JPH054973Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an injection molding mold, and more particularly to an injection molding mold that can mold more beautiful molded objects.

[Prior Art] FIG. 7 shows a sectional view of the main parts of a conventional injection mold. This mold includes a fixed mold 100 having a mold surface forming a cavity 400 and a cylindrical pot portion 101 opening to the mold surface;
a plunger 200 slidably held at 1;
It is composed of a fixed mold 100 and a movable mold 300 having a mold surface that is clamped to form a cavity 400.

To carry out injection molding using this mold, first, hot melted resin is poured into the pot portion 101, and after the mold is clamped, the plunger 200 is driven forward to inject the melted resin into the cavity 400. After the molten resin is cooled and solidified, the fixed mold 100 and the movable mold 30
0 and further advances the plunger 200 to release the molded body.

[Problems to be solved by the invention] By the way, when molding is performed using the above-mentioned conventional injection molding mold, there is a pot portion 1 on the surface of the molded product.
In some cases, a minute ring-shaped depression (sink mark) was formed at a position opposite to the opening of No. 01. In some cases, flowing patterns remained, detracting from the aesthetic appearance.

As a result of intensive research into the cause of the above problem, the present inventors found that it is caused by the molten resin being cooled on the surface of the pot when it is poured into the pot. That is, the molten resin poured into the pot is cooled by contacting the inner circumferential surface of the pot, and the viscosity of the surface increases to form a cylindrical thickened part. When the plunger is driven forward, the thickened portion is also pushed out into the cavity at the same time. However, the thickened part has a high viscosity and is difficult to flow, and may adhere to the surface of the movable mold facing the plunger and solidify as it is. In such a case, problems such as sink marks or lines appearing on the surface of the molded product occur in those areas. Furthermore, if the thickened portion remains on the mold surface of the fixed mold, the shape of the cavity becomes narrow in that portion, a gate effect occurs, and the flow rate of the resin between it and the movable mold surface increases. As a result, a flow pattern is formed on the surface of the molded product, impairing its aesthetic appearance.

To solve these problems, it is effective to heat the stationary mold to prevent the molten resin from cooling. However, it is necessary to newly provide a heating means to the fixed mold, and the conventional mold is not used, which increases the cost of the mold and consumes a lot of energy.

[Means for Solving the Problems] The present invention solves the above problems by simply slightly changing the shape of the mold without the need to heat the mold.

In other words, the injection mold of the present invention includes a fixed mold having a mold surface forming a cavity and a cylindrical pot portion opening into the mold surface, a plunger slidably held in the pot portion, and a fixed mold having a mold surface forming a cavity and a cylindrical pot portion opening into the mold surface. In an injection mold, the mold consists of a movable mold with a mold surface that is clamped to the mold to form a cavity, and a cavity is composed of the fixed mold surface, the movable mold surface, and the end surface of the plunger. is characterized by having a ring-shaped recess formed by the end side peripheral surface of the plunger and the inner peripheral surface of the pot portion and communicating with the cavity when the end surface of the plunger constitutes a cavity.

The biggest feature of this invention is the ring-shaped recess.
In conventional molds, the inner diameter of the pot and the outer diameter of the plunger are almost the same to prevent burrs from forming. However, in the present invention, burrs are actively generated by leaving the molten resin that has been cooled in contact with the inner peripheral surface of the pot in a fixed ring-shaped recess.
This prevents the cooled molten resin from entering the cavity.

In addition, in order to effectively utilize the burr, it is also preferable to form a ring-shaped recess and a groove communicating with the cavity in the fixed mold. In this way, a reinforcing rib can be formed from this groove, and the strength of the molded article is improved. Moreover, since the pressure at the time of injection is reduced by the groove portion, it is possible to prevent distortion of the molded product and fall of hair on the epidermis.

[Function] In the injection mold of the present invention, molten resin is first poured into the pot with the plunger retracted. At this time, the molten resin comes into contact with the inner circumferential surface of the pot portion and is cooled from the surface, forming a cylindrical thickened portion with increased viscosity along the inner circumferential surface of the pot portion. Then, in the injection step, the plunger moves forward to inject the molten resin in the pot into the cavity.

By the way, the mold of the present invention has a ring-shaped recess formed by the end side circumferential surface of the plunger and the inner circumferential surface of the pot portion and communicates with the cavity when the end surface of the plunger constitutes the cavity. Therefore, since the thickened part is difficult to flow, most of it remains in the ring-shaped recess, and the molten part at the high temperature in the center of the molten resin is injected into the cavity. When the molten resin is cooled and solidified, the portion formed by the ring-shaped recess remains as a ring-shaped burr protruding from the back side of the molded body.

[Effects of the invention] That is, according to the injection mold of the invention, the thickened portion is prevented from entering the cavity, and the molten resin with low viscosity is uniformly injected into the cavity. Therefore, defects are prevented from occurring on the surface of the molded product, and beautiful molded products can be molded with good reproducibility.

[Example] Hereinafter, this will be explained in detail using examples.

(Example 1) Figures 1 to 3 show the mold of this example. This mold has a mold surface 10 forming a cavity and a mold surface 1.
A fixed mold (lower mold) 1 having a cylindrical pot portion 11 opening at 0, a plunger 2 slidably held in the pot portion 11, and a mold surface that is clamped to the fixed mold 1 to form a cavity. The movable mold (upper mold) 3 has a movable mold 30. The mold surface 10 of the fixed mold 1, the mold surface 30 of the movable mold 3, and the end surface 20 of the plunger 2 constitute a cavity 4.

As shown in the plan view of the main part of the fixed mold 1 in FIG. A cylindrical recess 13 is formed with the inner peripheral surface of the pot portion 11 and communicates with the cavity 4.

The operation of the mold of this embodiment configured as described above will be explained below.

First, with the plunger 2 in a lowered state, a predetermined amount of molten resin 5, which is a thermoplastic resin melted by heat, is poured into the pot portion 11, and the movable mold 3 is clamped with the fixed mold 1. The state is shown in FIG.

Next, by raising the plunger 2, the molten resin 5 is injected into the cavity 4. By the way, when the temperature of the fixed mold 1 is, for example, room temperature, the molten resin 5 is cooled by contacting the inner circumferential surface of the pot part 11, and the molten resin 5 has a flow from inside toward the surface that contacts the pot part 11. A temperature gradient of decreasing temperature is created. Therefore, a cylindrical thickened part with increased viscosity is formed on the surface of the molten resin 5.

However, in the mold of this embodiment, the cylindrical recess 13 is formed by the rise of the plunger 2, so the thickened part that is difficult to flow remains in the recess 13 while being attached to the inner circumferential surface of the pot 11, and is melted. The center portion of the resin 5 where the temperature is high and the viscosity is low is injected into the cavity 4. Therefore, the thickened portion is prevented from entering the cavity 4, and problems such as molding abnormalities in the molded product are prevented.

After the injected molten resin cools and solidifies in the cavity, the movable mold 3 rises and opens the mold.
Plunger 2 further rises and fixes the molded object to mold 1.
Release from the mold.

A cylindrical protrusion formed by a cylindrical recess 13 is present on the back surface formed by the mold surface 10 of the fixed mold 1 of the obtained molded body.

(Example 2) FIG. 4 shows a mold of the second example. In this embodiment, the inner peripheral surface of the opening of the pot portion 11 that opens into the cavity 4 is cut into a convex R surface shape. Therefore, when the plunger 2 is raised and the end face 20 constitutes the cavity 4, a ring-shaped recess 13' is formed between the side peripheral surface of the plunger 2 and the inner peripheral surface of the pot portion 11. A thickened portion remains in this recess 13' as in Example 1, and is prevented from being injected into the cavity 4. In addition, even if the thickened part were to enter the cavity, the rounded shape allows the thickened part to easily move along the mold surface 10 of the fixed mold 1, preventing it from appearing on the design surface. be done.

(Example 3) FIGS. 5 and 6 show a mold of a third example. This example has the same structure as Example 1 except that the mold surface 10 of the fixed mold 1 has a cylindrical recess 13 and four grooves 14 that communicate with the cavity 4 and extend radially.

In the mold of this example, molding abnormalities are prevented as in Example 1. The molten resin is also injected into the groove 14 through the recess 13 . In other words, the recess 13 functions as a starting point for distributing the resin into the radially extending grooves 14. Reinforcing ribs are formed from the recesses 13 and the grooves 14, improving the strength of the molded body.

Furthermore, due to the presence of the groove portion 14, the injection pressure is reduced compared to the mold of Example 1. Therefore, for example, when in-mold molding is performed by arranging the skin along the mold surface 30 of the movable mold 3, hairs on the skin can be prevented from falling down.

[Brief explanation of the drawing]

Figures 1 to 3 relate to an injection mold according to an embodiment of the present invention, in which Figure 1 is an overall cross-sectional view, Figure 2 is a plan view of the main part of the fixed mold surface, and Figure 3 is a FIG. 3 is a cross-sectional view of the mold after molten resin has been charged and the mold has been clamped. Fourth
The figure is an overall sectional view of the injection molding die of the second embodiment. 5 and 6 relate to the injection molding die of the third embodiment, FIG. 5 is an overall sectional view thereof, and FIG. 6 is a plan view of a main part of the mold surface of the fixed mold. FIG. 7 is an overall sectional view of a conventional injection mold. 1... Fixed type, 2... Plunger, 3... Movable type, 4... Cavity, 5... Molten resin, 10...
... Fixed mold surface, 11 ... Pot portion, 13 ... Recessed portion, 14 ... Groove portion, 20 ... End surface, 30 ... Movable mold surface.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A fixed mold having a mold surface forming a cavity and a cylindrical pot portion opening into the mold surface, a plunger slidably held in the pot portion, Injection molding comprising a movable mold having a mold surface that is clamped with the fixed mold to form the cavity, and the cavity is constituted by the mold surface of the fixed mold, the mold surface of the movable mold, and the end surface of the plunger. In the mold for potting, the fixed mold has a ring-shaped recess that is formed by the end side peripheral surface of the plunger and the inner peripheral surface of the pot portion and communicates with the cavity when the end surface of the plunger forms the cavity. An injection mold characterized by: (2) The fixed type has a groove communicating with the recess and the cavity, as claimed in claim 1 of the utility model registration.
Injection mold as described in section.