JPH081734A - Injection molding method and device - Google Patents

Abstract

PURPOSE:To obtain a runnerless and high-precision molded product and even in the case of multiple cavity mold, the molded products having little difference between cavities are obtained, by a method wherein molten resin pressure within an injection molding space during a dwell process is measured and a valve gate is closed at a point of time when a measured value is attained to a fixed value. CONSTITUTION:A movable mold 1A is moved in the right direction of an arrow X and mold-clamped. Then a gate 7 is opened by retreating a needle pin 6 of a nozzle unit 13, an injection cylinder 2 is advanced immediately and a molten resin is injected and filled into a cavity 3. After filling, a dwell process wherein filling pressure of the injection cylinder 2 is maintained by a fixed value for a fixed time is performed. In the dwell process, pressure of the molten resin within the cavity 3 is measured. Thus, when measured value of the detected pressure is attained to a predetermined value, the needle pin 6 of the nozzle unit 13 is moved forward and the gate 7 is closed.

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, and more particularly to an injection molding method and apparatus capable of stabilizing the shape of a molded product during injection molding of a relatively thin product.

[0002]

2. Description of the Related Art Conventionally, various methods have been adopted in various fields of injection molding as is well known. A runnerless (hot runner) type molding die is widely used in order to reduce runner loss that occurs in injection molding and increase productivity. There are various types of hot runner type molds, and among them, there is a valve gate type in which a needle pin can be moved back and forth with respect to the gate to mechanically open and close the gate.

This valve gate system can prevent the failure of the gate part such as the stringing of the gate and can increase the gate diameter.
In addition to the effect of smoothing the flow of resin into the mold, the gate is mechanically closed, so that the molding cycle can be shortened. Normally, in opening / closing control of the gate in the valve gate system, an air cylinder or a hydraulic cylinder is incorporated in a mold, and these actuators are controlled in synchronization with the molding process. As a way to match this timing, generally open the valve with a mold clamping signal,
At the same time, a method of starting a timer and closing the gate when the timer shows a predetermined time elapse is adopted.

In another example, the gate is opened by a mold closing completion signal of the injection molding device, and the gate is closed by a pressure holding completion signal. Further, as another valve gate control method, as disclosed in Japanese Patent Publication No. 63-49605, Japanese Patent Publication No. 53-4319, and Japanese Patent Application Laid-Open No. 50-158654, injection molding material (resin) is used. Valve gates of the type in which the gate is opened and closed by such injection pressure are also known, and in these methods, a method of driving the needle pin by an urging force of a spring or the like that balances with the resin pressure is adopted.

[0005]

However, the valve-gate type mold has a drawback in that there is a large variation between molding shots as compared with the molds of other types. One of the causes of the variation is variation in the valve closing timing during the molding process. Normally, the timing for closing the valve is to start the timer from a certain point in the molding process and close the valve when the time measured by the timer reaches a predetermined time. In this method, if a consistent molding condition is guaranteed for each shot (cycle) of molding according to the design and setting of the mold, it is accurate in terms of time, so there should be no variation. In reality, it is customary that the molding conditions do not become constant, and variations occur. Therefore, in particular,
Molded products that require high molding accuracy have problems such as very low yield.

On the other hand, in the method disclosed in each of the above publications, the valve gate is a method of opening and closing by the injection pressure applied to the injection molding material (resin), and the needle pin is moved by the biasing force of a spring or the like which balances the resin pressure. It is driven. However, since the spring for giving such biasing force is incorporated in the nozzle unit, it is virtually impossible to increase or decrease the biasing force, and eventually a spring having the same biasing force was incorporated. That is, it is a valve gate in which the needle pin is closed by the same resin pressure. Therefore, the conditions of the mold and its peripherals may differ between the initial stage of use and the state in which they have been used to some extent. In the case of molding that adjusts the shape such as the warp shape) or in the case of thin-walled molded products that are easily affected by resin pressure, fine adjustments can hardly be made, so molded products of desired quality cannot be obtained. Was the current situation.

Furthermore, when a plurality of molded products are simultaneously molded in one shot, the conventional gate closing method is used to balance the mutual injection molding spaces (hereinafter, also simply referred to as "cavities") with each other, particularly the molded products. Since it is not possible to balance the cavities with respect to the shape adjustment such as warpage, there is a fatal defect that the quality of the molded product between the cavities varies and the yield is low.

The present invention has been made in view of the above conventional problems. Even in the injection molding of a thin product such as a plastic shutter, the valve gate system is used to achieve a runnerless highly accurate molding. It is an object of the present invention to provide a molding method and apparatus for obtaining a product and for obtaining a molded product with a small difference between cavities even in the case of multiple production.

[0009]

The above object of the present invention is to provide an injection molding method using an injection molding die having a valve gate that mechanically opens and closes a gate tip region facing the injection molding space. Can be achieved by an injection molding method characterized by measuring the molten resin pressure in the injection molding space during the pressure-holding step, and closing the valve gate when the measured value reaches a predetermined value. it can. The above object of the present invention is to provide an injection molding method using an injection molding die equipped with a valve gate that mechanically opens and closes a gate tip region facing the injection molding space, the time from the start of the pressure holding step in the molding step. It can also be achieved by an injection molding method characterized by controlling the timing of closing the valve gate according to the above. In a particularly preferred embodiment of the present invention, a multi-cavity injection molding die for simultaneously molding a plurality of molded products is used to simultaneously start injection into each injection space and close each valve gate in each injection space. A method of individually controlling the timing for each valve gate, further detecting the resin pressure in each injection space independently of each other when controlling the timing of closing the gate during the molding process individually for each gate, A method of closing the valve gates independently of each other by a detection signal, an injection molding method of controlling the valves of the valve gates by a timer corresponding to the valve gates, and a timing range of closing the valve gates. ,
It is from 0.2 seconds after the start of holding pressure until the gate seal is reached. In the case of molding a plastic shutter, the resin pressure during holding pressure is set within the range of 5% to 20% of the maximum injection pressure of the molding machine. In this case, it is preferable to use a resin selected from at least one of polyoxymethylene, polybutylene terephthalate and polypropylene as the resin used for injection molding. The present invention also provides an injection molding die including a valve gate that mechanically opens and closes a gate tip region facing the injection molding space, a resin filling means for injecting and filling a resin melted by heating into the injection molding space, Injection molding, comprising: a pressure measuring means for measuring the pressure of the molten resin filled in the injection molding space, and a valve gate control means for closing the valve gate in response to a pressure detection signal from the pressure measuring means. Provide a device. Furthermore, the present invention provides an injection molding die having a plurality of injection molding spaces and a valve gate for mechanically opening and closing a gate tip region facing the injection molding space, wherein the heated and melted resin is injected. Resin filling means for injecting and filling a molding space with a predetermined pressure, a timer for counting the time from the start of holding pressure by the resin filling means, and each of the plurality of injection molding spaces provided according to the time counted by the timer Provided is an injection molding apparatus, characterized by comprising gate control means for independently controlling the timing of closing a valve gate.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.
The injection molding process of a general injection molding apparatus using a valve gate includes (1) mold clamping step, (2) gate opening step, (3) injection filling of molten resin into an injection molding space, and ( 4) pressure-holding step, (5) gate closing step, (6) step of cooling the molten resin in the injection molding space (note that cooling of the molten resin in the injection molding space is actually injection filling in (3)) Since it starts from the process, the cooling process in this process (6) means the cooling process after the process of closing the gate in (5).), (7) mold opening process, and (8) The step of taking out the resin molded product in the injection molding space is one shot (or one cycle), and by repeating this one shot many times,
It is possible to obtain the desired number of injection-molded articles.

1 to 6 are views showing an embodiment according to the present invention. In this embodiment, a plastic shutter (hereinafter, abbreviated as a shutter) which is a floppy disk component is taken as an example and its injection molding will be described. FIG. 1 is a graph showing the relationship between the holding pressure and the holding time in the pressure holding step in the injection molding process and the warp of the shutter, which is a molded product, and FIG. 2 illustrates the warp of the shutter taken out as a molded product. It is a perspective view. FIG. 3 is a schematic view of the molding apparatus of this embodiment.

First, a schematic diagram of the apparatus shown in FIG. 3 will be described. The mold 1 has a cavity 3 formed by a fixed mold 1B, a movable mold 1A, a center core 1b, and a pair of slide cores 1a located on both sides of the core 1b. The mold 1 is configured to be separated from the stationary mold 1B and the parting line 1c (thick line) by moving the movable mold 1A (moving to the left in the arrow X). At this time, the slide cores 1a are respectively opened in the vertical direction, and the protrusion pins 8 protrude from the center core 1b so that the molded shutter 20 (see FIG. 2) is appropriately protruded from the mold.

FIG. 3 shows a state where the mold is clamped, and a state in which the resin heated and melted in the injection cylinder 2 is injected and filled into the cavity 3 through the nozzle unit 13 of the valve gate is shown. ing. At this time,
The entire nozzle unit is heated by the heater 4 so that the resin does not solidify in the nozzle unit 13. An example of the process to reach the state shown in FIG. 3 is as follows. First, the movable mold 1A is moved to the right of the arrow X to clamp the mold. When this mold clamping is completed, the needle pin 6 of the nozzle unit 13 is retracted to open the gate 7, and immediately the injection cylinder 2 is advanced to inject and fill the molten resin into the cavity 3.

After the cavity is filled with the molten resin in this way, a pressure holding step is carried out for maintaining the filling pressure of the injection cylinder 2 at a predetermined value for a predetermined time.
In this pressure holding step, the pressure of the molten resin inside the cavity is measured. This pressure is measured by a pressure detector 9 installed at the end of the protrusion pin 8 opposite to the cavity side as shown in FIG. 3, and the accurate pressure value of the molten resin in the cavity is measured. It is the most preferable as shown, but the pressure of the molten resin at the desired location in the vicinity of the nozzle unit 13 or in the hot runner from the injection cylinder 2 to the nozzle unit 13 is measured, and this value is taken as the pressure value of the molten resin in the cavity. Good. The “pressure of the molten resin in the injection molding space” in the present invention includes such latter pressure.

When the measured pressure value thus detected reaches a predetermined value, the needle pin of the nozzle unit 13 is advanced to close the gate. More specifically, the load cell as the pressure detector 9 detects the pressure of the molten resin in the cavity as an electrical signal, the amplifier 10 amplifies this electrical signal, and then the comparison circuit in the gate opening / closing controller 11. Enter in 11b. This comparison circuit 1
In 1b, the input electric signal is compared with an electric signal corresponding to a preset pressure value, and when the two values are equal, a signal is output to the gate opening / closing instruction device 11a, and the gate opening / closing instruction that receives this signal is issued. The device 11a operates the solenoid valve 12 to switch between air supply and exhaust from the air source 14 to operate the air cylinder 5, thereby moving the needle pin 6 forward and closing the gate 7. Needless to say, the timing of closing the gate is earlier than the time when the molten resin in the gate 7 is solidified. After closing the gate 7 in this manner, the ejection pin 8 is ejected through the cooling step (6) and the mold opening step (7) described above, and the molded product is taken out.

By such a series of operations, the shutter 20 as shown in FIG. 2 is molded. The shutter 20 has a top surface portion 21 and front and back surface portions 22 and 23 protruding in the same direction at substantially right angles to the top surface portion 21 and has a substantially U-shaped section, and is provided with a window portion 24. The thickness T of the shutter 20 is approximately 0.35 mm, the width W1 of the top surface portion 21 is 3.60 mm, and the distance W2 between the front and back surfaces is 0 mm with respect to the width of the top surface portion. The warp dimension t is in the range of plus 0.35 mm to minus 0.20 mm, and more preferably in the range of plus 0.20 mm to minus 0.10 mm. The distance W2 is set by setting an angle θ between the top surface portion 21 and the front and back surface portions 22 and 23.
The angle θ can also be adjusted by controlling the pressure-holding process during injection molding.

The method for specifically setting the pressure value of the molten resin in the cavity that closes the gate 7 with this apparatus is as follows, for example. First, the pressure value for closing the gate 7 is set to an appropriate value, injection molding is performed, and the obtained warp of the shutter is measured. This procedure is repeated while changing the pressure value to obtain a graph of the relationship between the warp and the pressure value. Based on this graph, the pressure value for closing the gate 7 is determined so as to be within the desired warp range, and is input to the comparison circuit. As described above, the pressure of the molten resin in the cavity directly reflects the state of the resin in the mold, but as described above, the timing of closing the gate 7 by directly detecting the pressure of the resin in the cavity. By controlling, it is possible to obtain a uniform molded product without being affected by the injection variation of the molding device. Furthermore, even if the mold is deteriorated by repeating injection molding for several shots and the molding accuracy is distorted, it can be adjusted by the same means as the above when the symptom appears. .

As described above, when the method of monitoring the pressure of the molten resin in the cavity at the time of holding pressure and controlling the timing of closing the gate based on the value is adopted, a multi-cavity injection molding die is used. It is extremely advantageous when injection molding is performed by using. For example, when performing injection molding using a mold having eight cavities for one injection cylinder, one nozzle unit is installed in each cavity, and By installing one sensor to monitor the pressure of the molten resin inside, it is possible to independently determine and control the pressure value that obtains the optimum molded product for each cavity. Based on the above, it is possible to control the closing timing of the gate installed in each cavity. Therefore, even if the manufacturing precision of the eight cavities is slightly different from each other, injection molding conditions suitable for each cavity can be set, and injection-molded products of the same quality can be obtained from all of the eight cavities. be able to. Conventionally, in such a case, the eight cavities are gradually modified depending on the feeling until an injection molded product of the same quality is obtained.
Although it was unavoidable to repeat this correction process or to remake the mold entirely from the beginning, according to the present invention, such correction process and remake of the mold can be omitted, or At least it can be simplified.

In the above embodiment, the pressure of the molten resin in the cavity is monitored, and the timing of closing the gate is determined by the value thereof. The timing of closing the valve gate is controlled according to the time from the start of holding pressure. The object of the present invention is also achieved by the method. Here, the "pressure-holding start" in the present invention means that the injection control of the molding machine at the time of injecting and filling the molten resin into the cavity by the injection cylinder is controlled by the control based on the position and speed of the screw in the injection cylinder. It means the time point at which the control is switched to the control based on the pressure of the molten resin and the passage of time.
Generally, the molten resin pressure (holding pressure) applied by the injection cylinder in the pressure holding process varies somewhat depending on the shape of the molded product, but it is approximately 5 times the maximum injection power of the molding machine.
% To 20%. The graph of FIG. 1 shows an example of the relationship between the amount of shutter warpage and the pressure holding time in such a pressure holding range. It can be seen from FIG. 1 that once the holding pressure is determined, the amount of warp is determined by the holding pressure time. The graph of FIG. 1 is a graph relating to a specific cavity, and if the cavity changes, the absolute value of the relationship between the amount of warp and the holding time changes, but the curve itself of the graph has the same tendency. . The above fact means that if the graph of FIG. 1 is created for each cavity of the manufactured mold, the amount of warpage of the shutter can be controlled by the pressure holding time. Therefore, by controlling the timing of closing the valve gate according to the time from the start of holding pressure, a shutter having a constant amount of warp can be obtained.

By the way, when injection molding is performed using a multi-cavity injection molding die, it is inevitable that the molten resin pressures in the cavities differ from each other even if the holding pressure is kept constant. This is based on the fact that the pressure in the injection cylinder experiences pressure loss before reaching each cavity and the fact that the manufacturing dimensions of each cavity cannot be exactly the same. Therefore, when performing injection molding using a multi-cavity injection molding die, all the timings for closing the gate of each cavity should be constant based on the holding pressure (that is, the pressure applied to the molten resin by the injection cylinder). Even if determined, only the shutters having different amounts of warp can be obtained for each cavity. However, if the holding pressure is determined, the molten resin pressure in each cavity is always uniquely determined (however, the value of the molten resin pressure between the cavities is different from each other). If the time from the start of pressure holding is independently set according to the resin pressure, shutters having the same amount of warp can be obtained from all the cavities. FIG. 4 is a schematic view of an injection molding apparatus using a multi-cavity injection molding die according to the method of controlling the timing of closing the valve gate according to the time from the pressure holding start as described above. The same number as 3 indicates the same as in FIG.

The gate opening / closing control device 41 includes the solenoid valve 1
The operation of No. 2 is controlled to drive each of the air cylinders 5 in the mold 1 to control the opening / closing timing of each of the gates 7. The gate opening / closing control device 41 includes one gate opening control timer 41a for controlling the timing of driving the needle pin 6 in the gate opening direction by the air cylinder 5, and the air cylinder 5 gates the needle pin 6. Eight gate closing control timers 41b corresponding to individual air cylinders for controlling the timing of driving in the closing direction are provided.

The gate opening control timer 41a is set to be started by the mold clamping completion signal 30 of the molding apparatus. The outputs of the gate opening control timer 41a are simultaneously output to the eight solenoid valves 12, and the eight gates 7 are simultaneously opened. The eight gate closing control timers 41b are set to start at the same time by an injection / holding pressure switching signal (that is, a pressure holding start signal) 40 of the molding machine and output timing signals during the pressure holding process of the molding machine. The output of each gate closing control timer 41b is output to each corresponding solenoid valve 12, and the gate 7 corresponding thereto is closed.

In the injection molding by the molding apparatus of this embodiment, the pressure holding time is set in consideration of the fact that the time of applying the pressure of the resin during the molding and the time of applying the pressure after the injection are closely related to the warp of the molded product. Set it for each cavity,
By independently setting the timing of closing the gate 7 for each cavity, the warp of the molded product peculiar to the cavity 3 can be made constant. In the above example, eight gate blocking control timers are used, but one timer is used and the timing of blocking each gate is independently controlled based on the elapsed time indicated by this timer. It is also possible.

An example of carrying out the above-described multi-cavity molding method using the apparatus shown in FIG. 4 will be described below. Here, in order to specifically shape and set the warp of the shutter 20, the eight cavities 3 are balanced in the following procedure. The resin used was polyoxymethylene, polybutylene terephthalate, and polypropylene. (1) Measure the warpage of the shutter that has been trial-molded. (2) Using the graph of FIG. 1, the measured warpage data is read for the proper gate closing timing of each cavity.
Fig. 1 shows holding pressure, holding time and shutter warpage (dimension t)
It is a graph showing the relationship with. (3) The read gate closing timing of each cavity 3 is set in the gate closing control timer 11b, and confirmation molding is performed.

As described above, the timing of closing each gate 7 during the molding process is controlled individually for each gate, but in this experiment, the range of the timing of closing each gate is set from the completion of resin filling into the cavity to the gate seal. Up to In fact, the gate seal at the time of shutter molding is about 0.7 seconds after the completion of filling, and this time becomes the upper limit time of the adjustment range of the pressure holding time, which is the vertical line C2 in FIG. Then, based on the judgment criteria as to whether or not it is practical as a shutter, the upper limit of the warp amount is plus 0.35 mm, which is the horizontal line B2 in FIG. 1, and the lower limit of the warp amount is minus 0.2.
It is the horizontal line B1 in FIG. 1 in mm. Furthermore, regarding the shortest holding time, the vertical line C1 at the position where the curve at the maximum holding pressure of 20% of the maximum injection pressure of the molding machine intersects the horizontal line B1 was 0.2 seconds. . The range surrounded by these four lines (the inside of the line is shown by diagonal lines) is the control range.

Referring to FIG. 5, in the case of the eight-die mold of the shutter 20, the closing timing of each gate 7 is 0.5 se under the condition that the holding pressure is 13% of the maximum injection pressure of the molding machine.
The amount of warpage when set to c is shown. As shown in the figure, all the parts except the cavity N0.3 showed a tendency toward a plus. FIG. 6 shows the results when the closing time of each gate 7 is adjusted (adjustment to make the warp to zero) by the method of the present invention. As a result, the minimum time is 0.32 seconds to the maximum time of 0.
The adjustment was for 60 seconds. As can be seen from FIG. 6, according to the method of the present invention, variation in each cavity can be easily adjusted.

As described above, when the shutter 20 is molded, the valve for each gate 7 is closed by a timer corresponding to each gate 7, or a signal from the pressure detector 9 is used. In any case based on the above, the range of the timing of closing each gate 7 is from 0.2 seconds after the start of pressure retention (even if the gate is open, the resin in the gate portion is solidified by cooling). , The state in which the resin cannot substantially come in and out at the gate portion, which was about 0.7 seconds)
It is up to. Also, when the maximum injection pressure of the molding machine is about 3000 kgf / cm ² , the resin pressure during holding pressure is 5% to 20% (about 140 kgf / c) of the resin pressure during injection.
Stable molding is possible by setting the range of m ^{2 to} 600 kgf / cm ² ).

There are a case where the holding pressure has a smooth curve with the passage of time, and a control method where the holding pressure is changed stepwise with the passage of time. The magnitude of the holding pressure here is the final value. This is the time when the gate 7 is closed. In addition, the relationship between the pressure holding time and the amount of warp is that the thinner the shutter, the greater the rate of change of the warp with respect to the pressure holding time, and the larger the amount of pressure holding, the rate of change of the warp with respect to the pressure holding time. Will be bigger.
The resin used here is polyoxymethylene, polybutylene terephthalate, polypropylene alone or in an appropriate mixture. Then, the melt flow index (MI) of these resins [ASTM D1238
The (ISO1133) standard] is preferably 40 to 65.

Further, the shutter 20 injection molding method shown in FIG. 2, the product shape taken out from the injection molding space is composed of a top surface portion and front and back surface portions protruding in the same direction substantially at right angles to the top surface portion. It has a substantially U-shaped cross section, and the interval between the front and back ends of the product shape is plus 0.35 mm to minus 0.20 m with respect to the width of the top surface.
It is controlled so that the range is m. The cavity 3 is shaped like the shutter shown in FIG.
(0.3 to 0.4 mm), and when the distance L from the gate 7 to the final filling position in the cavity is changed to 68 mm at the maximum, the L / T value at this time is within the range of 170 or less. Almost similar results were obtained. In the molding apparatus shown in FIG. 3, the needle pin driving means may be an air cylinder, a hydraulic cylinder, a cam mechanism, or other mechanical means. Further, in the above-described embodiment, the protruding pin is used as a part of the member for detecting the resin pressure, but the present invention is not limited to this, and other pressure detecting means may be appropriately arranged. Good.

[0030]

As described above, the present invention measures the molten resin pressure in the cavity during the pressure holding step in the molding step, and when the measured value reaches a predetermined value,
Alternatively, the valve gate is closed depending on the time from the start of the pressure holding step. Further, according to the present invention, by changing the set value of the molten resin pressure in the cavity for closing the valve gate, or the setting of the time from the start of the pressure holding step, the shape of the molded product, for example, thin-walled molding The amount of warpage of the product can be finely adjusted, and a molded product having a constant shape can be obtained at all times even if there are variations during the manufacture of the mold and changes due to the usage time of the mold. Also, in the case of a mold with multiple molded products, even if there is an error between the cavities due to the manufacturing accuracy of the mold or other reasons, the molded products obtained from each cavity have the desired shape. By setting the set value of the resin pressure or the time from the start of the pressure holding step independently for each cavity as described above, it is possible to manufacture a molded product of the same quality with no difference between cavities. it can.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a holding pressure and a holding time and a warp of a molded product in an embodiment of the present invention.

FIG. 2 is a perspective view of a shutter to which the present invention is applied.

FIG. 3 is a schematic view of a molding apparatus according to an embodiment of the present invention.

FIG. 4 is a schematic view of a molding apparatus according to another embodiment of the present invention.

FIG. 5 is a graph showing a warpage amount of a molded product of each cavity before adjusting a gate closing timing.

FIG. 6 is a graph showing the amount of warpage of a molded product of each cavity after adjusting the gate closing timing according to the present invention.

[Explanation of symbols]

 1 Mold 2 Injection Cylinder 3 Cavity 4 Heater 5 Air Cylinder 6 Needle Pin 7 Gate 8 Overhanging Pin 9 Pressure Detector 10 Pressure Monitoring and Comparing Device 11 Gate Opening and Closing Control Device (Pressure Detection) 11a Gate Opening and Closing Indicator 11b Comparison Circuit 12 Solenoid Valve 13 Nozzle unit 41 Gate opening / closing control device (timer) 41a Gate opening timer 41b Gate closing timer

Claims (5)

[Claims] 1. An injection molding method using an injection molding die including a valve gate that mechanically opens and closes a gate tip region facing the injection molding space, wherein the injection molding space is in the pressure holding step in the molding step. The molten resin pressure is measured, and the valve gate is closed when the measured value reaches a predetermined value. 2. An injection molding method using an injection molding die having a valve gate that mechanically opens and closes a gate tip region facing the injection molding space, according to the time from the start of the pressure-holding step in the molding step. And controlling the timing of closing the valve gate by means of an injection molding method. 3. The injection molding die has a plurality of injection molding spaces, and the timing of closing the valve gate provided in each of the plurality of injection molding spaces is controlled independently of each other. The injection molding method according to claim 2. 4. An injection-molding die having a valve gate for mechanically opening and closing a gate tip region facing the injection-molding space, a resin filling means for injecting and filling a resin melted by heating into the injection-molding space, Injection molding, comprising: a pressure measuring means for measuring the pressure of the molten resin filled in the injection molding space, and a valve gate control means for closing the valve gate in response to a pressure detection signal from the pressure measuring means. apparatus. 5. An injection-molding die comprising a plurality of injection-molding spaces and a valve gate for mechanically opening and closing a gate tip region facing the injection-molding space, wherein the heat-melted resin is injection-molded. Resin filling means for injecting and filling a space with a predetermined pressure, a timer for counting the time from the start of holding pressure by the resin filling means, and valves provided in the plurality of injection molding spaces according to the time counted by the timer An injection molding apparatus comprising gate control means for controlling the timing of closing the gate independently of each other.