Two-color molds can combine two resins with different characteristics and colors into a single two-color product, which can reduce assembly and post-processing of molded products. Reduce cost of melting and printing, increase appearance and visual effect of product, improve grade and added value of product. Not only has function of non-slip and increased friction, improvement of flexible resin material is more ergonomic and feels better. Two-color injection molding product has high quality stability, easy control of product deformation, short molding cycle and high output. Loss can be 7% lower than that of overmolding, and product manufacturing cost can be 20%-30% lower than that of overmolding.

 

Two-color injection molding usually refers to molding of two colors or different types of plastics. Since alignment injection unit and nozzle of two-color machine are independently separated, final color is mostly two-color distinct without overlapping. Generally speaking, two-color machines have independent separate injection units, while general injection machines have only one set of injection units. Configuration method has various forms according to design of each manufacturer. As for design of movable template, it is necessary to provide a rotating mechanism. Common designs such as adding a turntable or a rotating shaft mechanism, etc., to provide a 180° substitution of rotation function, so that mold produces cyclical alternating movements. Other special two-color molds do not need a turntable or shaft mechanism, and mold performs alternate sliding or horizontal rotation.

1. Two-color injection molding machine is composed of two sets of plastic injection devices with identical structures and identical specifications. Nozzle should have a special structure according to production method, or an injection molding mold with same structure that can be rotated and transposed. When plasticizing injection, process parameters such as melt temperature, injection pressure, and injection melt volume in two sets of plasticizing injection devices are required to be same, and difference in process parameters in two sets of devices should be reduced.
2. Compared with ordinary injection molded plastic products, two-color injection molded plastic products have higher parameter values for melt temperature and injection pressure during injection. First is that mold runner in two-color injection molding is relatively long, structure is relatively complex, and flow resistance of injected melt is coaxial.
3. Two-color injection molded plastic products should be supplemented with materials with good thermal stability and low melt viscosity, and decomposed due to high temperature of melt and shortened residence time in runner.
4. In injection molding of two-color plastic products, in order to make two melts of different colors be well welded in mold during molding and ensure molding quality of injection molded products, higher melt temperature, higher mold temperature, higher injection pressure and injection rate should be used.

Traditional two-color injection molds have two forms: "punch translation" and "punch rotation".
① There are two concave molds and one convex mold for "punch mold translation" mold. When the first barrel shoots, male mold is closed with the first female mold. Complete injection of first plastic. After the first type of plastic is solidified, concave and convex molds are separated, semi-finished product formed by first type of plastic stays in convex mold and moves along with  convex mold to a position aligned with second concave mold. After injection molding machine is closed, second barrel is injected with second plastic. After second plastic solidifies, injection molding machine opens mold and takes out complete product.
②Two-color mold in the form of "Punch Rotation" has two concave molds and a convex mold composed of two back-to-back. This convex mold can be rotated. Equipped with two injection molding machines with two barrels, second barrel is best designed in vertical direction of movement direction of injection molding machine. Two different plastics can be injected at the same time. When injected two kinds of plastics are cured, injection molding machine open and automatically ejects complete product. After taking out product, "rotatable punch" rotates 180 degrees. Injection molding machine close for next cycle.
Because first and second barrels in "punch translation" mode are injected in turn, first and second barrels in "punch rotation" mode are injected at the same time. Therefore, for same product, efficiency of production in "punch rotation" mode is twice that of production in "punch translation" mode.

 

Two-color injection molding machine is equipped with two barrels. Mold is single cavity, only first type of plastic ("hard rubber") and second type of plastic ("soft rubber") need in common. Required die and punch are single, which is fundamentally different from previous two production modes. After injecting first plastic into first barrel, wait for first plastic to partially solidify. Power cylinder drives isolation blades and retracts to be level with profile of punch. At this time, second barrel is injected with second plastic. After second plastic is completely solidified, injection molding machine opens and complete product is taken out. Then injection molding machine is shut down and next cycle begins. Obvious advantage of this technology is that it simplifies mold and reduces need for injection molding machine working space (you can use fewer two-color injection molding machines to reduce investment and reduce costs). Output can be doubled compared with previously used "encapsulation method", defective products caused by "hard rubber" that has been contracted and deformed are re-inserted into mold cavity.
Sixth, difference between plastic overmold and two-color mold:
1. Two-color mold: two plastic materials are injected on same injection molding machine, and mold is molded twice, but product is only ejected once. Generally, this molding process is also called two-component injection molding, which is usually completed by a set of molds and requires a special two-color injection molding machine. Two-color molds can combine two resins with different characteristics and colors into a single two-color product, which can reduce assembly and post-processing engineering of molded products, save cost of melting and printing, increase appearance and visual effect of product, enhance grade and added value of product. It also has function of anti-skid and increased friction. Improvement of flexible resin material is more ergonomic and feels better. Two-color injection product has high quality stability, easy control of product deformation, short molding cycle and high output. Consumption is 7% lower than that of overmolding, and product manufacturing cost can be 20%-30% lower than that of overmolding.
2. Overmolding (secondary molding): Two plastic materials are not necessarily injected on same injection molding machine, and are molded twice; after product is taken out from one set of molds, it is put into another set of molds for second injection molding.. Therefore, generally this kind of molding process is usually completed by two sets of molds, and no special two-color injection molding machine is needed. Mold structure is same as that of single-color injection mold. It mainly depends on adjusting injection parameters. Overmold is mainly soft rubber over hard rubber. Among them, soft rubber commonly used synthetic rubber, TPU, TPR and other rubber materials, hard rubber can be ABS, PC, PP, etc.