JPH08187752A - Injection molding method and machine - Google Patents

Abstract

PURPOSE: To stably perform gate cutting to obtain a clean cutting surface by lowering the injection holding pressure of a molding material to allow a male cutter to advance to fit the same in a female cutter and subsequently again increasing injection holding pressure. CONSTITUTION: When injection holding pressure is cut off at the time of the injection operation of a male cutter 34, the male cutter 34 is advanced by sufficiently small driving force without receiving the resistance force due to injection holding pressure to be fitted in a female cutter 28 and the increase of pressure in a sprue 20 or a runner 22 is reduced and a resin is prevented from entering the fitting gap of both female and male cutters 28, 34 to obtain a good cutting surface in a disc central hole 38. Next, injection holding pressure is increased to transfer to a cooling process and the molten resin 15 in a molding cavity 18 or the sprue 20 and the runner 22 is cooled and solidified.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an injection molding method and an injection molding machine for carrying out such a method, and more particularly to an injection molding method and an injection molding machine which can be advantageously applied to molding an optical disk substrate or the like.

[0002]

BACKGROUND ART In injection molding of synthetic resin or the like, an injection molding machine equipped with a mold clamping device equipped with a fixed mold and a movable mold and an injection device is generally used. After filling a predetermined resin material with an injection device at an injection filling pressure (injection primary pressure) into a molding cavity formed by mold matching, the injection holding pressure ( The molding operation is carried out by holding the injection secondary pressure) for a predetermined time, and after the cooling time has elapsed, the mold is opened and the molded product is taken out. Further, the fixed mold or the movable mold is provided with sprues or the like for guiding the molten resin injected by the injection device to the molding cavity, and is connected to the molding cavity through the gate.

By the way, the structure of the sprue, gate, etc. in such a mold is appropriately selected according to the size and shape of the molding cavity, the molding material and the like. One of them is a male cutter for a movable mold. The female cutters are provided on the fixed mold so as to face each other, and the male cutter is advanced toward the female cutter to be fitted into the female cutter in the injection holding step after the resin material is injected and filled into the molding cavity. A mold structure is known that is provided with a gate cut mechanism that cuts and separates the sprue part from the molded product.
In particular, it is preferably used for an injection molding machine having a disc gate-shaped gate structure such as an optical disc substrate used for CDs, LDs and the like.

However, in such a gate cut mechanism, the operation of advancing the male cutter and fitting it into the female cutter is performed under injection holding pressure, and therefore the male cutter must be moved forward against the resin pressure. Therefore, there is a problem that the resin easily enters the fitting gap between the male and female cutters due to the action of pressure when the male cutter moves forward, which causes burrs and the like in the gate cut portion.

Also, when the male cutter is advanced and fitted into the female cutter, the male cutter must be forcibly advanced against the resin pressure, so that the male cutter interferes with the opening of the female cutter. As a result, there is a problem in that scoring is likely to occur, which causes damage to the cutter parts, defective cutting of the gate cut portion, and the like.

In order to deal with such a problem, it is conceivable to lower the injection holding pressure and then advance the male cutter to perform gate cutting. If the injection holding pressure is lowered in the process, the resin pressure will not be sufficiently applied to the sprue part, so it will be difficult to properly form the cut part such as the sprue cut from the molded product, and the strength will be very weak. Therefore, when the mold is opened and the cut portion is released after being solidified by cooling, the cut portion is likely to be torn off in the middle and a part of the cut portion is likely to remain in the mold, which has a serious adverse effect on the subsequent molding operation. It was not a valid method.

Further, in Japanese Patent Publication No. 6-357, the center pin disposed inside the male cutter is retracted as the male cutter moves forward to absorb the resin pressure acting on the male cutter. Although a molding die for a disc having such a structure is disclosed, even in such a molding die,
In order to effectively prevent galling of both male and female cutters and burrs at the gate cut part, if you try to absorb the resin pressure sufficiently by retracting the center pin, the cut part such as sprue cut from the molded product will become normal. It was difficult to be formed and weakened in strength, and there was a risk that a part of the film would be torn off at the time of mold release and remain in the mold.

[0008]

The present invention has been made in view of the above-mentioned circumstances, and the problem to be solved is to stably perform a gate cut by a male and female cutter with a clean cut surface. (EN) A new injection molding method and an injection molding machine, in which cut parts such as sprues are normally formed and good mold releasability is obtained.

[0009]

In order to solve such a problem, a feature of the present invention resides in that a molding material is injection-filled into a molding cavity formed by fitting a fixed mold and a movable mold to each other. In the later injection holding step, the male cutter provided on the movable mold is moved forward,
At the time of gate cutting by fitting into the female cutter provided in the fixed mold, the injection holding pressure of the molding material is lowered to advance the male cutter, and after the male cutter is fitted into the female cutter, the male cutter is inserted again. There is an injection molding method for increasing the injection holding pressure.

Further, according to the present invention, the male cutter provided on the movable mold is advanced to be fitted into the female cutter provided on the fixed mold which forms a molding cavity in cooperation with the movable mold. In an injection molding machine equipped with a gate cutter mechanism that cuts the gate by, the injection holding pressure of the molding material injection-filled into the molding cavity is adjusted according to the forward movement of the male cutter, thereby maintaining the injection holding pressure. Another feature is an injection molding machine provided with injection holding pressure adjusting means for temporarily lowering the male cutter to move it forward.

[0011]

According to the method of the present invention, since the injection holding pressure is lowered when the male cutter is moved forward, the action of a large pressure on the male cutter can be avoided even when the male cutter is moved forward. Therefore, the fitting operation of the male cutter into the female cutter can be smoothly performed.

Therefore, even when the male cutter is moved forward, the action of a large pressure on the male cutter is avoided, the male cutter can be smoothly fitted into the female cutter, and galling of both male and female cutters is prevented. To get.

Further, even when the male cutter is fitted into the female cutter, the action of a large pressure on the male cutter can be avoided, and the resin or the like can be prevented from entering the fitting gap between the male and female cutters, and the gate cut portion can be prevented. It is possible to obtain a good cut surface without burrs.

Further, according to the method of the present invention, the injection holding pressure is increased again after the male cutter is fitted into the female cutter, so that the injection holding effective for the cut portion such as the sprue cut from the molded product is carried out. With the pressure applied, the injection holding process is shifted to the cooling process.

Therefore, the effective injection holding pressure is exerted on the cut portion such as the sprue, so that the cut portion can be normally formed with sufficient strength, and the mold release failure due to the insufficient strength of the cut portion. Etc. can be effectively prevented and excellent moldability can be exhibited.

Further, in the injection molding apparatus having the structure according to the present invention, the method of the present invention can be advantageously carried out, whereby any of the above effects can be effectively exhibited. Become.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to clarify the present invention more specifically, one embodiment of the present invention will be described with reference to the drawings.
The details will be described.

FIG. 1 shows a time chart as a specific example of the injection molding process according to the method of the present invention. In this embodiment, a case of molding an optical disk substrate using a mold clamping device and an injection device having a known structure will be specifically described. Further, the types and structures of the mold clamping device and the injection device to be used are not limited in any way, and various conventionally known ones can be adopted for them, and therefore detailed description thereof will be omitted.

That is, in injection-molding a substrate for an optical disk according to the method of the present invention, as shown in FIG. 1, first, as in the conventional injection-molding method, the molding cavities are formed by mutually matching the molding cavities. The fixed mold and the movable mold to be formed use the mold clamping devices mounted on the fixed plate and the movable plate, respectively, and bring the movable plate close to the fixed plate to align the fixed mold and the movable mold. The mold closing step is performed, and subsequently, the pressure increasing step of increasing the mold clamping pressure to clamp the fixed mold and the movable mold is performed.

Next, as shown in FIG. 2, the nozzle 14 of the injection device is pressed (nozzle touch) against the sprue bush 12 assembled to the fixed mold 10, and the molten resin 15 is predetermined from the nozzle 14. The molten resin 15 is injected by the injection filling pressure (primary injection pressure) of
Is injected into the disk molding cavity 18 formed between the mold mating surfaces of the fixed mold 10 and the movable mold 16 to perform the injection filling process.

Here, the molds 10 and 16 of this embodiment are
In the first embodiment, the molten resin 15 introduced through the sprue 20 of the sprue bush 12 passes through the small-diameter disk-shaped runner 22 formed at the tip of the sprue 20.
Is supplied to the inner peripheral edge of the disk molding cavity 18 having a large-diameter disk shape from the outer peripheral edge of the runner 22 corresponding to the punched part of the disk central hole.
A ring-shaped gate 24 is formed at a connecting portion between the molding cavity 18 and the molding cavity 18. Further, in the fixed mold 10, the tip portion of the sprue bush 12 is formed in the molding cavity 1
A circular recess 26 is formed which is recessed from the forming surface of 8 and is positioned toward the molding cavity 18 side, and the opening of the recess 26 forms an annular female cutter 28. There is. On the other hand, the movable mold 16
In the above, an annular stamper 29 having predetermined information engraved on the forming surface of the molding cavity 18 is disposed so as to overlap with each other. It is positioned and held by the presser foot 30. An ejector sleeve 32 for releasing the molded product is provided inside the inner stamper retainer 30 such that its tip end surface faces the molding cavity 18 and is movable in the axial direction. Inside the ejector sleeve 32, a male cutter 34 having an outer diameter substantially the same as the inner diameter of the female cutter 28 is disposed so as to be movable in the axial direction. In the retracted state of the male cutter 34, the gate 24 is formed between the male cutter 34 and the female cutter 28 as shown in FIG. An ejector pin 36 for releasing the sprue 20 and the runner 22 is disposed on the central axis of the male cutter 34 so as to be movable in the axial direction.

Furthermore, after the molten resin 15 is filled in the molding cavity 18 in the injection filling step, the injection pressure is switched to the injection holding pressure (secondary injection pressure),
An injection holding step of applying an injection holding pressure to the molten resin 15 filled in the molding cavity 18, the sprue 20, the runner 22 and the like is performed. The transition from the injection filling process to the injection holding process is similar to the conventional method, for example, by measuring the time of the injection filling process or detecting the position of the screw or the like that gives the injection pressure. It is performed with reference to the position and the like. Further, the injection holding pressure is generally set to be smaller than the injection filling pressure, as in the conventional case.

Then, in this injection holding step, as shown in FIG.
As shown in FIG. 3, the male cutter 34 of the movable mold 16 is moved forward and fitted into the female cutter 28 by a driving means such as a double-acting hydraulic cylinder (not shown). That is, since the resin material 15 is not yet solidified in the injection holding step, the male cutter 34 can be advanced to be fitted into the female cutter 28, and the forward movement of the male cutter 34 causes the gate 24 to move. Is cut to separate the sprue 20 and the runner 22 from the resin in the molding cavity 18, and the disk center hole 38 is punched out.

During the forward movement of the male cutter 34 in the injection holding process, the injection holding pressure for the filled resin material is lowered. Here, the decrease amount of the injection holding pressure is appropriately determined according to the forward stroke amount of the male cutter 34, the type of the resin material, etc., but it is reduced to 50% or less of the original injection holding pressure. It is preferable that the injection holding pressure is turned OFF in this embodiment.
In this state, the male cutter 34 is moved forward. Further, as shown in FIG. 1, the start of advancement of the male cutter 34 and the drop in the injection holding pressure take a predetermined delay time (forward advance delay) from the time of transition from the injection filling step to the injection holding step. It is desirable to perform the operation after the original injection holding pressure is applied for a predetermined time. As described above, a more stable operation control is achieved by taking a delay time before the male cutter 34 is advanced after the transition to the injection holding process. Is possible.

Further, in the injection holding process, the injection holding pressure once lowered during the forward movement of the male cutter 34 is increased again to make a predetermined injection holding pressure act on the resin material. It should be noted that the decrease / increase of the injection holding pressure does not necessarily have to be switched at the time of starting and stopping the forward movement of the male cutter 34, but in the present embodiment,
As shown in FIG. 1, the timing of decrease / increase of the injection holding pressure is controlled so as to coincide with the timing of starting / stopping the forward movement of the male cutter 34, and the forward movement end is started from the start of the operation of the male cutter 34. The injection holding pressure is cut off and lowered throughout the entire period until the time (at the time of stop), and the male cutter 34 is fitted into the female cutter 34 and stopped, and at the same time, the injection holding pressure is applied again. There is.

Incidentally, the injection holding pressure adjusting means for decreasing / increasing the injection holding pressure according to the operation of the male cutter 34 as described above, for example, opens and closes a drain valve incorporated in a hydraulic circuit of a hydraulic cylinder for giving the injection pressure. Alternatively, it can be easily realized by selectively operating the relief valve. If the injection holding pressure is controlled by adjusting the injection pressure as described above, it is not necessary to provide a special pressure absorbing device in the mold or the like, and the injection holding pressure adjusting means has a simple structure. It can be done. Further, to decrease / increase the injection holding pressure according to the operation of the male cutter 34, for example, a timer such as a motor timer or a digital timer is used to synchronize the operation of the male cutter 34 and the operation of the injection holding pressure adjusting means. In addition to the above, it is possible to easily perform the above, but in addition, the forward / backward position of the male cutter 34 and the position of a hydraulic cylinder or the like for giving an injection pressure,
Alternatively, it is also possible to detect the injection pressure and the like, and control the operation of the male cutter 34 and the operation of the injection holding pressure adjusting means so as to be synchronized with each other by a microcomputer or the like on the basis of the detected value.

That is, if the injection holding pressure is cut during the forward movement of the male cutter 34, the male cutter 34 is advanced with a sufficiently small driving force without receiving the resistance force due to the injection holding pressure. Since the male cutter 34 can be smoothly advanced and fitted therein, the male cutter 34 can be prevented from blurring when the male cutter 34 is moved forward, and shaving at the time of fitting into the female cutter 28 is effective. Will be prevented.

Further, when the male cutter 34 is fitted into the female cutter 28, the pressure increase in the sprue 20 and the runner 22 is advantageously reduced or avoided, so that the male and female cutters 28, 34 are fitted into the fitting gaps. The resin and the like can be prevented from entering, and a good cut surface can be obtained in the center hole 38 of the disk.

As described above, after the gate is cut in the injection holding step, the injection holding pressure is applied to the molding cavity 18, the sprue 20 and the runner 22 in the cooling step as in the conventional case. The filled molten resin 15 is cooled and solidified. After that, in accordance with a conventional method, a movable plate of the mold clamping device is separated from the fixed plate to open the mold, and the ejector sleeve 32 and the ejector pin 36 are protruded in the movable mold 16 to project the optical disk substrate. The ejector advancing step of separating the molded product and the cut portion made of the sprue and runner from each other is carried out to take out the molded product. In addition,
In the present embodiment, in the retracting process of the ejector sleeve 32 and the ejector pin 36 that are projected, at the same time,
The male cutter 34 projected in the injection holding process for punching out the disc center hole is also retracted to the retracted position shown in FIG.

In such a molding method, the injection holding pressure is cut in the injection holding step to punch out the center hole of the disc, and then the cooling step is performed again under the injection holding pressure. The cut portion composed of the sprue 20 and the runner 22 cut by 34 can be normally formed with sufficient strength, and therefore,
It is possible to effectively prevent mold release defects and the like due to insufficient strength of the cut portion, and to exhibit excellent moldability.

Moreover, since the injection holding pressure can be increased after the male cutter 34 is fitted into the female cutter 28,
Since a sufficient cooling effect can be obtained while ensuring a sufficient injection holding pressure to the sprue, there is also an advantage that the molding cycle can be shortened.

Although the embodiments of the present invention have been described above in detail, these are literal examples, and the present invention is not construed as being limited to such specific examples.

For example, the injection holding pressure does not necessarily have to be lowered throughout the forward movement of the male cutter.
For example, it is possible to lower the injection holding pressure only when the male cutter advances into the female cutter after advancing by a predetermined amount, or intermittently a plurality of times.

Further, when the injection holding pressure is lowered, it is not always necessary to maintain a constant pressure value, and for example, the injection holding pressure can be gradually lowered as the male cutter advances. .

Further, the injection holding pressure adjusting means adopted in the present invention may be any one capable of temporarily lowering the injection holding pressure in the injection holding step, and is not limited to the specific description of the above embodiment. For example, as disclosed in Japanese Examined Patent Publication No. 6-357, a center cutter movably arranged inside a male cutter is applied to drive the center pin backward / forward. It is also possible to employ, as the injection holding pressure adjusting means, a device in which the injection holding pressure is decreased / increased by being pressed.

The present invention can also be applied to injection molding of products other than optical disk substrates.

Although not listed one by one, the present invention is
Based on the knowledge of those skilled in the art, it can be implemented in various modified, modified, and improved modes, and
It goes without saying that all such embodiments are included in the scope of the present invention without departing from the spirit of the present invention.

[Brief description of drawings]

FIG. 1 is a diagram showing a time chart as a specific example of an injection molding process according to the method of the present invention.

FIG. 2 is an explanatory view of a main part for explaining an injection filling step according to the method of the present invention.

FIG. 3 is an explanatory view of a main part for explaining a punching operation of a disc central hole in an injection holding process according to the method of the present invention.

[Explanation of symbols]

 10 Fixed Mold 14 Nozzle 15 Molten Resin 16 Movable Mold 18 Molding Cavity 20 Sprue 22 Runner 24 Gate 28 Female Cutter 34 Male Cutter 38 Disc Center Hole

Claims (2)

[Claims] 1. A male cutter provided on the movable mold in an injection holding step after injection-filling a molding material into a molding cavity formed by fitting a fixed mold and a movable mold to each other. When the gate is cut by moving it forward and fitting it into the female cutter provided in the fixed mold, the injection holding pressure of the molding material is lowered to move the male cutter forward, and to the female cutter of the male cutter. The injection molding method is characterized in that the injection holding pressure applied again after the insertion is increased. 2. A gate is cut by advancing a male cutter provided in a movable mold and fitting it into a female cutter provided in a fixed mold that cooperates with the movable mold to form a molding cavity. In an injection molding machine equipped with a gate cutter mechanism, the injection holding pressure of the molding material injected and filled in the molding cavity is adjusted according to the forward movement of the male cutter to temporarily lower the injection holding pressure. An injection molding machine characterized in that injection holding pressure adjusting means for moving the male cutter forward is provided.