JP2984890B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In injection molding, dents called sink marks are formed on the surface of a molded article, which is a major obstacle in appearance. The present invention relates to an injection molding method for preventing such sink marks.

[0002]

2. Description of the Related Art In conventional injection molding, a gate is
In the filling process, the molten resin is always open, and the molten resin flows in the order of the sprue runner gate. Flows while receiving a pressure loss, and the molded product portion is filled with resin. For this reason, near the final filling position of the resin, during the flow, the heat of the molten resin moves to the mold side and the viscosity increases, and the flow resistance generally increases with the flow distance. In this molded product, since the flow resistance is maximized,
Even when pressure is applied to the sprue tip, almost no pressure is applied near the final filling position, so that a problem such as sink occurs. Therefore, conventionally, as a countermeasure for this, a product thickness is increased to reduce a pressure loss, and a high pressure is applied to the terminal. The shrinkage was reduced by increasing the gate diameter, reducing the pressure loss at the gate, applying sufficient resin pressure, and allowing sufficient pressure-holding time.

[0003]

However, measures such as enlarging the gate diameter and increasing the thickness of the molded product in order to improve the flow of the resin cause various problems in molding. First, increasing the gate diameter increases the time for cooling and solidifying the gate, during which time pressure must be applied continuously (if the holding pressure is stopped before the gate sealing, the gate is compressed and sent to the molded product side. This causes the resin to flow backward.) This increases the sealing time of the gate and the molding time, which leads to an increase in cost.
Even if the thickness of the molded article is increased, the amount of resin used for the molded article increases, and the cooling rate of the molded article in the mold also decreases. If the molded product is taken out, it will cause deformation, and the molded product will be cooled in the mold until the temperature becomes lower than a certain temperature.), Which also increases the cost.

In order to prevent sinking of molded products, ribs
Restrictions on the shape and position of the boss and increase in the thickness of the boss significantly limit the degree of freedom in design, which is not preferable in product design. Also, the gate diameter and
Even if the thickness of the molded product is increased, a decrease in the pressure at the final filling position is not hindered and is insufficient as an effect.

The present invention focuses on the actual situation as described above, and aims to find a more effective means for preventing sinking in order to deal with the situation. In particular, the final filling is performed by focusing on the set position of the gate and the opening / closing timing of the gate. The purpose is to apply resin pressure to the part where the sink mark most easily occurs in a timely manner, equalize the pressure inside the molded article, significantly reduce sink and deformation of the molded article, and mold the molded article with good appearance. Is what you do.

[0006]

That is, a feature of the method of the present invention that achieves the above object is that a gate is further provided near the final filling position of a molded product in the conventional gate, and the molten resin is filled by the conventional gate. The gate is opened at or immediately before the completion of the process, and the resin is caused to flow by applying the resin pressure to the molded article portion where pressure is hardly applied in the conventional method. In the conventional method, the gate is opened at a portion of the molded product to which pressure is not easily applied by moving a gate valve by a timer or a sensor set in a mold.

[0007]

When molded by the above method of the present invention, when filling in a mold, a sufficient resin pressure is applied to a portion where the resin pressure is the lowest, so that sink is remarkably reduced. Also, after the inside of the molded article is almost completely filled with the primary gate (a gate necessary for filling the molded article with the molten resin), the secondary gate (the gate provided at the final filling position or the gate provided near the sinkage occurrence position) Weld line (refers to linear unevenness that occurs at the joint when two or more flows of resin do not completely merge during molding) compared to the case where all gates are open from the beginning. Reduce the number of

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an example of a mold structure of an injection molding machine for carrying out the method of the present invention. In FIG. 1, reference numeral 1 denotes a fixed-side mounting plate, 2 denotes a movable-side mounting plate, and A locate ring is fitted in the center, and a sprue bush 4 is fitted in the center.

[0010] Between the fixed-side mounting board 1 and the movable-side mounting board 2, a runner levitating board 5 and a fixed-side mold plate 6 are sequentially disposed on the inner surface of the fixed-side mounting board 1. Sprue 7 and runner 8
And a gate 9, respectively, and a movable mold plate 10 is mounted on the inner surface of the movable mounting plate 2 on the opposite side.

In the above-described mold structure, the gate 9 is composed of a multipoint gate, and the fixed mold plate 6 and the movable mold plate 10
Are formed so that the movable side is the front side of the molded product and the fixed side is the back side of the molded product.
The spool 7, the runner 8 and the multi-point gate 9, which are the runners through which the molten resin flows, are all disposed on the back side of the molded product, and the product ejection board 16 is used as the ejector mechanism 14, and the slide member 15 is used. Of the ejector board 12 by linking the
Compared to the case of interlocking, it does not provide complicated holes and inclined pins in the mold part, improves reliability and processability, achieves space saving and reduces the space for fixing the gate structure on the back side. I have secured it.

Of course, the above-described injection molding machine is one example, and the method of the present invention is not limited to this. The present invention can be carried out in all conventionally known types of injection molding machines. It is about to include.

FIG. 2 shows an arrangement of gates for implementing the present invention in the above-described various injection molding machines. The figure shows a case of a box-shaped product. Such molded articles include molded articles such as front cabinets of televisions and door frames of microwave ovens. For such molded article, the gate is to issue a normal weld line position to a position inconspicuous corner, sets the gate G ₁ to the substantially cross shape from the center hole side aimed at the center of each side as shown in FIG. 2 It is common. However, in this case, if there is a boss B or the like on the back surface near the final filling position of the corner, the resin pressure is not sufficiently applied, so that sinking becomes a problem. Therefore, separately as further shown in FIG. 2 in the corner, providing the gate G _2. That is, the latter gate G ₂ if the questionnaire G ₁ and the primary gate is a secondary gate.

[0014] Then i.e. when the opportunity arises that the resin flows in the molded article through the primary gate G _1, open the filling by the primary gate is set to the corner point or immediately before completion was substantially complete secondary gate G _2, the resin Let in
Apply resin pressure.

The timing of opening the corner gate G ₂ can be achieved by opening the gate valve by a timer or a sensor set in a mold. Further, a signal for switching from primary injection to secondary injection, for example, may be received from the molding machine, and the screw advance position of the injection molding machine may be read from an encoder to open the secondary gate.

The opening and closing of these gates is performed by a cold runner,
Although both hot runners can be used, the hot runner is more suitable because there is no fear that the resin around the secondary gate is cooled and solidified to cause a malfunction.

In the case of a cold runner, the resin needs to be opened before the resin around the secondary gate is solidified, and the time for opening the secondary gate is restricted.

Thus, when the secondary gate is opened and the resin pressure is applied at an appropriate timing of the inflow of the resin into the molded article by the primary gate, the pressure inside the molded article is compared with the case where the molding is performed only by the primary gate. And the shrinkage ratio is made uniform. In addition, since the secondary gate is opened immediately after filling the mold, the flow of the resin is fused, and the generation of a weld line by the secondary gate is prevented, so that a molded product having a good appearance without sink marks can be obtained.

[0019]

According to the present invention, when setting the gate as described above, in addition to the position necessary for filling the molded article, the gate is set to a position where the sink occurs easily, and the gate is opened when the gate is filled. It is a method to open the resin at the time when filling is almost completed or just before completion, to inject the resin and apply resin pressure,
Sufficient resin pressure is applied to the most likely part of the final filling position to reduce sink marks, and the pressure inside the molded product is lower than the gate setting only at the position required to fill the conventional molded product. Therefore, since the shrinkage rate is averaged, the deformation of the molded article can be reduced.

Further, since the secondary gate is opened immediately after filling the mold, the flow of the resin is fused with the flow of the resin from the primary gate to each other, so that a weld line is not generated and the conventional primary gate is generally used. It has a remarkable effect of improving the appearance of the molded product as compared with the system and increasing its practical value.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a mold structure of an injection molding machine for implementing a method of the present invention.

FIG. 2 is an explanatory diagram showing an example of an arrangement mode of gates in the method of the present invention.

[Explanation of symbols]

G _{1 1} primary gate G _{2 2} primary gate

Continued on the front page (72) Inventor Takashi Kazuyuki 2-15-15 Harinakano, Higashisumiyoshi-ku, Osaka-shi (72) Inventor Toshihiko 800 Kanada, Kanada Prefecture 800 Kanada (72) Inventor Toshio Ogasawara 800 Kanada, Atsugi City Kanagawa Prefecture (72) Inventor Naoo Fukase 800 Kanada, Atsugi-shi, Kanagawa Prefecture (72) Inventor Shishio Kawamori 800-800 Kaneda, Atsugi-shi, Kanagawa Prefecture (56) References JP-A-58-145428 (JP, A) JP-A-6 JP-A-71683 (JP, A) JP-A-64-71715 (JP, A) JP-A-2-98416 (JP, A) JP-A-61-169216 (JP, A) (58) Fields investigated (Int. . ^6, DB name) B29C 45/00 - 45/84

Claims (2)

(57) [Claims] In a method of molding an injection-molded article, when setting a gate, a gate is set at a position where sinking is likely to occur, such as near a corner, in addition to a position necessary for filling the molded article. The injection molding method is characterized in that the gate is not opened at the time of normal filling, but is opened at a time when the filling is substantially completed or immediately before the completion to allow the resin to flow therein, and a resin pressure is applied. 2. The injection molding method according to claim 1, wherein the opening and closing of the gate at a position where sink marks easily occur is performed by a timer or a sensor set in a mold.