Solutions For Poor Gloss On The Surface Of Products
Low gloss (LowGloss) means that the surface is dark and dull, and the transparency of the transparent product is low, which causes many reasons for poor gloss. Other injection defects are also causes of poor gloss.
Since the surface of the plastic part is the reproduction of the cavity surface of the mold, if there are surface defects such as scratches, corrosion, micropores, etc. on the surface of the mold, it will be reproduced on the surface of the plastic part to produce poor gloss. If the surface of the cavity is oily, moisture, too much or improperly used, the surface of the plastic part will be dark.
Therefore, the cavity surface of the mold should have a good finish, preferably polished or chrome-plated. The surface of the cavity must be kept clean to remove oil and water stains in a timely manner. The selection and dosage of the release agent should be appropriate.
The mold temperature also has a great influence on the surface quality of the plastic parts. Generally, different types of plastics have different surface gloss under different mold temperature conditions, and the mold temperature is too high or too low, which may lead to poor gloss. If the mold temperature is too low, the melt will solidify immediately after contact with the mold cavity, which will reduce the reproducibility of the mold cavity surface.
In order to increase the gloss, the mold temperature can be appropriately increased. It is preferable to use a method of introducing warm water into the mold cooling circuit to transfer heat in the cavity to avoid prolonging the molding cycle. This method can also reduce residual stress during molding. . In general, in addition to polystyrene, ABS, AS, the mold temperature can be controlled above 100 degrees. However, it should be noted that if the mold temperature is too high, the surface of the plastic part will be dark.
In addition, the draft is too small, the thickness of the section is abrupt, the ribs are too thick, and the gate and runner cross sections are too small or abruptly changed. The shearing effect of the casting system is too large, the molten material flows in a turbulent state, and the mold is poorly discharged. Mold failure can affect the surface quality of the plastic parts, resulting in poor surface gloss.
2. Improper molding conditions
If the injection speed is too fast or too slow, the injection pressure is too low, the holding time is too short, the supercharger pressure is not enough, the cushion is too large, the nozzle hole is too small or the temperature is too low, and the filler property of the fiber reinforced plastic is too poor. The filler is exposed or the aluminum foil-like filler has no directional distribution, the temperature of the cylinder is too low, the plasticization of the melt is poor, and the supply is insufficient, which may result in poor gloss on the surface of the plastic part. In this regard, adjustments should be made to the specific situation.
If a dark area is created near the gate or at a variable cross section, the method can be eliminated by reducing the injection rate, changing the gate position, expanding the gate area, and increasing the arc transition at the variable cross section.
If the surface of the plastic part has a thin milky white color, the injection speed can be appropriately reduced. If the surface gloss is poor due to poor dispersion of the filler, replace the resin with better flow properties or replace the screw with stronger mixing ability.
3. Molding materials do not meet the requirements for use
(1) The content of moisture or other volatile substances in the molding raw material is too high, and the volatile components are condensed in the cavity wall of the mold and the melt during molding, resulting in poor gloss on the surface of the plastic part. The raw materials should be pre-dried.
(2) Discoloration of raw materials or colorants leads to poor gloss. Raw materials and colorants with high temperature resistance should be used.
(3) The flowability of the raw material is too poor, so that the surface of the plastic part is not dense and the gloss is poor. Replace the resin with better flow properties or add appropriate amount of lubricant and increase the processing temperature.
(4) Raw materials are mixed with foreign materials or incompatible materials. Should be replaced with new materials.
(5) The raw material particle size is not uniform. Raw materials with too different particle sizes should be screened out.
(6) The crystalline resin is poor in gloss due to uneven cooling. The mold temperature and processing temperature should be reasonably controlled. For thick-walled plastic parts, if the cooling is insufficient, the surface of the plastic part will be hairy and the gloss will be dark. The solution is to remove the plastic parts from the mold and immediately put them into the cold water. The cooling die is cooled and shaped.
(7) The proportion of recycled materials in the raw materials is too high, which affects the uniform plasticization of the melt. The amount should be reduced.