PC/ABS, polycarbonate and acrylonitrile-butadiene-styrene copolymers and mixtures, are thermoplastic plastics made of polycarbonate and polyacrylonitrile (ABS) alloys. It combines excellent properties of two materials, formability of ABS material and mechanical properties of PC, impact strength, temperature resistance, and ultraviolet (UV) resistance.

 

Common problems and solutions

Poor silver wire is the most common problem of PC/ABS materials. Silver wire, also known as silver pattern, water splash, material flower, etc., is phenomenon of silvery whitish filamentous streaks that appear on the surface of product along flow direction. Interference of gas, gas produced is mainly divided into three components:
(1) Air: air involved in glue melting and injection stage;
(2) Moisture: moisture contained in material itself;
(3) Cracked gas: gas produced by high-temperature hydrolysis/thermal decomposition.

First, check whether material is sufficiently dry, and after confirming that material is sufficiently dry, adjust injection molding process to improve silver wire defect. At the same time, poor injection molding silver wire is also related to mold exhaust.

Flow mark is produced during injection of material. Reason is that material has poor fluidity. Flow mark is different from silver streak. It is not caused by moisture or material decomposition, and appearance is also different.

It can be avoided by increasing temperature of material to improve fluidity. Appropriately increasing mold temperature to increase fluidity of material in mold and reducing injection speed can also be solved.

Shrinkage is caused by insufficient filling of material in cavity.

Properly increase mold temperature and material temperature to improve fluidity of material, extend holding time of injection, increase injection pressure, increase injection speed to improve mold filling, or increase size of gate, heat gate runner to reduce and eliminate product shrinkage;

 

Warpage of injection molded parts is caused by unreasonable part design, improper gate position and unreasonable injection molding processing conditions, resulting in internal stress, uneven or excessive shrinkage, excessive mold temperature or uneven mold temperature. It may cause difficulty in demolding part mucosa, or uneven cooling, which will also cause warpage and deformation.

(1) Processing technology: lengthen injection molding cycle, lower injection temperature, appropriately adjust injection pressure and injection speed, while slowing down ejection speed, increase ejection area, and maintain ejection force balance;
(2) Product design: increasing wall thickness, adding stiffeners and reinforcement at rounded corners can reduce warpage and deformation;

It is usually caused by "melt fracture" caused by expansion of melt into mold cavity during high-speed injection.

(1) In terms of molding process: increase material temperature, increase nozzle temperature, slow down injection speed, etc. to reduce appearance of markings;
(2) In terms of mold: increase mold temperature, add overflow groove, increase gate size, and modify gate shape.

(1) Poor dispersibility, add dispersant or oil, increase temperature, and add back pressure.
(2) Pay attention to whether there is a mold problem. Try with other materials.
(3) Whether baking temperature and time are sufficient.
(4) Mold temperature adjustment.

Dent is caused by improper material temperature and improper product design. When material temperature is too low, not only shrinkage holes will occur, but also dent problems. If material temperature is too high, mold temperature is too high, melt will shrink excessively during cooling, resulting in dents.

Use appropriate processing problems to increase injection speed and measures.

Peeling problem of plastic products is closely related to rupture of fluid caused by high shear. Under low shear stress or velocity, small disturbances caused by various factors are suppressed by melt; while under high shear stress or velocity, disturbance in fluid is difficult to suppress and develops into an unstable flow; when a critical shear force is reached, it will cause fluid to break.

(1) In terms of materials: PC and ABS components are partially compatible, so it is necessary to add appropriate compatibilizers to improve their compatibility during modification process. Of course, because of bad peeling caused by mixture, we need to eliminate it in the first step;
(2) Mould: Principle of mould design should be carried out in the direction of minimizing shear. Generally speaking, products with dense skin textures are more prone to skinning (due to frictional shear between melt in cavity and inner wall of cavity during high-speed filling); at the same time, in gate design, if gate size is too small, it will cause excessive shear when melt passes through gate, then cause surface of product to peel;
(3) Injection molding process: Main direction is to avoid excessive shearing. When product is difficult to fill, high-speed and high-pressure methods can be used to improve. Therefore, in actual injection molding process, it is also possible to consider increasing injection temperature/mold temperature and improving fluidity of material to reduce flow resistance during actual filling process, so as to avoid excessive shear caused by high speed and high pressure.