What gets marked on plastic parts
Moulders and assemblers mark part numbers, date codes, QR or DataMatrix codes, logos, switch and keypad legends, and material identification symbols such as >PA66-GF30< in the format set out in ISO 11469. A laser mark changes with every part without changing the mould, and it does not wear off the way a printed legend can.
There are four ways a plastic responds to a laser. In colour change, the surface carbonises and turns darker, which suits light coloured parts. In foaming, the heat creates tiny gas bubbles that scatter light and raise a pale mark, which suits dark parts. Engraving removes material, which is how a CO₂ laser marks acrylic. Layer removal takes off a top coat to show a different colour beneath, which is how backlit switch buttons are made (see laser marking on switches).
Which laser marking machine suits each plastic
ABS marks well with a fiber laser in most grades, dark on light colours and pale on dark ones, and has its own page on laser marking on ABS. Polycarbonate gives dark marks under fiber in many colours, though clear PC is harder and a UV source gives finer results. Nylon (PA6, PA66 and glass filled grades) foams to a light mark on black parts, which is why it is common on connectors. Black POM also foams to a pale mark, while natural POM usually needs an additive.
PP and PE absorb very little at 1064 nm, so natural grades often barely mark with fiber. A laser marking additive in the masterbatch, or a UV laser at 355 nm, is the usual answer, and UV is also the safer choice for white and pale parts that tend to yellow under fiber. Clear PET bottles and films are marked with CO₂ or UV, since a fiber beam passes through them. Acrylic (PMMA) is CO₂ territory: cast acrylic engraves to a frosted white, while extruded acrylic tends to stay clearer. The acrylic name plaque guide shows how gift makers use it.
PVC is the one hard rule in laser marking on plastic: never laser it. It releases chlorine compounds that are harmful to people and corrode the machine. Rigid PVC products such as window profiles are coded with continuous inkjet, as the page on uPVC marking explains.
When CIJ printing is the better choice
PVC parts and fast extrusion lines are often better served by continuous inkjet, as are resins that give poor contrast without additives. NMB deals with Markem-Imaje CIJ printers, which can code these products where a laser is not suitable.
Setting up the job
The first rule of laser marking on plastic is to trial on parts from the actual production colour, because a change in pigment or carbon black loading from one batch to the next can shift contrast noticeably. Mark parts after they have cooled fully from moulding. Thin walls and glossy surfaces need lower energy to avoid melting or a raised edge. On moving lines, an online laser can mark parts on a conveyor, with codes checked by a reader downstream. Plastic fumes need proper extraction with suitable filters, both for operator health and to keep the lens clean.
What to check before you buy
- Resin and grade list. List every resin grade and filler you mark, since glass filled nylon and unfilled nylon can behave quite differently.
- Production colours. Trial with parts from real colour lots, not one sample, and keep a reference part for each colour.
- Additive option. If contrast on PP, PE or natural POM is weak, ask your masterbatch supplier about a laser marking additive before choosing a different laser.
- Light or dark mark. Decide whether you need dark marks on light parts or light marks on dark parts, because that points towards fiber or UV.
- Thin and glossy parts. Check for melting or haze on thin walls and high gloss surfaces at your target speed.
- Fume extraction. Size extraction for continuous running, with filters suited to plastic fumes.
- PVC screening. Make sure operators can identify PVC parts and keep them away from the laser.
Laser marking on plastic in Tamil Nadu
Laser marking on plastic is everyday work for moulders in Chennai's Ambattur and Guindy industrial estates and for the automotive and electronics suppliers around Sriperumbudur, Oragadam and Hosur. Coimbatore's pump and motor makers mark plastic terminal boxes and fan covers as well. Gift and consumer product makers use the same lasers on items such as kids' bottles and lunch boxes and keyboard keycaps.
NMB Enterprises is based at Poonamallee, Chennai. Moulders and manufacturers anywhere in Tamil Nadu can call or WhatsApp 098417 60722 with the resin grade, colour, photos of the part and the mark required, and NMB will recommend the laser type and configuration that suits that material.