JPS5947650B2 - Synthetic resin injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel synthetic resin injection molding method equipped with a hot runner system.

Conventionally, in injection molding of synthetic resins, sprues and runners are molded at the same time as the molded product, and then unnecessary sprues and runners are molded.
A so-called cold runner method was common, in which the runner was removed and the desired product was finished.

However, due to rising costs due to rising material and labor costs, automation of molding has become a major theme, and labor-saving devices such as take-out devices are being rapidly adopted, and so-called runnerless molding, which eliminates cold runners, is attracting attention. It's here.

Runnerless molding methods include well-type nozzles, extended nozzles, and insulated runners, but all of them require advanced techniques and are unstable, and currently only hot runner types are suitable for full-fledged runnerless equipment. It has been put into practical use and is commercially available.

One-type hot runners can be roughly divided into two types: one that closes the gate thermally and one that closes it mechanically. There are methods in which the gate is repeatedly melted and solidified for each shot, and mechanical methods include a gate closing method using a needle and a gate cutting method using sliding molds.

Both of these hot runner types are superior to the cold runner type in terms of economy and product quality in the following points.

That is, (1) 100% production of materials In the conventional cold runner type, there is a material loss of 30 to 50%.

(2) Increased molding cycle Since there is no relatively thick runner, the cooling time is shortened and the cycle is improved.

(3) Improving quality Dimensional accuracy is stabilized and residual stress is reduced.

(4) No finishing process required Since only the product is molded, no post-finishing is required.

However, these existing hot runner systems require a part of the hot runner to heat the resin in the mold as a necessary condition for injection molding of molten resin, and the injection molding process involves repeated melting and solidification of the resin. Due to this, three parts of the gate part that cannot be exposed to high temperatures are essential.

Therefore, the high-temperature part, which is the hot runner part, and the low-temperature part, which is the gate part of the product, are necessarily adjacent to each other in the mold structure, so there are parts that have a cold and thermal effect on each other, and injection molding Various problems have arisen as work progresses.

That is, (1) workability ■ gate clogging, especially modified polyphenylene oxide, polycarbonate,
With resins such as polysulfone that require high processing temperatures, the temperature difference between the resin and the mold is large, resulting in insufficient temperature at the nozzle tip, and the melt viscosity of the resin increases significantly, causing the nozzle hole to close.

■ Crystalline resins such as nylon, polybutylene terephthalate, and polyethylene terephthalate have distinct melting points, so a slight drop in temperature at the nozzle tip will close the gate hole, and if the temperature rises too much, the gate will close. Resin may leak or become stringy.

It may cause a runny nose.

(2) Product quality If the cavity plate is in contact with a high-temperature nozzle, the cavity temperature may be too high or the temperature distribution may be too wide, resulting in uneven cooling of the product, which may cause deformation, sink marks, etc. Become.

(3) Scope of application Advanced temperature control and precise molding conditions are required.
The total cost of molds has become expensive and highly skilled molding techniques are required, narrowing the scope of application of the resins and products used.

In view of the above-mentioned circumstances, the present inventors have continued their intensive research and have arrived at the present invention.

The present invention overcomes all of the above-mentioned drawbacks of existing systems.

That is, the present invention involves a step of injection molding in a state in which a nozzle for injecting molten resin into the mold is fitted into a through hole of a cavity plate in molding using a synthetic resin injection mold having a hot runner; The present invention relates to a synthetic resin injection molding method comprising a step of separating the nozzle and the cavity plate after injection molding is completed.

The present invention will be described below based on an embodiment shown in the drawings.

FIG. 1 shows the process of injecting molten resin into a mold, and FIG. 2 shows the process of separating the nozzle and cavity plate after injection molding is completed.

In FIG. 1, the nozzle 4 and the cavity plate 5 have a heat insulating layer 11, and are in contact with each other at the nozzle tips that come into contact with a desired resin molded product.

The cavity plate 5 is provided with cooling water holes 6 for temperature adjustment.

The resin injected by the injection molding machine passes through a hot runner part 1 provided in a hot runner block 2, passes through a nozzle 4 and is distributed to each cavity 7.

After each cavity is filled with molten resin, the needle is advanced downward in the diagram to close the gate.

Here, since this embodiment is an example of a mechanical gate closing method using a needle, a needle is provided in the nozzle portion, but the presence or absence of a needle is not particularly limited in the present invention.

Moving the explanation to Figure 2.

After the injection molding is completed, as soon as the mold opens, the spring 10
Due to the elastic force, the cavity plate 5 slides along the slide pin 9, hits the stopper protrusion 8, and stops.

In the stopped state, the nozzle and cavity plate are completely separated.

As the sliding mechanism of the cavity plate in the present invention,
The spring method is preferable because it can be miniaturized, but is not particularly limited, and a hydraulic cylinder, an air cylinder, etc. can also be used.

As an example of the molding of the present invention, polysulfone (UCC P 1700) was prepared at one temperature in the cylinder and one temperature in the runner at 40°C.
When molding was carried out at a pressure of 1500wc'' with settings of 40°C and a mold temperature of 100°C, the temperatures of the nozzle and mold were almost as set, and a molded product with good dimensions and appearance was obtained.

Furthermore, as a comparative example, molding was performed under the same conditions as in the example using a mold having the same mechanism as in the example except that it did not have a separation mechanism for the nozzle and cavity plate.
The mold temperature reached 160° C. near the nozzle, and the nozzle became clogged, preventing resin from being injected.

Furthermore, when the cylinder temperature and runner temperature were raised to 370℃, injection was possible intermittently, but the mold temperature reached 200℃ near the nozzle, and the solidification of the molded product was insufficient. It was not possible to perform proper molding.

[Brief explanation of the drawing]

Both FIG. 1 and FIG. 2 are cross-sectional views of the mold. Figure 1 shows the process of injecting molten resin into a mold, and Figure 2 shows the process of separating the nozzle and cavity plate after injection molding is complete. 1...Hot runner-12...Hot runner block, 3...Needle, 4...
... Nozzle, 5... Cavity plate, 6...
...Cooling water hole, 7...Cavity, 8...
...Stock bar 19...Slide pin, 1
0... Spring, 11... Heat insulation layer,
12... Molten resin.

Claims (1)

[Claims] 1 In molding using a synthetic resin injection mold with a hot runner, the process of injection molding with the nozzle for injecting molten resin into the mold fitted into the through hole of the cavity plate, and the completion of injection molding. A synthetic resin injection molding method comprising the step of later separating the nozzle and the cavity plate.