We often encounter the appearance quality problems of plastic injection molded part such as matte surface, insufficient brightness and insufficient transparency.
The main reason for insufficient brightness in production is that the temperature of the melt drops too much during the glue injection process, which makes the surface of the melt not shiny enough, and the fluidity becomes poor, and the contact between the melt and the mold surface is not close enough. In this way, the shiny mold surface is not faithfully displayed by the plastic injection molded part.
To improve the surface brightness or transparency of the plastic injection molded part, it must be ensured that the melt cannot be cooled too fast when filling the mold, and it must have good fluidity. Therefore, the melt temperature and mold temperature have a significant impact on the appearance of the plastic injection molded part.
In fact, appropriately increasing the melt temperature by more than ten degrees, and slightly increasing the back pressure of the melt, do not shoot the glue too slowly, it can indeed play a better role, but if there is no matching of the mold temperature, it will be more difficult to achieve the desired effect.
When we raise the mold temperature to above 50 degrees (it will feel a little hot when touching the mold by hand), for injection molding ABS, HIPS, PP, PVC and other commonly used plastics, plastic injection molded parts with bright surface or excellent transparency can be obtained with just normal melt temperature. If it is injection molding PC material, the mold temperature needs to be higher, preferably above 80 degrees.
The effect is also obvious, and it has become an important condition and commonly used means to solve such problems. The increase of the melt temperature can only be moderate, and if it is too high, it is easy to cause problems such as shrinkage, burning and discoloration.
However, the increase in mold temperature also has a certain limit. For example, when the mold temperature of hard rubber such as ABS and HIPS exceeds 80 degrees (when touching, you will feel it very hot), or the mold temperature of PC material exceeds 120°C, the plastic injection molded part is prone to shrinkage and other problems, and the production cycle will become too long as a result.
On the contrary, if the plastic injection molded part needs a matte effect, lowering the melt temperature and mold temperature will also have a certain effect. However, the mold surface must be sandblasted or etched, which is the most important prerequisite to ensure the matte effect.