In carrier tape manufacturing, understanding the microscopic physical properties and processing characteristics of raw materials is the foundation for ensuring product precision. This article provides an in-depth technical analysis of the two core substrates: Polycarbonate (PC) and Polystyrene (PS).
1. Polycarbonate (PC): High-Strength Engineering Plastic
PC is a colorless, transparent, amorphous thermoplastic material, named after its internal CO3 groups.
Key Physical Parameters
- Specific Gravity: 1.18-1.20 g/cm³
- Molding Shrinkage: 0.5-0.8% (Low shrinkage, excellent dimensional stability)
- Molding Temperature: 230-320℃
- Temperature Resistance: Stable long-term use from -60~120℃
- Tensile Strength: 69 MPa
Chemical & Physical Properties
PC is resistant to weak acids and neutral oils but not resistant to UV light and strong alkalis. It has high impact strength and excellent electrical insulation. Its drawbacks include poor self-lubrication and susceptibility to hydrolysis at high temperatures, requiring strict storage and processing environments.
Injection Molding Challenges
PC is an amorphous material with poor fluidity and high sensitivity to moisture. Producing high-precision PC carrier tapes requires attention to:
- Drying: Strict drying is mandatory, typically 110-120℃ for 8 hours.
- Mold Design: Due to poor fluidity, the gating system should be "thick and short," with large gates, and the mold must be heated.
- Temperature Control: Too low leads to material shortage and dull finish; too high causes flash and bubbles. Mold temperature should be controlled between 85-110℃.
2. Polystyrene (PS): General Purpose Hard Plastic
PS, commonly known as hard glue, is a thermoplastic synthetic resin widely used in electronic/electrical packaging.
Key Physical Parameters
- Specific Gravity: 1.05 g/cm³ (Lighter than PC)
- Molding Shrinkage: 0.6-0.8%
- Molding Temperature: 170-250℃
Material Characteristics
PS has excellent high-frequency insulation and transparency second only to plexiglass. It has good chemical stability but is brittle and prone to stress cracking. It is not resistant to organic solvents like benzene and gasoline.
Molding Process Advantages
Compared to PC, PS is easier to process:
- No Deep Drying: Low moisture absorption, usually does not require long pre-drying.
- Good Fluidity: Easy to mold using screw or plunger injection machines.
- Stress Control: Although flow is good, it has a large coefficient of thermal expansion and is prone to internal stress. High material temperature, high mold temperature, and low injection pressure are recommended, along with extended injection time to reduce residual stress and prevent deformation.