Introduction To Two-color Injection Molding

1.1 The concept of two-color injection molding

Two-color injection molding (2K molding or two shot mold) refers to the process of one injection molding

A process in which two plastics (or two plastics of different colors) are molded into one body.

In this article, the first injected material is called base material, and the second injected material is called cover material.

The most common form of two-color injection molds is that two identical moving molds correspond to two different fixed mold cavities.

After the first injection of the base material, the movable mold is opened first, and then the movable mold is rotated 180° by the rotatable structure of the injection machine, and then the mold is closed and a raw material of a different color or a different raw material (covering material) is used for the second injection. 

After the second mold opening, the punch that has completed two injections is de-molded.

The first base material injection and the second cover material injection are carried out at the same time, requiring two injection nozzles on the injection machine to inject different colors or different base materials and cover materials respectively.

1.2 The difference between two-color injection molding and insert injection molding

The difference between two-color injection molding and insert injection molding (or over-molding) is:

1) Insert injection molding using an ordinary injection molding machine. After the product is taken out of one set of molds, it is put into another set of molds for the second injection molding.

Therefore, insert injection molding is usually completed by 2 sets of molds, without the need for a special two-color injection molding machine.

Two-color injection molding is a one-time injection molding of two plastics on a two-color special injection molding machine.

Two kinds of plastics are injected into the same injection molding machine and molded twice, but the product is only out of the mold once. Therefore, two-color injection molding is usually completed by a set of molds, and a special two-color injection molding machine is required.

2) During the whole process of two-color injection molding, the plastic is in a molten state without cooling shrinkage, which means that there is an opportunity to form a strong chemical link between the base material and the covering material, with high strength and at the same time reducing the risk of burrs.

3) Compared with insert injection molding, two-color injection molding does not require the insertion process of inserts, the molding cycle is shorter, and more efficient, and the quality is also higher.

Advantages and disadvantages of two-color injection molding

2.1 Advantages of two-color injection molding

1) Increase product design flexibility

Two-color injection molding can integrate multiple functions into one plastic part, such as soft surface, ergonomic design, two-color appearance, brand identity, feature improvement, noise reduction, shock absorption, waterproof and anti-collision, etc., which can save design space and reduce zero parts. the number of parts, etc.

2) Reduce the number of projects to reduce costs

Multifunctional plastic parts can be completed in one injection molding process, reducing secondary processing.

3) Different plastics are integrated into one body through chemical links, with higher quality and better strength.

2.2 Disadvantages or limitations of two-color injection mould

1) The compatibility between the two plastics needs to be considered

Because different plastics have different chemical properties, their compatibility will directly affect the bonding strength and bonding effect of the bonding surface, and not all plastics have good compatibility.

2) The difference in shrinkage rate of plastics is small

If the difference is too large, it will affect the bonding strength of the bonding surface and may cause warping of the product.

3) The shape of the finished product should not be too complicated