JP2007083650A - Injection mold and injection molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of finishing the design surface of a resin molded product so as to have an intended shape over a wide range even if the resin molded product has the rib protruded from its non-design surface. <P>SOLUTION: This injection mold 31 is used for injection-molding the resin molded product having the design surface and the non-design surface and having the rib protruded from its non-design surface. Cavities 27 and 28, which form the shape corresponding to that of the ribbed resin molded product are formed in the injection mold 31. Flow channels 43 and 44, which are opened to the surface of a cavity for molding the leading end surface of the rib at its one end and communicate with the outside of the mold at its other end, are formed to the injection mold 31. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for injection molding a resin molded product.

A technique for injection molding a resin product by filling a cavity formed in an injection mold with a molten resin is known. A resin molded product is molded by cooling and solidifying the resin filled in the cavity. The resin filled in the cavity shrinks when solidified. If the resin shrinks and peels from the cavity surface, the resin molded product cannot be molded into the intended shape.
In many cases, a resin molded product has a design surface (front surface) that needs to be finished in an intended shape and a non-design surface (back surface) that is allowed to have poor finish. The design surface is formed by the front cavity surface. The non-design surface is formed by the back cavity surface.
Patent Document 1 discloses a technique for injecting a pressurized fluid from an injection port that opens in a back cavity surface toward a non-design surface of a resin molded product after filling a cavity of an injection mold with a molten resin. ing. When the pressurized fluid is injected from the injection port, the pressurized fluid enters between the non-design surface of the resin molded product and the back cavity surface, so that the non-design surface of the resin molded product is separated from the back cavity surface. When the non-design surface of the resin molded product is peeled from the back cavity surface, the design surface of the resin molded product is solidified (shrinks) while maintaining a state of being in close contact with the front cavity surface. For this reason, the design surface of the resin molded product is finished in the intended shape.

Japanese Patent Laid-Open No. 10-58493

However, when the non-design surface of the resin molded product is to be peeled off from the back-side cavity surface by injecting a pressurized fluid from the inlet opening in the back-side cavity surface, the rib that the resin molded product protrudes from the non-design surface is provided. If it has, the pressurized fluid which wants to flow between a non-design surface and a back side cavity surface will be interrupted | blocked by the said rib part. Therefore, the pressurized fluid cannot be injected into a wide range of the non-design surface of the resin molded product, and the non-design surface of the resin molded product cannot be completely separated from the back cavity surface. For this reason, it becomes impossible to finish the design surface into the intended shape. On the other hand, if many injection ports are provided, the injection mold becomes complicated, which is not practical.
The present invention has been made to solve the problem, and even if the resin molded product has ribs protruding from the non-design surface, the design surface of the resin molded product can be finished to the intended shape. Provide technology.

The injection mold of the present invention is for injection molding a resin molded product having a design surface, a non-design surface, and a rib protruding from the non-design surface. The injection mold of the present invention includes a front side mold that molds a design surface of a resin molded product, and a back side mold that molds a non-design surface of the resin molded product.
A cavity surface having a groove for forming the rib is formed on the back mold. The back side mold further includes a flow path, and one end of the flow path is open to the bottom surface of the groove on the cavity surface, and the other end of the flow path communicates with the outside of the back side mold.
According to this injection mold, the pressurized fluid can be injected toward the tip surface of the rib. The pressurized fluid injected toward the tip of the rib is not only the gap between the tip of the rib and the corresponding cavity surface (more precisely, the bottom of the groove forming the rib tip), but also both sides of the rib. And the corresponding cavity surface (side surface of the groove), and further widely penetrates the gap between the non-design surface and the back cavity surface located on both sides of the rib. Therefore, the non-design surface and the back cavity surface of the resin molded product can be peeled over a wide range. Therefore, even if the resin molded product has ribs protruding from the non-design surface, the design surface of the resin molded product can be finished in the intended shape.

In the case of the injection mold described above, it is preferable that one end of the flow path is open to a region of the cavity surface beyond the bottom surface of the groove. In this case, the flow path also opens on both side surfaces of the rib.
If the flow path is also open on both side surfaces of the rib, the gap between both side surfaces of the rib and the corresponding cavity surface (side surface of the groove), as well as the non-designed surface and back side cavity surface located on both sides of the rib It is easy for the pressurized fluid to enter the gap.

The injection molding method created by the present invention injection-molds a resin molded product having a design surface, a non-design surface, and a rib protruding from the non-design surface. The injection molding method includes a step of filling molten resin into a cavity having a shape corresponding to a resin molded product with ribs formed inside the injection mold, and from the inside of the injection mold toward the rib tip surface. A step of injecting a pressurized fluid.
When pressurized fluid is injected toward the tip end surface of the rib, fluid enters between the tip end surface of the rib and the corresponding cavity surface, and between both side surfaces of the rib and the corresponding cavity surface. The pressurized fluid penetrates widely also between the non-design surface and the back cavity surface existing on both sides. Therefore, the non-design surface and the back cavity surface of the resin molded product can be peeled over a wide range. Therefore, even if the resin molded product has ribs protruding from the non-design surface, the design surface of the resin molded product can be finished in the intended shape.

  In the present invention, by injecting a pressurized fluid from the inside of the mold on the side for molding the non-design surface of the resin molded product toward the tip surface of the rib, the non-design surface of the resin molded product The back cavity surface can be peeled off. Even if the resin molded product has ribs protruding from the non-design surface, the design surface of the resin molded product can be finished to the intended shape.

The preferred embodiment of this invention is illustrated.
(Mode 1) An injection molding apparatus comprising the injection mold according to the claim and means for feeding fluid into the flow path.
(Mode 2) The opening width inside the mold of the flow path is wider than the width of the molding surface at the tip of the rib (the bottom surface of the groove formed in the cavity surface).
(Mode 3) An inlet for pressurized fluid is intermittently formed along the longitudinal direction of the molding surface (bottom surface of the groove) at the tip of the rib. A vent member having a width wider than the bottom surface of the groove is installed at the inlet. The vent member protrudes on both sides of the groove.
(Mode 4) The opening of the flow path and the tip end surface of the rib are asymmetric, and the flow path protrudes greatly on one side of the rib, and the flow path protrudes small on the opposite side of the rib.

An embodiment according to an injection molding technique of the present invention will be described with reference to the drawings.
An injection molding apparatus 30 (described later) performs injection molding of the resin molded product 10 shown in FIG. The resin molded product 10 is, for example, an automobile bumper. The resin molded product 10 includes a main body 14 whose end portions 11 and 12 are bent in the same direction, and ribs 15 and 16 protruding from the main body 14 in a direction in which the end portions 11 and 12 face. The resin molded product 10 has a front surface 17 and a back surface 18. The surface 17 is a design surface. The design surface is a surface whose shape needs to be accurately finished. The back surface 18 of the resin molded product 10 is a non-design surface. A non-design surface is a surface where shape accuracy is not important. The ribs 15 and 16 protrude from the non-design surface. The left and right side surfaces 20, the upper and lower side surfaces 24, and the front end surface 21 of the rib 15 are non-design surfaces. The left and right side surfaces 22, the upper and lower side surfaces 25, and the front end surface 23 of the rib 16 are also non-design surfaces.

As shown in FIG. 2, the injection molding apparatus 30 includes an injection mold 31 and an air supply unit 32. The injection mold 31 has a first mold 33 and a second mold 34 and is opened and closed by being driven by a mold opening / closing mechanism (not shown).
FIG. 2 shows a state where the injection mold 31 is closed. In the state where the injection mold 31 is closed, the main body cavity 26 and the rib cavities 27 and 28 are formed by the first mold 33 and the second mold 34. The main body cavity 26 and the rib cavities 27 and 28 communicate with each other to form one cavity as a whole. As will be described in detail later, molten resin is filled in the main body cavity 26 and the rib cavities 27 and 28, and the resin is cooled and solidified, whereby the resin molded product 10 having ribs is molded.

As shown in FIG. 2, the first mold 33 has a first cavity surface 35.
3 is a cross-sectional view of the second mold 34 at a position perpendicular to the plane of the drawing different from that shown in FIG. Accordingly, FIG. 3 does not depict the flow paths 43 and 44 (described later) shown in FIG. As shown in FIG. 3, the second mold 34 has a second cavity surface 36, a third cavity surface 37, a fourth cavity surface 38, a fifth cavity surface 39, and a sixth cavity surface 40. The first cavity surface 35 of the first mold 33 molds the surface 17 (see FIG. 1) of the resin molded product 10. The second cavity surface 36 of the second mold 34 molds the back surface 18 of the resin molded product 10. The third cavity surface 37 forms the rib side surface 20 of the rib 15. The fourth cavity surface 38 forms the rib tip surface 21 of the rib 15. The fifth cavity surface 39 forms the rib side surface 22 of the rib 16. The sixth cavity surface 40 forms the rib tip surface 23 of the rib 16. One side surface 24 and the opposite side surface of the rib 15, and one side surface 23 and the opposite side surface of the rib 16 are also formed by cavity surfaces (not shown) that define the rib cavities 27 and 28. The third cavity surface 37 and the fourth cavity surface 38 form a groove for molding the rib 15. The fourth cavity surface 38 is the bottom surface of the groove and forms the rib tip surface 21 of the rib 15. The fifth cavity surface 39 and the sixth cavity surface 40 form a groove for molding the rib 16. The sixth cavity surface 40 is the bottom surface of the groove, and the rib tip surface 23 of the rib 16 is formed.

  As shown in FIG. 2, an injection port 41 is opened in the first cavity surface 35 of the first mold 33. The injection port 41 and the outside of the first mold 33 are communicated with each other by a gate 42. Molten resin is injected into the gate 42 from an injection nozzle (not shown) provided outside the injection mold 31. The resin injected into the gate 42 is filled into the cavities 26, 27 and 28 from the injection port 41.

In the second mold 34, flow paths 43 and 44 are formed. An opening 45 is provided at one end of the flow path 43. The other end of the flow path 43 is connected to a flow path 50 (described later) disposed outside the injection mold 31. An opening 46 is provided at one end of the flow path 44. The other end of the flow path 44 is also connected to the flow path 50.
A vent member 51 is attached to the opening 45. A vent member 52 is attached to the opening 46. The opening 45 and the opening 46, and the vent member 51 and the vent member 52 have the same configuration. Therefore, in the following description, the opening 45 and the opening 46, and the vent member 51 and the vent member 52 will be described as being representative of the opening 45 and the vent member 51 unless otherwise required.

  As shown in FIG. 4, the vent member 51 has a shallow portion 53, an intermediate portion 54, and a deep portion 55. In the following, for convenience of explanation, the top and bottom of FIG. The side surface 59 of the intermediate portion 54 is disposed inside the side surface 62 of the shallow portion 53 and the side surface 60 of the deep portion 55. Four grooves 56 extending in the vertical direction are formed in the deep portion 55. In FIG. 4, only two of the four grooves 56 are shown. The remaining two grooves 56 are hidden behind the vent member 51. Two grooves 57 extending in the horizontal direction and intersecting in a cross shape are formed below the deep portion 55. The lower end of the groove 56 and the both ends of the groove 57 communicate with each other.

As shown in FIG. 5, the vent member 51 has the side surface 60 of the deep portion 55 in contact with the side surface 64 of the opening portion 45 and the bottom surface 61 abuts on the bottom surface 63 of the opening portion 45. It is positioned accurately. The vent member 51 is fixed to the second mold 34 by bolts (not shown). The width of the opening 45 is larger than the width of the tip of the rib cavity 27. As shown in FIG. 6, the length of the opening 45 is shorter than the length of the rib cavity 27 in the longitudinal direction (left and right direction in FIG. 6) (the vent member 51 is not shown in FIG. 6). is doing).
As shown in FIG. 5, a gap 68 is secured between the upper surface 65 of the vent member 51 and the surface 47 of the second mold 34 in a state where the vent member 51 is mounted in the opening 45. As shown in FIG. 7, a gap 66 that goes around the shallow portion 53 is also secured between the side surface 62 of the shallow portion 53 of the vent member 51 and the side surface 64 of the opening 45.

As shown in FIG. 2, the air supply unit 32 includes a flow path 50, a filter 71, a regulator 72, a solenoid valve 73, and a controller 74.
One end 70 of the flow path 50 is connected to an air source (for example, factory air). The other end side of the flow path 50 is bifurcated and one branch is connected to the flow path 43 of the second mold 34. The other branch of the channel 50 is connected to the channel 44 of the second mold 34.
The filter 71, the regulator 72, and the solenoid valve 73 are interposed in the flow path 50. The filter 71 removes foreign matters contained in the air supplied from the air source. The regulator 72 adjusts (depressurizes) the pressure of the air supplied from the air source to a predetermined value. The solenoid valve 73 is an open / close valve. When the solenoid valve 73 is open, the air regulated by the regulator 72 is supplied to the flow paths 43 and 44 of the second mold 34 via the flow path 50. Instead of the solenoid valve 73 which is an on-off valve, a flow rate adjustment valve can be used.
The solenoid valve 73 is connected to the controller 74. The controller 74 controls the operation of the solenoid valve 73, the injection nozzle, the mold opening / closing mechanism and the like in an integrated manner.

A process of molding the resin molded product 10 using the injection molding apparatus 30 will be described.
As shown in FIG. 8, when the resin molded product 10 is molded, a mold closing process is first executed. When the mold closing process is executed, the injection mold 31 is closed. At this time, the solenoid valve 73 is closed. Therefore, air is not supplied to the flow paths 43 and 44 of the second mold 34.
Following the mold closing process, an injection process is performed. When the injection process is executed, the molten resin injected from the injection nozzle passes through the gate 42 and fills the cavities 26, 27, and 28. The filled resin flows in the cavities 26, 27 and 28. In the following, the state of the resin in the rib cavity 27 and the rib cavity 28 will be described by using the rib cavity 27 as a representative.
FIG. 9 shows a state in which the filled resin 72 is flowing through the main body cavity 26 and the rib cavity 27. FIG. 10 shows a state in which the rib cavity 27 is filled with the resin 72. Even when the rib 72 is filled with the resin 72, the body cavity 26 is not filled with the resin 72. The sizes of the gaps 66 and 68 are set such that the resin 72 does not enter. The reason why the resin 72 does not enter the gaps 66 and 68 is that the resin 72 is viscous.

The controller 74 measures the elapsed time from when the injection mold 31 is closed. The controller 74 outputs a valve opening signal to the solenoid valve 73 based on the time measured. The valve opening signal is output to the solenoid valve 73 at the timing when the filling of the resin 72 into the rib cavity 27 is assumed. In setting the timing, pressure measurement data in the rib cavity 27, a flow analysis result of the resin 72, and the like are used. The timing at which the controller 74 starts timing is not limited to the time when the injection mold 31 is closed, and may be the timing at which the injection nozzle starts injection of the resin, for example.
When the solenoid valve 73 is opened, the air injection process shown in FIG. 8 is started. As described above, even if the rib cavity 27 is completely filled with the resin 72, the body cavity 26 is not completely filled with the resin 72. For this reason, an air injection process is started in the middle of an injection process. The air injection process can be started after the injection process is completed. When the solenoid valve 73 is opened, air is supplied to the flow paths 43 and 44 of the second mold 34 via the flow path 50 of the air supply unit 32. The air supplied to the flow path 43 flows into the groove 57 of the vent member 51 along the direction shown by the arrow 79 in FIG. The air that has flowed into the groove 57 further flows into the groove 56. The air flowing into the groove 56 passes through a space formed between the side surface 64 of the opening 45 (see FIG. 5) and the side surface 59 of the intermediate portion 54 of the vent member 51, the gap 66, and the gap 68.

The resin 72 filled in the cavities 26, 27, and 28 contracts as the temperature decreases. When the resin 72 contracts, a slight gap is generated between the third cavity surfaces 37 and 37 of the rib cavity 27 and the side surfaces 78 and 78 of the resin 72. The air that has passed through the gap 68 is injected into the slight gap. Air is injected between the third cavity surfaces 37 and 37 and the side surfaces 78 and 78 of the resin 72 while also flowing in the longitudinal direction of the rib cavities 27. The air further flows and is injected between the second cavity surface 36 and the back surface 75 of the resin 72. Then, as shown in FIG. 11, the back surface 75 of the resin 72 peels from the second cavity surface 36, and the third cavity surfaces 37 and 37 peel from the side surfaces 78 and 78 of the resin 72. The back surface 75 and the second cavity surface 36 can be peeled over a wide range. The air that has passed through the gap 66 and the gap 68 is also injected between the third cavity surface 38 and the tip end surface of the rib at a portion where the vent member 51 is not disposed. Since air also flows in the longitudinal direction of the rib cavity 27, air is injected between the third cavity surface 38 and the tip end surface of the rib over a long range in the longitudinal direction of the rib cavity 27. The second mold 34 has a core and a mold body. The injected air passes through a gap between the core and the mold body and is discharged to the outside. Fluids other than air can be injected.
The back surface 75 of the resin 72 becomes the back surface 18 when the resin 72 is solidified and molded into the resin molded product 10. The side surfaces 78 and 78 of the resin 72 become rib side surfaces 20 and 20 when the resin 72 is solidified and molded into the resin molded product 10.

As shown in FIG. 8, after the injection process is completed, the process proceeds to the pressure holding process. In the pressure holding process, the pressure applied from the gate 42 to the cavities 26, 27, and 28 is maintained substantially constant. In this embodiment, the pressure holding process and the air injection process are performed simultaneously. When carried out at the same time, the pressure required for the pressure holding step can be reduced. That is, if the pressure required when performing only the pressure holding process without performing the air injection process is P1, and the pressure required when simultaneously performing the pressure holding process and the air injection process is P2, P2 may be much smaller than P1. Similarly, P3 is an air pressure required when only the air injection process is performed without performing the pressure holding process, and P4 is an air pressure required when the pressure holding process and the air injection process are performed simultaneously. Then, P4 may be much smaller than P2. Furthermore, P2 + P4 may also be low, and P2 + P4 may be lower than either P1 or P2. If the pressure holding step and the air injection step are performed simultaneously, the pressure applied to the injection mold can be greatly reduced.
A cooling process is also started with the start of the pressure holding process. In the cooling step, the resin 72 is cooled by cooling water flowing through cooling passages (not shown) provided in the first mold 33 and the second mold 34. The resin 72 solidifies when cooled. The resin 72 contracts in the process of solidifying.
Even after the pressure holding process is completed, the air injection process and the cooling process continue. The air injection process and the cooling process are completed simultaneously. The air injection process is ended by the controller 74 outputting a valve closing signal to the solenoid valve 73. When the solenoid valve 73 is closed by the valve closing signal, the supply of air to the cavities 26, 27, and 28 is stopped.
After completing the air injection process and the cooling process, the process proceeds to a mold opening process and the injection mold 31 is opened. Finally, the resin molded product 10 is taken out from the injection mold 31 by executing a resin molded product take-out step.

  It is assumed that the back surface 75 of the resin 72 is not peeled off from the second cavity surface 36 in the process in which the resin 72 is cooled and contracts. If the back surface 75 of the resin 72 and the second cavity surface 36 are not peeled, the back surface 75 tends to peel from the second cavity surface 36 when the resin 72 contracts, and the front surface 76 is also separated from the first cavity surface 35. Try to peel off. When the resin 72 contracts, a force that resists peeling (a force for maintaining a close contact state) acts on the back surface 75 and the second cavity surface 36, and the front surface 76 and the first cavity surface 35. Accordingly, the back surface 75 side tends to peel the front surface 76 from the first cavity surface 35. The front surface 76 side tends to peel the back surface 75 from the second cavity surface 36. For this reason, when the surface 76 of the resin 72 is peeled off from the first cavity surface 35 and recessed, the sink may occur there. In the pressure holding step described above, when the resin 72 contracts, the resin 72 is pushed into the main body cavity 26 from the gate 42 so as to compensate for it. If the amount of shrinkage of the resin 72 is completely compensated, sink marks will not occur. However, if it is far from the injection port 41 of the gate 42 or there is a narrow part in the main body cavity 26, the holding pressure may not be sufficiently transmitted, and sink marks may occur.

As in the injection molding apparatus 30 of the present embodiment, when the air is injected and the back surface 75 of the resin 72 is peeled off from the second cavity surface 36 (see FIG. 10), the resin 72 contracts in the process of being cooled and solidified. Even so, the surface 76 of the resin 72 and the first cavity surface 35 remain in close contact with each other. This is because if the back surface 75 of the resin 72 is peeled off from the second cavity surface 36, the force for peeling the front surface 76 from the first cavity surface 35 does not act. According to this technique, even if the resin molded product has a portion where it is not effective to apply the holding pressure, the occurrence of sink marks can be prevented.
When the pressurized air is injected between the second cavity surface 36 and the back surface 75 of the resin 72, a force that presses the surface 76 of the resin 72 against the first cavity surface 35 acts. This also contributes to maintaining the state in which the surface 76 of the resin 72 and the first cavity surface 35 are in close contact with each other.
When the core is provided in the second mold 32, a step may be formed on the second cavity surface 36 by the main body of the second mold 32 and the core. Even if a step is formed on the second cavity surface 36, the effect of the step does not reach the surface 17 of the resin molded product 10 as long as the resin 72 is solidified with the back surface 75 peeled off from the second cavity surface 36. .
When the third cavity surfaces 37 and 37 are peeled off from the side surfaces 78 and 78, the resin 72 entering the rib cavities 27 easily moves in the direction of coming out of the rib cavities 27 when the resin 72 contracts. For this reason, the occurrence of sink marks on the surface (design surface) 17 on the opposite side of the ribs 15 and 16 is prevented.

  As shown in FIG. 12, the opening 45 can be offset with respect to the rib cavity 27. By offsetting the opening 45, it is possible to adjust the amount of air injected into the side surface 78 side of the resin 72 and the other side surface 78 side. Depending on the shape of the resin molded product, the range in which the injected air spreads can be freely set.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In addition, the technical elements described in the present specification or drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

The perspective view of a resin molded product. The system diagram of an injection molding apparatus. Sectional drawing of a 2nd type | mold. The perspective view of a vent member. The fragmentary sectional view in the state where the vent member is attached to the opening. VI-VI sectional view taken on the line of FIG. VII-VII line sectional drawing of FIG. Injection molding process drawing. Sectional drawing in the middle of resin filling a main body cavity and a rib cavity. Sectional drawing of the state with which the rib cavity was filled with resin. Sectional drawing of the state which resin peeled from the cavity surface. The fragmentary sectional view in the state where the vent member is attached to the opening (modification).

Explanation of symbols

10: resin molded product 11, 12: end 14: body 15, 16: rib 17: front surface 18: back surface 20: rib side surface 21: rib front end surface 22: rib side surface 23: rib front end surface 24, 25: end surface 26: Main body cavity 27:28: Rib cavity 30: Injection molding device 31: Injection mold 32: Air supply part 33: First mold 34: Second mold 35: First cavity surface 36: Second cavity surface 37: Third Cavity surface 38: Fourth cavity surface 39: Fifth cavity surface 40: Sixth cavity surface 41: Injection port 42: Gate 43, 44: Channel 45, 46: Opening 47: Surface 50: Channels 51, 52: Vent member 53: shallow part 54: intermediate part 55: deep part 56, 57: groove 59, 60: side face 61: bottom face 62: side face 63: bottom face 64: side face 65: top face 66, 68: gap 70: one end 71: filter 72 : Le Regulator 73: Solenoid valve 74: controller 75: the back surface 79: Arrow

Claims (3)

An injection mold for injection molding a resin molded product having a design surface and a non-design surface and having a rib protruding from the non-design surface,
A front mold for molding the design surface of the resin molded product;
A back side mold for molding the non-design surface of the resin molded product,
A cavity surface having grooves for molding the ribs is formed on the back side mold,
The back side mold further includes a flow path, one end of the flow path is open to the bottom surface of the groove on the cavity surface, and the other end of the flow path communicates with the outside of the back side mold. Injection mold characterized by.   The injection mold according to claim 1, wherein one end of the flow path is opened in a region of the cavity surface beyond the bottom surface of the groove. It is a method of injection molding a resin molded product having a design surface and a non-design surface, and having ribs protruding from the non-design surface,
Filling a molten resin into a cavity having a shape corresponding to a resin molded product with ribs formed inside an injection mold; and
Injecting pressurized fluid from the inside of the injection mold toward the rib tip surface;
An injection molding method characterized by comprising:

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