In the production of plastic molds, we will use plastic, and most of the plastic is composed of different chemical molecules. Today, Dongguan Plastic mold factory editor with everyone to see. The polymer is a crystalline polymer if its molecular chain configuration (structural morphology) can be aligned in the process of transition from a high temperature melt to a low temperature solid state.
The crystalline area of the crystalline polymer is in the weight percent of the polymer. (Most of the polymer crystallinity of about 10% to 60%, but some may also reach a high value, such as PP crystallinity of 70% to 95%, HDPE and PTFE can also be more than 90%)
2. Factors that affect crystallization
Pressure and shear stress
Increasing the pressure allows the polymer to crystallize at a melting temperature higher than normal; shear stress can lead to the formation of microcrystals, resulting in a uniform microcrystalline structure.
The simpler and more regular the molecular structure of the polymer, the faster the crystallization, the higher the crystallinity, and the maximum crystallization rate of the same polymer decreases with the increase of the relative molecular mass.
3. Crystalline effect on the performance of plastic parts
The density increases with increasing crystallinity.
The tensile strength increases with the increase of the crystallinity; the impact toughness will decrease; the elastic modulus will decrease.
Crystallization helps to improve the softening temperature and heat distortion temperature of the polymer.
The higher the degree of crystallization, the greater the volume shrinkage, so the crystalline plastic parts than non-crystalline plastic parts are more likely to shrink due to uneven warping.
surface roughness and transparency
After crystallization, the surface roughness of the plastic parts will be reduced and the transparency will be reduced or lost.
crystalline plastic with PE, PP, PTFE, POM, PA, CPT and so on
non-crystalline plastic PS, PMMA, PC, ABS, PSU and so on
In general, crystalline plastic is opaque or translucent, non-crystalline plastic is transparent.
Special case: poly-4-methyl pentene-1 is a crystalline plastic is highly transparent; ABS is non-crystalline plastic is not transparent.
4. Molded plastic molding should pay attention to the following issues
material temperature rise to the molding temperature of the heat required to use large plastic equipment
Condensation release heat, to fully cool
The difference between the molten state and the solid state is large, the shrinkage of the molding is large, and the pores and pores are easy to occur
Anisotropy is significant and internal stress is large
Narrow crystal melting point range, prone to unmelted powder injection mold or plug the gate
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