Nope, no comprehensive sites that I know of. I haven't even found a Padprinting forum with any decent traffic.
Stay the hell away from any non-powered units, there are enough variables without hand cranking levers etc. Those press-a-print units that they sell for $2200+ are not worth the scrap value of the metal they're made from. I'd say they're for kitchen table hobbyists, but I wouldn't wish the stress on any hobbyist I know of.
Here is the basics of it:
The plates are etched 20 - 30 microns deep, the difference in depth of a couple of microns makes a
big difference in how it prints. Learning how to manage those differences is the key to success, and there are dozens of variables to deal with, and exponential combinations of them. To a certain degree nothing will replace years of experience to give you educated guesses on what to change, but a good understanding of what is happening and why helps.
The plates also get a 1/2 tone throughout the entire image. 300LPI 80% or 200LPI 90% are common to use, and no you Epson won't cut it. you'll need a solid half tone film from and image setter, but if you take care of it it'll last a long time, and first you expose the image, then expose again with the 1/2 tone film. The half tone does not show in the image when printed, it's put there to keep the doctor blade from dipping into the image and scooping out the ink. Remember the images are etched less than .002" deep, so it wouldn't take much for the doctor blade to deflect and scoop out the ink and leave parts of the image blank or very weak.
The plate either goes in an open tray with the ink, or a cup filled with ink sits upside down on the plate.
In an open ink well a brush, roller or something similar to a flood bar brings the ink forward and covers/fills the image, then on the back stroke a flat doctor blade comes down, scraping all the ink off leaving the image filled.
In a closed cup system the cup filled with ink slides forward covering/filling the image on the plate, then slides back and scrapes all the excess ink off leaving the image filled.
From here on in both systems do the same thing.
Padprinting ink dries many times faster than the fastest drying solvent based ink you've ever screenprinted with, Put it on a screen and you'll be lucky to get a couple of passes before it dries in, even with fast printing and immediate flooding. I do sometimes use padprinting inks for screenprinting, but they need to be loaded up with retarder, and even then they need frequent thinning
There are several "speeds" of thinners that come with the inks so you can tailor the flashing off speed to your needs, and the flash-off speed is everything in padprinting.
Because the image filled with ink is exposed to air, the top surface of the ink becomes tacky, when the pad comes down on the image the tacky ink sticks to it, once the ink is on the pad the bottom layer of ink is exposed to the air and it becomes tacky, so when the pad comes down on the part it sticks to the part and transfers off the pad.
The shop heat and humidity very much affect the print!
There-in lies the rub. The deeper the plate, the longer it takes for the top and bottom layers to flash-off, too deep and it may not pick up all the ink, or may not drop all the ink off the pad. too shallow and you'll see the half tones and may not get a very opaque print. There are many products that we double-hit to get opacity, and unlike screenprinting, you do effectively get twice the ink deposit on two prints as the image effectively flash dries itself in a second or less on the part and the second print will sit right on top.
Controlling the flash-off of thinners from the image before it on the pad, and then once it's on the pad can be done in many many ways. Most machines have speed settings for the forward, back, up and down speeds of the carriage and pad, some machines have air lines that you can point at the pad to speed up flash-off. Various thinner types and retarders help too. We have a 2 speed/3 heat setting hair dryer on each machine with flexible stands. It can be easy to dry everything enough to get a good transfer to and from the pad, but with many inks, too much drying on the pad means that the ink won't bite onto the product. Remember that the part of the ink that touches the part getting partially dried before transferring, over dry it and it'll scrape right off once dry..... And the kicker is with epoxy ink you won't know until the next day until the ink has cured fully. it's possible to have a couple of thousand printed parts on a table with 1/2 of them good as gold, and half where you can easily scrape off the ink because the printer got a little too blow-dryer happy and skinned over the bottom layer of the print a little too much before it hit the part.
Pad printed images go on the part
much dryer than screenprinted images! and you need to make sure they aren't too dry. Some inks are much more forgiving than others!
We stock 5 different lines, all ITW Transtech:
Type "P" which is 10:1 with hardener, it a good all around ink for most plastics, wood or coated/painted surfaces that solvents will dissolve. it's not too tough or chemical resistant and gets most of it's strength by the solvent binding the ink with the surface it's printed on. Air-cure is fine, can be force cured
Type "B" 4:1 with hardener, good for some metals, anodized or powder coated surfaces, some hard plastics etc. Air cure is fine, ca be force cured.
Type "W" 2:1 with hardener, very tough ink, used for golf balls, some metals or coated surfaces, air cured is fine, can be force cured
Type "PH" 10:1 with hardener, for rubber, plasticized PVC and other flexible products, air cure is fine.
Type "BG/L" 20:1 with special hardener. For glass, ceramic, metals. It really need a good heat dry for full cure. humidity helps with the cure too.
At about $100/quart(litre) and 10-20 colours stocked in each type (5), the initial outlay is pretty steep. Some places will sell you 200mls rather than a full quart. I mix 30-45 grams per job, and no matter how much you print in a day, you'll be throwing out 80+% of the mixed ink at the end of the day. That's how little actually gets printed on the product.
Remember in 2 part solvent inks that
dried and
cured are two different things!
Groovy pad printing animated .gifs:
http://www.tampoprint.de/en/3techniken_en/tampondruck_en.htmlSome other light reading for you:
http://www.itwtranstech.com/Support/PadPrinting101/tabid/834/Default.aspxhttp://www.itwtranstech.com/Support/PadPrintingTips/tabid/853/Default.aspxhttp://www.tampoprintusa.com/Learning-Center.html
