JP3237496B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method in which a compression step by increasing a mold clamping force is added after an injection step and a dwelling step.

[0002]

2. Description of the Related Art Conventionally, an injection molding method as disclosed in Japanese Patent Publication No. 4-78093 has been known. FIG. 4 is a diagram shown in the same publication, and shows a change in the resin pressure in the mold from the start of the injection of the molten resin to the cooling and solidification. In this injection molding method, the molten resin is injected into the cavity of the clamped mold (injection step), and the injection pressure is reduced immediately before the cavity is filled with the molten resin (depressurization step). The pressure is gradually increased, and the pressure is maintained at an in-mold resin pressure that is larger than the maximum in-mold resin pressure at the time of injection (a pressure holding step).

According to this method, since the injection pressure is lowered immediately before the cavity is filled with the molten resin, it is possible to prevent the mold from opening when the resin is not solidified. In addition, in the pressure-holding step, the mold opens as the resin pressure in the mold increases, but since the surface of the molten resin is gradually cooled and fixed,
The molten resin does not enter into the gap between the divided surfaces of the mold, and the occurrence of burrs can be prevented.

On the other hand, there is known a method called injection compression molding in which after a cavity is filled with a molten resin, a mold is finely driven to perform molding while applying a compressive force to the molten resin.
As shown in FIG. 5 (a), this conventional method uses a female mold 51.
Molten resin 54 in a cavity 53 formed by
After filling, the excess resin is caused to flow out of the gate 55 by pressing the male mold 52 against the female mold 51, and at the same time, the gate 55 is moved by the male mold 52 as shown in FIG. The male mold 52 is finely driven at the same time as or after the gate cut, and then a compression force is applied to the resin in the mold to perform molding.

[0005]

By the way, in the conventional injection molding method, after filling the cavity with the resin, the holding pressure is applied by the pressure from the injection molding machine side. There has been a request to further perform high-density molding in order to improve such properties.

The conventional injection compression molding method is capable of high-density molding, so that good results can be obtained in terms of, for example, sinking and transferability. There has been a problem that marks and resin distortion may occur, and burrs are likely to appear due to wear of the sliding portion 56 (see FIG. 5) of the mold.

In view of the above circumstances, the present invention can perform high-density molding, and can also avoid the problem of resin flow during the compression step and the problem of wear of the sliding portion, thereby achieving dimensional accuracy of the product. An object of the present invention is to provide an injection molding method capable of greatly improving the injection molding method.

[0008]

According to the injection molding method of the present invention, after a mold is clamped by a first clamping force of a low pressure, a molten resin is injected into a cavity to form a cured skin layer. Injection step to fill the molten resin, depressurization step to lower the injection pressure just before the cavity is filled with the molten resin, and after depressurization step, gradually increase the in-mold resin pressure to increase the maximum greater than the resin pressure, by and performs pressure holding said first clamping force is exceeded type the resin pressure, a pressure holding process of opening the split surface of the mold, the gate after the pressure-holding step a closed
Flip, after closing the gate, in order to reduce the amount of opening of the divided surface caused by the pressure holding process, and a compression stroke to perform mold clamping with a second clamping force of pressure higher than the first clamping force It is characterized by having. At that time, the first clamping force is preferably set to a second clamping force substantially about half of.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining the steps of the injection molding method, FIG. 2 is a diagram showing changes in the ram pressure, the resin pressure in the mold, and the amount of mold opening from the start of the injection of the molten resin to the cooling and solidification, and FIG. FIG. 1 is a configuration diagram illustrating an example of a mold and an injection molding machine used for performing an injection molding method.

First, the mold A and the injection molding machine B will be described, but since these are common, they will be briefly described. To explain the details of the mold A, 1 is a movable type, 2 is a fixed type, 4 is a fixed side mounting plate, 5 is a fixed side spacer, 6 is a movable side spacer, 7 is a movable side mounting plate, and 8 and 9 are protruding. Board,
10 is a locate ring, 11 is a manifold, 12 is a torpedo, 13 is a runner bush, 14 is a protruding pin,
15 is a runner, 16 is a cavity formed between the movable mold 1 and the fixed mold 2, and 17 is a gate. 1a, 2a
Is a dividing surface of the movable mold 1 and the fixed mold 2. The mold A is provided with a mold clamping mechanism C such as a hydraulic cylinder type or a toggle mechanism type. However, this mold clamping mechanism C
Has a function of adjusting the mold clamping force in at least two stages (low pressure and high pressure).

The molding machine B will be described. A ram 19 reciprocally driven by a hydraulic cylinder 18 is slidably accommodated in a heating cylinder 21 heated by a heater 20, and a hopper 22 is provided at an upper rear portion of the heating cylinder 21. A nozzle 23 is provided at the tip.

Next, an injection molding method performed using the above-described mold A, injection molding machine B, and mold clamping mechanism C will be described with reference to FIGS. FIG. 1 schematically shows the configuration and movement of the mold A.

In this injection molding method, first, FIG.
As described above, after the mold is clamped with the first mold clamping force (small) of low pressure, the molten resin 41 is injected into the cavity 16 (injection step). At this time, the molten resin 41
As a result, a skin-hardened layer 42 that has been cooled and solidified is formed on the surface of the molten resin. In addition, the in-mold resin pressure gradually increases.

Immediately before the inside of the mold is filled with the molten resin 41, the injection pressure is reduced to zero (depressurizing step), and the state is maintained for a short time. As a result, although the mold is clamped at a low pressure, the molten resin 41 is filled into the cavity 16 in a state where the divided surfaces 1a and 2a of the mold are not opened.

Thereafter, the resin pressure in the mold is increased by increasing the ram pressure, and a holding pressure is applied so that the resin pressure in the mold is larger than the maximum resin pressure in the mold at the time of injection and exceeds the first mold clamping force. (Pressure holding step), thereby spreading the hardened skin layer 42 formed on the surface of the molten resin 41 to fill a gap formed between the hardened skin layer 42 and the inner surface of the mold. Remove. In addition, due to the increase of the holding pressure, FIG.
As shown in (2), the mold divided surfaces 1a and 2a clamped with a low clamping force are positively opened. At this time, the molten resin 4
Since the skin hardened layer exists on the surface of No. 1, the resin does not protrude into the gap between the divided surfaces 1a and 2a.

By maintaining the pressure for a predetermined time, the divided surfaces 1a, 2a
When the opening amount of “a” reaches the maximum value (for example, 0.15 mm), the gate 17 is cut (closed) as shown in FIG. 1C. Then, after the gate cut, FIG.
As shown in (d), the divided surfaces 1a and 2
In order to reduce the opening amount of a, mold clamping is performed with a second clamping force higher than the first clamping force (compression step). As a result, the resin inside is molded in a highly compressed state.

[0017] Therefore, compared with the conventional injection molding method which has been completed up to the pressure holding step, it is possible to improve the thinning, transferability, resin distortion and the like. In addition, since the mold is positively opened at the time of holding pressure, and then the compressive force is applied to the resin by increasing the mold clamping force, the resin in the cavity is made uniform without the resin flowing. Can be achieved. In addition, since the mold is not slid during the compression step, there is no possibility that burrs are generated due to wear of the sliding portion.

The first clamping force is the second clamping force.
Is preferably about 1/2 of the mold clamping force. Also,
When the mold is clamped with the second mold clamping force, the mold opening amount does not necessarily have to be zero.

[0019]

As described above, according to the present invention,
A compression step is added after the pressure-holding step to enable high-density molding, so that moldability such as flaking, transferability, and resin distortion can be improved. Further, in the compression step, by increasing the mold clamping force, the amount of mold opening is reduced to apply a compressive force to the resin, so that the resin distribution in the cavity can be made uniform without the flow of resin or the like. Further, since there is no portion to be slid in the compression step, there is no generation of burrs due to wear. As a result, the dimensional accuracy of the product can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of an injection molding method of the present invention.

FIG. 2 is a diagram showing a time change of a ram pressure, a resin pressure in a mold, and a mold opening amount in the injection molding method of the present invention.

FIG. 3 is a sectional view showing an example of a mold and an injection molding machine used for carrying out the injection molding method of the present invention.

FIG. 4 is a diagram showing a change in in-mold resin pressure in a conventional injection molding method.

FIG. 5 is an explanatory view of a conventional injection compression molding method.

[Explanation of symbols]

 C Clamping mechanism 1 Movable mold 2 Fixed mold 1a, 2a Dividing surface 16 Cavity 17 Gate 41 Molten resin 42 Skin hardened layer

Claims (1)

(57) [Claims] An injection step of injecting a molten resin into a cavity and filling the molten resin while forming a cured skin layer after the mold is clamped with a first clamping force of a low pressure; A pressurizing step of lowering the injection pressure immediately before is filled with the molten resin; and, after the depressurizing step, gradually increasing the in-mold resin pressure to be greater than the maximum in-mold resin pressure at the time of injection, and the first mold by performing the pressure keeping the clamping force is exceeded type the resin pressure, a pressure holding process of opening the split surface of the mold, close the gate after the pressure holding process, after closing the gate, resulting in the pressure holding process division In order to reduce the opening amount of the surface, the first
And a compression step of clamping with a second clamping force higher than the clamping force.