JPH07171861A - Injection mold - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an injection molding die capable of obtaining a good resin product in which the generation of weld marks and sink marks that may hinder the appearance is prevented. [Structure] Cavity 2 of mold 1 for molding a resin product having a front surface serving as an exterior surface and a back surface serving as a non-appearance surface
In addition, a runner portion 4 communicating with the film gate 3 is provided, and a plurality of resin injection portions 5 are provided in communication with the tabs 4a, 4b, 4b communicating with the runner portion 4. A narrowed portion 10 is provided on the tab 4b that communicates with the second resin injection portion 5b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection molding a resin product, and more particularly to an injection molding method suitable for injection molding a relatively large and thin resin product such as a bumper of an automobile.

[0002]

2. Description of the Related Art Generally, when a relatively large resin product is injection-molded, a molten resin is injected and injected into a cavity formed in a mold through a plurality of resin injection parts.

In this case, when the molten resin is simultaneously injected and injected from the respective resin injecting parts, the molten resin injected from the respective resin injecting parts flows in a direction in which they approach each other, and then their flow heads collide with each other in the cavity. Therefore, a weld mark may be formed along the collision position on the surface of the resin product obtained in the cavity. When such a weld mark occurs, not only is it unfavorable in terms of the appearance of the resin product, but the bending strength and impact strength at the weld mark generation position are reduced by about 20% as compared with the portion where no weld mark is generated. There is an inconvenience.

Therefore, in order to eliminate such inconvenience, the injection order of a plurality of resin injection parts is determined in advance, and for example, the molten resin injected and injected from the first-order resin injection part into the cavity is the second. There is known an injection molding method in which a molten resin is injected and injected from the second resin injecting section after reaching the position of the resin injecting section in the order. According to this method, since the molten resin injected from the second-order resin injecting section is included, even if the flow fronts of these molten resins collide with each other, the boundary surface is exposed on the surface of the resin product. Therefore, the weld mark as described above does not occur.

However, according to the above method, FIG.
As shown in FIG. 5, sink marks (sinks) d and e are generated on the front surface and the back surface of the resin product a along the flow front f of the molten resin c injected from the second-order resin injection portion on the surface of the resin product a. May be confirmed. Such sync marks d, e
It is considered that the occurrence of (1) occurs due to the orientation due to the flow of the respective molten resins b and c injected from the respective resin injection parts and the difference in shrinkage due to the temperature difference between the respective resins b and c.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above inconveniences, and the present invention provides an injection molding die capable of obtaining a good resin product in which the generation of weld marks and sink marks which hinder the appearance is prevented. The purpose is to provide.

[0007]

In order to achieve the above-mentioned object, the present invention provides a cavity formed corresponding to the shape of a resin product having a front surface serving as an exterior surface and a back surface serving as a non-appearance surface. , A runner portion which is provided in communication with the cavity through a film gate and extends substantially along the side edge portion of the cavity together with the film gate, and a molten resin is injected into the cavity through the runner portion and the film gate The first provided in communication with the runner portion for injection
And a first resin injecting section for injecting the molten resin into the cavity through the runner section and the film gate after the molten resin from the first resin injecting section is filled in the runner section. And a second resin injecting portion provided in communication with the runner portion at a distance in the extending direction of the runner portion, wherein the second resin injecting portion is a throttle. The runner communicating portion of the narrowed portion is provided so as to be biased toward the product back surface side of the cavity.

A plurality of the second resin injection parts may be provided. Then, each of the second resin injecting portions has a narrowing portion as in the above.

[0009]

According to the injection molding die of the present invention, when the resin product is injection molded, the following injection molding method is used.
The molten resin is injected and injected into the cavity, thereby molding the resin product in the cavity.

First, injection of molten resin into the cavity from the first resin injection portion is started. The flow front of the molten resin is second
When passing the position of the resin injecting section, the injection of the molten resin is started from the second resin injecting section. Thereby, the molten resin from the second resin injection section is included in the molten resin from the first resin injection section. At this time, there occurs a portion in which the flow direction of the molten resin from the second resin injection part flows in the opposite direction to the flow direction of the molten resin from the first resin injection part,
The inclusion of the molten resin from the second resin injecting section in the molten resin from the first resin injecting section prevents the occurrence of weld marks.

On the other hand, the molten resin injected from the second resin injecting portion penetrates in the cavity direction along the narrowed portion.

Subsequently, the molten resin injected from the second resin injecting portion enters the film gate while maintaining a relatively biased state on the back surface side of the product where the narrowed portion is located.

Further, the molten resin injected from the second resin injecting portion passes through the film gate and enters the cavity, but the flow front of the molten resin is relatively located inside the cavity on the side where the throttle portion is located. It maintains a biased state.

In this way, on the surface of the resin product away from the flow front of the molten resin injected from the second resin injection part, there is no difference in shrinkage due to difference in orientation or temperature difference, Sync mark does not occur.

Therefore, if the die is manufactured so that the narrowed portion of the second resin injecting portion is located on the side to be the back surface of the resin product, a good surface condition without sink marks is obtained on the external surface side. Obtainable.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. 1 is a sectional view of an essential part of an injection molding die, FIG. 2 is a plan view of an essential part of an upper die 1a of the injection molding die of FIG. 1, and FIG.
Of the molten resin in the section taken along the line II-II of FIG. 4, FIG. 4 is a diagram schematically showing the behavior of the molten resin in the section taken along the line III-III of FIG. 1, and FIG. 5 relates to the present invention. FIG. 6 is a cross-sectional view of a main part of a resin product, FIG. 6 is a cross-sectional view of a main part of a resin product according to a conventional technique, and FIG. 7 is a view for explaining another embodiment taken along the line III-III of FIG.

The injection mold 1 shown in FIGS. 1 to 4 is a mold for molding a resin product, and a resin product is molded between the upper mold 1a and the lower mold 1b. A cavity 2, a runner portion 4 communicating with the cavity 2 via a film gate 3, and tabs 4a, 4b, 4b communicating with the runner portion 4 are formed.

Further, as shown in FIGS. 1 and 2, the injection molding die 1 includes a plurality of resin injection portions (three in this embodiment) for injecting molten resin into the tabs 4a, 4b, 4b. 5 and a hot runner 6 communicating and connected to these resin injecting parts 5 are provided inside the upper mold 1a, and each resin injecting part 5
Are arranged at intervals in the longitudinal direction of the runner portion 4 between the runner 4 and the hot runner 6.

The hot runner 6 is connected to a resin injection nozzle 7 introduced toward the hot runner 6 at the upper part of the upper mold 1a.

Each resin injection part 5 is connected to and connected to a hot runner 6 and is directed toward the tabs 4a, 4b, 4b toward the upper die 1.
The valve gate 8 having a substantially cylindrical shape is attached to the a, and as shown in FIGS. 3 and 4, the tabs 4a and 4b are inserted through the injection hole 8a formed at the tip of the valve gate 8.
It is connected to 4b.

A gate pin 9 for opening and closing the injection hole 8a is inserted into the valve gate 8 toward the injection hole 8a by a cylinder or the like (not shown) so that the gate pin 9 can move forward and backward. By retreating, the opening / closing of the injection hole 8a is controlled.

Further, as shown in FIG. 3, the tab 4a communicating with the first resin injection portion 5a communicates with the runner portion 4 and further communicates with the cavity 2 via the film gate 3.

On the other hand, as shown in FIG. 4, the tabs 4b and 4b communicating with the second resin injecting portions 5b and 5b have a narrowed portion 10 formed between the injecting hole 8a and the runner portion 4. The tab 4b also communicates with the runner portion 4, and further communicates with the cavity 2 via the film gate 3.

Next, an injection molding method of a resin product using the injection molding die 1 will be described.

In FIG. 1, when molding a resin product, first, a molten resin is supplied from a resin injection nozzle 7 to a valve gate 8 of each resin injection portion 5 via a hot runner 6, and a resin injection portion in the center is further supplied. (First resin injection part) 5a
The valve gate 8 of the resin injection part 5 is opened.
The molten resin b is injected and injected from a into the tab 4a. At this time, as shown in FIG. 3, the tab 4a is provided only from the resin injection portion 5a.
The molten resin c injected and injected into the tub 4 flows in the tub 4a, then the runner portion 4 and the tubs 4b and 4b with almost no decrease in temperature or pressure, and the molten resin c is filled therein. It flows from the portion 4 into the cavity 2 through the film gate 3 at various places.

In this way, when the flow of the molten resin b injected and injected from the resin injecting portion 5a to the cavity 2 progresses to some extent, the valve gates 8 and 8 of the resin injecting portions 5b and 5b on both sides are opened next. As shown in FIG. 4, this causes the molten resin c to be injected and injected from the resin injection portions 5b and 5b into the tabs 4b and 4b.

The molten resin c injected and injected from the resin injecting section 5b merges with the molten resin b from the resin injecting section 5a to be fused, and then the film gate 3 of the resin injecting section 5b.
The runner communicating portion 10b of the narrowed portion 10 is passed along the narrowed shape 10a of the narrowed portion 10 provided on the side.

The molten resin c injected and injected from the resin injecting portion 5b reaches the runner portion 4c, but maintains a state of being relatively biased to the side where the runner communicating portion 10b of the narrowing portion 10 is located. While invading the film gate 3.

Further, the molten resin c injected and injected from the resin injecting portion 5b passes through the film gate 3 and enters the cavity 2, but the molten resin c also communicates with the runners of the throttle portion 10 even in the cavity 2. The state in which the part 10b is relatively biased to the side where it is located is maintained.

After that, the inside of the cavity 2 is filled with the molten resins b and c, and after cooling and solidifying, the upper mold 1a and the lower mold 1b of the injection molding die 1 are divided into upper and lower parts, and from inside of these parts. The resin product a is taken out, and the valve gate 8 of each resin injection part 5 is closed.

In this injection molding die, the molten resin b injected from the resin injection part 5a is injected into the resin injection part 5b.
Since the injected and injected molten resin c is contained, even if the flow heads of the molten resins b and c collide with each other, the boundary surface thereof is not exposed on the surface of the resin product, and no weld mark is generated.

Further, as shown in FIG.
The flow front f of the molten resin c injected and injected from b maintains a relatively biased state inside the resin product a in the direction in which the runner communication portion 10b of the narrowed portion 10 is located. Appearance surface g on the side where the flow front f is not unevenly distributed in
Does not cause shrinkage or the like due to the difference in orientation or temperature difference, and the sync mark d does not occur.

In this way, the narrowing portion 10 of the resin injection portion 5b is
If the injection molding die 1 is manufactured such that the runner communication portion 10b of the resin product a is biased to the non-appearance surface side of the resin product a, the resin having a good surface condition without sink marks on the appearance surface side. The product a can be obtained.

The drawing shape 10a of the drawing part 10 of the resin injection part 5b may be a slope having a certain angle with respect to the horizontal plane of the upper die 1a as shown in FIG. It may be a vertical surface as in the other embodiments shown.

Further, the cavity 2 of the film gate 3
The position relative to may be a position adjacent to the lower mold 1b as shown in FIG. 4, or may be slightly located on the upper mold 1a side as in the other embodiment shown in FIG.

[0036]

As is apparent from the above description, according to the injection molding of the present invention, the flow front of the molten resin injected and injected from the first resin injection portion into the cavity is located at the second resin injection portion. In addition to preventing the weld mark by injecting the molten resin from the second resin injecting section after reaching the temperature, the second resin injecting section can be provided only by providing a narrowed section in the second resin injecting section. By distributing the flow front of the resin injected from the part to the non-appearance side of the resin product, and preventing sink marks on the surface of the appearance side due to differences in orientation, temperature difference, etc. It is possible to obtain a resin product having an excellent appearance quality.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an example of an injection molding die of the present invention.

FIG. 2 is a plan view of a main part of an upper die 1a in FIG.

FIG. 3 is a diagram schematically showing the behavior of the molten resin in the section taken along the line II-II of FIG.

FIG. 4 is a diagram schematically showing the behavior of the molten resin in the cross section along the line III-III in FIG.

FIG. 5 is a sectional view of a main part of a resin product manufactured according to the present invention.

FIG. 6 is a sectional view of a main part of a resin product manufactured by a conventional injection molding technique.

FIG. 7 is a view for explaining another embodiment taken along the line III-III of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Injection mold, 2 ... Cavity, 3 ... Film gate, 4 ... Runner part, 5a ... 1st resin injection part, 5b ...
Second resin injection part, 10 ... throttle part, 10b ... runner communication part of the throttle part

Claims (1)

[Claims] 1. A cavity formed corresponding to the shape of a resin product having a front surface serving as an exterior surface and a back surface serving as a non-appearance surface, and the cavity provided in communication with the cavity through a film gate. A runner portion extending substantially along a side edge portion of the cavity together with the gate, and a first runner portion provided in communication with the cavity for injecting molten resin into the cavity through the runner portion and the film gate. A resin injecting section, and a first resin injecting section for injection-molding the molten resin into the cavity through the runner section and the film gate after the molten resin from the first resin injecting section is filled in the runner section. In an injection molding die including a second resin injecting portion provided in communication with the runner portion at a distance in the extending direction of the runner portion, the second resin injecting portion is a narrowed portion. Through which communicates with the runner, the injection mold, characterized in that provided to bias the runner communicating portion the narrowed portion in the product back side of the cavity.