JPS5949898B2 - Injection molding method for hygroscopic synthetic resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of molding a hygroscopic synthetic resin material using an in-line screw injection molding machine.

When injection molding a hygroscopic synthetic resin material such as polycarbonate, polyester, or ABS resin, the material is usually pre-dried or a molding machine equipped with a vent is used.

Vent-type molding is said to be more economical than pre-drying, which requires heating in a hopper dryer at a set temperature of 120°C for 3 to 8 hours, but conventional in-line screw injection molding machines In addition to the complicated structure of the injection cylinder and screw and the need for skill in the molding operation, there were disadvantages such as the tendency of some materials to undergo hydrolysis.

This invention does not require pre-drying, nor does it require special measures for the injection cylinder or screw, using a widely used injection molding machine with a common structure.
The object of the present invention is to provide a new injection molding method for hygroscopic synthetic resin in which the material supplied to the hopper can be molded in the same manner as when using a material with low hygroscopicity.

One feature of the invention according to the above object is that it uses a hopper equipped with heating means.

Further, the heating means is provided at the center of the interior of the hopper and at the lower part of the injection cylinder near the supply port, and the pellets in the hopper are dehumidified while reaching the supply port from the upper part of the hopper.

The heating temperature of the pellets differs between the center and bottom of the interior, and the temperature at which the pellets are initially heated is close to the deformation temperature so that the pellets do not deform and stick to the inner wall of the hopper or the heating member, and this heating temperature range is kept constant. The temperature after passing at a speed of , that is, the heating temperature at the lower part, is a deformation temperature at which the pellet becomes sticky and can change from a pellet shape to another shape.

Such a heating means is an indispensable condition for molding using an injection cylinder that does not require a vent, and the material that has lost its ability to fall due to stickiness is transferred into the injection cylinder by the transfer screw of the hopper. The moisture and volatile matter from the pellets and sticky pellets escape upward.

Since the material fed into the injection cylinder is already in a state where it is easily deformed, it is immediately deformed by the injection screw from the position of the supply port, and is sufficiently stretched to reach the melt zone ahead, thereby causing it to flow inside the hopper. The internal moisture and volatile matter that could not be dehumidified by heating are removed.

The gas containing water vapor generated in this injection cylinder is
As long as the supply of material from the hopper is not dense and there are gaps between pellets, it can be exhausted to the outside through the inside of the hopper.

The present invention will be explained in more detail below with reference to illustrated examples.

In the figure, 1 is an in-line screw injection device having an injection screw 3 of normal construction within an injection cylinder 2, and 4 is a hopper directly connected to a supply port 5 at the rear of the injection cylinder.

This hopper 4 is equipped with a heater 7.8 inside a truncated cone-shaped heating block 6 provided at the center of the interior and at the lower outer periphery connected to the supply port 5. A rotary shaft 12 having a lower end portion having a screw 11 inserted into the feed path 10 above the feed port is located through the feed port 6 .

This rotating shaft 12 communicates with an electric motor 13 attached to the center of the lid member 9, and the synthetic resin material that has passed through the gap between the hopper wall and the heating block 6 and reached the feeding path 10 is
It is sent out to the supply port 6 by the screw 11.

In the figure, 14 is a material input port, and 15 is a moisture drain port.

However, in order to injection mold a hygroscopic synthetic resin material using the above-mentioned in-line screw injection device, first, pellets a are introduced into the hopper 4, and the heating block 6 in the center of the interior is
is heated by heater T to near the deformation temperature of the material,
The lower part of the hopper 4 is heated by a heater 8 to the deformation temperature of the material.

Then, when the temperature of the injection cylinder 2 rises sufficiently and injection molding becomes possible, the rotating shaft 12 is started, and the screw 11 gradually feeds the pellets a to the lower part while heating them. and into the injection cylinder 2.

In this case, among the pieces (a) that were initially introduced, the one that entered the lower part is immediately heated to the deformation temperature, so dehumidification is incomplete, so the material in this part is injected and then molded. It is preferable to enter.

As the pellet a gradually passes through the gap between the heating block 6 and the hopper wall and is heated to near the deformation temperature, the moisture on the pellet surface and outer layer evaporates, causing primary dehumidification and vaporization. Moisture and the like escape upward through the gaps between the pellets and are exhausted to the outside of the hopper.

When the above pellet (a) reaches the lower part and is heated at the deformation temperature,
The outer layer of the pellet a becomes sticky and the inside becomes soft, making it difficult for the pellet to naturally fall from the feed path 10 to the supply port 5, unlike when it is heated to near the deformation temperature.

Since dehumidification progresses even in such a state, it is necessary to form a gap in the feeding path 10 for escape of volatile matter and moisture.
1, feed it to the injection cylinder 2 so as to scrape it off.

The time required from charging the pellets (a) to feeding them into the injection cylinder 2 varies depending on the type of hygroscopic synthetic resin material, but is approximately 15 to 20 minutes, and the amount of time per shot of the injection device used there Continuous feeding according to the cycle can be solved very easily by selecting the volume of the hopper.

Next, the pellet a sent into the injection cylinder is already in a state of being easily deformed, so it is elongated or thinned in the feed zone F from just below the supply port to the melt zone M by the rotation of the injection screw 3, and the surface area is reduced. The temperature is increased, and dehumidification is carried out again secondarily, so that the molten material is completely removed to the point where no more vaporization of volatile matter occurs.

Further, the gas generated in the feed zone F is discharged from the supply port 5 to the outside through the inside of the hopper.

This discharge is performed only after an escape gap is secured in the feed zone F and the feed path 10. Therefore, in order to secure this gap, the amount delivered to the injection cylinder by the screw 11 is adjusted to the charge of the injection screw 3. Control the amount to less than the amount.

The molten material is then injected into the cavity by normal operations.

As described above, this invention heats the pellets to near the deformation temperature and the deformation temperature in a hopper directly connected to the injection cylinder to dehumidify the pellets, and then feeds the pellets in a deformable state to the injection cylinder. It deforms and dehumidifies in the zone, thereby making it possible to injection mold a hygroscopic synthetic resin material without pre-drying or venting, so there is no need to use specific equipment during molding.

In addition, since the material put into the hopper can be molded continuously, there is no difference from molding materials with low hygroscopicity.
The effect is great not only in terms of molding but also economically.

[Brief explanation of the drawing]

The drawing is a schematic longitudinal sectional side view of an injection device used in the injection molding method of the present invention. 1... Injection device, 2... Injection cylinder, 3... Injection screw, 4... Hopper, 5... Supply port, 6 ...Heating block, γ, 8...Heater, 10...
Feeding path, 11... Screw, 12...
·Axis of rotation.

Claims (1)

[Claims] 1 Using an in-line screw injection device in which a hopper with a heating means in the center and lower part of the interior and a screw for material transfer is directly connected to an injection cylinder, the pellets of hygroscopic synthetic resin in the hopper are heated to near the deformation temperature. At the bottom of the hopper, the heating temperature is raised to the deformation temperature to make the pellets deformable, and the sticky pellets are supplied with gaps between each other. An injection molding method for hygroscopic synthetic resin, which is characterized by feeding a limited amount into an injection cylinder.