JPH0716416Y2 - Injection mold - Google Patents

Description

[Detailed Description of the Invention] (Industrial field of application) The present invention relates to an injection molding die, and in particular, injects a gas into a molten resin in the die to make a thick wall or an uneven wall portion hollow. The present invention relates to an injection molding die provided with a gas injection nozzle for improving sink marks and warpage of a molded product.

(Prior Art) Conventionally, gas injection injection molding, in which a gas is injected into a molten resin in a cavity of a mold to form a thick portion or an uneven thickness portion in a hollow shape, is effective in improving sink marks and warpage. This is well known.

Then, as a means for injecting gas into the molten resin, a special nozzle a as shown in FIG. 6 is provided in the mold b. The special nozzle a includes a nozzle body c,
The nozzle body (c) is provided with a valve body (d) that is movable back and forth, and the tip of the valve body (d) is arranged so as to face a molding portion that molds a thick wall portion such as a boss or an uneven thickness portion.

Therefore, at the time of injection molding, when gas is supplied into the nozzle body c, the valve body d retreats in the P direction in the figure against the urging force of the spring e, and between the tip of the valve body d and the nozzle body c. A hollow is created by injecting gas into the resin of the boss molding part from this clearance, and it is generated in the sink mark such as the thick part or uneven part such as the boss part, or the molded product I was trying to improve the sled.

(Problems to be solved by the invention) However, in the above-mentioned conventional one, when the filling of the resin such as a short shot varies, gas may not be introduced depending on the shape of the boss portion. Parts may collapse and gas may enter from other parts. Therefore, there is a problem that stable molding is difficult.

(Means for Solving the Problems) An injection molding die of the present invention is an injection molding die for molding a molded product having a thick portion or an uneven thickness portion, wherein the thick portion or the uneven thickness portion is formed. A gas injection nozzle having a valve body is provided facing the molding portion of the cavity, and the tip of the valve body is arranged so as to project from the injection port formed facing the molding portion of the cavity into the molding portion, The valve body is provided so as to move forward and backward so as to open and close the inlet by the pressure of the supplied gas, and when the valve body retracts due to the pressure of the gas, the gas is injected into the molding portion of the cavity through the inlet. It is composed of.

(Operation) At the time of injection molding, first, resin is injected into the cavity while the tip of the valve body of the gas injection nozzle is projected to the molding portion of the cavity for molding the thick portion or the uneven thickness portion. As a result, a recessed boss is formed on the bottom surface, and gas is supplied to the gas injection nozzle immediately after the resin is filled in the molding portion and immediately after the injection is completed, or after a certain time after the injection is completed.
As a result, the valve body retreats and gas is injected from the tip of the valve body into the resin filled in the molding part.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a gas injection nozzle provided in an injection molding die according to the present invention.

In the figure, 1 is a part of the cavity formed in the mold. In the cavity 1, a boss molding portion 1a is formed so as to mold the boss 3 on the molded product 5 as shown in FIG. Then, the cavity 1 on the bottom side of the boss 3
A gas injection nozzle 10 is provided so as to face the boss molding portion 1a.

The gas injection nozzle 10 includes a nozzle body 11 and this nozzle body.
The valve body 16 provided in 11 and the valve body 16
A spring 20 for urging the boss-formed portion 1a side and an adjusting screw 21 screwed to the rear end of the nozzle body 11 for adjusting the urging force of the spring 20.

The nozzle body 11 has a storage space 12 for storing the valve body 16 therein. The storage space portion 12 is composed of a small diameter space portion 13 and a large diameter space portion 15 formed in a tubular shape. The small-diameter space portion 13 has a tip portion formed to have a gradually smaller diameter, and an injection port 14 is formed at the tip of the small-diameter space portion 13 facing the boss molding portion 1a. Further, the nozzle body 11 is formed with a gas inflow passage 19 for supplying gas from the gas supply source (not shown) to the small diameter space portion 13.

The valve body 16 includes a piston member 18 near the rear end of the shaft member 17.
Are integrally provided. The valve element 16 is loosely fitted in the small diameter space 13 from the tip to the middle, and the piston member 18 is slidably fitted in the large diameter space 15.
The spring 20 is interposed between the piston member 18 and the adjusting screw 21, and the valve body 16 is urged by the urging force of the spring 20.
Is pressed toward the boss molding portion 1a. Thereby, the tip of the valve body 16 is configured to close the injection port 14 of the small-diameter space portion 13. Here, when the injection port 14 is closed by the tip of the valve body 16, the tip of the valve body 16 is inserted through the injection port 14 and is arranged so as to project from the injection port 14 to the boss molding portion 1a by an appropriate length. . The shape of the tip of the valve body 16 is not particularly limited,
Basically, a conical shape that facilitates mold release as shown in the drawing is preferable.

The projecting length for projecting the tip of the valve body 16 into the boss molding 1a is
The shape is determined in consideration of the shape of the boss 3 molded by the boss molding portion 1a, that is, the height and diameter of the boss 3, and the position of the boss 3 with respect to the gate. Optimally, 1/2 to 1/3 of the height of the boss 3 is preferably projected. If the protrusion length relative to the height of the boss 3 is greater than 1/2, the amount of molten resin in the boss 3 is reduced, and it becomes difficult for gas to enter. If the protrusion length is less than 1/3, the gas is in the molten resin. There is a risk of escaping into the gap between the resin and the mold without entering into.

Reference numeral 22 in the drawing is provided on the peripheral surface of the piston member 18, and gas supplied from the gas inflow passage 19 to the small diameter space portion 13 flows into the large diameter space portion 15 on the side where the spring 20 is provided. This is an O-ring that prevents

Next, the operation of the injection molding die thus configured will be described.

First, as shown in FIG. 1, the tip of the valve body 16 of the gas injection nozzle 10 is moved to the cavity 1 by the urging force of the spring 20.
The resin is injected into the cavity 1 while being protruded from the boss molding portion 1a. The injected resin is filled in the boss molding portion 1a of the cavity 1 to form the boss 3 having a concave bottom surface. Then, the gas is injected between immediately after the resin is filled in the boss-molded portion 1a and immediately after the injection is completed, or at a certain time after the injection is completed. At the time of this gas injection, the gas is supplied from the gas supply source to the small-diameter space portion 13 via the gas inflow passage 19, and the gas pressure presses the piston member 18 in the arrow Q direction.

As a result, the valve body 16 is retracted against the biasing force of the spring 20 as shown in FIG. 2, and a gap is formed between the tip of the valve body 16 and the inlet 14 to allow gas to flow. Therefore, the gas is smoothly injected into the boss 3 by pushing the recessed portion of the boss 3 formed in the boss forming portion 1a from this gap. When the gas injection is completed, the gas pressure in the small-diameter space 13 is weakened and the spring 20
The valve element 16 is moved by the urging force of, and the tip of the valve element again projects into the cavity 1 to close the injection port 14.

Then, the gas injected into the resin escapes from the gap between the boss 3 and the mold.

Since the gas is injected from the recessed portion of the boss 3 as described above, the gas can be easily injected and the shape of the boss 3 can be stabilized. The molded product thus obtained has a hollow in the uneven thickness portion or thick portion such as the boss 3, and it is possible to improve the sink mark and the warp by the gas pressure inside.

The table shows a test molded article A (FIGS. 4 and 5) having various bosses having different shapes, heights, and diameters using the injection molding die according to the present invention and the conventional injection molding die. reference)
The comparison result in the case of molding is shown.

The molding resin used was PP, and the molding conditions were an injection molding machine with a mold clamping force of 240 tons, the resin temperature was 240 ° C, the mold temperature was 40 ° C, and the gas pressure was 30 kg / cm ² .

As a result, the case where the gas was smoothly injected and the boss was able to be stably molded was evaluated as ◯, and the case where the boss was not stably molded was evaluated as x.

As can be seen from this table, by using the injection molding die of the present invention, gas can be smoothly injected and the boss can be stably molded.

The synthetic resin used in the present invention is not limited to the thermoplastic resin that can be used for injection molding, and a thermosetting resin can be used if necessary. The gas used in the present invention is preferably an inert gas such as nitrogen or air.

(Effects of the Invention) As described above, according to the present invention, the tip of the valve element is arranged so as to project into the molding portion of the cavity, and when the inside of the valve is retracted by the pressure of the gas, the gas is guided to the molding portion of the cavity. Since the gas is injected, it is possible to easily inject the gas into the thick wall portion or the uneven thickness portion, and it is possible to stabilize the shape of the thick wall portion or the uneven thickness portion.

[Brief description of drawings]

1 is a sectional view showing a resin filling state of an injection molding die according to the present invention, FIG. 2 is a sectional view showing a gas injection state of the injection molding die, FIG. 3 is a perspective view showing a boss, 4 and 5 are perspective views showing a test molded product molded by a test mold, and FIG. 6 is a cross-sectional view showing a conventional injection mold. 1 …… Cavity 3 …… Boss 10 …… Gas injection nozzle 11 …… Nozzle body 14 …… Injection port 16 …… Valve body

Claims (1)

[Scope of utility model registration request] 1. A gas for injection molding for molding a molded article having a thick wall portion or an uneven wall thickness portion, which has a valve body facing a molding portion of a cavity for molding the thick wall portion or the uneven wall thickness portion. An injection nozzle is provided, the tip of the valve body is arranged so as to project from the injection port formed facing the molding part of the cavity into the molding part, and the valve port is opened by the pressure of the gas supplied. An injection mold, which is provided so as to open and close so as to open and close, and is configured to inject gas into a molding portion of the cavity through an injection port when the valve body retracts due to gas pressure.