Poor Gloss (Low Gloss) refers to the surface is dim and no gloss, the transparency of transparent products is low, there are many reasons for poor luster, and some other injection defects are also causes of poor luster.

1, mold failure

Because the surface of the plastic part is the representation of the mold cavity surface, if the mold surface has scars, corrosion, microholes and other surface defects, it will be reflected to the surface of the plastic part to produce poor luster. If there is oil, water on the surface of the cavity, too much release agent or improper selection, it will also make the surface of the plastic part dark.

Therefore, the surface of the mold cavity should have a good finish, it is best to take polishing treatment or surface chrome plating. The surface of the cavity must be kept clean, and the oil and water stains should be removed in time. The variety and dosage of release agent should be appropriate.

Mold temperature also has a great impact on the surface quality of plastic parts, usually, different kinds of plastics in different mold temperature conditions surface luster difference is large, mold temperature is too high or too low will lead to poor luster. If the mold temperature is too low, the molten material will cure immediately after contact with the mold cavity, which will reduce the reproducibility of the mold cavity surface.

In order to increase the luster, the mold temperature can be appropriately increased, it is best to use the method of warm water in the mold cooling loop, so that the heat is transferred quickly in the mold cavity, so as not to extend the molding cycle, this method can also reduce the residual stress in the molding. Under normal circumstances, in addition to polystyrene, ABS, AS, the mold temperature can be controlled at more than 100 degrees. However, it must be noted that if the mold temperature is too high, it will also cause the surface of the plastic parts to be dark.

In addition, the demoulding inclination is too small, the section thickness mutation, the reinforcement is too thick and the section of the gate and runner is too small or sudden change, the pouring system shear effect is too large, the molten material is turbulent flow, the mold exhaust and other mold faults will affect the surface quality of the plastic parts, resulting in poor surface luster.

2, improper control of molding conditions

If the injection speed is too fast or too slow, the injection pressure is too low, the pressure holding time is too short, the booster pressure is not enough, the buffer pad is too large, the nozzle hole is too small or the temperature is too low, the dispersion performance of the fiber reinforced plastic filler is too poor, the filler is exposed or the aluminum foil filler is non-directional distribution, the barrel temperature is too low, Poor plasticization of molten material and insufficient feed will lead to poor surface luster of plastic parts. In this regard, it should be adjusted according to the specific situation.

If there is a dark area near the gate or at the variable section, it can be eliminated by reducing the injection rate, changing the position of the gate, expanding the gate area and adding the arc transition at the variable section.

If there is a thin layer of milky white on the surface of the plastic parts, the injection speed can be appropriately reduced. If the surface luster is poor due to the poor dispersion performance of the filler, it should be replaced by a resin with better flow performance or a screw with stronger mixing ability.

3, the molding raw materials do not meet the requirements of the use of

The content of water or other volatile materials in the molding raw materials is too high, and the volatile components condense between the mold cavity wall and the molten material during molding, resulting in poor surface luster of the plastic parts. The raw materials should be pre-dried.

Raw material or colorant decomposition discoloration resulting in poor luster. Raw materials and colorants with high temperature resistance should be selected.

The flow performance of raw materials is too poor, so that the surface of the plastic parts is not dense, resulting in poor luster. It should be changed to a resin with better flow performance or to add an appropriate amount of lubricant and increase the processing temperature.

Raw materials mixed with exotic or insoluble raw materials. New materials should be used.

Uneven particle size of raw material. Raw materials with too large a difference in particle size should be screened.

Crystalline resins have poor luster due to uneven cooling. Should reasonably control the mold mild processing temperature, for thick wall plastic parts, if the cooling is insufficient, it will also make the surface of the plastic parts hair, luster dark, the solution is to remove the plastic parts from the mold, immediately into the cold pressing mold immersed in cold water cooling.

The proportion of recycled materials in raw materials is too high, affecting the uniform plasticization of molten materials. The amount should be reduced.

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