JPH0159895B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hot runner system for plastic injection molding, and more particularly to the structure of a hot nozzle in a hot runner system using a hot runner type runnerless mold.

(Prior art) Conventionally, many plastic products used in daily necessities, home appliances, automobiles, etc. have been formed by injection molding.In such injection molding, heated and molten resin is heated and molten in the cavity of a mold through a runner under high pressure. After cooling, the molded product is taken out, but such a molded product inevitably contains resin that has solidified in the runner, and it is therefore essential to cut and remove this resin.

Such work requires a great deal of time and effort, reduces product yield, and requires additional troublesome work such as crushing for recycling, which is a significant disadvantage, especially in the case of multi-cavity molds. There was.

For this reason, there is a demand for a mold with no runners at all, or a mold with runners that does not need to be taken out each time molding is performed, and the hot runner system was devised in response to this demand.

The present invention is directed to such a hot runner system, particularly a hot runner system using a hot runner type runnerless mold.

Conventionally, in such hot runner systems,
As shown in FIG. 4, a cavity 103 formed between the cavity core 101 and the plunger core has a cavity core 1 instead of a runner.
A nozzle hole 104 formed in the nozzle hole 104 is in communication with the nozzle hole 104, and a nozzle member 105 connects its nozzle portion 105a to the nozzle hole 104.
It is installed with it protruding inward. The nozzle member 105 has a passage 107 that guides molten resin supplied from a nozzle of an injection molding machine (not shown) through a molten resin distribution manifold 106 into the nozzle hole 104.
is formed, and the molten resin is further guided into the cavity 103 through the gap 108 between the nozzle portion 105a of the nozzle member 105 and the nozzle hole 104. Here, an insertion hole 109 is provided inside the nozzle member 105 and extends almost to the tip of the nozzle portion 105a, and a heater 111 that is energized via a conductive wire 110 is inserted into the insertion hole 109. There is.

In such a hot runner system, the resin in the nozzle hole 104 corresponding to the runner is transferred to the heater 111 via the nozzle portion 105a of the nozzle member 105.
The molten state is always maintained because it is heated by
Therefore, the product removed from the cavity 103 after molding does not have a runner.

In addition to the internal heating type, the hot runner system also has a molten resin passage inside the nozzle and a heat band attached to the outside of the nozzle.
Alternatively, there is an external heating type in which a heater is integrated into the nozzle.

(Problems to be Solved by the Invention) However, in the former type of internally heated hot nozzle, the molten resin on the inner wall side of the nozzle hole 104 is cooled by the cavity core 101, so it becomes solidified and tends to stagnate. If you raise the temperature of the heater to prevent such accumulation, the resin near the nozzle will thermally decompose and stick to the nozzle, which will have the opposite effect, making temperature control difficult and increasing power consumption. It also happens. In addition, since resin always remains in the nozzle hole, the colors of the used resins are mixed, especially when changing the color of the resin, which may cause defective products. Furthermore, a structure in which an insertion hole is provided in the nozzle body and a heater is mounted therein has the disadvantage that machining is difficult and the structure itself is complicated.

On the other hand, in a configuration in which a resin passage is provided inside the nozzle and the nozzle is heated by a band heater or a heater integrated into the nozzle, the heat of the heater easily escapes to the cavity core through the inner wall of the nozzle hole, reducing the power consumption of the heater. This has resulted in an increase in the number of people. In addition, in order to heat the resin through the entire length of the nozzle hole, it is necessary to provide a heater along the entire length of the nozzle, and also to heat the tip of the nozzle to facilitate the flow of resin into the cavity. Since the heater is usually provided separately, the structure becomes more complicated and temperature control is difficult.

(Means for Solving the Problems) In view of the problems of the prior art described above, the present invention does not cause any accumulation of resin in the nozzle hole, almost no heat escape to the cavity core side, and furthermore, temperature control is achieved. The purpose of this invention is to provide a hot nozzle that is easy to use and has a simple structure, and is constructed as follows.

That is, the present invention has a main body consisting of a nozzle portion inserted into a nozzle hole formed in communication with a cavity of a plastic injection mold, and a base portion that guides molten resin from the injection molding machine nozzle into the nozzle portion. In the hot nozzle, at least a portion of the main body corresponding to the nozzle portion of the nozzle portion and the base portion is formed of a conductive metal having a predetermined electrical resistance, and a portion of the main body formed of the conductive metal is A groove is provided in the longitudinal direction of the nozzle portion, leaving at least a portion of the tip, extending from the base end to the tip end, and dividing the nozzle portion into approximately two parts, and each of the main body portions on both sides separated by the groove. By applying a voltage between the proximal ends, the nozzle itself can generate heat, particularly its tip. Furthermore, a coating having both insulation and heat insulation properties is formed on the outer surface of the main body portion made of the conductive material, thereby preventing leakage of the resin inside the nozzle from the grooves and short circuits.

(Example) Next, an example of the present invention will be described with reference to the accompanying drawings.

In FIG. 1, the main body 2 of the hot nozzle 1 consists of a base 2a and a tapered nozzle part 2b, and the base 2a is connected via bolts 4 to a manifold 3 that receives molten resin injected from an injection molding nozzle (not shown). The nozzle part 2b is locked by a fixed fixing plate 5 and inserted into a nozzle hole 7 formed in a cavity core 6 of the mold. A molten resin passage 8 is provided inside the body 2, and this passage 8 communicates with a molten resin distribution passage 9 in the manifold 3 at one end and with a cavity 10 at the other end. The main body 2 constituting the base portion 2a and the nozzle portion 2b is integrally formed of metal having a predetermined electrical resistance, and is particularly thin at the nozzle portion 2b.

As shown in FIGS. 2 and 3, the main body 2 includes:
A pair of narrow grooves 11 are formed in the longitudinal direction through the base 2a and the nozzle part 2b, excluding the tip of the nozzle part 2b.
11 are formed diametrically opposite to each other. Terminals 13, 13 of conductive wires 12, 12 are provided at the ends of the half portion of the base 2a separated by these grooves 11, 11, which face the grooves 11, 11 in the direction perpendicular to them.
Connecting parts 15, 1 each provided with screw holes 15a, 15a for fixing through screws 14, 14, respectively.
5 (in FIGS. 1 and 2, only one connection portion is shown, omitted), and conductive wires 12, 12 are connected to the power supply side or the ground side, respectively.

The outer surface of the main body 2 of the hot nozzle 1 includes a connecting portion for the terminals 13, 13 and an inlet portion 8 for the resin passage 8.
A ceramic coating 16 having insulating and heat-insulating properties is formed on the entire surface except for the grooves 11a and 8b to close the grooves 11, 11. Such a coating 16 is formed by adhering finely powdered ceramic to the outer surface by high-temperature spraying.

Furthermore, a ceramic protective tube 17 is inserted into the nozzle portion 2b of the hot nozzle 1 at a portion opposite to the nozzle hole 7, and this protective tube 17 protects the coating 16, especially when it is inserted into a mold. It is something. In addition, the outer diameter of this protection tube 17 is set smaller than the inner diameter of the nozzle hole 7, so that a gap is created between the protection tube 17 and the inner wall of the nozzle hole 7, further improving the heat insulation properties. There is.

Next, the operation of the above embodiment will be explained.

First, the molten resin injected from the injection molding nozzle passes through the distribution passage 9 in the manifold 3 to the passage 8 inside the hot nozzle 1, and from there flows further into the cavity 10. During this resin filling process, a low voltage and a high current are applied to the main body 2 of the hot nozzle 1 through the conductive wires 12, 12, and the hot nozzle itself generates heat mainly at the tip of the nozzle portion 2b.
The flow of the resin at the entrance to the cavity 10 is maintained well, and the resin inside the nozzle portion 2b is kept in a heated state. Here, since the main body 2 is formed with a thin wall, its heat capacity is small. Therefore, when the power is turned on as described above and when the power is turned off as described later, the temperature rises and falls in a short time, and the temperature can be accurately controlled by the temperature control mechanism. temperature control is now possible.

When the filling of the resin into the cavity 10 is completed, cooling water is passed through the mold to solidify the resin inside. On the other hand, when the filling process is completed, the power to the hot nozzle 1 is temporarily cut off, and when the resin in the cavity 10 is completely solidified, the tip of the nozzle part 2b, that is, the cavity 1
The resin at the entrance to 0 is also in a semi-solidified state.

When the solidification of the resin in the cavity 10 is completed, that is, the molding is completed, the molded product is taken out from the mold. When taking out such a molded product, since the resin at the entrance to the cavity 10 is in a semi-solidified state as described above, the resin may be stringy at the time of taking out, or the resin may come out from the nozzle part 2b after being taken out. leakage is prevented.

Once the molded product has been removed, the mold is closed, the main body 2 of the hot nozzle 1 is energized again, and after reaching a predetermined temperature, filling with resin is started again, and the same process is repeated.

(Effects of the Invention) The present invention provides a hot nozzle in which at least a portion corresponding to the nozzle portion of the main body constituting the nozzle portion and the base portion is formed of a conductive metal having a predetermined electrical resistance, and a main body formed of the conductive metal. A groove is provided in the longitudinal direction of the nozzle portion, leaving at least a portion of the tip, extending from the base end to the tip end, and dividing the nozzle portion into approximately two parts. Since the nozzle section itself is configured to generate heat mainly at its tip by applying a voltage between the base ends of each nozzle, the structure is simpler than when a heater is built into the nozzle or heating is performed from the outside with a band heater. This makes it possible to heat the nozzle part, and in particular, by forming the nozzle part with a thin wall, the heat capacity is small, so the temperature can be raised and lowered in a short time by turning on and off the electricity, and temperature control can be performed easily and accurately. can. Furthermore, by forming a coating made of, for example, ceramic, which has insulating and heat-insulating properties on the outer surface of the main body part made of a conductive material, covering the grooves, short circuits and leakage of resin from the grooves can be prevented, and the nozzle part This prevents heat from escaping from the nozzle, eliminating the need to overheat the nozzle to compensate for the dissipated heat. Retention and color mixing during color change due to this is prevented. Furthermore, by preventing heat from escaping from the nozzle portion in this way, power consumption is reduced, contributing to energy savings. Such heat dissipation can be further suppressed by inserting a protective tube made of ceramic, for example, over the nozzle portion and providing a gap between the protective tube and the inner wall of the nozzle hole.

[Brief explanation of drawings]

Figures 1 to 3 show an embodiment of the present invention; Figure 1 is a schematic front cross-sectional view showing the hot nozzle attached to the injection molding mechanism together with a part of the injection molding mechanism; is a front sectional view of the hot nozzle shown in Figure 1, Figure 3 is a bottom view of Figure 2,
FIG. 4 is a schematic front sectional view similar to FIG. 1 showing a conventional hot nozzle. 1... Hot nozzle, 2... Main body, 2a... Base, 2b... Nozzle part, 7... Nozzle hole, 8...
Passage, 10... Cavity, 11, 11...
Groove, 12, 12...conducting wire, 16...coating.

Claims (1)

[Scope of Claims] 1. Consists of a nozzle portion inserted into a nozzle hole formed in communication with a cavity of a plastic injection mold, and a base portion that guides molten resin from the injection molding machine nozzle into the nozzle portion. A hot nozzle having a main body, wherein at least a portion of the nozzle portion and the base portion corresponding to the nozzle portion is formed of a conductive metal having a predetermined electrical resistance, and the main body is formed of the conductive metal. A longitudinal groove is provided on the outer surface of the nozzle portion, leaving at least a portion of the tip, extending from the base end to the distal end and dividing the nozzle portion into approximately two parts;
The nozzle part itself is configured to generate heat by applying a voltage between the proximal ends of the main body parts on both sides separated by the groove, and furthermore, the main body part formed of the conductive material is insulated. 1. A hot nozzle in a hot runner system for runnerless injection molding of plastic, characterized in that a coating having heat-insulating properties as well as heat-insulating properties is formed to cover the grooves. 2. The hot runner system for runnerless injection molding of plastics according to claim 1, wherein the coating is a ceramic welded to the main body portion made of the conductive material. Hot nozzle. 3. The runnerless injection molding of plastic according to claim 1, wherein the main body is integrally formed through the nozzle part and the base part, and the grooves are formed in series therebetween. Hot nozzle in hot runner system for. 4. The outer diameter of the nozzle part is set smaller than the diameter of the nozzle hole, and a gap is formed between the nozzle part and the inner wall of the nozzle hole in an assembled state. A hot nozzle in a hot runner system for runnerless injection molding of plastics according to claim 4. 5. The runnerless injection of plastic according to claim 1, wherein a cylindrical protective tube is provided on the outer surface of the main body portion covered with the coating at a portion facing the nozzle hole. Hot nozzle in hot runner system for molding. 6. A hot nozzle in a hot runner system for runnerless injection molding of plastic according to claim 5, wherein the protective tube is made of ceramic.