JPH07290533A - Injection molding machine - Google Patents

Abstract

(57) [Summary] [Purpose] The quality of molded products is designed to prevent backflow without the provision of a check valve to avoid resin stagnation and to avoid adverse effects such as injection pressure reduction and injection volume reduction. Improve. The injection molding machine 2 has a heating cylinder 6 having a nozzle 4 at its tip, and a conical screw 8 rotatably provided in the heating cylinder 6 and capable of advancing and retracting in the axial direction of the heating cylinder 6. And a plunger 10 is provided in the screw 8 so as to be movable back and forth in the axial direction of the heating cylinder 6. A plunger space 12 serving as a reservoir for the molten resin is formed inside the tip of the screw 8, and the molten resin can be measured without providing a reservoir space between the heating cylinder 6 and the screw 8. ing. The forward movement of the screw 8 causes the inner surface of the heating cylinder 6 and the tip of the screw 8 to come into close contact with each other, thereby preventing the reverse flow of the molten resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine used for resin molding, and more particularly to an injection molding machine aimed at improving the backflow prevention of molten resin during injection.

[0002]

2. Description of the Related Art Since an in-line screw type injection molding machine uses a screw as a plunger, a so-called backflow occurs in which molten resin flows back through a screw groove of the screw at the time of injection, resulting in a decrease in injection amount and a mold cavity. Problems such as the reduction of the filling pressure in and the reduction of the holding pressure after injection were unavoidable.

For this reason, measures have conventionally been taken to add a check valve of ring type or ball check structure to the screw head.

[0004]

By the way, in the structure in which the check valve is added as described above, for example, in the case of a ring type, the resin that has entered the contact surface between the ring that rotates freely and the screw head is heated by friction heat. It easily causes burns and flashes, and has a fatal defect of a resin retention structure from the viewpoint of high quality molding such as optical lens molding.

For this reason, the ring is provided with a pawl so as to be rotated simultaneously with the screw, and a so-called straight type structure is used to minimize the gap between the screw head and the heating cylinder when the injection is completed to minimize the residual resin amount. Measures are taken.

However, in the structure in which the check valve is added, the problem of resin retention is still unsolved, and
With the straight type structure, the problem of a drop in injection pressure due to the existence of a gap cannot be ignored.

Therefore, an object of the present invention is to provide an injection molding machine capable of avoiding a resin retention structure and solving the problem of reduction in injection pressure, and therefore being able to sufficiently deal with high quality molding such as optical lens molding. .

[0008]

According to the present invention, a screw is rotatably provided in a heating cylinder having a nozzle at its tip and is movable back and forth in the axial direction of the heating cylinder, and a plunger is the same as the screw in the screw. A plunger space for accommodating molten resin is formed so that it can move forward and backward in a certain direction, and the forward movement of the screw causes the tip of the screw to come into close contact with the inner surface of the heating cylinder, cutting off communication between the groove of the screw and the plunger space. It is in the configuration.

According to the present invention, the gap between the tip of the screw and the inner surface of the heating cylinder during plasticization can be set to be narrower than the groove depth of the screw.

The screw may be formed in a conical shape in which the diameter gradually decreases toward the nozzle side, or the screw has a constant outer diameter throughout and a groove. It is also possible to adopt a configuration in which the shape is gradually reduced toward the nozzle side.

Further, a feature of the present invention is that a screw is rotatably provided in a heating cylinder having a nozzle at its tip, and a plunger is provided in the screw so as to be able to advance and retreat in the axial direction of the screw and the molten resin. A plunger space for storing the heat is formed, and the nozzle is installed in the heating cylinder so that it can move back and forth, and when the nozzle touches the mold, the nozzle moves in close contact with the screw tip to block the communication between the screw groove and the plunger space. It is in the configuration.

Further, in the above structure, the gap between the nozzle and the tip of the screw at the time of plasticizing can be set to be narrower than the groove depth of the screw.

The screw may be formed in a conical shape in which the diameter gradually decreases toward the nozzle side, or the screw has a constant outer diameter throughout and a groove. It is possible to adopt a configuration in which the shape is gradually shallowed toward the nozzle side.

[0014]

According to the present invention, the plasticized resin material is sent to the nozzle side by the rotation of the screw and stored in the plunger space. When a predetermined amount of the molten resin is accumulated in the plunger space, the screw advances and the tip of the screw comes into close contact with the inner surface of the heating cylinder, and the communication between the groove of the screw and the plunger space is cut off to perform the measurement. In this state, the plunger advances, and the measured molten resin is injected into the cavity of the mold without backflow. After the injection is completed, the screw retracts, and the molten resin is restarted to be fed into the plunger space.

In the structure in which the gap between the tip of the screw and the inner surface of the heating cylinder is set to be narrower than the groove depth of the screw during plasticization, the flow velocity and pressure of the molten resin increase in passing through the gap, and plasticization is promoted. To be done.

The screw is formed in a conical shape in which the diameter gradually decreases toward the nozzle side, or the screw has a constant outer diameter throughout and the groove gradually becomes shallower toward the nozzle side. In the formed structure, the compression ratio is increased toward the nozzle side, and the plasticization is promoted accordingly.

Further, according to the present invention, when the nozzle touches the mold, the nozzle is retracted to come into close contact with the tip of the screw,
The communication between the groove of the screw and the plunger space is cut off and the measurement is performed. In this state, the plunger advances, and the measured molten resin is injected into the cavity of the mold without backflow. When the nozzle touch is released after the injection is completed, the nozzle is advanced by the feeding pressure of the molten resin, and the feeding of the molten resin into the plunger space is restarted.

[0018]

1 to 3 show an embodiment of the present invention, which is an example corresponding to claim 3. In FIG. The injection molding machine 2 has a heating cylinder 6 having a nozzle 4 at its tip, and a conical screw 8 rotatably provided in the heating cylinder 6 and capable of advancing and retracting in the axial direction of the heating cylinder 6.
And a plunger 10 is provided in the screw 8 so as to be movable back and forth in the axial direction of the heating cylinder 6.

Further, a plunger space 12 as a storage portion for the molten resin is formed inside the tip side of the screw 8, and the molten resin is measured without providing a storage space between the heating cylinder 6 and the screw 8. You can do it. The screw 8 has a conical plasticizing portion 14,
The spiral groove 18 having a constant diameter is formed from the feed portion 16 to the tip of the plasticizing portion 14.

An orbiting slope 6 is provided at the inner surface of the heating cylinder 6.
a is formed, and correspondingly, a contact slope 8a is formed at the tip of the screw 8 so as to be in close contact with the orbiting slope 6a. Gap C between the orbiting slope 6a and the orbiting contact surface 8a
Has a so-called “seki” function, and its dimension t ₁
Is set to be smaller than the depth d ₁ of the spiral groove 18 during plasticization.

The material supply port 2 communicating with the spiral groove 18 is provided at a position corresponding to the feed portion 16 of the heating cylinder 6.
0 is formed, and a plurality of rod-shaped heaters 22 are embedded in a position corresponding to the plasticizing portion 14 substantially in parallel to the outer surface of the screw 8 and in a substantially radial shape. In FIG. 1, reference numeral 24
Indicates a band heater.

Next, the plasticizing function and the injection operation of the injection molding machine 2 will be described. The resin material P supplied from the material supply port 20 is sent to the plasticizing section 14 via the feed section 16, but the plasticizing section 14 has a conical characteristic, and the compression ratio is gradually increased toward the nozzle 4 side. As a result, plasticization is gradually promoted. Further, since the tip end side has the safety structure as described above, as shown in FIG.
The flow velocity and the pressure of the molten resin M increase in the gap C, which further promotes the plasticization. Since the resin material P is supplied from the feed portion 16 having a constant diameter, the resin material P can be smoothly supplied without being affected by the return pressure due to the high compression characteristic of the plasticizing portion 14.

When the molten resin M which has passed through the gap C is accumulated in the plunger space 12 and reaches a predetermined amount, the screw 8 advances and the abutment slope 8a at the tip thereof is advanced as shown in FIG.
Comes into close contact with the orbiting inclined surface 6a of the heating cylinder 6, whereby the dimension t _{1 of the} clearance C becomes zero, and the spiral groove 18 and the plunger space 12 are cut off from each other for measurement. After this, the plunger 10 advances, and the measured molten resin M is injected into the cavity (not shown) of the mold.

As is apparent from FIG. 4, the spiral groove 18 and the plunger space 12 are completely blocked by the close contact between the orbiting inclined surface 6a and the contacting inclined surface 8a, so that no backflow occurs during injection, In addition, since there is no check valve, resin retention can be avoided.

Since back flow does not occur, it is possible to avoid adverse effects on the molding due to a decrease in injection pressure and a decrease in injection amount, and it is possible to perform satisfactorily even with a material that requires a holding pressure after injection for a long time. In this example, the structure for promoting plasticization by the gap C is shown, but a structure without the function may be used.

Next, FIGS. 5 and 6 show an embodiment corresponding to claim 4, which is an example of application to an in-line screw type. The injection molding machine 26 is provided with a heating cylinder 30 having a nozzle 28 at its tip, and a screw 32 having a constant diameter rotatably provided in the heating cylinder 30 and capable of advancing and retracting in the axial direction of the heating cylinder 0. In the screw 32, a plunger 34 is provided so as to be movable back and forth in the axial direction of the heating cylinder 30.

Further, as in the above-mentioned example, a plunger space 36 as a molten resin reservoir is formed inside the tip of the screw 32, and the tip of the inner surface of the heating cylinder 30 and the tip of the screw 32 are respectively formed. An orbiting slope 30a and a contact slope 32a are formed. Further, the screw groove 32b of the screw 32 is formed so as to gradually become shallower toward the nozzle 28 side, so that the compression ratio is increased. Reference numeral 38 indicates a hopper. It should be noted that the heating configuration using a band heater or the like is omitted.

Similar to the above example, when the molten resin M accumulates in the plunger space 36 and reaches a predetermined amount, the screw 32 advances and the abutment slope 3 which is the tip thereof, as shown in FIG.
2a comes into close contact with the orbiting slope 30a of the heating cylinder 6, whereby the dimension t ₂ of the clearance C ₂ becomes zero and the thread groove 32
The communication between b and the plunger space 36 is cut off, and measurement is performed. After this, the plunger 34 advances and the measured molten resin M is injected.

Next, FIG. 7 to FIG. 10 show an embodiment corresponding to claim 7, wherein each of the above-mentioned examples has a shutoff structure by moving a screw, while an example of a shutoff structure by moving a nozzle. is there.

The injection molding machine 40 is provided with a heating cylinder 44 having a nozzle 42 at its tip, and a conical screw 46 rotatably provided in the heating cylinder 44. Inside the screw 46. A plunger 48 is provided so as to be movable back and forth in the axial direction of the heating cylinder 44, and a plunger space 49 is formed.

The screw 46 has a conical plasticizing portion 5
0 and a feed portion 52 having a constant diameter, and a spiral groove 54 having a constant depth is formed from the feed portion 52 to the tip of the plasticizing portion 50.

The nozzle 42 is provided so as to be displaceable in the axial direction of the heating cylinder 44, and its rear surface and the screw 46.
A rounded inclined surface 42a and a contacting inclined surface 46a are formed at the tips of the two so as to be in close contact with each other. Similar to the above example, the dimension t ₃ of the gap C ₃ is set to be smaller than the depth d ₂ of the spiral groove 54 during plasticization. Code 5
Reference numerals 6, 58 and 60 denote a heater, a band heater and a material supply port, respectively.

As shown in FIG. 8, the plasticized molten resin M passes through a gap C ₃ smaller than the depth d ₂ of the spiral groove 54, so that the flow velocity and the pressure can be increased in the same manner as in the above example.
Plasticization is promoted. When a predetermined amount of the molten resin M is accumulated in the plunger space 49, a nozzle touch operation on the mold 62 is performed as shown in FIGS. 9 and 10. With the nozzle touch, the nozzle 42 retreats by the horizontal distance w of the gap C ₃ ,
The orbiting slope 42a and the contact slope 46a are in close contact with each other and the spiral groove 54a
And the plunger space 49 is disconnected. The plunger 48 advances while the backflow does not occur, and the molten resin M is filled in the cavity of the mold 62.

When the injection unit is retracted and the nozzle touch is released, the nozzle 42 becomes free, so that it moves forward by the resin pressure, thereby forming the gap C ₃ and sending the molten resin M into the plunger space 49. Is resumed.

Next, FIGS. 11 and 12 show an embodiment corresponding to claim 8, which is an example of application of a nozzle moving structure to an in-line screw type. The injection molding machine 64 is provided with a heating cylinder 68 having a nozzle 66 at its tip, and a screw 70 of a constant diameter rotatably provided in the heating cylinder 68. The screw 70 has a heating cylinder. Plunger 7 with an axial direction of 68
2 is provided so that it can move forward and backward. The screw groove 70b of the screw 70 is formed so as to gradually become shallower toward the nozzle 66 side, so that the compression ratio is increased. Reference numeral 74 indicates a plunger space, and reference numeral 76 indicates a hopper. It should be noted that the heating configuration using a band heater or the like is omitted.

The nozzle 66 has its axis centered on the heating cylinder 68.
Is installed so that it can be moved in any direction and is prevented from coming off by the flange 66a.
The flange 66a and the tip of the screw 70.
Have contact surfaces 66b and 70a which can be in close contact with each other.
Has been formed. Between the contact surfaces 66b, 70a during plasticization
A dimension t smaller than the depth of the screw groove 70b of the screw 70 _Four
Gap C_FourIs set, and the flow velocity and pressure are the same as in the above example.
The power is getting stronger.

When the molten resin M is accumulated in a predetermined amount, as shown in FIG. 12, a nozzle touch operation to the die 78 is performed, and accordingly, the nozzle 66 is retracted by the dimension t ₄ and the contact surface 66.
b and the contact surface 70a are in close contact with each other, and communication between the thread groove 70b and the plunger space 74 is cut off. The plunger 72 is advanced and the molten resin M is injected without the backflow. The subsequent cycle operation is the same as the above example.

In each of the above examples, each component is shown in a specific shape, but the present invention is not limited to this, and the design can be changed as appropriate within the range in which the above function is satisfied.

[0039]

According to the present invention, since it is not necessary to provide a check valve, it is possible to avoid the adverse effect on the molding due to resin retention, and to perform the injection with the backflow path completely shut off. It is possible to avoid a molding defect due to a decrease in injection amount and a decrease in injection pressure, and thus it is possible to improve the quality of a molded product.

Further, even in the case of a material which requires a holding pressure after injection for a long time, the pressure does not drop, so that the range of use can be expanded.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an essential part at the time of plasticization showing an embodiment of an injection molding machine according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a screw tip portion of FIG.

FIG. 3 is a cross-sectional view of a main part at the time of injection.

FIG. 4 is an enlarged cross-sectional view of the screw tip portion of FIG.

FIG. 5 is a cross-sectional view of essential parts at the time of plasticizing, showing a second embodiment.

FIG. 6 is a cross-sectional view of essential parts at the time of injection in the second embodiment.

FIG. 7 is a cross-sectional view of essential parts at the time of plasticizing, showing a third embodiment.

8 is an enlarged cross-sectional view of the screw tip portion of FIG. 7.

FIG. 9 is a cross-sectional view of essential parts at the time of injection in the third embodiment.

10 is an enlarged cross-sectional view of the screw tip portion of FIG.

FIG. 11 is a cross-sectional view of essential parts at the time of plasticizing, showing a fourth embodiment.

FIG. 12 is a cross-sectional view of essential parts at the time of injection in the fourth embodiment.

[Explanation of symbols]

4,28,42,66 Nozzle 6,30,44,68 Heating cylinder 8,32,46,70 Screw 10,34,48,72 Plunger 12,36,49,74 Plunger space C ₁ , C ₂ , C ₃ , C ₄ Gap M Molten resin

Claims (8)

[Claims] 1. A screw is rotatably provided in a heating cylinder having a nozzle at its tip and is movable back and forth in the axial direction of the heating cylinder, and a plunger is provided in the screw movably in the same direction as the screw. An injection molding machine in which a plunger space for accumulating molten resin is formed, and when the screw moves forward, the tip of the screw and the inner surface of the heating cylinder come into close contact with each other and communication between the groove of the screw and the plunger space is blocked. 2. The injection molding machine according to claim 1, wherein the gap between the tip of the screw and the inner surface of the heating cylinder during plasticization is set to be narrower than the groove depth of the screw. 3. The injection molding machine according to claim 1, wherein the screw is formed in a conical shape whose diameter gradually decreases toward the nozzle side. 4. The injection molding machine according to claim 1 or 2, wherein the screw has a constant outer diameter over the whole thereof, and the groove is formed in a shape gradually becoming shallower toward the nozzle side. 5. A screw is rotatably provided in a heating cylinder having a nozzle at its tip, a plunger is provided in the screw so as to be able to advance and retreat in the axial direction of the screw, and a plunger space for accumulating molten resin is formed. The nozzle is installed in the heating cylinder so that it can move back and forth, and when the nozzle touches the mold, the nozzle moves back and forth so that the nozzle is in close contact with the screw and the communication between the screw groove and the plunger space is blocked. 6. The injection molding machine according to claim 5, wherein the gap between the nozzle and the tip of the screw during plasticization is set to be narrower than the groove depth of the screw. 7. The injection molding machine according to claim 5, wherein the screw is formed in a conical shape whose diameter gradually decreases toward the nozzle side. 8. The injection molding machine according to claim 5, wherein the screw has a constant outer diameter over the whole, and the groove is formed in a shape gradually becoming shallower toward the nozzle side.