JPS5839425A - Low pressure injection molding method - Google Patents

Abstract

PURPOSE:To obtain a molded item excellent in quality under a low injection molding pressure and a clamping pressure, by injecting a resin into a cavity space having a volume larger than the volume of the intended item, and compressing the resin to the volume of the intended item under a low pressure. CONSTITUTION:After a movable mold 2 is lowered to a fixed mold 2, and is stopped at a first clamping position to form the cavity space 4a whose volume is several times or several tens times the volume of the intended item 1 and that is in communication with an injection port 12 for the resin, the molten resin 13 is injected from an injection nozzle 5 through an injection port 5 into the cavity space 4a under a low pressure. Then the movable mold 3 is lowered under a low pressure of 20-100kg/cm<2> to a second clamping position so as to form a closed cavity space 4b that has approximately the same dimensions and shape as those of the item 1 and is cut off from the injection port 12, so that the molten resin 13 is compression molded, cooled and solidified to obtain the item 1.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for low-pressure injection molding of synthetic resins, particularly a method for performing injection molding at low clamping pressure and injection pressure.

The injection molding method involves injecting a molten thermoplastic resin (including rubber) into a mold, but requires high mold clamping pressure and injection pressure. To explain the case of molding the molded product shown in Figure 1, Figure 1 (a) is a perspective view showing the molded product, (b) is a sectional view taken along I-1, and Figure 2 is a conventional injection molding case. 3 is a plan view of the fixed mold, 1 is a molded product, 2 is a fixed mold, 3 is a movable mold, 4 is a cavity space, 5 is an injection nozzle, 6 is a sprue, and 7 is a vertical sectional view showing the mold. is the runner and 8 is the gate.

In the conventional injection molding method, a fixed mold 2 and a movable mold 3 are combined and clamped to form a cavity space 4 having approximately the same size and shape as the molded product 1, and a sprue is injected into this cavity space 4 from an injection nozzle 5. Molten resin was injected through a runner 7 and a dart 8t to form a molded product 1. In such conventional injection molding methods, press operations are either horizontal or vertical, and the operations include mold clamping, injection, cooling, IIi opening, and ejection of the molded product.

However, in such a conventional injection molding method, in order to uniformly inject the resin into the cavity space 4 after the mold clamping is completed, the resin is distributed by the runner 7 and a small 1ky-
Since the injection was made from point B, the mold clamping pressure was increased (-250 to 350 m
kg/cm”), the power consumption is large,
■Due to high pressure injection from a small nozzle, there is a risk that distortion will remain in the molded product, resulting in deformations such as warping, twisting, and unevenness. Even if this part of the resin is recycled, there are problems such as a large amount of energy is required for crushing, regritting, etc.

This invention was made by focusing on such conventional problems, and after injection molding with a deep mold engraving surface,
The object of the present invention is to provide a low-pressure injection molding method that can produce molded products of excellent quality with little waste of resin at low injection pressure and mold clamping pressure by clamping the mold at low pressure.

In this invention, at the first mold clamping position, a cavity space having a volume larger than the volume of the molded product and communicating with the resin injection port is formed, and at the second mold clamping position, the cavity space has a volume larger than the volume of the molded product. Using a mold having the same size and shape and forming a cavity space that is blocked from the resin injection port, the resin is injected at the first mold clamping position, and then the resin is injected at low pressure to the 20th clamping position. This is a low-pressure injection molding method characterized by compressing to obtain a molded product.

Hereinafter, this invention will be explained based on the drawings. FIG. 4 is a vertical sectional view showing the first mold clamping position of a mold in an embodiment of the present invention, FIG. 5 is a V-V sectional view thereof, and FIG. 6 is a vertical sectional view showing the second mold clamping position. Vertical sectional view, FIG. 7 is a vertical sectional view showing the mold opening position, and the same reference numerals as in FIGS. 1 to 5 indicate the same or corresponding parts.

In the drawing, reference numeral 9 denotes a sprue block, which is supported on the movable mold 3 by a spring 10, and has first and second sprue blocks.
At the mold clamping position, it fits into a notch 11 provided on the upper surface of the fixed mold 2 to form a resin injection port 12 therebetween. Although the sprue block 9 is adapted to be pressed against the fixed W2 by a spring 10, other pressure sources may be used, such as a pneumatic or hydraulic cylinder.

The fixed mold 2 and the movable mold 3 have a volume larger (several to several tens of times) than the volume of the molded product 1 at the first mold clamping position, and are connected to a chain which communicates with the resin injection port 12. From this position, the movable mold 3 further descends to proceed with mold clamping, and at the second mold clamping position, the molded product 1 has approximately the same size and shape as the molded product 1, and a molded product 1 is formed from the injection port 12. The fixed mold 2 has a deep mold engraving surface so as to form a blocked second closed cavity space 4b, and the movable mold 3 has a slidable mold surface corresponding to this mold engraving surface. is formed. The injection port 12 is designed to be able to inject a large amount of molten resin at low pressure in a short time, and is formed to have a larger diameter than the conventional gate 8.

The molding method involves lowering the movable mold 3 from the mold opening position, and
It stops at the mold clamping position, and as shown in Figures 4 and 5'
As shown, one injection nozzle 5 injects the molten resin 16 into the cavity space 4aK through the injection port 12 at low pressure. The amount of resin 13 to be injected is the amount necessary to mold the molded product 1.

After injecting the resin 13, the first moving mold 3 is lowered as shown in Figure 6, and the mold is clamped at low pressure (20 to 100#/α2) to the second mold clamping position to compress the molten resin 13. Then, it is cooled and solidified to form a molded article 1.

At this time, the injection port 12 is blocked by the movable die 3 and the injection port 12 is held under pressure. Thereafter, as shown in FIG. 7, the movable mold 3 is raised to open the mold, the ejecting pins 14 are protruded, and the molded product 1 is taken out. At this time, since the sprue block 9 also rises, the ejection pin 15 is ejected to remove the sprue portion 16.

Repeat the above operations to form the mold.

FIG. 8 is a vertical sectional view showing the first clamping position of the mold in another embodiment, and the mold is arranged so as to clamp and open in the horizontal direction, and the injection nozzle 5 The sprue 17 is connected to the injection port 12 so that the injection direction thereof is parallel to the mold clamping direction. In this way, the direction of mold clamping and the direction of injection can be changed arbitrarily.

In the above description, the structures of the fixed mold 2, movable mold 3, sprue block 9, etc. are not limited, and the injection and mold clamping pressures can also be selected arbitrarily. Furthermore, there are no restrictions on the shape, structure, material, use, etc. of the molded product 1.

As described above, according to the present invention, the resin is injected without completely closing the molding die, and then the mold is clamped under low pressure and compressed to perform molding, so that the following effects can be obtained. .

(2) Molding can be performed at 1/2 to 1/10 the pressure of conventional injection molding, resulting in energy savings and cost reductions.

■There is no distortion in the molded product, and there are no shape defects such as warping, twisting, or unevenness.

■Can be molded even with resin raw materials with low fluidity.

■ Runners and sprues required in general injection molding are no longer required, resulting in a reduction in the number of raw materials required.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view showing a molded product, FIG. 1(b) is a sectional view taken along I-■, and FIG. 2 is a vertical sectional view showing a conventional injection mold.
FIG. 3 is a plan view of the fixed mold, FIG. 4 is a vertical cross-sectional view showing the first clamping position of the mold in an embodiment of the present invention, and FIG. 6 is a vertical sectional view showing the second mold clamping position, FIG. 7 is a vertical sectional view showing the mold opening position, and FIG. 8 is a vertical sectional view showing the first mold clamping position of the mold in another embodiment. FIG. In each figure, the same reference numerals indicate the same or equivalent parts, 1 is a molded product, 2 is a fixed type, 3 is a movable type, 4.4a, 4b are cavity spaces, 5 is an injection nozzle, 9 is a sprue block,
10 is a spring, 11 is a notch, 12 is an injection port, 13 is a resin, and 14 and 15 are ejection pins. (a) Ii Figure 1 Figure 2 Figure 3 Figure 1 Figure 5 yJ $6 Figure

Claims (1)

[Claims] (11 At the first mold clamping position, a cavity space having a volume larger than the volume of the molded product and communicating with the resin injection port is formed, and at the second mold clamping position, Using a mold that has approximately the same size and shape as the molded product and that forms a cavity space that is closed off from the resin injection port, the resin is injected at the first mold clamping position, and then the second mold is injected. A low-pressure injection molding method characterized by compressing at low pressure to a mold clamping position to obtain a molded product (2) A patent in which the cavities and spaces formed at the first and second mold clamping positions are closed spaces. Low-pressure injection molding method according to claim 1 (3) Abutting against a fixed mold at a first mold clamping position to form a resin injection port therebetween; Claim 1 or □ is the low-pressure injection molding method according to claim 2, which uses a molding mold equipped with a sprue block that comes into contact with the movable mold and separates from the fixed mold at the mold opening position.