1. What is two-color injection molding
The so-called two-color injection molding refers to a molding method in which two plastics of different colors are injected into the same mold. It can make the plastic parts appear in two different colors, and can make the plastic parts present regular patterns or irregular cloud patterns to improve the practicality and aesthetics of the plastic parts.
2. Principle of two-color injection molding
Dual-mixed color injection molding
It has two barrels, and the structure and use of each barrel are the same as those of ordinary injection molding barrels. Each barrel has its own channel connected to the nozzle, and the opening and closing valves 2 and 4 are also installed in the nozzle passage. During molding, after the molten material is plasticized in the barrel, the opening and closing valves 2 and 4 control the order of the molten material entering the nozzle and the proportion of the discharged material, and then inject it into the mold cavity from the nozzle. You can get a variety of plastic products with different mixed color effects.
Double pattern injection molding principle
Double pattern injection molding principle
It also has two barrels 1 and 5, and its nozzle structure is somewhat special. In addition to the functions of the usual nozzle, it can also be driven to rotate by the gear 3 installed at the rear. During molding, the barrels 1 and 5 plasticize the melts of different colors respectively, and the gear 3 drives the rotating shaft 4 to rotate, so that the melts of different colors alternately enter the mold cavity, thereby obtaining plastic products of different colors and patterns radiating from the center to the surroundings.
3. Double-color injection molding requirements
Material requirements
The paired materials for double-color injection molding must meet two basic compatibility conditions, namely, bonding compatibility and processing compatibility.
Process requirements
Soft and hard double-shot design
The two materials must have a certain temperature difference in melting point, generally recommended to be 60℃, and at least 30℃ is recommended. The melting point temperature of the first shot material is high. Generally, the first shot is PC or PC/ABS, and the second shot is TPU or TPE. The thickness of PC is 0.6-0.7mm, and the thickness of software is 0.4mm or more.
Try to widen the contact area, make grooves to increase adhesion, or use core pulling for the first shot, and inject part of the material into the first shot in the second shot. Try to make the surface of the first shot mold rough.
Transparent and non-transparent double shot design
Double shot design for small lenses: the first shot is non-transparent, the second shot is lenses, try to use PC with high melting point for the first shot, and PMMA for the second shot.
Transparent and non-transparent double shot design for decoration: the first shot is non-transparent material, the second shot is transparent material, non-transparent material is usually PC with high material temperature, and the second shot transparent material is PMMA or PC. PC needs to be sprayed with UV for protection, PMMA can choose UV or strengthening, if there are characters on the surface, UV must be selected.
Mold requirements
Two-color mold: two plastic materials are injected on the same injection molding machine, molded in two times, but the product is only molded once. Generally, this molding process is also called double-material injection molding, which is usually completed by a set of molds and requires a special two-color injection molding machine. Generally, the following requirements are imposed on it:
1. The two shapes of the female mold must be different, forming a product respectively, while the two shapes of the male mold must be exactly the same;
2. The front and rear molds of the mold must match after rotating 180° around the center;
3. The total thickness of the front mold panel plus the A plate cannot be less than 170mm. The maximum mold thickness, minimum mold thickness, KO hole distance, etc. need to be carefully checked;
4. The sprue of the three-plate mold should preferably be designed to be able to automatically demold;
5. When designing the female mold for the second injection molding, in order to avoid the secondary female mold from scratching the glue position of the first molded product, a part of the airtightness can be designed. However, the strength of each sealing position must be carefully considered (i.e., during injection molding, will the plastic be deformed under high injection pressure, resulting in the possibility of a second injection having a front edge?);
6. During injection molding, the size of the product molded in the first injection molding can be slightly larger, so that it can be pressed more tightly with the other male mold in the second molding to achieve the effect of sealing;
7. Pay attention to whether the flow of plastic will impulsively affect the first molded product and deform its glue position during the second injection molding;
8. Before closing the A and B plates, pay attention to whether the front mold slider or inclined top will reset first and crush the product;
9. The water transport arrangement of the two female molds and the male mold should be as sufficient and balanced as possible;
10. In 99% of cases, the hard plastic part of the product is injected first, and then the soft plastic part of the product is injected, because the soft plastic is easy to deform.
4. The difference between two-color injection molding and secondary injection molding
1. The former is injection molded on a two-color machine, which can be molded in one time and can have two color effects and different material compositions; while the latter is completed with an ordinary injection molding machine. The once molded product is taken out and then put into another injection molding machine for molding again;
2. The former has two sets of molds, the rear molds are the same and interchangeable; the latter has no requirements.