JPH09109214A - Injection mold and manufacture of injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection mold which makes it possible to heat the cavity surface in a short time before a molten resin is injected in the cavity and has a simple structure and a method for manufacturing an injection molding which makes it possible to obtain the molding having excellent external appearance and quality. SOLUTION: The engaging part 7 sliding in the mold switching direction on the outer periphery of the mold mating surface of the periphery of a cavity 4 is provided in an injection mold 1. Gas supply holes 10, 11 for supplying high- temperature gas are provided at the knockout surfaces 8, 9 for forming the opening of a molding, and a gas exhaust groove 12 is formed at the mating surface 5. To mold the molding by using the mold of such a structure, the method having the steps of temporarily interrupting the mold closing step immediately before the mold is completely closed, externally exhausting the high- temperature gas through the groove 12 of the periphery of the cavity 4 while supplying the gas into the cavity 4 via the surfaces 8, 9 from the holes 10, 11 in the state that the mold is opened at a small amount 6, thereby heating the cavity surface is adopted.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an injection molding die and a method for manufacturing an injection molded article.

[0002]

2. Description of the Related Art As a method of injection molding a thermoplastic resin, a pair of molding dies (fixed mold and movable mold) which form a cavity in a closed state are used, and a molten resin is injected into the cavity from a heating cylinder. After injection-filling the resin, cooling and solidifying the resin, the mold is opened and the molded product is taken out of the mold.

In such injection molding, when the surface temperature of the mold cavity is low at the time of filling the molten resin, the injected molten resin begins to cool and solidify at the portion where it contacts the cavity surface, which increases the viscosity of the resin. The flow resistance increases. As a result, a defective appearance of the molded product such as a weld line, a flow mark or a silver streak occurs. In addition, when the temperature of the cavity surface is low during resin filling, it may be difficult to obtain a molded product with a smooth surface appearance due to the floating of the filler when molding a molded resin-filled product. is there.

On the other hand, when the surface temperature of the cavity at the time of filling the molten resin is high, it becomes possible to fill the cavity with the molten resin by low-pressure injection, which eliminates the above-mentioned defective appearance of the molded product. Further, by filling the molten resin by high-pressure injection, it is possible to obtain a glossy molded article having excellent transferability during shaping.

However, if the surface temperature of the cavity is raised to a high temperature, the cooling time after the resin filling is completed until the temperature reaches the temperature at which the molded product can be taken out, and the productivity is deteriorated. From the above, it is ideal that the surface temperature of the cavity is high at the time of filling the molten resin and the surface temperature of the cavity rapidly decreases after the completion of filling, and various technologies have been proposed to achieve this. Has been done.

[0006] For example, Japanese Patent Publication No. 45-22020,
JP-A-4-201306 and JP-A-1-241
Japanese Patent No. 408 each discloses a method of heating a cavity surface by supplying a high temperature gas to the cavity before filling the molten resin.

Further, JP-A-57-4748 and JP-A-2-162007 disclose methods of heating the cavity surface immediately before resin filling by high-frequency induction heating, and further, JP-A-61-1. Japanese Patent No. 143109 also discloses a method using an electric heater as a heating means for the cavity surface.

On the other hand, in addition to the above heating method, for example, in Japanese Patent Laid-Open No. 5-38721, the cavity surface is insulated by covering the cavity surface with a material having a low thermal conductivity, and the filling resin A technique for preventing the temperature from rapidly decreasing is disclosed.

Further, in JP-A-51-5362 and JP-A-61-16821, a mold having a passage for a heat medium fluid around a cavity is used, and a heating medium is supplied to the passage. There is disclosed a technique in which the molten resin is filled with the cavity surface heated to an appropriate temperature, and then a cooling medium is supplied to the passage to shorten the cooling and solidification time of the filled resin.

[0010]

By the way, in the method described in Japanese Patent Publication No. 45-22020, the heating fluid is supplied from the gate having a very small cross-sectional area. Supply of heating fluid is difficult. Moreover, it is difficult to provide a temperature difference between the surface layer and the deep layer of the cavity. That is, since the mold is made of a metal material, the heat applied to the surface layer diffuses throughout, and it is difficult to make a temperature difference between the surface layer and the deep layer.

Further, according to the method of induction heating with a high frequency current described in Japanese Patent Laid-Open No. 57-4748, etc., the equipment cost of the high frequency oscillator is expensive, and each time according to the shape of the cavity, There is a problem that the heating coil needs to be manufactured and lacks versatility.

Further, when an electric heater is used as a heating means as described in Japanese Patent Laid-Open No. 61-143109, heating of a flat plate-shaped cavity can be easily dealt with, but a cavity having a complicated shape with irregularities is provided. In this case, it is necessary to manufacture a heater element having the same cavity shape, and the manufacturing cost is high. Moreover, the heat efficiency is poor due to the heating by radiation, and the temperature distribution on the cavity surface is not uniform. Furthermore, since it is necessary to heat the entire volume of the fixed and movable molds, it is necessary to heat and melt the mold. There is a problem that it takes time to cool the resin.

On the other hand, according to the method of coating the cavity surface described in Japanese Patent Laid-Open No. 5-3871, it is difficult to finish the cavity surface to a mirror surface state.
When a part of the coating is peeled off, cracked, worn, or the like, it is difficult to repair the coating.

Here, in the methods described in JP-A-51-5362 and JP-A-61-16821, the surface temperature of the cavity at the time of filling the molten resin can be set to an appropriate temperature, and after the completion of the filling, the cavity can be set. This method is superior to the other methods described above in that it can cool the temperature to an appropriate temperature, but the method described in this publication leaves the following two problems.

(1) Since the heat medium fluid passage cannot be formed close to and equidistant to the cavity surface, a temperature distribution is generated on the cavity surface, which causes variations and deformations in the appearance quality of the molded product. In this regard, although it is possible to form the passage for the heat transfer fluid in the mold for molding the flat plate-shaped product in the vicinity of the cavity surface at an equal distance, many molds (for example, housings of OA equipment, In the case of TV housings, vacuum cleaner housings, etc.), the shape of the cavity is complicated, and due to the presence of ejector pins and restrictions on the nesting structure, the cavity surface can be heated to a high temperature and almost uniformly. It is virtually impossible to install a medium fluid passage.

(2) It takes a considerable amount of time for heat to be transferred from the heat medium fluid passage to the cavity surface, and the entire die having a large heat capacity is heated and cooled instead of heating only the vicinity of the cavity surface. Therefore, it is inevitable that the temperature rising / falling time is prolonged, and these points become a factor to impair the molding productivity.

The present invention has been made to solve the above-mentioned problems, and the surface of the cavity can be heated in a short time before injecting the molten resin into the cavity, and the injection molding metal has a simple structure. It is an object of the present invention to provide a mold and a method for producing an injection-molded product that enables molding of a molded product with excellent appearance quality using such a mold.

[0018]

In order to achieve the above-mentioned object, an injection mold of the present invention comprises a fixed mold and a movable mold which form a cavity inside in a mold closed state, and a molded product in the cavity. In an injection-molding die provided with an abutting surface that forms the opening of the, a fitting portion that slides in the die opening and closing direction is provided on the outer periphery of the die mating surface around the cavity, and a fixed die or a movable die. In any one of the above, a gas supply hole for supplying a high temperature gas to the abutting surface is provided, and a gas discharge groove is provided on the mold matching surface around the cavity.

The method of manufacturing an injection-molded article according to the present invention is
When molding an injection-molded product using the above-mentioned injection molding die, the mold closing process is temporarily interrupted immediately before the mold closing of the fixed mold and the movable mold is completed, and a slight amount of the mold is opened, and a high temperature gas is added to the above gas. It is characterized by heating the surface of the cavity by supplying the gas into the cavity from the supply hole and discharging the gas to the outside through the gas discharge groove of the mold matching surface around the cavity.

Here, in the method of manufacturing an injection-molded article of the present invention, a low-temperature heat medium is supplied to the heat medium passages formed in each of the fixed mold and the movable mold of the injection molding die, and the molten resin to the cavity is formed. The mold may be cooled by supplying only during the period from the time when the filling is completed to the time when the molded product is taken out.

In this case, since the cooling of the mold by the low temperature heat medium is interrupted during the heating of the cavity surface by the high temperature gas, the heating of the cavity surface by the high temperature gas can be performed more effectively. The molding time can be shortened.

In addition, in the method of manufacturing an injection-molded article according to the present invention, in parallel with the heating of the cavity surface by the high-temperature gas, a high-temperature heat medium is supplied to each of the fixed-type and movable-type heat medium flow paths to obtain a mold. By heating, the surface temperature of the cavity can be raised rapidly. Further, if the low-temperature heat medium is supplied instead of the high-temperature heat medium to the fixed-type and movable-type heat medium flow paths after the cavity is completely filled with the molten resin, the cooling time of the molded product is shortened. Therefore, the molding time can be shortened.

[0023]

[Function] Generally, the heat transfer coefficient between the gas and the cavity surface is proportional to the flow velocity of the gas flowing in the cavity to the power of 0.5 to 0.8. Therefore, the heat transfer coefficient should be increased to rapidly increase the cavity surface temperature. In order to raise the temperature, it is essential to flow a large amount of gas in the cavity.

In the present invention, paying attention to such a point, by making the portion for supplying the high temperature gas through the gas supply hole the abutting surface for forming the opening of the molded product in the region of the cavity, the gas Make the cross-sectional area of the supply hole large,
A large amount of gas can be supplied.

In addition to such a gas supply hole, a gas discharge groove is provided on the mold matching surface around the cavity of the mold, and a fitting that slides in the mold opening / closing direction on the outer periphery of the mold matching surface around the cavity. A large area gas passage is ensured as a structure in which the inside of the cavity communicates with the outside only through the gas supply hole and the gas discharge groove in a state in which the mold is opened with a slight amount just before the completion of the mold closing. The pressure loss of the high temperature gas in the cavity is reduced.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical sectional view showing a structural example of an injection molding die of the present invention.

The injection molding die 1 of this example is a molded product having a structure shown in FIG. 2, that is, a molded product S having openings A1 and A2.
Is a mold used for molding a mold, and is composed mainly of a fixed mold 2 and a movable mold 3 that form a cavity 4 inside in a mold closed state. The fixed die 2 has a locate ring 13 at a substantially central portion and a sprue bush 15 having a sprue 14 for injecting a molten resin into the cavity 4.
Is provided.

Now, the cavity 4 is provided in the injection molding die 1.
There are mold matching surfaces 5, 6, 7 around the outside of
Of these, the mold matching surface 7 is a sliding portion having a structure capable of sliding in the mold opening direction.

Further, abutting surfaces 8 and 9 for forming the openings A1 and A2 of the molded product S are provided in the cavity 4, and these abutting surfaces 8 and 9 in the mold closed state. The fixed mold 2 side and the movable mold 3 side contact each other to prevent the molten resin from flowing in.

Further, inside the movable mold 3, gas supply holes 10 and 11 are provided, one end of which faces the abutting surfaces 8 and 9 and the other end of which is guided to the outside of the mold through the gas supply passage 20. The high temperature gas can be supplied into the cavity 4 through the gas supply holes 10 and 11. Further, a gas exhaust groove 12 is provided at the position of the die matching surface 5 on the movable die 3 side, and an exhaust passage 22 is provided inside the movable die 3.

In the injection mold 1 shown in FIG. 1, heat medium flow paths 16 and 17 for controlling the mold temperature are provided in the fixed mold 2 and the movable mold 3 as in the case of a normal mold. Are provided inside each.

When the injection molding die 1 having the above-described structure is in the state of being on the verge of completion of mold closing, as shown in FIG. 3, the fixed mold side surface 5a and the movable mold side surface 5 of the mold matching surface 5 are formed.
There is a slight gap δ between the mold fitting surface 7 and the outer peripheral surface of the mold b, and the mating surface 7 around the outside is maintained in the fitted state. Therefore, in the state just before the completion of the mold closing, the inside of the cavity 4 is opened to the outside only through the gas supply holes 10 and 11 and the gas discharge groove 12.

Further, in the injection molding die 1 having the above-described structure, in the state shown in FIG. 3, since the gap 21 having the interval δ is formed on the mold matching surface 5 facing the gas supply holes 10 and 11, the gas supply is performed. A gas passage having a large cross-sectional area can be secured from the holes 10 and 11 to the gas discharge groove 12.

In the structure shown in FIG. 1, the gas supply holes 10 and 11 and the gas discharge groove 12 are provided in the movable die 3, but they may be provided in the fixed die 2 or the fixed die 2. It may be provided in both the movable mold 3 and.

Next, the heating / cooling system of the above injection molding die 1 will be described with reference to the system diagram of FIG. First, the gas heating device 1 is installed in the gas supply passage 20 of the injection molding die 1.
8 are connected via a heat resistant hose 19. The gas heating device 18 is a device having an electric heater, a blower, etc. built therein, and has a gas temperature of 250 to 400 ° C. and a gas pressure of 0.3 to
It has the ability to generate high temperature and high pressure gas of 1.0 kg / cm ² .

Further, a hose 32 is connected to the exhaust passage 22 of the injection molding die 1, and gas can be discharged to the outside of the die from the hose 32. On the other hand, in this system, the heat medium flow paths 16, 1 of the injection molding die 1 are
Cooling mold temperature controller 23 for supplying heat medium to
And a heating mold temperature controller 24. These two temperature controllers 23 and 24 are connected to the electromagnetic switching valve 2
5 through pipes 26, 27 and 28, 29, respectively, and an electromagnetic switching valve 25 is connected to the hose 3
The heat medium flow paths 16, 1 of the injection molding die 1 through 0, 31
7 is connected.

In such a heat medium supply system, the low temperature heat medium from the cooling mold temperature controller 23 is
After flowing into the heat medium flow paths 16 and 17 in the mold through the pipe 26, the electromagnetic switching valve 25 and the hose 30 to cool the mold, the hose 31, the electromagnetic switching valve 25 and the pipe 27.
A circulation path is formed by returning to the cooling mold temperature controller 23 through the above, and a similar circulation path is also configured for the heating mold temperature controller 24 by the switching operation of the electromagnetic switching valve 25.

Next, a molding method using the injection molding die 1 will be described with reference to the system diagram of FIG. 3 and the flow chart of FIG. First, in this molding method, a two-stage mold closing method is adopted, and in the first mold closing step, as shown in FIG. 3, a slight gap δ is formed between the mold matching surface 5, the abutting surfaces 8 and 9. The mold is closed until it is opened, and in the second mold closing step, the mold is completely closed when the interval δ is 0.

In the process shown in FIG. 4, first, when the first mold closing process is completed, high-temperature gas is supplied from the gas heating device 18 through the gas supply passage 20 to the gas supply holes 10 and 11.
To supply. At this time, the cavity 4 is shielded from the outside except the gas supply holes 10 and 11 and the gas discharge groove 12 as shown in FIG.
The high temperature gas supplied to is blown into the cavity 4 at high speed. Then, the gas flowing into the cavity 4 flows while heating the surface of the cavity 4 and reaches the gap 21 of the mold matching surface 5, and then passes through the gas discharge groove 12, the exhaust passage 22 and the hose 32 to the mold. It leaks to the outside.

Here, the gas supply holes 10 and 11 are in the region of the cavity 4, and the high temperature gas blown into the cavity 4 flows radially toward the gas discharge groove 12 provided around the cavity 4. Therefore, the surface of the cavity 4 can be heated to every corner.

Further, in parallel with the above heating process by the high temperature gas, a high temperature heating medium is supplied from the heating die temperature controller 24 to the heating medium flow paths 16 and 17 in the injection molding die 1 to produce the metal. The step of heating the surface of the cavity 4 from the inside of the mold may be performed if necessary. When the heating with the high temperature heating medium is not performed, the heating medium (low temperature heating medium) does not flow through the heating medium flow paths 16 and 17 during the heating process with the high temperature gas.

Next, the second mold closing step is performed, and the molten resin is injected into the cavity 4 from the molding machine. When the resin injection is completed, the heat medium flow passage 16 in the injection molding die 1,
A low temperature heat medium is supplied to the cooling die temperature controller 23 to start cooling the die. Then, when the pressure holding step, the cooling step, and the mold opening / mold release step of the molded product are completed,
After stopping the supply of the low-temperature heat medium from the cooling mold temperature controller 23, the process returns to the next process of closing the first mold,
After that, the same steps are sequentially repeated.

When the surface of the cavity 4 is heated, the temperature of the high-temperature heat medium supplied to the heat medium flow paths 16 and 17 of the injection molding die 1 depends on the molding material, the required appearance quality of the molded product, and the gas. It depends on the heating performance, the desired heating time, and the temperature of the discharge heat medium of the mold temperature controller used.
Usually, it is good to select an appropriate temperature within the range of 90 to 140 ° C.

The temperature of the low-temperature heat medium used when cooling the mold is determined by the above-mentioned high-temperature heat medium temperature similarly in accordance with the molding conditions, the appearance quality of the molded product, etc.
About 60 ° C is suitable.

Further, regarding the surface temperature of the cavity 4, it is said that a temperature near the glass transition point is desirable in view of the appearance quality of the molded product in the case of molding an amorphous resin, but if it is too high, it takes time to cool. Since it takes a lot of productivity, it is desirable to make a decision considering both the quality of the molded product and the cooling time.

In the above system, the high temperature gas supplied into the cavity 4 is 100 to 2 even at the discharging stage.
Since the temperature is as high as 00 ° C., heat can be effectively used by adopting a method in which the gas is discharged from the mold and then sent again to the gas heating device 18 for recycling. Further, by adopting a system in which the exhaust gas from the mold is guided to the outside and then released into the atmosphere, environmental pollution at the molding site due to high temperature gas can be prevented.

Further, in the system described above, the heating medium flow paths 16 and 17 of the injection molding die 1 are alternately supplied with the high temperature heat medium and the low temperature heat medium to heat and cool the die. However, if there are restrictions on the number of temperature controllers, or if it is not necessary to significantly shorten the heating time of the cavity surface due to the small number of molding lots, the mold temperature control is performed by supplying a low-temperature heat medium. It may be limited only to cooling by. In this case, the heating mold temperature controller 24, the electromagnetic switching valve 25, etc. are unnecessary.

Here, in the above embodiment, the molded product S having a simple shape was described as an object to be molded, but a molded product other than such a shape, for example, a personal computer cover or a TV front cover. The manufacturing method of the present invention is suitable for molding telephone housings, automobile instrument panels, and the like.

[0049]

As described above, according to the present invention,
In the cavity area of the injection mold, a gas supply hole for supplying high-temperature gas is provided on the abutting surface that forms the opening of the molded product, and a gas discharge groove is provided on the die matching surface around the cavity. When heating the cavity surface by blowing hot gas before injecting resin into the cavity, it becomes possible to supply a large volume of hot gas into the cavity, which allows the surface temperature of the cavity to rise in a short time. . Moreover, since the supplied high-temperature gas effectively flows due to the gas discharge groove provided around the cavity, it is possible to uniformly heat all the surfaces of the cavity.

Further, since the surface temperature of the cavity can be raised to a high temperature, the solidification of the molten resin injected into the cavity is delayed and the fluidity is improved. As a result, the following effects can be expected.

(1) Improving transferability and appearance quality of molded products. (2) Large-sized, thin-walled molding becomes easy. (3) Low pressure molding becomes possible.

(4) Elimination of defective molding phenomena such as weld lines, flow marks and silver streaks, and floating phenomenon of the filler. Further, in the present invention,
The injection mold is provided with a gas supply hole, a gas discharge groove, and a sliding portion on the outer periphery of the mold matching surface around the cavity, and moreover, a high temperature gas generator for supplying high temperature gas to the gas supply hole. Since it can be applied to various molds, the above-mentioned effects can be achieved at a low equipment cost.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing a structural example of an injection molding die of the present invention.

FIG. 2 is a perspective view showing an external shape of a molded product obtained by the injection molding die.

FIG. 3 is a system diagram for explaining a heating / cooling method of the injection mold 1 of FIG.

FIG. 4 is a flow chart for explaining steps of a method for manufacturing an injection-molded product according to the present invention.

[Explanation of symbols]

 1 Injection Mold 2 Fixed Mold 3 Movable 4 Cavity 5,6 Mold Matching Surface 7 Mold Matching Surface (Sliding Part) 8,9 Abutting Surface 10,11 Gas Supply Hole 12 Gas Discharge Groove 16,17 Heat Medium Flow Line 18 Gas heating device 23 Heating temperature controller for cooling 24 Heating temperature controller for heating S Molded products A1, A2 Opening

Claims (2)

[Claims] 1. An injection molding mold comprising a fixed mold and a movable mold that form a cavity inside in a mold closed state, and an abutment surface that forms an opening of a molded product is provided in the cavity. A fitting part that slides in the opening and closing direction of the mold is provided on the outer periphery of the mold matching surface, and a high-temperature gas is supplied to the abutting surface inside at least one of the fixed mold and the movable mold. An injection-molding die, characterized in that a hole is provided and a gas discharge groove is provided on a die-matching surface around the cavity. 2. A method of molding an injection-molded product using the injection-molding die according to claim 1, wherein the mold closing step is temporarily interrupted immediately before the mold closing of the fixed mold and the movable mold is completed, In a state where the amount of the mold is opened, it is possible to heat the cavity surface by supplying the high temperature gas into the cavity from the gas supply hole while discharging the gas to the outside through the gas discharge groove of the mold matching surface around the cavity. A method for producing a characteristic injection molded product.