JP3118188B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an injection molding method.

[0002]

2. Description of the Related Art Conventionally, an injection molding machine has an injection device, and a screw is disposed in a heating cylinder of the injection device so as to be rotatable and movable back and forth, and the screw is rotated or moved forward and backward by driving means. Or to be able to. Then, at the time of the measuring step, the screw is retracted while rotating forward, the resin dropped from the hopper is melted and stored in front of the screw head, and at the time of the injection step,
The screw is advanced to inject the molten resin from the injection nozzle.

By the way, during the injection step, the resin stored in front of the screw head is prevented from flowing backward. To this end, the screw head has a conical (conical) head body at the front and a small diameter at the rear. Then, an annular check ring is provided on the outer periphery of the small diameter portion, and a resin flow path is formed between the small diameter portion and the check ring. Further, a seal ring is provided at a front end of the screw so as to be able to freely contact and separate from a rear end of the check ring.

In the injection molding method using the injection device having the above-described structure, when the screw is advanced during the injection step, the resin stored in front of the screw head tends to flow backward. At this time, the check ring moves backward relative to the screw due to the pressure of the resin, and the rear end of the check ring contacts the seal ring to perform sealing. As a result, it is possible to prevent the resin stored in front of the screw head from flowing backward.

On the other hand, when the screw is retracted while rotating forward during the measuring step, the check ring moves forward relative to the screw due to the pressure of the resin, and the front end of the check ring is in the head body. Although it abuts on the rear end, since the notch extending in the axial direction is formed at a plurality of locations around the head main body, the movement of the resin is not hindered.

[0006]

However, in the conventional injection molding method, not only the time required for the rear end of the check ring to come into contact with the seal ring during the injection step, but also for the sealing to be completed, becomes longer. However, the amount by which the screw advances before the sealing is completed increases.

When the measuring step is completed, the pressure of the resin behind the check ring (hereinafter referred to as "rear pressure") is increased by the pressure of the resin before the check ring (hereinafter referred to as "front pressure"). .)). FIG. 2 is a pressure distribution diagram before the start of the injection process in the heating cylinder in the conventional injection molding method, and FIG. 3 is a diagram showing a pressure change after the start of the injection process in the conventional injection molding method. In FIG. 3, the horizontal axis represents time t, and the vertical axis represents resin pressure P.

In FIG. 2, R is a check ring (not shown).
Where P is located, P₁Is the forward pressure, P_TwoIs the back pressure
is there. By the way, during the measurement process, the resin is
The resin flow formed between the small diameter portion of the
To move forward through the channel and notch,
The notches do not have a sufficient cross section and therefore have high resistance.
Therefore, after the weighing process is completed, the injection process starts.
In the meantime, as shown in FIG. _TwoIs forward
Pressure P₁Higher, P₁<P_Two become.

In this state, when the injection step is started and the screw is advanced, the resin stored in front of the screw head is pushed forward by the screw head, and as shown in FIG. pressure P ₁ becomes gradually higher. At this time, since the rear end of the check ring is not in contact with the seal ring, sealing is not performed, and a portion of the resin in front of the screw head flows back through the space between the check ring and the seal ring. Therefore, the rear pressure P ₂ is also gradually increases.

[0010] Subsequently, the accompanying to the distance between the non-return ring and the seal ring is reduced, the amount of reverse flow to the resin is reduced, the rear pressure P ₂ is gradually lowered. Then, when the differential pressure ΔP, that is, ΔP = P ₂ −P ₁ becomes 0, and subsequently, the front pressure P ₁ becomes higher than the rear pressure P ₂ , the check ring starts retreating. Thereafter, when the backflow prevention ring reaches the closed point, seal is completed, the rear pressure P ₂ becomes zero.

As described above, when the metering process is completed, that is, when the injection process is started, the rear pressure P ₂ is higher than the front pressure P ₁ , so that the time required for the check ring to start retreating is reduced. Not only is the time longer by the differential pressure ΔP, but also the time until the sealing is completed is longer. As a result, the amount of advance of the screw from the start of the injection process to the end of the sealing increases.

Since the rear pressure P ₂ when the measuring step is completed differs depending on the plasticization state of the resin, the differential pressure ΔP varies for each molding. Therefore, the timing at which the sealing is performed for each shot also varies, and the amount of resin flowing back through the space between the check ring and the seal ring varies before the sealing is completed.

As a result, molding defects such as shorts and burrs occur in the molded product. An object of the present invention is to solve the problems of the conventional injection molding method and to provide an injection molding method in which molding defects do not occur in a molded product.

[0014]

For this purpose, in the injection molding method of the present invention, after the weighing step is completed and before the injection step is started, the reverse position in the heating cylinder is maintained while maintaining the position of the screw. After lowering the pressure of the resin behind the stop ring and starting the injection step, the screw is advanced to bring the rear end of the check ring into contact with the seal ring.

In another injection molding method of the present invention, the pressure of the resin behind the check ring in the heating cylinder is further reduced by rotating the screw in a direction opposite to that in the measuring step.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of a main part of an injection device according to an embodiment of the present invention. In the figure, reference numeral 11 denotes a heating cylinder;
1 has an injection nozzle 13 at the front end (left side in the figure). A screw 12 is provided in the heating cylinder 11 so as to be rotatable and movable back and forth, and the screw 12 can be rotated and advanced and retracted by a driving means (not shown). Usually, an injection cylinder, an electric motor or the like is used as the driving means.

The screw 12 extends rearward (to the right in the drawing) in the heating cylinder 11, is connected to the driving means at a rear end, and has a screw head 14 at a front end. The surface of the metering portion 18 of the screw 12 has a spiral flight 1
5 are formed, and the grooves 15 are formed by the flights 15.

A hopper (not shown) is provided at a predetermined position behind the heating cylinder 11, and a pellet-shaped resin is charged into the hopper. In the injection device having the above-described configuration, in the measuring step, when the driving unit is driven and the screw 12 is retracted while rotating forward, the pellet-shaped resin in the hopper falls into the heating cylinder 11,
The groove 16 is advanced.

A heater (not shown) is provided on the outer circumference of the heating cylinder 11 so that the heating cylinder 11 can be heated by the heater to melt the resin in the groove 16. Therefore, when the screw 12 is retracted by a predetermined amount while rotating forward, one shot of the melted resin is stored in front of the screw head 14.

Next, when the driving means is driven to advance the screw 12 during the injection step, the resin stored in front of the screw head 14 is injected from the injection nozzle 13 and the mold cavity (not shown) is formed. The space is filled. By the way, during the injection process, the resin stored in front of the screw head 14 is prevented from flowing backward.

For this purpose, the screw head 14
Has a conical head body 21 at the front and a small diameter portion 19 at the rear. An annular check ring 20 is provided on the outer periphery of the small diameter portion 19, and the small diameter portion 19 and the check ring 20
And a resin flow path 24 is formed. A seal ring 22 is provided at the front end of the metering portion 18 of the screw 12 so as to be able to freely contact and separate from the rear end of the check ring 20.

Therefore, when the screw 12 is advanced during the injection step, the resin stored in front of the screw head 14 tends to flow backward. At this time, the check ring 20 moves rearward relative to the screw 12 due to the pressure of the resin, and the rear end of the check ring 20 contacts the seal ring 22 to perform sealing. As a result, the resin stored in front of the screw head 14 can be prevented from flowing backward.

On the other hand, when the screw 12 is retracted while rotating forward during the measuring step, the check ring 20 moves forward relative to the screw 12 due to the pressure of the resin, and the front end of the check ring 20 is moved. It comes into contact with the rear end of the head main body 21. However, since the notch 25 extending in the axial direction is formed at a plurality of locations around the head main body 21, the movement of the resin is not hindered.

When the measuring step is completed, suck-back can be performed so that the resin does not drop from the tip of the injection nozzle 13. In that case, the screw 12 is further retracted by a small amount without being rotated. By the way, when the rear pressure P ₂ (see FIG. 3) becomes higher than the front pressure P ₁ at the time when the measuring process is completed, the rear end of the check ring 20 comes into contact with the seal ring 22 during the injection process, and the sealing is completed. Not only does the time required for the screw 12 to increase, but also the amount by which the screw 12 advances by the time the sealing is completed is increased.

FIG. 4 is a pressure distribution diagram in the heating cylinder at the time of completion of the measuring step in the embodiment of the present invention, and FIG. 5 is a pressure distribution diagram in the heating cylinder before the start of the injection step in the heating cylinder in the embodiment of the present invention. FIG. 6 is a diagram showing a pressure change after the start of the injection step in the heating cylinder according to the embodiment of the present invention. In FIG. 6, time t is plotted on the horizontal axis, and pressure P of the resin is plotted on the vertical axis.

[0026] In FIG 4, R is a position check ring 20 (FIG. 1) is disposed, P ₁ is a front pressure, P ₂ is the rear pressure. By the way, the resin moves forward through the resin flow path 24 and the notch 25 during the measuring step, but the resin flow path 24 and the notch 25 do not have a sufficient cross section, so that the resistance is large, and the measuring step is not performed. during the period from the completion of the exit step is started, as shown in FIG. 4, the rear pressure P ₂ is higher than the front pressure P _1, it becomes P ₁ <P _2.

Therefore, when the injection process is started,
And the rear pressure P_TwoIs the forward pressure P ₁Higher, so reverse
The time until the stop ring 20 starts retreating is the differential pressure ΔP ΔP = P_Two−P₁ Not only the length, but also the
The time will be longer. As a result, after the injection process started
The amount by which the screw 12 advances before the sealing is completed
Will increase.

Therefore, before the injection step is started, the screw 12 is rotated by a predetermined amount in a direction opposite to that in the measuring step. In this case, the resin of the take (oysters) Preparative effect flight 15 of the screw 12, the lower the rear pressure P _2, as shown in FIG. 5, the rear pressure P ₂ is lower than the front pressure P _1. For this purpose, when the weighing process is completed, the delay timer is operated, and the screw 12 is rotated in a direction opposite to that in the weighing process for a set time, or the screw 12 is rotated in a direction opposite to that in the weighing process for the set number of revolutions. As a result, screw 1
The rotation angle in the opposite direction of 2 is set to 1/4 to 1/2 rotation.

When the screw 12 is rotated by a predetermined amount in a direction opposite to that in the measuring step, a small amount of resin flows back through the space between the check ring 20 and the seal ring 22, so the pressure P ₁ is also slightly lower. Then, when suckback is performed when the weighing process is completed, the screw 12 is rotated in the opposite direction while performing suckback.

Subsequently, in this state, the injection process is started, and when the screw 12 is advanced, the resin stored in front of the screw head 14 is pushed forward by the screw head 14, so that as shown in FIG. ,
Front pressure P ₁ is gradually increased. At this time, since the rear end of the check ring 20 is not in contact with the seal ring 22,
Sealing is not performed, a part of the front of the resin of the screw head 14 from flowing back missing between the check ring 20 and the seal ring 22, since the rear pressure P ₂ is lower than the front pressure P _1, the injection step The check ring 20 starts retreating simultaneously with the start.

Accordingly, as the distance between the check ring 20 and the seal ring 22 becomes shorter, the amount of the resin flowing backward decreases, and the rear pressure P ₂ rapidly decreases. When the check ring reaches the closed point, seal is completed, the rear pressure P ₂ becomes zero. Thus, when the metering step is completed, i.e., at the time the injection process is started, since the rear pressure P ₂ is lower than the front pressure P _1,
The check ring 20 starts retreating with the start of the injection process. Therefore, the time from the start of the injection process to the end of the sealing is shortened, and the screw 1 during that time is shortened.
2 can be reduced in the amount of advance.

As a result, the variation in the timing at which the sealing is performed for each shot is reduced, and the variation in the amount of resin flowing back through the space between the check ring and the seal ring is reduced before the sealing is completed. It is possible to prevent the occurrence of molding defects such as short-circuits and burrs on the molded product. FIG. 7 is a hydraulic circuit diagram of the driving unit according to the embodiment of the present invention, FIG. 8 is a diagram illustrating a control device of the hydraulic circuit according to the embodiment of the present invention, and FIG. 9 is an operation of the driving unit according to the embodiment of the present invention. It is a figure showing a table.

In FIG. 7, reference numeral 141 denotes an injection cylinder as a driving means for moving the screw 12 (FIG. 1) forward and backward in the injection process. The injection cylinder 141 is movable in and out of the cylinder body 142 and the cylinder body 142. And a piston rod 146 in front of the piston 143 is connected to the screw 12. And the piston 143
A first oil chamber 144 is formed further forward (left side in the figure), and a second oil chamber 145 is formed rearward (right side in the figure). In this case, the oil is supplied to the first oil chamber 144, and the piston 143 is retracted by draining the oil from the second oil chamber 145, so that the oil is supplied to the second oil chamber 145, and the first oil chamber is supplied. By draining the oil from 144, the piston 143 can be advanced.

Reference numeral 148 denotes an oil motor as a driving means for rotating the screw 12 forward or backward, and drives the oil motor 148 in the forward direction in the measuring step. Can be rotated forward. After that, the screw 12 can be rotated in the reverse direction by driving the oil motor 148 in the reverse direction during a set period from the completion of the measuring step to the start of the injection step.

Reference numeral 149 denotes a hydraulic pressure source. The hydraulic pressure source 149 is connected to the switching valve 151 via an oil passage L-1.
-2, to the on-off valve 153, to the pressure reducing valve 154 via the oil passage L-3, and to the switching valve 155 via the oil passage L-4. Further, the switching valve 151 is provided with an oil passage L-6.
And the switching valve 152 is connected to the second oil chamber 145 of the injection cylinder 141 via an oil passage L-7.

Further, the on-off valve 153 is connected to the first oil chamber 144 of the injection cylinder 141 via an oil passage L-8, and the switching valve 155 is connected via an oil passage L-9. Note that a check valve 162 is provided in the oil passage L-9. The switching valve 152 is connected to the oil motor 148 via oil passages L-10 and L-11, and the pressure reducing valve 154 is connected to the oil passage L-L.
The switching valve 156 is connected to the switching valve 156 via a pilot oil passage L-13.
3 is connected. The oil pressure source 149 and the first oil chamber 144 of the injection cylinder 141 are connected via an oil passage L-14, and a check valve 161 is provided in the oil passage L-14.

The switching valve 151 is provided with solenoids a and b. When the solenoid a is turned on and the solenoid b is turned off, the position A is set. When the solenoids a and b are turned on, the position B is set.
When the solenoid a is turned off and the solenoid b is turned on, the position C is taken. Then, at the position A, the oil passage L-1 and the oil passage L-7 are communicated, and the oil from the hydraulic source 149 is supplied to the second oil chamber 145 of the injection cylinder 141. At this time, the oil passage L-6 and the oil tank 160 are shut off. Further, at the position B, the oil passage L-7 and the oil tank 160 are communicated, and the oil in the second oil chamber 145 is drained. Then, at the position C, the oil passage L
-1 and the oil passages L-6 and L-7 are communicated.

The switching valve 152 has a solenoid b,
When the solenoid b is turned off, the position A is moved to the solenoid b.
Is turned on, the position B is taken. Then, at the position A, the oil passage L-6 and the oil passage L-10 are communicated, and the oil motor 148 is driven in the forward direction. Further, at the position B, the oil passage L-6 and the oil passage L-11 communicate with each other, and the oil motor 148 is driven in the opposite direction.

The switching valve 156 has a solenoid b,
When the solenoid b is turned off, the position A is set, and when the solenoid b is turned on, the position B is set. Then, at the position A, the pilot oil passage L-13 and the oil tank 160 are communicated, and the pilot pressure applied to the on-off valve 153 is eliminated. Further, at position B, the oil passage L-12 and the pilot oil passage L-13 are communicated, and a pilot pressure is applied to the on-off valve 153.

The on-off valve 153 is connected to the pilot oil passage L
Position A is taken when pilot pressure is applied via -13, and position B is taken when pilot pressure is not applied. Then, at the position A, the oil passage L-2 and the oil passage L-8 are shut off, at the position B, the oil passage L-2 and the oil passage L-8 are communicated, and oil from the oil pressure source 149 is discharged from the injection cylinder. 141 is supplied to a first oil chamber 144.

The switching valve 155 includes a solenoid a.
When the solenoid a is turned on, the position A is moved to the solenoid a.
Is turned off, position B is taken. Then, at the position A, the oil passage L-4 and the oil passage L-9 are communicated, and the hydraulic pressure source 14
9 is supplied to the first oil chamber 144 of the injection cylinder 141. Further, at the position B, the oil passage L-9 and the oil tank 160 are communicated, and the oil in the first oil chamber 144 is drained.

Next, each of the switching valves 151, 152, 155,
The operation of 156 will be described. In FIG. 8, 171
Is a control device, and the control device 171 and each switching valve 15
1, 152, 155, and 156, drivers 172 to 175 are provided, respectively.
5, the solenoids a (FIG. 7), b,
The solenoid b of the switching valve 152, the solenoid a of the switching valve 155, and the solenoid b of the switching valve 156 are turned on / off.

In the measuring step, as shown in FIG. 9, the switching valve 151 is at the position C and the switching valve 152 is at the position A.
Respectively. Also, the switching valve 156 is located at the position A, and as a result, the on-off valve 153 is located at the position B. Therefore, the oil motor 148 can be driven in the forward direction and the screw 12 can be moved backward while rotating forward. At this time, the switching valve 155 is placed at the position B.

When the measuring step is completed, the switching valve 151 is placed at the position C and the switching valve 152 is placed at the position B. Further, the switching valve 156 is also located at the position B, the pilot pressure is applied to the on-off valve 153, and the on-off valve 153 is located at the position A. Therefore, the screw 12 is rotated by a predetermined amount in the direction opposite to the direction of the measuring step, and the rear pressure P ₂ (FIG. 6) is made lower than the front pressure P ₁ . At this time, the switching valve 155 is placed at the position B.

Then, the screw 12 (FIG. 1) tries to move forward, but on the suckback side of the injection cylinder 141,
That is, since the oil remains in the first oil chamber 144, the screw 12 does not move and is placed at the position where the measuring process is completed. Thus, the position of the screw 12 is maintained. Thereafter, in the suckback process, the switching valve 151 is placed at the position B, and the switching valve 152 and the switching valve 155 are placed at the position A. Also, the switching valve 15
6 is placed in position B, so that on-off valve 153 is in position A
To be placed. Therefore, the screw 12 is retracted,
Suck back can be done.

Next, in the injection step, the switching valve 151 and the switching valve 152 are set at the position A. Also, the switching valve 15
6 is also located at position A, so that on-off valve 153 is at position B
To be placed. Therefore, the screw 12 can be advanced. At this time, the switching valve 155 is in the position B
To be placed. In the present embodiment, the screw 12
The injection cylinder 141 moves the screw 12 forward and backward, and the oil motor 14 moves the screw 12 forward and reverse.
8 are used, but an electric motor may be used instead of the injection cylinder 141 and the oil motor 148.

The present invention is not limited to the above embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0048]

As described above in detail, according to the present invention, in the injection molding method, after the weighing step is completed and before the injection step is started, the heating is performed while maintaining the screw position. After lowering the pressure of the resin behind the check ring in the cylinder and starting the injection step, the rear end of the check ring is brought into contact with the seal ring by advancing the screw.

In this case, if the pressure of the resin behind the non-return ring in the heating cylinder is reduced while maintaining the position of the screw, the resin flying behind the non-return ring is reduced by the effect of scraping the resin by the flight of the screw. Is lower than the forward pressure. Therefore, the check ring starts retreating simultaneously with the start of the injection process. Then, as the distance between the check ring and the seal ring becomes shorter, the amount of the resin flowing backward decreases, and the pressure of the resin behind the check ring rapidly decreases.

Further, the time from the start of the injection step to the end of the sealing is shortened, and the amount of advance of the screw during that time can be reduced. As a result, fluctuations in the timing at which sealing is performed for each shot are reduced, and variations in the amount of resin flowing back through the space between the check ring and the seal ring are reduced before the sealing is completed. It is possible to prevent occurrence of molding defects such as short-circuits and burrs in the molded product.

In another injection molding method of the present invention, the pressure of the resin behind the check ring in the heating cylinder is further reduced by rotating the screw in a direction opposite to that in the measuring step. In this case, while holding the position of the screw, when the screw is rotated in the opposite direction to the time of the metering process, due to the scraping effect of the resin by the flight of the screw, the pressure of the resin behind the check ring is lower than the front pressure. .

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an injection device according to an embodiment of the present invention.

FIG. 2 is a pressure distribution diagram before a start of an injection step in a heating cylinder in a conventional injection molding method.

FIG. 3 is a diagram showing a pressure change after the start of an injection step in a conventional injection molding method.

FIG. 4 is a pressure distribution diagram at the time of completion of a measuring step in a heating cylinder according to the embodiment of the present invention.

FIG. 5 is a pressure distribution diagram before the start of an injection step in the heating cylinder according to the embodiment of the present invention.

FIG. 6 is a diagram showing a pressure change after a start of an injection step in a heating cylinder in the embodiment of the present invention.

FIG. 7 is a hydraulic circuit diagram of a driving unit according to the embodiment of the present invention.

FIG. 8 is a diagram showing a control device of the hydraulic circuit according to the embodiment of the present invention.

FIG. 9 is a diagram showing an operation table of a driving unit in the embodiment of the present invention.

[Explanation of symbols]

11 heating cylinder 12 screw 20 backflow prevention ring 22 sealing ring P ₁ front pressure P ₂ rear pressure

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/00-45/17 B29C 45/46-45/63 B29C 45/76-45/84

Claims (2)

(57) [Claims] (A) After the completion of the measuring step and before the start of the injection step, while maintaining the position of the screw,
Reducing the pressure behind the resin than the check ring in the heating cylinder, and characterized by contacting the (b) after starting the injection step, the rear end of the sealing ring of the check ring by advancing the screw Injection molding method. 2. The injection molding method according to claim 1, wherein the pressure of the resin behind the check ring in the heating cylinder is reduced by rotating the screw in a direction opposite to that in the measuring step.