JP2000052372A - Method and apparatus for preparing injection-molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for preparing an injection- molded article which can shorten time for cooling and solidifying a molten resin and can prevent such defects as sink marks from being generated on the surface of a product of the molded article. SOLUTION: A molten resin is fed into cavities 3 and 4 of a fixed mold 1 and a movable mold 2 from a cylinder 8 for plasticization through a gate 9. In this case, a sliding member 5 sliding on the side faces of the cavities 3 and 4 therein and by retreating successively this sliding member 5, injection processes and cooling processes are repeated a plurality of times. A specified thickness of a shape of a molded article is obtd. thereby by a plurality of resin layers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing an injection-molded article obtained by injecting a molten resin into a mold cavity to obtain a molded article, and more particularly to an injection molding method suitable for manufacturing thick parts. The present invention relates to a method and apparatus for manufacturing a molded article.

[0002]

2. Description of the Related Art Conventionally, in injection molding of a molten resin,
A desired amount of molten resin is injected into a mold cavity at a time to obtain a molded product having a predetermined shape, thereby forming a desired shape.

[0003]

However, the above-described injection molding has the following disadvantages. First, the first problem is that, for parts requiring transparency, the required characteristics cannot be satisfied when a hollow portion is provided inside a molded product or when a portion that does not appear on the surface is thinned. In the case of a lens and a transparent case, it is necessary to transmit a light source and an image, and the inside of a molded product may be modified, but if so, the required characteristics cannot be satisfied.

[0004] After the molten resin is injected and filled into the cavity of the mold, cooling proceeds from the surface portion in contact with the inner surface of the mold. As a result, as shown in FIG. 3, in the cavity, in the cross-sectional direction of the thickness of the molded product, cooling of the surface layer contacting the inner surface of the mold is completed, and the solidified layer 15 is formed. However, the fluidized bed 13 in a molten state remains at the center. For this reason, as the heat transfer 14 is generated and the fluidized bed 13 is solidified, the surface layer portion is drawn in. As a result, a concave portion called sink is generated in the molded product, and a desired shape cannot be formed. As a result, as the thickness increases,
Deformation due to heat shrinkage occurs remarkably, and it is difficult to form a required shape.

Further, heat transfer occurs from the surface of the mold product toward the inside of the molded product. However, this heat conduction is not constant, and the heat transfer speed becomes slower as the thickness of the molded product increases. However, there is a problem that the molding cycle becomes long.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and can reduce the time for cooling and solidifying a molten resin, and can prevent defects such as sink marks on the surface of a molded product. An object of the present invention is to provide a method and an apparatus for manufacturing a molded article.

[0007]

According to the present invention, there is provided a method of manufacturing an injection-molded article, wherein a molten resin is injected into a cavity formed by a pair of molds and molded. An injection step of injecting the molten resin using a space partitioned by the sliding member as a cavity, a cooling step of holding and cooling the molten resin, And performing a combination of the injection step and the cooling step a plurality of times to produce a molded article having a desired shape.

An apparatus for manufacturing an injection-molded article according to the present invention comprises a fixed mold, a movable mold that can move close to and away from the fixed mold, and a movable mold provided in a cavity of the movable mold. A slidable sliding member, a driving member for moving the sliding member toward and away from the fixed mold,
A gate provided in the fixed mold for injecting the molten resin into the cavity, and an injection nozzle for injecting the molten resin into the gate are provided.

In the present invention, the injection step and the cooling step are divided into a plurality of times, injection-molded, sequentially molded and laminated to obtain a desired shape. The thickness can be reduced. For this reason, the time for cooling and solidifying the molten resin can be shortened, and the difference in cooling time between the surface side of the product and the central portion of the molten resin is reduced. It is possible to prevent the occurrence of a defect having a concave shape.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a graph showing the relationship between the elapsed time of the injection time and the injection pressure in the embodiment of the present invention, and FIG. 2 is a schematic diagram showing the injection device used in the embodiment.

The fixed mold 1 is supported by the support member 11, and the movable mold 2 is supported by the support member 10. Molded product-shaped cavities 3 and 4 are formed in the fixed mold 1 and the movable mold 2, respectively. The movable mold 2 is a support member 1
0 together with the fixed mold 1, the molten resin can be injected into a cavity space formed by overlapping the fixed mold 1 and the movable mold 2 with each other. By retracting the movable mold 2, the molded product can be taken out.

In the cavity 4 of the movable mold 2, there is provided a sliding member 5 that slides on the side surface of the cavity 4, and the sliding member 5 moves toward and away from the fixed mold 1. be able to. The sliding member 5 includes two connecting rods 6.
Are connected, and the sliding member 5 is driven by an appropriate driving member via the connecting rod 6, so that the position in the cavity 4 is adjusted. The sliding member 5 defines the back surface of the molded product.

A gate 9 is formed in the stationary mold 1 so as to penetrate from the outer surface to the inner surface. The gate 9 is connected to a nozzle 7a of a plasticizing cylinder 7 disposed outside the support member 11. Have been. A screw 8 is built in the plasticizing cylinder 7, and the rotation of the screw 8 causes the molten resin to be extruded from the nozzle 7a.

Next, the operation of the embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. First, the movable mold 2 is placed on the fixed mold 1, the sliding member 5 is positioned at the most advanced position, and the thinnest cavity space is formed between the movable mold 2 and the fixed mold 1. The thickness of the cavity space is, for example, １ ／ of the thickness of a predetermined molded product. Then, the first injection step is performed, the screw 8 is rotated at a predetermined speed, and the molten resin is injected into the cavity. Thereafter, the state is maintained until the injected resin is solidified, and the resin is cooled.

After the first layer is formed in this manner, the cooling and solidification of the molten resin proceeds, and after the solidification is completed, the sliding member 5 provided on the movable mold 2 is moved rearward by the driving member on the forming machine side. And the first resin layer moves rearward while being in close contact with the sliding member 5. In the present embodiment, the retreat distance of the sliding member 5 is, for example, １ ／ of a predetermined molded product thickness.
It is.

Then, the second molten resin is injected and filled in the mold having a space with the movement of the first resin layer by a second injection step. Then, a second resin layer is laminated. After a lapse of a predetermined time, the second resin layer is cooled and solidified, and then the sliding member 5 is retracted by １ ／ of a predetermined molded product thickness, and a third injection step and a third cooling step are performed. Is carried out, and the sliding member 5 is set to a predetermined molded product thickness of 1 mm.
Then, the fourth injection step and the fourth cooling step are sequentially performed. In this way, a molded article having four layers is obtained. Next, the pressure for holding the mold is reduced, the mold is opened, and the molded product is taken out.

In this embodiment, since the thickness of the molded article in one injection molding step is small, the time required for cooling and solidifying the molten resin can be shortened, and sink marks and the like generated on the surface of the molded article can be reduced. Defects can be prevented.

In the above embodiment, the injection molding step is performed four times. However, the number of the injection molding step is not limited to four, but may be plural times depending on the thickness of a predetermined molded product. Further, the molding thickness per operation is not limited to the one obtained by equally dividing a predetermined molded product thickness. Further, in the next injection step, it is not always necessary to wait until the resin injected in the previous injection step is completely solidified.

[0019]

As described above, according to the present invention,
Since the injection step and the cooling step are performed a plurality of times, the resin layer formed at one time is thin, so that the time for cooling and solidifying the molten resin can be reduced. Further, since the difference in cooling time between the surface side of the injection molded article and the central portion of the molten resin is reduced, defects such as sink marks appearing on the product surface can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method according to an embodiment of the present invention, wherein the horizontal axis represents elapsed time, and the vertical axis represents injection pressure of a molten resin.

FIG. 2 is a view showing an injection apparatus used in a method according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a solidification process of a molten resin.

[Explanation of symbols]

 1: Fixed mold 2: Movable mold 3, 4: Cavity 5: Sliding member 7: Plasticizing cylinder 8: Screw 9: Gate

Claims (4)

[Claims] 1. A method of manufacturing an injection-molded article in which a molten resin is injected into a cavity formed by a pair of dies, and the sliding member slides in one of the dies. And a cooling step of injecting the molten resin with the space partitioned by the sliding member as a cavity, and a cooling step of holding and cooling the molten resin. The combination of the injection step and the cooling step is performed a plurality of times. A method for producing an injection-molded article, which is performed to produce a molded article having a desired shape. 2. The method according to claim 1, wherein the injection step is performed after the molten resin is solidified in a cooling step in a preceding stage. 3. The mold is a fixed mold and a movable mold, the sliding member is provided on the movable mold, and the molten resin is injected from a nozzle provided on the fixed mold. The method for producing an injection-molded article according to claim 1 or 2, wherein: 4. A fixed mold, a movable mold capable of moving close to and away from the fixed mold, a sliding member provided in a cavity of the movable mold and slidable on a side surface of the cavity, A driving member for moving the sliding member toward and away from the fixed mold, a gate provided on the fixed mold for injecting the molten resin into the cavity, and an injection nozzle for press-fitting the molten resin into the gate. An apparatus for manufacturing an injection-molded article, comprising: