JPH1158448A - Hot runner mold - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent an abrupt decrease in the temperature of a molten resin near a gate of a hot runner mold and achieve an ideal temperature distribution of the resin in the runner. [MEANS FOR SOLVING PROBLEMS] A heat conductive layer having high heat conductivity is provided around the tip of a nozzle, and a heater for heating is provided via the heat conductive layer. A heat insulating layer that can insulate between the heater for heating and the molten resin inside the nozzle upstream of the nozzle tip is provided. Further, heat insulation is provided at the nozzle end to prevent heat radiation from the nozzle to the cavity of the molded product due to heat conduction. Attach the materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot runner mold, and more particularly, to a hot runner mold with improved gate defects and cold slug defects.

[0002]

2. Description of the Related Art Injection molding using a cold runner mold requires a complicated post-process in which a molded product is taken out and then the runner is cut off. Therefore, a hot runner mold has been used conventionally.

In this hot runner mold, a heater is provided around the nozzle to heat the resin inside the nozzle and keep it in a molten state, so that only the molten resin discharged into the molded product cavity is solidified. Then, the mold is opened and the nozzle is retracted at the same time as the mold is opened, and the molten resin inside the nozzle and the molded product solidified in the cavity are cut off by a gate. Therefore, not only can a molded article without a runner be produced, but also the runner resin that has been cut and discarded can be used for the molded article.

[0004] By the way, the molded product must be divided at the gate so that burrs do not remain on the molded product.
If the temperature of the surface of the molded product near the gate is not sufficiently lowered and remains at a high temperature, the molten resin that is torn off by the gate remains like a thread, and the molded product becomes “defective gate remaining”. In addition, if the temperature of the molten resin inside the nozzle cannot be maintained sufficiently high during filling, the molten resin causes "cold slug" which is a poor transfer to the molded product surface.

For this reason, it is necessary to make the inside of the nozzle as ideal as possible the temperature distribution state. That is, it is desirable that the temperature distribution is such that the temperature of the molten resin is high just before the gate, and the temperature of the gate rapidly drops to the molten resin temperature immediately before the molded product is solidified.

However, since the heat actually escapes from the gate to the cavity, the temperature of the molten resin inside the nozzle gradually decreases toward the gate, and the temperature of the molten resin near the gate is reduced by the molten resin inside the upstream nozzle. It will be lower than that.

Conventionally, to solve this problem,
A device in which the nozzle is heated by electromagnetic induction to raise the temperature of the molten resin near the gate (Japanese Patent Publication No. 3-60298), and a device in which the nozzle is a heating element (Samocongate Technical Data p5 U-Shin Seiki 1993)
/ 1 revised version) is known.

[0008]

However, these require a dedicated temperature control device and complicate the structure of the hot runner mold, so that the nozzle can be heated with a simpler structure, and There has been a demand for a method that can make the internal resin temperature an ideal temperature distribution.

If a simple heating device such as a heater is used, the mold structure becomes simple. Therefore, a means for installing a dedicated heater near the gate is conceivable. However, in order to heat a narrow area near the gate, the heater is required. Needs to be downsized. However, for example, 22 commonly used in factories
When using a 0V power supply, the heater must be at least 200W. This is because if the wattage is too small, current will flow excessively and the circuit will be short-circuited. That is, there is a lower limit to the size of the heater due to the restriction of the wattage, and it is usually difficult to make the diameter smaller than about 30 mm and about 25 mm in length. Naturally, if the operating voltage is reduced, the size can be reduced. However, additional equipment such as a transformer is increased, and the device is eventually complicated.

Therefore, conventionally, it has been difficult to heat only a narrow area near the gate portion to an appropriate temperature distribution state using a simple heater as a heat source. Therefore, the problem to be solved by the present invention is to use a heater or the like,
An object of the present invention is to provide a hot runner mold capable of maintaining a portion close to a gate in an appropriate temperature distribution state.

[0011]

According to a first aspect of the present invention, in a hot runner mold having a heater disposed around a nozzle tip, a tip heater is disposed near a nozzle tip via a heat conductive layer. The hot runner mold is characterized in that a heat insulating layer is provided between the tip heater and the runner resin upstream of the nozzle tip.

According to a second aspect of the present invention, there is provided a hot runner mold in which a heater is disposed around a nozzle tip.
A tip heater is arranged in the vicinity of the nozzle tip via a heat conductive layer, and a heat insulating layer is provided between the tip heater and a runner resin upstream of the nozzle tip, and at the nozzle end. A hot runner mold provided with heat insulating means.

(Operation) The tip heater at the tip of the nozzle heats the tip of the nozzle via the heat conductive layer. However, the runner resin upstream of the nozzle tip is insulated by a heat insulating layer provided between the nozzle tip heater and the nozzle.
Since those portions are not heated, the nozzle tip heater can be a heater that heats only the nozzle tip. As a result, even if the resin at the nozzle tip comes into contact with the cavity and the temperature drops, the tip heater can heat those parts to compensate for the lost heat.

When a heat insulating material is attached to the end of the nozzle, the end of the nozzle and the cavity are insulated from each other, so that it is possible to prevent a large temperature drop that occurs through the gate.

Therefore, the temperature of the resin in the runner portion can be kept at a very high temperature just before the tip of the nozzle, and the temperature of the resin in the gate portion which has not been heated decreases rapidly due to the heat escaping to the cavity. Therefore, it is possible to achieve an ideal temperature distribution for cutting the molded product at the gate.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a sectional view of an example of the hot runner mold of the present invention. A plurality of annular heaters (2) are mounted around the nozzle (1). The runner resin (8) is melted by heating with the annular heater (2).

The heat conductive layer (4) is provided around the nozzle tip (3) located at the nozzle tip. The heat-conducting layer (4) has a tip heater (6) attached to the periphery thereof, and the heat-conducting layer (4) is heated by the tip heater (6), and the nozzle tip inside the heat-conducting layer is heated. The part (3) is also heated by heat conduction. The shape of the distal end heater (6) may be any shape as long as the molten resin can be uniformly heated. For example, a plurality of heaters may be arranged in the circumferential direction.

A heat insulating layer (7) is disposed between the tip heater (6) and the runner resin upstream of the nozzle tip. As a result, only the required portion of the resin can be heated to maintain the resin temperature appropriately.

The heat-insulating layer (7) may have any structure so as not to heat the resin of the runner part by the heater (6) at the tip, and the heat-insulating layer (7) is airtight as shown in FIG. It may be formed by an air layer in which air is confined in a room having a property, or may be formed by a heat insulating material using a material such as a resin such as polyimide or titanium as shown in FIG. As shown in FIG. 3, two or more heat insulating layers (7) may be provided, or as shown in FIG. 4, the heat conductive layer (4) may be provided with a heat insulating layer (7).

As a heat insulating means at the nozzle end including the gate, for example, a nozzle tip heat insulating material (9) is attached. The nozzle tip insulation (9) prevents the nozzle end from being cooled by heat conduction to the cavity when the nozzle end comes into contact with the cavity, thereby preventing an inappropriate temperature drop.

With respect to the hot runner mold of the present invention shown in FIG. 1 and the hot runner mold having no heat insulating layer shown in FIG. 5, a thermocouple is inserted from the gate in a state where the flow path is not filled with resin. FIG. 6 shows the result of measuring the temperature distribution on the inner wall surface of the nozzle. From FIG. 6, it is possible to heat a portion close to the gate in a narrow range by providing the heat conductive layer as in the present invention. can do.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, injection molding is carried out using an open gate type hot runner mold shown in FIG.
A flat plate having a thickness of 3 mm and a weight of 300 g was formed from hard vinyl chloride (Tokuyama Sekisui) as a raw material at a nozzle temperature of 175 ° C. When the molded product was visually evaluated, a good sample was obtained without any remaining gate defect or cold slug defect of the sample.

(Comparative Example) Injection molding was carried out under the same conditions as in the example using a hot runner mold having no heat insulating layer shown in FIG. 5 to form a rigid vinyl chloride flat plate having a thickness of 3 mm and a weight of 300 g. When the molded product was visually evaluated, no gate residual defect was found in the sample, but a cold slug defect occurred on the surface of the molded product near the gate in a region having a radius of about 40 mm.

Table 1 shows the above results.

[0025]

[Table 1]

[0026]

The nozzle tip heater can heat only the nozzle tip in a narrow range, so that the temperature distribution of the runner resin near the gate can be made closer to the ideal distribution. As a result, the resin charged into the cavity of the molded product is maintained at an appropriate temperature, and a hot runner molded product free from defective gates and defective cold slugs can be manufactured using the present mold.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view showing a hot runner mold of the present invention having a heat insulating layer. FIG. 1B is a bottom view of the hot runner mold of the present invention viewed from the AA plane.

FIG. 2 is a cross-sectional view showing a hot runner mold using a heat insulating material for a heat insulating layer.

FIG. 3 is a cross-sectional view showing a hot runner mold provided with two heat insulating layers.

FIG. 4 is a cross-sectional view showing a hot runner mold in which a heat insulating layer is provided in a heat conductive layer.

FIG. 5 is a cross-sectional view showing a hot runner mold having no heat insulating layer.

FIG. 6: Temperature distribution on the inner wall surface of the nozzle of the hot runner mold

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle 2 Heater 3 Nozzle tip 4 Heat conduction layer 6 Tip heating heater 7 Insulation layer 9 Nozzle tip insulation

Continuation of the front page (72) Inventor Toshihiko Mitsuhara 2-2, Kamitobakamichochocho, Minami-ku, Kyoto Sekisui Kagaku Kogyo Co., Ltd.

Claims (2)

[Claims] In a hot runner mold in which a heater is arranged around a nozzle tip, a tip heater is arranged near a nozzle tip via a heat conductive layer, and the tip heater and the nozzle tip are arranged in the vicinity of the nozzle tip. A hot runner mold characterized in that a heat insulation layer is provided between the resin and the runner portion resin upstream. 2. A hot runner mold in which a heater is arranged around a nozzle tip, a tip heater is arranged near a nozzle tip via a heat conductive layer, and the tip heater and the nozzle tip are arranged in a vicinity of the nozzle tip. A hot runner mold characterized in that a heat insulating layer is provided between the upstream runner resin and a heat insulating means at the nozzle end.