How to improve laser marking through functional pigments!
Silvia Rosenberger, Technical Marketing Manager at Merck KGaA, Darmstadt Germany, held a lecture as part of the FOBA “Virtual Manufacturing Day 2020” webinar series on January 14, 2021. As an expert for laser pigments, she explained together with her colleague Stefan Gutberlet, Global Marketing Manager Industrial Pigments, how plastics can be optimized for obtaining best laser marking results.
During the webinar, which attracted many participants, numerous questions came up which could not all be answered due to limitations of time. Therefore, as a webinar follow-up, Silvia Rosenberger and Stefan Gutberlet kindly provide their missing answers for the FOBA blog.
The webinar recording “Lasermarking of polymers and the improvement through laser pigments” from January 14, 2021, is available on demand.
Just in a nutshell: What is the benefit of using laser pigments?
Stefan Gutberlet: Customers either ask for an improvement in speed or in marking quality. So, we say: Once the lasers become faster, the material must keep up with it. And this is what our pigments do. They improve the marking speed, the contrast and the line definition with pulsed DPSS or fibre lasers in polymers. Without laser pigments most polymers do not contrast mark at all.
Why did you mainly refer to fiber laser technology to be applied for plastic marking?
Stefan Gutberlet: Fibre lasers are the work horse amongst the lasers of today. They are robust and work 24/7 over years with hardly any maintenance. Additionally, they have increased in power which enables an even faster marking. So: if customers are looking for process stability, marking on the fly and low maintenance fiber is the best choice. In contrast DPSS laser (YAG and vanadate) are still a good choice when the quality of the laser mark and not the speed is the limiting factor.
Do your pigments react to different laser wavelengths apart from IR laser? What if we have low power UV lasers?
Silvia Rosenberger: UV lasers have the benefit that they also might work without laser pigments. You get a color reaction already with TiO2 in the polymer. But what if you have a transparent polymer? We have seen that also here our laser pigments can help to achieve a dark marking with the UV laser. In addition, we have seen, that in a black formulation, leaving out the carbon black and replacing it with our black Iriotec 8835 helps to improve the durability of the light mark. The white marking containing Iriotec 8835 was much stronger than compared to a formulation containing carbon black. But of course, we recommend doing application tests yourself as it is always a question of the system: polymer, laser pigment, laser settings and applications.
Are there also pigments available for the optimization of CO2 laser marking?
Silvia Rosenberger: Actually, for CO2, we only see the engraving in the polymer, even with laser pigments. With the wavelength of 10.6 µm and 9.3 µm for the CO2 lasers the material is evaporated. We think, this has to do with the missing pulse energy and the heat influence over time. With pulsed lasers you get out of a 10 W laser maybe 5000 W over a time of the pulse length of nanoseconds, while the pulses of the CO2 lasers are quasi-simultaneous and do not show the high pulse energy; this means a constant energy input over time into the material.
Which marking speed can I expect using your pigments?
Stefan Gutberlet: Clear answer: as fast as your laser can go! But it also depends on your design and expectations. So the first question is: how do you define marking speed? One aspect is the sensitivity of the material: with an optimized pigmentation it is possible to get the laser marking process faster. But a mark you are thinking of might be a logo, a QR code or just a batch number. And as you can imagine marking times differ according to the area you want to mark: marking just a line is of course faster than marking defined areas.
Do your pigments allow color marks? Or is it only white and black?
Stefan Gutberlet: The mark is neither white nor black, but always grey. A grey scale mark, from nearly white to very dark. This has to do with the side effects like foaming when you want a color change or vice versa. The tinting strength of the laser pigment is not so high. After all: you do not want to see it in your colored polymer formulation until it is laser marked.
It is possible to achieve colored markings in dark colored formulations by hiding an organic colorant in the dark - in general black formulation. The results look fancy, but the formulations have limited use in the industry, as identification is in general the target and decorative properties are rarely required.
What is your advice for the optimization of transparent materials?
Silvia Rosenberger: With transparent materials you might need to find a compromise between marking speed and color influence of the laser pigment. Our most transparent laser pigment is Iriotec 8825 which is usually used in a concentration of 0.1 – 0.3%. In a thin film application, you might not see the haze of the product at all, while in thicker parts you see the light scattering and also some color influence.
With which polymers are laser pigments compatible?
Silvia Rosenberger: I see two ways to understand the question: compatible in the sense of “compatible with the existing polymer process” or in the sense of “resulting in a good laser mark”? I guess you as the user want a positive answer for both cases: good processability plus good marking results. Because there are so many different polymers, colors and further pigments available, we see several possibilities: Firstly, your masterbatcher knows already about our pigments and their combinations and you ask him for some advice or material. Secondly you might want to check out on our web page Iriotec.com where we installed a product configurator. You put in your polymer and its color and you will get one to three recommendations which pigment is best to use. You will also see laser marked plastic chips from our demo boxes which we produced to show our customers how good a marking can be. Also, to give a realistic view on what is possible with lasers, because there is no real white and no 100% black mark, but a lot of grey shades are possible. In general, our solutions are used in all kind of polymers. However, in very rare occasions, there might be no recommendation, for example we do not offer pigments suitable for CO2 lasers.
How can laser pigments be integrated into a polymer?
Silvia Rosenberger: Laser pigments are treated like polymer colorants, added to a masterbatch or compound, just as for other colorants. If you are already used to coloring your product, you will know exactly what to do. Our direct customers are the masterbatchers or compounders. A masterbatch is a color concentrate which is used during the injection molding, extrusion or any other polymer process. The let-down rate of a masterbatch is usually 1-4%. So, the pigments are incorporated into the polymer.
Which is the particle size of these pigments?
Silvia Rosenberger: We offer pigments in different sizes. Iriotec 8850 is < 1 µm very comparable to a TiO2 pigment. We also have the platelet pigments based on mica which have an average particle size of approx. 12 µm. But this is usually the task of the masterbatcher to incorporate the pigments into the polymer and disperse well for an easy handling during the molding process.
How do your pigments differ in terms of power sensitivity to higher or lower energy?
Silvia Rosenberger: Very good question and I would actually like to say, yes, there is such thing as activating energy. I get the impression that Iriotec 8210 has a lower activation energy than Iriotec 8208 and 8850; that is why we see that the combination of Iriotec 8850 and Iriotec 8210 achieves darker marking than both on their own; 8850 is chosen for the speed while 8210 lowers the activation energy. Iriotec 8208 is the best in contrast and marking speed and is at nearly all laser settings equally dark which makes this product so unique. Conversely, Iriotec 8825 is the work horse of the laser pigments, being the most “universal” but also requiring the most laser power and slower speed to provide acceptable laser marks in comparison.
There seem to be special Iriotec pigments for each polymer: but is it possible to combine several Iriotec pigments to get a special solution?
Silvia Rosenberger: Also here, this is the task of the masterbatcher as he will know best which combinations fit well to the other components of a formulation. But yes, we sometimes recommend combining as one pigment is best in speed and the other is best in contrast so combinations might be good but might give challenges in other ways. Synergy between the laser pigments is dependent upon many factors and so there is no set mix of functional pigments that could show a particular synergy for a given application and criteria.
Are there disadvantageous interactions from Iriotec with polymers, additives or pigments?
Silvia Rosenberger: We have inert and stable materials. So, I like to say: no interactions. But as in life there is no 100%, there might be something I have not thought about. E.g. thinking about it now, we know that there are flame retardants with the tendency for foaming: so, if you want to achieve a dark marking with the laser, it might be that the flame retardant reacts at the same time with the laser and the mark does not get as dark as it could be without the flame retardant. At normal addition rates there is little reaction with the polymer system in to which the Iriotec may be employed. However, very high levels as may be in masterbatch production, can cause interaction between some of the Iriotec laser pigments and the carrier system and extra stabilizers or incorporation methods to make the masterbatch may be needed. This is the expertise of the masterbatch producer.
If you had to pick a “one size fits all” solution from the portfolio: which pigment would you choose?
Stefan Gutberlet: In my opinion, there is no such thing as a “one size fits all”, as it is either chosen on cost, performance or color influence – or maybe regulations thinking about food contact applications in different regions. But of course, we have pigments which suit for most of the applications which are more universal. My current favorite is the Iriotec 8850 as it works in all polymers, is heat stable up to 600°C and can therefore be also used in all polymers. It always gives a dark mark and is the fastest pigment powder we currently have. We have seen it also works very well for film applications.
Does the offshore cable industry use your pigments in their cables?
Stefan Gutberlet: The question is: can I tell about customer projects? No. But I can tell you about the benefits that laser marking might bring to an application like this. We cannot be made liable for such a comment. You as the producer of the final product know more about the demand for your product, the composition of the formulation and its uses. With the laser the polymer becomes the mark. The reaction takes place inside the polymer and is as durable as the polymer itself. Mechanical stress can do it no harm. Nevertheless, we always recommend that you do your specific tests to be on the safe side.