JPH07178752A - Method for manufacturing thick annular molded body - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for a thick annular molded body with an excellent appearance such as an annular frame with a large cross sectional area or grip for a strap of train, etc. CONSTITUTION:A die for which a movable core is arranged for a die cavity to constitute a thicker part is used, and a molten resin is injected in the die cavity under a condition wherein the thickness of the thicker part is reduced by advancing the movable core. Then, after the completion of the injection of the molten resin, the movable part is moved backward to increase the capacity of the die cavity, and a pressurized fluid is injected to the inside of the molten resin while increasing the capacity of the die cavity. Then, the molten resin is cooled and hardened while maintaining the condition wherein the inside of the thicker part being constituted into an annular form is pressurized by the pressurized fluid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thick annular molded body or a thick annular molded part. More specifically, the present invention relates to a method for manufacturing a thick annular molded body having an excellent appearance such as an annular frame having a large cross-sectional area and a grip of a train hanging leather.

[0002]

2. Description of the Related Art Conventionally, a thick-walled molded article such as a grip of a hanging strap of a train is formed of a thermosetting resin or a thermoplastic resin.
In the case of applying the conventional molding method, the surface must be glossy, a high injection pressure is required to prevent shrinkage, and a long cooling time is required to set the mold temperature to a high temperature. Is inefficient. In addition, since a frame for holding heavy parts requires strength, a welded structure of metal parts is often used. Manufacturing a frame with metal parts requires a great number of man-hours such as punching, bending, welding, post-treatment, and finish of painting, resulting in poor production efficiency and risk of work.

In recent years, in injection molding of thermoplastic resins,
Molding method that injects pressurized gas into the molten resin during or after the injection of molten resin (gas injection molding)
This has made it possible to manufacture hollow pipe-shaped molded products, but by simply injecting a gas body into the molten resin in the cavity using an ordinary mold, a ring-shaped hollow molded body can be produced. It was not possible to hollow the inside of the whole circumference, and the solid part where the gas channel was not formed had a poor appearance due to volume contraction due to cooling. That is, when molding a ring-shaped molded product by gas injection, it is possible to partially hollow the product by gas injection, but the ring-shaped molded product is applied over the entire circumference inside the thick-walled ring shape for the reasons described below. Since it cannot be penetrated by the pressurized fluid, the appearance characteristics of the thick portion where the hollow portion is not formed were inferior.

When molding a circular ring-shaped molded product as shown in FIG. 1, when a pressurized gas body is injected from one location of the mold, the pressurized gas body is divided into left and right rings from the gas inlet. The resin moves in the opposite direction while hollowing the resin.
When the thickness of the circular ring is large, for example, about 20 mm, the pressurized gas body is injected and injected to the extent that the molten resin fills a part of the mold cavity, and then the resin is pressed into the ring while pushing out the resin in the traveling direction of the gas body. The inside is made hollow. Such a molding method is called a short shot method. When the thickness of the ring is thin, for example, about 6 mm, the molten resin may be filled into the mold cavity and then the pressurized gas body may be pressed therein. In this case, the gas body advances while hollowing so as to compensate for the volume shrinkage of the molten resin injected and injected into the mold. This method is called the full shot method.

In the above-mentioned two molding methods, a molded product obtained by injecting a pressurized gas body cannot make the entire inner circumference of the ring uniformly hollow, and the side opposite to the injection port of the pressurized gas body is impossible. A resin wall is formed at the site located at. This state is shown in FIG. Further, in the case of a product having a combination of ring shapes, resin walls are generated at a plurality of places, and this state is shown in FIG. The gas body pressed into the molten resin partially pushes the resin as an interface from both sides, and if the pressure of the gas body is the same, the molded product cannot be hollowed. In order to solve this, it is considered to change the gas pressure value at both the interfaces so that the gas body penetrates from the higher pressure side to the lower pressure side, but it is difficult to predict the balance of hollowing. As a result, multiple gas inlets are required, which complicates the system.

Although it is considered to increase the hollowing rate by injecting gas at multiple points, it is impossible to hollow the entire product without hollowing the interface. This state is shown in FIG. Further, if it is necessary to close the gas injection port, the number of post-treatment steps will increase. further,
JP-A-3-138126 and JP-A-3-1381
As disclosed in Japanese Patent Publication No. 15, it is conceivable to install an auxiliary cavity for resin discharge in a portion that cannot be hollowed, but this method is effective and thick when the flow of the gas body is in one direction. It is difficult to uniformly hollow an annular shaped body of meat, and a post-treatment step such as cutting off the auxiliary cavity is also required, which is not suitable for industrial production.

If a part of the thick-walled ring-shaped molded product cannot be hollowed, the molten resin will remain inside the molded product in the thickness direction of the product, and the product will be sinked and deformed and the product quality cannot be satisfied. So I couldn't commercialize it.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to mold a thick-walled ring-shaped molded product, in which the molded product has no shrinkage over the entire circumference of the molded product or the entire circumference of the thick-walled annular molded product. It is to provide a molding method for hollowing.

[0009]

DISCLOSURE OF THE INVENTION As a result of intensive studies for solving the above-mentioned problems, the present inventors have arranged an operating core on the entire circumference or a part of a mold cavity that constitutes a thick portion. The inventors have found that the above problems can be solved by the above and completed the present invention.

That is, the present invention is a method for producing a thick-walled annular molded body, which uses a mold in which a movable core is arranged in a mold cavity forming a thick portion, and the movable core is advanced to a thicker thickness. The molten resin is injected into the mold cavity with the thickness of the flesh reduced, and the movable part is retracted after or after the injection of the molten resin to increase the mold cavity volume or after the mold cavity volume is increased. While injecting the pressurized fluid into the molten resin and maintaining the pressurized state inside the thick portion formed in an annular shape with the pressurized fluid, the molten resin is cooled and solidified, and the pressure of the pressurized fluid is adjusted after cooling is completed. The invention relates to a method for producing a thick annular molded body, which is characterized in that a molded product is taken out after the pressure is reduced so that the product does not deform.

The mold used in the present invention has a structure in which the mold cavity forming the thick wall portion can arbitrarily control the wall thickness defining the product with the movable core. Before or during the injection of molten resin into the mold, the product thickness of the thick annular portion is reduced by the movable core, the molten resin is injected into the cavity, and then the mold cavity volume is increased by the movable core. Or, after being increased, the pressurized fluid is injected into the molten resin to fill the annular thick portion with the pressurized fluid,
Holds the pressure of the pressurized fluid.

On the other hand, before or during injection of the molten resin,
The movable member reduces the product thickness of the thick annular portion, and after injecting the molten resin into the cavity, the volume of the die cavity is increased while injecting the pressurized fluid to pressurize the inside of the thick portion formed in the annular shape. Hold the pressure of the pressurized fluid while filling it with fluid. That is, the full shot method can be used as a method of retracting the movable core after the injection of the molten resin to increase the mold cavity volume. When injecting pressurized fluid,
Since the cavity is enlarged by the movable member forming the mold cavity, the pressurized fluid can be easily injected into the annular thick portion provided in the product.

The movable member according to the present invention can be used to prevent the sinking of the annular thick portion by enlarging the mold cavity when pressurizing the pressurized fluid, and the entire circumference can be easily pressed. It is also possible to fill it with fluid. When the pressurized fluid cannot penetrate the entire circumference of the annular thick-walled body and the resin wall is generated, the wall thickness becomes much thinner than the conventional method and the pressurized fluid penetrates. It has the same effect as. If the movable core is arranged around the entire circumference of the thick-walled ring, it is possible to penetrate the hollow structure of the ring-shaped molded product. Even if the hollow structure is not completely penetrated, sinking and deformation of the product can be prevented. As the pressurized fluid to be injected into the molten resin, any of a gas body, a liquid and a foaming agent can be used, but it is preferable to use a gas body. After injecting the pressurized fluid, the molten resin is cooled and solidified while maintaining the pressure of the pressurized fluid, and after the cooling is completed, the pressure of the pressurized fluid is reduced to a pressure that does not deform the product, and then the molded product is taken out. As a result, it is possible to obtain a molded product in which the pressurized fluid is injected all around the inside of the thick annular molded body.

[0014]

According to the present invention, it is possible to continuously inject a pressurized fluid over the entire inner circumference of the thick portion forming the ring shape in the production of a ring-shaped molded article formed of a thick wall. . When the pressurized fluid is a gas or liquid, the molten resin injected into the mold is cooled and solidified, and then the pressurized fluid is depressurized and removed to make the inside of the annular product evenly hollow and reduce the weight of the product. It is also possible to do so. When the pressurized fluid is a molten resin body containing a foaming agent, the entire thick annular portion can be filled with the foaming resin from the inside of the product, so that partial sinking or deformation can be prevented. It is also a remarkable effect of the present invention that by reducing the product thickness by the movable member during the injection of the molten resin, it is possible to prevent the jetting generated in the injection process of the resin, the appearance defect due to the entrainment of gas, and the like. Further, by using the movable member, it is possible to reduce the occurrence of welds because the mold cavity is fully filled with the resin.

[0015]

【Example】

 Example 1 Using the mold shown in FIG. 6, a triangular shaped product shown in FIG.
Was molded. The thermoplastic resin used for molding is Mitsubishi Gas
Polycarbonate resin (trade name: gray)
S3000). As shown in Figure 6,
Cylinder with movable core6For the mold cavity
It is possible to move forward and backward. In this example, the cylinder6
Used a hydraulic cylinder. Movable core5Is the mold
It moves forward and backward with a stroke of 10 mm with respect to Vity. Yes
The dynamic core is installed with the thickness 20 of the lower part of the product shown in FIG.
mm part.

The width of the movable core was 150 mm. At the time of molding, the polycarbonate resin was plasticized and melted at 280 ° C. Prior to injecting the resin into the mold, the movable core 5 was caused to enter the product cavity by 10 mm. The molten resin was injected and injected into the mold cavity while the movable core was moved forward.
Immediately after the injection of the resin was stopped, the movable core 5 was retracted by 10 mm while injecting a pressurized gas body from the gas nozzle 7 . Pressurized gas body is press-fitted at 80 kg / cm ² , 50 kg / c
It was cooled while being held at a pressure of m ² . After the cooling was completed, the pressure of the gas body was released to the atmosphere, and then the molded product was taken out. The obtained molded product is shown in FIG. The molded product was hollowed all around the inside of the molded product from the gas injection port, and the mold cavity was shaped without sinking or deformation of the product being observed.

Comparative Example 1 Molding was carried out using the mold shown in FIG. The difference from the example was that the movable core was not advanced prior to molding, and the thickness defined by the movable core was 20 mm. After the polycarbonate resin was plasticized and melted, it was injected into a mold. After the mold cavity was filled with 80%, a gas body was pressed in from the gas nozzle 7 . Pressurized gas body is press-fitted at 80 kg / cm ² , and
It was cooled while being held at a pressure of 0 kg / cm ² . After the cooling was completed, the pressure of the gas body was released to the atmosphere, and then the molded product was taken out. The resulting molded article are shown in FIG. As shown in FIG. 8 , the thick portion of the lower part of the molded product was not hollowed by the gas body and a solid resin body was present, and it was confirmed that sink marks were generated.

[0018]

EFFECTS OF THE INVENTION By adopting the production method of the present invention, it is possible to obtain a molded product which has no sink mark over the entire circumference of the thick-walled ring-shaped molded product, and is hollow all around the inside of the thick-walled tubular molded product. Can be transformed.

[Brief description of drawings]

FIG. 1 is a plan view and a front view of a circular ring-shaped molded product.

FIG. 2 is a front view and a sectional view of a circular ring-shaped molded product.

FIG. 3 is a sectional view of a circular ring-shaped molded product.

FIG. 4 is a plan view and a sectional view of a crown-shaped molded product.

5A and 5B are a plan view and a side view of a triangular molded product molded in Example 1.

FIG. 6 is a mold used in Example 1.

FIG. 7 is a cross-sectional view of a triangular molded product molded in Example 1.

FIG. 8 is a sectional view of a triangular molded product molded in Comparative Example 1.

[Explanation of symbols]

1: Fixed mold mounting plate 2: Movable mold mounting plate
3: Fixed type 4: Movable type 5: Movable core 6: Cylinder for moving core control 7: Gas nozzle 8: Cylinder 9: Piping 1
0: Product cavity 11: Resin gate 12: Gas gate

Claims (9)

[Claims] 1. A method for manufacturing a thick-walled annular molded body, comprising: using a mold in which a movable core is disposed in a mold cavity that constitutes a thick-walled portion, and moving the movable core forward; The molten resin is injected into the mold cavity in a state where the amount of fluid is reduced, and while the volume of the mold cavity is increased by increasing the volume of the mold cavity by retracting the movable part after or during the injection of the molten resin, pressurizing fluid. Is injected into the molten resin, and while maintaining the pressurized state with the pressurized fluid inside the thick portion formed in an annular shape, the molten resin is cooled and solidified, and after cooling is completed, the pressure of the pressurized fluid does not deform the product A method for producing a thick annular molded body, which comprises removing a molded product after reducing the pressure. 2. The method for producing a thick annular molding according to claim 1, wherein the injection of the pressurized fluid is started during the injection of the molten resin. 3. The method for producing a thick annular molded body according to claim 1, wherein the injection of the pressurized fluid is started after the injection of the molten resin is completed. 4. The method for producing a thick annular molded body according to claim 1, 2 or 3, wherein the movable core is provided over the entire circumference of the thick annular shape. 5. The method for manufacturing a thick annular molding according to claim 1, 2 or 3, wherein the movable core is provided in a part of the thick annular shape. 6. The pressurizing fluid is a gas body.
Alternatively, the method for producing a thick annular molded body according to item 3. 7. The method for producing a thick annular molding according to claim 1, 2 or 3, wherein the pressurized fluid is a liquid. 8. The method for producing a thick annular molded body according to claim 1, wherein the pressurized fluid is a molten resin body containing a foaming agent. 9. The method for producing a thick annular molding according to claim 1, 2 or 3, wherein the pressurized fluid penetrates the entire circumference of the thick annular portion.