicating with the gas supply and discharge passage. The on/off valve consists of two split bodies separated along the axis of the gas through hole. At the start of charging of the resin, the on/off valve is set at the closing position, and, after the start of the charging to immediately before completion of the charging, the on/off valve is set at the supply and discharge position so as to initiate discharge of the gas in the cavity. After completion of the charging of the resin and successive completion of the discharge of the gas, the on/off valve moves to the closing position, and, on mold opening, the on/off valve returns to the two-split state. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an injection mold used for a gas counter pressure method and a method for producing a foam molded article using the injection mold.

Conventionally, a gas counter pressure method has been used as a foam injection molding method for improving the appearance.
In this gas counter pressure method, a gas (for example, CO ₂ or air) having a pressure higher than the foaming pressure of the molten resin immediately before filling the thermoplastic foamable molten resin (hereinafter referred to as “molten resin”) into the cavity. Hereinafter, after only injecting “gas” and pressurizing the inside of the cavity, the molten resin is injected and filled into the cavity.

Then, immediately after injection filling, during injection filling, or immediately after completion of injection filling, this high-pressure gas is discharged out of the mold to promote foaming of the molten resin.
As described above, as a method of discharging gas out of the mold, a method of discharging from a slight gap on the parting surface, a gap between protruding pins, or a porous material is common, but a gas counter pressure method is used. When there is a slight gap, it is difficult to maintain a gas having a pressure higher than the foaming pressure of the molten resin. Therefore, a groove that communicates with the cavity on the parting surface is provided on the outer periphery of the cavity, a structure that discharges high pressure inside the cavity to the outside of the mold from several places, a pin using a spring, a pin or valve that operates with hydraulic pressure, air pressure, etc. There is a structure that shuts off the gas supply and exhaust passage. In particular, in a structure in which the gas supply / exhaust passage is blocked by a pin or a valve, the gas is discharged in an operation that is timed according to molding conditions.

  However, in the conventional mold structure, not only the gas is discharged from the gas supply / exhaust passage, but also resin, oil, dust, dust, etc. are slightly discharged mixed with the discharged gas. There is a problem that the gas supply / exhaust passage is blocked and deposited on the hole wall surface, causing malfunction of pins and valves. Further, the molten resin itself may stick to the gas supply / exhaust passage and be blocked. In addition, the gas supply / exhaust passage tends to be narrow to maintain airtightness in the cavity or prevent resin leakage. Due to poor exhaust, molding defects such as burrs and short shots, and poor appearance due to burns and sink marks, etc. There is also the problem of causing.

  Therefore, until the resin filled in the cavity reaches the gas vent (air vent) installed at an arbitrary position in the cavity, this resin releases the gas from the gap of the gas vent outside the mold. Thus, there has been proposed a method (see Patent Documents 1 and 2) in which the slide member is slid by the pressure of the resin and the gap of the gas venting portion is closed simultaneously with the tip of the resin coming into contact with the slide member.

  However, in this method, the resin filling the cavity at high speed collides with the slide member, and the slide member slides due to the resin pressure. In the method, timing deviation is likely to occur. Therefore, there is a possibility that the gas vent part bends or the resin bites into the gap between the slide member and the gas vent part and the slide member does not operate well.

JP 2001-030309 A JP 2001-162625 A

  In view of the above circumstances, in the production of a foam molded article using a gas counter pressure method, the present invention can quickly and surely exhaust gas and has a good surface condition (high surface smoothness, high transferability, It is an object of the present invention to provide an injection mold that can be a molded product that is free from sink marks and surface breakage) and a method for producing a foam molded product using the injection mold.

  In order to achieve the above object, an injection mold according to the present invention has a gas supply / exhaust passage for supplying / exhausting gas to / from a cavity, and an open / close valve is provided at an end of the gas supply / exhaust passage on the cavity side. The on-off valve has a gas passage hole for connecting the gas supply / exhaust passage and the cavity, and the gas passage hole communicates with the gas supply / exhaust passage. And a closed position where the gas supply / exhaust passage is not communicated with each other can be moved in a mold-closed state, and is divided into two parts along the axis of the gas passage hole. At the start, the on-off valve is arranged at the closed position, and after the resin filling starts and immediately before the resin filling is completed, the on-off valve is arranged at the supply / exhaust position, and the exhaust of gas in the cavity is started. After the exhaust is completed, the open / close valve is closed. Moves to the position, the mold is opened after the core back, it is characterized in that it has a configuration in which the on-off valve when the mold is opened is two split state.

In the injection mold of the present invention, when a part of the resin injected into the cavity flows into the gas passage hole and the inflowed resin solidifies in the gas passage hole, it solidifies when the mold is opened and remains in the divided body. Further, it is preferable that a mechanism for discharging the solidified product of the resin is provided, or that the gas passage hole is enlarged from the opening end on the cavity side toward the center portion.
In addition, although it is not specifically limited that it expands toward the center part from the both opening ends of a gas passage hole, For example, it means that it is cross-sectional drum type, rugby ball type, and the abacus shape of an abacus.

  The size of the gas passage hole is not particularly limited, but the opening end on the cavity side has a slit shape, and the slit width (gap) at the opening end on the cavity side is 0.03 mm or more and 0.2 mm or less. Preferably, the opening end on the gas supply / exhaust passage side is slit-shaped, and the slit width (gap) of the opening end on the gas supply / exhaust passage side is preferably 0.05 mm or more and 0.3 mm or less.

That is, if the slit width (gap) at the opening end on the cavity side is less than 0.03 mm, it takes time to supply and exhaust gas, and there is a possibility that the time required for pressurization and exhaustion becomes longer. The resin tends to flow into the gas vent hole during exhaust, and as a result, the resin may easily flow into the supply / exhaust passage.
If the slit width (gap) at the open end of the gas supply / exhaust passage is less than 0.05 mm, it takes time to supply and exhaust gas, which may increase the time required for pressurization and exhaust. The resin tends to flow into the gas vent hole during exhaust, and as a result, the resin may easily flow into the supply / exhaust passage.

In the method for producing a foam molded product according to the present invention, the gas pressure in the cavity of the injection mold of the present invention is set to a pressure state exceeding (atmospheric pressure + 0.05 MPa) and not exceeding (atmospheric pressure + 1.0 MPa). In addition, the molten thermoplastic resin composition containing the chemical foaming agent is injected and filled into the cavity, and the gas in the cavity is supplied between the gas filling hole and the gas supply / exhaust of the on-off valve immediately before the start of injection filling and immediately after the filling. A process of performing a foaming process by slightly moving the movable mold backward with a part of the resin flowing into the gas passage hole together with the gas exhausted while reducing the pressure in the cavity by exhausting through the passage It is characterized by having.
The pressurizing pressure in the cavity is atmospheric pressure + 0.05 MPa to atmospheric pressure + 1 MPa, and preferably needs to be equal to or higher than the pressure capable of controlling the foaming of the foaming gas dissolved in the foamable molten resin.

The thermoplastic resin contained in the thermoplastic resin composition used in the method for producing a foam molded article of the present invention is not particularly limited, and examples thereof include polyolefin resins such as polypropylene, polyethylene, polystyrene, and propylene / ethylene copolymers. .
Although it does not specifically limit as a chemical foaming agent, Bicarbonate (inorganic compound), such as azodicarbonamide (organic compound) and sodium bicarbonate, etc. are mentioned.

  In addition to the thermoplastic resin and the chemical foaming agent, the thermoplastic resin composition includes, as necessary, known foaming aids, foam nucleating agents, foam molding stabilizers, stabilizers, ultraviolet absorbers, Antioxidants, antistatic agents, lubricants, colorants, flame retardants, crosslinking agents and / or fillers can be blended.

Incidentally, as the foaming aid, for example, stearates such as sodium stearate, calcium stearate, magnesium stearate, potassium stearate, zinc stearate, montanates such as calcium montanate (octadocosanoate), zinc montanate, etc. Higher fatty acid metal salts such as urea, urea or urea compounds, paraffin, and other stearamides.
Examples of the foam nucleating agent include inorganic fillers such as talc, silica, calcium carbonate, and calcium silicate.

  As described above, the injection mold according to the present invention has a gas supply / exhaust passage for supplying / exhausting gas to / from the cavity, and an injection having an opening / closing valve at the cavity side end of the gas supply / exhaust passage. In the molding die, the on-off valve has a gas passage hole for connecting the gas supply / exhaust passage and the cavity, and the gas supply / exhaust position where the gas passage hole communicates with the gas supply / exhaust passage, The gas supply / exhaust passage and the closed position that is in a non-communication state can be moved in the mold closed state, and consist of two divided bodies divided into two along the axis of the gas passage hole. The on-off valve is arranged at the closed position, and the on-off valve is arranged at the supply / exhaust position immediately after the resin filling is started and immediately before the resin filling is completed, and the exhaust of the gas in the cavity is started. Resin in cavity in gas passage hole of valve After the inflow and exhaust are completed, the opening / closing valve moves to the closed position, the mold is opened after the core back, and the opening / closing valve is divided into two when the mold is opened. The gas supply / exhaust passage can be made larger. Therefore, stable gas supply / exhaust is possible, and uniform pressure in the cavity and complete rapid exhaust of residual gas can be performed.

And the gas in a cavity is exhausted completely by flowing a part of resin into a gas passage hole. That is, the resin is densely filled in the cavity. Therefore, the obtained foamed molded product is free from short shots and sink marks.
In addition, the resin that has flowed into the gas passage hole is completely separated from the resin on the cavity side by moving the open / close valve to the closed position after filling the resin, resulting in a burr-like resin residue in the resulting foam molded product. do not do.

  Further, since the on-off valve is split into two divided bodies when the mold is opened, even when a part of the resin flows into the gas passage hole during resin filling and exhaust, the gas passage hole The solidified resin solidified by flowing in can be easily removed from the gas passage hole. In addition, foreign substances and dust that easily adhere to and accumulate on the wall surface of the gas supply / exhaust passage can be removed together with the solidified material. Therefore, the gas supply / exhaust passage can always be kept clean.

  That is, it is possible to obtain a molded product that can quickly and surely exhaust gas and has a good surface condition (high smoothness of the surface, high transferability, no sink, no surface breakage).

Further, if the structure is provided with a mechanism for discharging the solidified resin remaining in the divided body when the mold is opened, the solidified material can be easily and reliably removed.
Furthermore, if the gas passage hole of the on-off valve has a shape that expands from the opening end on the cavity side of the gas passage hole toward the center portion, the resin flowing into the gas passage hole from the cavity side will pass through the gas passage. Since the resin flows from the narrow inlet to the wide central portion, the flow rate of the resin is relaxed and cooled, so that it remains in the gas passage hole more reliably. That is, only the gas is exhausted from the gas supply / exhaust passage to the outside of the mold through the gas passage hole.

  On the other hand, in the method for producing a foam molded article according to the present invention, the gas pressure in the cavity of the injection mold of the present invention is a pressure exceeding (atmospheric pressure + 0.05 MPa) and not exceeding (atmospheric pressure + 1.0 MPa). The molten thermoplastic resin composition containing the chemical foaming agent is injected and filled into the cavity, and the gas in the cavity is supplied immediately before the start of injection filling and immediately after the filling to the gas vent hole and gas of the on-off valve. With a part of the resin flowing into the gas passage hole along with the gas exhausted while reducing the pressure inside the cavity by exhausting through the air supply / exhaust passage, the movable mold is slightly moved backward to perform foaming treatment. Since the process is provided, a molded product having a good surface condition (high surface smoothness, high transferability, no sink, no surface bubble breakage) can be obtained with certainty.

Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.
1 to 11 show an embodiment of an injection mold according to the present invention.

As shown in FIGS. 1 to 10, the injection mold 1 includes a fixed mold 2 and a movable mold 3, and a cavity 4 and a gas supply / exhaust gas for supplying and exhausting gas into the cavity 4. A passage 5 and an opening / closing valve 6 for opening and closing the end of the gas supply / exhaust passage 5 on the cavity 4 side are provided.
As shown in FIG. 11, the on-off valve 6 has a central portion that makes the gas supply / exhaust passage 5 and the cavity 4 communicate with each other in an expanded state, for example, a drum shape or an abacus bead shape. As shown in FIG. 2, an air supply / exhaust position where the gas passage hole 61 communicates with the gas supply / exhaust passage 5 and a state where the gas supply / exhaust passage 5 is not in communication as shown in FIG. It is possible to move in the closed state of the mold.

The on-off valve 6 is divided into two along the central axis of the gas passage hole 61, one divided body 6 a is supported on the movable mold 3 side, and the other divided body 6 b is supported on the fixed mold 2 side. .
That is, the split body 6a is provided with the movable die 3 having a concave portion 61a having a half shape of the gas passage hole 61 on the surface on the fixed die 2 side, and a ring-shaped seal material 62 fitted around the periphery. It fits in the guide groove 31 and can move forward and backward in the fixed mold 2 direction.

An urging spring 32 and a push pin 33 are provided in the guide groove 31.
The urging spring 32 is provided inside the guide groove 31, one end is fixed to the divided body 6 a, the other end is fixed to the movable mold 3, and the divided body 6 a protrudes from the parting surface of the movable mold 3. Is energized.
The push pin 33 is advanced and retracted in the direction of the fixed mold 2 by a power mechanism (not shown) such as a pneumatic cylinder, and the end face of the fixed mold 2 is in contact with the end surface of the divided body 6a. Is pressed in the direction of the fixed mold.

The divided body 6b is provided with a recess 61b having the remaining half of the gas passage hole 61 on the surface on the movable mold 3 side, a ring-shaped sealing material 62 is fitted around the periphery, and a guide provided on the fixed mold 2 It fits in the groove 21 and can move forward and backward in the three movable directions.
In addition, the divided body 6b is provided with a through-hole 64 that penetrates in the advancing and retracting direction of the divided body 6b and has one end opened in the center of the recessed portion 61b, and a protruding pin 23 described later is slidably fitted therein. A protrusion 63 serving as an undercut is provided on a part of the bottom of 61b.

In the guide groove 21, an urging spring 22 and a protruding pin 23 are provided.
The biasing spring 22 is provided inside the guide groove 21, one end is fixed to the split body 6 b, and the other end is fixed to the fixed mold 2, and the split body 6 b protrudes from the parting surface of the fixed mold 2. Is energized.

The protruding pin 23 is advanced and retracted in the movable three directions by a power mechanism (not shown) such as a pneumatic cylinder.
The operation of the on-off valve is controlled by a mold clamping start signal or a filling start signal of an injection molding machine, a sensor, a timer, or the like.
In addition, although this injection mold 1 is not shown, the cavity 4 portion must be in a state of high airtightness in advance, and the contact surface of the fixed mold 2 and the movable mold 3 is sealed with an O-ring or packing. Alternatively, the eyelash seal is provided by unevenness, and the fixing portion is sealed by an O-ring or packing, and the sliding portion such as a slide core or a protruding pin is subjected to precise eye-eye processing or sealing by an O-ring or packing.

  Furthermore, with respect to the injection nozzle, the nozzle touch surface is sealed with an O-ring or packing, or a hail-eye seal with irregularities to improve airtightness, and a shutoff valve or the like enhances airtightness toward the injection screw.

Next, the manufacturing method of the foam molded product of the present invention using the injection mold 1 will be described in detail with reference to FIGS.
That is, this manufacturing method manufactures the foam molded product F in the following steps. (1) As shown in FIG. 1, the fixed mold 2 and the movable mold 3 in the mold open state with a part of the divided body 6a or the divided body 6b protruding from the parting surfaces of the fixed mold 2 and the movable mold 3, respectively. Is in a closed state as shown in FIG.

In this mold closed state, the end surfaces of the divided body 6a and the divided body 6b are brought into contact with each other to form a gas passage hole 61 by the concave portion 61a and the concave portion 61b, and the cavity 4 and the gas supply / exhaust passage 5 are connected via the gas passage hole 61. The on-off valve 6 is arranged at the air supply / exhaust position where is in the communication state.
Further, in this mold closed state, the push pin 33 operates to move the position of the on-off valve 6 so that the bottom of the concave portion 61b coincides with the parting surface at the end of the concave portion 61b of the divided body 6b on the cavity 4 side. .

(2) When a control means such as a microcomputer (not shown) receives a mold closing completion signal, the gas pressure in the cavity 4 exceeds (atmospheric pressure + 0.05 MPa) (atmospheric pressure + 1) as shown in FIG. Gas G is supplied into the cavity 4 through the gas supply / exhaust passage 5 and the gas passage hole 61 by a high pressure gas generator and a gas supply / exhaust control device (not shown) until the set pressure state is less than 0.0 MPa). The

  When the control means receives a signal indicating that the gas pressure in the cavity 4 has reached the set pressure state, the push pin 33 slides in the direction of the fixed mold 2 as shown in FIG. The open / close valve 6 reaches the closed position where the open end on the 4 side enters the guide groove 21 on the fixed mold 2 side and the open end on the cavity 4 side of the gas passage hole 61 is blocked by the wall surface of the guide groove 21 on the fixed mold 2 side. Is moved to the fixed mold 2 side, and injection filling of the molten resin P into the cavity 4 is started. The protruding pin 23 slides together with the on-off valve 6 to the fixed mold 2 side.

As shown in FIG. 5, the extrusion pin 33 is retracted in the direction of the movable mold 3 and the on-off valve 6 is supplied and exhausted by the urging force of the urging spring 22 until the resin filling is completed after the injection filling of the molten resin is started. The gas G in the cavity 4 is exhausted through the gas passage hole 61 and the gas supply / exhaust passage 5 by the resin pressure.
Then, as shown in FIG. 6, the remaining gas G is exhausted, and the resin filling is completed with a part of the molten resin filled in the cavity 4 flowing into the gas passage hole 61. The molten resin that has flowed into the gas passage hole 61 suddenly expands from the narrow entrance of the gas passage hole 61, so that the flow rate of the resin is relaxed and cooled, so that the molten resin stays in the gas passage hole 61. That is, only the gas G passes through the gas passage hole 61 and is discharged out of the mold 1 from the gas supply / exhaust passage 5.

As shown in FIG. 7, the movable mold 3 is core-backed to foam the resin, and as shown in FIG.
After the foaming and cooling are completed, the extrusion pin 33 is slid in the fixed mold 2 direction to move the on-off valve 6 to the closed position, and the resin solidified product X that has entered the gas passage hole 61 is expanded into the foamed molded product F in the cavity 4. Cut from. By this cutting, the obtained foamed molded product F can be made free from burrs.

As shown in FIG. 9, the mold is opened. At the same time as the mold is opened, the on-off valve 6 is also divided into a divided body 6a and a divided body 6b, and a protrusion 63 serving as an undercut is provided at the bottom of the recess 61b of the divided body 6b on the fixed mold 2 side. The solidified resin X solidified in 61 remains on the divided body 6b side in a state of being fitted into the recess 61b.
As shown in FIG. 10, the protruding pin 23 protrudes in the direction of the movable mold 3 to remove the solidified product X from the divided body 6 b and the protruding pin (not shown) provided with the foamed molded product F from the movable mold 3 on the movable mold 3. ) Foreign matter and dust that easily adhere to and accumulate on the wall surface due to the protrusion of the solidified product X can be removed together with the solidified product, and an accident that the gas supply / exhaust passage is clogged with foreign matter and dust can be prevented.

  Specific examples of the present invention will be described below in comparison with comparative examples, but the present invention is not limited to the following examples.

Example 1
An injection mold 1 shown in FIG. 1 in which the slit width of the opening end on the cavity 4 side of the gas passage hole 61 of the on-off valve 6 is 0.1 mm and the slit width of the opening end on the gas supply / exhaust passage 5 side is 0.3 mm. Was used to mold a plate-like foam molded product (length 116 mm, width 326 mm, thickness 4.6 mm) under the following conditions.
Cavity dimensions: 118mm long, 330mm wide, 2.0mm thick
Gas pressure before injection filling in the cavity: atmospheric pressure + 0.8 MPa
Core back: 2.1mm
Injection resin composition: A composition obtained by adding 5 parts by weight of azodicarbonamide as a chemical foaming agent to 100 parts by weight of polyethylene.
The foam molded product obtained as described above had a maximum sink amount of 0.1 mm, the surface appearance was free from dirt and burrs, and had a glossiness of 90%. Further, the weight of the solidified product X in the gas passage hole 61 was 0.13 g.

(Example 2)
An injection mold 1 shown in FIG. 1 in which the slit width of the opening end on the cavity 4 side of the gas passage hole 61 of the on-off valve 6 is 0.05 mm and the slit width of the opening end on the gas supply / exhaust passage 5 side is 0.3 mm. A plate-like foam-molded product was obtained in the same manner as in Example 1 except that was used.
The foam molded product obtained as described above had a maximum sink amount of 0.2 mm, the surface appearance was free from dirt and burrs, and had a glossiness of 90%. Moreover, the weight of the solidified product X in the gas passage hole 61 was 0.09 g.

(Comparative Example 1)
There is no on-off valve 6, the cavity and the gas supply / exhaust passage are directly connected, the slit width of the opening end of the gas supply / exhaust passage on the cavity side is 0.03 mm, and the opening (gap) on the supply / exhaust groove side is 0.03 mm. A plate-like foamed molded product was obtained in the same manner as in Example 1 except that a conventional mold having a gas supply / exhaust passage opening / closing valve having no gas passage hole was used.
The foam molded product obtained as described above had a slightly yellowish surface appearance except for the molten resin flow end portion, and was slightly wavy and glossy 90%. Further, the maximum sink amount was 1.2 mm and it was a short shot.

  According to the method for producing a foam molded article using the injection mold of the present invention from Examples 1 and 2 and Comparative Example 1, the surface condition is good (high smoothness of the surface, high transferability, no sink, surface It can be clearly seen that a molded product having no bubble breakage can be obtained with certainty.

In Examples 1 and 2 and Comparative Example 1, the maximum sink amount and glossiness were determined as follows.
[Maximum sink volume]
Using a depth gauge, measure the depth from the flat part of the surface of the foam molded product to the deepest part of the recess.
[Glossiness]
A gloss meter is used to measure the amount of reflected light when light having an incident angle of 60 ° is applied to the surface of the foam molded article. (JIS-Z-8741-1959 glossiness measurement method)

It is one Embodiment of the injection mold concerning this invention, Comprising: It is sectional drawing of the on-off valve part of the mold open state. It is sectional drawing of the on-off valve part of the state immediately after mold closing of the injection mold of FIG. It is sectional drawing of the on-off valve part at the time of gas filling of the injection mold of FIG. It is sectional drawing of the on-off valve part at the time of resin injection filling of the injection mold of FIG. It is sectional drawing of the on-off valve part just before completion of the resin injection filling of the injection mold of FIG. It is sectional drawing of the on-off valve part at the time of resin injection filling completion of the injection mold of FIG. It is sectional drawing of the on-off valve part at the time of the core back of the injection mold of FIG. It is sectional drawing of the on-off valve part after completion of foaming of the injection mold of FIG. It is sectional drawing of the on-off valve part immediately after mold opening of the injection mold of FIG. It is sectional drawing of the on-off valve part at the time of the solidified substance protrusion of the injection mold of FIG. It is a notch cross-sectional perspective view of the on-off valve of the injection mold of FIG.

Explanation of symbols

1 Injection mold 2 Fixed mold 23 Extrusion pin (Mechanism for discharging resin solidified material)
3 Movable mold 4 Cavity 5 Gas supply / exhaust passage 6 On-off valve 6a, 6b Split body 61 Gas passage hole G Gas P Resin X Resin solidified product F Foam molded product

Claims (4)

An injection mold having a gas supply / exhaust passage for supplying / exhausting gas to a cavity, and having an open / close valve at a cavity side end of the gas supply / exhaust passage,
The on-off valve has a gas passage hole that connects the gas supply / exhaust passage and the cavity, and the gas passage hole communicates with the gas supply / exhaust passage, and the gas supply / exhaust passage is not in communication. It is movable in a closed state where the mold is closed, and consists of two divided bodies divided into two along the axis of the gas passage hole,
At the start of resin filling, the on-off valve is arranged at the closed position, and immediately after the resin filling is started and immediately before completion of resin filling, the on-off valve is arranged at the air supply / exhaust position to start exhausting gas in the cavity. After completion, after the exhaust is completed, the on-off valve moves to the closed position, the mold is opened after the core back, and the on-off valve is split into two when the mold is opened. Mold.   When a part of the resin injected into the cavity flows into the gas passage hole and the inflowed resin solidifies in the gas passage hole, the solidified product of the resin remaining in the divided body is solidified when the mold is opened. The injection mold according to claim 1, further comprising a mechanism.   The injection mold according to claim 1 or 2, wherein the gas passage hole of the on-off valve is enlarged from the opening end on the cavity side of the gas passage hole toward the center portion.   The gas pressure in the cavity of the injection mold according to any one of claims 1 to 3 is set to a pressure state exceeding (atmospheric pressure + 0.05 MPa) and not more than (atmospheric pressure + 1.0 MPa). In addition, the molten thermoplastic resin composition containing the chemical foaming agent is injected and filled into the cavity, and the gas in the cavity is supplied between the gas filling hole and the gas supply / exhaust passage of the opening / closing valve immediately before the start of the injection filling and immediately after the filling. A step of performing a foaming process by slightly moving the movable mold backward in a state where a part of the resin flows into the gas passage hole together with the gas exhausted while reducing the pressure inside the cavity by reducing the pressure inside the cavity. A method for producing a foam molded product, comprising:

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