A potential print brokering client of mine sells glasses and bottles of various colors with imprinted text and logos. She came to me looking for a source for metallic black drinking ware that was food safe. This is a good example of both industrial printing—metallic black pigment on food-safe plastic—and promotional item custom printing.
If I could provide her with black metallic bottles and cups, my potential client would then use screen printing equipment and pad printing equipment to imprint logos, type, etc., on these items. I had studied custom screen printing and felt reasonably comfortable with this technology, but I had never heard of pad printing. So I went to school on the subject.
What Is Pad Printing?
Actually, pad printing seems to be a hybrid of gravure and offset commercial printing. In this process, a sponge-like, bulbous pad picks up an inked image from a metal or polyester plate (with recessed image areas holding the ink) and then deposits this image on an irregular surface. I watched some videos to supplement my reading, and I encourage you to do the same. Nothing explains the process of pad printing as well as a video.
Steps in the Process
Making the Plates
Let’s say you wanted to pad print a two-color logo on a golf ball. You would first print a positive of each color, in register, on clear acetate film using a laser printer. You would then place this film over the emulsion of a metal or polyester plate and expose the plate to intense light in a suitably constructed lightbox. The light would harden the emulsion on the plate except where the positive image of the logo blocked the light and prevented it from hitting the plate.
You would then make a second exposure with a halftone screen placed over the entire plate. The dots on the halftone screen (again a positive image) would keep the light of the second exposure from hitting image portions of the logo. (You would go through this same process to prepare a plate for each color of your final image.)
Since the opaque film positive will have prevented light from hardening the plate emulsion behind the logo art, and since the dots of the halftone screen will have kept the light from hitting a halftone dot pattern of your art, once you have washed away the remaining soft emulsion from the plate, you will have a recessed image area composed entirely of halftone dots. This is the prepared plate, ready to use after you have exposed it to a little more light to complete the emulsion curing process.
Printing the Image
The pressman locks up the plate in the moving bed of the press (which is very small compared to an offset press). Specially formulated ink comes out of a reservoir (a cup, of sorts) and is spread over the plate with a flood blade. Then a doctor blade passes across the plate, removing any ink not within the recesses of the image area halftone dots (hence the resemblance to the recessed plate of gravure custom printing—an intaglio process).
Once the inked plate is ready, a silicone pad in the shape of a “loaf,” a “bar,” or a “circle” presses into the plate. At this point the ink transfers to the pad (hence the resemblance to the blanket of an offset press ink unit), and from the pad the image transfers to the substrate—all within the mechanized assembly line of the small pad press.
Let’s get back to the golf ball I had initially mentioned. Pad printing is ideal for irregular surfaces like this. Whereas you can roll a cylindrical drinking cup or bottle under a flat custom screen printing unit as the squeegee presses the ink through the fabric, this process wouldn’t work on a golf ball (or perhaps a small metal toy car) due to the item’s irregular surface.
In one of the videos I saw, a holder for the golf ball had been molded out of a clay-like substance that would harden and hold every golf ball in the press run in the exact same position.
The plate, the inking device, and the pads themselves (from one to four pads for multiple color work) all moved in tandem. As the equipment inked up the plate and the pad lifted the image from the plate and deposited it onto the golf ball, the inking units were getting the plate ready for the next golf ball.
The whole process worked smoothly, yielding printed golf ball after printed golf ball.
Why You Should Care
Here’s an excerpted list of pad printing applications from the Wikipedia article on pad printing:
- “Medical devices (surgical instruments, etc.)”
- “Implantable and in body medical items (catheter tubes, contact lenses, etc.)”
- “Hockey pucks”
- “Letters on computer keyboards and calculator keys”
- “Automotive parts (turn signal indicators, panel controls, etc.)”
- “Hot Wheels or Matchbox toy cars”
As you can see, any item or surface you normally couldn’t print on because of its irregular shape is perfect for pad printing. Furthermore, the tacky nature of the solvent-based ink will stick to many different substrates. And as I’ve said before in many blog articles, custom printing includes much more than just marketing and editorial work. Industrial custom printing is definitely in a growth spurt.
New Developments in Pad Printing
Here are a couple of things to consider when you study pad printing to see if it’s a useful technology for your particular line of commercial printing or design work:
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- UV inks are now being used in this process. This may be a good way to avoid solvent-based inks. In addition, the UV inks have the advantage of curing instantly upon exposure to UV light.
- Direct laser imprinting is becoming available for platemaking. This avoids the analog process of producing a film positive and then exposing the emulsion on the printing plate to light.
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on Thursday, July 4th, 2013 at 8:54 pm and is filed under Printing.
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