Laser Marking for Plastic
This section describes information ranging from the principles of plastic marking and processing to advantages grouped by laser wavelength. It introduces marking examples and the optimal laser markers for a variety of materials such as ABS, epoxy, and PET.
- Plastic marking/processing types
- Mechanism of plastic colour development
- Absorption rate for plastic
- ABS plastic
- Epoxy resin
- PET plastic
Plastic marking/processing types
Paint peeling
Peel the paint or printing on the target surface to bring out the contrast with the colour of the base material.
- (Example) Automobile instrument panel switch
- When the design is changed, conventional methods using printing or stamps required the printing plate to be changed. With a laser marker, you can handle it flexibly by just changing the program.
Surface peeling
Remove/engrave the surface layer with a laser.
- (Example) Half cut
- Use a laser marker to process a cutting section. A cutter was used in the conventional method; however, there were problems such as difficult adjustment and time-consuming changeover between product types. Moreover, the method incurred costs for replacing the blade and there was a risk of the blade being left in the product.
Colour development
Irradiate a plastic target with a laser to develop a colour in the target itself.
- (Example) Wide-area marking on LSI
- Using a laser to irradiate the plastic for colouration without engraving ensures minimal damage to the target during marking. In addition, areas of up to 330 × 330 mm can be marked all at once, mechanical equipment costs can be reduced thanks to the elimination of the need to convey the target as with conventional methods.
Welding
Use the heat of laser radiation to weld and join plastic parts.
- (Example) Welding transparent and coloured plastic material
- Whereas ultrasonic and vibration welding are known to adversely affect products and cause burrs due to melting, laser welding is non-contact and does not damage the product or cause burrs.
Mechanism of plastic colour development
Foaming
When the base material is irradiated with a laser, gas bubbles are generated inside the material due to the thermal effect of the radiation. Gasified, evaporated bubbles are contained in the surface layer of the base material and create a whitish swelling. These bubbles are particularly visible with darker base materials and result in “thin” colouration.
- (Example) Base material colour:
-
- Black→
- Changes to Grey
- Red→
- Pink marking
Condensing
When the base material absorbs the laser energy, the thermal effect increases the molecular density. The molecules are condensed and the colour changes to a darker colour.
Carbonisation
When an area continuously receives high energy, macromolecules of the element around the base material are carbonised and turn black.
Chemical change
The “pigment” elements in the base material always contain metallic ions. The laser radiation changes the crystal structure of the ions and the hydration level in the crystal. Consequently, the composition of the element itself changes chemically, resulting in colour development due to the increased intensity of the pigment.
Absorption rate for plastic
Material absorption rate variations by wavelength
The graph below shows the transmission ratio of a fundamental laser (1064 nm), a green laser (532 nm), and a UV laser (355 nm) for various plastic materials. PVC, ABS, and polystyrene, both fundamental and green lasers show low transmission ratio and high absorption ratio, which ensures good marking. On the other hand, the transmission ratio for polyimide is about 30% with a green laser (532 nm) but more than 90% with a fundamental laser (1064 nm). The absorption ratio varies greatly depending on the wavelength.
- Absorption rates for various plastic materials
- The values are for reference only and do not account for surface reflectivity.
ABS Plastic
Black-annealed Marking
Irradiation from the laser light results in a black colour on the surface of the plastic. Marking provides a print-like finishing on designs and other surfaces that cannot be erased.
- Selection factor
- Factors such as the degree of colouring and the density depend on the nature of the target plastic. Hybrid laser markers capable of producing a high peak power even at the standard wavelength are optimal. CO2 laser markers do not typically discolour plastic surfaces during engraving.
- Recommended model
- MD-X Series Hybrid Laser Marker
White Marking
Irradiation from the laser light results in a highly visible white colour on the surface of the plastic. Marking provides a print-like finishing on designs and other surfaces that cannot be erased.
- Selection factor
- Factors such as the degree of colouring and the density depend on the nature of the target plastic. Hybrid laser markers capable of producing a high peak power even at the standard wavelength are optimal. CO2 laser markers do not typically discolour plastic surfaces.
- Recommended model
- MD-X Series Hybrid Laser Marker
Epoxy resin
White Marking
Markings are white and clear, making for an ideal replacement for stamps, labels, and printing. The highly visible, print-like finishing does not disappear like ink.
- Selection factor
- Shifting the focal point for defocus marking allows for high-grade printing with good visibility, all while keeping the engraving amount to a minimum.
- Recommended model
- MD-X Series Hybrid Laser Marker
Damage-free Marking
Marking on IC package
Damage-free marking is the best method for marking targets where damage to the product surface or the inside due to laser energy is a concern.
- Selection factor
- Green lasers are effective at suppressing damage to the inside of a product minimal with low-profile packages and in other situations. The high absorption rate for various materials allows users to achieve ultra-shallow marking at only a few μm from the surface.
PET Plastic
Damage-free Marking
Marking that appears as if the white characters are floating from the surface is possible with transparent/translucent PET plastic. From PET bottles to thin film materials, marking can be achieved with no pin holes.
- Selection factor
-
Pin holes can appear as a result of overheating when marking under high power. Using a laser with a short wavelength (9.3 μm) enables clear marking with minimal damage.
- Standard wavelength
-
Conventional method
There is a large amount of damage and the engraving is deep and rough.
- Short wavelength
-
ML-Z
There is a small amount of damage and the engraving is shallow and sharp.
- Recommended model
- ML-Z Series CO2 Laser Marker
