JPS6236851B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a mold for transfer molding.

The process of resin molding will be explained in the case of transfer molding of thermosetting resin shown in FIGS. 1a to 1d. In FIG. 1, the mold consists of an upper mold 4 and a lower mold 5. First, (a) the resin preformed into the tablet 1 is filled into the pot 2 provided in the mold. Next, (b) the tablet 1 is heated and the molten resin 12 is pushed downward by the plunger 3 to fill the cavity 9 through the runner 6 -> sub-runner 7 -> gate 8. In this case, the cavity 9
The insert 10 is set in advance. (c) After the molten resin 12 fills the cavity 9, the resin 12 starts to harden. (d) After the required curing time has elapsed, the molds 4 and 5 are opened, and the molded product 13 is pushed up with the ejector pin 11 to be released. Finally, fold part 14 of molded product 13 at the gate position to create product 1.
5 is obtained.

A transfer molding die that has been conventionally used to mold a large number of products per shot will be explained with reference to FIGS. 2 and 3.

In the figure, the same parts as in FIG. 1 are denoted by the same numbers. Figure 2 is Figure 3 (plan view of the mold)
FIG. 3 is a sectional view taken along the direction of FIG. 2. As is clear from these figures,
The cross-sectional area of the runner 6 is constant regardless of the distance from the pot 2, and the dimensions of the sub-runner 7 and the gate 8 and the aperture angle θ of the sub-runner 7 are also different from each cavity 9.
They are identical in position. Here, the aperture angle θ of the sub-runner 7 refers to the angle formed by the upper and lower surfaces of the sub-runner 7.

Since the cross-sectional area of the runner 6 is thus constant, there is a large difference in the time it takes for the molten resin 12 to arrive at each cavity 9. That is, the farther the cavity 9 is from the pot 2, the greater the delay in the resin filling start time. In addition, since the runner 6 becomes longer as the distance from the pot 2 increases, the molten resin 12 during the flow
As a result, the farther the cavity 9 is from the pot 2, the slower the resin filling speed becomes. Therefore, as shown in FIG. 3, at the time when the cavity 9 closest to the pot 2 has completed filling with resin, the cavity 9 which is the fastest is still hardly filled. Such a phenomenon of large differences in filling speed is extremely undesirable from the viewpoint of making the quality of molded products uniform. In fact, it has been confirmed that in molded products molded with conventional molds having flow path structures, the rate of occurrence of internal voids, the adhesion of inserts, and the degree of bending vary depending on the cavity position.

The object of the present invention is to eliminate the drawbacks of the above-mentioned conventional techniques, and to improve the quality of insert resin-sealed products by uniformly filling the thermosetting resin into each cavity with a simple configuration. To provide molds for use.

In order to achieve the above object, the present invention melts a tablet filled in a pot and made of a thermosetting resin by heating, presses it with a pressing means, and forms a gate along a runner branched from the pot. This is a transfer molding mold for molding an insert molded product by injecting into a plurality of cavities arranged through a pot, and the cross-sectional area of the runner decreases as it moves away from the pot, and the aperture of the sub-runner This is a transfer molding die characterized in that the corners are increased for each block.

The present invention will be explained below with reference to an embodiment shown in FIGS. 4 to 6. In the figure, the same parts as in FIG. 1 are denoted by the same numbers. FIG. 4 is a cross-sectional view taken from FIG. 5 (plan view of the mold), that is, a vertical cross-sectional view of the runner 6. As is clear from the diagram, runner 6
The height h of the runner 6 decreases linearly in the traveling direction of the molten resin, and therefore the cross-sectional area of the runner 6 also decreases linearly.

Further, FIG. 6 is a vertical view of each sub-runner 7 branching from the runner 6, from A-A to I-I in order of distance from the pot 2. The aperture angle Θ of the sub-runner is increased in units of three cavities 9 on one side of the runner 6 (six cavities 9 on both sides of the runner 6) as the distance from the pot 2 increases.

That is, Then, Θ _a < Θ _d < Θ _g ...(2). With this configuration, the flow velocity of the molten resin 12 in the runner 6 becomes faster as it moves away from the pot 2 than in the conventional case. Therefore, the difference in the start time of filling the molten resin 12 into each cavity 9 is reduced.

On the other hand, as the constriction angle Θ of the sub-runner 7 increases, the pressure loss of the molten resin passing through it decreases, so by increasing the sub-runner constriction angle the farther the cavity is from the pot 2, the pressure loss up to each cavity can be reduced. (=pressure loss when passing through the runner + pressure loss when passing through the sub-runner) can be made equal. If the pressure loss is equal, the flow rate of the molten resin within each cavity will also be equal. In order to strictly equalize the flow velocity in each cavity 2, it is necessary to change the subrunner aperture angle θ for each cavity 9, but in the present invention, it is possible to change the subrunner angle θ for each cavity 9 to the extent that it does not affect the reliability of the molded product. Overall, the subrunner aperture angle Θ can be changed.

In this embodiment (Figs. 4 to 6), three cavity groups (A-A to C-C, D-D to F-F, G-G to I) have the same subrunner aperture angle.
-I) center cavity (B-B,E-
The constriction angle of the sub-runner was changed so that the total pressure loss was equal in E, HH). This allows the mold manufacturing cost to be reduced by several percent.

FIG. 7 shows numerically the state of resin filling in each cavity for the conventional mold, and FIG. 8 for the mold of the present invention. In Figures 7 and 8, the horizontal axis represents the dimensionless time t/T (T: time from the start of filling the cavity to completion), and the vertical axis represents the resin filling rate α within the cavity. Each has a scale. As is clear from FIG. 7, in the conventional mold, the filling speed of cavity No. 5, which is farthest from the pot, is considerably slower than that of cavity No. 1 at the initial stage of filling. Furthermore, in the latter stage of filling, filling is completed in the cavity near the pot, so the filling speed of the No. 5 cavity increases. Furthermore, the difference in filling start time and the difference in filling rate at any given time between cavity No. 1 closest to the pot and cavity No. 5 farthest are considerably large. On the other hand, in the mold of the present invention, although the number of cavities is increased compared to the conventional mold, the difference in filling start time is shortened,
Also, the filling speed is almost the same for each cavity.
Therefore, when manufacturing insert molded products by sealing them with thermosetting resin using a transfer molding mold,
Workability and yield of molded products can be improved.

In the above embodiments, a mold for transfer molding of a thermosetting resin was described, but the present invention can be similarly applied to a mold for molding a thermoplastic resin.

As explained above in detail, according to the present invention, even in large molds, the difference in the filling start time of each cavity is reduced, and each cavity is filled with resin at approximately the same speed, so that the resin and insert are The variation in adhesive properties and the variation in the occurrence of internal voids are reduced compared to conventional molded products, and the quality of the molded products can be made uniform.

[Brief explanation of the drawing]

Figure 1 is an explanatory sectional view showing the process of resin molding. Figures 2 and 3 show conventional molds.
Figure 3 is a plan view of the mold, Figures 4 to 6 show an embodiment of the present invention, Figure 4 is a cross-sectional view of Figure 5, and Figure 5 is the mold. The plan view of FIG. 6 is AA, B-B, C-C, D- of FIG.
D, E-E, F-F, G-G, H-H, I-I sectional views, Figure 7 is a diagram numerically showing the resin filling situation in each cavity of a conventional mold, FIG. 8 is a diagram numerically showing the filling state of resin in each cavity by the mold of the present invention. 2... Pot, 4... Upper die of the mold, 5... Lower die of the die, 6... Runner, 7... Sub-runner, 9...
...Cavity, Θ...Subrunner aperture angle.

Claims (1)

[Claims] 1. A tablet filled in a pot and made of thermosetting resin is melted by heating, pressed by a pressing means, and injected into multiple cavities arranged through gates along runners branched from the pot. This is a transfer molding mold for molding insert molded products, and the cross-sectional area of the runner decreases as it moves away from the pot, and the drawing angle of the sub-runner increases for each block. A mold for transfer molding characterized by having the following structure.