JP2010125670A - Method for injection molding of resin component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance appearance by controlling the occurrence of sink marks at the gate part and reduce molding cycle time in injection-molding a resin molding. <P>SOLUTION: A sprue 51, runner 52, and gate 53 (a composite gate structure of main gate 53A and sub-gate 53B) are employed for a resin path 50 for molten resin M to be injected into the cavity C partitioned between the cavity die 20 and the core die 30. Since the resin injected through the main gate 53A being an existing gate tends to shrink at the gate 60a, the molten resin M is directly injected to the gate 60a from the back side through the sub-gate 53B to effectively apply holding pressure. This hampers the resin to shrink and surely prevents sink marks a from occurring. No change in molding conditions eliminates the occurrence of uneven luster, burrs, etc., and reduces holding pressure time. The composite gate system reduces injection time and cycle time. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an injection molding method for a resin molded product, and in particular, injection of a resin molded product that can reliably prevent the sink of a gate portion, eliminate appearance defects such as uneven gloss and burrs, and shorten the molding cycle. The present invention relates to a molding method.

  Various molding methods such as an injection molding method, a mold press molding method, a cold press molding method, a slush molding method, and the like are performed as molding methods for resin molded products. And, there is a tendency that the injection molding method is frequently used in terms of cost. FIG. 5 shows a schematic configuration of an injection mold 1 used in the injection molding method. The injection mold 1 is roughly composed of a cavity mold 2 and a core mold 3, and these two molds 2, 5 is clamped as shown in FIG. 5, and then the resin molded product 7 is molded into a required shape by injecting and filling the molten resin M into the cavity C through the sprue 4, the runner 5, and the gate 6 which are resin passages. is doing.

  6 to 8 show the molten resin in the cavity C via the runner 5 and the gate 6 (the overlap gate 6a is used in FIGS. 6 and 7 and the side gate 6b is used in FIG. 8). Although M is injected and filled, and a form that is injection molded into a required shape is shown, the overlap gate 6a and the side gate 6b are set to have a small cross-sectional area in consideration of gate cut processing, The gate part is easily sealed with the molten resin M, a sufficient holding pressure is not applied, and a sink mark a is likely to occur in the vicinity of the gate 6 (hereinafter referred to as the gate part 7a) in the resin molded product 7, causing a defect in appearance. is there. As a countermeasure, when the shrinkage a is eliminated by changing the holding time or holding pressure when the molten resin M is supplied, appearance defects such as gloss unevenness and burrs occur in places other than the gate portion 7a. End up. Further, when the holding time is extended, there is a problem that productivity is lowered due to an increase in the molding cycle.

  As another countermeasure, as shown in FIG. 9, an attempt is made to reduce the shrinkage difference and prevent the occurrence of sink marks by reducing the thickness of the gate portion 7 a by setting a thinning 7 b on the back surface side of the gate portion 7 a. In this case as well, gloss unevenness due to the difference in plate thickness occurs. The conventional injection molding method and injection mold are described in detail in Patent Document 1.

JP 2001-309992 A

  As described above, in the injection molding method using the conventional injection mold 1, the molten resin passes through the sprue 4 and the runner 5 and enters the cavity C through the gate 6 such as the overlap gate 6 a or the side gate 6 b. When M is injected and filled, sink marks a are likely to occur on the surface near the gate portion 7a, and in order to eliminate the sink marks a, it is necessary to extend the holding time of the molten resin M and increase the holding pressure. In this case, it has been pointed out that there is a tendency that appearance defects such as uneven gloss and burrs occur in areas other than the gate portion 7a, and that when the holding time is extended, the molding cycle is increased and the productivity is lowered. .

  The present invention has been made in view of such circumstances, and is an injection molding method for a resin molded product. In addition to not causing sink marks in the gate portion, gloss unevenness, burrs, etc. are also generated in other parts. An object of the present invention is to provide an injection molding method of a resin molded product that can provide a beautiful appearance without causing appearance defects and can maintain good moldability without extending a molding cycle.

  In order to solve the above-mentioned problems, the present inventor has paid attention to the fact that, as a result of earnest research, the use of a composite gate system in which a sub-gate is added in addition to the existing gate can suppress the sink of the gate part. Thus, the present invention has been completed.

  That is, the present invention is a resin molding that molds a resin molded product of a required shape by injecting molten resin into a cavity defined by a cavity mold and a core mold through a resin passage composed of a sprue, a runner, and a gate. In the product injection molding method, the gate in the resin passage adopts a composite gate system of a main gate and a sub-gate, and injects and fills molten resin into the cavity through the main gate having a small cross-sectional area, and toward the gate portion. In addition to intensively injecting molten resin through the subgate, even if the main gate is sealed, the holding pressure can be effectively applied by supplying the molten resin from the subgate, and the shrinkage of the sink part is directly suppressed. It is characterized by.

  Further, the injection mold used in the method of the present invention is an injection mold of a resin molded product obtained by molding a resin molded product into a required shape by injecting molten resin into a cavity. The mold is composed of a cavity mold and a core mold that can be clamped and opened with each other, and a resin passage for supplying molten resin is provided in the cavity between the molds. The resin passage includes a sprue, a runner, and a gate. It is characterized in that a composite gate structure of a main gate that supplies most of the molten resin as a gate and a sub-gate for suppressing sink marks is employed.

  Here, the injection mold is composed of a cavity mold and a core mold that can be clamped together and opened, and a sprue, a runner, which is a resin passage in a state where the cavity mold and the core mold are clamped By injecting and filling molten resin into the cavity through the gate, the resin molded product is formed into a required shape. In addition, an ejector pin connected to an ejector plate as an ejecting mechanism for projecting a resin molded product in the mold release direction, with either the cavity mold or the core mold as the movable side and the other as the fixed side, A sprue lock pin or the like protrudes the resin molded product, the sprue, and the resin end material in the runner.

  The method of the present invention is a composite gate that uses a spur, a gate for supplying molten resin from the runner to the cavity, and a sub-gate for suppressing the sink of the gate portion in addition to the main gate such as the side gate and the overlap gate. The method is adopted. This subgate is drilled on the core mold side, and the tip of the subgate may be set on the back surface of the resin molded product, or may be connected to the tip of the rib protruding from the back surface of the resin molded product. . Alternatively, the molten resin may be supplied to the cavity side through a notch provided on the side of the ejector pin that projects the resin molded product.

  As described above, according to the method of the present invention, the sub-gate is set on the back side of the gate portion in the resin molded product, the molten resin is injected from the sub-gate, and an appropriate holding pressure is applied. The resin shrinkage can be directly suppressed, and the effect of preventing sink marks is remarkable. In addition, since measures can be taken without changing the molding conditions, gloss defects, burrs and other appearance defects other than sink marks do not occur, and it is not necessary to extend the holding time, so the molding cycle is not prolonged, Excellent formability.

  As described above, the injection molding method of the resin molded product according to the present invention is a composite in which molten resin is supplied into the cavity through the main gate, but a sub gate is set in addition to the main gate in order to suppress the sink of the gate portion. Adopting the gate system, the molten resin can be directly supplied to the gate portion through the sub-gate and the holding pressure can be effectively applied, so that the resin shrinkage of the gate portion can be suppressed. Therefore, in addition to preventing sink marks, it is not necessary to adjust the holding time and holding pressure, so it is possible to eliminate gloss unevenness and burrs, significantly improve the appearance of the appearance, and to extend the holding time. Therefore, the molding cycle can be shortened and the productivity can be maintained satisfactorily.

  Hereinafter, preferred embodiments of a method for injection molding a resin molded product according to the present invention will be described in detail with reference to the accompanying drawings. Note that the gist of the present invention is as described in the scope of claims, and the contents of the embodiments described below are merely examples of the present invention.

  1 to 4 show an embodiment of the present invention. FIG. 1 is an explanatory view showing the overall configuration of an injection mold used in the method of the present invention. FIG. 2 is a composite gate structure in the injection mold. FIG. 3 is an explanatory view showing a state at the time of injection by the injection mold, and FIG. 4 is a cross-sectional view of an essential part showing a modification of the injection mold used in the method of the present invention.

  In FIG. 1, an injection mold 10 used in the method of the present invention is roughly composed of a cavity mold 20 and a core mold 30, and a cavity side mold plate 21 is attached to a mounting plate 22 in the cavity mold 20. The mounting plate 22 is provided with a sprue bush 23, and a nozzle of an injection device (not shown) is connected to the sprue bush 23 to supply molten resin from the injection device.

  On the other hand, the core mold 30 has a core mold 31 supported by a mounting plate 33 via a spacer block 32. The mounting plate 33 is connected to a movable ram (not shown), and moves forward and backward by a predetermined stroke. Clamping and mold opening are performed between 20 and the core mold 30. In the injection mold 10 shown in FIG. 1, the mold opening direction and the clamping direction are set in the vertical direction, but the mold opening direction and the clamping direction can be set in the lateral direction. In addition, an ejector mechanism 40 that protrudes in the mold releasing direction after molding the molded product is provided inside the core mold 30, and a resin passage 50 is further set. As the ejector mechanism 40, an ejector pin 42 and a sprue lock pin 43 are supported by an ejector plate 41, and the ejector pin 42 and the sprue lock pin 43 are moved up and down by the lifting and lowering operation of the ejector plate 41. Eject 60 and mill ends in the direction of mold removal.

  Further, in FIG. 1, a cavity C is formed when the cavity mold 20 and the core mold 30 are clamped (specifically, the cavity side mold plate 21 and the core side mold plate 31 are clamped). The resin passage for supplying the molten resin M into C includes a sprue 51 provided on the sprue bush 23, a runner 52 formed on the parting surface of the cavity mold 20 and the core mold 30, and a gate 53. . The gate 53 is drilled in the core-side template 31 so as to branch from a main gate 53A such as a side gate connected to the tip 52a of the runner 52 and a branching portion 52b spaced from the tip 52a of the runner 52. Thus, a composite gate structure including the sub-gate 53B provided is employed.

  In this embodiment, a rib 61 is formed on the back surface of the resin molded product 60, and the tip of the sub-gate 53B communicates with the tip of the rib 61. As described above, for the main gate 53A and the sub-gate 53B, the main gate 53A uses a side gate that is easy to perform the gate cutting process, and a portion where the sink a near the main gate 53A is likely to occur (gate portion 60a). ) Is formed on the back surface thereof, and a submarine gate is provided as a sub-gate 53B so as to be connected to the recess 31a.

  Therefore, when molding the resin molded product 60, as shown in FIG. 3, most of the molten resin M is injected and filled into the cavity C from the tip 52a of the runner 52 through the main gate 53A through the sprue 51 and the runner 52. At that time, the molten resin M is supplied from the branch portion 52b of the runner 52 to the recessed portion 31a of the cavity C from the branch portion 52b of the runner 52 through the sub-gate 53B, and the molten resin M is directly injected into the gate portion 60a. In addition, an effective holding pressure can be applied to the gate portion 60a.

  Therefore, according to the method of the present invention, by using the composite gate system in which the sub-gate 53B for suppressing the sink a in the gate portion 60a is adopted, the occurrence of sink a that has conventionally occurred in the resin molded product 60 is ensured. In addition to preventing the molding conditions from being changed, the molding cycle of the resin molded product 60 having an excellent appearance is not extended, and other appearance defects such as gloss unevenness and burrs are not generated. Can be mass-produced without any problems. Further, since the composite gate system of the main gate 53A and the sub gate 53B is adopted, the supply time of the molten resin M can be shortened, and the molding cycle can be shortened.

  Next, FIG. 4 shows a modification of the injection mold 10 used in the injection molding method according to the present invention. As the structure of the gate 53, a main gate 53A consisting of a side gate and a sub-gate consisting of a submarine gate are shown. Although it is the same to adopt a composite gate system composed of the gate 53B, in this modification, a vertically long concave groove 42a is provided on the outer surface of the ejector pin 42, and the sub-gate 53B has an inside of the concave groove 42a. This is because the molten resin M is injected into the cavity C via, and the molten resin M is supplied to the gate portion 60a intensively through the sub-gate 53B, and the holding pressure can be effectively applied to the gate portion 60a. Also in the modified example, the resin molded product 60 having no appearance defects such as sink marks a and excellent appearance can be mass-produced without extending the molding cycle. It has the effect of say. In particular, in this modification, since the sub-gate 53B is formed in a linear shape instead of a parabolic shape, there is an advantage that the gate processing can be simplified.

  In this embodiment, a side gate is adopted as the main gate 53A, but it can be changed to an overlap gate. Further, although the sub-gate 53B is provided so as to communicate with the rib tip or the concave groove 42a of the ejector pin 42, it may be directly connected to the cavity C.

It is explanatory drawing which shows the whole structure of the injection mold used for the injection molding method of the resin molded product which concerns on this invention. It is explanatory drawing which shows the principal part structure in the injection mold shown in FIG. It is explanatory drawing which shows the state at the time of the injection | pouring of the molten resin from the composite gate structure in the injection mold shown in FIG. 1 in a cavity. It is sectional drawing which shows the principal part structure of the modification of the injection mold used for the injection molding method of the resin molded product which concerns on this invention. It is explanatory drawing which shows the outline | summary of the conventional injection molding die. It is explanatory drawing which shows the relationship between the resin channel | path and the resin molded product in the conventional injection molding die. It is explanatory drawing which shows the gate structure in the conventional injection molding die. It is sectional drawing which shows the gate structure in the conventional injection molding die. It is explanatory drawing which shows the prior art example which gave the thin wall countermeasure of the gate part in the conventional injection molding die.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Injection molding die 20 Cavity die 21 Cavity side die plate 22 Mounting plate 23 Sprue bush 30 Core die 31 Core side die plate 32 Spacer block 33 Mounting plate 40 Ejector mechanism 41 Ejector plate 42 Ejector pin 42a Concave groove 43 Sprue lock pin 50 Resin passage 51 Sprue 52 Runner 52a Tip 52b Branch part 53A Main gate (side gate)
53B Subgate (Submarine Gate)
60 resin molded product 60a gate part C cavity M molten resin

Claims (1)

Resin passage (50) comprising molten resin (M) in the cavity (C) defined by the cavity mold (20) and the core mold (30), including a sprue (51), a runner (52), and a gate (53). In the injection molding method of the resin molded product (60) for molding the resin molded product (60) of a required shape by injection filling through
The gate (53) in the resin passage (50) adopts a composite gate system of a main gate (53A) and a sub-gate (53B), and a molten resin is introduced into the cavity (C) through the main gate (53A) having a small cross-sectional area. A method for injection molding of a resin molded product, characterized in that (M) is injected and filled, and holding pressure is applied from the back surface through a sub-gate (53B) toward the gate portion (60a).

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