Warner-Jenkinson Company v. Hilton Davis Chemical Co.
520 U.S. 17 (1997)
Hilton invented a process to
purify dyes, and got a patent on it. The patent specified that a solution
used in the process must have a pH between 6.0 and 9.0.
The 9.0 limit was added so
that Hilton's process wouldn't conflict with a different patent that
claimed 9.0+. But Hilton never said why they chose 6.0 as their lower
Warner came along and
developed a process that used a solution at pH 5.0. Hilton sued for infringement.
Warner argued that 5.0 was
outside of the range that Hilton claimed in their patent.
Warner argued that Hilton
couldn't figure out how to make the process work below 6.0.
Hilton countered that they
made the process work all the way down to 2.2, but chose 6.0 as their
lower limit for no particular reason.
Hilton argued that Warner's
process was still infringing because of the Doctrine of Equivalents (aka non-textual infringement).
The Doctrine of
Equivalents says that a product or
process that does not literally infringe upon the express terms of a
patent claim may nonetheless be found to infringe if there is an
"equivalence" between the elements of the accused product or
process and the claimed elements of the patented invention.
See Graver Tank v. Linde
Air Products Co. (339 U.S. 605
The Trial Court found for
Hilton. Warner appealed.
Warner argued that the Doctrine
of Equivalents (an old common law
doctrine) was no longer good law because the Patent Act of 1952
(specifically 35 U.S.C. §112 ¶6)
made it obsolete.
Basically, the purpose of
the Doctrine of Equivalents was
correct errors in the patent process for people who didn't claim
everything they should have claimed. But under the new law there was a
provision to reissue patents, and so it was no longer needed.
The Appellate Court affirmed.
The Appellate Court found
that the Doctrine of Equivalents
still existed and the only issue was whether substantial differences existed
between Warner's process and Hilton's. That was a question of fact for a
jury to decide.
The US Supreme Court vacated
The US Supreme Court found
that Congress had not explicitly intended to get rid of the Doctrine
of Equivalents in §112 ¶6.
The Court found that when
applying the Doctrine of Equivalents,
you have to look at every limitation in the patent and compare it to the
infringer. Every single limitation must be either literally infringed or
infringed by equivalence.
That's known as the All
Elements Rule (aka the All
The Court found that the Doctrine
of Prosecution History Estoppel holds
that when a claim limitation is added in order get around prior
art, then a patentee could not use
the Doctrine of Equivalents
to extend the bounds of the claim they previously limited.
The Court found that if
Warner can prove the reason they chose 6.0 as their lower bound was not
to limit the patent, then infringement was still possible.
The Court remanded the case
to determine if Warner could explain their choice of pH limit.
Basically, if it turned
out that Warner chose 6.0 as their limit because they never figured out
how to make the process work at a lower pH, or some other good reason
like that, then they don't get the benefit of the Doctrine of
Equivalents. On the other hand, if
they just pulled that number out of thin air and could show that
Hilton's process was substantially the same as their process, then the Doctrine
of Equivalents would apply.
Warner limited is scope to
<9.0 to get around the prior art,
but that didn't require him to limit his scope to >6.0 to get around
the prior art.
Warner argued that patents
can be reissued to fix claims, and patents must meet a definiteness
requirement. Therefore there was no reason to keep the Doctrine of
Equivalents because Hilton should
have been more definite about the outer limits of their invention, and if
they didn't like their original limits, they could always go back and try
to reissue the patents. However, the Court felt that the existence of
these other methods to fix a patent claim didn't mean that the Doctrine
of Equivalents wasn't still another