Pad Printing F.A.Q.'s - Pad Print Machinery of Vermont - Pad Printing Machines & Equipment, Pads, Inks, Plates & Accessories

QUESTION: I have etched thin steel plates that are etched to about 30 microns and am using a sealed cup pad printer. I run and print 5-10 parts that look great and then the image starts becoming washed out looking with voids. If I leave the machine for few minutes the print looks good again and then goes back to the missing pieces syndrome. I am new to pad printing and would appreciate some advice.

ANSWER: This is indicative of an ink viscosity problem. If your ink is drying too fast, the pad won't be able to pick the entire image up from the etched area of the cliché. In that case, you’d add a little thinner to the ink – or retarder if the ink is already quite thin. Another option would be to remove any pauses that may be set in the printer controls to slow the drying process a little. If, however, your ink is too thin it will not completely release from the pad. Then, when the pad goes to pick up the image for the next print cycle it will deposit some of the previous image back into the cliché. To remedy this, either slow the print cycle down – putting a pause on the print side of the cycle (and maybe even one on the pickup side) or try directing some hot air at the pad after it has picked up the image to help the ink dry a little more before printing. If this doesn't help you may want to start with a fresh batch of ink that you know has been set to the correct viscosity.

QUESTION: We have been printing on polycarbonate substrates and are having significant problems with spider webbing. We've tried thick ink, thin ink, grounding the pad, increased ambient humidity. We’re currently using PLT272 (black). Any other suggestions?

ANSWER: The humidity level, not only in your production area, but also where the raw product is stored should be kept at around 80%. This is VERY important when working with polycarbonate materials. It is also important when working with the PLT272 series inks due to the fact that they are inheritantly prone to static. One other thing to try when working with this type of ink and polycarbonate, is to put one or two drops of some dishwashing liquid in the ink cup or well. This helps neutralize the molecules just enough to allow the release of the static charge before it becomes a problem.

QUESTION: I was asked to pad print an ISO 9002 imprint, in white, on cobalt blue mugs that had been previously been imprinted with the company's name. I suspect they had been screen printed. My white was not fully opaque and did not come out as solid a white as the name that was imprinted on it. I could also clearly feel that the name imprint was thicker and heavier. Since I have only one white ink, is there something I could have done with the mix to make it more opaque?

ANSWER: The problem you're facing is rather common. When pad printing white on dark backgrounds, especially large image areas, good opacity is difficult to achieve. You can waste a lot of time trying different plate depths and ink viscosities, and find that you still can't get the opacity you want. The most economical solution to this problem is to simply double-hit them, provided that your fixture or nest allow this without any movement between hits. Even though it may take an extra couple of seconds per part to do this it's still quicker than spending hours experimenting with the other parts of the equation. In fact, this has been standard practice in the automotive industry when printing on black parts, due to the same type of problems. The cliché to be used for double-hitting should not be as deep as other plates you use for single-hits.

QUESTION: I'm having a little trouble sometimes with plate etch depth when I make my 100 x 100mm aqua nylon pad printing plates. I mostly expose for 84 seconds on both my film and screen exposure. I want to know the science as well as the logic behind either legthening or shortening the exposure times to make either a lesser or deeper etched plate. I get confilcting reports, please help. What technically should happen when my screen exposer time changes to either 60 seconds or to 90 seconds?

ANSWER: First you might want to read our article on selecting the correct clich� Articles_CorrectCliche.cfm. The exposure process can be a bit confusing but here is the basics of what happens (keep in mind that the purpose of the light is to harden any area of the plate not protected by the screen or film):

1) The first exposure is with the film. The light or exposure time should only be long enough to sufficiently harden the area around the image. Too short of an exposure will result in the surrounding surface staying soft and thus allowing the screen to be etched into the entire plate. Too long of an exposure will result in under-cutting the image. This is described as light cutting into the image by sneaking in under the film from the sides, thus deteriorating the image. It will be most noticeable in areas of fine lines and detail. This sets the stage for the second exposure.

2) The screen exposure is the ONLY exposure that controls depth. Typically, the is 50% to 70% of the time used for the first exposure. The polymer is hardened from the bottom up … meaning that: the longer you expose with the screen, the more of the previously protected surface is being hardened. Undercutting affects this stage as well. Too long of an exposure at this stage will actually cause the image to virtually disappear.

To recap, only use enough time during the first exposure to harden to surrounding surface area. Then, set the second exposure at a relatively shorter time than the first, and lengthen it until you get the plate to the preferred depth, keeping in mind that the longer it is exposed the less deep the plate will become.

NOTES:

a) It's best to experiment with scraps first so as to not waste valuable plate materials.

b) Also make sure to check the density of the film. If the film is not dense enough or of even density, you will get a shallow etch. If your film density varies from art to art it will be challenging trying to maintain a constant etch depth. Some plate types need very dense art for a deep etch.

QUESTION: I am a "new guy" that has plans to do in house pad printing. I know a closed system is the best for me and in general. I plan to do small amount lots of 250 to 500 printing at a time, as low as 50 at a time. Working within my budget, is it possible to do a multi-color printing one color at a time? To explain a little more: Print one color, then Print another color on the same piece.

ANSWER: Certainly, it is possible to do short run multi-color printing with a single-color printer provided the following:

1) Your product must have some part that is shaped in such a way to allow it to be used as a point of consistent registration and re-registration.

2) The fixture (or nest) is made in such a way to provide tight and consistent registration on the product. This is usually achieved by making a mold from the actual parts to be printed.

3) The entire lot of product is consistent in shape and the position of the point of registration is also consistent.