JP3136416B2 - Injection molding method for hollow mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a hollow injection-molding method of a blow molding mold having a large hollow portion. More specifically, a wide range has a large hollow portion over a, and relates to an injection molding method for molding a reinforced hollow mold product by forming a support portion for supporting the hollow portion to a predetermined position.

[0002]

2. Description of the Related Art Conventionally, a molten resin is injected in an amount smaller than the volume of a mold cavity and a pressurized fluid (mainly a gas body) is injected.
Is pressed into a mold cavity to form a hollow injection mold having a hollow portion, so as to obtain necessary strength by partially leaving a solid rib.

For example, US Pat. No. 4,247,515 discloses that a projection is provided on a mold cavity and the viscosity, elastic density, and interfacial tension between a molten resin and a pressurized fluid are adjusted. ing. Since the thickness of the mold cavity becomes small at the place where the projection is attached, and the pressurized fluid becomes difficult to pass, a plurality of hollow portions are formed around the location where the projection is attached, and the vicinity of the projection is It will remain as a solid rib.

Japanese Patent Publication No. 53208/1986 discloses that the fluidity and the amount of the molten resin in the mold cavity have a distribution, and the molten resin portion having a high fluidity and the amount of the molten resin in the mold cavity are small. It is shown that a gas body is guided to a molten resin portion to form a hollow portion, and the other portions are left as solid ribs. In addition, the molten resin and the gas body are press-fitted into the mold cavity provided with portions having different thicknesses, or the molten resin and the gas body are press-fitted into the mold cavity, and the mold cavity is partially enlarged, so that the mold is formed. A gas is preferentially introduced into a thick portion or an enlarged portion of the cavity to form a hollow portion, and a thin portion or an unexpanded portion of the mold cavity is left as a solid rib, and both are used in combination. It is also shown.

[0005]

SUMMARY OF THE INVENTION U.S. Pat. No. 4,247,751.
According to the method disclosed in the specification of Japanese Patent No. 5,028,095, the introduction point of the pressurized fluid can be reliably separated by attaching a high protrusion, but the portion corresponding to the high protrusion becomes a deep concave portion of the hollow injection mold and becomes a rib. The wall thickness is reduced, and the strength is rather reduced. This can be prevented by reducing the height of the projection, but the division of the pressurized fluid introduction location becomes inaccurate.
For this reason, the position and size of the rib tend to be controlled by chance, and as shown in FIGS.
Since the position and the shape of 1 become irregular and it is not necessary to design them in advance, it is not possible to reliably form the rib 101 having a necessary size at a truly necessary place. In addition, the projections attached to the mold cavity will form the originally unnecessary concave portions 102 in the obtained hollow injection molding die.

On the other hand, among the methods disclosed in Japanese Patent Publication No. 61-53208, the method of imparting a distribution to the fluidity and the amount of the molten resin in the mold cavity is based on the viscosity and amount of the molten resin in the mold cavity. Cannot be precisely controlled. Therefore, the position and size of the ribs are apt to be governed by chance, and as shown in FIG. 15, the positions and shapes of the ribs 101 become irregular, so that these cannot be designed in advance and the hollow ratio cannot be so large. There is. In the method of partially changing the thickness of the mold cavity or partially enlarging the mold cavity, as shown in FIG. 16, a concave portion 102 (or a convex portion) is formed in the obtained hollow injection mold. There is a problem that it is unavoidable that they are formed. In particular, when a large thickness change is not given to the hollow injection mold, induction of preferential gas to a thick portion becomes insufficient, and the position and size of the rib 101 are governed by chance, These cannot be designed in advance. Furthermore, in a hollow injection mold having a wide range of locations having a constant large thickness, one hollow portion 103 is formed over the entire location having a constant large thickness. However, there is a problem that the size of the hollow portion is limited.

As described above, conventionally, the rib cannot be formed at a predetermined position in a predetermined size, and therefore, the size and shape of the hollow injection mold that can be formed and the size of the hollow portion (hollow ratio) ).

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and it has been found that a hollow injection mold having a large hollow portion can be reliably formed by forming a solid rib at a predetermined position and size. It is an object of the present invention to obtain a required strength of a hollow injection mold.

Another object of the present invention is to ensure that the strength can be obtained without giving unnecessary hollows or steps to the obtained hollow injection mold.

[0010]

As shown in FIG. 1, the present invention is capable of projecting into a mold cavity 4 and retreating from the projecting position, and is capable of providing a pressurized fluid pressure inlet 2.
0 to the movable core 5 and having a mold 6 of the mold cavity 4 with injecting a molten resin, hollow by press-fitting the pressurized fluid in a further state in which the movable core 5 projects into the mold cavity 4 Part 1
Is formed , and the hollow core 1 is formed by retracting the movable core 5.
An injection molding method for a hollow mold, characterized by being enlarged .

[0011]

The present invention will be further described.

First, as shown in FIG. 1A, a molten resin is injected into the mold cavity 4 via a sprue 9 and a gate 8. The injection amount of the molten resin is adjusted according to the desired shape and hollow ratio of the hollow mold 3. To ensure the formation of the hollow portion 1 by press-fitting the pressurized fluid, the movable core 5 is required. It is preferable that the amount is sufficient to fill the inside of the mold cavity 4 in a state where the mold is projected into the mold cavity 4.

The injection of the molten resin is usually performed with the movable core 5 protruding into the mold cavity 4 as shown in FIG. 1 (a). The movable core 5 can be protruded or the movable core 5 can be protruded after the injection of a predetermined amount of molten resin is completed.

FIG. 1A shows an example in which the molten resin is injected into the mold cavity 4 from one gate 8. However, the shape and size of the target hollow mold 3 are shown. In some cases, as shown in FIGS. 2 and 3, molten resin is injected from a plurality of gates 8.

Next, as shown in FIG. 1B, with the movable core 5 protruding into the mold cavity 4, the pressurized fluid is melted from the pressurized fluid pressure inlet 20 into the mold cavity 4. Press into resin. Thereby, when the amount of the molten resin is insufficient to fill the inside of the mold cavity 4, the pressurized fluid in an amount corresponding to the insufficient amount of the molten resin also melts enough to fill the inside of the mold cavity 4. In the case of the resin amount, a pressurized fluid in an amount corresponding to the volume shrinkage caused by cooling is injected, and the hollow portion 1 is introduced into the molten resin at the position of the movable core 5.
Is formed.

The pressurized fluid pressure inlet 20 is provided in the movable core 5. The position is not particularly limited as long as it is on the distal end surface of the movable core 5, but it is preferable that the position is opened near the center of the distal end surface. And this pressurized fluid pressure inlet 2
By press-fitting the pressurized fluid from 0, the hollow portion 1 is formed at a position in contact with the movable core 5.

Simultaneously with, during or after the press-in of the pressurized fluid, the movable core 5 is retracted from the projecting position in the mold cavity 4 to a predetermined position, as shown in FIG. With the retreat of the movable core 5, the hollow portion 1 is enlarged so as to follow the retreat of the movable core 5, so that a desired hollow ratio can be obtained, and between the adjacent movable cores 5 or the movable core 5. When a gap is provided in the hollow portion 5 itself, the hollow portion 1 is formed by a resin layer formed of a molten resin filled in the gap.
Is formed.

As described above, since the hollow portion 1 is formed substantially at the center of the movable core 5, the position where the movable core 5 is provided depends on the position where the hollow portion 1 is to be formed. You only have to decide. The position where the hollow part 1 is formed may be determined according to the shape and size of the hollow mold 3 to be molded.
The shape of the movable core 5 also depends on the size and shape of the hollow portion 1 according to the shape and size of the hollow mold 3 to be formed.
For example, the shape may be a polygon such as a square, a rectangle, or the like, or a column, a block, or the like having a cross section having irregularities in a circle, an ellipse, or a jade. In addition, a plurality of hollow portions 1
Is formed, the movable cores 5 may be provided in a number and a position corresponding to the number and the positions of the hollow portions 1.

Further, as described above, the support portion 2 is made of a resin layer formed of a molten resin filled between the movable core 5 or the gap provided in the movable core 5 itself.
The shape and size of the support 2 can be set according to the shape and size of the gap provided in the movable core 5 itself and the space between the movable cores 5. The shape and size of the support 2 may be determined according to the shape and size of the hollow mold 3 to be formed.

The retreat completion point of the movable core 5 is usually a point at which the tip end surface of the movable core 5 substantially coincides with the cavity surface 7.
By retracting to this position, it is possible to form the support 2 without leaving a recess or projections on the surface of the hollow forming the shape type product 3. However, if there is no problem even if some concaves and convexes are formed on the surface, or if it is desired to form concaves and convexes on the surface, the distal end surface of the movable core 5 projects into the mold cavity 4. In this state, the movable core 5 can be stopped from retreating, or the movable core 5 can be retracted until the distal end surface of the movable core 5 is retracted from the cavity surface 7. In the case of forming a concave portion or a convex portion on the surface, it can be performed by providing a concave portion or a convex portion on the distal end surface of the movable core 5.

After the retraction of the movable core 5 is completed, the resin in the mold cavity 4 is sufficiently cooled, the pressurized fluid in the hollow portion 1 is discharged, the mold 6 is opened, and the hollow mold 6 is taken out. .

FIGS. 4 to 11 show examples of typical shapes of the hollow mold 3 thus obtained. However, in the present invention, since the shape of the hollow portion 1 changes according to the shape of the movable core 5, the hollow mold 3 having the hollow portion 1 of various shapes is not limited to these examples. It is possible.

The hollow mold 3 shown in FIGS. 4 and 5
Has nine hollow portions 1 each having a square cross section divided by a support portion 2 crossing in a grid pattern, and the hollow mold 3 shown in FIGS. 6 to 8 extends radially from near the center. Support 2
9 and has a hollow portion 1 having a triangular cross section and communicating with each other at the center, and the hollow molds 3 shown in FIGS. 9 to 11 are supported in parallel with each other. Part 2
It has three hollow portions 1 each having a rectangular cross-section and partitioned by.

The hollow mold 3 shown in FIGS. 4 and 5
Is obtained by using a mold 6 having a movable core 5 having a position and a shape as shown in FIG. 2 and FIG.
The mold 6 will be described. As shown in the drawing, each movable core 5 has a block shape having a substantially square cross section, and is arranged with a space between adjacent movable cores 5. A pressurized fluid pressure inlet 20 is provided at the center of the distal end surface of each movable core 5. Further, the movable core 5 faces the intersection of the gap between adjacent movable cores 5. Four gates 8 are provided on the side opposite to the installation side.

Using the mold 6 having such a movable core 5, the mold cavity 4 (each movable core 5) in the state of FIG.
(Including the gap between them) is filled with the molten resin, and press-fitting of the pressurized fluid and retraction of the movable core 5 to the state of FIG. 3B are performed, as shown in FIG. 4 and FIG. A hollow mold 3 having a grid-like support 2 is obtained. That is, the hollow portion 1 is formed corresponding to the position of each movable core 5, and the portion corresponding to the gap between the movable cores 5 forms the support portion 2.

The hollow mold 3 shown in FIGS. 6 to 8 has one movable part having a shape and position corresponding to the triangular hollow part 1 integrated at the center shown in FIG. 9 to 11 can be formed by a mold 6 having a die 5. The hollow mold 3 shown in FIGS. 9 to 11 has three shapes and positions corresponding to the rectangular hollow portion 1 shown in FIG. It can be formed by a mold 6 having a movable core 5.

As the resin used in the present invention, general thermoplastic resins used for general injection molding or extrusion molding can be used, and if necessary, thermosetting resins can also be used. Various additives can be added to the resin as needed.

The pressurized fluid used in the present invention is a gaseous or liquid fluid at normal temperature and pressure that does not react or mix with the resin used at the temperature and pressure at the time of injection. Specifically, for example, nitrogen gas, carbon dioxide gas, air,
Helium gas, water, glycerin, liquid paraffin and the like are preferable, and an inert gas such as nitrogen gas and helium gas is preferable.

Next, a molding apparatus suitable for carrying out the hollow injection molding method will be described with reference to FIG.

In the figure, reference numeral 11 denotes an injection nozzle.
The rear injection cylinder 13 is similar to a normal injection cylinder and incorporates a screw 14. When the screw 14 advances, the molten resin inside is pushed out and injected from the injection nozzle 11.

The mold 6 is provided with a movable core 5 on the side opposite to the pressure contact side of the injection nozzle 11, and the movable core 5 is provided with a needle 12 communicating with a pressurized fluid pressure inlet 20. ing. The movable core 5 can be advanced and retracted by a hydraulic cylinder 19, and projects into the mold cavity 4 when the movable core 5 advances.

Needle 1 communicating with pressurized fluid pressure inlet 20
A compression cylinder 17 is connected to 2 via a check valve 15 and a valve 16. In the compression cylinder 17, the pressurized fluid is compressed by the advance of the piston 18, and is maintained at a high pressure. The pressurized fluid is supplied from a pressurized fluid source (not shown) into the compression cylinder 17 by opening the valve 10.

In the illustrated apparatus, all the movable cores 5 are simultaneously moved back and forth by one hydraulic cylinder 19. However, the movable cores 5 are divided into several groups, It can be made to advance and retreat each time, or it can be made to advance and retreat one by one.

According to the apparatus described above, the injection nozzle 11 is pressed against the mold 6 as shown in the figure, and the hollow injection mold 3 can be formed by the procedure described with reference to FIG.

[0036]

【Example】

Example 1 Using a mold 6 having a mold cavity 4 shown in FIGS. 2 and 3, a hollow mold 3 as shown in FIGS. 4 and 5 was formed. The mold cavity 4 is a flat plate having a length of 170 mm × a width of 170 mm × a thickness of 5 mm in a state shown in FIG. 3A, and has a length of 50 mm × a width of 50 mm at positions where the mold cavity 4 is divided into nine parts. The movable cores 5 were arranged in three rows of three each, with a 10 mm gap between adjacent movable cores 5. On the upper surface of the movable core 5, along a side adjacent to the other movable core 5, a thickness of 2 mm and a height of 3 m
m, and a pressurized fluid pressure inlet 20 in the center.
Was provided.

The gate 8 is located on the opposite side to the side where the movable core 5 is provided, corresponding to the intersection of the gap between the movable cores 4.
The pressure of the molten resin finger in the mold cavity 4 at the time of completion of filling the molten resin was made as uniform as possible.

Prior to the injection of the molten resin, the state shown in FIG.
After injecting high-impact polystyrene heated and melted at 0 ° C. to completely fill the mold cavity 4, 70 kg /
A nitrogen gas having a pressure of ² cm ² was injected into the molten resin in the mold cavity 4 from the pressurized fluid pressure inlet 20.

Simultaneously with the injection of the nitrogen gas, the movable core 5 was retracted by 30 mm as shown in FIG. 3 (b).

After cooling and solidifying the resin in the mold cavity 4, the pressurized nitrogen gas was discharged, the mold 6 was opened, and the hollow mold 3 was taken out. The obtained hollow mold 3 is
The cross-section support member 2 was formed to have a thickness of 35 mm, a weight of 370 g, a hollow ratio of 65%, a light weight, and a cross section corresponding to the position of the gap between the movable cores 5 of the mold. This support portion had a minimum thickness of 3 mm, and the inside of the hollow mold 3 had six independent hollow portions 1 by the support portion 2. The hollow mold 3 having this structure was extremely excellent in rigidity.

[0041]

The present invention is as described above. It is possible to form a support 2 having a desired size at a desired position, and to provide a hollow mold 3 excellent in lightness and rigidity. It can be formed integrally and is very useful in industry.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a hollow injection molding method of the present invention and a mold used therein.

FIG. 2 is a plan view showing an example of a mold cavity.

FIG. 3 is a sectional view taken along line AA of FIG. 2 and is an explanatory view of a movable core projecting and retracting.

FIG. 4 is a cross-sectional view showing an example of the present hollow injection mold.

FIG. 5 is a sectional view taken along line AA of FIG. 4;

FIG. 6 is a cross-sectional view showing another example of the present hollow injection mold.

FIG. 7 is a sectional view taken along the line AA of FIG. 6;

FIG. 8 is a sectional view taken along line BB of FIG. 6;

FIG. 9 is a cross-sectional view showing another example of the hollow injection mold.

FIG. 10 is a sectional view taken along line AA of FIG. 9;

FIG. 11 is a sectional view taken along line BB of FIG. 9;

FIG. 12 is an explanatory view of a molding apparatus suitable for the hollow injection molding method.

FIG. 13 is an explanatory diagram of a conventional technique.

FIG. 14 is an explanatory view of a conventional technique, and is a cross-sectional view taken along the line AA of FIG. 18;

FIG. 15 is an explanatory diagram of a conventional technique.

FIG. 16 is an explanatory diagram of a conventional technique.

DESCRIPTION OF SYMBOLS 1 Hollow part 2 Support part 3 Hollow injection mold 4 Mold cavity 5 Moving core 6 Mold 7 Cavity surface 8 Gate 9 Sprue 10 Valve 11 Injection nozzle 12 Needle 13 Injection cylinder 14 Screw 15 Reverse valve 16 Valve 17 Compression cylinder 18 Piston 19 Hydraulic cylinder 20 Pressurized fluid pressure inlet

Continuation of front page (56) References JP-A-3-87224 (JP, A) JP-A-3-9820 (JP, A) JP-A-1-168425 (JP, A) JP-A-53-9870 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (1)

(57) [Claims] 1. A possible retreat from projecting the projecting position into the mold cavity, and a molten resin is injected into the pressurized fluid press-mold having a movable core provided with a port of the mold cavity A hollow portion formed by press-fitting a pressurized fluid with the movable core protruding into the mold cavity, and expanding the hollow portion by retracting the movable core. Injection molding method for products.