7 problems of PC/ABS and how to solve them

PC/ABS is an alloy material of polycarbonate (PC) and acrylonitrile-butadiene-styrene copolymer (ABS).

The feature of the materials:

1. Good performance, high impact strength, chemical stability, and good electrical properties;

2. It has good weldability with organic glass and can be made of two-colors plastic things,the surface can be chrome-plated and spray-painted;

3. The high level of impact resistance, high heat resistance, flame retardant, reinforcement, and transparency;

4. The fluidity is slightly worse than HIPS, but better than PMMA, PC, etc., and has good flexibility.

The application of the materials:

1. The decoration of the car : instrument panel, decorative pillars, instrument front cover, grille, interior and exterior decoration parts;

2. Business equipment casings and built-in components: laptop/PC, copiers, printers, plotters, monitors;

3. Telecommunications, mobile phone casings, accessories and smart cards (SIM cards);

4. Electrical products, electronic product casings, meter covers and casings, household switches, plugs and sockets, cables and wire ducts;

5.Household appliances, such as washing machines, hair dryers, internal and external parts of microwave ovens, etc.

Problems and the solutions

1. silver lining problem

Defective silver wire is the most common problem of PC/ABS materials. Silver wire, also known as silver streaks, water splashes, material flowers, etc., is a phenomenon of silvery white filamentous stripes appearing on the surface of the product along the flow direction. It is caused by gas interference. The gas produced is mainly divided into three components:
1. Air: air involved in the melting and injection stages;
2.  Moisture: the moisture contained in the material itself;
3. Pyrolysis gas: gas produced by high-temperature hydrolysis/thermal decomposition.

Solution:

Firstly check the material is completely fully dry. After confirming that the material is fully dry, adjust the injection molding process to improve the silver wire defects. At the same time, poor injection molding silver wire is also related to mold exhaust.

2. Flow mark problem

Flow marks are produced when the material is injected. The reason is that the material has poor fluidity. Flow marks are different from silver streaks. They are not caused by moisture or material decomposition, and their appearance is also different.

Solution:

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

3. Shrinkage and dent problems

Shrinkage cavities are caused by insufficient filling of the material in the mold cavity.

Solution:

Appropriately increase the mold temperature and material temperature to improve material fluidity, extend the injection holding time, increase the injection pressure, and increase the injection speed to improve mold filling. You can also increase the size of the gate and heat the gate runner to reduce and eliminate product shrinkage;
Dents are caused by improper material temperature and improper product design. When the material temperature is too low, not only shrinkage holes will occur, but also dent problems will occur. If the material temperature is too high, the mold temperature will be too high, which will cause the molten material to cool down. Excessive shrinkage may result in dents. Appropriate processing methods can be used to increase injection speed and measures.

4. Warping deformation problem

Warp deformation of injection molded parts is caused by unreasonable part design, improper gate location and unreasonable injection molding processing conditions, resulting in internal stress, uneven or excessive shrinkage, excessive mold temperature or uneven mold temperature. It will cause the mucous membrane of the part to be difficult to demould, or uneven cooling will also cause warping deformation;

Solution:

1. Processing technology: lengthen the injection molding cycle, lower the injection temperature, appropriately adjust the injection pressure and injection speed, while slowing down the ejection speed, increasing the ejection area, and maintaining a balanced ejection force;
2. Product design: increasing wall thickness, adding reinforcement ribs and rounded corners can reduce warpage deformation;

5. brindle problem

It is usually caused by "melt rupture" caused by the expansion of the molten material into the mold cavity during high-speed injection;

Solution:

1. In terms of molding process: increase the material temperature, increase the nozzle temperature, slow down the injection speed, etc. to reduce the appearance of 

2. Mold aspect: Increase the mold temperature, add an overflow tank, increase the gate size, and modify the gate shape.

6. Pocket problem

Solution:
1. Poor dispersion, add dispersant or oil, increase temperature, and add back pressure.
3. Make sure that the time and the temperature of baking material are enough.
4. The adjustment of the mold temperature.

7. Product “peeling” problem

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

Solution:

1. Materials parts: the two components of PC and ABS are partially compatible, so appropriate compatibilizers must be added during the modification process to improve their compatibility. Of course, we need to eliminate the bad peeling caused by mixing materials in the first step;

2. Mold parts: The principle of mold design must be in the direction of minimizing shearing. Generally speaking, products with dense textured surfaces are more likely to produce peeling (caused by frictional shearing between the melt in the cavity and the inner wall of the cavity during high-speed filling); at the same time, in terms of gate design, the gate size is too small. It will cause excessive shearing when the melt passes through the gate, which will lead to peeling on the surface of the product;

3. Injection molding process: The main direction is to avoid excessive shearing. When product filling is difficult, high speed and high pressure can be used to improve it. Therefore, in the actual injection molding process, you can also consider increasing the injection temperature/mold temperature and improving the fluidity of the material to reduce the flow resistance during the actual filling process, thereby Avoid excessive shearing caused by high speed and high pressure.