Laser Marking PPS with Fibre Lasers

Laser Marking PPS Polyphenylene Sulfide Using Fibre Lasers

Abstract

Marking and engraving on PPS (polyphenylene sulfide) is very difficult because it can withstand high temperatures when heated with a laser. Recent advancements in colourant technology, laser-specific carbon blacks, and fibre lasers enable high-contrast, light-coloured, scratch-resistant marking of black glass-filled PPS, and certified by Yellow Card. This significant advancement enables the marking and micro-marking of data matrices, barcodes, QR codes, and unique part identification across multiple sectors, including automotive, aerospace/NASA MIL electronics, pumps and valves, appliances, and more. The setup and optics of ytterbium fibre lasers require precision to achieve robust, scratch-resistant markings.

Key Takeaways

• PPS resists marking because it resists heat. High-temperature stability means the surface reactions that form contrast are hard to trigger.
• MOPA ytterbium fibre lasers are the correct choice, with pulse durations of 20–40 ns and pulse frequency above 100 kHz.
• Surface temperature control decides scratch resistance. Get rise and fall times wrong and the mark rubs off.
• Resin-rich surfaces are mandatory. Glass emergence on 30–40% glass-filled PPS produces inferior marks.
• Mould at 275–300°F or above for full crystallinity, or the part changes dimensionally in service.

Optimal laser marking. To create scratch-resistant, high-contrast, light-coloured markings on black glass-filled PPS, MOPA Ytterbium fibre lasers are the best choice because they can precisely control pulse width and focused power density. This precision allows for better control of the surface chemical foaming process at a near-infrared wavelength of 1060-1070nm. The best pulse duration is between 20 and 40 nanoseconds, with a pulse frequency over 100 kilohertz. A precise laser setup is necessary to control the surface temperature (rise and fall times); otherwise, the marking can easily be scratched off.

To achieve high-quality laser marking on glass-filled polymers, including PPS, requires robust injection moulding and dispersion/distribution of laser optimised colourants and precompounded materials. The addition of glass fibres can deleteriously affect moulding processes, which in turn affects the quality of laser marking. Resin-rich part surfaces are necessary to achieve robust marking. Surfaces rich in glass fibre will produce inferior marking results.

Polyphenylene Sulfide (PPS)

Polyphenylene Sulfide (PPS) is a high-temperature, semi-crystalline engineering thermoplastic. Within the industry, PPS is known as THE plastic that performs like metal. The properties of PPS, similar to other high-temperature performance plastics including PEEK and LCP, depend on its crystallisation behaviour. Two distinct forms of PPS are sold: “Branched” molecular structure and “Linear”. Among the most recognisable brands are Celanese Fortron® Solvay Ryton®, SABIC Supec, Toray Torelina, and DIC PPS. The branched version tends to be more rigid. The linear usually offers better mechanical and flexural strength, as well as higher melt stability. Linear PPS also has fewer ionic impurities. Glass-filled fibres (30 percent and 40 percent) and glass fibre/mineral mixtures to standard PPS allow for specialised and demanding applications. Electronics manufacturers commonly select 40 percent glass-filled PPS for insulation and connector products.

To achieve a fully crystalline state, mould temperatures of at least 275 to 300 degrees Fahrenheit are required. When PPS is moulded below 275 degrees Fahrenheit, the mouldings are amorphous, or semi crystalline, and remain in this state until they are exposed to higher service temperatures. If the service temperature exceeds the moulding temperature, the parts will become more crystalline, resulting in dimensional and property changes.

Materials used to make fibreglass are silica, limestone and soda ash. Silica is the main material used to form the glass while soda ash and limestone are used to lower the melting temperature. “Glass emergence” is a serious surface defect that commonly affects fibreglass-filled injection moulded products. The exposure of glass fibres causes a glass fibre-rich surface. Excess glass forms on the surface during plastic melt filling and moulding. After condensation and moulding, white marks appear on the surface. Moulded part surfaces must be “resin-rich” in order to produce high quality marking, whereby the energy from the laser interacts with the polymer matrix. Conversely, glass fibre-rich surfaces mark poorly, and the issue gets worse with higher fibre content. Fibreglass itself is not a good absorber of near-IR (NIR) laser light.

Industrial Fibre Lasers

Nanosecond Ytterbium fibre lasers (MOPA and Fixed pulse) are ideal for marking, engraving, and etching plastics due to their superior beam quality (M2) and high brightness “radiance”. They can focus to a small spot size (less than 20 microns), resulting in high energy density. One significant advantage of using MOPA (Master Oscillator Power Amplifier) lasers is ability to fine tune the pulse width. Laser irradiance (W/cm2) and fluence (J/cm2) are important parameters in plastic marking. Irradiance is essentially the intensity of the laser beam which is a function of the focused spot size. Fluence determines the amount of energy that is transferred to the material surface. If the fluence is too low, the material may not be affected at all. If it’s too high, the material can be damaged excessively, beyond the desired marking effect.

Laser pulse repetition rate and peak power density are critical in forming the mark and achieving the optimal contrast and speed. The arithmetic curves of power versus pulse repetition rate are inversely proportional. High peak power at low frequency increases the surface temperature rapidly, vaporising the material while conducting minimal heat into the substrate. As the pulse repetition increases, lower peak power produces minimal vaporisation but conducts more heat.

Contact The SABREEN Group to learn more…bring us your toughest laser marking challenges!

Frequently Asked Questions

Why is PPS so hard to laser mark?

PPS is a high-temperature semi-crystalline thermoplastic that withstands the heat a laser applies, so the carbonisation and foaming reactions that create contrast in ordinary plastics are much harder to trigger. Glass filling, common in PPS parts, compounds the problem.

What laser settings produce scratch-resistant marks on black glass-filled PPS?

A MOPA ytterbium fibre laser with pulse duration between 20 and 40 nanoseconds and pulse frequency above 100 kHz. Precise setup is what controls surface temperature rise and fall times; without that control the marking scratches off easily.

Does glass content affect marking quality on PPS?

Substantially. Fibreglass does not absorb near-infrared, so glass-rich surfaces mark poorly and the problem worsens as fibre content rises. Electronics connectors commonly use 40% glass-filled PPS, which makes resin-rich surface formation a moulding priority.

What mould temperature does PPS require?

At least 275 to 300°F to reach a fully crystalline state. Moulded below that, parts stay amorphous or semi-crystalline and will crystallise later if service temperature exceeds the moulding temperature, causing dimensional and property changes.

What is the difference between linear and branched PPS?

Branched PPS tends to be more rigid. Linear PPS generally offers better mechanical and flexural strength, higher melt stability and fewer ionic impurities.

Scott R. Sabreen is founder and president of The Sabreen Group, Inc., which is an engineering company specialising in secondary plastics manufacturing processes – surface pretreatments, bonding decorating and finishing, laser marking and product security. He has been developing new technologies and solving manufacturing problems for over 30 years. Sabreen can be contacted at 972.820.6777 or by visiting www.sabreen.com or https://sabreen.com/solutions/plastics-laser-marking/

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