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

Paint peeling

Paint peeling
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

Surface peeling
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

Colour development
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

Welding
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

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

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

Carbonisation

When an area continuously receives high energy, macromolecules of the element around the base material are carbonised and turn black.

Chemical change

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
Absorption rates for various plastic materials
The values are for reference only and do not account for surface reflectivity.

ABS Plastic

Black-annealed Marking

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

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

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

Standard wavelength laser
Standard wavelength laser
MD-U
MD-U

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.
Recommended model
MD-U Series UV Laser Marker

PET Plastic

Damage-free Marking

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

Standard wavelength
There is a large amount of damage and the engraving is deep and rough.
Short wavelength

ML-Z

Short wavelength
There is a small amount of damage and the engraving is shallow and sharp.
Recommended model
ML-Z Series CO2 Laser Marker

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