JP2019155816A - Injection molding method - Google Patents

Abstract

To provide an injection molding method capable of filling a thermoplastic resin into a cavity while maintaining fluidity of the thermoplastic resin.SOLUTION: An injection molding method according to the present invention separates at least two molds 13 and 14 in the horizontal direction, forms a cavity 16 for filling a thermoplastic resin, and injects the thermoplastic resin in a softened state from a gate of the mold 13 positioning on the upper side of the cavity 16 to the lower surface of the mold 13 positioning on the lower side of the cavity 16 so as not to touch the side surfaces of the at least two molds 13 and 14.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an injection molding method.

  As a method for processing a thermoplastic resin such as plastic, there is an injection molding method. The injection molding method is a method in which a thermoplastic resin is heated and softened, and a pressure is applied to the softened thermoplastic resin so as to push the thermoplastic resin into the mold, thereby filling the mold with the thermoplastic resin and molding.

  The fluidity of this softened thermoplastic resin not only determines the ease of filling the mold cavity, but also determines whether sufficient pressure is transferred to the thermoplastic resin in the cavity after filling, so It affects not only dimensional accuracy and appearance, but also high-level transfer of fine information on the mold surface required for molded products such as optical disks, and is an important factor in determining the processability of the resin.

  In Patent Document 1, in an injection molding method in which a molten thermoplastic resin is injected and filled into a mold cavity, a pressurized gas is filled in the mold cavity in advance, and then the molten thermoplastic resin has a moving speed of the flow front. An injection molding method is described in which the injection is performed so that the speed is higher than the slip generation speed.

  Further, in Patent Document 1, in an injection molding method in which a molten thermoplastic resin is injection-filled into a mold cavity, a lubricant is previously applied to the inner surface of the mold cavity, and then the molten thermoplastic resin is transferred to a flow front moving speed. An injection molding method is described, in which the injection is performed so as to have a speed equal to or higher than the slip generation speed.

JP 2005-125504 A

  However, the method of Patent Document 1 has a problem that it is difficult to fill the cavity with the thermoplastic resin while maintaining the fluidity of the thermoplastic resin.

  Specifically, in the method of Patent Document 1 using a pressurized gas, the pressurized gas is foamed on the surface of the thermoplastic resin and the product surface quality is deteriorated. If the filling pressure is too high, the mold opens. There was a problem that it was difficult to ensure an appropriate product thickness.

  In addition, in the method of Patent Document 1 using a lubricant, it is difficult to ensure the uniformity of application, and there is a problem that fluidity varies in the mass production process, and the lubricant is applied while the mold is open. Therefore, there is a problem that the cycle time is increased.

  In the injection molding method of the present invention, at least two molds are separated in the horizontal direction to form a cavity filled with a thermoplastic resin, and from the mold gate located at the upper part of the cavity to the lower part of the cavity. A soft thermoplastic resin is injected onto the lower surface of the mold so as not to contact the side surfaces of the at least two molds.

  According to the injection molding method of the present invention, the softened thermoplastic resin is not contacted with the side surface of the mold from the gate of the mold located at the upper part of the cavity to the lower surface of the mold located at the lower part of the cavity. By injecting, the cavity can be filled with the thermoplastic resin while maintaining the fluidity of the thermoplastic resin.

  ADVANTAGE OF THE INVENTION According to this invention, the injection molding method which can be filled with a thermoplastic resin in a cavity can be provided, maintaining the fluidity | liquidity of a thermoplastic resin.

It is sectional drawing which shows schematic structure of the injection molding apparatus concerning this Embodiment. It is a flowchart which shows the procedure of the injection molding method concerning this Embodiment. It is sectional drawing which shows the outline of the state by which resin was inject | emitted in the injection molding method concerning this Embodiment. It is sectional drawing which shows the outline of the state which closed the movable metal mold | die in the injection molding method concerning this Embodiment. It is sectional drawing which shows the outline of the state which injection | pouring and mold closing were completed in the injection molding method concerning this Embodiment. It is sectional drawing which shows the outline of the state by which mold opening and product taking-out are made | formed in the injection molding method concerning this Embodiment. It is sectional drawing which shows the flow of resin in a general cavity. It is sectional drawing which shows the relationship between the thickness of the cavity in the injection molding method concerning this Embodiment, and the thickness of the resin in the flow.

(This embodiment)
Embodiments of the present invention will be described below with reference to the drawings. In the present application, “lower” is the direction of action of gravity, and “upper” is the opposite side. The horizontal direction is a direction parallel to the horizontal plane, that is, a direction orthogonal to the direction in which gravity works.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an injection molding apparatus according to the present embodiment. In FIG. 1, an injection molding apparatus 10 includes a hopper 11, an injection unit 12, a fixed mold 13, and a movable mold 14.

  The hopper 11 is an input port that receives the resin pellets to be input and guides them to the injection unit 12.

  The injection unit 12 includes a heater for heating the resin and a mechanism (for example, a cylinder and a screw) for extruding the resin (not shown). The injection unit 12 then extrudes the resin softened by heating and sends it to the hot runner 15 in the fixed mold 13.

  The fixed mold 13 is a mold that forms a cavity 16 that is a cavity corresponding to the shape of a molded product by being combined with the movable mold 14. The fixed mold 13 has a hot runner 15 inside. The hot runner 15 is a flow path that connects the first end to the injection port of the injection unit 12 and connects the second end to the upper portion of the cavity 16. The fixed mold 13 has a gate 17 (opening) for the hot runner 15 on the surface corresponding to the upper portion of the cavity 16. For example, the gate 17 is provided on the uppermost surface of the cavity 16 of the fixed mold 13.

  The movable mold 14 is a movable mold. Specifically, by moving the movable mold 14 in the horizontal direction, the movable mold 14 is separated from the fixed mold 13 from the state where the movable mold 14 is combined with the fixed mold 13 to form the cavity 16. Thus, the cavity 16 can be changed to an open state. It can also be changed to the opposite state. The power for moving the movable mold 14 can be applied by human power, electric power, or the like.

  The injection molding apparatus 10 of FIG. 1 is used in a form in which the movable mold 14 moves in the horizontal direction and the resin is injected downward from the gate 17 on the surface corresponding to the upper portion of the cavity 16.

  With the above configuration, injection molding is performed. Next, the procedure of the injection molding method of this embodiment will be described. FIG. 2 is a flowchart showing the procedure of the injection molding method according to the present embodiment.

  First, in step S21, the fixed mold 13 and the movable mold 14 are separated to such an extent that the cavity 16 can be formed, and the softened resin is injected from the gate 17 into the cavity 16. Then, after a predetermined amount of resin is injected, the process proceeds to step S22. FIG. 3 is a cross-sectional view schematically showing a state in which a resin is injected in the injection molding method according to the present embodiment. As shown in FIG. 3, the resin is injected downward from the gate 17 facing the upper portion of the cavity 16, so that the lower portion of the cavity 16 is not touched with the fixed mold 13 and the movable mold 14 on the side surface of the cavity 16. To the fixed mold 13 facing.

  Next, in step S <b> 22, the resin is injected from the gate 17 into the cavity 16, and the movable mold 14 moves so as to approach the fixed mold 13. As a result, the cavity 16 formed by the fixed mold 13 and the movable mold 14 becomes narrow, and becomes a cavity 16 corresponding to the shape of the molded product. The resin in the cavity 16 is also pushed by the movable mold 14 and molded into the shape of the molded product. FIG. 4 is a cross-sectional view schematically showing a state in which the movable mold is closed in the injection molding method according to the present embodiment. Then, the process proceeds to step S23.

  In step S23, in a state where the fixed mold 13 and the movable mold 14 are completely closed, the fixed mold 13 and the movable mold 14 are cooled, whereby the resin in the cavity 16 is cooled in the shape of the molded product. . FIG. 5 is a cross-sectional view schematically showing a state in which injection and mold closing have been completed in the injection molding method according to the present embodiment. As shown in FIG. 5, when the fixed mold 13 and the movable mold 14 are in contact with each other at the portion other than the cavity 16, the resin is filled in the cavity 16 in the shape of the molded product. In this state, the resin is solidified by cooling the resin. After cooling, the process proceeds to step S24.

  In step S <b> 24, the movable mold 14 is moved away from the fixed mold 13. Then, the resin solidified in the shape of the molded product 18 is removed from the movable mold 14 (or the fixed mold 13). FIG. 6 is a cross-sectional view schematically showing a state where the mold is opened and the product is taken out in the injection molding method according to the present embodiment. As shown in FIG. 6, the resin adheres to the movable mold 14 in a state where the movable mold 14 is separated from the fixed mold 13. By removing this resin from the movable mold 14, a molded product 18 is obtained.

  Injection molding is performed by the above method. Next, the effect of the injection molding method of the present embodiment will be described.

  In general injection molding, the resin is flown from the upstream side to the downstream side in the cavity. However, since the resin flowing out from the gate flows while contacting the mold, the resin flows from the resin while flowing in the cavity. Heat is conducted to the mold and the temperature of the resin decreases. FIG. 7 is a cross-sectional view showing the flow of resin in a general cavity. As shown in FIG. 7, the resin flows in the direction of the arrow, and flows while contacting the surface of the mold that forms the cavity. Therefore, the resin gradually solidifies during flow and becomes difficult to flow.

  In the injection molding method of the present embodiment, the resin is caused to flow so that the resin does not touch the mold during the flow. For example, using a mold that opens in the horizontal direction, having a gate at the top of at least one mold, and letting the resin flow downward with at least one of injection pressure and gravity, the resin does not touch the side mold Reach the bottom mold.

  For example, as shown in FIG. 8, while the resin is flowing into the cavity 16, the thickness of the cavity 16 formed by the fixed mold 13 and the movable mold 14 in the horizontal direction is the horizontal level of the flowing resin. It is desirable that the thickness be larger than the thickness in the direction. FIG. 8 is a cross-sectional view showing the relationship between the thickness of the cavity 16 and the thickness of the flowing resin in the injection molding method according to the present embodiment. In FIG. 8, the cavity thickness A indicates the thickness in the horizontal direction of the cavity 16 in a state where the fixed mold 13 and the movable mold 14 are completely closed. In FIG. 8, the resin thickness B indicates the thickness in the horizontal direction of the resin flowing from the upper part to the lower part of the cavity 16.

  As shown in FIG. 8, when the cavity thickness A is larger than the resin thickness B, the resin can reach the lower fixed mold 13 without touching the fixed mold 13 and the movable mold 14 during the flow. . When the cavity 16 is not a constant thickness, the maximum value of the resin thickness B is made larger than the minimum value of the cavity thickness A, so that the resin can reach the lower mold without touching the mold during the flow. it can.

  In addition, when the shape of the cavity 16 is a complicated shape having unevenness or the like, the gate 17 is disposed at a position where the resin flowing region does not overlap the side surface of the mold when the cavity 16 is viewed from the top to the bottom. During the flow, the resin can reach the lower mold without touching the mold.

  In general, the thermal conductivity and heat capacity of air are smaller than the thermal conductivity and heat capacity of metals. Therefore, the temperature of the resin flowing while touching the air in the cavity 16 without touching the mold is not easily lowered.

  Further, in the injection molding method of the present embodiment, since the resin flows from the top to the bottom of the cavity 16, the resin can be flowed by gravity. Therefore, even when the molded product is large in the vertical direction, the resin can be injected from the gate with a low pressure to reach the lower mold.

  As described above, according to the injection molding method of the present embodiment, the mold gate located at the upper part of the cavity is softened from the lower surface of the mold located at the lower part of the cavity so as not to contact the side surface of the mold. By injecting the thermoplastic resin in a state, it is possible to fill the cavity with the thermoplastic resin while maintaining the fluidity of the thermoplastic resin.

  In addition, since the temperature of the resin is unlikely to decrease in the injection molding method of the present embodiment, a thermoplastic resin having a high viscosity can be made to flow far while maintaining fluidity. Therefore, even when molding a molded part having a large size, the resin can be flowed into the cavity with a small number of gates.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, in the above-described embodiment, an example in which resin is injected directly from the gate 17 is described. The resin may be injected in an oblique direction. There may be a plurality of gates 17 provided on the upper portion of the fixed mold 13. Further, an auxiliary gate may be provided on the side surface of the mold in the cavity 16 (at least one of the fixed mold 13 and the movable mold 14). For example, it is effective to provide an auxiliary gate when the molded product has a complicated shape and it is difficult for the resin to flow in the cavity 16 only by flowing the resin from above to below.

  The fixed mold 13 and the movable mold 14 are closed continuously, for example, immediately after the resin reaches the lower surface or after several seconds (after a predetermined number of seconds have elapsed). When the resin is injected up to the molded product volume (product volume), it is desirable that the fixed mold 13 and the movable mold 14 be closed to the molded product thickness (product thickness). The timing and speed for closing the fixed mold 13 and the movable mold 14 are determined by comprehensively judging, for example, cycle time, surface quality, warpage deformation, and the like.

DESCRIPTION OF SYMBOLS 10 Injection molding apparatus 11 Hopper 12 Injection unit 13 Fixed mold 14 Movable mold 15 Hot runner 16 Cavity 17 Gate 18 Molded product

Claims (1)

At least two molds are spaced apart horizontally to form a cavity filled with thermoplastic resin;
Injection of injecting a soft thermoplastic resin from the gate of the mold located at the upper part of the cavity to the lower surface of the mold located at the lower part of the cavity so as not to contact the side surfaces of the at least two molds Molding method.

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