JP2008155503A - Manufacturing method of injection-molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection-molded article which has a presentable appearance and almost uniform quality over the entire product, despite its thick wall. <P>SOLUTION: First, a cavity-side part 12 and a movable half 14 of a mold configuring an injection molding machine 10, are used to form a cavity 18 and the cavity 18 is filled with a molten resin R. Next, the molten resin R is loaded to a specified level while the cavity 18 is enlarged by moving the movable half 14 backward to a specified position. Then the molten resin R is compressed by advancing the movable half 14. Under this state, the molten resin R is cured by cooling into the injection-molded article. Finally, the injection-molded article is unloaded by moving the movable half 14 backward to open the mold. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of manufacturing an injection molded product that is performed using an injection molding machine having a fixed mold and a movable mold.

  A fuel cell has a stack in which a predetermined number of unit cells each having an electrolyte / electrode assembly interposed by a pair of separators are stacked. End plates are disposed on both ends of the stack via insulating plates. If necessary, a spacer may be interposed between the insulating plate and the stack (see, for example, Patent Document 1).

  For these spacers and insulating plates, for example, resin molded products produced by an injection molding method are frequently used. That is, it is a molded product provided by a molding method in which molten resin is filled into a plurality of molds and then cooled and cured, and the molded product has a shape corresponding to the shape of the cavity.

  Here, if a thick resin molded product having a thickness corresponding to both the spacer and the insulating plate is produced, it is not necessary to produce each of the spacer and the insulating plate, and the number of injection moldings is reduced, and the work efficiency is reduced. It is considered that the number of parts of the fuel cell is reduced and the assembly of the fuel cell is facilitated. However, when such a thick-walled resin molded product is produced by an injection molding method, sink marks are likely to occur when the molten resin undergoes volume shrinkage as it cools and cures. There is a bug.

  In order to solve such problems, Patent Documents 2 and 3 propose that the molten resin is injected while increasing the volume of the cavity by displacing the movable mold.

JP 2004-227894 A Japanese Patent Laid-Open No. 7-112457 JP-A-6-320591

  When the injection molding method is adopted to produce a thick resin molded product, the density on the inner side is smaller than that on the outer skin side, which may result in a low-strength molded product. The reason for this is that when a large amount of molten resin is introduced into the cavity to obtain a thick resin molded article, the curing rate of the molten resin on the inner side of the thick resin molded article is slower than that of the molten resin on the outer skin side. Because. That is, the molten resin on the inner side flows downward from the cavity, and as a result, the outer side formed below the cavity becomes dense while the inner side becomes sparse.

  As described in Patent Documents 2 and 3, it is difficult to eliminate this problem only by filling the molten resin while changing the volume of the cavity.

  The present invention has been made to solve the above-described problems, and even when a thick-walled resin molded product is produced, it is possible to ensure an aesthetic appearance, and the inner side of the thick-walled resin molded product. An object of the present invention is to provide a method for manufacturing an injection molded product that can be made substantially equal in density to the outer skin side.

To achieve the above object, the present invention is an injection molded product manufacturing method for manufacturing an injection molded product using an injection molding machine having a fixed mold and a movable mold,
Providing a cavity with the fixed mold and the movable mold;
Injecting raw materials into the cavity;
Injecting the raw material into the cavity while expanding the volume of the cavity by retracting the movable mold; and
Advancing the movable mold and compressing the raw materials;
Retreating the movable mold to perform mold opening and taking out an injection molded product formed by curing the raw material;
It is characterized by having.

  That is, in the present invention, first, a raw material is injected by forming a cavity having a relatively small volume, and then a predetermined amount of the raw material is injected while expanding the volume of the cavity by retracting the movable mold. After that, the movable mold is advanced to compress the raw material. In the small volume cavity, the raw material on the inner side of the injection-molded product is suppressed from flowing below the cavity. Further, by compressing the raw material by moving the movable mold forward, it is possible to suppress the injected raw material from flowing while expanding the volume of the cavity. In addition, since the raw material is introduced while expanding the volume of the cavity, it is possible to produce a thick injection molded product.

  For the reasons described above, the internal defect such as voids is extremely small despite the thickness being thick, and the quality is substantially constant throughout. Therefore, the density is substantially equal on the inner side and the outer skin side. An injection molded product exhibiting strength can be obtained.

  In addition, by performing the above-described compression, it is possible to suppress the occurrence of sink marks when shrinking due to cooling and hardening of the raw material. As a result, the external appearance is good.

In the present invention, it is preferable to balance the expansion volume of the cavity and the amount of raw material introduced. This is because if the expansion volume of the cavity is excessively smaller than the introduction amount of the raw material, it is difficult to introduce the raw material, and if it is excessively large, the molten resin flows, so that molding may not be easy. Specifically, the expansion volume of the cavity due to the retraction of the movable mold is preferably set to 40 to 4800 cm ³ / sec, while the filling amount of the raw material is preferably set to 80 to 220 cm ³ / sec.

  In addition, it is preferable that the end point of the backward movement of the movable mold is a position that is at a maximum more than 100% to 110% of the thickness of the injection molded product. Thereby, it becomes remarkably easy to obtain an injection molded product having a thickness of the design dimension.

  Furthermore, when forming the first cavity, the clearance between the fixed mold and the movable mold is preferably within 10 mm. In this case, since the raw material on the inner side of the injection-molded product is remarkably suppressed from flowing below the cavity, an injection-molded product in which the density on the inner side is substantially equal to the density on the outer skin side can be easily obtained. Because it becomes like this.

  According to the present invention, a cavity having a relatively small volume is first formed to inject raw materials, and then a predetermined amount of raw material is injected while expanding the cavity volume by retracting the movable mold. Since the raw material is compressed by advancing the movable mold, the internal defects such as voids are extremely small, and the quality is substantially constant throughout, and therefore the density is approximately equal on the inner side and the outer skin side. An injection molded product exhibiting high strength can be obtained.

  Furthermore, injection molded articles having various thicknesses can be obtained by adjusting the retraction amount of the movable mold.

  In addition, since the raw material is introduced while expanding the volume of the cavity, it is also possible to produce the injection molded product as a thick one.

  Hereinafter, preferred embodiments of the method for producing an injection molded product according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a longitudinal sectional explanatory view of a main part of an injection molding machine 10 for carrying out the manufacturing method according to the present embodiment. The injection molding machine 10 includes a fixed mold 12, a movable mold 14, and a screw 16 installed on the movable mold 14. A flat plate shape is formed by a cavity 18 formed by the fixed mold 12 and the movable mold 14. The injection-molded product is molded.

  In the fixed mold 12, a recess 20 is formed on the end surface facing the movable mold 14. The vertical dimension and horizontal dimension of the recess 20 are set to, for example, about 400 mm and about 200 mm.

  In addition, a knockout pin (not shown) is disposed in the recess 20 so as to freely advance and retract. The knockout pin is embedded in the fixed mold 12 while a first step S1 to a fourth step S4 (described later), which is a step of providing an injection molded product, is performed, and a fifth step of taking out the injection molded product. It is energized when performing S5 process and it exposes from side 20a of crevice 20.

  And in the end surface in which the recessed part 20 was formed, the shims 22 and 22 are installed in the vicinity of this recessed part 20. As shown in FIG. As will be described later, these shims 22 and 22 serve to stop the movable mold 14 at a position separated from the fixed mold 12 by a predetermined distance. In the present embodiment, the predetermined distance is set within 10 mm. In other words, the height h of the shims 22 and 22 is within 10 mm.

  On one end face of one movable mold 14, a convex part 24 is formed at a position corresponding to the position of the concave part 20 of the fixed mold 12. As shown in FIG. 1, the convex portion 24 is inserted into the concave portion 20 when the movable mold 14 comes closest to the fixed mold 12. With this insertion, a cavity 18 is formed.

  The screw 16 installed on the other end surface of the movable mold 14 constitutes an injection mechanism for injecting the molten resin R. In addition, a runner 26 that is a passage for introducing the molten resin R injected from the screw 16 into the cavity 18 is formed inside the movable mold 14. That is, the runner 26 is formed so as to penetrate from one end surface of the movable mold 14 to the other end surface (the front end surface of the convex portion 24), and the molten resin R is introduced into the cavity 18 from the front end surface of the convex portion 24.

  The movable mold 14 is formed with a gas supply path (not shown) for holding pressure. Further, the movable mold 14 approaches and separates from the fixed mold 12 under the action of a movable mechanism (not shown) such as a servo motor or a hydraulic control motor. The displacement and stoppage of the movable mold 14 are determined by a control circuit (not shown) controlling the movable mechanism (servo motor or hydraulic control motor). Note that the position of the movable mold 14 is detected by a position sensor (not shown).

  Next, a method for manufacturing an injection molded product according to the present embodiment will be described with reference to FIG. In this manufacturing method, the first step S1 for providing the cavity 18, the second step S2 for injecting the molten resin R (raw material), and the molten resin R while expanding the volume of the cavity 18 by retracting the movable die 14. The third step S3 for performing the injection, the fourth step S4 for advancing the movable mold 14 to compress the molten resin R, and the fifth step S5 for taking out the injection molded product.

  In the first step S1, mold closing is performed. That is, the movable die 14 approaches the fixed die 12, and finally the movable die 14 comes into contact with the front end surfaces of the shims 22 and 22, as shown in FIG. By this contact, the fixed mold 12 and the movable mold 14 are separated by the height h of the shims 22 and 22. In other words, an appropriate clearance within 10 mm is provided between the fixed mold 12 and the movable mold 14.

  On the other hand, the convex part 24 of the movable mold 14 is inserted into the concave part 20 of the fixed mold 12, and the cavity 18 is formed accordingly. In the present embodiment for producing a flat plate-shaped injection molded product having a constant thickness, the clearance between the side surface 20a of the concave portion 20 forming the cavity 18 and the tip surface of the convex portion 24 is such that the movable die 14 is a fixed die. 12 is substantially the same as the value obtained by adding the height h of the shims 22 and 22 to the separation distance between the side surface 20a and the tip surface of the convex portion 24 when approaching 12 again. Here, in the present embodiment, the separation distance between the side surface 20a and the front end surface of the convex portion 24 when the movable mold 14 approaches the fixed mold 12 again is larger than the height h of the shims 22 and 22. Remarkably small. Therefore, the clearance between the side surface 20 a of the concave portion 20 and the tip surface of the convex portion 24 approximates the height h of the shims 22 and 22.

Next, in the second step S2, the injection of the molten resin R from the screw 16 is started. Here, as the molten resin R, general thermoplastic resins such as modified polyphenylene ether, polypropylene, polystyrene, polycarbonate, acrylonitrile-butadiene-styrene copolymer can be used. Moreover, what is necessary is just to set a mold temperature, an injection pressure, and an injection speed, for example in the range of 70-150 degreeC, 900-1700 kgf / cm < ² >, 80-220 cm < ³ > / sec, respectively.

  In the second step S2, the cavity between the side surface 20a of the concave portion 20 and the front end surface of the convex portion 24 corresponding to the dimension in the thickness direction of the injection molded product is the height h of the shims 22 and 22, that is, a cavity within 10 mm. 18 is filled with molten resin R. When the dimension in the thickness direction is about this level, even if the molten resin R is only pressed by the convex portion 24, the molten resin R is remarkably suppressed from flowing below the cavity 18. Accordingly, it is possible to avoid the production of a molded product having a small density on the inner side and a large density on the outer skin side.

  Note that a pressure of about 60 MPa is sufficient for the molten resin R. This pressing force can be detected by measuring the pressure of the molten resin R with a pressure sensor disposed in the cavity 18. In the following description, the measured pressure of the molten resin R is expressed as “in-mold pressure”.

  In the present embodiment, as shown in FIG. 3, a third step S3, which is the next step, is performed in the middle of reducing the in-mold pressure. That is, as shown in FIG. 4, the molten resin R is injected while the movable mold 14 is retracted. Note that the solid line in FIG. 3 represents the pressure inside the mold, and the broken line represents the separation distance between the fixed mold 12 and the movable mold 14. Further, S1 in FIG. 3 means that the first step S1 is in progress, and the remaining S2 to S4 are also in progress of the second step S2 to the fourth step S4, respectively. Means.

As the movable die 14 is retracted, the volume of the cavity 18 gradually increases. In the third step S3, the molten resin R is introduced into the cavity 18 whose volume is increasing in this way. At this time, if the expansion volume of the cavity 18 is excessively smaller than the introduction amount of the molten resin R, it is difficult to introduce the molten resin R. On the other hand, if the expansion volume is excessively large, it is not easy to mold the molten resin R. Therefore, it is preferable that the movable mold 14 is retracted and the molten resin R is introduced while balancing the expansion volume of the cavity 18 and the amount of the molten resin R introduced. Specifically, it is preferable to injection in an amount of molten resin R 80~220cm ³ / sec while extending the cavity 18 by 40~4800cm ³ / sec. Note that the expansion volume of the cavity 18 and the introduction amount of the molten resin R are preferably proportional.

  As shown in FIG. 5, the movable die 14 is retracted to a predetermined position and ends the displacement. In the present embodiment, the displacement end point is set so that the distance between the side surface 20a of the concave portion 20 and the tip surface of the convex portion 24 is larger than the design dimension in the thickness direction of the molded product. For example, when producing an injection molded product having a thickness direction dimension of 20 mm, the displacement end point of the movable mold 14 is set so that the separation distance between the side surface 20a of the concave portion 20 and the front end surface of the convex portion 24 exceeds 20 mm. The

  In addition, it is preferable to set the displacement end point of the movable mold 14 so that the separation distance between the side surface 20a of the concave portion 20 and the front end surface of the convex portion 24 is within 110% of the design dimension in the thickness direction of the molded product. In this case, it is because an injection molded product whose dimension in the thickness direction is a substantially designed value can be easily obtained. For example, in the case of the above example, it is preferable to stop the movable mold 14 so that the separation distance between the side surface 20a of the concave portion 20 and the tip surface of the convex portion 24 is within 22 mm.

  During the execution of the third step S3, so-called pressure holding is performed, in which the molten resin R is cooled and cured while pressure is applied in order to compensate for the shrinkage caused by the molten resin R becoming an injection-molded product. This holding pressure is provided by a gas supplied from the gas supply path (not shown).

  And in 4th process S4, as shown in FIG. 6, the movable mold | type 14 is advanced toward the fixed mold | type 12. As shown in FIG. As a result, the movable mold 14 approaches the fixed mold 12 again, and as a result, the molten resin R is pressed by the convex portion 24 and compressed. In this state, the molten resin R is cooled and cured.

  During the cooling and curing, the molten resin R is pressed by the convex portion 24 as described above. This suppresses the occurrence of sink marks when the molten resin R shrinks with the cooling and curing. Therefore, even if it is thick, an injection molded product F having an excellent appearance is obtained. In addition, since the molten resin R is suppressed from flowing below the cavity 18 by the pressing, the density on the inner side and the density on the outer skin side of the injection molded product F are substantially equal. That is, although the obtained injection molded product F is thick, there are very few internal defects such as voids, and the quality is substantially constant over the whole, and therefore shows high strength.

  FIG. 3 also shows changes in the pressure in the mold and the changes in the separation distance between the fixed mold 12 and the movable mold 14 in the first step S1 to the fourth step S4.

  Finally, in the fifth step S5, the movable mold 14 is moved backward to open the mold, and the injection molded product F (flat plate material) is pressed under the action of the knockout pin (not shown). Thereby, the injection molded product F is taken out.

  As described above, in the present embodiment, the cavity 18 is first formed and injected with the molten resin R, and then the movable mold 14 is moved backward to expand the cavity 18 while expanding the cavity 18. Further injection is performed, and after the injection is finished, the movable mold 14 is advanced to press the molten resin R. Thereby, even if it is thick, the appearance of the appearance is good, and there can be obtained a substantially homogeneous injection molded product F with few internal defects throughout.

  As a specific example of the injection molded product F produced in this way, there is a member that is interposed between the stack and the end plate constituting the fuel cell and has the functions of an insulating plate and a spacer. Alternatively, various spacers having different thicknesses may be used.

  In the above-described embodiment, the movable mold 14 is continuously displaced to a predetermined position in the third step S3. However, the movable mold 14 may be displaced stepwise. In this case, the molten resin R may be injected only while the movable mold 14 is displaced.

  Further, in this embodiment, the advancing end of the movable mold 14 is defined by providing the fixed mold 12 with shims 22, 22, whereby the side surface 20 a of the concave portion 20 of the fixed mold 12 and the convex portion 24 of the movable mold 14 are defined. Although a predetermined clearance is provided between the front end surface and the protrusion 24, the protruding dimension of the protrusion 24 is made smaller than the depth of the recess 20, so that the movable mold 14 is closest to the fixed mold 12. At this time, a predetermined clearance may be provided between the side surface 20a and the tip surface of the convex portion 24.

  Furthermore, the injection molded product F is not particularly limited to the constituent members of the fuel cell, and may be any member. The shape is not limited to a flat plate shape, and various shapes can be produced. Of course, an injection molded product having a bent portion or a curved portion may be provided.

It is principal part longitudinal cross-section explanatory drawing of the injection molding machine for enforcing the manufacturing method of the injection molded product which concerns on this Embodiment. It is a flowchart of the said manufacturing method. It is a graph which shows the change of the pressure in a type | mold during performing the process which produces an injection molded product from molten resin, and the change of the separation distance of a fixed mold | type and a movable mold | type. It is principal part longitudinal cross-section explanatory drawing of the injection molding machine in the middle of performing the 3rd process which inject | emits molten resin, expanding a cavity. It is principal part longitudinal cross-section explanatory drawing of the injection molding machine at the time of the movable mold | type complete | finishing the backward displacement to a predetermined position. It is principal part longitudinal cross-section explanatory drawing of the injection molding machine in the middle of performing the 4th process which advances a movable mold and compresses molten resin.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Injection molding machine 12 ... Fixed mold 14 ... Movable mold 16 ... Screw 18 ... Cavity 20 ... Concave part 22 ... Shim 24 ... Convex part 26 ... Runner F ... Injection molded product R ... Molten resin

Claims (4)

An injection molded product manufacturing method for manufacturing an injection molded product using an injection molding machine having a fixed mold and a movable mold,
Providing a cavity with the fixed mold and the movable mold;
Injecting raw materials into the cavity;
Injecting the raw material into the cavity while expanding the volume of the cavity by retracting the movable mold; and
Advancing the movable mold and compressing the raw materials;
Retreating the movable mold to perform mold opening and taking out an injection molded product formed by curing the raw material;
A method for producing an injection-molded article, comprising: 2. The injection molding product according to claim 1, wherein the raw material is injected in an amount of 80 to 220 cm ³ / sec while expanding the cavity by 40 to 4800 cm ³ / sec by retreating the movable mold. Manufacturing method.   3. The method of manufacturing an injection molded product according to claim 1, wherein the movable mold is retracted to a position where the movable mold reaches a maximum of more than 100% to 110% of the thickness of the injection molded product.   The manufacturing method according to any one of claims 1 to 3, wherein the cavity is formed with a clearance between the fixed mold and the movable mold within 10 mm.

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