The same type of material of different colors is usually used for two-color injection molding（or 2k injection molding）so that the bonding strength of the first color and the second color plastic is the best, but due to the functional requirements of the product, the performance difference of the two materials actually used may be very big, if the elastomer is injected into the surface of a rigid material, the most difficult thing to solve during 2k moulding process is the delamination and shedding of the bonding surface of the two materials.
In addition to meeting the requirements of product function and appearance in the material selection of two-color products, whether the adhesion between raw materials can be solved well will be related to the success of two-color products in 2k moulding process is also the difficulty of 2k moulding technology.
The following four points should also be considered in the selection of materials for two-color injection molded products:
1. In terms of the effect of the bonding surface, if the force of the bonding surface of the two materials cannot be enhanced by the structure, the bonding performance between the selected materials is better, the material has good adhesion performance, the bonding surface layer has a large force, and it is not easy to delaminate and fall off.
2. In terms of shrinkage rate, if the two-color injection molded product is prevented from falling off and delamination through structural embedding or wrapping, it should be noted that the thermal shrinkage rate of the two materials cannot be too different, and try to match the shrinkage rate completely. Generally, the shrinkage rate of the first color material is slightly smaller.
3. In terms of processing parameters, for the two-color injection molding process, because in the 2k injection molding process, although the two injection cycles are relatively independent, the entire injection cycle time is the same, so it is necessary to focus on controlling the injection time of the two-cavity injection cycles, cooling time and pressure holding time, so as to ensure that the product can be produced normally; at the same time, it is also necessary to control the injection volume, injection speed, and mold temperature, this is because in 2k plastic injection moulding, changing the injection volume and mold temperature can make the degree of mixing of the plastic part or the thickness of each layer occur. Change, and whether the injection speed is appropriate or not, will directly affect whether the melt may have turbulent flow or cause the outer layer of the plastic part to rupture during the flow process.
4. In terms of temperature difference, it is necessary to avoid too much temperature difference between the two-component materials.
Structural design is the most important part of 2k molding product design, the structure design of the product should not only consider the function of the product but also consider whether it meets the processing conditions and the complexity of the processing mold, in the design of two-color injection products, in addition to the issues to be considered for ordinary injection products, the following aspects should also be considered:
1. The quality ratio of the two materials: since the injection time is related to the injection volume, the coordination of time is also related to the product design. To control the injection volume ratio, the difference in the injection quality between the two cavities should not be too big.
2. Product structure shape design: in order to increase the 2k moulding product's fusion strength, the measure in the product structure design is to increase the contact area of the two parts. For example, if possible, the contact area of the two parts can be enlarged through the non-joining surface, and concave and convex grooves can be designed around the small cavity products (which can be generated by forced demolding, and the depth can reach 2mm).