The Difference between insert molding and Double Color molding

The Difference between insert molding and Double Color molding

The so-called two-color injection molding refers to the molding method of injecting two kinds of plastics with different colors into the same mold.

It can make the plastic parts with two different colors, and can make the plastic parts show regular patterns or irregular patterns, so as to improve the practicability and aesthetics .

Compared with traditional injection molding, two-color injection molding has the following advantages:

the two-color mold can inject two resins with different characteristics and colors into a single two-color product, which can reduce the assembly and post-treatment of molded products.

The printing cost is saved, and increase the beautiful visual effect of the product .

Two-color injection molding not only has the function of anti-slip and friction-increase, but the flexible resin material makes it more ergonomic and feels better.

The quality of the two-color injection molding product is high, the product deformation is easy to control, the molding cycle is short .

7% lower loss than insert molding, and the product manufacturing cost is 20%-30%  lower than encapsulated injection molding.

  • Principle:

Injection machine has two barrels, each of which has the same structure and use as ordinary injection molding machine barrels.

Each barrel has its own channel connected with the nozzle, and two opening and closing valves are also installed in the nozzle. During molding, after the molten material is plasticized in the barrel, two valves respectively control the sequence of molten material entering the nozzle and the proportion of discharged material, and then the molten material is injected into the mold cavity from the nozzle. Various plastic products with different color mixing effects can be obtained by this way.

Production process

1. The two-color injection molding machine consists of two sets of plasticizing injection devices with identical structures and specifications. The nozzle should have a special structure according to the needs of the production .

Plastic mold need to be installed with two core insert with identical structures that can rotate.

When plasticizing and injecting, the melt temperature, injection pressure, and the volume injected  in the two sets of plasticizing and injecting devices should be the same, and the difference of process  in the two sets of devices should be minimized as much as possible.

2. Compared with common injection molding plastic products, two-color injection molding adopt higher melt temperature and injection pressure during injection.

The main reason is that the molding flow  in two-color injection molding is relatively long, the structure is relatively complex, and the flow resistance of injection melt is relatively large.

3. Two-color injection molding should use raw materials with good thermal stability and low melt viscosity to avoid decomposition due to high melt temperature and long residence time in the barrel.

4. During injection molding , in order to ensure the mixing of two different colors in the mold and the molding quality , higher melt temperature, higher mold temperature, higher injection pressure and injection rate should be adopted.

  • Insert mold

Insert mold (secondary molding): Two kinds of plastic materials are not necessarily injected on the same injection molding machine and are molded in two times;
After the product is taken out of one mold, it is put into another mold for second injection molding. Therefore, in general, this molding process is usually completed by 2 sets of molds, without the need for a special two-color injection molding machine.
The mold structure is the same as that of a single-color injection mold, and the combination of 2 plastic materials is mainly controlled by adjusting the flow rate of injection molding.
The insert coating  is mainly made of soft material inserted in to and hard material. The soft material is usually artificial rubber, TPU, TPR, etc. The hard material can be ABS, PC, PP, etc.

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