JPH02220822A - Molding die - Google Patents

Abstract

PURPOSE:To prevent the generation of defective molding and enhance flatness of a molded product by setting the diameter of a cold slag well larger than the diameter of a discharge port of a sprue. CONSTITUTION:A molding die 10 is provided with a cold slag well 19 in a section opposite to a discharge port 17A of a sprue 17 in a movable slit mold 12. The sprue 17 is thin, and the cold slag well 19 can collect and contain cold slag of molten resin. The diameter D2 of cold slag well 19 is set larger than the diameter D1 of the discharge port 17A of the sprue 17. Thus, flow fronts A are symmetrical between the side of a chain surface bush 13 and the side of chain surface bush 14, and the flow in the thickness direction of a molding cavity 15 is uniformized to uniformize stretching, and as a result, the flatness of a molded product is good.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mold for molding a substrate for an information recording medium made of synthetic resin and suitable for use in substrates of magnetic disks, optical disks, and the like.

[Prior Art] A conventional mold for molding a substrate for an information recording medium includes a molding cavity defined between a pair of split molds, a molding cavity provided on one of the split mold sides, and connected to an injection molding machine. A sprue that guides the molten resin injected by the injection molding machine and discharges it to the molding cavity side, and a cold slug of the molten resin that is provided on the other split mold side and is placed opposite to the sprue discharge port and accommodates the cold slug of the molten resin that the sprue guides. A cold slug well.

According to the conventional molding mold described above, cold slag is generated when relatively low temperature molten resin waiting at the injection port of the injection molding machine is injected into the sprue of the mold and rapidly cooled. is captured and contained in a cold slag well (resin reservoir) at the initial stage of injection. This prevents cold slag from flowing into the molding cavity and prevents molding defects such as the formation of a boundary layer between the resin and other healthy resins.

[Problem M to be solved by the invention] However, as a result of experiments by the present inventor, in the above-mentioned conventional molding die, the diameter of the cold slug well is set to be equal to or smaller than the diameter of the sprue outlet. There is a disadvantage that the flatness of the resulting molded product is poor.

An object of the present invention is to prevent molding defects caused by cold slag and improve the flatness of a molded product with a simple configuration.

[Means for Solving the Problems] The present invention includes a molding cavity defined between a pair of split molds, a molding cavity provided on one split mold side and connected to an injection molding machine, and a molten cavity injected by the injection molding machine. A sprue that guides the resin and discharges it to the molding cavity side, and a cold slug well that is provided on the other split mold side and is arranged opposite to the sprue discharge port to accommodate the cold slag of the molten resin that the sprue guides. In this molding die, the diameter of the cold slug well is set larger than the diameter of the sprue outlet.

[Effect] Hereinafter, the effects of the present invention will be explained.

FIG. 1 is a cross-sectional view conceptually showing the principle of a molding die 10 of the present invention, and the relative dimensions of each member are exaggerated in order to clearly show the effects of the present invention. Items not related to the essence of are not shown.

The molding die 10 includes a pair of fixed split molds 11 and a movable split mold 12.
A molding cavity 15 is defined between the mirrored bushings 13, 14 incorporated in each of the mirror bushings 13,14.

The molding die 10 includes a fixed split mold 11 and a mirror bush 13.
A sprue bush 16 is provided at the center of the sprue bushing 16, thereby forming a sprue 17. The sprue 17 is connected to an injection molding machine 18 and guides the molten resin injected by the injection molding machine 18 and discharges it to the molding cavity 15 side. At this time,
Molding cavity 15 via outlet 17A of sprue 17
The flow front A of the molten resin flowing into the tube is schematically shown in FIGS. 2(A) and 2(B).

The molding die 10 has a sprue 1 in a movable split mold 12.
A cold slug well 19 is provided at a portion opposite to the discharge port 17A of 7. The cold slug well 19 can capture and contain the cold slag of molten resin guided by the sprue 17 .

Thus, in the molding die 10, the diameter D2 of the cold slug well 19 is set larger than the diameter D1 of the discharge port 17A of the sprue 17. As a result of the inventor's experiments, the diameter D2 of the cold slug well 19 was determined by the sprue 1.
It was found that by setting the diameter DI of the discharge port 17A of No. 7 as described above, it was possible to prevent molding defects due to cold slag and improve the flatness of the molded product.

Here, as shown in FIG. 3, the flatness of the molded product is expressed by the value of the larger value of the height difference hl on the front surface of the molded product and the height difference h2 on the back surface.

It is presumed that the improvement in flatness of the molded product is due to the following reasons. That is, when D2≦DI, which is the conventional structure, the flow front A of the molten resin that has flowed into the molding cavity 15 is between the mirror bushing 13 side and the mirror bushing 14 side as shown in FIG. 2(C). Asymmetry occurs, and the non-uniformity of the flow in the thickness direction of the molding cavity 15° results in non-uniform orientation. On the other hand, according to the structure of the present invention, D2>Di, this flow front A becomes symmetrical between the side of the mirrored bushing 13 and the side of the mirrored bushing 14, and the flow is made uniform in the thickness direction of the molding cavity 15. It is possible to achieve uniform orientation, and as a result, the flatness of the molded product is improved.

The diameter D2 of the cold slug well 19 is the diameter D2 of the sprue 1.
It is sufficient if D2>DI as compared to the diameter D1 of the discharge port 17A of No. 7, but preferably 2D1>D2>DI. D
If 2>2Dl, the cold slag will move into the molding cavity 1.
This is because there is a risk that the water may flow into the side of No. 5. Therefore, depending on the type of resin, molding conditions, etc., the ratio of Di and D2 is as follows:
It is sufficient to set the optimum value within the range of 2D1>D2>Di.

[Example] Using polyetherimide resin as the molding resin, an injection molding machine (
Mold temperature: 180°C), outer diameter: 130mm, thickness: 1.
A disc-shaped molded product weighing 9 mg+ was molded. At this time, the diameter D1 of the sprue outlet and the diameter D of the cold slug well are
2 were molded with different diameter ratios as shown in Table 1, and their flatness was measured. Note that all molding conditions were the same.

According to Table 1, it is recognized that by implementing the method of the present invention, molding defects due to cold slag can be prevented and the flatness of molded products can be improved with a simple configuration.

In addition, in carrying out the present invention, the molding cavity may be formed only by the split mold body, not by the mirror-finished bushing.
Alternatively, it may be formed by a stub bar or the like provided on the split mold body.

[Effects of the Invention] As described above, according to the present invention, with a simple configuration, molding defects due to cold slag can be prevented and the flatness of the molded product can be improved.

[Brief explanation of the drawing]

Figure 1 is a sectional view conceptually showing the principle of the molding die of the present invention, Figure 2 is a schematic diagram showing the flow front of molten resin flowing into the molding cavity, and Figure 3 is a diagram showing the flatness of the molded product. It is a schematic diagram showing a definition. DESCRIPTION OF SYMBOLS 10...Molding mold, 11.12...Split mold, 13.14...Mirror bushing, 15...Molding cavity, 17...Sprue 17A...Discharge port, 19... Cold Slugwell. Patent applicant Sekisui Chemical Co., Ltd. Representative Hiroshi 1) Kaoru Diagram 1 (A) (B) (C)

Claims (1)

[Claims] (1) A molding cavity is defined between a pair of split molds, and is connected to an injection molding machine provided on one of the split molds to guide the molten resin injected by the injection molding machine and discharge it to the molding cavity side. and a cold slug well provided on the other split mold side to face the sprue discharge port and containing a cold slag of molten resin guided by the sprue, A molding die characterized in that the diameter of the cold slug well is set larger than the diameter of the sprue outlet.