Principle and process requirements of two-color injection molding

I. The meaning of two-color injection molding
Two-color injection molding is a molding method of injecting two different colors of plastic in the same mold. It can make the plastic parts appear in two different colors, and can make the plastic parts appear in regular patterns or irregular cloud-like colors to improve the practicality and beauty of the plastic parts.
Second, the principle of two-color injection molding
Two-color mixed injection molding
Two-color grinder
It has two barrels, and the structure and usage of each barrel is the same as the traditional injection barrel. Each barrel has its own channel connected to the nozzle, and the opening and closing valves 2 and 4 are also installed on the nozzle channel. During the molding process, after the melt is plasticized in the barrel, the sequence of the melt entering the nozzle and the ratio of the discharge is controlled by the opening and closing valves 2 and 4, and then injected into the cavity by the nozzle. Various plastic products with different color mixing effects can be obtained.
Principle of double-layer pattern injection molding
It also has two barrels 1, 5 with a somewhat special nozzle structure, which can be rotated by the gear 3 installed at the rear, in addition to the functions of a general nozzle. During the molding process, different sizes of melt are plasticized in the barrels 1, 5 respectively, and the gear 3 drives the rotation shaft 4 to rotate, so that different colors of melt enter the cavity alternately, thus obtaining different colors radiating from the center to the periphery. Patterned plastic products.
Third, the requirements of two-color injection molding
Material requirements
The paired materials for two-color injection molding must meet two basic compatibility conditions, i.e. adhesive compatibility and process compatibility.
Process requirements
Soft and hard plastic dual injection design
There must be a certain temperature difference between the two materials. 60°C is generally recommended, with a minimum of 30°C recommended, and a high melting temperature for the first shot material. Generally speaking, the first shot is PC or PC/ABS, the second shot is TPU or TPE. with PC thickness 0.6-0.7mm and software 0.4mm or more. Try to expand the contact area, make grooves to increase adhesion, or use the core to make the first shot, and the second part of the material is injected into the first shot. The surface of the first needle is as rough as possible.
Transparent and non-transparent double lens design
Double lens design for small lens: the first shot is opaque, the second shot does the lens, the first shot uses PC with the highest possible melting point, the second shot uses PMMA.
Transparent and opaque double shot design for decoration: the first shot is opaque material, the second shot is transparent material, the opaque material is usually PC with higher temperature, the second transparent material is PMMA or PC. the PC needs to be sprayed with UV to protect it. the PMMA can be UV or reinforced. If there are characters on the surface, UV must be chosen.
Mould requirements
Two color molds. Two plastic materials are molded on the same injection molding machine in two parts, but the product is molded only once. Generally, this molding process, also called dual material injection, is usually done by one set of molds and requires a special two-color injection molding machine. It generally has the following requirements.
1. The two shapes of the female mold must be different to form a product separately, while the two shapes of the male mold are identical.
2. The front and rear molds of the mold must match after rotating 180° from the center.
3. the total thickness of the front die panel plus the A plate should not be less than 170mm. the maximum die thickness, minimum die thickness, KO hole pitch, etc. need to be checked carefully.
4. the nozzle of the three-panel mold can be designed for automatic mold release.
5. When designing the second injection master mold, a sheltered part can be designed in order to avoid the second master mold from scratching the glue position of the first molded product. However, the strength of each sealant location must be carefully considered (i.e., will the plastic be deformed under the large injection pressure during molding, thus leading to the possibility of a second front injection).
6. When molding, the size of the product for the first injection can be slightly larger so that it can be pressed tighter with the other male mold during the second molding to achieve the sealing function.
7. Pay attention to whether the flow of plastic will impinge on the product of the first injection and deform the glue position during the second injection.
8. Before the A and B plates are closed, pay attention to whether the front mold slider or slant top will reset first and crush the product.
9. The water transportation arrangement for both male and female models should be as full and balanced as possible.
10. 99% of the time, the hard plastic part of the injection molded products are available first, followed by the soft rubber part of the injection molded products, because the soft rubber is easily deformed.