Both devices use the same HP 792 latex inks that are used in HP's larger LX series and feature an enhancement to allow double-sided applications.

Joan Pericot, worldwide marketing director for HP's Large Format Print division cited the use of the new ink as a "major enhancement" for the Designjet range.

It is said to enable richer blacks and a glossier finish, while also featuring improved water resistance that is needed for fabric and textile applications.

In addition, HP's new double-sided printing workflow allied with an Optical Media Advance Sensor (OMAS) on the printer enables double-sided printing with minimal operator intervention.

The OMAS controls registration automatically by locating a registration mark when the printed media is reloaded to print the reverse side.

Both printers feature a more robust take-up reel than the L25500, which will now be discontinued, with the L26500 capable of up to 40kg reel capacity and the L28500 capable of up to 100kg, thereby allowing longer unattended operation.

The 2.64m wide L28500 is also between 34% (on the same print width) and 70% faster (when printing at full width) than the L25500, due in part to a faster carriage speed.

The maximum print speed of the L28500 is 40sqm/hr in four pass mode, versus 22.8sqm/hr on the L26500; in 16 pass mode the print speed falls to 8sqm/hr and 6.3sqm/hr respectively.

Pricing for the L26500, which is shipping immediately, is flat on the L25500 at $24,800 (£15,500), while the list price for the new L28500, which will ship from 20 January 2012, is set at $62,000 (£38,800).

Both printers are compatible with more than 500 substrates, including HP's new double-sided HDPE reinforced banner material.

Santi Morera, vice president and general manager of HP's Large Format Business, said that expanding HP's portfolio of latex printers was central to its strategy.

"We want to lead the analogue-to-digital conversion," he said. "Only a third of printed signage is digital at the moment. A lot is still being printed screen and offset.

"We also want to drive the conversion of solvent-based digital printers to the new technology, latex and UV, and to help our signage customers expand their business into new applications."

Morera added that HP has now installed more than 9,000 latex printers worldwide while more than 44m sqm of media had been printed using its latex print range.

HP also announced the online HP Latex University, which it said contains a wealth of content on how to produce a wide range of indoor and outdoor wide format graphic applications using HP latex technology.

The digital manufacturer also introduced a free eco-training programme to teach print service providers how to communicate the environmental benefits.