I’ve noticed that the most commonly-litigated category of clean tech patents seems to be light-emitting diode (LED) patents.  I suspect this is because LEDs have such a wide variety of uses, from instrument panels to traffic lights to cell phones as an energy-efficient substitute for incandescent bulbs. 

One such use that I recently learned about is as an ultra-violet light source to dry ink in digital ink jet printers. 

Leggett & Platt, Inc. (L&P) is a Missouri-based company with several different product segments, including residential furnishings, industrial materials, and specialized products such as sewing machines and industrial printers. 

In May 2005, L&P sued VUTEk (which now appears to be owned and operated by Electronics for Imaging, Inc.) in the Eastern District of Missouri, alleging that the digital printer maker’s  PressVu UV printers infringe L&P’s U.S. Patent No. 6,755,518 (‘518 patent).

Some printing materials bend or warp when exposed to the heat or infrared radiation used by digital printers.  The ‘518 patent describes a method and apparatus for printing ink on such deformable materials without causing them to deform. 

To print on these materials, the ‘518 patent describes a “cold” ultra-violet (UV) radiation source and the use of an ink that can be cured (i.e., dried) by exposure to UV radiation.  Some of the claims of the ‘518 patent recite a cold UV assembly effective to “substantially cure the ink,” a term the district court interpreted to mean “cured to a great extent or almost completely cured.”

Last month, the U.S. Court of Appeals for the Federal Circuit (the federal court that hears all appeals of patent cases) affirmed the district court’s judgment that the asserted claims of the ‘518 patent are invalid as “anticipated” by a prior art reference (if all of the elements of a patent claim are expressly or inherently disclosed by a publication that pre-dates the filing date of a patent, the patent is anticipated by the reference and deemed invalid). 

The dispositive issue in the case was whether the prior art reference, U.S. Patent No. 6,457,823 (‘823 patent), discloses a cold UV source that is effective to substantially cure the ink.  The Federal Circuit found that the ‘823 patent expressly discloses that LEDs, which can provide cold UV light, will cure the ink 75-80%.

The court further held that the LEDs disclosed by the ‘823 patent necessarily are effective to substantially cure the ink, and therefore the ‘823 patent inherently anticipates the ‘518 patent:

Thus, while the ‘823 patent may not expressly disclose that the LEDs cure the ink to a great extent, it inherently discloses LEDs that are “effective to” do so.

The Federal Circuit affirmed that P&L’s ‘518 patent is invalid and, because an invalid patent cannot be infringed, VUTEk escaped infringement. 

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