JPH06285917A - Sink mark preventing rein forming mold device - Google Patents

Abstract

PURPOSE:To provide a sink mark preventing resin forming mold device by which a molded piece requiring good appearance can be molded without sink mark. CONSTITUTION:A mold has void injection pins for forming voids by injecting pressure gas into a melted resin in a cavity. A pressure gas supply means 5 supplies the pressure gas to the void injection pins. Pressure control means 6 and 7 set the pressure of the pressure gas for the void injection pins to a prescribed value. Further, pressure open/close means 8 and 9 are provided between the pressure control means 6, 7 and the void injection pins, and a pressure releasing open/close means 10 is provided between the void injection pins and the atmosphere. A void injection section has a control means 11 for carrying out a cycle of pressurizing and releasing by the pressure gas supply means 5, the pressure control means 6, 7, the pressure open/close means 8, 9, and the pressure releasing open/close means 10 with a preset pressure and a preset timing at each void injection pin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic resin molding die apparatus, and more particularly to a sink preventing resin molding die apparatus.

[0002]

2. Description of the Related Art Conventionally, in injection molding of a thermoplastic resin, there is a problem that "sinker" occurs on the surface of a molded product due to shrinkage when a molten resin injected and filled in a mold cavity is cooled and hardened. There is. This problem can be solved to some extent by examining various injection molding conditions according to the shape and size of the molded product and setting the optimum conditions when the thickness of the molded product is relatively uniform. In the case of a molded product having different wall thickness portions, it is impossible to uniformly cool and harden portions having different wall thicknesses at the same time, and sink marks occur on the surface of the thick portion where cooling and hardening are delayed. Solving the problems in this case has become a major problem in resin injection molding.

Recently, a void injection pin for injecting a pressurized gas from the outside is provided inside the thick portion in the cavity of the mold, and the cavity is filled when molding the thermoplastic resin. Pressurized gas is injected into the thick wall of the resin through a void injection pin, and a void with a volume matching the shrinkage amount of the molten resin during cooling and hardening is formed instead of the sink mark to prevent sink marks. A resin molding die device has been proposed.

A conventional example of a resin molding die device for preventing a sink by forming a void instead of a sink will be described with reference to FIGS. 1 and 4.

FIG. 1 shows a mold part. A cavity 23 is formed by a movable mold 20 and a fixed mold 21, and molten resin is injected and filled into the cavity 23 from the injection side through a sprue 22 and a gate 28. To be done. In this case, cavity 2
3 has a thick portion 24 that constitutes the rib portion of the molded product,
A sink mark tends to occur on the back side of the thick portion 24, that is, on the front side of the molded product. In order to prevent the sink mark, the cavity 2 corresponding to the thick portion 24 of the movable mold 20.
The pressurized gas supplied from the outside of the movable mold 20 through the ventilation circuit 27 is injected into the molten resin filled in the cavity 23 so that the void 25 is formed. And a void injection pin 26 for opening the pressurized gas in the injected void 25 to the atmospheric pressure through the ventilation circuit 27, and sending the pressurized gas from the outside to the void injection pin 26. A void 25 is formed in the molten resin, and a ventilation circuit 27 is provided to open the pressurized gas in the void 25 to the outside atmospheric pressure.

FIG. 4 shows a void injecting section, and the void injecting section generates a pressurized air to be supplied to the void injecting pin 26 and a compressed air generating means 1 for generating the pressurized air. Pressurized gas supply means 2 for supplying pressurized air to the void injection pin 26, pressurized release means 3 for releasing the pressurized gas in the void injection pin 26 to atmospheric pressure, pressurized gas supply means 2 and And a control unit 4 for controlling opening / closing of the pressure release unit 3. The solid line in FIG. 4 indicates the ventilation circuit and the dotted line indicates the control circuit.

Next, the operation of the conventional example will be described with reference to FIGS.

1 and 4, the pressurized air generating means 1 is operating, but the pressurized gas supply means 2 is closed and the pressurized release means 3 is open before the start of injection molding. .
Simultaneously with the start of injection molding, the pressure releasing means 3 is closed and the injected molten resin is filled in the cavity 23. After a lapse of a predetermined time from the completion of this filling, the pressurized gas supply means 2 is opened, and the pressurized air from the pressurized air generation means 1 is discharged from the void injection pin 26 via the pressurized gas supply means 2. , Is injected into the resin filled in the cavity 23 to form voids in the filled resin. Then, after a lapse of a predetermined time, the pressurized gas supply means 2 is closed and the pressure release means 3 is opened to open the pressurized gas in the void to the atmospheric pressure. Voids that open the pressurized gas to atmospheric pressure then grow by absorbing outside air from the atmosphere due to shrinkage due to cooling and hardening of the molten resin, and grow into voids of a size commensurate with the amount of shrinkage. The loss is improved by the amount.

[0009]

However, in the structure of the above-mentioned conventional example, if voids are first injected, the voids are released to the atmospheric pressure, and then the voids are contracted by cooling and hardening of the molten resin. It grows while sucking in the outside air,
When there are multiple void injection pins, it is assumed that the void grows to a size corresponding to the shrinkage amount due to cooling and hardening of the molten resin, and sink marks are improved by this void size, and good results are obtained. However, it is only possible to supply pressurized air of the same pressure to all the void injection pins at the same timing and to release the atmospheric pressure at the same timing.
In this method, the growth state of voids differs due to the difference in fluidity during cooling / curing / contraction of the molten resin due to differences in the shape, size, gate position and wall thickness of the molded product. It is impossible to match the volume of the voids formed by the pins with the amount of shrinkage of the molten resin at each position due to cooling, and there is a problem that some void injection pins lose the function of eliminating the sink mark.

The present invention solves the above problems and eliminates the sink marks by forming voids instead of sink marks, regardless of the difference in shape, size, gate position and wall thickness of the molded product. An object of the present invention is to provide a sink preventive resin molding die device.

[0011]

In order to solve the above-mentioned problems, the sink preventing resin molding die device of the present invention is arranged so that the tip of the resin molding die projects from an arbitrary position on the inner surface of the cavity into the cavity. The pressurized gas supplied from outside the mold is injected into the molten resin filled in the cavity of the mold to form voids, or the pressurized gas in the injected void is depressurized to atmospheric pressure. A mold part having a void injection pin and a ventilation circuit for the void injection pin, a pressurized gas supply means for supplying a pressurized gas to each void injection pin, and a pressurized gas supply means for each void injection pin Pressure adjusting means for setting the pressure of the pressurized gas for each void injection pin, pressurizing opening / closing means provided between the pressure adjusting means and each void injection pin, and provided between the void injection pin and the atmosphere. Pressure open / close Step, the pressurized gas supply means, the pressure adjusting means, the pressurizing opening / closing means, and the pressurizing opening / closing means, the cycle of pressurizing / opening any number of times is preset for each void injection pin. And a timing, and a void injecting section having a control circuit for controlling so as to be performed according to the timing and a ventilation circuit from each of the means to each of the void injecting pins.

[0012]

[Function] In the injection molding of the resin, "sink" is often generated in the thick portion. The molten resin filled in the cavity of the mold is shrunk when it is cooled and hardened, but the portion that is cooled and hardened first receives the pressure maintained by the volume of the portion that has not yet been cooled and shrunk, resulting in sink marks and voids. Cools and cures without. However, in the thick part, the cooling and hardening are delayed compared to the other parts. Therefore, when the cooling and hardening is performed here, the entire resin is contracted by cooling and the pressure drop is unavoidable, and the delayed pressure drop phenomenon in the cooling part occurs. When it appears on the surface, it becomes a sink, and when the mold temperature is low and the surface of the molded product is cooled and hardened first, an uncured portion inside is pulled toward the surface to generate a void, but a sink is not generated.

According to the present invention, in the thick portion where the sink mark is likely to occur,
The void injection pin is used to inject voids and grow the voids instead of the sink marks to absorb the cooling shrinkage of the resin to eliminate the sink marks.

In this case, if the voids are first injected, the voids become large while sucking the outside air due to the contraction accompanying the cooling and hardening of the molten resin after being released to the atmospheric pressure. It has the effect of growing into voids of a size commensurate with the amount of shrinkage and improving the sinkage by the size of the voids.The action of growing the voids while sucking the atmospheric air is the fluidity of the molten resin. If the fluidity is large, even if the injection void is small, the void grows sufficiently and it is possible to effectively prevent sink marks.However, if the fluidity is small, the first injected void cannot grow so much and the first injection occurs. If the void size is not proper, sink marks cannot be effectively prevented.

The fluidity of the molten resin is determined by the conditions of the mold such as the type of resin, the size and shape of the cavity, the thickness of the thick portion, and the molding conditions such as temperature, injection pressure and cooling rate. . In order to prevent sink marks, when there are a plurality of thick portions provided with void injection pins, the fluidity of the molten resin differs at each of the portions. Therefore, since the growth state of the injected void is different for each thick portion provided with the void injection pin, the pressure and the pressurization time of the pressurized gas to be injected in order to first create a void of an appropriate size. It will be different for each injection pin.

Since the sink preventive resin molding die device of the present invention is provided with the void injection pin at an arbitrary position in the cavity of the mold portion and has the ventilation circuit to the void injection pin, the sink mark of the molded product is obtained. It is possible to prevent sink marks by injecting voids into the molten resin at the portion where it is desired to prevent.

Further, since the void injecting section has the pressure adjusting means, the pressurizing opening / closing means, the pressurizing opening / closing means and the control means, the above-mentioned desired effect is provided inside the portion of the molded article where it is desired to prevent sink marks. In order to form a void of a size that matches the fluidity of the molten resin in that part, pressurizing gas is injected into the molten resin at a preset pressure and timing to form a void and then pressure is applied. Can be released. If the size of the void is insufficient in the first pressurization / release in the first cycle, the desired effect can be obtained by performing pressurization / release in any number of cycles.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the sink mark preventing resin molding die apparatus of the present invention will be described with reference to FIGS.

FIG. 1 shows a mold part. A cavity 23 is formed by a movable mold 20 and a stationary mold 21, and molten resin is injected and filled into the cavity 23 from the injection side through a sprue 22 and a gate 28. To be done. In this case, cavity 2
3 has a thick portion 24 that constitutes the rib portion of the molded product,
A sink mark tends to occur on the back side of the thick portion 24, that is, on the front side of the molded product. In order to prevent the sink mark, the tip of the movable mold 20 is protruded from the inner surface of the cavity 23 of the thick portion 24 of the movable mold 20 into the cavity 23, and is supplied from the outside of the movable mold 20 through the ventilation circuit 27. A void injection pin 26 for injecting the pressurized gas into the molten resin filled in the cavity 23 to form a void, or for releasing the pressurized gas in the injected void to the atmospheric pressure through the ventilation circuit 27. Provided in the movable mold 20 is to send a pressurized gas from the outside to the void injection pin 26 to form a void in the molten resin, or to release the pressurized gas in the void to the external atmospheric pressure. A ventilation circuit 27 is provided.

FIG. 2 shows a void injecting portion. The void injecting portion is a pressurized gas supply means 5 for supplying a pressurized gas from the outside of the mold to each void injection pin 26 and the pressurized gas supply means 5.
Pressure adjusting means 6 for setting the pressure of the pressurized gas to each void injection pin from each of the void injection pins 26, the low pressure pressure adjusting means 7, the high pressure pressure adjusting means 6 and the void injection pin 26. High-pressure pressure opening / closing means 8 provided between
And the low pressure adjusting means 7 and the void injection pin 2
6, a low pressure pressure opening / closing means 9 and a pressure release opening / closing means 10 provided between the void injection pin 26 and the atmosphere.
The pressurized gas supply means 5, the high pressure pressure adjusting means 6, the low pressure pressure adjusting means 7, the high pressure opening / closing means 8, the low pressure opening / closing means 9, and the pressure opening / closing means 10. Control means 11 for controlling an arbitrary number of cycles of pressurization / release by means of pressure and timing preset for each void injection pin 26, and a ventilation circuit from each means to each void injection pin 26. 27 and.

FIG. 3 is a diagram showing opening / closing timings of the high pressure pressure opening / closing means 8, the low pressure pressure opening / closing means 9 and the pressure release opening / closing means 10.

In FIG. 3, for each void injection pin 26, pressurization of the high pressure adjusting means 6 for forming a void of an appropriate size according to the fluidity of the molten resin at the position of the void injection pin 26. The pressure of the gas, the opening / closing timing of the high-pressure pressure opening / closing means 8 and the opening / closing timing of the pressure release opening / closing means 10 are set in advance in the control means 11, and a void having an appropriate size is set in accordance with the fluidity of the molten resin. It is the pressure of the pressurized gas of the high pressure adjusting means 6, the opening / closing timing of the high pressure opening / closing means 8 and the opening / closing timing of the pressure opening / closing means 10 that determine whether or not the pressure can be formed. Therefore, the pressure of the pressurized gas of the high pressure adjusting means 6, the opening / closing timing of the high pressure opening / closing means 8 and the opening / closing timing of the pressure opening / closing means 10 must be set separately for each void injection pin 26. There is. Next, in common with each of the void injection pins 26, in order to supplementarily grow the voids formed above, the pressure of the pressurized gas of the low pressure pressure adjusting means 7 and the opening / closing timing of the low pressure pressure opening / closing means 9 are applied. The opening / closing timing of the pressure opening / closing means 10 is set in advance in the control means 11. Since the pressurization / release in the second cycle is auxiliary, the pressurization / release in the first cycle is sufficiently set. It is not necessary if it is proper and there is no variation in molding work conditions, but if the setting of pressurization / release in the first cycle is insufficient or there is variation in molding work conditions, it is an auxiliary It is effective as a means.

Next, the operation of this embodiment will be described with reference to FIGS.

1 to 3, before the start of injection molding, first, for each void injection pin 26, a void having an appropriate size is formed in accordance with the fluidity of the molten resin at the position of the void injection pin 26. The pressure of the pressurized gas of the high pressure adjusting means 6 and the opening / closing timings T ₁ and T _{2 of the} high pressure opening / closing means 8 and the opening / closing timing of the pressure opening / closing means 10 and T ₂ are set in the control means 11 in advance. To do. In this case, the pressure of the pressurized gas of the high-pressure adjusting means 6 may be set to any value depending on the fluidity of the molten resin, but it is 5 Kg / c.
In many cases, it is about m ^{2 to} 15 kg / cm ² . Next, in common with each void injection pin 26, in order to supplementarily grow the voids formed above, the pressure of the pressurized gas of the low pressure pressure adjusting means 7 and the opening / closing timing T _{3 of the} low pressure pressure opening / closing means 9 are increased. , setting the opening and closing timing T _3, T ₄ of the T ₄ and the pressure releasing opening and closing means 10 in advance in the control means 11. In this case, the pressure of the pressurized gas of the low pressure pressure adjusting means 7 may be set in any way, but is often 5 Kg or less.

When the above setting is completed, the molds 20 and 21 are set based on the molding operation conditions, and the molten resin is injected and filled into the cavity 23. Based on the above settings, the control means 11 injects a high-pressure pressurized gas from each void injection pin 26 at the set pressure and timing to form a void in the molten resin in the thick portion, and the setting is performed. At the timing, the pressurized gas in the void is released to the atmospheric pressure. A void of an appropriate size is initially formed for each void injection pin 26, and after the void is released to the atmospheric pressure, air is sucked from the atmosphere based on the shrinkage amount of the cooling and hardening of the molten resin to form the void. Each of the grown voids becomes a void having a volume commensurate with the shrinkage amount of the cooling and hardening of the molten resin, and absorbs the shrinkage amount accompanying the cooling and hardening of the molten resin to prevent the occurrence of sink marks.

If the initial void formation is appropriate,
As described above, sink marks can be effectively prevented, but as a countermeasure when the above-mentioned initial void formation is improper or there is variation in molding operation conditions, the low-pressure pressurized gas set above is used. Pressurize and release in the second cycle.

Of course, if the setting and operation of the first cycle are proper, the second cycle is not necessary, but as a measure against variations, the reliability of the sink mark prevention effect is improved.

[0028]

The sink mark preventing resin molding die apparatus of the present invention is
The void injection pin provided in the mold injects pressurized gas into the molten resin in the thick-walled part where the sink of the molded product is likely to occur at the time of molding, forming a void, and opening this void to atmospheric pressure. In addition to the basic effect of preventing sink marks by growing a void with a volume that corresponds to the amount of shrinkage due to cooling and hardening of the molten resin, it is also possible to properly pressurize and release pressurized gas for each void injection pin. There is a plurality of points where sink marks should be prevented due to the fact that even if there are variations in this adjustment, the correction is effective due to the pressurization / release of the second cycle. In addition, even if the growth state of voids is different due to the difference in fluidity at the time of cooling, hardening, and shrinking of the molten resin due to the difference in shape, size, gate position, wall thickness, etc. of the molded product, all voids Void of injection pin It is possible to match the product to the amount of shrinkage of each of the cooling of the molten resin, emphasizes appearance as the outer case, an effect that can be molded without shrinkage moldings dislike shrinkage occurring extreme.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a mold part.

FIG. 2 is a block diagram showing a configuration of a void injection part according to an embodiment of the present invention.

FIG. 3 is a diagram showing operation timing of the present invention.

FIG. 4 is a block diagram showing a configuration of a void injection unit of a conventional example.

[Explanation of symbols]

 5 Pressurized Gas Supply Means 6 High Pressure Pressure Adjusting Means 7 Low Pressure Pressure Adjusting Means 8 High Pressure Pressurizing Opening / Closing Means 9 Low Pressure Pressurizing Opening / Closing Means 10 Control Opening / Opening Means 11 Control Means 20 Movable Side Mold 21 Fixed Sided Metal Mold 22 Sprue 23 Cavity 24 Thick part 25 Void 26 Void injection pin 27 Vent circuit 28 Gate

Claims (1)

[Claims] 1. A molten resin in which a tip of a resin molding die is protruded from an arbitrary position on the inner surface of the cavity so that a pressurized gas supplied from the outside of the die is filled in the cavity of the die. To form voids,
A mold part having a void injection pin for depressurizing the pressurized gas in the injected void to the atmospheric pressure, a die part having a ventilation circuit to the void injection pin, and a pressurized gas supply for supplying the pressurized gas to each void injection pin. Means, pressure adjusting means for setting the pressure of the pressurized gas from the pressurized gas supply means to each void injecting pin for each void injecting pin, and an adder provided between the pressure adjusting means and each void injecting pin. Pressurization by pressure opening / closing means, pressurizing opening / closing means provided between the void injection pin and the atmosphere, pressurizing gas supplying means, pressure adjusting means, pressurizing opening / closing means, and pressurizing opening / closing means.・ Void injection part having a control means for controlling an arbitrary number of cycles of opening to be performed at a preset pressure and timing for each void injection pin, and a ventilation circuit from each means to each void injection pin And Shrinkage prevention resin molding die and wherein the obtaining.