JPH04267115A - Injection molding device - Google Patents

Abstract

PURPOSE:To obtain the product with good appearance by a method in which in the device provided with the runner becoming the path of molten resin and a filmlike gate placed along a thin and large cavity, the lateral cross sectional area of the runner is gradually increased to downstream side from upstream side. CONSTITUTION:The mold for injection molding is provided with the thin and large cavity 3 of the shape corresponding to e.g. the bumper for a vehicle which is defined by the template 1 of stationary side and the template 2 of movable side brought in close contact with each other. The T shape-runner 4 having the lateral rod 4a placed along the cavity 3 which is formed sectionally respectively by both templates 1, 2 to fill said cavity 3 with molten resin, is provided. Further the film like gate 5 which communicates the cavity 3 to the runner 4 along the lateral rod 4a, is provided. In said case, the lateral rod 4a is formed so that its thickness (y) is gradually increased to both ends B of downstream side from the position at the distance Lo of 1/2 of longitudinal rod 4b-width from the central line of the central part A becoming the upstream side of resin flow.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention includes a runner that extends along a thin and large cavity and serves as a flow path for molten resin, and also provides communication between the cavity and the runner along the runner. The present invention relates to a thermoplastic resin injection molding apparatus, that is, an injection mold, which includes a film-like gate.

0002

2. Description of the Related Art An example of a thermoplastic resin injection mold having a thin and large cavity (molding space) is a mold for manufacturing a thermoplastic resin bumper by injection molding.

[0003] As shown in FIG. 8 showing a cross section of the central part, and as shown in a perspective view of the cross section in FIG. In addition to providing a thin and large cavity 3 with a shape corresponding to the bumper, this is also a fixed side mold plate 1 in order to uniformly fill the molten resin into the cavity 3 in a short time.
and a T-shaped runner 4 having a horizontal bar portion 4a extending along its cavity 3, each defined by a movable side template 2;
It is provided with a film-like gate 5 that communicates between the cavity 3 and the runner 4 along the horizontal bar portion 4a of the runner 4, and here, the central vertical bar portion 4b of the runner 4 is connected to the fixed side. It communicates with a nozzle of a molten resin injection device (not shown) through a sprue 6 provided on the template 1, and also with a runner 4.
The horizontal bar portion 4a has a uniform width x and thickness y in the direction of the gate width L, that is, a uniform area from the vicinity of the center connected to the vertical bar portion 4b to both ends (not shown). , has a trapezoidal cross section.

In such an injection mold, molten resin is injected from the molten resin injection device into the runner 4 through the sprue 6, and is filled from the runner 4 through the gate 5 into the cavity 3. When the resin cools and solidifies,
As shown in FIG. 10, the sprue 6, the horizontal bar part 4a and the vertical bar part 4b of the runner 4, the sprue part 7a, the runner horizontal bar part 7b, the runner vertical bar part 7c, and the gate part corresponding to the gate 5 and the cavity 3, respectively. 7d and a bumper portion 7e, and when the bumper portion 7e is separated from the gate portion 7d, the bumper becomes a large and thin product.

[0005]

[Problem to be Solved by the Invention] By the way, with the recent trend toward weight reduction of automobiles, the internal reinforcing materials and stays of resin bumpers, which were conventionally separated from the outer surface member, are now integrated with the outer surface member. Therefore, physical properties such as rigidity and low-temperature impact resistance of the resin material of the outer surface member have been dramatically improved.

However, this creates disadvantageous conditions for moldability. For example, when manufacturing polypropylene bumpers, nearly twice as much talc as before is added to the resin to improve rigidity, and the rubber content is often doubled to improve impact resistance.
As a result, the flowability of the resin material, which was conventionally close to 20 in terms of melt index, has decreased from 5 to a limit value of 15 at best, and as a result, in the conventional injection mold, There are problems in that the end portion of the cavity 3 is not filled with resin, and small irregularities and sink marks occur on the surface of the bumper portion 7e of the molded product, making it difficult to obtain a product with good appearance quality. Ta.

[0007]

[Means for Solving the Problems] It is an object of the present invention to provide an injection molding apparatus that advantageously solves the above problems, and the present invention provides an injection molding apparatus for thermoplastic resin, that is, an injection molding tool. The mold includes a runner that extends along a thin and large cavity and serves as a flow path for the molten resin, and a film-like gate that communicates between the cavity and the runner along the runner. The cross-sectional area of the runner is gradually increased from the upstream side to the downstream side of the flow of molten resin.

[0008]

[Function] In such an injection mold, when filling the cavity with molten resin from the runner through the film-like gate, the pressure loss decreases from the upstream side to the downstream side of the runner. The flow rate of the molten resin into the cavity becomes uniform at each part in the width direction of the gate, and the holding pressure after filling is also applied uniformly. Therefore, according to the injection mold of the present invention, even when a resin material with poor flowability is used to improve the physical properties of the product, there may be cases where the end of the cavity is not filled with resin or small irregularities on the surface of the molded product. It is possible to prevent the occurrence of burn marks and the like, and it is possible to easily manufacture products with high appearance quality.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view showing a cross section of the central part of an injection mold which is an embodiment of the injection molding apparatus of the present invention, similar to FIG. 9, and the mold of this embodiment is generally similar to the conventional example. In the drawings, parts similar to those of the conventional example are designated by the same reference numerals.

That is, the mold of this embodiment also includes a thin and large cavity 3 having a shape corresponding to a bumper, which is defined by a stationary mold plate 1 and a movable mold plate 2 that are in close contact with each other. In order to uniformly fill the cavity 3 with molten resin in a short time, a horizontal bar portion 4a extends along the cavity 3, which is also defined by the fixed mold plate 1 and the movable mold plate 2, respectively. A T-shaped runner 4 and a horizontal bar portion 4a of the runner 4 are inserted between the cavity 3 and the runner 4.
The central vertical bar portion 4b of the runner 4 is connected to a molten resin injection (not shown) via a sprue 6 provided on the stationary template 1. It communicates with the nozzle of the device.

However, although the horizontal bar portion 4a of the runner 4 in this embodiment has a trapezoidal cross section and its width x is uniform, its thickness y is as schematically shown in FIG. From a position L0, which is 1/2 the width of the vertical bar part 4b from the center line of the central part A that is connected to the vertical bar part 4b and is on the upstream side of the flow of molten resin, is connected to the downstream side of the flow of molten resin. ymin. in the direction of gate width L toward both ends B where ymin. from ymax. Therefore, in this embodiment, the area of the cross section of the horizontal bar portion 4a gradually increases from near the center portion A toward both ends B. Note that the thickness ratio ymax. of the horizontal bar portion 4a. /ymin. is set to 2.0 in this example.

In such an injection mold, molten resin is injected from the molten resin injection device into the runner 4 through the sprue 6, and is filled from the runner 4 through the gate 5 into the cavity 3. When the resin cools and solidifies,
As shown in FIG. 3, the sprue 6, the horizontal bar portion 4a and the vertical bar portion 4b of the runner 4, the sprue portion 7a, the runner horizontal bar portion 7b, the runner vertical bar portion 7c, and the gate portion corresponding to the gate 5 and the cavity 3, respectively. 7d and a bumper portion 7e, and when the bumper portion 7e is separated from the gate portion 7d, the bumper becomes a large and thin product.

Here, when filling the cavity 3 with molten resin from the runner 4 via the gate 5, the pressure loss increases as the molten resin moves from the upstream side to the downstream side of the horizontal bar portion 4a of the runner 4. is reduced, the flow rate of the molten resin into the cavity 3 becomes uniform at each part in the direction of the width L of the gate 5, and the holding pressure is also applied uniformly. Therefore, according to the injection mold of this embodiment, even when a resin material with poor flowability is used to improve the physical properties of the product, there may be cases where the end portion of the cavity 3 is not filled with resin or the molded product 7 is not filled with resin.
It is possible to prevent the occurrence of small irregularities, sink marks, etc. on the surface of the bumper portion 7e, and it is possible to easily manufacture a product with a high quality appearance.

4 to 6 show the thickness ratio ymax. of the horizontal bar portion 4a of the runner 4. /ymin. The figures show the results of a computer analysis of the filling situation of the molten resin by changing the molten resin in various ways. 80 of molten resin
Shows the pressure distribution expressed by contour lines of the pressure at each part when % filling,
Further, FIG. 4 shows the thickness ratio ymax. /ymin. FIG. 5 shows the results for the conventional mold with thickness ratio ymax.=1. /ymi
n. FIG. 6 shows the results for the mold of the above example where thickness ratio ymax.=2.0. /ymin. The results for the mold of the comparative example with = 3.0 are shown, and in each figure (
a) Middle arrows F1, F2, F3 indicate the center part A of the horizontal bar part 4a of the runner 4, the intermediate part C between the center part A and the end part B, and the end part B of the horizontal bar part 4a, respectively. The flow velocity of the molten resin flowing from the gate 5 into the cavity 3 at the corresponding position is indicated by its length. Also, each figure shows only the right half of the runner 4, gate 5, and cavity 3, and therefore,
In the figure, the left end portion indicates their center portion.

As is clear from these FIGS. 4 to 6, the thickness ratio ymax. /ymin. In the case of the conventional mold with =1, the flow velocity between the center part A, middle part C, and end part B of the horizontal bar part 4a of the runner 4 has a relationship of F1 > F2 > F3, The molten resin arrives at the end of cavity 3 (the right end in the figure) later than other parts, and furthermore,
% filling, it is estimated that a pressure difference of as many as 5 steps will occur in the molten resin in the horizontal bar part 4a between the center part A and the end part C, resulting in uneven holding pressure after filling. However, the thickness ratio ymax. /ymin. = 2.0 in the mold of the above embodiment, the flow velocity between the center part A, intermediate part C, and end part B of the horizontal bar part 4a of the runner 4 is F1 ≈F3 <F
2, and the difference between them becomes smaller,
The filling speed of the molten resin is relatively uniform in each part in the cavity 3, and when the cavity 3 is filled to 80%, the molten resin in the horizontal bar part 4a is filled in one step between the center part A and the end part B.
It is presumed that since only a pressure difference of 20% is generated, the holding pressure after filling is equalized, and as a result, the above effect can be obtained.

On the other hand, the thickness ratio ymax. /ymin. =3
．． In the case of the mold of the comparative example where As in the case of the above embodiment, the filling speed of the molten resin is relatively uniform in each part in the cavity 3, and moreover, when 80% filling is performed, the horizontal bar part 4
Although only one step of pressure difference is generated between the center part A and the end part B of the molten resin in the gate 5,
It was found that the spacing between nearby contour lines changed greatly along the contour lines, indicating that the pressure was uneven, and that this uneven pressure caused unevenness in the pressure holding effect at various parts after filling. is estimated. Therefore, the thickness ratio ymax.
/ymin. It can be seen that making it too large also produces undesirable results.

FIG. 7 shows the average flow velocity of the molten resin in the horizontal bar part of the T-shaped runner, which is similar to that in the molds of the above embodiment and the conventional example, and which communicates with the cavity through the film gate. The pressure loss between the center and the end of the horizontal bar is expressed as the thickness ratio ymax. /ymin. As is clear from this figure, 1.1≦(thickness ratio ymax./ymin.)≦
As long as it is within the range of 2.4, the thickness ratio of the conventional runner (thickness ratio ymax.
/ymin. = 1.0), resulting in higher average flow velocity and lower pressure drop, and therefore products with high appearance quality can be easily produced even when using resin materials with poor flow properties.

Although the present invention has been described above based on the illustrated example, the present invention is not limited to the above-mentioned example, and can be applied to the production of thin-walled products other than resin bumpers.

[0019]

[Effects of the Invention] Thus, according to the injection mold of the present invention, it is possible to equalize the flow rate of the molten resin into the cavity at each part in the width direction of the gate, and also to equalize the holding pressure after filling. Even when a resin material with poor flowability is used to improve the physical properties of the product, it prevents the end of the cavity from being filled with resin and small irregularities and sink marks on the surface of the molded product, resulting in a product with a high quality appearance. can be easily manufactured.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a cross section of the central part of an injection mold which is an embodiment of the injection molding apparatus of the present invention.

FIG. 2 is an explanatory diagram schematically showing how the thickness of the horizontal bar portion of the runner in the mold of the above embodiment increases.

FIG. 3 is a perspective view showing the entire molded product injection-molded using the mold of the above embodiment.

FIGS. 4(a) and 4(b) are explanatory diagrams showing analysis results of a filling pattern of molten resin and pressure distribution in a conventional mold.

FIGS. 5(a) and 5(b) are explanatory diagrams showing analysis results of the filling pattern of molten resin and pressure distribution in the mold of the above example.

FIGS. 6(a) and 6(b) are explanatory diagrams showing analysis results of a filling pattern of molten resin and pressure distribution in a mold of a comparative example.

FIG. 7 is a characteristic diagram showing changes in the average flow velocity of molten resin and pressure loss when the runner thickness ratio is changed.

FIG. 8 is a sectional view of the center of a conventional injection mold.

FIG. 9 is a perspective view showing a cross section of the central part of the conventional mold.

FIG. 10 is a perspective view showing the entire molded product injection-molded using the conventional mold.

[Explanation of symbols] 3 Cavity 4 Runner 4a　Horizontal bar part 5 Gate y Runner thickness A Central part B End

Claims (1)

[Claims] Claim 1: A runner (4a) that extends along a thin and large cavity (3) and serves as a flow path for the molten resin, and the cavity and the runner are communicated along the runner. In a thermoplastic resin injection molding apparatus comprising a film-like gate (5), the cross-sectional area of the runner is gradually increased from the upstream side (A) to the downstream side (B) of the flow of molten resin. An injection molding device featuring: