It may seem like a small inconvenience--plant labels marked with a china marker grease pencil become unreadable over time because they fade from UV exposure or disappear because of the abrasive dirt splashed after rain storms. So what, you say. Well, if you have almost 300 varieties, in my case hostas, and with multiples totaling more than 450, you need to identify them when planning future additions.
The most convenient commercially available product is molded from white plastic in a T shape, a little like a slice thought a lollipop. The marking area is large enough for characters that can be read from a distance and the leg of the T thin enough to penetrate into the dirt around the plant.
My solution was to consider laser marking, and as I was attending the regional Eastec trade show, which is a favorite of many of the laser marking equipment companies, I had a wealth of experience to draw on. I thought the request was straight forward--what laser would mark a white plastic product. After querying about a dozen suppliers it became evident that further investigation would have to be done, as it turns out that plastic isn't just plastic when it comes to laser marking.
The New York based marking product distributor was helpful, identifying the plastic polypropylene, molded in China. Not quite enough information it turns out because the laser suppliers needed to know what type of polypropylene was used. Forget trying to track down the Chinese manufacturer, it was easier to make some tests.
Fortunately a casual discussion about the problem with a local system supplier, Rofin-Baasel Inc. (Boxborough, MA), resulted in an offer to determine which laser would be appropriate. It turned out that the best results were obtained using a diode-pumped Nd-YVO4 (vanadate) Powerline E Series unit. Mike Donaldson, general manager of Rofin-Baasel, generously offered the use of this laser if I was willing to do the marking. I supplied an Excel file with all the data to be marked and Steve Schertzer, applications manager, set up the marking program and arranged a simple fixture that would allow multiple parts to be loaded and marked.
The Powerline E operating at the fundamental wavelength of 1064 nm is a galvo marking system with 120 x 120 mm marking field size. Tests had set the pulse frequency and peak power that would produce a readable brown mark, one with a very slight scribing effect. The unit uses LaserCAD or Visual Laser Marker Graphical User Interface software; we used the latter for our simple three-line marking application. The fill feature was selected to give the sharpest, most readable mark. And with that the "production" process was off, and in a little over an hour I had marked 325 plant markers.
The hostas are located in eight gardens around my property, and replacing the greased pencil marked labels with the laser marked ones took much longer than the laser marking process. As new plants are added to the gardens I will have to use grease pencil marking, until some point where I have enough to warrant appealing to my friends at Rofin-Baasel for a more permanent solution.
David A. Belforte