JPH04357009A - Hollow injection-molded article and hollow injection molding method and mold - Google Patents

Abstract

PURPOSE:To positively obtain the necessary strength of a hollow injection molded article by not depending on the rib of a mere solid remained part that is unstable in its position and size in regard of a hollow injection molded article having a large hollow part. CONSTITUTION:Molten resin and pressurized fluid are force-fed into a mold cavity and a movable core 5 projected into the mold cavity 4 is withdrawn, and a support part 2 is formed on the trace of the movable core 5. In this manner, by the position and size of the movable core 5, the position and size of the support part 2 to be formed can be set.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow injection molded article having a large hollow portion, a method for hollow injection molding thereof, and a mold thereof. More specifically, the present invention relates to a hollow injection molded product having a large hollow part over a wide area and partially reinforced by forming a support part that supports the hollow part, a hollow injection molding method thereof, and a mold. .

0002

[Prior Art] Conventionally, molten resin was injected in an amount smaller than the volume of the mold cavity, and at the same time pressurized fluid (mainly gas) was injected.
When molding a hollow injection molded article having a hollow part by press-fitting it into a mold cavity, it is attempted to obtain the necessary strength by leaving solid ribs partially.

For example, US Pat. No. 4,247,515 discloses that a protrusion is attached to a mold cavity and the viscosity, elastic density, and interfacial tension between the molten resin and pressurized fluid of the molten resin are adjusted. ing. The thickness of the mold cavity becomes smaller at the point where the protrusion is attached, making it difficult for pressurized fluid to pass through, so multiple hollow parts are formed around the point where the protrusion is attached, and the area near the protrusion is It will remain as a solid rib.

In addition, Japanese Patent Publication No. 61-53208 discloses that the fluidity and amount of molten resin in the mold cavity are distributed, and the molten resin in the mold cavity has a high fluidity portion and a small amount. It is shown that a gas body is introduced into the molten resin part to form a hollow part, and the other part is left as a solid rib. In addition, by press-fitting molten resin and gas into a mold cavity that has sections with different thicknesses, or by press-fitting molten resin and gas into a mold cavity and partially enlarging the mold cavity, mold By preferentially introducing the gas into the thick or enlarged parts of the mold cavity to create a hollow part, and leaving the thin or unexpanded parts of the mold cavity as solid ribs, or even using both in combination. It has also been shown that

[0005]

[Problem to be solved by the invention] U.S. Patent No. 424751
In the method shown in Specification No. 5, the introduction point of the pressurized fluid can be reliably separated by adding tall protrusions, but the part corresponding to the tall protrusions becomes a deep recess of the hollow injection molding, and the ribs are separated. This results in a thinner wall, which in turn leads to a decrease in strength. This can be prevented by reducing the height of the protrusions, but this results in inaccurate division of pressurized fluid introduction points. For this reason, the position and size of the ribs are easily controlled by chance, and as shown in FIGS. 18 and 19, the ribs 10
The positions and shapes of the ribs 101 become irregular, and since these cannot be designed in advance, it becomes impossible to reliably leave ribs 101 of the required size in the truly necessary locations. Moreover, the protrusion attached to the mold cavity forms an essentially unnecessary recess 102 in the resulting hollow injection molded product.

On the other hand, among the methods shown in Japanese Patent Publication No. 61-53208, the method of giving distribution to the fluidity and amount of the molten resin in the mold cavity has a method that distributes the viscosity and amount of the molten resin in the mold cavity. It is not possible to precisely control the distribution of Therefore, the position and size of the ribs are likely to be controlled by chance, and as shown in FIG. 20, the position and shape of the ribs 101 become irregular, which makes it impossible to design them in advance, and also makes it impossible to increase the hollowness ratio very much. There is. Furthermore, in the method of partially changing the thickness of the mold cavity or partially enlarging the mold cavity, as shown in FIG. There is an unavoidable problem that they will form. In particular, if a hollow injection molded product does not have a large thickness change, the preferential guidance of gas to the thicker portions will be insufficient, and the position and size of the ribs 101 will be controlled by chance. These cannot be designed in advance. Furthermore, in a hollow injection molded product in which a portion having a constant large thickness extends over a wide range, one hollow portion 103 is formed over the entire portion having a constant large thickness, so that it is difficult to maintain strength. However, there is a problem in that the size of the hollow part is limited.

[0007] Conventionally, it has not been possible to leave ribs in a predetermined position and with a predetermined size, and for this reason, the size and shape of the hollow injection molded product that can be molded, as well as the size of the hollow part (
Hollowness ratio) is limited.

The present invention has been made in view of the above-mentioned problems in the prior art, and it is possible to eliminate ribs, which are simply solid residual parts whose position and size are unstable, in hollow injection molded products having a large hollow part. The purpose is to ensure that the necessary strength of hollow injection molded products can be obtained regardless of the

Another object of the present invention is to ensure that the above-mentioned strength can be obtained without adding unnecessary recesses or steps to the resulting hollow injection molded product.

0010

[Means and operations for solving the problem] The invention of claim 1 is a single piece with a hollow ratio of 20 to 90%, as shown in FIGS. 4 to 6, 7 to 9, 10 and 11. A support part 2 of a predetermined size that extends integrally between opposing surfaces with a hollow part 1 in between, at a predetermined position in the cross section of the molded article.
This is a hollow injection molded article 3 having the following.

The invention of claims 2 and 3 is a method for molding the hollow injection molded article 3, and the invention of claim 2 is a method for molding the hollow injection molded article 3, and as shown in FIG. Molten resin is injected into the mold cavity 4 of a mold 6 having a movable core 5 that can be retracted from the position, and pressurized fluid is further injected into the mold cavity 4 with the movable core 5 protruding. Then, the movable core 5 is moved backward. Further, as shown in FIG. 1, the invention of claim 3 provides a mold 6 having a movable core 5 similar to that described above and capable of expanding the mold cavity volume by moving the cavity surface 7. Molten resin is injected into the cavity 4, pressurized fluid is pressurized into the mold cavity 4 with the movable core 5 protruding, and the mold is formed by retreating the movable core 5 and moving the cavity surface 7. This is to expand the cavity volume.

Furthermore, the invention of claim 4 is a mold 6 used for molding the hollow injection molded article 3 of claim 1, as shown in FIG. A mold having a movable core 5 capable of protruding into the mold cavity 4 and retracting from this protruding position at a position where a supporting part 2 that is integrally continuous between opposing surfaces with a hollow part 1 in between is formed. Type 6
It is.

The present invention will be further explained.

As shown in FIGS. 4 to 6, 7 to 9, 10 and 11, the hollow injection molded article 3 has 20 to
It has a hollowness ratio of 90% and has a support portion 2 of a predetermined size at a predetermined position within its cross section. This support part 2 is
It is integrally connected between opposing surfaces with the hollow part 1 in between, and is shaped like a support wall or a support column. In particular, the hollow injection molded articles 3 shown in FIGS. 4 to 6 have supporting parts 2 extending radially from near the center, and the hollow injection molded articles 3 shown in FIGS. The hollow injection molded article 3 shown in FIGS. 10 and 11 has supporting portions 2 arranged in parallel, and further has supporting portions 2 intersecting in a checkerboard pattern.

The shape of the support portion 2 may be, for example, a straight wall shape, a wave shape, a polygonal shape, a wall shape of a flat surface, for example, a cylindrical shape, a prismatic shape,
It can have a columnar shape such as an elliptical columnar shape. When the wall shape is used, the wall shape may be appropriately selected from long to short as necessary. Furthermore, the diameter of the columnar shape can be appropriately selected as necessary.

[0016] The arrangement of the support part 2 can be selected from various forms, such as radial, parallel line, checkerboard, staggered, etc., depending on the shape and size of the hollow injection molded product 3, the size of the hollow part 1, etc. be able to. Moreover, wall-shaped and column-shaped supporting parts 2 can be mixed.

The support portion 2 in the present hollow injection molded product 3 is in the shape of a support wall or support column as described above, and is formed at a predetermined position and size, so even if it is a large hollow Even if it is part 1, it is possible to reliably maintain the necessary strength.

The hollow injection molded article 3 can be molded by the hollow injection molding method and mold 6 shown in FIG.

First, as shown in FIG. 1(a), molten resin is injected into the mold cavity 4. In addition to performing this injection in a so-called mold clamped state, it can also be performed in a state in which the volume of the mold cavity 4 is arbitrarily expanded by moving the cavity surface 7, which will be described later. The state of the mold 6 in which the molten resin is injected depends on the hollow injection molded object 3 to be molded.
It may be selected depending on the shape, hollowness ratio, etc.

The amount of molten resin injected is adjusted depending on the shape and hollowness ratio of the target hollow injection molded product 3, but the shape of the mold cavity 4 has no uneven thickness and is centered around the gate 8. When the movable core 5 has a substantially symmetrical shape, the amount is preferably 40 to 95% of the volume of the mold cavity 4 with the movable core 5 protruding into the mold cavity 4. In addition, if the shape of the mold cavity 4 is such that there is uneven thickness or a thin wall portion, the amount is sufficient to fill the inside of the mold cavity 4 with the movable core 5 protruding into the mold cavity 4. It is preferable. In the latter case, the hollowness ratio is determined by the expansion rate of the mold cavity volume due to the retreat of the movable core 5 and the movement of the cavity surface 7.

In the following description, the mold cavity 4 will be described with the movable core 5 protruding into the mold cavity 4.
A case in which injection is performed in an amount smaller than the amount that fills the mold cavity 4 is called a "short shot," and a case in which injection is performed in an amount sufficient to fill the mold cavity 4 in a similar state is called a "full shot."

The injection of the molten resin is normally carried out with the movable core 5 protruding into the mold cavity 4, as shown in FIG. 1(a). 5 may be made to protrude, or the movable core 5 may be made to protrude after injection of a predetermined amount of molten resin is completed.

Injection of the molten resin into the mold cavity 4 is as follows:
As shown in FIG. 2, when each movable core 5 is provided radially from the vicinity of a gate 8, the operation can be performed through one gate 8 located at the center. In addition, as shown in FIG. 3, when the movable cores 5 are arranged in parallel, it is difficult to uniformly supply molten resin between the movable cores 5 from one location. A gate 8 may be provided in the center, and molten resin may be supplied through the plurality of gates 8.

Next, as shown in FIG. 1(b), with the movable core 5 protruding into the mold cavity 4, pressurized fluid is forced into the molten resin in the mold cavity 4. In the case of a short shot, the molten resin in the mold cavity 4 is cooled in contact with the wall surface of the mold cavity 4 and the movable core 5, leaving the resin that has become difficult to flow, while leaving the uncooled resin that is easy to flow inside. is pushed deep into the mold cavity 4 by the pressurized fluid, forming the hollow part 1. Further, in the case of a full shot, an amount of pressurized fluid is injected in accordance with the amount of volumetric contraction caused by cooling the molten resin, and the hollow portion 1 is formed.

[0025] The pressurized fluid is pressurized into the mold cavity 4 by
Usually, it can be performed from the gate 8 via the injection path of the molten resin. However, depending on the shape of the target hollow injection molded product 3, etc., the gate 8, which is the supply port for the molten resin, is not used, and a pressure inlet exclusively for the pressurized fluid is provided in the mold cavity 4. It is also possible to directly inject pressurized fluid into. Particularly, as shown in FIG. 3, when there are a plurality of gates 8 serving as molten resin supply ports, it may be preferable to directly inject pressurized fluid into the mold cavity 4.

In the case of a short shot, the pressurized fluid can be injected simultaneously with the injection of the molten resin, or after the injection of a predetermined amount of the molten resin has been completed. In the case of a full shot, it is performed after injection of a predetermined amount of molten resin is completed.

When the pressurized fluid is injected at the same time as the molten resin is injected, it is necessary to align the flow direction of the molten resin with the pressurized fluid and supply it to the mold cavity 4 so that the molten resin surrounds the pressurized fluid. be. This is done by pressurizing the pressurized fluid together with the molten resin from the sprue 9 through the gate 8 into the mold cavity 4, and by arranging the movable core 5 and the gate 8 as shown in FIGS. 2 and 3. It can be carried out.

Simultaneously with, during, or after press-fitting the pressurized fluid, the movable core 5 is retreated from the protruding position in the mold cavity 4 to a predetermined position, as shown in FIG. 1(c). The resin in the periphery of the gap created by the retreat of the movable core 5 is moved and crushed, and the support part 2 is formed. This support part 2 is always formed at the position of the movable core 5 according to the shape of the movable core 5, so by appropriately selecting the installation position and shape of the movable core 5, the support part 2 can be formed at the required position and according to the shape of the movable core 5. The size and shape of the support part 2 can be formed.

The position where the movable core 5 is provided depends on the shape of the hollow injection molded product 3 to be molded, the size of the hollow part 1, etc., and the position where the movable core 5 is provided supports the space between two opposing surfaces with the hollow part 3 in between. Just select the areas that need reinforcement. The shape of the movable core 5 may be, for example, a plate shape with a planar shape such as a straight line, a wave shape, or a polygonal shape, or a pin shape with a cross section such as a circle, a polygon, or an ellipse, depending on the reinforcement range etc. By doing this, the support part 2 obtained can be made into a wall shape or columnar shape of various shapes, and the size of the support part 2 can be obtained by adjusting the length, thickness, diameter, etc. of the movable core 5. can be adjusted. Also,
The movable core 5 can be arranged in various ways, such as radial, parallel line, checkerboard, staggered, etc. Moreover, plate-shaped and pin-shaped movable cores 5 can be arranged in a mixed manner.

The shape of the movable core 5 can be various as described above, but in particular, if it is shaped like a pin with a circular cross section, the process for installing it in the mold 6 involves drilling a hole. This is preferable because it simplifies processing of the mold 6. In addition, in the case of a pin-shaped movable core 5, the movable core 5
If the distance between the comrades is large, a columnar support part 2 is formed,
If the movable cores 5 are arranged with narrower spacing, the movable cores 5
A wall-shaped support portion 2 is formed with continuous gaps.

The point at which the movable core 5 completes retraction is usually the point where the tip end surface of the movable core 5 almost coincides with the cavity surface 7, and by retracting to this position, the surface of the hollow injection molded product 3 is The support portion 2 can be formed without leaving any concave portions or convex portions. However, when molding the hollow injection molded article 3, which does not pose any problem even if some concave or convex portions are formed on the surface,
Stop the retreat of the movable core 5 with the tip surface of the movable core 5 protruding into the mold cavity 4, or move the movable core 5 back until the tip surface of the movable core 5 is slightly retracted from the cavity surface 7. You can also do it.

The mold 6 may be opened after the resin in the mold cavity 4 is sufficiently cooled and the pressurized fluid in the hollow part 1 is discharged at the stage shown in FIG. 1(c). In order to further enlarge the hollow part 1 and reduce the weight of the hollow injection molded product 3 obtained, it is preferable to expand the mold cavity volume by moving the cavity surface 7 shown in FIG. 1(d). . This movement of the cavity surface 7 may be performed before the movable core 5 retreats, together with the retreat of the movable core 5, or after the movable core 5 retreats, as long as it is simultaneous with the start of pressurization of the pressurized fluid. .

The cavity surface 7 to be moved is usually the cavity surface 7 on the side where the movable core 5 is provided, but it may also be the cavity surface 7 on the opposite side or both cavity surfaces 7 facing each other.

If the mold cavity volume is expanded by moving the cavity surface 7 after the movable core 5 has retreated, the thickness and diameter of the support portion 2 can be made smaller than the thickness and diameter of the movable core 5. If this is done before the movable core 5 retreats, the thickness and diameter of the support portion 2 can be made larger than when it is done after the movable core 5 retreats. Regardless of the timing, by adjusting the expansion rate of the mold cavity volume depending on the thickness of the movable core 5, its retreat distance, and the moving distance of the cavity surface 7, the thickness and diameter of the support portion 2 obtained can be adjusted. Hollow injection molded product 3
The hollow ratio of can be adjusted arbitrarily.

[0035] In this way, the necessary hollow part 1 and supporting part 2 are
After the shaping of the hollow injection molded article 3 is completed, the pressure inside the hollow part 1 is returned to about normal pressure, the mold 6 is opened, and the hollow injection molded article 3 is taken out.

To discharge the pressurized fluid in the hollow part 1, an injection nozzle (not shown in FIG. 1) is separated from the mold 6, and a gate 8 is removed.
This can be done by discharging it into the atmosphere through the sprue 9. Alternatively, a pressurized fluid nozzle may be built into the injection nozzle, or a recovery port may be provided within the injection nozzle, and the injection nozzle may be placed in pressure contact with the mold 6 from the pressurized fluid nozzle or recovery port of the injection nozzle. , the pressurized fluid can also be recovered for reuse.

The hollow injection molded article 3 thus obtained has a hole at the location where the pressurized fluid is press-fitted. When pressurized fluid is injected through the gate 8 of the mold 6, the hole can be closed by discharging the pressurized fluid in the hollow portion 1 and then injecting a small amount of molten resin again.

When molding is carried out using a mold 6 having a movable core 5 and its arrangement as shown in FIG. 2, a hollow injection molded article 3 as shown in FIGS. 4 to 6 is obtained. Further, when molding is performed using a movable core 5 and a mold 6 having the movable core 5 and its arrangement as shown in FIG. 3, a hollow injection molded article 3 as shown in FIGS. 7 to 9 is obtained.

As the resin used in the present invention, all thermoplastic resins used in general injection molding, extrusion molding, etc. can be used, and thermosetting resins can also be used if necessary. Moreover, various additives can be added to the resin as necessary.

The pressurized fluid used in the present invention is one that is gaseous or liquid at room temperature and pressure, and that does not react with or mix with the resin used at the temperature and pressure during injection. Specifically, for example, nitrogen gas, carbon dioxide gas, air,
Examples include helium gas, water, glycerin, and liquid paraffin, but inert gases such as nitrogen gas and helium gas are preferred.

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

In the figure, reference numeral 11 denotes an injection nozzle, and a pressurized fluid nozzle 12 is built into the injection nozzle 11. The injection cylinder 13 behind the injection nozzle 11 is similar to a normal one and has a built-in screw 14, and when the screw 14 moves forward, the molten resin inside is pushed out.
Injection nozzle 11 through a gap around pressurized fluid nozzle 12
It is ejected from.

A compression cylinder 17 is connected to the pressurized fluid nozzle 12 via a check valve 15 and a valve 16 . Within the compression cylinder 17, the pressurized fluid is compressed and maintained at a high pressure by the advancement of the piston 18. still,
Pressurized fluid is supplied into the compression cylinder 17 from a pressurized fluid source, not shown, by opening the valve 10.

The mold 6 is provided with a movable core 5 on the side opposite to the pressure contact side of the injection nozzle 11.
can move forward and backward by a hydraulic cylinder 19, and protrudes into the mold cavity 4 when moving forward.

In the illustrated device, all the movable cores 5 are moved forward and backward at the same time by one hydraulic cylinder 19, but the movable cores 5 are divided into several groups. It is also possible to advance and retreat each time, or to advance and retreat one by one.

According to the above-mentioned apparatus, the injection nozzle is pressed into contact with the mold 6 as shown in the figure, and the hollow injection molded article 3 can be molded according to the procedure explained in FIG. 1.

[0047]

【Example】

Example 1 FIG. 13 shows the planar shape of the mold cavity 4 used in this example, and the mold cavity 4 is 200 mm x 20 mm.
It has a square flat plate shape with a diameter of 0 mm, has a gate 8 in the center (on the opposite side to the side where the movable core 5 is provided), and has a built-in pressurized fluid nozzle 12 as explained in FIG. 12. Molten resin and pressurized fluid are injected through the gate 8 by the injection nozzle 11.

Eight movable cores 5 are plate-shaped and are provided radially around the gate 8, and the cavity surface 7 on the installation side of the movable core 5 expands the mold cavity volume. It is possible to move in the direction. Moreover, the thickness of the movable core 5 is 6 mm.

As shown in FIG. 14(a), prior to injection of molten resin, the position of the cavity surface 7 on the side where the movable core 5 is provided and the movable core 5 are adjusted, and the mold cavity 4 is
The thickness t of the movable core 5 was adjusted to 16 mm, and the protrusion length h of the movable core 5 into the mold cavity 4 was adjusted to 8 mm.

The mold 6 in the above state is filled with 70% of the volume of the mold cavity 4 in the above state with high impact polystyrene heated and melted at 220°C.
Inject nitrogen gas at a pressure of 0 kg/cm2 into mold cavity 4.
It was press-fitted into the molten resin inside.

Immediately after the nitrogen gas is pressurized, move the movable core 5 by 8 m until the tip end surface of the movable core 5 coincides with the installation side cavity surface 7 of the movable core 5, as shown in FIG. 14(b).
m, and then, as shown in FIG. 14(c),
The cavity surface 7 on the side where the movable core 5 was provided was moved together with the movable core 5 by 10 mm to expand the mold cavity volume.

After the resin in the mold cavity was cooled and solidified, the nitrogen gas that had been injected was discharged, the mold was opened, and the hollow injection molded product was taken out. The obtained hollow injection molded product is
It was lightweight with a thickness of 26 mm, weight of 471 g, and hollowness ratio of 52%, with no irregularities on the surface, and eight wall-shaped support parts were formed inside the cross section corresponding to the positions of the movable core of the mold. . This support part had a minimum wall thickness of 2 mm, extended radially from the center of the hollow injection molded article, and was continuous with the peripheral wall of the hollow injection molded article. The hollow injection molded product obtained had excellent rigidity.

Example 2 Using the mold used in Example 1, before retracting the movable core, the cavity surface on the side where the movable core was provided was moved to expand the mold cavity volume, Example 1 except that the movable core was then retreated and the mold operation was performed to align the tip end surface of the movable core with the cavity surface on the side where the movable core was installed.
Hollow injection molding was performed in the same manner as above.

The obtained hollow injection molded product was almost the same as that obtained in Example 1, but the thickness of the formed support part was 3 mm at the minimum part.

Example 3 Using the mold used in Example 1, with the movable core protruding 8 mm into the mold cavity, the mold cavity volume was determined by moving the cavity surface at the same time as the movable core retreated. Hollow injection molding was carried out in the same manner as in Example 1, except for enlarging.

The obtained hollow injection molded product was almost the same as that obtained in Example 1, but one surface had unevenness, and the thickness of the formed supporting part was smaller than that at the minimum part. 3mm
Met.

Comparative Example 1 A mold having the same dimensions and shape as the mold used in Example 1 but without a movable core was used.

First, one cavity surface (cavity surface opposite to the gate installation side) was moved to adjust the thickness of the mold cavity to 16 mm, and then high impact polystyrene heated and melted at 220° C. , 70% of the volume of the mold cavity in this state is filled, and 30k after filling.
Nitrogen gas at a pressure of g/cm2 was injected into the molten resin in the mold cavity.

After the nitrogen gas was pressurized, one cavity surface, which was the same as above, was moved by 10 mm to make the thickness of the mold cavity 26 mm.

The obtained hollow injection molded product weighed 473
g, It was lightweight with a hollow ratio of 51.5%, but the support part formed inside the cross section was not in a fixed position, and the wall thickness became extremely large toward the peripheral wall of the hollow injection molded product. The wall thickness was uneven. As a result, depressions were partially formed in the thick portion due to heat shrinkage.

Comparative Example 2 Hollow injection molding was carried out in the same manner as in Example 1, except that the movable core was not retreated and the cavity surface was not moved after the injection of the molten resin and the injection of nitrogen gas. went. The obtained hollow injection molded product has a thickness of 16 mm and a width of 200 m.
m, length 200mm, weight 471g, hollowness ratio 26.
It was as low as 4%, and one surface was uneven. The formed supporting portion had a minimum wall thickness of 9 mm, which required a long cooling time.

Example 4 FIG. 15 shows the planar shape of the mold cavity 4 used in this example. The mold cavity 4 is a rectangular flat plate with a width of 110 mm and a length of 385 mm. An injection nozzle 11 having four gates 8 in the center between the cores 5 (on the side opposite to the side where the movable core 5 is provided) and incorporating a pressurized fluid nozzle 12 as described in FIG. By,
Molten resin and pressurized fluid are forced into the gate 8. In addition, the gate 8 and the resin passage on its upstream side are
The respective diameters are adjusted so that the molten resin is evenly injected into the mold cavity 4 in the length direction.

The movable cores 5 are plate-shaped, and three movable cores 5 are provided parallel to each other at equal intervals in the width direction of the mold cavity 4. The cavity surface 7 on the installation side of the movable cores 5 It is movable in the direction of expanding the cavity volume. Moreover, the thickness of the movable core 5 is 7 mm, and the length is 379 mm.

As shown in FIG. 16(a), prior to injection of the molten resin, the positions of the cavity surface 7 on the side where the movable core 5 is provided and the movable core 5 are adjusted, and the mold cavity 4 is
The thickness t of the mold cavity 4 of the movable core 5 is set to 6 mm.
The inner protrusion length h was adjusted to 3 mm.

[0065] High impact polystyrene heated and melted at 220°C is injected into the mold 6 in the above state to fill the mold cavity 4 in the above state, and after this filling, 30 kg/cm
Nitrogen gas was injected into the molten resin in the mold cavity 4 at a pressure of 2.2 cm.

Simultaneously with the injection of nitrogen gas, as shown in FIG. 16(b), the movable core 5 and the cavity surface 7 on the side where the movable core 5 is provided are moved by 24 mm to increase the mold cavity volume. Then, as shown in FIG. 16(c), the movable core 5 was moved back 3 mm to a position where the distal end surface of the movable core 5 coincided with the installation side cavity surface 7 of the movable core 5.

After the resin in the mold cavity was cooled and solidified, the nitrogen gas that had been injected was discharged, the mold was opened, and the hollow injection molded product was taken out. The obtained hollow injection molded product is
It was lightweight with a thickness of 30 mm, weight of 233 g, and hollowness ratio of 82%, with no irregularities on the surface, and three wall-shaped support parts were formed inside the cross section corresponding to the position of the movable core of the mold. . The support portions had a minimum wall thickness of 1.5 mm, were arranged in parallel in the width direction of the hollow injection molded article, and were continuous with the peripheral wall on the short side of the hollow injection molded article. The hollow injection molded product obtained had excellent rigidity.

Embodiment 5 As shown in FIG. 17, a pressurized fluid pressure inlet 20 is provided on the installation side of the movable core 5, and pressurized fluid (nitrogen gas) is supplied to the gate 8.
Hollow injection molding was performed in the same manner as in Example 4 except that the pressurized fluid was press-fitted from the pressurized fluid inlet 20 instead.

As a result, a hollow injection molded product similar to that of Example 4 was obtained.

[0070]

[Effects of the Invention] The present invention is as explained above, and it is possible to form a support portion of a desired size at a desired position, and also to provide a hollow injection molded product having excellent lightness and rigidity. Moreover, it can be integrally molded, making it very useful industrially.

[Brief explanation of drawings]

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

FIG. 2 is an explanatory diagram showing an example of a mold cavity.

FIG. 3 is an explanatory diagram showing another example of a mold cavity.

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

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

FIG. 6 is a sectional view taken along line BB in FIG. 4;

FIG. 7 is a cross-sectional view showing another example of the hollow injection molded product.

FIG. 8 is a sectional view taken along line AA in FIG. 7;

9 is a sectional view taken along line BB in FIG. 7. FIG.

FIG. 10 is a cross-sectional view showing another example of the hollow injection molded product.

FIG. 11 is a sectional view taken along line AA in FIG. 10;

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

13 is a plan view of the mold cavity of the mold used in Example 1. FIG.

FIG. 14 is an explanatory diagram of the operating procedure of Example 1.

15 is a plan view of the mold cavity of the mold used in Example 4. FIG.

FIG. 16 is an explanatory diagram of the operating procedure of Example 4.

FIG. 17 is an explanatory diagram of a mold used in Example 5.

FIG. 18 is an explanatory diagram of the prior art.

FIG. 19 is an explanatory diagram of the prior art, and is a sectional view taken along the line AA in FIG. 18.

FIG. 20 is an explanatory diagram of the prior art.

FIG. 21 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

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

Claims (4)

[Claims] Claim 1: An integral molded article with a hollowness ratio of 20 to 90%, at a predetermined position within its cross section, a molded article of a predetermined size extending integrally between opposing surfaces with the hollow part in between. A hollow injection molded article characterized by having a support part. 2. Injecting molten resin into the mold cavity of a mold having a movable core capable of protruding into the mold cavity and retracting from this protruding position, and further injecting the movable core into the mold cavity. A hollow injection molding method characterized by injecting pressurized fluid into a state in which the movable core is protruded and retracting the movable core. 3. A mold cavity of a mold having a movable core capable of protruding into the mold cavity and retracting from this protruding position, and capable of expanding the mold cavity volume by moving the mold cavity surface. Molten resin is injected into the mold cavity, and pressurized fluid is injected into the mold cavity with the movable core protruding, causing the movable core to retreat and the mold cavity surface to move, thereby expanding the mold cavity volume. A hollow injection molding method characterized by performing the following steps. 4. At a position where a support part is to be formed which is integrally connected between opposing surfaces of the hollow injection molded product to be molded with the hollow part interposed therebetween, there is provided a support part protruding into the mold cavity and from the protruding position. A mold characterized by having a movable core that can be retreated.