JPH0126852B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention eliminates sink marks in thick parts of molded products by molding two-color one-piece molded products separately and molding them simultaneously in the same mold without joining and assembling them. This relates to double-molded products that can prevent this from occurring, improve quality, and reduce production costs.More specifically, a cavity for primary molding and a cavity for secondary molding that have different shapes in the same mold. Or, by separately providing a primary molding core and a secondary molding core, and rotating or moving either the cavity side or the core side of the mold, the molded product is formed by primary molding. This invention relates to a double molded product characterized in that the molded product remains in either the cavity or the core and is quickly transferred to the secondary molding side and continuously double molded.

Conventionally, when manufacturing this type of two-color molded product, two-color molded products were molded separately, and these were combined and joined using ultrasonic waves or adhesives, or the walls of both were bonded together. It was common practice to combine the provided undercut parts and forcibly press-fit them, but the two-color single products combined in this way have variations in dimensions depending on the mold hole number, warping of the molded product, etc. Therefore, when these are combined, there are disadvantages such as a step in the Sakai area, which deteriorates the appearance and reduces the commercial value of the product.Also, when the product is made thicker, the injection time and cooling time are longer. This lengthens the growth cycle and reduces productivity, and if the wall thickness exceeds the limit, sink marks will occur on the surface, seriously impairing the appearance quality.In addition, molds and molding machines are required to join the two-color single products. Since multiple units are required, equipment costs are high and productivity is also reduced.

On the other hand, there is also a method of inserting a pre-molded product into a mold and performing injection molding on the inner or outer surface of the product to integrate it, but in both cases the mold is divided into two parts.
It is difficult to implement automation because it requires two times of surface and molding, and a complicated process of inserting the insert, which reduces productivity and also reduces fusion bonding strength. However, there was a drawback that it deteriorated.

To specifically explain one embodiment of the method for manufacturing a molded product according to the present invention with reference to the drawings, Fig. 1 shows a set of 180-degree rotatable two-pieces for simultaneously molding the lid and body of two-color compact containers. This is a diagram showing the spool, runner, and molded product molded from the cavity opening of an injection mold A using a two-tube injection molding machine for heavy molding, with the cavity section omitted. The synthetic resin in this state enters the primary spool 1, passes through the runner 2, flows through the secondary spool 3, and is injected into the cavity through the gate 4 to form primary molded products 5, 6 as shown in FIGS. 1 and 2. mold at the same time.

Primary molded products 5 and 6 molded simultaneously in this way
As will be explained by enlarging a part of it in FIG. 3, the volume gradually shrinks during cooling, and sink marks a, b, and c occur particularly in the thick parts.

Next, in the present invention, the primary molded products 5 and 6 molded as described above are rotated 180 degrees while remaining on the core side of the mold, thereby forming the secondary molded products 5' and 6'. The mold is clamped as shown in Figure 3, and then the primary spool is inserted around the primary molded products 5 and 6 from the second injection molding machine for secondary molding, as shown in Figure 4. 7. A synthetic resin having a different color from the primary molded products 5 and 6 is injected through the runner 8, secondary spool 9 and gate 10 to produce the primary molded product 5,
The secondary molded products 11 and 12 are integrally and simultaneously molded around the primary molded products 5 and 6, and sink marks a, which are being formed in the thick parts of the primary molded products 5 and 6 due to the secondary molding
By pressing and supplementing b and c with the internal pressure d and melting heat during injection injection of the secondary molded products 11 and 12, the surface is shaped to eliminate sink marks a, b and c, and a product with a smooth surface is obtained. I can do it.

When the same material is used to join the primary molded product and the secondary molded product according to the present invention, it is heated and melted in the primary molding, becomes a fluid state, is injected into the mold, and is cooled and solidified midway through the secondary molded product. Because it is molded, the fusion bonding strength is much better than that in a completely cooled state as in conventional insert molding.

Further, even in the case of a combination of different materials, by providing a concave or convex shape on the side wall of the primary molding, an anchor effect can be obtained by the secondary molding, and the materials can be completely joined together.

As mentioned above, the molded product according to the present invention uses an injection mold with a two-cylinder injection molding machine for double molding that can rotate 180 degrees, and molds the two-color molded products simultaneously while rotating each one. Therefore, there is no need to combine monochromatic molded products that have been molded separately and join them using adhesives or ultrasonic waves as in the past.
There is no risk of unevenness appearing in the molded product, and extremely high quality products can be molded at high speed. Since it is injection molded, the sink marks that occur during cooling due to volumetric shrinkage, etc. can be completely compensated for by the injection internal pressure and melting heat, thereby preventing the occurrence of sink marks, shortening the molding cycle as a whole, and reducing the molding cycle. It has features such as being able to improve productivity.

[Brief explanation of drawings]

FIG. 1 is an overall explanatory diagram showing the method for manufacturing the product of the present invention, and FIGS. 2 to 5 are explanatory diagrams of main parts showing the steps. A: Mold, 1, 3, 7, 9: Spool, 2,
8: Runner, 4, 10: Gate, 5, 6: Primary molded product, 11, 12: Secondary molded product, a, b, c:
Sink.

Claims (1)

[Claims] 1 The primary molded product formed by primary injection molding is left in the core and quickly transferred to the secondary molding side, and the secondary injection molding is performed around the primary molded product while the primary molded product is not completely solidified. The secondary molded product is integrally molded, and the sink marks on the outer surface that occur due to volumetric shrinkage in the thick part of the primary molded product are compensated for and pressed using the melting heat and injection pressure from the secondary molding. 2, which is characterized by preventing the occurrence of sink marks.
Heavy molded products.