JPH0720636B2 - Injection molding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an injection molding method for preventing thread pulling that occurs in a sprue opening when a molded product is taken out after filling with a resin in injection molding.

[Conventional technology]

Generally, in injection molding, a molded product is taken out after the temperature of the molded product after the resin is filled is cooled to a temperature not higher than the softening point. However, since the sprue portion is in contact with the high temperature nozzle, cooling may be delayed, and the temperature of the sprue tip portion may exceed the softening point when the molded product is taken out.

For this reason, as shown in FIG. 4, when the molded article 51 is taken out, a phenomenon called thread pulling occurs in which the softened resin of the sprue tip portion 53 extends into a thread shape with the nozzle 31 and solidifies.
In the figure, 4 is a thread pulling portion.

When this stringing occurs, the fixed mold 11
The thread pulling part 4 is sandwiched between the movable mold 21 and the movable mold 21. As a result, the parting surfaces 11a, 21a are worn or deformed, and burrs are generated on the molded product, or in some cases, the mold is damaged or damaged. It was causing a malfunction.

Conventionally, the following methods have been taken to prevent this stringing.

The first method is to take a long cooling time after filling the resin and take out the molded product after the resin in the sprue portion is solidified. That is, since the high temperature nozzle is in contact with the sprue part, the cooling will be delayed and the solidification will be final.Therefore, the nozzle should be separated from the sprue part after filling, and after the sprue part has solidified, the mold should be opened and the molded product should be taken out. To

The second method is a method in which the resin temperature at the time of molding is set low and molding is performed.

[Problems to be solved by the invention]

However, in the first method of the above-mentioned conventional example, it takes time to solidify the resin in the sprue portion to the extent that it does not cause stringing due to cooling, the molding cycle becomes long, and it is not suitable for mass-produced products. is there.

In the second method, the fluidity of the resin deteriorates, and the injection pressure has to be increased, resulting in a problem that the dimensional accuracy of the molded product is adversely affected.

〔Purpose〕

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to prevent so-called stringing of the molten resin generated between the nozzle and the sprue opening when the nozzle retracts after the resin is filled. An object of the present invention is to provide an injection molding method that enables the above.

[Means for solving problems]

The above object is according to the present invention, in an injection molding method for filling a melt through a nozzle into a mold through a sprue opening and solidifying the melt in the mold to obtain a molded article; This is achieved by an injection molding method, which comprises injecting a cooled gas and / or liquid into the vicinity of the sprue opening at the time of leaving the nozzle after filling the melt in the mold.

〔Example〕

Hereinafter, embodiments according to the present invention will be described specifically and in detail with reference to the drawings.

FIG. 1 is a vertical sectional view of a mold apparatus for carrying out the injection molding method of the present invention, and FIG. 2 is a vertical sectional view of the mold apparatus for explaining the operation of the present invention.

In FIG. 1, 11 is a fixed-side die, which is attached to a fixed-side platen 13 via a base plate 12.
Reference numeral 21 denotes a moving side mold, which is attached to the moving side platen 23 via a base plate 22. The fixed-side mold 11 and the movable-side mold 21 form a cavity 41 corresponding to the shape of the molded product. 42 is a sprue and 43 is a sprue opening.

Reference numeral 31 is a nozzle attached to the heating cylinder 32, and 33 is a screw. Reference numeral 1 denotes an air supply hole formed in the base plate 12, and one end portion 1a thereof is connected to a compressor 62, which is a pressurized air supply source, via a solenoid valve 61. Further, the other end 1b of the air supply hole 1 is opened near the sprue opening 43 so as to inject air.

The injection molding method of the present invention having the above structure will be described.

As shown in FIG. 1, with the nozzle 31 pressed against the sprue opening 43, the screw 33 is pressed to melt the molten resin 34 and sprue 42
To inject and fill the cavity 41. After completion of the filling, the nozzle 31 is retracted as shown in FIG. 2 after a lapse of a predetermined time. At this time, the softened resin 34a remains between the sprue opening 43 and the nozzle 31. When the solenoid valve 61 is operated to inject the cooling air from the opening 1b of the air supply hole 1 toward the vicinity of the sprue opening, the resin 34a is cooled and solidified. Then, the movable platen is retracted, the mold is opened, and the molded product 51 is taken out, whereby the resin 34a is pulled and cut without causing stringing.

FIG. 3 is a partial cross-sectional view of a mold apparatus showing another embodiment of the present invention, more specifically an enlarged cross-sectional view of the sprue opening.

In the figure, 71 is a sprue bush, 72 is a ring for preventing the sprue bush 71 from coming off, and is fixed to the base plate 12 by a bolt or the like not shown. Reference numeral 73 denotes an air supply hole formed in the base plate 13, one end of which is connected to a compressor 62 which is a pressurized air supply source through an electromagnetic valve 61. Reference numeral 74 is an air supply hole formed in the ring 72, and the supply holes 73 and 74 are arranged such that the positions of the openings 73b and 74b thereof coincide with each other, as shown in the figure. Supply hole
The other opening 74a of 74 opens toward the vicinity of the sprue opening 43. In this embodiment as well as in the above-mentioned embodiments, after the completion of filling, the solenoid valve 61 is operated when the nozzle retracts to open the opening.
Cooling air is jetted from 74a. The operation is similar to that of the above embodiment.

The injection molding method of the present invention is not limited to the embodiment described above, and any other suitable method may be used as long as air or the like is injected near the sprue opening. Further, without using the solenoid valve 61, air may be constantly ejected after passing through an appropriate throttle.

Further, as a medium for injecting in the vicinity of the sprue opening, other cooling medium (for example, cooling gas, cooling liquid, etc.) may be used instead of air.

〔The invention's effect〕

As described above, by cooling the vicinity of the sprue opening, it is possible to prevent so-called stringing of the softened resin when the molded product is taken out. Therefore, it is not necessary to use special molding conditions to prevent stringing as in the conventional case, and it is possible to prevent damage to the mold.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a mold apparatus for carrying out the injection molding method of the present invention, FIG. 2 is a vertical sectional view of a mold apparatus for explaining the operation of the present invention, and FIG. 4 is a partial cross-sectional view of a mold apparatus showing the embodiment of FIG. 4, and FIG. 4 is a vertical cross-sectional view showing a conventional example of the mold apparatus. 1: Air supply hole, 11: Fixed side mold, 21: Moving side mold, 31: Nozzle, 41: Cavity, 41: Sprue, 43: Sprue opening.

Claims (2)

[Claims] 1. An injection molding method in which a melt is filled into a mold through a sprue opening through a nozzle, and the melt is solidified in the mold to obtain a molded article; melting in the mold An injection molding method, characterized in that after the object is filled, the cooled gas and / or liquid is injected into the vicinity of the sprue opening when the nozzle is detached. 2. The cooled gas and / or liquid is cooling air, according to claim (1).
The injection molding method according to the item.