Double-sided printing: Block-out or Day & Night?

What is what?

Double-sided block-out (DSBO) printing is for frontlit signs where both sides are printed such as hanging banners. “Block-out” means that the substrate is opaque, allowing different images on the front than the back.

Double-sided Day & Night (DSDN) printing is for signs placed in lightboxes which are frontlit during the day (lights off) and backlit at night (lights on) with the same appearance by day as by night.

Which materials can be used?

DSBO is most commonly used on block-out PVC banners. These substrates are printable on both sides and include a “block-out” layer between them which prevents the two images from interfering with each other.

DSDN is designed for translucent PVC banners and paper, which are intended for backlit applications.

How do they work?

For DSBO, the printer adds a registration line on the first side that is detected by the Optical Media Advance Sensor (OMAS) when printing the second side, so the second side is printed in-register with the first.

For DSDN, the printer adds registration marks all the way around the image on the first side, and then scans these marks using a set of lights inside the platen and a camera on the carriage. By scanning these marks, the printer continually adjusts the image on the second side as it is printed to ensure optimal registration of the second side to the first.

The following videos illustrate the two processes:

What is the expected front-to-back registration accuracy?

For DSBO, given the two images are only aligned at the beginning of the image, the differences between sides increase with the length of the print. Given the two images are independent, this is sufficient for “block-out” applications.

For DSDN, the continuous adjustment of the second side thanks to the multiple registration marks ensures a registration accuracy of 2mm or less, irrespective of the physical size of the print. This provides sufficient registration for outdoor backlit signs.

Which printers have these features?

For DSBO: All of the current HP Latex printers except the HP Latex 110, 315 and 335 are able to produce DSBO prints, so the HP Latex 365, 375, 560, 570, 1500 and all of the 3000 Series models. Check your printer’s user guide for more information.

For DSDN, this is offered as an accessory for the 3.2m HP Latex printers, so the HP Latex 1500 and the HP Latex 3000-series machines. The part numbers are as follows: P4P91A for the HP Latex 1500, and J8J14A for the HP Latex 3000 Series models.

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