JPH07112462A - Method and apparatus for injection molding - Google Patents

Abstract

PURPOSE:To prevent the generation of an end material accompanied by punching processing by performing the advance movement of a screw by a pressure control mode subjecting the internal pressure of an injection mechanism to feedback control to transfer to a dwelling process. CONSTITUTION:The max. length from a gate 3b of a molded product is set to L and the thickness of the molded product is set to (t) and an ultrathin-walled molded product of t < 1mm and L/t >=150 is molded within a cavity 1A. At this time, an injection process is started in a speed control mode subjecting the advance moving speed of a screw 4 to feedback control while detecting the advance speed of the screw 4 due to an injection mechanism 16. The internal pressure of the injection mechanism 16 is detected and, when the internal pressure of the injection mechanism 16 rises abnormally, the advance movement of the screw 4 is performed by a pressure control mode subjecting the internal pressure of the injection mechanism 16 to feedback control. By this constitution, an injection process is advanced while a required injection speed is ensured by the speed control mode to suppress the warpage and strain of the molded product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method and apparatus for molding an ultra thin molded product.

[0002]

2. Description of the Related Art Conventionally, an ultra-thin product made of synthetic resin is generally formed by punching with a press, not by injection molding. Here, an ultra-thin product is a product that satisfies t <1 mm and L / t ≧ 150 in the cavity, where L is the maximum length from the gate of the molded product and t is the thickness. There is a container material. That is, when an ultra-thin product of this type is obtained by injection molding at a normal injection speed, the cooling speed and flow resistance of the molten molding material flowing into the cavity are large.
The molten molding material that first flows into the cavity is solidified at an early stage, causing a pressure gradient that gradually drops from the gate toward the tip of the molded product during injection, which causes insufficient filling and warpage of the molded product. Such problems can be mitigated by increasing the injection speed, but when performing the injection process while controlling the forward speed of the screw to obtain a high injection speed,
As indicated by the broken line in FIG. 6, the pressure inside the cavity is abnormally increased immediately before the holding pressure switching point, that is, at the end of the injection process, and burrs are generated, the weight of the molded product is varied, and the thin pin in the mold falls or is damaged. Cause In addition, when a screw having a normal plasticizing ability is used, a slight unmelted portion or a non-uniform melting temperature is generated in the molten molding material, which causes warpage and distortion of the molded product.

On the other hand, when an ultra-thin product is obtained by punching with a press, a resin sheet having a predetermined thickness (t) is produced in advance and punching is performed, so that the production process is multistage. In addition to being inferior in work efficiency, it is generally unavoidable that scrap materials are generated during punching, resulting in a decrease in yield.
In addition, there is a technical problem that it takes time to reuse the scrap material.

[0004]

The present invention has been made in view of the above-mentioned conventional technical problems, and the structure thereof is as follows.
It is as follows. The invention of claim 1 is provided with an injection mechanism 16 for moving the screw 4 forward by an internal pressure, and the molten molding material melted and kneaded by the screw 4 is screw 4
, The screw 4 is moved forward, and is injected into the cavity 1A from the nozzle 5b through the sprue 3a and the gate 3b in the mold 1 to the gate 3b of the molded product.
An injection molding method for molding an ultrathin molded product of t <1 mm and L / t ≧ 150 in the cavity 1A, where L is the maximum length from L and t is the thickness, and a high kneading screw is used as the screw 4. Is used to obtain a molten molding material that has been sufficiently melted and kneaded, and the forward movement speed of the screw 4 is feedback-controlled while detecting the forward movement speed of the screw 4 by the injection mechanism 16 and the internal pressure of the injection mechanism 16. The pressure for feedback-controlling the internal pressure of the injection mechanism 16 so as to reduce the internal pressure of the cavity 1A when the injection process is started in the speed control mode and the internal pressure of the injection mechanism 16 abnormally rises during the injection process. This is an injection molding method characterized by advancing the forward movement of the screw 4 in the control mode and then shifting to the pressure holding step. The invention of claim 2 is the injection molding method according to claim 1, wherein the screw 4 is a highly kneading screw having a double flight portion. The invention of claim 3 advances the forward movement of the screw 4 in a pressure control mode in which the internal pressure of the injection mechanism 16 is feedback-controlled from the end of the injection process to the completion of the pressure holding process. It is the injection molding method of 1 or 2. The invention of claim 4 is the cavity 1
The injection step is started in a speed control mode in which the forward movement speed of the screw 4 is feedback-controlled so that an injection speed of 350 mm / sec or more is given to the molten molding material flowing into A. There are two or three injection molding methods. In the invention of claim 5, in the cylinder barrel 5, the screw 4 is rotationally driven to knead and melt the molding material, and the molten molding material is stored in front of the screw 4, and then the pressure oil supply source 28 The screw 4 is moved forward by the injection mechanism 16 in which the pressure oil is supplied to the pressure chamber 6a, and the molten molding material is sprued with the sprue 3a and the gate 3 in the mold 1.
Injection into cavity 1A from b, gate 3b of molded product
Is an injection machine that molds an ultra-thin molded product of t <1 mm and L / t ≧ 150 in the cavity 1A, where L is the maximum length from T and t is the thickness, and the screw 4 is a double flight. And a pressure detector 17 that constantly detects the internal pressure of the pressure chamber 6a during the injection process.
6 is a speed control mode in which the forward movement speed of the screw 4 during the injection process is feedback-controlled while the forward speed of the screw 4 is detected by the speed detector 9, and the pressure chamber 6a of the pressure chamber 6a is controlled by the pressure detector 17. And a pressure control mode in which the pressure of the pressure chamber 6a of the injection mechanism 16 during the injection process is feedback-controlled while detecting the internal pressure. When the internal pressure of the injection mechanism 16 rises abnormally, the screw 4 is operated in the pressure control mode. The injection molding apparatus is characterized by comprising speed control-pressure control switching means 13 for advancing the forward movement of the.

[0005]

According to the invention of claim 1, the gate 3b of the molded product is formed.
When a super-thin-wall molded product with t <1 mm and L / t ≧ 150 is molded in the cavity 1A, where L is the maximum length from L and t is the thickness, first, it is melted and kneaded by the screw 4. To obtain a melt molding material. Since a high-kneading screw is used as the screw 4, a melt-molded material that is sufficiently homogeneously melted and kneaded can be obtained by storing and measuring the melt-formed material in front of the screw 4. After that, the process proceeds to the injection process, and the injection mechanism 16
The screw 4 is moved forward by the internal pressure of 1, and the molten molding material is injected from the nozzle 5b into the cavity 1A through the sprue 3a and the gate 3b in the mold 1 to obtain a molded product.

At this time, the injection process is started in a speed control mode in which the forward movement speed of the screw 4 is feedback-controlled while detecting the forward movement speed of the screw 4 by the injection mechanism 16. Then, during the injection process, the injection mechanism 16
When the internal pressure of the injection mechanism 16 is abnormally increased, the forward movement of the screw 4 is advanced in a pressure control mode in which the internal pressure of the injection mechanism 16 is feedback-controlled. As a result, the injection process is advanced while ensuring the required injection speed in the speed control mode, warpage and distortion of the molded product are suppressed, and a defect (occurrence of flash) due to an abnormal increase in the internal pressure of the cavity 1A is generated. , Variations in weight of molded products, falling or damage of thin pins in the mold, etc.)
Is satisfactorily prevented. Then, the pressure-holding step is performed. Thus, the melt-molded material that is sufficiently homogeneously melted and kneaded is injected into the cavity 1A based on the speed control mode to obtain a molded product, so that a high-quality ultra-thin molded product is molded.

According to the invention of claim 2, the screw 4 is
Is a high kneading screw having a double flight part, so that a melt molding material at a uniform temperature, which is sufficiently homogeneously melted and kneaded, is stored and measured in front of the screw 4.
As a result, warpage and distortion of the molded product are suppressed.

According to the third aspect of the present invention, since the forward movement of the screw 4 is advanced in the pressure control mode at the end of the injection process, when the measurement completion position changes while the holding pressure switching position is fixed. As a result, the peak pressure at the time of filling, which occurs during the filling process, is eliminated, and a defect due to an abnormal increase in the internal pressure of the cavity 1A is reliably prevented, and stable molding is ensured.

According to the invention of claim 4, the speed control mode of the injection step is performed while giving an injection speed of 350 mm / sec or more to the molten molding material flowing into the cavity 1A. Therefore, the melt molding during the injection step is performed. The material is quickly filled into the cavity 1A, the filling property is improved, and the warp of the molded product is prevented.

According to the fifth aspect of the present invention, the melt-molded material melted and kneaded to a sufficiently uniform and uniform temperature by the screw 4 having the double flight portion is accumulated in front of the screw 4 and is obtained by weighing. To be After that, shift to the injection process,
The forward movement of the screw 4 is performed by supplying the pressure oil from the pressure oil supply source 28 to the pressure chamber 6a of the injection mechanism 16. At that time, the injection mechanism 16 causes the speed control-pressure control switching means 13 to operate.
Therefore, while the forward speed of the screw 4 is detected by the speed detector 9, the injection process is started by the speed control mode in which the forward movement speed of the screw 4 during the injection process is feedback-controlled, and at the same time, the pressure The injection process proceeds while the internal pressure of the pressure chamber 6a is detected by the detector 17. When the internal pressure of the injection mechanism 16 rises abnormally, the pressure control mode is switched by the action of the speed control-pressure control switching means, and the pressure chamber 6 of the injection mechanism 16 is switched.
The pressure of a is feedback-controlled to a predetermined value. As a result, it is possible to favorably prevent defects (occurrence of burrs, variation in weight of molded products, tipping or damage of thin pins in the mold, etc.) due to abnormal increase in internal pressure of the cavity 1A. In this way, the molten molding material stored in front of the screw 4 is injected into the cavity 1A from the sprue 3a and the gate 3b in the mold 1, and the maximum length of the molded product from the gate 3b is L, the thickness is Where t is t <1 mm and L / t ≧ 15
An ultra-thin molded product of 0 is molded in the cavity 1A.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 show an embodiment of an injection molding device according to the present invention. First, the outline of the injection molding apparatus will be described with reference to FIG. In FIG. 1, reference numeral 5 indicates a horizontally arranged cylinder barrel, an injection cylinder 6 is connected to the rear of the cylinder barrel 5, and an injection piston 7 is slidably fitted inside the injection cylinder 6. . The injection cylinder 6 and the injection piston 7 define a rear pressure chamber 6a, and constitute an injection mechanism 16 that moves the screw 4 forward by the internal pressure of the pressure chamber 6a. The injection cylinder 6 has an injection piston 7 and thus a screw 4
A speed detector 9 for detecting the forward speed of and transmitting a speed signal a is attached. An output shaft 8a is rotatably supported in the injection piston 7 with the injection piston 7 in a penetrating state and is relatively immovable in the central axis direction. A front end portion of the output shaft 8a is inserted into the cylinder barrel 5. And a rear end of the output shaft 8a is connected to a rotating mechanism 8 including a hydraulic motor. Output shaft 8
a is extendable with respect to the rotating mechanism 8 by a spline.

Therefore, the output shaft 8a is provided by the rotating mechanism 8.
The screw 4 is rotatably driven via the, and the molding material supplied from the hopper 5 a is melted and kneaded by the screw 4 while being heated by the heater attached to the cylinder barrel 5. Next, by supplying pressure oil from the pressure oil supply source 28 to the rear pressure chamber 6a, the injection piston 7,
The output shaft 8a and the screw 4 can be integrally moved forward, and the molten material stored in front of the screw 4 can be injected into the mold 1 from the nozzle 5b at the tip of the cylinder barrel 5. The pressure oil supply source 28 includes a pump 26 and an accumulator 24, and the pump 26 and the pressure chamber 6a are connected by a flow path 29.

In the flow path 29, sequentially from the pump 26 side,
A relief valve 27 that regulates the maximum pressure in the flow path 29, and a check valve 2 that allows a flow from the pump 26 toward the pressure chamber 6a.
5, the accumulator 24, the switching valve 23, the servo valve 2
1 and the pressure detector 17 which detects the internal pressure of the pressure chamber 6a and sends out the pressure detection value h is connected. The switching valve 23 is
It has a pressure increasing position I that allows the flow from the accumulator 24 and the pump 26 toward the pressure chamber 6a, a pressure reducing position II that allows the drain from the pressure chamber 6a, and a pressure holding position III that keeps the pressure chamber 6a at a predetermined pressure. The servo valve 21 is
A controller 20 is attached and constitutes a servo mechanism 22.
The controller 20 is connected to the controller 20, and the opening degree of the servo valve 21 is adjusted to be increased or decreased by control signals d and e provided from the controller 10 to the controller 20.

The control device 10 receives a speed mode switching signal b or a pressure mode switching signal c, which will be described later, and selectively switches to a speed control mode or a pressure control mode.
3 and the contact s of the switching device 13, and the speed control signal d
A speed comparator 11 for sending a pressure control signal e, and a pressure comparator 15 for sending a pressure control signal e, which is connected to the contact p of the switch 13.
Speed control comparator 30 for sending speed mode switching signal b
And a pressure control comparator 3 for transmitting a pressure mode switching signal c
1 and 1. Reference numeral 12 is a speed setter, which sends out a set speed value f. Moreover, 14 is a pressure setting device which sends out the set oil pressure value g. The set speed value f and the set hydraulic pressure value g can be arbitrarily changed and set.

The speed comparator 11 compares the speed signal a with the set speed value f, adjusts based on the comparison result, and sends the speed control signal d. In the speed control comparator 30,
The speed signal a is compared with the set speed value f, the speed mode switching signal b is sent out based on the comparison result, and the switch 13 is switched to the speed control mode position (the state where the contact s is closed). The speed control comparator 30 can force the switch 13 to take the speed control mode switching position by a switching signal i from a controller (not shown).

Further, in the pressure comparator 15, the pressure detection value h
And the set oil pressure value g are compared with each other, adjustment is performed based on the comparison result, and the pressure control signal e is transmitted. In the pressure control comparator 31, the pressure detection value h and the set oil pressure value g are compared,
Based on the comparison result, the pressure mode switching signal c is sent, and the switch 13 is switched to the pressure control mode position (contact p is closed). The pressure control comparator 31 can force the switch 13 to take the pressure control mode switching position by a switching signal j from a controller (not shown). The switching device 13 normally takes the speed control mode position in which the contact s is closed, and when the pressure detection value h becomes larger than the set oil pressure value g, a predetermined switching signal c from the pressure control comparator 31. Is input to cause the switch 13 to assume the pressure control mode switching position. This switch 13
Configures speed control-pressure control switching means for switching from the speed control mode to the pressure control mode.

The screw 4 is a high kneading screw. As this type of screw 4, one having a double flight is known. As shown in FIG. 2, the screw 4 having a double flight has a supply unit A, a compression unit B, and a measuring unit C in sequence, and the screw 4 has a measuring unit C of the main flight 4a extending from the supplying unit A to the measuring unit C. , The sub-flight 4b is provided in combination. As shown in FIG. 3, the subflight 4b has a pitch larger than that of the main flight 4a, and the height h ₂ of the subflight 4b is slightly lower than the height h ₁ of the main flight 4a. Thus, the valley portion of the measuring portion C of the screw 4 has the first valley portion 4 whose volume gradually decreases toward the tip.
c and a second valley 4d that gradually increases in size.

According to the screw 4, the solid molding material (pellet) supplied from the hopper 5a by the rotation about the central axis is subjected to the heater heat from the cylinder barrel 5 at the supply section A while being compressed. It is sent to B and, in addition to the heat of the heater, it receives shearing heat by rotation and begins to melt. The molding material sent out from the compression section B is mainly sent to the first valley portion 4c in a state where the molten molding material and the solid molding material coexist, and is gradually compressed as it advances toward the tip. It flows into the 2nd valley part 4d through the clearance gap (delta) between the sub-flight 4b and the cylinder barrel 5 shown in FIG. This gap δ is set to be smaller than the particle size of the solid molding material,
Since the unmelted solid cannot pass through, only the molten molding material passes through the gap δ. When passing through this gap δ, it undergoes shearing heat insulation and is sufficiently homogeneously melted and kneaded. In this way, the molten molding material flowing into the second valley portion 4d is not mixed with unmelted solid, is homogeneously kneaded at a substantially uniform temperature, and is gradually measured in front of the screw 4. In addition,
It is desired that the measured temperature difference of the molten molding material be within ± 2 ° C. for molding the ultra-thin molded product, but the screw 4 having the double flight can satisfy this condition. .

The mold 1 comprises a fixed mold 3 and a movable mold 2. The movable platen 2a for supporting the movable mold 2 is a fixed platen 3c.
And a mold clamping plate 36, the tie bars 18 are installed between the mold clamping plate 36 and the mold clamping plate 36 so that the tie bars 18 can move forward and backward. This movable plate 2
It is desired that the a, the fixed plate 3c, and the tie bar 18 each have higher rigidity and suppress the tendency of the mold to open in response to the action of injection pressure in the mold clamped state. One cavity 1A formed between the fixed mold 3 and the movable mold 2 is formed through the sprue 3a and the gate 3b of the fixed mold 3,
You may take multiple pieces.

The molded product is an ultra-thin molded product (where the maximum length of the molded product from the gate 3b is L and the thickness is t, t <1 mm
L / t ≧ 150), which is a video cassette storage container material 33 made of polypropylene, for example, as shown in FIG. The video cassette storage container material 33 includes a front surface portion 33a, a rear surface portion 33b, a bottom surface portion 33c, and one side surface portion 3
3d, the other side surface portion 33e, and a plurality of joint surface portions 33f, and the boundaries between the surface portions 33a to 33f form a linear groove-shaped bent portion 33g. The thickness t of each of the surface portions 33a to 33f is about 0.4 to 0.6 mm, and the bending portion 33
The thickness t _{1 of} g is about 0.15 to 0.3 mm, and the outer shape of the video cassette housing container material 33 is 230 × 240.
mm. The cavity 1A of the mold 1 has a shape adapted to the video cassette storage container material 33, and has a bottom surface portion 33c.
There is a cut trace of the gate 5b, which is a pinpoint gate, in the center of the. The ratio (about 280) of the length L (about 170 mm) from the gate 5b to the corner of the video cassette housing container material 33 and the minimum wall thickness t (0.4 mm) is L / t ≧ 15.
0 is satisfied.

Next, the operation of the above embodiment will be described. However, the molding cycle of the injection molding apparatus is the same as the normal one, and the steps of mold closing, mold clamping, injection, pressure holding, cooling, and plasticization proceed sequentially. In the plasticizing step, the screw 4 is rotated by the rotation mechanism 8 via the output shaft 8a in a state where the screw 4 is at the forward position and the switching valve 23 is at the depressurized position II. As a result, the molding material supplied from the hopper 5a is melted and kneaded in the cylinder barrel 5, receives thrust by the main flight 4a, and the molten molding material is gradually extruded toward the measuring section C.

The molten molding material that has reached the measuring section C is melted and kneaded to a sufficiently uniform and uniform temperature in the main flight 4a and the sub-flight 4b, flows to the nozzle 5b side, and then the screw 4
Is gradually weighed and stored in front of. Since the screw 4 retreats in accordance with the storage amount of the molten molding material, when the predetermined amount is measured, the rotation mechanism 8 is stopped and the rotation drive of the screw 4 is stopped. Thus, the melt molding material is screw 4
And the plasticizing process is completed.

After the predetermined amount of the molten molding material is metered and stored, the injection process is started. At that time, the accumulator 24
The pressure oil of a predetermined pressure is stored in the pump 26, and the switching device 13 of the control device 10 adopts the speed control mode position in which the forward movement speed of the screw 4 is feedback-controlled by the switching signal i. The set speed value f of the speed setter 12 and the set oil pressure value g of the pressure setter 14 are the same as the screw 4
Is set to a predetermined value so that a constant forward speed is applied to the pressure chamber 6a and a constant pressure is obtained in the pressure chamber 6a of the injection cylinder 6. In this state, when the injection mechanism 16 is driven by causing the switching valve 23 to take the pressure increasing position I by a signal from a controller (not shown), the pressure oil of the accumulator 24 becomes
It is supplied to the pressure chamber 6a through the switching valve 23 and the servo valve 21 having a predetermined opening. As a result, the screw 4 moves forward through the injection piston 7 and the output shaft 8a, and the molten molding material that is metered and stored in front of the screw 4 in the cylinder barrel 5 is stored in the mold 1 from the tip of the nozzle 5b. It is injected into the cavity 1A through the sprue 3a and the gate 3b. The backflow of the molten molding material toward the screw 4 is prevented by a backflow prevention valve (not shown).

The forward movement speed of the screw 4 is detected by the speed detector 9, and the speed signal a is input to the speed comparator 11. The speed comparator 11 is the speed setter 12
The speed control signal d, which is obtained by comparing the set speed value f from 1 to the speed signal a and adjusted based on the result, is input to the switch 13. On the other hand, the speed signal a and the set speed value f are also input to the speed control comparator 30, and the speed control comparator 30
Sends the speed mode switching signal b to the switch 13, and the switch 13 closes the contact s. Then, the speed of the screw 4 rapidly rises from the injection start point as shown in FIG. 7, and after reaching a predetermined speed, the injection state is maintained at the predetermined speed.

On the other hand, simultaneously with the start of the injection process, the pressure oil in the pressure chamber 6a of the injection cylinder 6 is detected by the pressure detector 17, and the pressure detection value h is sent to the pressure comparator 15.
The pressure comparator 15 compares the set oil pressure value g from the pressure setter 14 with the pressure detection value h from the pressure detector 17, and the pressure control signal e adjusted based on the result is used as a switching device. 13 is input. On the other hand, the pressure control comparator 31 also contains the pressure detection value h and the set oil pressure value g, but the pressure detection value h is smaller than the set oil pressure value g set by the pressure setter 14. Since it is determined that the switch 13
The speed control signal d enters the controller 20 via the switch 13 while keeping the speed control mode position by the action of the speed control comparator 30, and the forward movement speed of the screw 4 follows the set speed value f. The servo valve 21 is subjected to speed feedback control so that the injection process proceeds. That is, the pressure chamber 6
The pressure of the cavity 1A obtained according to the pressure of a gradually increases from the injection start point as shown in FIG. 6, but does not reach the first set pressure according to the set oil pressure value g, so the switching device 13 The speed control mode position is still taken.

When the detected pressure value h rises above the set oil pressure value g, the pressure mode switching signal c, which is the comparison result in the pressure control comparator 31, is sent, and the switching device 13 switches the contact p. Switch to close. As a result, the pressure control signal e from the pressure comparator 15 is input to the controller 20, and the servo valve 21 is pressure-feedback controlled so that the oil pressure in the pressure chamber 6a follows the set oil pressure value g, and the injection process is performed. finish. That is, the pressure in the cavity 1A corresponding to the pressure in the pressure chamber 6a is suppressed to the constant first set pressure that produces the set oil pressure value g at the pressure control switching point as shown in FIG. The switch 13 takes the pressure control mode position so that the point is reached.

On the other hand, the speed of the screw 4 gradually decreases from the pressure control switching point to reach the holding pressure switching point as shown in FIG. As a result, the peak pressure at the time of filling (shown by the broken line in FIG. 6) that occurs when the measurement completion position changes, etc. is eliminated with the holding pressure switching position fixed, and stable molding is achieved. Secured. That is, it is possible to reliably prevent the occurrence of burrs, the variation in weight of the molded product, and the collapse or damage of the thin pins in the mold. Then, the pressure-holding step is performed. The pressure maintaining process proceeds by pressure feedback control, and the servo valve 21 is set based on the set oil pressure value g so that the oil pressure in the pressure chamber 6a is maintained at a constant second set pressure as shown in FIG. Pressure feedback control.

By the way, in the injection step for obtaining such an ultra-thin molded product, the injection speed is set to a high speed, specifically 35
It is desirable to set the pressure to 0 mm / s or more and inject it to promote the filling of the cavity 1A. As a result, the injection speed is initially set to the predetermined value (350
(mm / s or more) and when an abnormal rise in pressure is detected, the pressure in the cavity 1A is maintained at a predetermined pressure by switching from the speed control mode to the pressure control mode by the switch 13. As a result, the adverse effects caused by the increase in pressure are prevented, so that stable molding can be ensured while ensuring a high injection speed and performing precision molding of an ultra-thin molded product. that time,
It is desired that the injection pressure (the pressure of the molten molding material in front of the screw 4 at the time of injection) be 900 Kgf / cm ² or more. As a result, molding with L / t ≧ 300 is also possible.

As the high-kneading screw, in addition to a screw having a double flight, a screw in which the cross-sectional area of the screw groove sharply increases or decreases, or a screw having grooves or protrusions called mixing at the tip or the middle is provided. Good. Further, as the ultra-thin molded product, in addition to a flat plate-shaped product such as the video cassette storage container material 33, a three-dimensional molded product having a hollow portion like a ball-point pen cap may be used.

[0030]

As can be understood from the above description,
According to the injection molding method and the apparatus therefor of the present invention, the following effects can be obtained. In the plasticizing step, by the action of the high kneading screw, a melt molding material that is sufficiently homogeneous and melted and kneaded at a uniform temperature can be obtained while shortening the molding cycle. Next, in the injection step, a high injection speed can be realized while preventing an abnormal rise in the pressure inside the cavity. As a result, it is possible to perform highly accurate injection molding of an ultra-thin molded product while preventing warpage, distortion, etc. of the molded product that has occurred in the conventional injection molding apparatus, without causing any adverse effects due to punching.

[Brief description of drawings]

FIG. 1 is a diagram showing an injection molding apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a screw in the same manner.

FIG. 3 is an explanatory view of the action of the screw.

FIG. 4 is a diagram showing a video cassette storage container material.

FIG. 5 is an enlarged sectional view of a bent portion of the video cassette container material.

FIG. 6 is a diagram showing pressure characteristics in the same time-cavity.

FIG. 7 is a diagram similarly showing a time-speed characteristic of a screw.

[Explanation of symbols]

1: mold, 1A: cavity, 2: movable mold, 3: fixed mold, 3a: sprue, 3b: gate, 4: screw,
5: Cylinder barrel, 5b: Nozzle, 6: Injection cylinder, 6a: Pressure chamber, 7: Injection piston, 8: Rotation mechanism,
9: speed detector, 10: control device, 11: speed comparator,
12: speed setting device, 13: switching device (speed control-pressure control switching means), 14: pressure setting device, 15: pressure comparator,
16: injection mechanism, 17: pressure detector, 18: tie bar,
19: Mold clamping device, 20: Controller, 21: Servo valve, 2
2: Servo mechanism, 23: Switching valve, 24: Accumulator, 26: Pump, 28: Pressure oil supply source, 30: Speed control comparator, 31: Pressure control comparator, L: Maximum length of ultra-thin molded product , T: thickness of the ultra-thin molded product.

Claims (5)

[Claims] 1. An injection mechanism (16) for moving the screw (4) forward by an internal pressure, wherein a molten molding material melted and kneaded by the screw (4) is stored in front of the screw (4). After that, the screw (4) is moved forward and injected into the cavity (1A) from the nozzle (5b) through the sprue (3a) and the gate (3b) in the mold (1), and the screw from the gate (3b) of the molded product is ejected. An injection molding method for forming an ultra-thin molded product of t <1 mm and L / t ≧ 150 in a cavity (1A), where L is a maximum length and t is a thickness, and a high screw (4) is used. While obtaining a melt-molded material that has been sufficiently homogeneously melted and kneaded using a kneading screw, while detecting the advancing speed of the screw (4) by the injection mechanism (16) and the internal pressure of the injection mechanism (16),
When the injection process is started in the speed control mode in which the forward movement speed of the screw (4) is feedback-controlled and the internal pressure of the injection mechanism (16) abnormally rises during the injection process, the internal pressure of the cavity (1A) is adjusted. An injection molding method characterized by advancing the forward movement of the screw (4) in a pressure control mode in which the internal pressure of the injection mechanism (16) is feedback-controlled so as to decrease, and then shifting to a pressure holding step. 2. The injection molding method according to claim 1, wherein the screw (4) is a highly kneading screw having a double flight portion. 3. The screw (4) is moved forward in a pressure control mode in which the internal pressure of the injection mechanism (16) is feedback-controlled from the end of the injection process to the completion of the pressure holding process. The injection molding method according to claim 1 or 2. 4. The injection process is started in a speed control mode in which the forward movement speed of the screw (4) is feedback-controlled so as to give an injection speed of 350 mm / sec or more to the molten molding material flowing into the cavity (1A). The injection molding method according to claim 1, 2, or 3, wherein 5. A screw (4) is rotationally driven in the cylinder barrel (5) to knead and melt the molding material, and the molten molding material is stored in front of the screw (4), and then pressure oil is supplied. The screw (4) is moved forward by the injection mechanism (16) in which the pressure oil from the source (28) is supplied to the pressure chamber (6a), and the molten molding material is sprued (3) in the mold (1).
a) and the gate (3b) are injected into the cavity (1A), where L is the maximum length of the molded product from the gate (3b) and t is the thickness, and t is less than 1 mm and L / t is more than 150. An injection machine for molding a molded product in a cavity (1A), wherein the screw (4) has a double flight part, and a pressure detector for constantly detecting the internal pressure of the pressure chamber (6a) during an injection process. (17) having the injection mechanism (16)
However, a speed control mode in which the forward movement speed of the screw (4) during the injection process is feedback-controlled while the forward movement speed of the screw (4) is detected by the speed detector (9),
A pressure control mode for performing feedback control of the pressure of the pressure chamber (6a) of the injection mechanism (16) during the injection process while detecting the internal pressure of the pressure chamber (6a) by the pressure detector (17), An injection molding apparatus comprising: speed control-pressure control switching means (13) for advancing the forward movement of the screw (4) in a pressure control mode when the internal pressure of the injection mechanism (16) rises abnormally.