Two-color injection molding technology is also called double-material injection molding technology. This is a technology that uses two plastic materials to mix and inject plastic products. Its technical connotation is actually to use a mold component to shape shape and weld molding work in mold. Therefore, fundamental principle is to plasticize two different plastic raw materials, then use mold for welding and installation to achieve purpose of two-color injection molding.

This technology is also called core-rotating two-color injection molding technology. Its technical principle is to first use injection equipment to inject the first raw material plastic into small hole of mold. When it is formed, it becomes the first plastic. Then mold is rotated 180° and second raw material plastic is injected using same injection equipment. After second plastic is formed, final encapsulation work is performed, and a basic two-color injection molding work is completed.

 

This technology is relatively simple to use and operate. Generally, workers with a little training can operate it freely, and it can greatly improve design freedom of plastic products. At the same time, it can be processed with simple tools.

Shrink mold core two-color injection molding technology mainly uses hydraulic devices to compress mold. First, under control of hydraulic device, core that can move up and down is pushed to top rising position like a piston, and plastic raw material is injected. After the first raw material solidifies, movable core is controlled to fall down, then another plastic raw material is injected, hydraulic device is controlled to press core up and wait for it to solidify and form.
Plastic products pressed by this technology are initially completed, then molded plastic parts are taken out for subsequent processing and production. This technology is also relatively simple to operate, and timing of hydraulic device movement must be controlled.

Before this technology works, the first raw material must be injected. During injection, the other parts of mold are closed, mold is gradually cut and separated during injection. Rear part of insert will gradually retreat, but it still exists on stripping plate, and mold will dynamically retreat, passing through ejector and pelletizing rod of the entire injection molding machine, then cool and fall off, and the first part is completed;

 

Next step is to perform injection molding operation of second part, which is roughly same as the first part, but second injection uses two nozzles to inject at the same time, and wait for it to solidify before ejecting two parts together, completing an injection cycle.

Working principle of core sliding two-color injection technology is to classify core into two times for use. During the first injection, core used will be slid to specified position, and mold closing injection work will be implemented. The first raw material plastic is injected into mold, and mold is opened once after cooling.
Transmission device slides out the first core, slides second core to cavity, then injects plastic for second time. After it cools and forms, an injection cycle is completed, then finished product synthesized twice is ejected. This technical mode is more suitable for needs of large-scale two-color injection molding plastic parts.

Due to influence of its product production purpose, two-color injection molding machine needs to be equipped with two identical machine plasticizing injection devices. This is not only a requirement of its process, but also requires ability to perform rotation transformation.
In addition to same structure, these two sets of injection devices with same specifications also need to have same function. During injection molding, raw material temperature, injection pressure and injection rate in two sets of equipment can be adjusted consistently, so that various indicators of injection molded plastic products are kept at same level, then relevant fusion and welding work is carried out. If parameters of two sets of equipment are inconsistent, they should be adjusted to same level as much as possible.

 

Due to unique characteristics of plastic products produced by two-color injection molding components, there are some obvious differences in machine structure setting from ordinary injection molding materials machines.
First of all, melt temperature used in two-color injection molding components is higher, which is a certain gap compared with ordinary injection molding components. High temperature is required to maintain ability to operate and flow in mold; secondly, injection pressure is also high, not only because two different plastic raw materials are used, and strong pressure is required to fuse them for pressing and welding, but also to overcome huge resistance of melt to flow in mold, so as to ensure smooth injection.

Two-color injection molding technology uses two different materials to make plastic products. Therefore, it is necessary to consider materials before injection molding. Not only quality standards of selected materials should be considered, but also control of parameters such as temperature and pressure of materials during injection molding should be paid attention to.
Since mold used in two-color injection molding technology is different from mold used in ordinary injection molding, material parameters used in two-color injection molding technology must have a higher melt temperature to ensure that melt will not solidify in advance before injection is completed. At the same time, injection device must be used to control pressure of raw material so that it can reach all parts of mold smoothly, thereby achieving purpose of injection molding.

Structure of two-color injection molding products is very different from that of ordinary plastic products. Since two different materials are used for injection molding, products have two different properties, which is fundamentally different from ordinary injection molding products. At the same time, detailed two-color injection molding product structure design is required before injection molding, and compatibility characteristics of two materials should be fully considered.

 

Combined with functions and use environment of plastic product, mixing ratio and connection method of two materials are designed, complexity of process is analyzed in detail, use intensity is also considered and designed, so that two-color injection molding products can meet relevant material standards and requirements.

Two-color injection molding technology uses two different materials for injection molding, so selection of two different materials is also an important process. Generally, two plastics of different colors are used, which can greatly improve strength and durability of injection molded products, make them easier to fuse and mold. However, products with special uses may need to use two materials with extremely different properties, which requires solving problem of difficulty of fusing two materials with large differences.
Main problem is that there will be stratification and shedding problems, which are fatal to injection molded products. Therefore, it is necessary to carefully consider shrinkage rate and different interface conditions, and adjust proportion of materials used.

Design of structure and shape of product first needs to be considered from purpose and use of product, to conduct detailed research in terms of size and internal structure.
Generally, it is necessary to increase contact area of two raw materials to enhance firmness. Here, some small grooves and convex grooves can be designed inside product for inlaying and stitching, which achieves purpose of increasing contact area of two materials. During injection molding, strength and service life of product can be better improved, and practicality can be enhanced.

This type of mold requires different considerations in molding part. First, concave and convex grooves of two injection molds need to be carefully designed to ensure that they can fit tightly when docking. At the same time, when designing demoulding mechanism, demoulding work can only be carried out after secondary injection. Different injection molding methods must also be carefully distinguished. After demoulding by vertically rotating injection molding machine, product is ejected to complete relevant work. In the case of demoulding that cannot be ejected by injection molding machine, a hydraulic device is required for demoulding.

 

In summary, two-color injection molding technology has been developed for many years, but it has only been gradually valued and applied in recent years, because finished products produced by it have good adaptability to use environment, and production efficiency is extremely high. It can meet different practical requirements well. Therefore, it has gradually been widely used. It has good economic benefits in automotive industry and other fields. It is a technology with great development potential.