The scientific probing at Domino’s Laser Academy in Hamburg, Germany is often comparable to that of a forensics team working to crack a case. Laser physicist Katharina Janβen reveals how the Laser Academy is analysing substrates and enabling customers to code with confidence.
Every day, the laboratory receives a new batch of substrate samples to test. Samples can include PET plastics, flexible foils or films, a variety of cardboards and cartons, aluminium cans or natural materials such as glass, wood or stoneware.
It could be that our customer is keen to ensure their Domino laser will continue delivering high-quality codes after a move to sustainable packaging for example. Or perhaps the need to code an entirely different packaging profile has arisen due to a new product launch.
In one instance, we showed that one customer’s materials supplier had changed the composition of their packaging without advising the customer. Changing the composition of packaging can impact on a company’s sustainability targets and cause coding quality issues which can result in downtime and product waste. Without Domino’s investigative capacities, the composition change might never have been established.
Probing with precision
High quality marking relies on the alignment of the laser’s wavelength and absorptive characteristics of the substrate – which essentially, means achieving a favourable interaction between light and matter.
Once we receive a sample for coding, we take it to our analytical laboratory to understand the substrates’ characteristics. There we’re able to map out the molecular functionality of the material using a device called a spectrometer which gives us a picture of how the material’s structural elements bond together.
We also have another spectrometer where we can detect the suitability of substrates for fibre and UV laser coding.
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Domino’s database of ‘fingerprints’
The depth of analytical information these state-of the-art-devices provide allows us to create unique fingerprint profiles of the samples we receive. Currently, we have 10,000 of these fingerprint profiles digitally stored. The earlier analysis allows us to create a new substrate profile and immediately see if it matches any logged in the digital library. This allows us to see which laser was used to create a good code for which profile resulting in faster identification of the optimal laser for customers.
Every substrate fingerprint is classified, which is how we can recommend the right laser solution to our current and new customers for the substrate they seek to code. In some cases, we may recommend coating the substrate with a laser sensitive coating or inserting a coloured field for better contrast.
Matching the wave-length
Polyethylene terephthalate (PET) is a popular choice for water and carbonated drinks bottles and our scans will show several peaks and valleys when analysing the material. Our goal is to find the wavelength with which we can radiate the material so that it matches the peaks (hotspot), as this creates an optimal laser mark. Radiating the valleys (cold spots) with a laser wavelength would leave the material cold resulting in poor code quality.
All materials have their unique fingerprints; they all have hot spots and cold spots, but the location of those spots differs a great deal from material to material.
Checking the code quality of machine-readable codes is an important step when sampling for customers. We use a grading device which grades the code quality as the quality needs to be appropriate to the product-type. For example, machine-readable 2D codes for medicine packaging is a very different requirement from the use-by date on a pizza box which humans read.
Collaboration and knowledge-sharing is Domino’s style so we’re a very close-knit team. Making time for fellow team members proves as fascinating an experience as what we discover in the labs.
When analysing one sample, I was excited to discover why coding using the fibre laser did not work on this specific black substrate and that I was able to analyse this using our UV spectrometer. I found out the reason why coding was not possible was that the black colour comprised only of primary colours, and the fibre laser does not bleach “false colour black”.
The work we do in our laboratories is exciting because so much of it is exploratory. Due to the fast-moving nature of materials, using science innovation we have the opportunity to uncover the influence of the substrate’s composition to the laser process for the very first time.
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