JPH07227888A - Injection molding method and injection mold - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] The present invention relates to an injection molding method and a mold for preventing a weld line from being generated during injection molding to reduce mechanical strength. [Structure] After injection-filling the molten resin into the cavity 3,
The molten resin is moved from the cavity 3 on one side to the cavity 3 on the other side across the weld line 4 generated during holding pressure, and when the molded product is cut in a direction orthogonal to the weld line 4, the cut surface is cut. Make the appearing line shape approximately wedge-shaped. Therefore, a resin reservoir 5 that can be opened and closed is provided near the cavity 3 near the weld line 4, closed during injection, and opened during pressure holding to allow the resin around the weld line 4 to flow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method and a mold for preventing a decrease in mechanical strength of a weld line portion in injection molding of a product in which a weld line is likely to occur.

[0002]

2. Description of the Related Art Conventionally, for example, when a holed product is injection-molded, a convex portion of a mold protrudes into a cavity corresponding to a holed portion, and an upstream portion of the convex portion of the resin flow mold. Then, the molten resin splits once and joins on the downstream side to form a weld line at the joining portion.

Therefore, in the case of Japanese Utility Model Publication No. 55-15100, for example, a heater and a cooling circuit are provided in the vicinity of the weld line generation position, and the mold at the weld line generation position is heated to a high temperature before molding. This improves the bondability when the ends of the divided molten resins join together.

[0004]

However, in the case of the above method, since it is necessary to bring the heater close to the position where the weld line is generated, it may not be applicable depending on the shape of the molded product. Since the mold is heated in, the bonding condition of the surface layer of the molded product that is in contact with the mold is good and the appearance quality etc. can be improved, but the effect does not reach the inner layer. In many cases, the mechanical strength was inferior.

[0005]

Therefore, in order to improve the mechanical strength of the weld line portion, the present invention, after the molten resin is injected and filled into the cavity, is sandwiched by the weld line from the cavity on one side to the cavity on the other side. The molten resin was moved during the holding pressure toward.

As a device for realizing such a method, a resin reservoir is provided in the vicinity of the cavity near the weld line, and the resin reservoir and the cavity near the weld line are communicated with each other by a communication passage, and the resin is connected to the communication passage. An opening / closing mechanism is provided to control the connection / disconnection between the reservoir and the cavity.The opening / closing mechanism cuts off the communication and injects the molten resin. It was introduced into the resin pool, and at the same time, the molten resin around the weld line was moved.

Further, a variable volume preliminary reservoir is provided at a position opposite to the resin reservoir centering on the weld line so as to communicate with the cavity, the resin reservoir is blocked, and the volume of the preliminary reservoir is expanded and injected. During the holding pressure, the resin reservoir was opened and the volume of the preliminary reservoir was reduced to extrude the molten resin inside at a pressure higher than the holding pressure, and this pressure introduced the molten resin in the cavity into the resin reservoir.

[0008]

[Function] The weld line generation mechanism is that the tip of the molten resin shunted in the cavity is cooled by the mold and oxidized, forming a semi-molten thin film, and at the time of merging, the resins are complicated at the molecular level. It is caused by entanglement.

The weld line is formed linearly in the direction connecting the two dies (usually in the plate thickness direction of the product), and the mechanical strength is said to be about 60 to 70% of that of the base material. ing.

Therefore, if the molten resin is moved from one side to the other side across the weld line while holding pressure,
Since the deeper the inner part away from both molds, the better the flowability at high temperature, the weld line normally formed in a straight line can be formed into a substantially wedge shape. Then, by forming the substantially wedge shape, the joint portion expands laterally and the joint strength increases.

A resin reservoir that can be opened and closed is provided near the cavity near the weld line, the resin reservoir is closed and injected, and then opened during pressure holding to introduce the molten resin in the cavity into the resin reservoir. By doing so, the molten resin on the side where the resin pool is not provided across the weld line,
The weld line is moved to the side where the resin reservoir is provided, and the weld line is formed in a substantially wedge shape.

In addition, a variable volume preliminary reservoir is provided on the side where the resin reservoir is not provided, and the molten resin filled in the preliminary reservoir at the time of injection is extruded during holding pressure so that the resin reservoir holds the cavity. If the molten resin is introduced, the movement of the molten resin in the cavity becomes smoother.

[0013]

Embodiments of the injection molding method and injection molding die of the present invention will be described with reference to the accompanying drawings. 1 is an explanatory view showing a state change of a weld line, FIG. 2 is a perspective view of a molded product, FIG. 3 is an explanatory view showing a resin flow in a cavity, and FIG. 4 is a sectional view taken along the line AA of FIG. .

The injection molding method of the present invention is applied, for example, when injection molding a molded product 1 having a rectangular through hole as shown in FIG. 2, and a cavity for molding such a product is penetrated. It is necessary to close the cavity portion corresponding to the hole with the convex portion of the mold.

Therefore, as shown in FIG. 3, the molten resin injected from the gate 2 flows in the cavity 3 in the direction indicated by the solid line, and is divided into two directions upstream of the convex portion T of the mold, and then the convex portion of the mold is pressed. Merge downstream of section T.

Therefore, a weld line 4 as shown in FIG. 2 is formed at the merging portion, and the mechanical strength is weak in this weld line 4 because the bond at the molecular level is weak.

Therefore, in the mold of the present invention, a resin reservoir 5 as shown in FIG. 3 is provided in the vicinity of the cavity 3 in the vicinity of the weld line 4 and communicated via a communication passage 6. In the embodiment, the direction of the communication passage 6 is orthogonal to the direction of the weld line 4.

As shown in FIG. 4, an opening / closing cylinder unit 7 as an opening / closing mechanism is provided in the middle of the communication passage 6 to allow the shutoff valve 8 to move back and forth, and the shutoff valve 8 shuts off the communication passage 6. I am trying to open it. Incidentally, FIG.
12 is the upper mold and 13 is the lower mold.

Further, the driving means of the opening / closing mechanism is not necessarily limited to the cylinder type, and may be a driving means such as a motor. Further, as shown in FIG. The pinion 10 is meshed with the rack portion 9a provided on the sealing member 9 having a diameter larger than the diameter, and the sealing member 9 is moved back and forth in the extension direction of the communication passage 6 by driving the motor 11, and the front taper of the sealing member 9 You may make it seal with a part.

Alternatively, as shown in FIG. 8 (a) which is another structural example of the drive means of the opening / closing mechanism, or (b) which is a bottom view of (a), the drive device is a motor (or a servo) 24. , A cam 25 is attached to the tip of the output shaft 24a of the motor 24, and the cam 25 is brought into contact with the tappet 26,
The sealing member 28 integrated with the tappet 26 is attached to the spring 2
It may be biased toward the cam 26 side by 7.

When the cam crest 25a of the cam 25 comes into contact with the tappet 26, the sealing member 28 is made to project into the communication passage 6, and the motor 24 is rotated to rotate the cam 25 in the pressure holding step. Then, the cam crest 25a is separated from the tappet 26, and the communication passage 6 is opened by the force of the spring 27.

A molding method using the above injection molding die will be described.

The open / close cylinder unit 7 connects the communication passage 6
The molten resin is injected into the cavity 3 from the gate 2 shown in FIG.

Then, the molten resin is divided into two parts in the upstream of the mold convex portion T and flows, and then merges in the downstream of the mold convex portion T,
A weld line 4 is formed at this junction. When the weld line 4 formed on the molded product 1 is viewed in a vertical cross section, the upper mold 12 and the lower mold 13 are vertically connected by a substantially straight line as shown in FIG.

Therefore, when the primary injection for filling the cavity 3 is completed and the holding pressure (secondary pressure) step is started, the opening / closing cylinder unit 7 is driven to open the communication passage 6.

Since the molten resin in the cavity 3 is pressurized, it flows into the resin pool 5, and along with this, the molten resin near the weld line 4 also flows in the direction of the broken line in FIG.

That is, as shown in FIG. 1B, the mold 1
Since the resin of the inner core c flows in the direction indicated by the arrow except for the skin layer s which starts cooling early after coming into contact with Nos. It exhibits a wedge shape.

The mechanical strength can be increased by laterally expanding the weld line 4 in such a form. The position of the resin reservoir 5 may be any position as long as the resin flow effect of the resin in the cavity 3 flows into the weld reservoir 4 when the resin in the cavity 3 flows into the resin reservoir 5, and the direction of the communication passage 6 is not always required. It need not be orthogonal to the weld line.

Further, the substantially wedge-like shape does not necessarily have to be a single mountain shape as shown in (b), but may be one having a plurality of mountains as shown in (c).

Next, another configuration example will be described with reference to FIGS.

In this case, as shown in FIG. 5, the cavity 3 is connected to the cavity 3 via the communication passage 16 at a substantially symmetrical position opposite to the resin reservoir 5 with the resin joining portion (weld line generation position) as the center. A preliminary reservoir 15 having a variable volume is provided. Further, in the case of the embodiment, the communication passage 16 communicating with the resin reservoir 15 is arranged so as to be on the same straight line as the communication passage 6 communicating with the resin reservoir 5 at a substantially symmetrical position.

As shown in FIG. 6 which is a sectional view taken along the line BB of FIG. 5, the volume of the preliminary pool 15 is variable by the forward / backward movement of the pushing member 18 attached to the rod tip of the pushing cylinder unit 17. . The other configurations are the same as those in the above example.

In this configuration example, the opening / closing cylinder unit 7 shuts off the communication passage 6 leading to the resin reservoir 5,
Further, the extruding member 18 is fully retracted and the molten resin is injected into the cavity 3.

Therefore, when the molten resin is filled in the cavity 3, the preliminary reservoir 15 is also filled at the same time.

When the primary injection is completed, the opening / closing cylinder unit 7 is operated during the holding pressure (secondary pressure), and the resin pool 5
The communication passage 6 communicating with the above is opened, and the pushing cylinder unit 17 is advanced to push the resin in the preliminary reservoir 15 into the cavity 3. The pushing pressure is higher than the holding pressure.

Therefore, the molten resin in the cavity 3 flows in the direction shown by the broken line arrow in FIG. 6, and the influence of the molten resin pushed into the weld line 4 can be further enhanced.

Further, in the case of the embodiment, the resin reservoir 5
Since the communication passage 6 and the communication passage 16 of the preliminary reservoir 15 are on the same straight line and substantially orthogonal to the weld line 4, the resin flow effect more effectively extends to the weld line, and more effectively approximately. A wedge shape can be formed.

The weld line is shown in FIG.
The bumper 20 as shown in FIG. 3 also tends to occur during injection molding. For example, in the runner 21, the film gate 22, and the bent portion Q of the product portion 23 as shown in (b), from the product portion 23 around the bent portion Q. Since the resin that wraps around is faster, the weld line 4 is likely to occur in the product portion 23.

Therefore, it is effective to apply the bumper 20 made of such a resin to the injection molding.

[0040]

As described above, according to the present invention, after the molten resin is filled in the cavity by injection, the resin is moved from one side to the other side across the weld line during the pressure holding step. The weld line has a substantially wedge shape, and the mechanical strength is increased. The formation of the substantially wedge shape forms a resin reservoir that communicates with the cavity near the weld line, closes the resin reservoir at the time of injection, and fills the molten resin into the cavity, and the resin reservoir is held during pressure retention. It can be effectively formed by opening it and introducing the molten resin into the cavity. If a preliminary reservoir is provided with the weld line in between, the wedge shape can be formed more effectively.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a state change of a weld line.

FIG. 2 is a perspective view of a molded product.

FIG. 3 is a plan view showing the flow of resin in a cavity.

FIG. 4 is a sectional view taken along line AA of FIG.

FIG. 5 is a plan view showing a flow of resin in a cavity of a second configuration example.

6 is a sectional view taken along line BB of FIG.

FIG. 7 is a diagram showing another configuration example of the opening / closing mechanism.

8A and 8B are views of another configuration example of the opening / closing mechanism, in which FIG. 8A is a sectional view and FIG.

FIG. 9 is an explanatory view of a weld line at the time of bumper molding,
(A) is a perspective view, (B) is a partial view from the front, (C)
Is a cross-sectional view taken along line CC of (b)

[Explanation of symbols]

 3 Cavity 4 Weld line 5 Resin reservoir 6 Communication passage 7 Open / close cylinder unit 15 Preliminary reservoir 17 Extrusion cylinder unit

Claims (3)

[Claims] 1. An injection molding method comprising: injecting and filling a cavity with a molten resin, and then moving the molten resin from the cavity on one side toward the cavity on the other side while holding pressure while sandwiching the weld line. 2. An injection molding die in which a weld line is formed when a molten resin is injected into the cavity, a resin reservoir is provided in the vicinity of the cavity in the vicinity of the weld line, and the resin reservoir and the vicinity of the weld line are provided. The cavity is communicated by a communication passage, and an opening / closing mechanism is provided in this communication passage to control communication / interruption between the resin reservoir and the cavity. An injection molding die, characterized in that a communication passage is opened by an opening / closing mechanism to introduce the molten resin in the cavity into the resin reservoir and at the same time move the molten resin around the weld line. 3. The pre-reservoir having a variable volume provided at a position opposite to the resin reservoir centering on the weld line to communicate with the cavity so as to block the resin reservoir and reduce the volume of the pre-reservoir. After expanding and injecting, the resin reservoir is opened during holding pressure and the volume of the preliminary reservoir is reduced to extrude the molten resin inside at a pressure higher than the holding pressure, and this pressure causes the molten resin in the cavity to reach the resin reservoir. An injection mold characterized by being introduced.