JP2550086B2 - Gate seal injection molding method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gate seal injection molding method, and more particularly to an injection molding method capable of obtaining a highly accurate resin molded product in a short cycle time.

(Prior Art) Recently, in order to improve the accuracy of an optical element molded from a resin material, for example, a lens, etc., it is provided on a sprue of a mold after injecting a molten resin into a cavity of an injection molding mold. A gate seal injection molding method is adopted in which the gate is closed to confine the molten resin in the cavity and the pressure in the cavity is kept uniform until the molten resin is solidified.

As a conventional gate seal injection molding method of this type,
Those shown in FIGS. 9 to 12 are known.

In FIG. 9, reference numeral 1 denotes a cavity unit, and one end of the cavity unit 1 is fitted and mounted in a concave portion 4a of a movable side mold plate 4 provided in a moving die plate 3 of a molding machine 2 to move the movable die plate. When 3 is driven by the molding machine 2 and moves rightward in the drawing, the other end of the cavity unit 1 is provided on the fixed die plate 5 of the molding machine 2 so as to face the movable side template 4 6 is inserted into the recess 6a. Then, after the cavity unit 1 is clamped by the movable side mold plate 4 and the fixed side mold plate 6, the nozzle 7 of the molding machine 2 approaches the fixed die plate 5 and the injection hole 5a formed in the fixed die plate 5. Molten resin is injected from the nozzle 7 into the cavity unit 1 through the through. As shown in FIG. 10, the cavity unit 1 is composed of a pair of molds 8 and 9, and the molds 8 and 9 are inserted into a plurality of bolt holes 10 and 11 formed in the molds 8 and 9, respectively. It is integrally connected via a bolt (not shown). Cavities 8a and 9a are formed in the molds 8 and 9, respectively, and when the molds 8 and 9 are combined, the nozzle 7 is communicated with the cavity 9a and through the sprue 9b formed in the mold 9. The molten resin supplied from the injection hole 5a is injected, and a resin molded product corresponding to the shapes of the cavities 8a and 9a can be obtained. The mold 8
And 9 correspond to one end and the other end of the above-mentioned cavity unit 1, respectively. As shown in FIG. 11, the sprue 9b is provided with a gate 12 for opening and closing the sprue 9b.The gate 12 is opened and closed by a drive mechanism (not shown), and when molten resin is injected into the cavities 8a, 9a, The gate 12 closes the sprue 9b to confine the molten resin in the cavities 8a, 9a, and the gate seal injection molding method is performed.
Here, when the injection pressure of the nozzle 7 is shut off when the molten resin in the sprue 9b or the injection hole 5a is not sufficiently solidified, the molten resin causes a backflow, and after injection in order to avoid the backflow, Continue to apply injection pressure,
That is, when the pressure is maintained, only the resin in the vicinity of the sprue 9b is compressed and the molded product is apt to be distorted, which deteriorates the accuracy of the molded product. The gate seal injection method described above can eliminate these factors and improve the precision of the molded product.

Here, FIGS. 12 (a) and 12 (b) show the resin pressure in the cavities 8a, 9a and the molds 8 and 9 when the acrylic resin is used as the resin material in the above-described gate seal injection molding method. It is a graph which shows the change of mold temperature, respectively. As shown in FIG. 12 (b), the molds 8 and 9 are preheated to 125 ° C. when the resin is injected and filled, and the cavity 8
When a and 9a are filled with 230 ° C molten resin, the resin pressure is
As shown in FIG. (A), the gate is sealed at C after the injection is completed after the ascending at about 1000 kgf / cm ² . During this time,
The temperature of the resin in the cavities 8a and 9a is rapidly cooled because there is a temperature difference of 105 ° C from the mold temperatures of the molds 8 and 9, and after about 2 minutes, the temperature becomes substantially equal to the mold temperature at D. As a result, the resin pressure decreases to about 250 kgf / cm ² . After that, the molds 8 and 9 are gradually cooled, and after about 30 minutes, the temperature drops to about 90 ° C. at E,
When the resin pressure becomes almost normal pressure, the movable side mold plate 4 in FIG.
Is retracted by the molding machine 2 together with the movable die plate 3 and separated from the fixed-side mold plate 6, and the cavity unit 1 is taken out from the concave portion 4a of the movable-side mold plate 4. Then, the cavity unit 1 is disassembled into the molds 8 and 9 and the cavity 8
The resin molded product is taken out from a and 9a. Next, the cavity unit 1 is mounted again between the movable side mold plate 4 and the fixed side mold plate 6, heated for 10 minutes or more, and heated to 125 ° C.,
Next injection filling is performed. In addition, FIG. 12 (a),
The graph shown in (b) is a graph in which the resin pressure and the mold temperature are plotted on a chart that is fed at a constant speed. The chart is fed at high speed in the section indicated by A in the figure, and the horizontal axis is one scale. Indicates 1 second, and in the section indicated by B, the chart is fed at a low speed and the scale indicates 5 minutes.

(Problems to be Solved by the Invention) However, in such a conventional gate seal injection molding method, the cavity unit 1 is clamped by the molding machine 2 to raise the temperature of the molds 8 and 9 of the cavity unit 1. Since the cavity unit 1 is cooled while the cavity unit 1 is clamped by the molding machine 2 even after the injection and filling of the resin, the idle time of the molding machine is long. Therefore, even if the number of molds of the molding machine 2 is increased to increase the size of the molding machine 2 by, for example, 4 pieces or 8 pieces, the cost of the product increases because the molding cycle per resin molded product is long. There was a problem. Further, since the idle time after injection is long, the molten resin stays in the nozzle 7 of the molding machine 2 or the injection cylinder for supplying the molten resin to the nozzle 7 for a long period of time so that the quality of the resin is prevented. There is also a problem that the resin in the injection cylinder has to be purged as appropriate, resulting in a large loss of material.

(Object of the Invention) Therefore, the present invention provides a mold clamping member for clamping the mold of the cavity unit, and after the resin is injected into the cavity, the mold is clamped by the mold clamping member and the gate seal is performed to reduce the resin pressure. At this time, the cavity unit is taken out and cooled alone to shorten the molding cycle per resin molded product, eliminate the loss of the material, and reduce the cost of the product.

(Structure of the Invention) In order to achieve the above object, the present invention comprises a pair of molds that can come into contact with and separate from each other, and has a cavity between the pair of molds and a sprue that communicates with the cavity is a mold. The cavity unit formed in is heated to a temperature above the glass transition point of the resin to be injection-molded, and the cavity unit is clamped by the mold clamping mechanism of the molding machine to melt the melted resin into a cavity through a sprue. , The gate provided in the sprue of the cavity unit is closed, and the cavity unit is gradually cooled to the heat deformation temperature of the resin while the injected resin is confined in the cavity, and then the cavity unit is released from the mold clamping mechanism. In a gate seal injection molding method for separating a pair of molds and taking out a resin molded product, Provided with a mold clamping member that clamps the mold and opens and closes the sprue, injects molten resin into the cavity and confine it in the cavity by the mold clamping member, the cavity unit is cooled and the pressure of the resin drops to a specified value. At this time, the cavity unit releases the cavity unit from the mold clamping mechanism of the molding machine while the mold clamping member self-holds the mold clamping force against the resin pressure, and the cavity unit alone cools the resin. It is characterized by having done.

 Hereinafter, specific description will be given based on examples of the present invention.

1 to 5 are views showing a first embodiment of the present invention. First, the configuration will be described.

In FIG. 1, 21 is a cavity unit, and the cavity unit 21 is composed of a pair of molds 22 and 23. On the other hand, one of the molds 22 and 23 is a concave portion 26 of a movable side mold plate 26 provided on a moving die plate 25 of a molding machine 24.
The other mold 23 is mounted on the fixed side die plate 27 of the molding machine 24, which is mounted on the fixed side die plate 27 of the molding machine 24 so as to face the movable side die plate 26. And
The molds 22 and 23 are driven by a mold clamping mechanism 29 of a molding machine 24, and can be brought into contact with and separated from each other by a movable die plate 25 that is close to and away from the fixed side die plate 27. Further, the molds 22 and 23 are formed with a pair of concave portions 30a and 30b facing each other, and the pair of concave portions 30a and 30b form the cavity 30 of the cavity unit 21, respectively. Further, the mold 23 is formed with a sprue 31 communicating with the recess 30b, that is, communicating with the cavity 30, and the molten resin injected from the injection nozzle 32 of the molding machine 24 is injected into the injection hole 33 of the fixed-side mold plate 28 and It is injected into the cavity 30 through the sprue 31.

On the other hand, the recesses 26a and 28a formed in the movable side mold plate 26 and the fixed side mold plate 28, respectively, are open at the bottom in the figure, and the pair of molds 22 and 23 of the cavity unit 21 have a pair of vertically long Holes 22a and 23a are formed. hole
The lower ends of both 22a and 23a are opened downward, and a pair of holes 22a
The upper end of one hole 22a of a and 23a is sealed near the recess 30a, and the upper end of the other hole 23a is open to the sprue 31. In FIGS. 1 and 2, reference numeral 34 denotes a U-shaped mold clamping member, which is a pair of engaging portions which are formed at both ends of the bar 34a and the bar 34a so as to project substantially at right angles to the bar 34a and which are provided in equilibrium with each other. It has 34b and 34c. Of the engaging portions 34b and 34c, the engaging portion 34b
Is inserted into the hole 22a of the mold 22, and similarly the engaging portion 34c is
Is inserted into the hole 23a. Then, the inner surface 34d of the engaging portion 34b
The engaging portion 34b is formed with a taper that shrinks upward in the figure, and the molds 22 and 23 are firmly clamped by the mold clamping member 34 due to the wedge effect of the taper.
When the engaging portions 34b and 34c are shallowly inserted into the holes 22a and 23a, the engaging portion 34c opens the sprue 31, and when these are deeply inserted, the tip of the engaging portion 34c. Part seals the sprue 31, that is, the mold clamping member 34.
Has a function as a gate for closing the pair of molds 22 and 23 and opening and closing the sprue 31.

 Next, the operation will be described.

In FIGS. 1 and 3, the movable die of the movable die plate 25
The mold 22 of the cavity unit 21 is mounted in 26, and similarly the mold 23 is mounted in the fixed-side mold plate 28 of the fixed-side die plate 27. Then, the mold clamping mechanism 29 of the molding machine 24 is driven, the pair of molds 22 and 23 are brought into contact with each other and clamped, and the cavity unit 21 is made into a cavity by a heater (not shown).
It is heated to a temperature exceeding the glass transition point of the resin injected into 30, for example, 125 ° C. Next, as shown in FIGS. 1 and 4, the engaging portions 34b and 34c of the mold clamping member 34 are connected to the holes 22 of the molds 22 and 23.
The cavity unit 21 is inserted into a and 23a respectively.
Is independently clamped by the mold clamping member 34. And
The resin melted by the injection nozzle 32 is
Is injected into the cavity 30 via the injection hole 33 and the spool 31 of the mold 23, and the pressure of the resin in the cavity 30 reaches, for example, 1000 to 1500 kgf / cm ² at the beginning of filling. At this point, the engaging portion 34c of the mold clamping member 34 is inserted into the position where the injection hole 33 is opened, and the resin pressure is supported by the mold clamping mechanism 29. When the injection of resin into the cavity 30 is completed,
The mold clamping member 34 is inserted further deeply so that the engaging portion 34c closes the sprue 31 and the resin is confined in the cavity 30, that is, the gate unit is cooled, and the cavity unit 21 is cooled. By cooling the cavity unit 21, the pressure of the resin in the cavity 30 reaches a predetermined value, for example 200 to 400.
When the pressure decreases to kgf / cm ² , as shown in FIG. 5, the mold clamping mechanism 29 retracts and the cavity unit 21 keeps the mold clamping force against the resin pressure by the mold clamping member 34. Then, the mold clamping mechanism 29 of the molding machine 24 is released. Further, the cavity unit 21 is removed from the movable side mold plate 26, and is cooled alone, for example, by natural cooling, and after the cooling is completed, the mold clamping member 34 is removed from the cavity unit 21, and the resin molding in the cavity 30 is performed. The product is taken out as a product.

Here, as shown in FIG. 12, when acrylic resin is used as the resin material, in this embodiment, the resin pressure is reduced to ²⁰⁰ to 400 kgf / cm ² after about 2 minutes from the start of injection and filling of the resin. In D, since the cavity unit 21 self-holds the mold clamping force sufficient to withstand the resin pressure by the mold clamping member 34, the mold clamping mechanism 29 moves the cavity unit 21 into the cavity unit.
21 can be opened. Then, the cavity unit 21 is removed from the molding machine 24 and gradually cooled by itself, and another cavity unit 21 is attached to the molding machine 24,
The next molding operation can be started. That is, even in the case of the single cavity unit 21, the molding cycle is about 2 minutes, and the molding cycle can be remarkably shortened. In this case, if the number of cavity units 21 per molding machine 241, the slow cooling time and the temperature rising time of the cavity units 21 are 30 minutes and 6 minutes, respectively, and about 15 units, efficient recycling is possible. It is possible.

Thus, according to this embodiment, the cavity unit
A mold clamping member 34 for clamping the pair of molds 22 and 23 of 21 is provided, and the molds 22 and 23 after resin injection into the cavity 30 are clamped.
The mold is clamped to 34, the gate is sealed, and when the resin pressure drops, the cavity unit 21 is taken out and cooled independently, which shortens the molding cycle per resin molded product and reduces material loss. It is possible to solve the problem and increase the accuracy of the resin molded product. As a result, the cost of the product can be reduced and the following effects can be obtained.

(1) When the number of cavity units is one, full operation can be performed with a small molding machine, so that equipment cost can be reduced.

(2) Since the mold forming the cavity unit is downsized, it becomes easy to handle the mold and adjust the eccentricity,
In addition, it is easy to make minor changes to the molds, and it is possible to support production plans for high-mix low-volume production.

(3) Since the retention of resin in the injection cylinder is eliminated,
The quality of molded products can be improved.

(4) Since the cavity unit is removed from the molding machine and cooled alone, the quality of the molded product can be easily controlled by separately setting the slow cooling conditions of the cavity unit.

Next, a second embodiment of the present invention will be described. In this embodiment, a bolt is applied as a mold clamping member of the cavity unit.

In FIG. 6, 35 is a mold 22 of the cavity unit 21.
Is a plurality of mold clamping bolts that penetrate through and are screwed into the mold 23. One of the multiple mold clamping bolts 35 Mold clamping bolt 35
In a, a through hole 3 is formed at a position where it engages with a sprue 36 formed between the molds 22a and 23 and is orthogonal to the axis of the mold clamping bolt 35a.
7 is provided, and as shown in FIGS. 7 and 8, the sprue 36 is opened and closed by rotating the mold clamping bolt 35a. Then, after the resin is injected into the cavity 30, the cavity unit 21 is clamped by another mold clamping bolt 35, and the spool 36 is closed by one mold clamping bolt 35a, so that the gate seal injection molding method can be performed. . The other configurations and operations are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained in this embodiment.

(Effect) According to the present invention, a mold clamping member for clamping the mold of the cavity unit is provided, and after the resin is injected into the cavity, the mold is clamped by the mold clamping member and gate sealing is performed, and the resin pressure is reduced. Since the cavity unit is sometimes taken out and cooled alone, the molding cycle per resin molded product can be shortened and the loss of the material can be eliminated. As a result, the cost of the product can be reduced, and further, the facility cost can be reduced, the handling of the mold can be facilitated, the product quality can be improved, and the production plan can be flexibly dealt with.

[Brief description of drawings]

1 to 5 are views showing a first embodiment of a gate seal injection molding method according to the present invention. FIG. 1 is a front sectional view showing the configuration of a cavity unit, and FIG. 2 is a mold clamping member having a cavity. FIG. 6 is a perspective view showing a state where the unit is attached to the unit, FIGS.
FIG. 8 is a diagram showing a second embodiment of the gate seal injection molding method according to the present invention, FIG. 6 is a front sectional view showing the structure of the cavity unit, and FIGS. 7 and 8 are partial sectional views showing the action thereof. FIGS. 9 to 12 are views showing a conventional gate seal injection molding method, FIG. 9 is a front view showing the structure of the molding machine, and FIG. 10 is a perspective view showing the structure of the cavity unit. Fig. 11 is a view taken along the line XI-XI in Fig. 10, Fig. 12
The figure is a graph showing changes in the resin pressure and the mold temperature. 21 …… Cavity unit, 22,23 …… A pair of molds, 24 …… Molding machine, 29 …… Clamping mechanism, 30 …… Cavity, 31 …… Sprue, 34 …… Clamping member (gate).

Claims (1)

(57) [Claims] 1. A cavity unit formed of a pair of molds capable of abutting and separating from each other and having a cavity between the pair of molds and communicating with the cavity is formed by injection molding a cavity unit. It is heated to a temperature above the glass transition point of the resin, the cavity unit is clamped by the mold clamping mechanism of the molding machine, and the molten resin is injected into the cavity through the sprue. The cavity unit is gradually cooled to the heat deformation temperature of the resin while the gate is closed and the injected resin is confined in the cavity, then the cavity unit is released from the mold clamping mechanism, and the pair of molds are separated to separate the resin. In the gate seal injection molding method that takes out the molded product,
The cavity unit is provided with a mold clamping member that clamps a pair of molds and opens and closes the sprue, injects molten resin into the cavity and confine it in the cavity by the mold clamping member, and the cavity unit is cooled to cool the resin. When the pressure drops to a predetermined value, the cavity unit releases the cavity unit from the mold clamping mechanism of the molding machine while maintaining the mold clamping force against the resin pressure by the mold clamping member. A gate seal injection molding method, characterized in that the resin is cooled.