What is the cause of uneven color of plastic parts, and how can plastic manufacturers exclude it?

(1) Defect characteristics

The main manifestation of uneven color of plastic parts is that the color of the surface of plastic parts is not uniformly reflected, but has deep and shallow, and lacks the due color uniformity.

(2) Causes of defects and elimination methods

The main reasons for uneven color are the uneven distribution of pigments used by Plastic Manufacturers, raw material problems are the main problems leading to uneven color, and there are also reasons for injection molds and injection molding operations, which are analyzed as follows.

1) Injection mold

A. The moving parts on the mold produce dirt due to friction, and this dirt mixed with the plastic melt leads to uneven color of the plastic parts. In this respect, the friction dirt on the injection mold should be cleaned and wiped in time.

B. If the exhaust system of the injection mold is poor, it will also produce uneven color, which needs to improve the exhaust system.

C. The oil and release agent in the injection mold are mixed into the plastic melt, which will make the surface of the plastic part change color and uneven color, in this regard, the oil should not enter the mold cavity, and the release agent should be used as little as possible.

2) injection molding process

A. If the temperature at the barrel is too high, the plastic melt is easy to decompose at high temperature and the color is uneven, which should be selected according to the characteristics of the raw material process temperature.

B. If the temperature at the nozzle is too high, the plastic melt will carbonize and coking at the nozzle, making the surface color of the plastic parts uneven, in this regard, the temperature at the nozzle should be appropriately reduced.

C. The injection and pressure holding time is too long, the injection back pressure and injection pressure are too high, which is easy to make the surface color of plastic parts uneven. Therefore, the injection and pressure holding time should be shortened, and the back pressure and injection pressure should be reduced.

3) injection molding equipment

A. The plasticizing ability of the injection machine is not strong, and the various raw materials can not be uniformly plasticized together, which is easy to appear uneven color, in this regard, it is necessary to check the plasticizing device of the injection molding machine to ensure its normal work.

B. There are accumulated materials or dead corners in the cylinder of the injection molding machine. If these old materials are mixed with the plastic melt, the color is uneven, and the cylinder should be thoroughly cleaned.

C. The plastic melt stays in the injection molding machine for too long, which is easy to be overheated and decomposed, and the color is uneven. In this case, the time of the plastic melt staying in the barrel should be controlled.

4) Plastic raw materials

A. If the thermal stability of the colorant is poor, it is decomposed by high heat, resulting in uneven color, and the colorant with good thermal stability should be selected.

B. Some colorants are thin, if directly mixed into plastic raw materials after plasticizing molding, easy to form a directional arrangement and produce uneven color, in this case, it is necessary to crush the thin flake colorants into powder.

C. If there is too much impurity in the plastic raw materials, these impurities of different colors will make the plastic parts uneven color. In this regard, impurities should be removed as far as possible, so that impurities do not enter the molten material.

D. If the crystallinity of the resin is too poor, it will affect the transparency of the plastic parts and make the color uneven, in this regard, the formula can be appropriately changed.

E. The colorant particles are small and light, it is easy to float in the air, and then adhere to the hopper and other devices, so that the injection molding and mold are polluted, causing uneven color, in this regard, the floating of the colorant should be controlled. If the injection molding machine, mold, etc., is contaminated, it should be thoroughly cleaned.

F. Some colorants are added to the raw material by dry mixing. If the mixture is not uniform, the colorant may adhere to the surface of the particle, which is difficult to plasticize evenly and lead to uneven color. In this regard, attention should be paid to the mixing of the colorant.

G. For fibre-reinforced plastics, if the fibers are not evenly mixed, they may accumulate, or bare, or lack, making the surface color of the plastic parts uneven, in this regard, the distribution of fibers in the melt should be improved.

H. Excessive moisture or volatile content in plastic raw materials, injection molding is also easy to produce uneven color, which should be purified plastic raw materials, and the raw materials for pre-drying treatment.