Lusterless (Low Gloss) refers to dull surface and a transparent product that is Low in transparency. Gloss may be caused by a variety of factors, including other injection defects. Today, we listed the defect analysis and elimination methods of bad luster (Lusterless) below.
Since the surface of the plastic part is the secondary performance of the mold cavity surface, if the surface of the mold has scars, corrosion, micro holes and other surface defects, will show to the plastic part surface to produce poor luster. If the cavity surface has oil, water, demoulding agent dosage too much or improper selection, that will produce the plastic surface hair dark. Therefore, the mold cavity surface should have a better finish, the best polishing treatment or chrome surface and keep clean. The type and dosage of mold release agent should be appropriate.
Mold temperature also has a great impact on the surface quality of plastic parts. Different types of plastic in different conditions of mold temperature gloss difference, mold temperature too high or too low will lead to poor gloss. If the mold temperature is too low, the molten material will solidify immediately after contact with the mold cavity, which will reduce the reproducibility of the mold cavity surface. In order to increase the luster, can appropriately improve the mold temperature, it is best to use in the mold cooling loop through warm water method, so that the heat in the cavity rapid transmission, so as not to extend the molding cycle, this method can also reduce the residual stress in the molding. Generally, except polystyrene, ABS and AS, the mold temperature can be controlled above 100 degrees. However, it should be noted that if the mold temperature is too high, will also lead to plastic surface hair dark.
In addition, demoulding slope is too small, section thickness changes suddenly, the bar is too thick and the gate and runner section is too small, the casting system shear effect is too big, mold exhaust bad and other mold faults will affect the surface quality of plastic parts, resulting in poor surface gloss.
2.Improper control of forming conditions
If the injection speed is too fast or too slow, the nozzle hole is too small or temperature is too low, low injection pressure, the holding time is short, the supercharger pressure is not enough, cushion is too big, bad filler dispersion properties of fiber reinforced plastics, packing the leakage or aluminum foil packing non-directional distribution, cylinder temperature is too low, plasticizing bad melting and underfeeding, can lead to bad parts surface gloss. To this, should undertake adjusting according to specific circumstance.
If dark areas are generated near the sprue or at the variable section, they can be eliminated by reducing the injection rate, changing the location of the sprue, expanding the area of the sprue, and increasing the arc transition at the variable section. If plastic surface has a thin layer of milky white, can be appropriate to reduce the injection speed. If the poor dispersion of the filler due to poor surface gloss, should be replaced by a resin with better flow performance or a better mixing capacity of the screw.
3．Molding materials do not meet the requirements
Raw materials do not meet the requirements of use will also lead to plastic surface gloss. The moisture content or other volatile substances in the molding materials are too high, and the volatile components coagulate and shrink between the mold cavity wall and the molten material, resulting in the bad surface gloss of the plastic parts. The raw materials shall be pre-dried. Raw materials or coloring agents caused by decomposition and discoloration of poor luster, should choose high temperature resistance of raw materials and coloring agents.
Poor flow performance of raw materials, plastic surface is not dense lead to poor luster. Resin with good flow property should be used instead or proper lubricant should be added to improve the processing temperature. If the raw materials are mixed with different or insoluble raw materials. New materials should be used; Raw material particle size is not uniform. Raw materials with large particle size differences should be screened.
As a result of cooling uneven crystal resin will produce poor luster. Should be reasonable control of mold and processing temperature, thick wall plastic parts if the cooling is insufficient will also produce a rough surface, gloss dark, the solution is to take the plastic parts out of the mold immediately into the cold water in the cold mold cooling stereotypes. The proportion of recycled material in the raw material is too high, which affects the uniform plasticization of molten material. Its dosage should be reduced.