JPH1076555A - Method for injection molding of plastic molded article with partly thin part and mold used for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent weld from being generated on a thin part and to speed up molding cycle by performing molding while development of a skin layer is suppressed when the thin part is molded by using a movable core. SOLUTION: This method for molding is performed in such a way that a movable core 2 is combined in a mold for injection molding of a plastic and just after a resin is filled, this movable core 2 is forwarded to a definite distance and a thin part is molded there. In this case, a cartridge heater 5 and a cooling medium circulation flow path 2a are combined in the movable core 2 and when the movable core is forwarded into the mold, the movable core 2 is heated by driving the cartridge heater 5 to heat the resin of the thin part and when the mold is cooled, a cooling medium is circulated in the cooling medium circulation flow path 2a to cool the thin part. Development of a skin layer can be suppressed by this effect of heating and cooling and as the result, weld is not generated. In addition, by performing forcible cooling, molding cycle can be sped up (shortened).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection-molding a plastic product partially having a thin portion and a mold for injection-molding a plastic product used in the method.

[0002]

2. Description of the Related Art In a molded plastic product, if a part of the molded product is thin or has a hole, a non-uniform resin flow causes welding. Such welds not only deteriorate the appearance of the molded product, but also have a limitation in that the strength of the welded portion is inferior to other parts, so that the molded product must be designed so as not to have an extremely thin portion. .
Also, since the resin is not filled depending on the position of the thin portion and the thickness of the molded product, in such a case, the molded product is divided into several parts and molded, and then bonded later. Next processing is required.

However, in terms of cost reduction and weight reduction,
In recent molded products, the thickness is thin, and the shape of a complicated shape such as a mixture of a thin portion and a thick portion is increasing. Such a tendency further increases the weld portion and lowers the strength of the molded product. Furthermore, when trying to perform injection molding all at once to integrate various parts, the resin is not filled in the thin part, and if the filling pressure is further increased to improve it, new appearance defects such as warpage will occur I do.
In addition, when the cavity temperature of the mold is raised to suppress the weld, the molding cycle becomes longer, and the warpage after the removal becomes a problem.

In order to solve these problems, Japanese Patent Laid-Open No.
JP-A-3-295228, JP-A-63-302013, JP-A-2-92607, JP-A-2-141219, JP-A-3-39219 and JP-A-5-8262 disclose techniques and welds relating to thin-wall molding. The method of forming without causing the generation is specified. In these methods, molding is performed using a mold having a thin-wall molding core that can advance and retreat in a cavity. Further, in addition to simply moving the core forward and backward, JP-A-3-112616 discloses a mold in which the core is inserted into the resin in the cavity while being vibrated and vibrated.

[0005]

However, for example, when the thickness of a required molded product is extremely thin, or when a portion to be thinned exists in a portion close to the gate and a portion far from the gate, for example, the movable core has a large thickness. Prior to advancing, skin layers develop on the fixed and movable sides, resulting in impeding the formation of thin sections. In addition, in the method of forming a thin portion by vibration and pressure, the shear stress of the movable core against the resin is eased and the movable core is easily advanced into the cavity, but the development of the skin layer that hinders the formation of the thin portion cannot be suppressed. Can not. Also, when the skin layer is relatively undeveloped, that is, when the core is advanced during resin filling, the formation of the thin portion is easy, but the quality of the molded product is unstable due to the insertion timing of the movable core. Become. The same applies to the case where the resin is filled at a high speed. Further, when injection molding is performed in a high-temperature cavity, problems such as a long molding cycle occur, and a thin-walled portion cannot be formed efficiently. As described above, it is necessary to suppress the development of the skin layer in order to efficiently form a thin portion in a part of a molded product.

[0006]

Means for Solving the Problems The present inventor has proposed an injection molding method for forming a thin portion in a part of a plastic molded product using a movable core, and a method for preventing a skin layer from developing in a mold used for this molding. As a result of extensive studies, it was found that the use of the following method and mold effectively suppressed the development of the skin layer, and as a result, prevented the occurrence of weld. The points of this method and the configuration of the mold are as follows.

[0007] 1. In the injection molding method of incorporating a movable core in a plastic injection mold and immediately moving the movable core to a certain distance after filling with a resin to form a thin portion here, a heating means and a cooling means are provided in the movable core. By incorporating the resin into the mold and moving the movable core forward, the heating means is driven to generate heat in the movable core to heat the resin in the thin portion, and when the mold is cooled, the cooling means is driven to drive the thin portion to reduce the thickness. A method of injection-molding a plastic molded product having a thin part in part while cooling the part to suppress the development of the skin layer.

[0008] 2. In a mold for injection molding of a plastic molded product having a thin part in a part, a movable core for molding a thin part is incorporated in a part of the mold so as to be able to advance and retreat, and heating means is provided in the movable core. Injection of a plastic molded article having a thin part in a part configured to suppress the development of the skin layer by driving the heating means during product molding and driving the cooling means during cooling to incorporate the cooling means Mold for molding.

3. 3. A mold for injection molding a plastic molded product having a thin part in part as described in the above item 2, wherein an electric heater is incorporated in the movable core as a heating means, and a refrigerant circulation channel is formed in the movable core as a cooling means.

[0010] 4. A heating medium circulating passage is formed in a movable core as a heating means and a cooling means, and a heating medium is circulated in the heating medium circulating passage during heating, and a refrigerant is circulated during cooling. A mold for injection molding of a plastic molded product having a thin portion in a part of the description.

5. An auxiliary core incorporating a heating means and a cooling means is incorporated on the mold side opposite to the mold incorporating the movable core, and the thin portion is formed by the action of the auxiliary core and the movable core. 5. A mold for injection molding a plastic molded product having a thin part in part according to 3 or 4.

6. The injection molding of a plastic molded article having a thin part in part as described in the above item 5, wherein the thin part is formed in the middle of the thickness of the molded article by advancing the auxiliary core in accordance with the advance of the movable core. Mold.

7. 7. A mold for injection molding of a plastic molded product having a thin part in a part according to item 2 or 3, wherein a heat insulating material is arranged between the movable core or the auxiliary core and the mold.

[0014]

In the injection molding, in the step of filling the resin into the cavity and the step of advancing the movable core, when the heating means in the movable core is driven, the movable core is held at a high temperature by this heating means, and the movable core is connected to the movable core. The surrounding resin in contact therewith, in particular, the resin at the portion forming the thin portion on the distal end surface of the movable core is heated. Then, in the mold cooling step, the cooling means in the movable core is driven,
The thin part is cooled. By this action, the development of the skin layer generated in the thin portion is suppressed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A movable core for moving forward and backward by a driving means such as a hydraulic cylinder is incorporated in a mold for molding a plastic molded product having a thin portion in part according to the present invention. The movable cores can be incorporated into the movable side and / or the fixed side of the mold, and the number, position, size, and the like are determined according to the product design. The driving means of the movable core includes a hydraulic cylinder, an air cylinder,
Alternatively, a drive motor or the like can be used. However, in the present invention, this drive means may be any means as long as it can move the movable core forward or backward with good timing.

The means for heating the movable core incorporated in the movable core may be a heater using a rod-shaped resistance utilizing Joule heat, or a heater using a high-temperature oil or the like as a heat medium. Further, the refrigerant circulation passage for cooling the movable core after the formation of the thin portion is designed so that rapid cooling is possible, and the refrigerant is circulated through a cylinder or a pump here. The refrigerant to be used may be a gas such as nitrogen or air, or a liquid such as water or silicone oil. To get the effect of heating or cooling,
It is good to arrange a heat insulator around the movable core. However, since this heat insulating material needs strength as a mold material,
For example, ceramic is preferable.

The timing of heating the movable core during injection molding is a step of filling the resin and a step of moving the movable core forward to form a thin portion. At the same time as the filling of the resin is completed, the refrigerant circulates in the movable core to rapidly cool the movable core, thereby cooling the thin portion. The movable core retracts when the mold leaves.

[0018]

Embodiment 1 First, an embodiment of a mold will be described with reference to the accompanying drawings. FIG. 1 shows a basic configuration of a mold according to an embodiment of the present invention. In this mold, as shown in FIG. 1, a movable core 2 is incorporated in a direction perpendicular to the cavity 1, and the periphery of the movable core 2 is insulated by a heat insulating material (ceramic) 4 and a movable portion. There is a gap, and the heat insulating material 4 insulates the mold main mold 3. The movable core 2 is connected to a hydraulic cylinder head or the like (not shown), and is advanced by a hydraulic source outside the mold in the same direction as the cavity 1 or in a direction perpendicular to the cavity to form a thin portion. Is what you do.

FIG. 2 shows the internal structure of the movable core 2 used in the first embodiment. Inside the movable core 2,
A cartridge heater (resistor) 5 for heating the core by Joule heat is incorporated in a tip portion near the cavity 1. Further, a coolant introduction pipe 6 is inserted into the movable core 2 to guide a coolant for cooling the movable core 2, and a connection hole 8 is formed at a tip of the coolant introduction pipe 6. The refrigerant that has flowed out from the refrigerant introduction pipe 6 through the communication hole 8 into the refrigerant circulation flow path 2a in the movable core 2,
The movable core 2 is moved upward as shown by arrow a from the return port 9.
It flows out and returns to a coolant supply source (not shown).

Using the above-mentioned mold, the temperature rise and the cooling state of the movable core were confirmed. The mold main mold 3 was made of a normal mold steel S55C, and zirconia having low thermal conductivity was used as the heat insulating material 4 around the movable core 2. The temperature of the mold main mold 3 was set to 50 ° C. using an external cold / hot water unit.
In this state, power supply to the cartridge heater (50 V-30 W) 5 inside the movable core 2 was started. About 15 seconds after the start of energization, the cavity surface temperature of the movable core 2 reached about 100 ° C., and 10 seconds later, the surface temperature of the movable core 2 reached about 130 ° C. Further, if the energization time is further extended, the tendency tends to increase.

Next, a 20 ° C. N ₂ gas (10 kgf / cm ₂₎ as a refrigerant is introduced into the movable core 2 heated to 100 ° C.
² ) was injected, and the movable core 2 was cooled. About 10 seconds after the N ₂ gas injection, the cavity surface temperature of the movable core 2 becomes 65
C., and 5 seconds later, the temperature dropped to 55.degree.

[0022]

Embodiment 2 In Embodiment 2, the movable core 2 and the mold main mold 3 are used.
This is an example in which the heat insulating material 4 is not arranged on the surface in contact with the movable core 2, and the movable core 2 is heated and cooled using the cavity 1 in which the movable core is generally surrounded by a steel material as shown in FIG. The mold main mold 3 was made of a normal mold steel material S55C, and the temperature of the mold main mold 3 was set to 50 ° C. by an external cooling / heating water unit. In this state, power supply to the cartridge heater (50 V-30 W) 5 inside the movable core 2 was started. After about 15 seconds from the start of energization, the temperature reached 75 ° C. and further about 10 seconds later, about 85 ° C., but the heating rate was slower than in Example 1, and the mold main mold 3 near the movable core 2 Temperature was also rising.

Next, N ₂ gas (10 kgf / cm ² ) at 20 ° C. was injected into the movable core 2 heated to about 90 ° C. to cool the movable core 2. About 10 after N ₂ gas injection
After 2 seconds, the temperature of the cavity surface of the movable core 2 was 75 ° C., and after 5 seconds, 68 ° C. From Examples 1 and 2, it was confirmed that the movable core 2 could be heated or cooled by the heating and cooling means. However, in Example 2 in which the heat insulating material 4 was not used around the movable core 2, it was confirmed that heat dissipation from the movable core 2 was large and heat was taken in the direction of the mold main mold 3. Therefore, in order to shorten the production cycle, the arrangement of the heat insulating material 4 is indispensable, but when there is a margin in the production cycle, the heat insulating material 4 is not necessarily required.

[0024]

Example 3 Using the mold of Example 1, a molded product having a partially thin portion was injection-molded. The size of the molded product is 3
This is a case where a thin portion having a diameter of 20.0 mm and a thickness of 0.10 mm is formed at the center of a molded product, having a thickness of 00 mm × 300 mm and an average thickness of 2.5 mm. In order to perform injection molding using the mold of Example 1, a hydraulic cylinder and a hydraulic unit (YA16-C-6 manufactured by Yuken Kogyo Co., Ltd.) serving as a drive source of the movable core 2 that advances into the cavity 1 are used.
3.7-14) was used. Here, the external hydraulic unit pressure was 100 kgf / cm ² . The cavity 1 is closed by a fixed-side main mold and a movable-side main mold by an injection molding machine (IS350E manufactured by Toshiba Machine Co., Ltd.), and the movable core 2 for forming a thin-walled part is a cavity having a thickness of 2.5 mm. It is at the same level as 1. Before filling the resin, the movable core 2 was previously heated to about 120 ° C. with a cartridge heater (50 V-30 W) 5 and filled with a high-impact polystyrene resin (HT560 manufactured by Idemitsu Petrochemical Co., Ltd.).

Next, after the entire cavity 1 was filled with resin, the movable core 2 was advanced into the cavity 1 by operating the hydraulic cylinder. By the advance of the cavity 1,
The resin in front of the movable core 2 is extruded to the periphery, and the movable core 2 has a specified position of 2.4 m to form 0.10 mm.
It stopped at the position where it moved forward m. At the same time as the movable core 2 reaches the specified position, the power supply to the cartridge heater 5 is stopped, and instead, N ₂ gas (10 k
gf / cm ² ) was injected from the refrigerant introduction pipe 6, and N ₂ gas was circulated in the refrigerant circulation channel 2 a to cool the movable core 2. As a result, the thin portion and its surrounding resin were rapidly cooled. As a result, 0.10m without weld
m was able to be molded.

[0026]

Embodiment 4 This embodiment is an example in which a heat medium is used for heating and cooling. As shown in FIG. 4, a heat exchange unit 10 in which a fluid is used as a heat medium is built in the movable core 2. Mold. The heat medium used here uses silicone oil,
This was heated and cooled by a high-frequency induction heating device (not shown), and the heat medium supplied from the heat medium inlet 11 was returned to the high-frequency induction device from the heat medium outlet 12 via the heat exchange unit 10. . The molding method was the same as in the case where the mold of Example 1 was used. As a result, it was possible to form a 0.10 mm thin portion in which no weld was formed as in Example 3.

[0027]

Embodiment 5 This embodiment is an embodiment in which a thin portion is formed by incorporating a movable core 2 incorporating heating and cooling means and an auxiliary core 13 on a fixed side and a moving side in a mold. As shown in the figure, an auxiliary core 13 is incorporated in a portion facing the movable core 2 with the cavity 1 as a boundary,
Injection molding was performed in the same manner as in Example 3. In this case, the start of heating and cooling of the auxiliary core 13 was synchronized with the movable core 2. However, the auxiliary core 13 is fixed and does not move forward. The internal structures (heating and cooling means) of the movable core 2 and the auxiliary core 13 are the same as in the first embodiment. As a result, as in the case of Example 2, no weld was generated.
mm thin part could be formed. In the above embodiment, the heating and cooling timings of the auxiliary core 13 are synchronized with the movable core 2, but the timings may be shifted depending on the molding conditions of the thin portion.

[0028]

Embodiment 6 This embodiment is different from Embodiment 5 in that the auxiliary core 13 is advanced simultaneously with the movable core 2,
It is designed to retreat. According to this embodiment, for example, as shown in FIG. 6, it is possible to form a thin portion a into a thickness (W) in a molded product b. Also in this example, it was possible to form a thin portion having a thickness of 0.10 mm which does not cause welding.

[0029]

As described above, according to the present invention, the heating means and the cooling means are incorporated in the movable core, and when the resin is filled and the movable core is advanced, the heating means is driven to heat and mold the thin-walled resin. Then, at the time of cooling the mold, the cooling means was driven to cool the thin portion. As a result, it is possible to perform molding that suppresses the development of the skin layer and does not generate weld in the thin portion. Further, by forcibly cooling the movable core and the auxiliary core, the molding cycle can be shortened.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a mold cavity according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the internal configuration of the movable core according to the first embodiment.

FIG. 3 is a cross-sectional view of a mold cavity portion according to a second embodiment.

FIG. 4 is a cross-sectional view of a mold cavity portion and the inside of a movable core when a heating medium is used for heating and cooling according to a fourth embodiment.

FIG. 5 is a cross-sectional view of a mold cavity portion and an inside of a movable core using an auxiliary core according to a fifth embodiment.

FIG. 6 is an explanatory diagram of a molded product in which both a movable core and an auxiliary core are advanced to form a thin portion in a sixth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cavity 2 Movable core 2a Refrigerant circulation channel 3 Mold main mold 4 Insulation material 5 Cartridge heater 6 Refrigerant introduction pipe 7 Transmission medium port 8 Communication hole 9 Return medium port 10 Heat exchange part 11 Heat medium inlet 12 Heat medium outlet 13 Auxiliary core

Claims (7)

[Claims] 1. An injection molding method in which a movable core is incorporated in a plastic injection mold, and immediately after filling with a resin, the movable core is advanced to a predetermined distance to form a thin portion here. Means for cooling the thin-walled resin by driving the heating means to generate heat in the movable core when filling the resin into the mold and moving the movable core forward, and for cooling the mold when the mold is cooled. A method of injection-molding a plastic molded product having a thin part in a part while controlling the development of the skin layer by cooling the thin part. 2. A mold for injection molding of a plastic molded product having a thin part in a part thereof, wherein a movable core for molding a thin part is incorporated into a part of the mold so as to be able to advance and retreat, and the movable core is formed in the mold. A heating means and a cooling means are incorporated in the core, the heating means is driven at the time of product molding, and the cooling means is driven at the time of cooling, so that a part configured to suppress the development of the skin layer has a thin portion. Mold for injection molding of plastic molded products. 3. The injection of a plastic molded product having a thin part in part according to claim 2, wherein an electric heater is incorporated in the movable core as heating means, and a refrigerant circulation channel is formed in the movable core as cooling means. Mold for molding. 4. A heating medium circulating passage is formed in a movable core as a heating means and a cooling means, and a heating medium is circulated in the heating medium circulating passage during heating, and a refrigerant is circulated during cooling. 3. A mold for injection molding a plastic molded product having a thin part in part according to claim 2. 5. An auxiliary core incorporating a heating means and a cooling means is incorporated into a mold opposite to a mold incorporating a movable core, and a thin portion is formed by the action of the auxiliary core and the movable core. The injection molding die for a plastic molded product having a thin part in a part according to claim 2, 3 or 4. 6. A plastic partly having a thin part according to claim 5, wherein the auxiliary core is advanced in accordance with the advance of the movable core so that the thin part is formed in the middle of the thickness of the molded product. Mold for injection molding of molded products. 7. A heat insulating material is arranged between a movable core or an auxiliary core and a mold.
A mold for injection molding of a plastic molded product having a thin portion in a part of the description.