JPH0214885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mold used for high-pressure molding of silicone resin such as injection molding or transfer molding.

Conventionally, silicone resins are useful resins having rigid or elastic physical properties, but compression molding and transfer molding have generally been used to obtain molded products of silicone resins. Recently, silicone resins suitable for injection molding are being developed. In general, an injection mold is a material introduction part of the mold that is provided on an extension of the nozzle as an injection path from the nozzle of the injection molding machine until the material is introduced into the mold and filled into the cavity. It consists of a sprue, a runner, which is a runner connecting the sprue and the gate, and a gate, which is the end of the runner and is the injection port for material into the cavity. Conventionally, injection molds for silicone resin have the same shape and design conditions as injection molds for other thermoplastic materials, and the cross-sectional area of the sprue and runner is 3. ~78
mm ² (2 to 10 φ), the cross-sectional area of the gate is 1 to 15 mm ² , the taper of the sprue is 2 to 6 degrees, and the taper of the trapezoidal runner is 2.5 to 5 degrees.

However, silicone resin materials that are heat-cured or vulcanized during injection cannot be recovered and recycled, so there are many cases where the yield of materials cannot be improved, and this has become a bottleneck in reducing product costs. Ta.

The present inventors investigated a mold that can produce silicone resin molded products with high material yield and good quality performance by high-pressure molding such as injection molding and transfer molding. It was possible to provide a mold for molding silicone resin, characterized in that the cross-sectional area of the runner part is 1 mm ² or less, and the draft angle between the inlet and outlet of the sprue part is substantially 0. .

Recent silicone resins for injection molding include silicone resins with a viscosity of 8,000,000 cp or less at room temperature, such as YE-5626 manufactured by Toshiba Silicone Corporation. Focusing on the fluidity of silicone resin, we created sprues and runners with an unprecedented ultra-fine cross section of 1 mm ² or less and an extremely small technique gradient to withstand the production of molded products and achieve a high material yield. The result was that it was moldable.

Next, this invention will be explained based on the drawings.

FIG. 1 shows an injection path commonly used in the past. In other words, the injection path when manufacturing the molded product 1 is the sprue 2, the runner 3, and the gate 4.
A shape consisting of is often used. The numerical ranges of their cross-sectional areas and draft angles have been described above. Sprue 2 is tapered to allow smooth release from the mold, and has a root diameter larger than the mouth diameter. runner 3
is the same diameter as sprue 2, and gate 4 is also the same diameter as runner 3.
It is of a size commensurate with the size. There are restrictions on these due to resin flow design, and silicone resin molding molds are generally used as they are. A shows the edge gate, b shows the submarine gate.

We focused on the fact that silicone resin has slightly different characteristics from other thermoplastic resins and thermosetting resins, and conducted actual tests. As shown in Figure 2, we found that silicone resin has a cross section of 1 mm ² or less, preferably a wall thickness. Sufficient molded products were obtained using sprues and gates of 50 μm or more. The sprue 5 is obtained by using a sprue bushing with a cross-sectional area of 1 mm ² or less and a draft angle of almost 0. A suitable undercut is attached to the movable type near the sprue outlet, so that the sprue can be pulled out even if the working slope is almost 0. Runner 6 has a cross-sectional area of 1 mm ²
If the cross-sectional area is the same as that of the sprue 5 or slightly larger, the stability of pulling out is better. The runner 6 may have a circular, semicircular, or trapezoidal cross-section and be combined with the sprue 5 without a taper, or the runner 6 may have a rectangular square cross-section without a taper and be combined with the sprue 5 without a taper. The sprue 5 and the runner 6 may be omitted by using various runnerless systems, as long as the injection path is 1 mm ² or less and there is no substantial draft angle.
Gate 7 also has a cross-sectional area of less than 1 mm ² . In the case of the gate of the present invention, it is also preferable to prevent the gate from remaining in the molded product by making the cross-sectional area of the gate on the molded product side smaller than the cross-sectional area of the gate on the runner side. As for the shape of the gate, various types of gates can be adopted in addition to the conventional a edge gate and b submarine gate.

According to the present invention, since the amount of resin filled into the injection channel is small, the material yield of the molded product is good, the curing time is faster than that of a mold using a conventional injection channel, and the gate sealing effect is good and the molded product It also has a positive effect on the quality of

[Brief explanation of drawings]

FIG. 1 shows a conventional injection path and molded product. A is for the edge gate, and b is for the submarine gate. FIG. 2 shows an injection path and a molded article embodying the invention. What a and b indicate are the same as a and b in FIG. 1... Molded product, 2, 5... Sprue, 3, 6...
...Runner, 4, 7...Gate.

Claims (1)

[Claims] 1. A mold for molding silicone resin, characterized in that the cross-sectional area of the sprue part and the runner part is 1 mm ² or less, and the draft angle between the inlet and outlet of the sprue part is substantially 0. Mold for silicone resin molding.