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There are many types of ink adhesion testing methods, each best suited to different kinds of printing methods and substrates. Here’s what you should know about the types of ink adhesion testing methods used for digital printing inks.
John Maher: Hi, I’m John Maher, and I’m here today with Matthew Macioci, Digital Sample Technician, that Inkcups, a leading supplier and manufacturer of industrial inkjet printing equipment, pad printing equipment, inks and accessories. Today we’re talking about adhesion testing methods. Welcome, Matt.
Matthew Macioci: Thank you, John. I’m happy to be here.
John: Matt, what is adhesion testing and why do you do it?
Matthew: So, typically adhesion testing is just testing the abrasion resistance of ink on a substrate. And the reason why we do this is because customers want to know if their bottles are going to match with our ink. And if they are going to pursue a machine with our ink, they need to know if it’s going to work out, if it’s going to be a feasible option for them.
John: Right. What types of different products are we talking about here that you can print on?
Matthew: It can be anything from sport bottles, to glass, to coolers, lunchboxes, anything like that. We do a wide range of products that we print on.
John: Okay. And what are some of the typical ways that you test for adhesion of the ink?
Matthew: There’s four categories. The four categories are tape, scratch, Crosshatch A, and Crosshatch B, and all of those come from the ASTM’s standardized tests. And we abide by those as a passing result for Inkcups.
So when we get substrates in that pass all four of those adhesion criteria, we know that it’s leaving our building in a passing situation, so that we are comfortable relaying that to the customer and saying that, “Listen, we were able to pass these ASTM standardized test criteria. If you have any additional tests or anything that you want us to test, it’s going to have to be on your end, or you’re going to have to provide additional information for us.”
John: Okay. So let’s go through each one of those. What is the tape adhesion testing?
Matthew: Sure. So tape adhesion testing is essentially a pressure sensitive tape that we use on a substrate, and you apply it to the ink on the substrate and basically peel the tape off rapidly and as close to 180 degree angle as possible. If any delamination of the ink occurs, that’s a failure. If none occurs, then that’s a pass and you move on to the next step.
John: And what is that kind of testing for in terms of a real world situation?
Matthew: If I were to bring it into a real world situation, I would probably guess that it would be the closest simulated to, if someone were to drag their nail across the ink and test for that or maybe rub with their thumb. That would be the most ideal situation I can think of, where it would apply.
John: Some sort of outside force that’s just scratching at the ink and it’s peeling off or whatever it is.
Matthew: Yeah, exactly.
John: Okay, so, and then the second method was the scratch method. What is that?
Matthew: Scratch is, so that we have a special tool, it’s called a Sclerometer. It’s a pretty funny word, but essentially it’s a pen tool, a pen-like tool that has a spring in it with a specific spring constant.
And when you depress the spring, there’s a collar inside that depresses the spring, and it has a carbide tip that you basically put on the substrate, and you drag it across across the ink to see if there’s any delamination of the ink.
A passing result for that would be if you have the pen tool, the Sclerometer, dragging through the ink and it doesn’t delaminate any of the ink, then that’s a pass. If it’s a hard line that’s delaminated, it’s still a pass, but there’s any jagged edges or anything in between the ink and the substrate, that’s going to be deemed a failure.
John: Okay, interesting. And then the next two were the Crosshatch A and Crosshatch B. What are those?
Matthew: Yeah, those are the most aggressive tests that we perform here. Crosshatch A is simply a razor blade in the shape of an X on the ink, and then the same pressure sensitive tape and peel.
Peel that in the same manner as the tape test. And if there’s any delamination again, that’s going to be deemed a failure.
John: So you’re doing both the things. You’re both scratching it with the razor blade and then also doing the tape lifting test.
Matthew: Correct. So that’s where the aggressiveness comes in, is with the scratch and the tape incorporated.
John: Okay. And how do you determine which of those methods you’re going to use for a particular ink or product?
Matthew: Sure, that’s a great question. Typically, for glass companies we’ll abide by all four of them, go to the most aggressive test and then include dishwasher as well, which is an additional test. We can talk about that later. But basically, the customer will spec out what they are required for.
We give recommendations on what we think would be the ideal adhesion test criteria that they would want to follow. Typically with promotional, we want to stick to either tape and scratch only, and then major brands and glassware companies, we want to stick to Crosshatch B.
John: Right, because there might be a difference between somebody just giving away a promotional product, where they might not be expecting that it’s going to last for years or something like that. And like you said, a glassware company that wants what’s printed on their glassware to last for a long time.
Matthew: Yeah, exactly. I mean, the more and more companies that are coming to us with glass, their standards are pretty high, and we’re willing to abide by those and we’re happy to accommodate for those standards.
John: Okay. You mentioned a dishwasher test. What is that? And then are there other types of additional tests that you can do, depending on what the product is?
Matthew: Yeah, sure. Glass companies, not alone, but typically glass companies, we’ll recommend a certain number of dishwasher cycles that they need to pass in order for it to be a feasible option for them to consider a machine.
Matthew: So we have the basically send these glass or water bottle or whatever the item is through the dishwasher a certain number of cycles, specified by the customer. And when they come out of the dishwasher without any delamination, that’s deemed to pass. Any sort of delamination is a failure.
John: Right. Because again, obviously the people who are making these glasses, if they’re going to put on that glass, “Hey, this is dishwasher safe,” they need to test that and make sure that that’s true.
Matthew: Yeah. People are normally going to throw their glassware in the dishwasher, and they want to have that confidence that it’s not going to flake off right away on the first or second cycle.
John: Yeah. I remember getting some nice promotional glasses, or something like that, when I was younger and throwing them in the dishwasher a few times and then all that ink was gone after a few times through the dishwasher.
Matthew: Yeah, it’s a tricky situation. A lot of the customers, they’ll save themselves by saying, “Hand wash only,” on a lot of their items. So typically, the higher end brands, you can’t throw those in the dishwasher because sometimes the structure of the bottle will deteriorate. That’s why it’s hand wash only, so that saves us in those cases where maybe we can’t pass a dishwasher on those. But for glass, yeah, typically they want to pass a dishwasher cycle.
John: Do you have an actual dishwasher where you’re working, where you’re just throwing things in a real dishwasher? Or is it some sort of industrial thing?
Matthew: No, so there’s two. There’s the commercial side. There’s also the residential side, residential being much more aggressive than commercial.
John: Interesting.
Matthew: That not really what you want to hear, but residential is a lot more aggressive when it comes to the dishwasher cycles. And so when we pass our dishwasher cycles, we make sure that the residential dishwasher is used over the commercial one.
John: And how many times typically are you throwing something through the dishwasher?
Matthew: Again, it all comes back to what the customer specs out. But basically, it’s usually for stainless steel items, usually, it’s around 50 to 100. For glassware it’s anywhere around 250, for residential.
John: And what other types of tests like that are you doing for different types of substrates and materials?
Matthew: Sure. That’s a good question. Additional one would be probably flexible bottles, bike bottles, any flexible plastic in the flat form. Those would have to pass the extreme squeeze test, which is essentially squeezing the bottles so the inner walls touch and then releasing the bottle. And then there can’t be any delamination, cracking, splitting of the ink, anything like that. So that would be the tests that we would use for flexible bottles.
John: That does sound like an extreme squeeze, where you’re literally squeezing it so that the whole entire bottle crushes in upon itself.
Matthew: Yeah. And we have a formulated ink specifically designed for those types of skews.
John: Okay. And like a flexible ink of some kind?
Matthew: That’s exactly right. It’s a super flexible ink. We can actually compress it and then also twist the bottle too, and it’ll bring a passing result to us, which is really nice because we were struggling with that for awhile. A lot of companies were looking at for us for answers, for flexible items, and we didn’t have an option to give them until we discovered this really flexible ink.
John: Right. Choosing the methods that you’re doing, it just really depends on what types of inks you’re using, what types of substrates, what the material itself is, what the product itself is, whether it’s a squeezable bottle or a glassware. That’s what’s going to determine which tests you need to do.
Matthew: Absolutely. The customer is obviously the driving force, but then there’s also the product, which is also the driving force as well. If they’re asking for a promotional cup to pass 250 dishwasher cycles in the residential dishwasher, and that’s not really feasible. It’s not really a goal. It shouldn’t be a goal for a promotional product.
John: For a promotional product. And you can guide the customer and tell them that, that, “Hey, that’s not a reasonable expectation for this type of product or this type of plastic,” or whatever.
Matthew: And it’s my job and responsibility to relay that to the customer and educate them on certain areas where they may not have a lot of information.
John: Right. So if I can’t perform those types of testing in-house, what are my options?
Matthew: So a good example would be migration testing. So some food companies will test for migration, because they obviously don’t want the ink migrating into the food, and we can’t perform migration testing in-house. So we would have to send that out to an outside company to perform those tests.
John: Okay. All right. Well, that’s really great information, Matthew. Thanks again for speaking with me.
Matthew: Yeah, no problem. Thank you.
John: And for more information about Inkcups and Inkcups printing equipment, visit the website at inkcups.com or call (978) 646-8980.
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