Polycarbonate (PC) process characteristics, how much do you know?

The comprehensive excellent properties of polycarbonate are unmatched by ordinary plastics, which are particularly suitable for manufacturing small parts with more precise and accurate dimensions, complex shapes, and can withstand light loads or less counterweight loads.

Due to the increase in temperature, the viscosity will be very easy to reduce, forming is not difficult at first, but it is not easy to maintain such good characteristics intact.

1. Raw material drying

The most outstanding thing about polycarbonate is its sensitivity to trace moisture at high temperatures. Coupled with high melting temperatures and high melt viscosity, cracking and other quality accidents often occur due to improper handling, so it must be strictly and thoroughly dried before injection molding. After drying, the moisture content of the material should not exceed 0.02%. The existence of trace moisture can cause destructive degradation of polycarbonate, annual decline, release of carbon dioxide and other gases, plastic discoloration, and deterioration of performance. Forming workpieces with silver wire, bubbles, strength reduction, cracking. The higher the moisture content, the more destructive the degradation.

• If the degree of dryness is poor, there is a lot of moisture in the plastic, the melt viscosity decreases sharply, the melt drips out quickly, and the barrel nozzle continuously ejects foam-like snowballs, white smoke or gas in a crackling sound.
• Parts formed with such plastics are very dark in color, have a lot of silver pattern pigment on the surface, have bubbles inside, and are extremely brittle due to high internal pressure. Many parts crack immediately when demoulded.
• If the degree of dryness is average, the melt slowly injected from the nozzle is turbid and unclear, the surface is not bright, and there are a small number of small bubbles inside. The surface of the formed workpiece is rough and tarnished near the gate or other parts, and the impact strength is low.

2. Injection temperature

The thermal processing properties of polycarbonate have two advantages:

Has high thermal stability and a wide molding temperature range; the viscosity changes greatly due to temperature changes, and the viscosity changes slightly due to shear rate changes. That is, the melt fluidity of polycarbonate is greatly affected by temperature changes, while the effect of pressure is not significant.

Therefore, the adjustment of injection molding temperature has always been regarded as a necessary and effective means for smooth molding and quality control of parts.

However, it should be noted that if the temperature is too low, due to high viscosity, insufficient feed, the surface of the part shrinks or ripples, dull, and messy silver wire; if the temperature is too high or higher than 320 ° C and the residence time is too long, it will cause serious degradation, the part will have flying edges and turn dark brown. The surface has silver wire dark strips, spots and traces, and there are bubbles inside, causing all kinds of performance to deteriorate.

3. mold temperature

Polycarbonate has high viscosity, poor fluidity, is not very sensitive to shearing, and has a fast cooling rate. It is easy to cause defects on the surface of the part and form pressure inside.

If the mold temperature is too low, the part may be difficult to fill or have apparent defects such as large shrinkage rate, ripples, hair spots, dark strips, voids, etc., and the residual pressure of the part may increase.

If the mold temperature is too high, the part will cool slowly, the molding cycle will be long, and the surface gloss will be poor, which will cause sticking to the mold, making ejection and demoulding difficult, and the part bridge area will be warped and deformed.

4. Injection pressure

The influence of injection pressure on the performance of the part is mainly manifested in the holding time, the holding time is short, the part shrinks or there are shrinkage voids, vacuum bubbles; lengthening the holding time, especially for large-area thick-walled parts, can increase its density, eliminate vacuum holes, and stabilize the size; holding time is too long, because it is forced to fill the mold, it will cause the part to generate internal pressure and easy to crack.

5. Internal pressure check

There are two common methods: polarized light test and solvent impregnation.

Polarized light inspection method is commonly used in the inspection of various transparent plastic parts. Using the transparency of the parts, the parts are placed between polarized lenses, and the size of the color band area on the surface of the production is observed from the mirror to determine the size of the internal pressure. The larger the light band area, the larger the internal pressure range.

Micro-injection molding, reprinting should indicate the source, and failure to note the source will be regarded as infringement.