JPH0338103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an injection molding method suitable for use in thick-walled molded products that require a relatively long cooling time after injection filling.

(Prior Art) In injection molding using synthetic resin materials, an injection device is connected to a closed mold, and molten resin material is injected and filled into the mold cavity from the injection device to perform molding.

Conventionally, in such injection molding methods, the mold after injection filling takes a certain cooling time to sufficiently solidify the molded product, and after this cooling time has elapsed, the mold is opened, the molded product is ejected, and the mold is clamped (mold closed). I'm going. In addition, the injection device after injection filling is an injection plunger (injection device) in parallel with the cooling process.
A new material is immediately supplied to the mold, and the material is kept in a molten state under constant temperature control until the mold is completely clamped.

(Problems to be Solved by the Invention) However, the conventional injection molding method described above has the following problems.

In other words, the injection molding cycle process time varies from a few seconds to several tens of minutes depending on the size, wall thickness, shape, material, etc. of the molded product, but it is the largest proportion of the cycle process time. The process that occupies most of the time is the mold cooling process, which generally occupies 50% to 90% of the total process time. Note that the cooling process time increases as the thickness of the molded product increases and the specific heat of the material increases.

By the way, as described above, in the injection device, the resin material is maintained in a molten state under constant temperature control during the cooling process. For this reason, relatively thick molded products such as optical lenses require several tens of minutes of cooling time while remaining in a high-temperature molten state, and even when the mold is opened,
This will be maintained until the molded product is ejected and the mold is clamped.

Normally, the temperature of the resin material in the injection device (heating tube) is set within a range where material deterioration due to heat does not pose a problem, but in the case of resin, even within the set molding temperature range, there is a considerable amount of temperature. There is a problem that deterioration occurs, and the longer the residence time under such conditions, the more the deterioration progresses and the strength of the molded product decreases. Furthermore, if the deterioration progresses, depending on the material of the resin, it may decompose and become impossible to be molded.

This is a serious problem, especially in optical components that require high quality, such as plastic lenses, because even a slight change in quality directly affects the product performance.

(Means for solving the problem) In order to solve the above problem, the present inventor proposed a method disclosed in Japanese Utility Model Application Publication No. 59-24321, that is, after injection filling into the mold is completed. We adopted a method that delays the start of measurement and completes the measurement process at the same time as cooling is completed.

In this method, deterioration of the molding material accumulated at the tip of the heating cylinder due to thermal history can be prevented if the start of metering can be delayed without increasing the temperature of the heating cylinder and the injection nozzle.

However, it has been found that the injection nozzle connected to the cooled mold is likely to become clogged.

For this reason, when the set temperature of the injection nozzle is raised to prevent clogging of the injection nozzle, it is necessary to also raise the set temperature of the heating cylinder to maintain the temperature balance with the heating cylinder. However, this will still result in deterioration of the molding material due to heat.

Based on this knowledge, the inventors of the present invention decided to delay the start of metering after injection and filling into the mold than before, and to temporarily release the connection between the injection nozzle and the cooled mold to speed up the injection process. The present invention was arrived at as a result of consideration and consideration of the possibility of avoiding an increase in the set temperature of the heating cylinder including the nozzle and preventing clogging of the injection nozzle.

That is, the present invention uses an injection device equipped with a heating cylinder into which a screw is inserted and an injection nozzle at the tip, and when injection molding a thick molded product such as a lens, the inside of the heating cylinder is heated. The material supplied from the hopper, melted and accumulated at the tip of the heating cylinder is injected and filled into the closed mold connected to the tip of the injection nozzle through the injection nozzle.
The connection between the mold and the injection nozzle is temporarily released for a predetermined hold time set corresponding to the cooling time of the mold without supplying material from the hopper to the heating cylinder, and after the cooling hold time elapses, the mold is removed. This injection molding method is characterized by reconnecting the hopper and the injection nozzle and restarting the supply of material from the hopper to the heating cylinder.

(effect) Next, the operation of the present invention will be explained.

In the injection molding method according to the present invention, after the material is injected into the mold from the injection device, when a new material is supplied to the injection plunger, the supply is not performed immediately after the injection, but a certain holding time is set. As a result, the melting time of the material is shortened, and in particular, since the holding time is set in accordance with the cooling time of the mold, the melting time under heating is minimized.

Moreover, since the connection between the cooled mold and the injection nozzle is temporarily released, heat transfer between the mold and the injection nozzle can be substantially interrupted.

Therefore, it is possible to avoid a temperature drop due to heat dissipation from the injection nozzle to the mold, and it is also possible to avoid increasing the set temperature of the injection nozzle and heating cylinder, thereby reducing the thermal history of the molding material accumulated at the tip of the heating cylinder. It is possible to achieve further shortening.

Furthermore, since heating of the mold due to the heat of the injection cylinder can be prevented, the cooling time can be shortened, and the molding cycle can also be shortened.

(Example) Hereinafter, preferred embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a longitudinal sectional side view of an in-line screw type injection molding machine suitable for carrying out the injection molding method according to the present invention.

First, the overall configuration of the in-line screw injection molding machine 1 will be explained with reference to the same figure.

The molding machine 1 includes an injection device 3 disposed on one side of a machine stand 2 and a mold device 4 disposed on the other side.

The injection device 3 includes a heating cylinder 30 forming the first half thereof, and has an injection nozzle 31 at its front end, and its rear end is connected to an injection cylinder 32 forming the second half of the device 3. There is a screw 3 inside the heating cylinder 30.
3 (injection plunger 6) is inserted, and its rear end is connected to the injection ram 34 in the injection cylinder 32. The injection ram 34 is moved back and forth by pressure oil supplied to the front oil chamber 32a or the rear oil chamber 32b within the cylinder 32. On the other hand, an oil motor 35 is disposed at the rear end of the injection cylinder 32, and this rotating shaft 36 is connected to the injection ram 34.
Connect the spline to the rear end of the In addition, the heating cylinder 30
A hopper 37 for supplying the resin material W to the injection plunger 6, that is, the screw 33, is provided at the rear end.

On the other hand, the bottom of the injection cylinder 32 is connected to the slider 10.
The slider 10 is mounted on the machine base 2 so as to be able to move forward and backward with respect to the mold device 4.

The reason why the connection is made here is to prevent the material W from leaking out from the injection nozzle 31 due to back pressure when measuring in the next step.

On the other hand, the mold device 4 includes a fixed platen 40 which is fixed upright at an intermediate portion on the machine stand 2, and this fixed platen 40 and the slider 10 are connected by a moving device 11. The device 11 includes, for example, a moving cylinder 12 coupled to a slider 10, and a piston (piston rod) inserted into the cylinder 12 and having its tip coupled to a fixed plate 40.
It can be configured from 13. Therefore, the moving cylinder 12
The entire injection device 3 can be connected to or disconnected from the mold device 4 by means of pressure oil supplied to the mold device 4.

On the other hand, a fixed mold 41 is fixedly installed on the fixed platen 40, and a plurality of tie bars 42 are fixedly installed around the periphery.
The tie bars 42 extend toward the movable mold side, and their tips are coupled to a support portion 44 that is integral with the mold clamping cylinder 43.

A movable platen 45 is slidably attached to the tie bars 42. A movable mold 46 facing the fixed mold 41 is fixed to the movable platen 45, and the tip of a clamping ram 47 inserted into the mold clamping cylinder 43 is fixed.

The movable mold 46 and the fixed mold 41 constitute a mold 5, and a cavity 49 for molding a relatively thick molded product (for example, a lens) is formed on the opposing surface (parting line). It communicates with a material filling port 50 at the outer end of the fixed mold 41 via a runner, sprue, etc.

In addition, a fixed plate 40 located around the filling port 50
is opened and a nozzle introduction port 51 is provided.

Next, the overall operation of the injection molding machine 1 including the injection molding method according to the present invention will be explained with reference to FIGS. 2 to 4. FIGS. 2 to 4 are longitudinal sectional side views showing a part of the mold device and injection device in each step.

(a) First, FIG. 2 shows the state immediately after the injection device 3 is connected to the mold 5 and material is injected and filled into the mold 5 by advancing the screw 33 (injection plunger 6).

(b) After the gate sealing by injection filling is completed, the movable cylinder 12 is operated to move the injection device 3 backward as shown in FIG. That is, the connection between the mold 5 and the injection device 3 is released. After this connection is released, the injection device 3 remains in the same state. The reason for releasing the connection in this way is to prevent the injection nozzle 31 from dissipating heat due to contact between the mold 5 and the injection nozzle 31, solidifying the material inside the nozzle based on this heat dissipation, and further preventing clogging of the nozzle and preventing the mold from being This is to prevent heat conduction. Note that it is not impossible to carry out the process even if the connection is not released, but in this case, cooling of the mold is inhibited and the temperature of the injection nozzle 31 must be further increased.

On the other hand, in the mold 5, the cooling process begins immediately after injection and filling.

By the way, if the necessary cooling time in the cooling process is Tc, the holding time Ts of the injection device 3 after the above-mentioned disconnection is appropriately set in accordance with the cooling time Tc. In other words, Tc>Ts,
When Tc is large, Ts is increased, and when Tc is small, Ts is decreased.

(c) When the holding time Ts has elapsed, the moving cylinder 12
is activated, thereby advancing the injection device 3 and connecting it to the mold 5 (nozzle touch).

(d) In this state, when the motor 35 is rotated, the injection ram 34 and further the screw 33 are rotated, and the material W in the hopper is transferred to the front of the screw 33 by the rotating action of the screw 33, and the heating cylinder 30 is It is melted and accumulated by the heating effect and the shearing effect of the screw when being kneaded and transferred by the rotation of the screw 33. Due to this accumulation, the screw 33 gradually retreats, and once it has retreated to a predetermined position, metering is completed and the motor 35 is stopped. This state is shown in FIG.

(e) Next, the moving cylinder 12 is operated, the injection device 3 is moved backward, and the connection between the mold 5 and the injection device 3 is released.

(f) After completing step (e) above, the mold 5 is opened and the molded product is discharged. Since the mold opening is performed after the cooling time Tc in the mold 5 ends, the holding time Ts is the cooling time when the above (e) ends.
It is desirable to set it immediately before Tc ends.

(g) After that, the mold clamping cylinder 43 is operated to clamp the mold (the state shown in Fig. 1), and the moving cylinder 12 is further operated to advance the injection device 3,
The mold 5 and the injection device 3 are connected.

(h) Then, in this state, the injection cylinder 32 is operated to advance the injection ram 34, that is, the screw 33, to perform injection filling. As a result, the material W is filled into the cavity 49, and the screw 33 is brought to the most advanced position. This state is shown in FIG.

Therefore, by continuously repeating the cycle steps (a) to (h), molding is performed in sequence.

Although the embodiments have been described in detail above, the present invention is not limited to these embodiments. For example, although the mold clamping device and the moving device are of the direct pressure type, other known driving means such as a motor can be used. Furthermore, although an in-line screw type injection device is illustrated as an example, other injection devices such as a plunger type can be used. In addition to the above, detailed configurations, procedures, etc. may be arbitrarily changed without departing from the spirit of the present invention.

(Effects of the Invention) As described above, the injection molding method according to the present invention injects and fills the material from the injection device into the closed mold for a predetermined holding time set corresponding to the cooling time of the mold. The mold and the injection device are disconnected, and after the holding time has elapsed, the mold and the injection device are reconnected and the material is supplied to the injection plunger. Also, the melting time of the material during molding does not become unnecessarily long. Therefore, the material can be molded in the best possible condition without quality deterioration such as deterioration or decomposition. Therefore, it is particularly suitable for use in molding thick optical lenses that require a long cooling time, and high-quality molded products can be obtained.

Furthermore, since heating of the mold caused by the injection nozzle can be prevented, the molding cycle can be shortened.
It is possible to improve molding productivity.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional side view of an in-line screw type injection molding machine suitable for carrying out the injection molding method according to the present invention, and FIGS. FIG. 2 is a longitudinal side view showing a part of the injection device. In the drawings, 1... In-line screw type injection molding machine, 3... Injection device, 4... Mold device, 5... Mold, 6
...Injection plunger.

Claims (1)

[Claims] 1. When injection molding a thick molded product such as a lens using an injection device equipped with a heating cylinder into which a screw is inserted and an injection nozzle at the tip, the heating cylinder The material supplied from the hopper and melted and accumulated at the tip of the heating cylinder is injected and filled into a closed mold connected to the tip of the injection nozzle through the injection nozzle, and then heated from the hopper. The connection between the mold and the injection nozzle is temporarily released for a predetermined hold time set corresponding to the cooling time of the mold without supplying material to the cylinder, and after the cooling hold time elapses, the mold and the injection nozzle are disconnected. An injection molding method characterized by reconnecting the hopper and restarting the supply of material from the hopper to the heating cylinder.