Polymers (or plastics) are everywhere in our lives. They are made of large chains of molecules with various arrangements and structures that offer a wide range of mechanical, thermal, electrical, chemical and optical properties. Polymers are among the most important building blocks for the next generation of cars and packaging, but also for the next medical, electronic and photonic devices.
With the increasing complexity and the constant miniaturization of polymer-based devices, precise manufacturing of these materials must also evolve. In many cases, the cutting, drilling, marking, micro-bumping or texturing of such material must now be realized with very small features (< 50 µm), straight and smooth edges while avoiding the discoloration, the delamination or the weakening of the polymer. Lasers are indeed the tool of choice for such precise manufacturing.
In laser processing, the removal of material with a laser is what we call “ablation”. The material must absorb enough laser energy to reach its ablation threshold. The most critical laser parameters to increase the precision of a laser process are the laser wavelength and temporal regime (Continuous Wave, quasi-CW, short pulse, ultrashort pulse). More specifically, laser ablation of polymers is highly dependent on the absorption length of the material at the laser wavelength. The higher the absorption, the more efficient and precise the ablation. Short, pulsed lasers (nanosecond to femtosecond range) are also preferred for precise processing because the deposition of short pulses on the polymer limits the heat accumulation around the ablated zone (namely called “heat affected zone” or “HAZ”), as shown in Figure 1.
Up to now, CO2 lasers at wavelengths between 9.3 and 10.6 µm have been extensively used for polymer processing since most polymers are strongly absorbed by laser radiation in this spectral range. While CO2 lasers offer great coarse processing applications at very high speed, the processing precision is fundamentally limited by the long wavelength and long pulse duration (generally above a microsecond) produced by such lasers. As shown in the equation box and figure below, for a given focusing lens and input beam diameter, the beam diameter at the focus increases proportionally with the laser wavelength:
Due to their relatively short wavelength and short pulse duration as compared to CO2 lasers, mid-IR fiber lasers around 3 µm could thus have a major impact in the precise manufacturing of polymers. Here, we review six of the most important polymers and explain their value in our world. We also show why mid-IR lasers around 3 µm can help in the precise manufacturing of those polymers by highlighting their strong absorption in this spectral region and by showing polymer processing results.
PMMA – Poly (methyl methacrylate)
PMMA, also known as acrylic, belongs to the thermoplastic polymer group. It offers great optical transparency and high resistance. It is used abundantly for light protection, fiber optics cladding , medical and ophthalmic implant, cheap camera lenses, protective shield, etc. It is a cheaper, optically-clear alternative to glass and polycarbonate.
PET – Polyethelene terephthalate
PET is a thermoplastic polymer that is lightweight and impact resistant. It figures as an excellent water and moisture barrier and it is thus mainly used for packaging food and beverages. In the textile industry, PET refers to the more common name “polyester”. More recently, PET became a transparent substrate of choice for flexible electronics and solar cells due to its high resistance to solvents, low cost and high transparency in the visible range.
Polyimide belongs to the family of thermoset polymers and is known for its high thermal, chemical and mechanical properties. In the flexible electronics industry, it is thus used as an insulating layer on which conductive films can be deposited. Considered as a very resistant cladding, it can protect optical fibers and thin electrical wires in very harsh conditions or within the human body. Polyimide is well known for having a yellowish color.
Nylon – Polyamide
Nylon is a thermoplastic polymer. Not only it can be used in textiles (tents, outside gears, etc.), certain types on nylon (like the PA 66) exhibit high strength and stiffness at high temperature. This polymer has good fatigue resistance and excellent fuel and oil resistance. It is a strong, cheap and lightweight alternative to metal parts under the hood of a vehicle. It is also a great material for additive manufacturing especially through the selective laser sintering (SLS) process where the nylon powder is sintered with a laser to produce complex parts for rapid prototyping.
PLA – Polylactic acid
PLA is a thermoplastic belonging to the important family of bioplastics because it is made from renewable biomass sources. PLA is also widely used in low-cost 3D printers, but its main advantages are its bio-compatibility and bio-degradability. It is thus used for disposable packaging and also for temporary medical device or implants that need to gradually disappear in the human body. Anchors or screws that serves as supporting structure after a surgical procedure are generally made from this material.
PC – Polycarbonate
Polycarbonate is part of the thermoplastic polymer group. Polycarbonate is a strong, impact resistant and, in most case, optically clear material. It was extensively used in the past for compact discs or DVD. Nowadays, thanks to its very good optical properties, it is used for lighting lenses in the automotive industry. PC found several other applications in the medical device and mobile phone industries.