JPH051127B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pre-plastic tandem injection molding machine.

(Prior art) Figure 3 shows a conventional pre-plastic injection molding machine.
A raw material (not shown) is supplied to the raw material hopper 31, and the resin plasticized by the screw 32 is injected into the injection cylinder 34, and the extrusion pressure causes the injection plunger 3
5 retreats. The injection amount is measured by the backward stroke of the injection plunger 35, and when the measurement is completed, the screw 32 stops. Injection into a mold (not shown) is performed by advancing an injection plunger 35 using a hydraulic cylinder 36. At this time,
The on-off valve 38 at the connection between the screw cylinder 37 and the injection cylinder 34 is closed to prevent the resin from flowing back into the screw cylinder 37, and the plasticized resin is injected into a mold (not shown) through the nozzle 33. Ru.

However, in the conventional injection molding machine, a large amount of resin leaks toward the hydraulic cylinder 36 from the clearance between the injection cylinder 34 and the injection plunger 35.
Therefore, the process of removing this resin was difficult and uneconomical. If the clearance is made small in order to reduce the amount of resin leaking, the resin may deteriorate at the sliding part between the injection cylinder 34 and the injection plunger 35, causing burns, or in severe cases, the sliding part between the injection cylinder 34 and the injection plunger 35 may deteriorate. The parts make metal contact and galling occurs. As described above, in conventional injection molding machines, the lubrication and cleaning properties of the sliding parts are poor, and it has been impossible to eliminate resin leakage. In addition, the injection plunger 35 only moves forward and backward repeatedly, making it difficult to change the color or resin.

In general commercially available injection molding machines that are not pre-plastic type, the screw that plasticizes the resin also has the function of injecting the resin into the mold, and the screw moves back and forth as it rotates. In the resin plasticizing process, from the start of plasticization when the screw begins to rotate until the completion of plasticization when the screw stops rotating, the screw retreats as plasticized resin accumulates at the tip of the screw. For this reason, the L/D of the screw from the raw material hopper opening to the tip of the screw changes, resulting in a large difference in the plasticization quality of the resin between when plasticization starts and when plasticization is completed.

In addition, the distance from the raw material supply hopper opening to the screw compression section changes as the screw retreats, and as the screw retreats, the high-temperature screw section approaches the hopper opening. The plasticization form during the process changes significantly, causing galling wear between the screw and cylinder, the so-called wrapping phenomenon of the resin around the screw that drastically reduces the resin feed, and the formation of air in the resin. In many cases, problems such as entanglement occurred.

Therefore, if we use a pre-plastic method in which the resin plasticization and injection processes are separated, it is easy to obtain a very stable and high quality plasticized resin because there is no screw setback in the plasticization process, and therefore the current high quality, In order to obtain products with high added value, this pre-plastic injection machine is desirable. However, as mentioned above, the conventional prep-plastic tandem injection machine has resin leakage, retention, and deterioration between the cylinder and injection plunger, or galling wear between the two, so an injection molding machine that can somehow solve this problem was expected to appear.

(Problems to be Solved by the Invention) The present invention attempts to solve problems such as resin leakage, retention, deterioration, and galling wear between the cylinder and injection plunger in conventional tandem injection molding machines. It is something.

(Means for solving the problem) Therefore, the present invention has a rotational action as a main action, a first screw that plasticizes the resin, and an injection stroke of axial movement as a main action, and a rotational action as a side effect. At the same time, the injection molding machine has a second screw whose rotation speed is lower than that of the first screw, and the resin plasticized by the first screw is discharged from the cylinder portion of the second screw. A small amount of solid phase resin is injected into the second screw and supplied from the base of the second screw, and this is used as a means to solve the problem.

(Function) The first screw has almost no movement in the axial direction, and plasticizes the resin by rotating almost in place. This plasticized resin is injected into the second screw, and at the same time, a solid phase is placed at the base of the second screw. Resin is supplied, this resin is plasticized and transported forward by the rotation of the second screw, joins with the plasticized resin in the first screw, and is metered.

(Example) An example of the present invention will be described below with reference to the drawings. Fig. 1 is a side sectional view of a tandem injection molding machine showing an example of the present invention. In the figure, the first screw 3 plasticizes the resin 2 supplied to the raw material hopper 1 by rotating almost at a fixed position with almost no movement in the axial direction. The plasticized resin is transferred to the injection cylinder 7
is metered into the front of the injection cylinder 7 by the second screw 6 which is rotated by the motor 8 at a relatively low speed. At this time, the resin 10 (resin 10
and resin 2 may be the same or may be other pigmented resins. ), as the second screw 6 rotates, a small amount of resin is plasticized and transported to the front of the injection cylinder 7, where it joins the plasticized resin in the first screw 3 and is measured.

Further, for injection into a mold (not shown), the second screw 6 is advanced by a hydraulic cylinder 9. At this time,
The check valve 5 is activated by the resin pressure difference and is closed.
The resin is injected into a mold (not shown) through the nozzle 4 while preventing the resin from leaking backward. In addition, the first screw 3
The rotational speed of the second screw 6 and the rotational speed of the second screw 6 can be adjusted respectively, and are usually set to rotate at a certain constant ratio matching the discharge amount of the first screw 3.

On the other hand, it is desirable for the screw groove depth to be Hb>Ha.
Since Ha is extremely shallow and the second screw 6 is mainly cleaned, the amount of resin transported is also small. In other words, the characteristics of the tandem prep plastic injection system, in order to suppress the occurrence of defects, are that compared to the plasticizing ability of the first screw 3, the plasticizing ability of the second screw 6 (the second screw moves back and forth, so the plasticizing amount is lower than that of the first screw 3). (It is desirable to obtain a homogeneous plasticized product by extremely reducing the number of screws) is small, and the number of revolutions of the second screw 6 is made smaller than the number of revolutions of the first screw 3.

Next, FIG. 2 shows another embodiment in which the plasticized resin is always placed closer to the mold than the resin backflow prevention valve 5 (so-called check ring) of the second screw 6 whose main function is injection. 13 is a resin inflow port from the first screw 3 to the second screw 6. Also, 14 is the second screw 6
This valve is for preventing plasticized resin from flowing backward from the supply port 13 toward the cylinder of the first screw 3 as the screw moves forward.

(Effects of the Invention) Since the present invention is configured as described above in detail, the injection device part is changed from a conventional plunger to an injection screw, and a small amount of solid phase resin is supplied from the base and plasticized. Since the resin on the outer surface of the injection screw can be cleaned, the resin will not leak behind the injection cylinder unlike in conventional plungers. In addition, the ability to change resin and color is improved because the injection screw rotates, and galling and burning of the resin at the injection part can be eliminated.

Further, since the screw of the plasticizing device rotates at a fixed position to plasticize the resin, the plasticized product becomes homogeneous and a high quality molded product can be obtained. In addition, the pigmented resin is supplied to the second screw, and although the amount of plasticization is small, it can be completely plasticized (melted).
This can be mixed and dispersed with the plasticized and melted base polymer by the first screw 3, which improves the color dispersion effect compared to an injection molding machine that performs the normal injection and plasticization processes with a single screw. do. In addition, because the ease of melting and melt viscosity of pigmented masterbatch solid phase resin particles and base resin particles differ, it is difficult to uniformly plasticize a blend of both particles in a solid phase with a single screw. .

[Brief explanation of the drawing]

1 and 2 are side sectional views of a tandem injection molding machine showing an embodiment of the present invention, and FIG. 3 is a side sectional view of a conventional pre-plastic injection molding machine. Explanation of the main parts of the diagram, 1, 11... Raw material hopper, 2, 10... Resin, 3... First screw, 6
...Second screw, 7...Injection cylinder, 9...
hydraulic cylinder.

Claims (1)

[Claims] 1. A first screw whose main action is a rotational action to plasticize the resin, whose main action is an injection stroke of axial movement, whose side effect is a rotational action, and whose rotational speed is lower than that of the first screw. The injection molding machine has a second screw having a smaller size, wherein the resin plasticized by the first screw is injected into the second screw from the cylinder portion of the second screw, and the resin is injected into the second screw from the cylinder portion of the second screw. A tandem injection molding machine characterized by supplying a small amount of solid-phase resin from a small amount of solid phase resin.