JP3132605B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin injection molding method, and more particularly to control of a process including a pressure holding process and a measuring process.

[0002]

2. Description of the Related Art In injection molding of a thermoplastic resin, respective steps of mold closing, injection, holding pressure, measuring, cooling, and mold opening are performed. For example, to explain the case of using an in-line screw type injection molding machine, in the measuring process, the pallet of the thermoplastic resin supplied into the heating cylinder,
It is melted by heating by a heater and shearing force accompanying rotation of the screw. The resin melted in this manner is stored in a predetermined amount at the tip end in the heating cylinder by retreating while rotating the screw. After the completion of the measuring step and after the mold closing, the injection step is performed.
In this injection step, the screw advances and the molten resin in the heating cylinder is injected from a nozzle at the tip of the heating cylinder, and the nozzle is filled in a cavity in a mold to which the nozzle is connected. Next, a pressure-holding step is performed. In this pressure-holding step, a predetermined pressure is applied to the screw forward. This prevents the backflow of the molten resin from the cavity, and replenishes the cavity with shrinkage due to the cooling and curing of the molten resin in the cavity. After the end of the pressure-holding step, the injection molding machine starts the measuring step again. On the other hand, during this measuring step, the resin in the cavity, that is, the cooling of the product is continued, but after the product is sufficiently cooled, the mold is opened and the product is taken out. The above steps are repeated as one cycle.

Usually, in the injection step, the screw is
It is controlled according to the speed and the position. Further, in the pressure holding step, the screw is controlled according to the pressure and the time.
Table 1 shows an example of the control.

[0004]

[Table 1]

In Table 1, V is the screw speed, HP
Is the holding pressure, which is expressed as a percentage of the maximum speed and the maximum pressure, respectively. The unit of the position S is mm and the unit of the time T is seconds. At the end of the weighing process, the screw
It is in the position of S0. In the injection process, the screw speed is 4
The stage is switched to the next stage, and the screw moves forward at the speed of Vn to the position of Sn (n = 1, 2, 3, 4). When the screw reaches the position of S4, a pressure-holding step is started, and HPn is sequentially performed for Tn (n = 1, 2, 3) seconds.
The pressure is applied to the screw. The setting is such that the curing of the resin in the cavity has been completed along with the end of the pressure holding step. The injection process is completed in about 0.8 seconds. The reason why the pressure-holding step is divided into several stages is to improve the quality of the product. In general, the pressure should be gradually lowered.

[0006] In the conventional injection molding method, the measuring step is started after the pressure holding step as described above is completed. In particular, when the nozzle is once separated from the mold after the pressure-holding step, the nozzle is closed with a shut-off valve after the pressure-holding step to prevent leakage of the molten resin, and a delay time for further ensuring reliability The weighing process is started after the process. However, if the weighing process is started after the pressure-holding process is completed as described above, the molding cycle becomes long, and the productivity is poor. Also, if the weighing process is to be shortened, a large load will be concentrated on the weighing process in the molding machine. Therefore, there is a limit to the shortening of the weighing process due to the capability of the molding machine.

On the other hand, for example, Japanese Patent Application Laid-Open No. Hei 1-108017 proposes a method of starting a measuring step in the middle of a pressure holding step. The reason for this is that the time for the entire pressure-holding step is set with a margin, and after the resin at the gate to the cavity is completely cured, the meaning of the pressure-holding is lost, and at the beginning of the measuring step, the screw is Attention is paid to the fact that there is no need to retreat, and around the time when the resin of the gate portion is expected to be cured, the screw is started to be rotated and the measuring process is started. Even if the weighing process starts,
Until the end of the pressure-holding step, the screw has a pressure-holding force and does not retreat. However, even in this method, since the measuring process is started when the resin in the gate portion is hardened, the overlapping time between the pressure holding process and the measuring process cannot be significantly increased, and the molding cycle can be significantly reduced. Not something.

[0008]

As described above, in the conventional injection molding, since the weighing step is started after the pressure-holding step is completed, there is a problem that the molding cycle becomes long and the productivity is poor. Was. Also, the method described in JP-A-1-108017 also starts the measuring step around the time when the resin of the gate portion is cured, so that the overlapping time between the pressure-holding step and the measuring step can be significantly increased. It is not possible to shorten the molding cycle significantly.

Further, Japanese Patent Application Laid-Open No. Hei 4-85221 discloses that a valve (closing valve) is provided on a nozzle of a cylinder, the valve is closed when the screw has re-advanced a predetermined distance during the pressure-holding step, and then the screw is closed immediately. It is described that by restarting the rotation, a plasticizing step for the next shot molding is started during the pressure holding step. However, in this method, the screw is advanced again by a predetermined distance before the valve is closed during the pressure-holding step, so that the pressure-holding may not be performed reliably. Japanese Patent Application Laid-Open No. 4-28521 also discloses that a valve is closed when a predetermined cavity internal pressure is detected. However, this requires a cavity internal pressure detecting means, and the control is complicated. There is a problem that can be troublesome.

[0010] The present invention is intended to solve such a problem, without adding a special structure to a conventional molding machine or mold, and without complicating and complicated control. And while ensuring weighing and holding pressure,
An object of the present invention is to enable the pressure-holding step and the measuring step to be largely overlapped in time, and to shorten the molding cycle.

[0011]

According to the injection molding method of the present invention, in order to achieve the above object, a cavity is formed between a plurality of mold members which are opened and closed, and a resin is communicated with the cavity and plasticized therein. A mold having a resin passage to maintain the state, a resin reservoir connected to the resin passage of the mold, and a pressing member movably provided in the resin reservoir, and the position and speed or A molding machine having control means for controlling according to pressure and time, and a valve provided in a resin passage from a resin reservoir of the molding machine to a cavity of the mold, and a predetermined amount of resin is supplied to the resin reservoir. A measuring step of storing the resin in a plasticized state, and after the measuring step, controlling the pressing member according to its position and speed to feed the resin in the resin reservoir into the mold by the pressing member. And a pressure-holding step of applying pressure to the resin in the mold following the injection step to compensate for the shrinkage of the resin due to the curing of the resin in the cavity. In this pressure-holding step, a constant pressure is applied. After pressing the pressing member for a certain period of time and applying a pressure sufficient to hold the resin in the mold by the pressing member, the valve is closed, and then the pressure of the resin in the mold causes the resin to enter the cavity. After the filling is advanced and the valve is closed, the measuring step is started in the middle of the pressure-holding step.

[0012]

According to the injection molding method of the present invention, in the injection step, the pressing member is controlled in accordance with the position and speed of the pressing member to fill the cavity of the mold with a resin in a plastic state. Pressure is applied to the resin in the mold to compensate for the shrinkage of the resin due to the curing of the resin in the cavity. In this pressure-holding step, the pressing member is pressed at a constant pressure for a certain period of time, and the mold is pressed by the pressing member. After applying sufficient pressure to the resin in the mold, the valve in the resin passage from the resin reservoir of the molding machine to the cavity of the mold is closed, and the resin passage on the resin reservoir side and the resin passage on the cavity side are closed. And cut off. Although the resin in the resin passage is kept in a plastic state, after the nozzle is closed, the resin in the cavity-side resin passage holds a sufficiently high pressure. Thus, the resin is supplemented from the resin passage into the cavity. On the other hand, on the molding machine side, after the valve is closed, measurement can be performed without any problem even during the pressure holding step.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. First, the configuration of the molding machine used will be described. This injection molding machine is of an in-line screw type. In FIG. 3, 1 is a fixed side platen, 2
Is a tie bar, 3 is a movable side platen, and 4 is a base. The movable platen 3 is driven by the mold closing device 5 to move the tie bar 2.
And moves toward and away from the fixed-side platen 1. The mold closing device 5 includes a toggle mechanism 7 driven by a servo motor 6 and the base 4.
And a hydraulic drive mechanism 8 acting on the tie bar 2. To the servomotor 6, control means 9 including a computer or the like is connected via a driving means 10 for the control thereof. Further, the hydraulic drive mechanism 8 is also connected to the control means 9 via the drive means 11 for the control.

Reference numeral 21 denotes a heating cylinder having a resin reservoir therein. The heating cylinder 21 is located on the opposite side of the movable platen 3 with respect to the fixed platen 1 and has a nozzle.
22 is provided at the left end. The nozzle 22 is provided with a rotary valve 23 for opening and closing the nozzle. As shown in detail in FIG. 4, the rotary valve 23 has a cylindrical shape and is rotatably slidably fitted to a valve seat 25 formed in a resin passage 24 in the nozzle 22.
It has a through hole 26 penetrating in the radial direction. Then, it is hydraulically driven, and the resin passage 24 and the through hole 26 are continuously opened as shown by a chain line, and are rotated by 90 ° and closed as shown by a solid line. The heating cylinder 21 has a band heater 27
Are provided on the outer peripheral surface, and a hopper 28 is provided on the upper right side. Then, the heating cylinder 21
Inside, a screw 29 as a pressing member is slidably fitted in the left-right direction in the figure. The screw 29 is connected to an output shaft of a motor 31 via a gear train 30 so as to be movable in the axial direction, and is driven to rotate by the motor 31. The screw 29 is rotatably connected to a slider 33 via a thrust bearing 32. A ball screw screw is attached to the slider 33.
34 is threaded. This ball screw screw 34
It is connected to the output shaft of a servomotor 36 via a gear train 35. With this configuration, when the output shaft of the servo motor 36 rotates, this rotation is transmitted to the ball screw 34 via the gear train 35, and the screw 29 advances with the slider 33 with the rotation of the ball screw 34. Or retreat. The motor 3
The control means 9 is connected to 1 and 36 via driving means 37 and 38 for the control. Further, a load cell 39 for detecting the pressure applied to the screw 29 is incorporated in the thrust bearing 32, and the control means 9 includes a load cell 39 for detecting the pressure applied to the screw 29.
Connected through 40. And the screw 29
Of the screw 29 detected based on the rotation of the servomotor 36, or controlled according to the pressure and time detected by the load cell 39. It has become.

Next, the configuration of the mold 50 will be described with reference to FIG. This mold is a hot runner mold
50, a fixed mold 51 attached to the fixed platen 1 and a movable mold attached to the movable platen 3
52 for forming a cassette half of a VHS video tape. Then, the fixed mold 51 and the movable mold 52, which are mold members, open and close as the movable platen 3 moves, and when the mold is closed, a product-shaped cavity 53 is formed between the fixed mold 51 and the movable mold 52. Things. The fixed mold 51
The fixed side mounting plate 58 is fixed to the back of the fixed side mold plate 54 forming the cavity 53 via the receiving plates 55 and 56 and the spacer block 57, and the receiving plate 56 and the fixed side mounting plate 58 A manifold 59 is provided between them. A sprue bush 60 to which the nozzle 12 of the molding machine is connected is fixed to the fixed mounting plate 58 in a penetrating state, and the inside of the sprue bush 60 is a sprue 61 which is a resin passage. A heater 62 is provided around the sprue bush 60. In the manifold 59, a runner 63 which is a resin passage communicating with the sprue 61 is formed.
Is provided. Further, the fixed side mold plate 54 and the receiving plate
A through hole 65 forming a resin passage is formed in each of 55 and 56, and a spear 67 is provided in a bush 66 embedded in the through hole 65.
Is provided. The runner 63 of the manifold 59 communicates with the bush 65. In addition, the through hole
The tip of 65 is a gate 68 that opens into the cavity 53. On the other hand, in the movable mold 52, a movable-side mounting plate is fixed via a receiving plate and a spacer block (not shown) to the back of a movable-side mold plate 69 forming the cavity 53. A protruding plate is provided between the movable plate and the movable-side mounting plate. The fixed mold 51 and the movable mold
The cooling water passage 70 is formed in the 52 so as to surround the cavity 53.

Next, an injection molding method using the molding machine and the mold 50 will be described. On the molding machine side,
The measuring step, the injection step, and the pressure holding step are sequentially repeated. In the measuring process, the rotary valve 23 is
With the 22 closed, the pallet of the thermoplastic resin supplied into the heating cylinder 21 is melted by the heating by the heater 27 and the shearing force accompanying the rotation of the screw 29.
A predetermined amount of the resin melted in this way is accumulated at the front end in the heating cylinder 21 by the retreat of the screw 29 while rotating. The injection step is performed after the end of the measuring step and when the mold is closed. In this injection step, after the rotary valve 23 is opened, the screw 29 advances and the molten resin in the heating cylinder 21 is injected from the nozzle 22 into the mold 50. Following the injection step, a pressure holding step is performed, and a predetermined pressure is applied to the screw 29 forward. Thereafter, the rotary valve 23 closes and the measuring process starts again. As shown in Table 2, the screw 29
Is controlled according to the speed and the position in the injection step, and is controlled according to the pressure and the time in the pressure holding step.

[0017]

[Table 2]

In Table 2, V is the speed of the screw 29,
HP is the holding pressure, which is expressed as a percentage of the maximum speed and the maximum pressure, respectively. The unit of the position S is mm and the unit of the time T is seconds. At the end of the weighing process, screw 29
Is at the position of S0. In the injection process, the speed of the screw 29 switches to four stages, and Sn (n = 1, 2, 3, 3)
The screw 29 advances at the speed of Vn to the position 4). When the screw 29 reaches the position of S4, a pressure-holding step is performed, and the screw 29 is pressurized with HP pressure for T seconds. As shown in FIG. 1, the injection process ends in about 0.75 seconds. Further, the rotary valve 23 closes 0.2 seconds after the end of the injection step. Further, the weighing process starts 0.3 seconds after the rotary valve 23 is closed.

In the case of the mold 50, the mold closing step is performed by the mold closing device 5 of the molding machine prior to the injection step. In this mold closing, the speed of the movable mold 52 with respect to the fixed mold 51 gradually decreases. The setting is gradually increased to 70 at maximum speed.
%, 60% and 40%. At that time, first, the movable mold 52 is generally closed with respect to the fixed mold 51 by the toggle mechanism 7. Next, the hydraulic drive mechanism 8 generates a sufficient mold clamping force of, for example, 150 t against the resin pressure. In terms of time, Figure 1
As shown in (2), the movable mold 52 comes into contact with the fixed mold 51 in 0.6 seconds from the start of mold closing (mold touch). At this point, only the contact is made, and no mold clamping force is generated. 0.3 seconds later, the final clamping force is reached. Then, the injection process starts at the time of mold touch 0.6 seconds after the start of mold closing. At the beginning of the injection process, since a large mold clamping force is not originally required, there is no problem if the injection process is started before the mold clamping is completed. Then, in the injection step, the molten resin injected from the nozzle 23 of the molding machine flows around the sprue 61, the runner 63 of the manifold 59, and the spear 67 sequentially, and flows into the cavity 53 from the gate 68. During the injection process, the cavity 53 is filled with a molten resin. In the pressure-holding step subsequent to the injection step, pressure is applied to the resin in the mold 50 to prevent the backflow of the molten resin from the cavity 53, and to reduce the amount of shrinkage due to cooling and curing of the resin. It is supplemented in the cavity 53. Then, after the resin in the cavity 53, that is, the product is sufficiently cooled and cured, the mold is opened,
The product is taken out. In addition, on the molding machine side, the rotary valve 23 is opened for a certain time immediately before the mold is opened, and suckback is performed. FIG. 2 shows the timing of opening and closing the rotary valve 23 throughout one molding cycle. And
One molding cycle takes about 13 seconds. Throughout the entire process, the sprue 61, the runner 63, and the resin in the through hole 65 of the mold 50 are always kept in a molten state by heating the heaters 62, 64.

By the way, from the start of the pressure-holding step to the closing of the rotary valve 23, the molten resin in the mold 50 is directly pressurized by the screw 29 of the molding machine. However, direct pressurization by the screw 29 becomes ineffective. When the rotary valve 23 closes, the resin in the cavity 53, including the gate 68,
It has not yet been cured, and is in the process of holding pressure. However, during the period from the start of the pressure holding process to the closing of the rotary valve 23, the pressurization of the screw 29 causes the die
The pressure of the molten resin in the resin passage centered on the runner 63 of the manifold 59 in 50 is sufficiently increased. After the rotary valve 23 is closed, the resin pressure inside the runner 63 and the like is maintained sufficiently high as described above,
Resin corresponding to shrinkage due to curing of the resin in the cavity 53 is supplemented from the through hole 65 into the cavity 53. In other words, the screw until the rotary valve 23 closes
The above-mentioned setting of the holding pressure and the time with respect to 29 is set so that the resin in the mold 50 obtains a pressure sufficient for the holding pressure after the rotary valve 23 is closed. Then, the filling of the cavity 53 with the resin proceeds until the resin in the mold 50 is pressure-saturated. Thereafter, the resin in the gate 68 is completely cured and the gate is sealed. Note that, in order to effectively maintain the pressure by the resin pressure in the mold 50, the volume of the runner 63 is preferably about 1.5 times the volume of the cavity 53, but is not limited thereto.

Thus, according to the configuration of the embodiment, the measuring step can be started during the pressure-holding step and at the stage where the resin in the cavity 53 including the gate 68 is not cured. And the weighing process can be largely overlapped in time. That is, compared to the conventional method, the time until the start of the measuring process can be reduced by about 5 seconds, and in combination with starting the injection process before the end of the mold clamping, other conditions are the same as in the conventional method.
The time for one molding cycle, which took about 19 seconds, can be greatly reduced to about 14 seconds. And as already explained,
Since the pressure is maintained by the pressure of the molten resin in the mold 50, and the measurement is performed after the nozzle 22 is closed by the rotary valve 23, the measurement can be performed reliably and accurately. Such a reduction in time is possible without adding a special structure to a conventional molding machine or mold, and the performance of the molding machine can be maximized. Furthermore, during the pressure-holding process, the screw 29 is pressurized at a constant pressure for a certain period of time until the weighing process starts, so that the control is not complicated and troublesome. The control becomes simpler than the control of switching the pressure and time to be used in a plurality of stages. As an additional effect of shortening the molding cycle, depending on the product or the like, the spear 67 may always be turned off. This is because the resin in the gate 68 always maintains a certain degree of fluidity. However, when starting up,
It is necessary to heat the spear 67.

It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made. For example,
The time of each step, the position and speed of the screw, the setting of the holding pressure, and the like naturally vary depending on the product to be molded and other conditions. In the above embodiment, the rotary valve 23 was closed during the period from the mold opening process to the mold closing process.
It may be left open as shown in FIG. Further, the mold and the molding machine are not limited to those of the above-described embodiment. For example, in addition to the in-line screw type as in the above-described embodiment, a pre-plasticization type molding machine may be used. Further, the valve for opening and closing the nozzle is not limited to the rotary valve.
However, the structure must be able to sufficiently withstand the resin pressure.
In addition, the position where the valve is provided is not limited to the nozzle on the molding machine side, but may be on the mold side. In addition, the mold,
In addition to the spear system, a valve system can be used. In a mold for a valve system that opens and closes a gate with a valve, the gate is closed immediately before the mold is opened.

[0023]

According to the present invention, in the injection molding using a mold in which the resin in the resin passage to the cavity is kept in a plastic state, in the pressure-holding step, the molding machine is kept at a constant pressure for a fixed time. After applying a pressure sufficient to hold the resin in the mold by the pressing member, the valve provided in the resin passage from the resin reservoir of the molding machine to the cavity of the mold is pressed. Close, after this, the filling of the resin into the cavity is advanced by the pressure of the resin in the mold, and after the valve is closed, the weighing process starts in the middle of the pressure-holding process. The pressure-holding process and the weighing process can be largely overlapped in time without adding a complicated structure, making the control complicated and complicated, and ensuring the weighing and holding pressure. The molding cycle can be shortened.

[Brief description of the drawings]

FIG. 1, showing an embodiment of the present invention, is a timing chart showing steps from mold closing to weighing.

FIG. 2 is a timing chart for opening and closing the valve.

FIG. 3 is a schematic explanatory view of the injection molding machine.

FIG. 4 is a cross-sectional view of the mold.

FIG. 5 is a timing chart for opening and closing a valve according to another embodiment of the present invention.

[Description of Signs] 9 Control means 21 Heating cylinder (resin reservoir) 23 Rotary valve (valve) 24 Resin passage 29 Screw (pressing member) 50 Mold 51 Fixed mold (mold member) 52 Movable mold (mold member) 53 Cavity 61 Sprue (resin passage) 63 Runner (resin passage) 65 Through hole (resin passage)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (1)

(57) [Claims] A mold having a cavity formed between a plurality of mold members to be opened and closed and having a resin passage communicating with the cavity and keeping a resin in a plastic state inside, and connected to a resin passage of the mold. A molding machine having a resin reservoir portion and a pressing member movably provided in the resin reservoir portion, and having control means for controlling the pressing member according to its position, speed or pressure and time. Using a valve provided in a resin passage from the resin reservoir to the cavity of the mold, a measuring step of storing a predetermined amount of resin in a plastic state in the resin reservoir, and after this measuring step, the pressing member is moved to its position and An injection step in which the resin in the resin reservoir is fed into the mold by a pressing member under control according to the speed, and a pressure is applied to the resin in the mold following this injection step to harden the resin. And a pressure holding step of supplementing the resin in the cavity with the amount of shrinkage caused by the pressure change. In this pressure holding step, the pressing member is pressed with a constant pressure for a certain period of time and the pressing member holds the resin in the mold. After applying sufficient pressure, the valve is closed, then the filling of the resin into the cavity is progressed by the pressure of the resin in the mold, and after the valve is closed, the weighing process starts in the middle of the pressure-holding process. Injection molding method.