U.S. District Judge Gregory M. Sleet of the District of Delaware.

A Delaware federal judge on Thursday confirmed a $50.3 million infringement verdict against Ardagh Glass Inc. for infringing a patent held by a small Pennsylvania-based glass company.

In a 28-page memorandum opinion, U.S. District Judge Gregory M. Sleet of the District of Delaware turned away Ardagh's attack on a Wilmington jury's finding last April that an American subsidiary of the European glass manufacturer willfully infringed Green Mountain Glass' patent, which covers technology used to recycle glass in the manufacturing process.

Though Sleet tacked another $12 million in prejudgment interest onto the original verdict, he declined Green Mountain's request for enhanced damages.

Ardagh said Friday that it planned to “vigorously appeal” the ruling.

“Ardagh continues to disagree with the jury verdict and strongly believes that the case is without merit,” the company said in a statement.

In court documents, Green Mountain said it acquired the so-called '737 patent in 1998 to reuse mixed-colored recycled glass, or cullet, in the glassmaking process. Cullet is prized in the industry for its ability to save energy, reduce emissions and extend glass furnace life.

Green Mountain, based in Bryn Mawr, Pennsylvania, accused Ardagh in 2014 of willfully infringing its product after company officials met over a period of years to discuss the technology. According to Green Mountain, Ardagh's brass knew Green Mountain held the patent for recycling mixed-color cullet, but still went ahead and used the technology without a license.

According to Sleet's opinion, Ardagh did not dispute that it used similar methods. Rather, it argued in its post-trial briefing that the jury overlooked prior patents, which would have prevented a finding of infringement.

However, Sleet said he warned Ardagh during trial that its prior use of the technology could “seriously undermine” its standing in the eyes of the jury, but Ardagh opted to press ahead with its anticipation defense anyway.

“Despite this warning, defendant proceeded with their defense. Accordingly, a reasonable jury could have found infringement based on all the aforementioned evidence,” he wrote.

Sleet also said he gave “much thought” to inappropriate comments that Green Mountain's lawyers made in front of the jury.

According to the opinion, a Green Mountain attorney pressed a lay witness on claim construction, closing his questioning by saying, ”You have just proven infringement … correct?” Though the remark earned the attorney a rebuke from the bench, counsel for Green Mountain repeated the statement again in his closing, Sleet said.

Sleet immediately instructed jurors to disregard the comments.

Ardagh said the statements amounted to egregious misconduct by Green Mountain. The company asked Sleet for a new trial, arguing the plaintiff's conduct swayed the jury on the issue of infringement.

But Sleet cited the instructions, and his admonishment of Green Mountain's attorneys in denying the request.

“While counsel behaved inappropriately and unprofessionally at this and other times during the trial, after much thought the court believes its curative instructions sufficed to adequately ameliorate the harm caused by counsel,” he said.

Matthew R. Berry, an attorney for Green Mountain, praised the ruling Friday, but declined to comment further.

“We are grateful that the court affirmed the verdict and awarded our prejudgment interest request,” said Berry, a partner in Susman Godfrey's Seattle office.

Green Mountain did not comment on the ruling.

The case is captioned Green Mountain Glass v. Saint-Gobain Containers.