This is good news as once again we have a smooth operation for printing and dispatching SIM cards. The printer has a contact station which allows us to talk to the card as part of the printing process. In practice, all we need is to read the ICCID, but we could do whatever we want.
This means the printer is a sensible way to process cards for dispatch, even if we are not printing them - i.e. reading in from a hopper of cards, talking to the card, and sending out to the output hopper. We have the option of diverting the card to a reject bin if the card won't talk or we are not happy with it (including the possibility that someone put the wrong type of cards in the hopper). Obviously we normally combine this with printing on the cards.
There are a lot of card printers on the market, typically aimed at printing ID badges and the like. The Zebra ZXP8 is a tad special though. It is one of the only printers we can use on SIM cards.
Apart from the contact station, which is obviously important for the SIMs, the important feature is that the printer does not try and print directly on to the card.
Most printers do print directly to the card using a thermal transfer process. This process is very effective and allows 300dpi full colour (256 levels of Cyan, Magenta and Yellow) which gives a photo quality output. They usually also do black as a separate layer using some sort of resin that is thermally transferred (1 bit per pixel), giving a crisp sharp and very black extra layer that is ideal for bar codes and text. There are, however, some problems with printing directly. It is not easy (for some reason I do not understand) to print edge to edge using direct thermal transfer. It also works well only on a good smooth flat card surface. Obviously blank ID cards are a smooth surface like this and ideal for direct printing.
SIM cards are different. For a start, the card itself is not the same - it is not a smooth surface. It usually has some texture to it. It also has cut-outs around the SIM, and of course the SIM contacts themselves as well as an uneven surface on the rear of the card behind the chip. What we found using an Evolis printer was that we could just about get the black ribbon to print on the cards. This depended on the type of card, and a slightly different material in the next batch meant the black ribbon came out a feint grey. Colour was almost impossible. Hence we got the Zebra.
The Zebra ZXP8 has two important features to work with SIMs. The main one is that the printing, which uses the same thermal transfer and colour+black printing, does not print on the card. Instead it prints on to a transfer ribbon. The card is then sandwiched in the transfer ribbon between heated rollers applying pressure. The end result is that the transfer ribbon is fixed to the card leaving a smooth glossy surface and the full printing colour (under the glossy surface). This looks really good, and because the transfer ribbon is larger than the face of the card (slightly) it allows printing properly edge to edge.
The other feature is that the ribbon can have an inhibit panel in addition to colour and black. This sticks to the transfer ribbon and pulls it off the backing selectively. When the transfer is applied to the card this leaves gaps. These are ideal for ensuring no print or glossy transfer ribbon is applied to the SIM contacts, or a mag stripe or signature strip. In our case we clear the SIM contacts and the cut-out. If we print over the cut-out it creates a sort of cellophane effect over the gaps that comes off and sticks to your fingers. Similarly, if we print over the contacts or a mag stripe then it does wipe off. But that is messy, and the inhibit works really well to make a professional looking card.
I'd like to thank Jim in their Bourne End office for all his help and patience on this, and I can definitely recommend these printers to anyone doing SIM cards. Do read up on the meaning of "contact station" though.