Base elements → Materials

PLASTICS AND POLYMERS

Table of main properties of plastics and polymers

 

Property Typical Value Remarks
Density ~0.9–2.2 g/cm³ Very low
Young’s modulus (E) ~1–5 GPa Very low
Tensile strength ~20–150 MPa Depends on polymer
Hardness (HV) ~5–30 HV Very low
Thermal conductivity ~0.1–0.5 W/m·K Very low
Electrical conductivity Very low Insulating material
Thermal expansion ~50–150 ×10⁻⁶ /K Very high
Melting point ~100–350 °C Depends on polymer
Magnetism No Non-magnetic
Corrosion resistance Excellent Chemically resistant
Machinability Easy Injection, machining, molding

Plastics and polymers encompass a broad family of organic materials composed of macromolecular chains. Gradually introduced into watchmaking during the 20th century, they now play an important role, both in external components and in certain quartz—and even mechanical—movements, as well as in tooling.

Their success is based on their low density, wide range of properties, and ease of processing, allowing the production of complex parts at controlled cost. Depending on their nature (thermoplastics, thermosets, or composites), they can meet a variety of requirements, from external components to functional movement parts.

Main Properties

Polymers used in watchmaking exhibit variable characteristics, but generally:

  • Low density (~0.9–1.5 g/cm³)
  • Good corrosion resistance
  • Non-magnetic materials
  • Low thermal and electrical conductivity
  • Low to moderate Young’s modulus (~1–5 GPa)
  • Good chemical resistance
  • Possibility of self-lubrication (depending on the polymer)

These properties make them particularly suitable for lightweight and low-stress applications.

1. Thermoplastics

Thermoplastics can be melted and reshaped.

Examples:

  • ABS → cases, cost-effective components
  • PMMA (acrylic / plexiglass) → watch crystals
  • Polycarbonate (PC) → impact-resistant transparent elements
  • PEEK → technical applications

2. Thermosets

These polymers harden irreversibly after polymerization.

Examples:

  • Epoxy resins
  • Phenolic resins

They are notably used in composites (carbon, etc.).

3. High-Performance Engineering Polymers

Some polymers offer advanced properties:

  • PEEK (polyether ether ketone)
  • PTFE (Teflon)
  • PA (engineering polyamides)

Characteristics:

  • Good mechanical strength
  • Low friction coefficient
  • Improved thermal resistance

Polymers are shaped using various industrial processes:

1. Injection Molding

  • Melting of the polymer
  • Injection into a mold
  • Cooling and solidification

👉 The most common process in industrial watchmaking

2. Machining

  • Material removal from a solid block
  • Used for technical polymers

3. Compression / Molding

  • Used for resins and composites
  • Enables complex shapes

4. Additive Manufacturing (more marginal)

  • 3D printing
  • Prototyping or small production runs

1. External Components

👉 Advantages: lightweight, shock resistance, cost efficiency

2. Movement

  • Wheels and pinions (specific applications)
  • Low-friction components
  • Insulating parts

Advantages

  • Very lightweight
  • Low cost
  • High design freedom
  • Corrosion-resistant
  • Non-magnetic
  • Electrical insulation
  • Possibility of self-lubrication
  • Good shock resistance (for certain polymers)

Limitations

  • Low stiffness
  • Sensitivity to temperature
  • Aging (UV, oxidation)
  • Limited mechanical strength
  • Less prestigious than traditional materials
  • Susceptibility to scratching (depending on the polymer)