JPH02200409A - Injection molding method - Google Patents

Abstract

PURPOSE:To obtain a product having no flaw even when a large product is prepared by a resin inferior to flowability by bringing the cavity of a mold to a negative pressure state and subsequently injecting a molten resin in the cavity. CONSTITUTION:When a vacuum chamber 20 is reduced in pressure by a vacuum pump 22 to reach set pressure, a cavity approaches a core 11 and a hermetically closed space 14 is demarcated between the core 11 and the cavity 12. The first valve 26 is opened and a mold 10 communicates with the vacuum chamber 20 and the space 14 in the mold 10 is set to the almost same vacuum degree as that in the vacuum chamber 20. Subsequently, when a molten resin is injected in the mold 10 from an injection molding machine 1, the molten resin is uniformly spread to all parts of a mold cavity 13 because the mold cavity 13 is in a vacuum state. Next, the first valve 26 is closed while the second valve 27 is opened by the order of a controller to return the pressure in the mold 10 to atmospheric pressure and, thereafter, the core 11 is separated from the cavity 12 to take out a cooled solidified resin product.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a resin injection molding method.

[Prior art] To injection mold a resin product, first, a plurality of molds are assembled to define a desired mold space, and then molten resin is injected into this mold space, so that the resin flows inside the mold. After cooling and solidifying the product, the mold is opened and the product is removed. Note that when the molten resin is injected into the mold space, the air in the mold space is forced out through the gaps between the molds and the gaps between the molds and the knockout pins. [Problem to be solved by the invention] Nowadays, large products are sometimes manufactured using resins with poor fluidity when melted, such as engineering plastics for exterior panels. Occasionally, the product was not completely distributed, resulting in product defects. In order to solve this problem, it is possible to increase the temperature of the molten resin to increase its fluidity, but raising the temperature of the resin may cause problems such as foaming, decomposition, or burning. Undesirable.

In view of the above-mentioned circumstances, an object of the present invention is to provide an injection molding method that can produce defect-free products even when large-sized products are manufactured using resins with poor fluidity when melted.

[Means to solve the problem]

In the present invention, the above object was achieved by first creating a negative pressure state in the mold space of the mold, and then injecting molten J1M resin into the mold space.

[Operation] The resin injected into the mold space of the mold is completely spread to every corner of the mold space due to the negative pressure within the mold space.

〔Example〕

EMBODIMENT OF THE INVENTION Hereinafter, the specific structure of this invention is demonstrated in detail based on drawing which shows one Example.

Fig. 2 shows an injection molding apparatus for manufacturing products by the injection molding method according to the present invention, and 1 indicates the injection molding type;
10 is a mold, and 20 is a vacuum chamber.

The injection molding machine 1 includes a cylinder 2 and a hopper 3, and the cylinder 2 is equipped with a heater, a plunger, a screw, etc. (not shown). Above injection molding machine 1
The structure and operation are no different from conventional injection molding.

The mold 10 consists of a core 11 and a cavity 12, and a core recess 11a of the core 11 and a cavity 12
A mold space 13 is defined by the cavity recess 12a.

As clearly shown in FIG. 1, the core 11 has a core convex portion 11.
A recess 11b is formed around the core 1.
1 is formed with a passage 11G that opens between the four parts 11b and the outer peripheral surface of the core.

On the other hand, a protrusion 12b# is formed in the cavity 12 so as to surround the cavity recess 12a, and a rubber ring 14 is fitted around the outer periphery of the tip of the protrusion 12b.

As shown in FIG. 2, a vacuum pump 22 is connected to the vacuum chamber 20 via a pipe 21.
A pressure regulating valve 23 is interposed therein. The vacuum chamber 20 is also provided with a release valve 24 . Further, the vacuum chamber 20 and the passage 11c of the core 11 are communicated with each other by a pipe 25, and the pipe 25 has a first valve 2 which is operated as described in detail later.
6 and a second valve 27 are interposed. The space of the vacuum chamber 20 is set to be about 5 to 100 times the capacity of the mold space 13 in the mold 10.

The operation of the injection molding apparatus described above will be explained below.

When the apparatus starts operating, the pressure inside the vacuum chamber 20 is reduced by the vacuum pump 22. At this time, the release valve 24. The first valve 26 and the second valve 27 are in the closed state, and the set pressure in the vacuum chamber 20 is <1X1.
0'~3001111H! ]), the pressure regulating valve 23 automatically closes.

During the depressurization operation of the vacuum chamber 20, the core 11 and the cavity 12 are located apart from each other as shown in FIG. 1(a).

When the pressure in the vacuum chamber 20 is reduced to the set pressure, the cavity 12 approaches the core 11, and the convex portion 12b of the cavity 12 slightly retracts into the concave portion 11b of the core 11, as shown in FIG. 1(b). At this time, the rubber ring 12
c and the inner peripheral surface of the recess 11b are in close contact with each other, and a sealed space 14 is defined between the core 11 and the cavity 12.

When the space 14 is defined in the mold 10, the first valve 26 is opened according to an instruction from a controller (not shown). As a result, the mold 10 and the vacuum chamber 20 are communicated with each other, and the space 14 within the mold 10 has a degree of vacuum comparable to the degree of vacuum within the vacuum chamber 20.

When the cavity 12 continues to move further and the core 11 and the cavity 12 are completely tightened as shown in FIG. 1(C),
A mold space 13 in a vacuum state is defined.

Next, when the molten MA resin is injected from the injection molding part 1 into the mold 10, since the mold space 13 is in a vacuum state, the mold space 1
The molten resin spreads to every corner of 3.

Next, the first valve 26 was closed according to instructions from the controller, and the inside of the mold was returned to atmospheric pressure by listening to the second valve 27, and then the core 11 and the cavity 12 were separated and cooled and solidified. Take out the resin product.

After the product is taken out from the mold 10, the second valve 27 is closed, and the vacuum chamber 20, which has been pressurized by opening the first valve 26, is turned on by the vacuum pump via the closed pressure regulating valve 23. The pressure is again reduced by step 22, and the operation of molding the products 81 is repeated in the manner described above. Note that after stopping the operation of the apparatus, the release valve 24 is opened to return the inside of the vacuum chamber 20 to atmospheric pressure.

[Effects of the Invention] As detailed above, according to the injection molding method of the present invention, the mold space in the mold is brought into a negative pressure state, so that the injected molten resin is Since it reaches every corner of the mold space, it is possible to obtain defect-free products even when making large products using resin with poor fluidity.

[Brief explanation of the drawing]

Figure 1 (a), (b), fc) shows resin molded products made using the injection molding method related to Kikomei! FIG. 2 is a cross-sectional view sequentially showing the operation of the mold during 4U manufacturing, and FIG. 2 is a conceptual overall view of an injection molding apparatus using the injection molding method according to the present invention. DESCRIPTION OF SYMBOLS 1... Injection molding machine, 10... Mold, 11... Core 12... Gabity, 13... Mold space, 20...
- Vacuum chamber, 22... vacuum pump, 25... vibrator.

Claims (1)

[Claims] An injection molding method characterized by creating a negative pressure inside a mold space of a mold, and then injecting molten resin into the mold space.