Claim Construction III: Amendment of Patent Claims under Section 58

A decision was delivered by the Delhi High Court in September on amendment of patent claims in a case between AGC Flat Glass (Plaintiff/Patentee) and Anand Mahajan and Ors (Defendants). This is one of those rare instances where claim construction principles have been elucidated upon by an Indian Court and SpicyIP thanks Kamakhya for bringing this decision to our notice.

This decision comes out of an interim application made by the plaintiff to amend the specification of its patent during the pendency of a suit for infringement of its patent. The plaintiff was granted a patent for a mirror without a copper layer in its coating and without lead in the protection paint, besides a process for producing the same. I would like to digress here before I proceed with the case.

If product patents prevent third parties from manufacturing the product by any process, why do we still find patents protecting the product and the process (with the patent not being a product-by-process patent)? Is it to ensure that even if the product stands invalidated, the process may still survive? If yes, atleast in the instant case there seems to be nothing novel about the process alone which is capable of standing on its own merits if the product were to be invalidated.

Anyways, moving to the judgment, the principal claim of the plaintiff reads thus:
1) A Mirror with no copper layer comprising:
i) a vitreous substance,
ii) at least one material selected from the group consisting of bismuth, chromium, gold, indium, nickel, palladium, platinum, rhodium, ruthenium, titanium, vanadium and zinc at the surface of the said substrate,
iii) a silver coating layer on the surface of the said substrate, said silver layer optionally comprising at least one material selected from the group consisting of tin, chromium, vanadium, titanium, iron, indium, copper, and aluminium present at the surface of the silver coating layer and/or traces of silane; and
iv) at least one paint layer covering said silver coating layer.

To this claim, the plaintiff sought to add the words “a sensitizing material, typically tin” in clause ii of the claim. This application of the plaintiff under Section 58 of the Patents Act to amend the patent was opposed by the defendants on the grounds:
1. that the amendment was sought by the plaintiff 12 years after grant
2. that the unamended patent had been enforced against competitors in other infringement proceedings where the plaintiff did not feel the need to amend his patent
3. and that the amendment would alter the nature of the patented invention itself

Now, let’s move to the law on amendment of patents. When can a patent be amended? Section 58 of the Act states that the patent can be amended in a proceeding for revocation of the patent before the IPAB or the High Court (Section 57 too allows for amendment of a patent, but in a different situation).

To what extent can a patent be amended under Section 58? What circumscribes the extent and nature of the amendment? The amendment under the Section is subject to the conditions set out in Section 59. The amendment has to be in the nature of a correction, disclaimer or explanation. It cannot bring in new subject-matter or widen the scope of claims. So this indirectly means delimitation of claims is possible to the extent that amended limited claim lies within the scope of the unamended version i.e. if multiple combinations of elements have been claimed originally, the amendment can have the effect of claiming only one of those combinations and therefore disclaiming the rest. This follows as a corollary from Section 59 which allows an amendment that is in the nature of a disclaimer.

But is such an amendment allowable in all situations? The rationale behind bar on widening the scope of claims is apparent, but can there be instances where the patentee may not be allowed to limit the scope of his claims further, even if the amendment is a disclaimer? The answer, according to the Court, is in the affirmative; this typically occurs when the patentee has proactively enforced his patent in its wider version against competitors and seeks to amend it all of a sudden when the broad scope is challenged.

Is there a public interest factor at play when an amendment is sought? Yes, if the result of the amendment is a clear specification, the sooner such amendment is undertaken the better it is for practitioners of the art and the public- the recipients in the quid pro quo equation. However, if the amendment is undertaken to survive an invalidation bid and that too after a considerable period post grant, then public interest could require that the amendment be refused.

On this point, the Court referred to UK decisions and endorsed the slotting of such amendments into 2 categories: the first one is a situation where the patentee has been apprised of prior art by an opponent and amendment is undertaken to overcome the prior art; the second is a situation where the patentee himself has been aware of the prior art but has never taken steps to amend the patent on his own. UK Courts have held the second situation as being inexcusable, where the patentee must not be allowed to amend his patent.

Since allowable amendments have to be in the nature of a correction, disclaimer or explanation, the Court in the instant case had to check if the amendment sought by the plaintiff fell within any of these categories. The defendants said the amendment would not fall under any of the aforesaid categories since insertion of the words “a sensitizing material, typically tin” would alter the very nature of the subject-matter sought to be protected by the patent.

The Court observed that the patent document had to be read as a whole. Since the written description of the plaintiff clearly mentioned the presence of a sensitizing process as one of the three stages in manufacture of mirrors, the insertion sought by the plaintiff would amount to a mere explanation with no change in scope of claims. Also, since tin is ubiquitously used as sensitizing material, it is not the focal point of the patent and its insertion does not affect the inventive step or the nature of the invention claimed. Therefore, the amendment was held as permissible.

This judgment is reflective of a welcome development in Indian patent litigation- clear application of claim construction principles. We hope to see more of these in the future.

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