JPH06134885A - Hollow molded product and method and device for molding the same - Google Patents

Abstract

PURPOSE:To enhance cushioning properties, buffer properties, shape retentivity and bonding strength by forming a hollow object from a soft hollow object composed of a soft resin and embedding and sealing the contact part of a seal piece and a part to be contacted by a hard resin. CONSTITUTION:A soft resin (e.g. polyethylene) is injected in a primary molding cavity 7 to form an annular preparatory molded object 21 and the annular seal piece 22 of the preparatory hollow object 21 is brought into contact with a part 23 to be contacted while the annular guide part 11 of a mold 6 is bent and the contact part with the seal piece 22 is pressed by an annular pressing part 12. Subsequently, a molten hard resin (e.g. polypropylene) is injected in a secondary molding cavity to seal the contact part with the seal piece 22 to obtain a hollow molded product wherein a soft hollow object such as a tire having a hollow part and a hard part such as a wheel are bonded. By this method, the soft hollow product excellent in cushioning properties, buffer properties and shape retentivity can be formed and the bonding strength with the hard part can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded product having a hollow body, for example, a hollow molded product such as a synthetic resin wheel used for an electric vacuum cleaner and the like, a manufacturing method thereof and a molding apparatus.

[0002]

2. Description of the Related Art A wheel of an electric vacuum cleaner comprises a tire portion and a wheel portion extending from the tire portion. As such a wheel, an integrally molded product of polypropylene is known. However, since such a wheel does not have a cushioning property, when the floor surface is easily scratched or the floor surface with a step is run, not only noise is generated but also vibration is transmitted to the cleaner body, and The vacuum cleaner itself is also easily damaged.

Therefore, there has been proposed a wheel in which the tire portion is formed of a soft resin such as soft polyvinyl chloride, ethylene-vinyl acetate copolymer and thermoplastic elastomer.
However, since the tire portion is formed of a solid soft resin, the amount of the soft resin used is large, the material is wasted, and the cushioning property and the cushioning property are still small.

Further, it has been proposed to form the tire portion with a solid soft foam, for example, a foamed ethylene-vinyl acetate copolymer. However, the foamed soft resin is likely to be permanently deformed due to long-term use, and smooth running is likely to be impaired. In addition, since the tire part is a foam, the surface strength is weak and sand particles etc. may bite, which may damage the floor surface, and the bonding strength with the hard wheel part necessary to secure the mechanical strength. Becomes smaller.

The applicant of the present application discloses in Japanese Patent Application Laid-Open No. 3-253402 that a pair of rings, which are made of an elastic material such as rubber, can be brought into contact with each other at the opening of the inner circumference and have a bulge at the tip. A method for manufacturing a wheel is proposed, in which a hollow tire portion having a circular contact portion is molded, the contact portion is held by a mold, and molten synthetic resin is injected into the cavity to mold the wheel portion. .

The wheel obtained by this method has a hollow tire portion, and therefore, unlike the above wheels, has excellent cushioning properties and cushioning properties, and the bulging portion of the abutting portion is embedded in the wheel portion. Therefore, the unity is great. However, since the tire portion is made of rubber, the floor surface may be contaminated as the wheels run.

On the other hand, in order to prevent the floor surface from being contaminated, it is effective to form the hollow tire portion with a soft resin. However, since the tip of the abutting portion is an undercut shape that bulges out, if the tire portion is formed of a soft resin with a small degree of elastic deformation, it takes time for demolding, and the productivity of the wheel decreases. , Difficult to automate. Further, in the above method, the preformed tire portion is loaded into the mold,
Since the insert molding method of injecting a synthetic resin is adopted, it takes time to mold and the cost becomes high.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a hollow molded article which is excellent in cushioning property, cushioning property and shape retaining property and has a large bonding strength between a hollow body and a hard portion. .

Another object of the present invention is to provide a hollow molded article such as a wheel that can run smoothly over a long period of time without fear of contaminating the running surface.

It is still another object of the present invention to provide a method capable of easily producing a hollow molded article having the above-mentioned excellent characteristics, which is easy to remove from the mold, even though a soft resin is used. is there.

Another object of the present invention is to provide a molding apparatus useful for continuously producing the hollow molded article as described above.

[0012]

Means for Solving the Problems As a result of intensive studies, the present inventor has paid attention to the fact that a thin portion of a soft resin is easily bent, and as a result, bends a sealing piece of a soft resin to the opposite contacted portion side, The present invention has been completed by finding that the hard portion can be integrally formed with the hollow body by injecting the hard resin into both contact portions.

That is, the hollow molded article of the present invention is a hollow molded article having a hollow body made of a soft resin and a hard portion extending from the hollow body and made of a hard resin. The hollow body is composed of a hollow soft body in which a seal piece is bent and is brought into contact with a contacted portion, and a contact portion with the seal piece is embedded and sealed with a hard resin. The hollow molded article may be a wheel in which a hollow body constitutes an annular tire portion and a hard portion constitutes a wheel portion extending inward from the tire portion.

Further, in the method for producing a hollow molded article of the present invention, a preliminary hollow body having a sealing piece is formed of a soft resin, the sealing piece is bent and pressed against a contacted portion of the preliminary hollow body, and melted. By injecting the hard resin described above, the contact portion with the seal piece is sealed to form a hollow body and the hard portion extending from the hollow body is molded. This method is useful in molding wheels.

Further, the molding apparatus of the present invention comprises the first and second molding devices.
While the primary molding cavity formed by the molding die is formed corresponding to the annular preliminary hollow body having the sealing piece, while guiding the sealing piece to the third molding die as the mold is clamped. A guide part for bending and contacting the contacted part of the annular preliminary hollow body, and a pressing part for pressing the contact part with the seal piece are formed.

[0016]

In the present invention, when the seal piece of the preliminary hollow body made of the soft resin is bent and brought into contact with the contacted portion, and the molten hard resin is injected, the contact portion with the seal piece is embedded / sealed. The hollow body thus formed and the hard portion extending from the hollow body can be integrally molded with high joint strength. Moreover, since the hard resin is injected by pressing the contact portion with the seal piece,
It is not necessary to make the preliminary hollow body into an undercut shape, and mold release is easy. Further, the hollow body formed of the soft resin can ensure high cushioning property, cushioning property, shape retention property and stain resistance, and the hard portion formed of the hard resin can ensure high mechanical strength.

[0017]

Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings.

1 to 6 are schematic sectional views for explaining the method of the present invention. FIG. 7 is a partial sectional view showing a hollow molded article obtained by the method of the present invention. In this example, wheels are shown.

The molding apparatus 1 includes first molding dies 5a and 5b, two second molding dies 2 and a third molding dies 6, which are mounted on both sides of a reversible platen 4 which is reversible about a shaft 3, respectively. It has and. The reversing plate 4 can be positioned at a position where each of the first molding dies 5a and 5b faces the second molding die 2, and the first molding die 2 and the reversing plate 4 move relative to each other. To do. In this example, the first molds 5a and 5b constitute a reversible fixed mold, and the second and third molds 2 and 6 move forward and backward with respect to the first molds 5a and 5b. Make up the mold.

An annular primary molding region 7a and a secondary molding region 8a located inside the primary molding region 7a are formed in the first molding dies 5a and 5b. Is formed with a molding region 7b corresponding to the primary molding region 7a. The molding regions 7a and 7b are clamped between the first molding dies 5a and 5b and the second molding dies 2 by
The primary molding cavity 7 is formed. The primary molding cavity 7 is formed corresponding to the annular preliminary hollow body 21 having a U-shaped cross section and having an annular sealing piece 22.

The third molding die 6 includes the first molding die 5
Molding regions 8b are formed corresponding to the secondary molding regions 8a of a and 5b, and each of the molding regions 8a and 8b is formed by the first molding die 5
The secondary molding cavity 8 is formed by clamping the a and 5b and the third molding die 6.

A gate 9 for injecting a primary molding resin into a primary molding cavity 7 is formed in the second molding die 2, and a secondary molding cavity 8 is formed in the third molding die 6. A gate 10 for injecting the secondary molding resin is formed.

Further, the third molding die 6 is composed of an inner die 6a in which a secondary molding region 8b is formed, and an outer die 6b which is arranged on the outer periphery of the inner die 6a so as to be movable back and forth. ing. The outer peripheral die 6b projects further than the inner die 6a in the mold open state, and with the advance thereof, the outer die 6b retreats due to contact with the first molding die 2.

At the inner end of the outer peripheral die 6b, an annular seal piece formed by using the primary molding cavity 7 is formed along with the mold clamping with the first molding dies 5a, 5b. Two
An annular guide portion 11 having a curved surface curved inward is formed in order to bend the 2 while guiding it inwardly to make contact with the contacted portion 23 of the annular preliminary hollow body 21. Further, the inner die 6a is formed with an annular pressing portion 12 for pressing the contact portion between the annular seal piece 22 and the contacted portion 23 as the third molding die 6 advances.

Further, as shown in FIGS. 1 and 6, in order to take out a hollow molded product from the first molding dies 5a and 5b,
Rods 13 and 14 that move forward and backward by hydraulic pressure or air pressure are provided in association with mold clamping and mold opening between the first molds 5a and 5b and the third mold 6.

The method for molding a hollow molded product by using such a molding apparatus is as follows.

First, the second molding die 2 and the third molding die 6 are clamped to the first molding dies 5a and 5b, and the melted soft resin is injected into the primary molding cavity 7 from the gate 9. Then, a ring-shaped preliminary hollow body 21 having a U-shaped cross section and having a seal piece 22 is formed. The preliminary hollow body 21 is formed with a contacted portion 23 that comes into contact with the annular seal piece 22 when the annular seal piece 22 is bent, and a curved receiving portion 24 is formed at an end portion facing the seal piece 22. ing.

Then, as shown in FIG. 1, the second and third molding dies 2 and 6 are retracted to open the mold, and as shown in FIG. The third molds 2 and 6 are opposed to the first molds 5a and 5b and moved forward. As shown in FIGS. 3 and 4, as the third molding die 6 advances, the annular seal piece 22 is guided inward along the curved surface of the annular guide portion 11 of the outer peripheral die 6b. While being bent in a curved shape, the tip of the seal piece 22 comes close to or comes into contact with the contacted portion 23 and the receiving portion 24 of the preliminary hollow body 21.

When the third mold 6 further advances and comes into contact with the first mold 5a, the outer mold 6b is restricted from moving forward,
The inner die 6a advances relative to the outer die 6b, and the contact portion between the annular seal piece 22 and the contacted portion 23 is pressed by the annular pressing portion 12 of the inner die 6a. The annular pressing portion 12 has a tapered tip. Therefore, not only does it hinder the demolding, but also the pressing portion 12 allows the tip of the annular seal piece 22 to be brought into close contact with the contacted portion 23 and the receiving portion 24. In particular, since the annular seal piece 22 is formed of a deformable soft resin, the degree of adhesion between the annular seal piece 22 and the contacted portion 23 and the receiving portion 24 can be increased.

As shown in FIG. 5, the first molding die 5b
The primary molding cavity 7 is formed by clamping the second molding die 2 and the second molding die 2, and the secondary molding cavity 8 is formed by clamping the first molding die 5a and the third molding die 6. It is formed.

The primary molding soft resin melted from the gate 9 formed in the second molding die 2 is injected into the primary molding cavity 7, and the secondary molding cavity 8 is filled with the third molding resin. Molten hard resin is injected from the gate 10 formed in the mold 6.

When molten hard resin is injected into the secondary molding cavity 8, as shown in FIGS. 6 and 7, the contact portion between the tip of the seal piece 22 and the contacted portion 23 and the receiving portion 24 becomes A tire portion 26 having an annular hollow portion 25 that is embedded and sealed with a hard resin is formed, and a wheel portion 28 is formed by a hard portion 27 that connects the tire portions 26.

The wheel portion 28 includes a rim portion 28a which is in close contact with the tire portion 26, a disc portion 28b which extends inward from the rim portion 28a, and a cylindrical hub which is formed in the central portion of the disc portion 28b. It is composed of a portion 28c.

After the wheel portion 28 made of the hard portion 27 is formed by the secondary molding in this way, the second and third molding dies 2 and 6 are retracted and opened to open the first molding die 5
The hollow molded product is taken out by the rods 13 and 14 of a and 5b.

After the above operation, the reversing plate 4 is reversed and the first
The forming dies 5a, 5b and the second and third forming dies 2, 6 are opposed to each other and moved forward, and the first forming dies 5a, 5b and the second and third forming dies 2, 6 are clamped. To be done. With the clamping of the first molding die 5b and the third molding die 6, the sealing piece 22 is bent and the contacted portion 23 and the receiving portion 24 are brought into close contact with each other. Then, similarly to the above, injection of the soft resin into the primary molding cavity 7 and secondary molding cavity 8
The injection of the hard resin into the mold, the mold opening, the reversal of the reversing plate 4, and the mold clamping operation are repeated.

In such a molding method, the hollow tire portion 26
It is possible to continuously manufacture a wheel constituted by the wheel portion 28 and the wheel portion 28, and there is no need to insert a pre-molded preliminary hollow body into a mold for secondary molding unlike the insert molding method. Moreover, since the annular seal piece 22 is pressed against the contacted portion 23 by the pressing portion 12 for secondary molding, it is not necessary to form the preliminary hollow body into an undercut shape. Therefore, despite forming the hollow tire portion 26 with a soft resin,
It does not interfere with demolding.

Further, the obtained wheel has a cushioning property because the tire portion 26 made of a soft resin is hollow.
It excels in cushioning and shape retention, and there is no risk of contaminating or scratching the running surface such as the floor. Further, since the mechanical strength of the wheel can be secured by the hard resin, it is possible to smoothly run the vehicle for a long period of time. Furthermore, since the molten hard resin is injected and secondary molding is performed, the tire portion 26 and the wheel portion 28 can be fused and the joint strength can be significantly increased.

The preliminary hollow body may have any shape as long as the hollow body can be formed by bending the seal piece. For example, the preliminary hollow body may have a U-shaped cross section or an L-shaped cross section. . Further, the receiving portion formed in the preliminary hollow body is not always necessary. Further, the hollow body formed by the preliminary hollow body does not need to be annular, and may have an appropriate shape corresponding to the shape of the hollow molded article, such as a box shape or a curved shape whose side surface can be closed by a seal piece. Good. That is,
The present invention can be applied not only to wheels but also to various hollow molded products having a hollow body and a hard portion, such as floats, floats, and buoys.

The seal piece can be formed at an appropriate portion depending on the shape of the hollow molded product, but when forming an annular hollow body such as a tire portion, it is preferably formed on the outer circumference.

The shape of the hard portion extending from the hollow body is not particularly limited. For example, the buoy or the like may have a flat plate shape or a rod shape that extends from the hollow body and to which a weight can be attached.

It is sufficient that the guide portion bends by guiding the seal piece to the contacted portion, but it is preferable that the guide portion has an inclined surface inclined toward the contacted portion side, particularly a curved surface. When the guide portion having the inclined surface is formed in this manner, even if the annular seal piece formed on the outer circumference is regulated from bending outward, the seal piece is contacted inward along the inclined surface. The parts can be smoothly guided and bent.

The pressing portion may have an appropriate shape corresponding to the shape of the seal piece, for example, a flat plate-shaped cross section, as long as it does not prevent the demolding.

The guide part and the pressing part may be formed in one integrated mold, but when forming an annular hollow body, the third mold is a seal piece bent by the guide part. To press the contacted portion, an inner mold having a pressing portion,
It is preferable that the outer die is configured to move forward and backward with respect to the inner die and has a guide portion. When the hollow body is not annular, it has a guide part for bending the seal piece, and it moves back and forth relative to this mold to press the bent seal piece against the contacted part. It may be configured with a mold having a pressing portion for.

The forming die is movable relative to the first forming die having a primary forming area and a secondary forming area, and is formed corresponding to the primary forming area. A second molding die having a shaped molding region and forming a primary molding cavity by clamping with the first molding die, and is relatively movable with respect to the first molding die. At the same time, a third molding die that has a molding region formed corresponding to the secondary molding region and that forms a secondary molding cavity by clamping with the first molding die is provided. Good. For example, as in the above-described embodiment, a rotatable and positionable rotating body including a molding die in which a primary molding region and a secondary molding region are formed; a molding die in which a primary molding region is formed; And a mold having a secondary molding region formed therein, comprising at least one mold having a primary forming region formed therein and at least one mold having a secondary forming region formed therein. And a positionable rotary body, and at least one mold in which a primary molding region and a secondary molding region are formed,
The mold for the rotating body may be a movable mold or a rotatable fixed mold.

The rotating body provided with the above-mentioned forming die is not limited to every 180 ° as in the above-mentioned embodiment, but is, for example, 60 ° or 90 °.
As described above, it is preferable to rotate sequentially at equal angles and to be able to position at an even number of places.

As the soft resin forming the hollow body,
Examples thereof include olefin polymers such as polyethylene and polypropylene, ethylene-vinyl acetate copolymers, and soft thermoplastic elastomers (for example, styrene elastomer, olefin elastomer, polyester elastomer).

As the hard resin, a styrene polymer,
Examples thereof include polycarbonate, polypropylene, and hard thermoplastic elastomers (for example, styrene elastomer, olefin elastomer, polyester elastomer).

The soft resin and the hard resin are preferably polymers having a high affinity for each other, for example, polymers containing the same or similar constitutional units.

In a preferred hollow molded article, the hollow body can be formed of a soft olefin polymer or thermoplastic elastomer, and the hard portion can be formed of polypropylene or the like.

As the hard resin, a resin that is more rigid and tougher than the soft resin is frequently used in order to secure mechanical strength and rigidity. The soft resin and the hard resin may be colored in the same or different colors as needed. The hard resin may be injected at a temperature higher than that of the soft resin in order to increase the bonding strength between the soft resin and the hard resin.

[0051]

According to the hollow molded article of the present invention, the hollow body is formed of a soft hollow body made of a soft resin, and the contact portion between the seal piece and the contacted portion is buried and sealed with a hard resin. Therefore, the cushioning property, the cushioning property, and the shape retaining property are excellent, the bonding strength between the hollow body and the hard portion is large, and the hard portion made of the hard resin can secure a large mechanical strength. Further, when it is applied to a hollow molded article such as a wheel, there is no risk of contaminating the running surface, and smooth running can be achieved for a long period of time.

According to the method of the present invention, since the seal piece is bent, brought into contact with the contacted portion and pressed, and the hard resin is injected, the mold release is easy despite the use of the soft resin.
It is possible to efficiently produce a hollow molded article having the above-mentioned excellent properties.

In the molding apparatus of the present invention, it is possible to continuously inject the soft resin into the primary molding cavity, bend and press the seal piece, and inject the hard resin into the secondary molding cavity. The hollow molded product can be continuously manufactured, and the productivity can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining a method of the present invention, showing a mold open state after primary molding.

FIG. 2 is a schematic cross-sectional view for explaining the method of the present invention, showing an inverted state after primary molding.

FIG. 3 is a schematic cross-sectional view for explaining the method of the present invention, showing a transition state to secondary molding.

FIG. 4 is a schematic cross-sectional view for explaining the method of the present invention, showing a transition state to secondary molding.

FIG. 5 is a schematic cross-sectional view for explaining the method of the present invention, showing a mold clamping state in secondary molding.

FIG. 6 is a schematic cross-sectional view for explaining the method of the present invention, showing a mold open state after primary and secondary molding.

FIG. 7 is a partial cross-sectional view showing a hollow molded article obtained by the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Molding apparatus 2 ... 2nd shaping | molding die 4 ... Inversion board 5a, 5b ... 1st shaping | molding die 6 ... 3rd shaping | molding die 7a, 7b ... Primary shaping | molding area 7 ... Primary molding cavity 8a, 8b ... Secondary Molding area 8 ... Secondary molding cavity 9, 10 ... Gate 11 ... Guide portion 12 ... Pressing portion 21 ... Preliminary hollow body 22 ... Sealing piece 23 ... Contacted portion 25 ... Hollow portion 26 ... Tire portion 27 ... Hard portion 28 ... Wheel part

Claims (6)

[Claims] 1. A hollow molded article comprising a hollow body made of a soft resin and a hard portion extending from the hollow body and made of a hard resin, wherein the hollow body is a seal piece. Is a hollow soft body that is bent and is in contact with the contacted portion, and the contact portion with the sealing piece is embedded and sealed with a hard resin to form a hollow molded article. 2. The hollow molded article according to claim 1, wherein the hollow body constitutes an annular tire portion, and the hard portion constitutes a wheel portion extending inward from the tire portion. 3. A preliminary hollow body having a sealing piece is formed of a soft resin, the sealing piece is bent and pressed against a contacted portion of the preliminary hollow body, and a molten hard resin is injected into the sealing piece. A method for producing a hollow molded article, which comprises forming a hollow body by sealing a contact portion with the hollow body and molding a hard portion extending from the hollow body. 4. An annular preliminary hollow body having a sealing piece on the outer periphery is formed of a soft resin, the sealing piece is bent inward and pressed against the contacted portion of the annular preliminary hollow body, and the pressing section and its inward direction. The method for producing a hollow molded article according to claim 3, wherein a molten hard resin is injected into the side to form a wheel including an annular hollow tire portion formed of a soft resin and a wheel portion formed of a hard resin. . 5. A ring-shaped preliminary hollow body having a seal piece is formed by injecting a soft resin into a primary molding cavity formed by a primary molding die, and with the die clamping,
The guide part of the secondary molding die bends the seal piece while guiding it to contact the contacted part of the annular preliminary hollow body,
The pressing portion of the secondary molding die presses the contact portion with the seal piece to inject the hard resin into the secondary molding cavity, and the annular hollow tire portion formed of the soft resin and the hard resin are formed. Forming a wheel with a wheel portion
Or the method for producing a hollow molded article according to item 4. 6. A first molding die having a primary molding region and a secondary molding region, and a mold which is movable relative to the first molding die and corresponding to the primary molding region. A second molding die having a shaped molding region and forming a primary molding cavity by mold clamping with the first molding die;
The second molding is movable relative to the first molding die, has a molding region formed corresponding to the secondary molding region, and is secondary-molded by clamping with the first molding die. A third molding die for forming a molding cavity, and a gate for injecting a primary molding resin into the primary molding cavity,
A molding apparatus comprising a gate for injecting a secondary molding resin into the secondary molding cavity, wherein the primary molding cavity is formed corresponding to an annular preliminary hollow body having a sealing piece. And the third mold,
A guide part for guiding and bending the seal piece along with mold clamping to make contact with the contacted part of the annular preliminary hollow body, and a pressing part for pressing the contact part with the seal piece are formed. Molding equipment.