Newcomers must have a complete knowledge of two-color injection molding

Two-color injection molding refers to the molding method of injecting two different colors of plastic 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-like patterns, to improve the practicality and beauty of the plastic parts.



Two-color injection molding principle

Dual-color mixing injection molding

Schematic diagram of two-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 channel connected to the nozzle, and the nozzle channel is equipped with opening and closing valves 2 and 4. When molding, after the molten material is plasticized in the barrel, the opening and closing valves 2 and 4 control the sequence of molten material entering the nozzle and the ratio of discharged material and then inject into the mold cavity from the nozzle. Then various plastic products with different color mixing effects can be obtained.


Principle of double pattern injection molding

It also has two barrels 1 and 5, and its nozzle structure is somewhat special. In addition to the usual nozzle function, it can be driven by gear 3 installed at the rear to rotate. During molding, the molten materials of different colors are plasticized in the barrels 1 and 5 respectively, while gear 3 drives the rotary shaft 4 to rotate, so that the molten materials of different colors enter the mold cavity alternately, thus obtaining plastic products of different colors and patterns in the form of radiation from the center to the surroundings.



Three, two-color injection molding requirements

Material requirements

The paired materials for two-color injection molding must meet two basic compatibility conditions, namely bonding compatibility and process compatibility.



Process requirements

Soft and hard plastic double injection design

There must be a certain temperature difference between the melting point of the two materials, generally recommended to be 60℃, it is recommended to be at least 30℃ or more, the melting temperature of the first shot material is high, generally, the first shot is PC or PC/ABS, the second shot is TPU or TPE, PC thickness 0.6-0.7mm, software 0.4mm or more.

Try to widen the contact area, do grooves, etc. to increase the adhesion, or the first shot using core extraction, the second shot part of the material injection to the first shot inside, the first shot mold surface tries to do rough.



Transparent and non-transparent double shot design

Double shot design for small lenses: the first shot does non-transparent, the second shot does lenses, the first shot tries to use PC with the high melting point, the second shot uses PMMA.

Transparent and non-transparent double shot design for decoration: the first shot is non-transparent material, the second shot is a transparent material, the non-transparent material is commonly PC with high material temperature.

PC needs to spray UV to protect, PMMA can choose UV or reinforced, if the surface has characters then must choose UV.



Mold requirements

Two-color mold: two kinds of plastic materials in the same injection molding machine, molding in two times, but the product only once out of the mold. Generally, this molding process is also called double material injection, usually completed by a set of molds, and requires a special two-color injection molding machine. There are general requirements for it as follows.

1, the two shapes of the female mold must be different, molding a product respectively, while the two shapes of the male mold should be the same;

2、The front and rear mold must match after rotating 180° with the center;

3、The total thickness of the front mold panel plus A plate should not be less than 170mm, and the maximum mold thickness, minimum mold thickness, KO hole distance, etc. should be checked carefully;



4、The water outlet of the three-plate mold should be designed to automatically release the mold;

5, in the design of the second injection of the mother mold, to avoid the second mother mold erasure of the first time the good products have been molded glue position, can be designed to avoid part of the empty. But we must carefully consider the strength of each sealing bit, (i.e.: in the injection, whether there will be a large injection pressure, the plastic deformation, resulting in the second injection will have the possibility of batch front?) ;

6, injection molding, the first injection molding product size can be slightly larger, to make it in the second molding with another male mold pressed more tightly, to achieve the role of sealing glue;

7, pay attention to the second injection, the flow of plastic will not impulse the first time the product has been molded, so that its plastic position deformation;

8、Before the A and B plates are combined, pay attention to whether the front mold slider or slant top will be reset first and crush the product;

9, the two female and male mold water transport arrangement as full as possible, and balanced;

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 easily deformed.



Fourth, the difference between two-color injection molding and secondary injection molding


1、The former is injection molding on a two-color machine, which can be molded at one time, and can have two color effects and different material compositions; while the latter is done with an ordinary injection molding machine, and now the products are taken out once, and then put into another injection molding machine again;

2, the former has two sets of molds, the same rear mold, interchangeable; the latter has no requirements.