An application for a patent of addition must disclose an improvement in, or modification of, the “main invention” applied for or granted in the parent specification ( (1956) RPC 121 and (1957) RPC 143). The “main invention” must be the invention claimed in the parent specification, as distinct from an invention merely disclosed in it (sec 81(1)(a);see also [2018] APO 26 at [60]-[62]). The mere claiming of the parent invention from a different aspect, or the claiming of subject matter described in the earlier specification, but not claimed therein, does not constitute an improvement or modification ().

Furthermore, a patent of addition cannot claim matter that was disclosed in the parent specification, as this would give rise to an objection of lack of novelty in the light of the parent. This applies even if the claims also encompass an improvement in, or modification of, what was disclosed in the parent (Welwyn Application supra). Note, however, that an objection of lack of inventive step with respect to the parent is not applicable (sec 25; see also ‘Failure to Meet Requirements for “Improvement” or “Modification”’ below and 2.19.6 Differentiation From the Parent).

A patent of addition cannot validly claim something that was implicit in the parent (Aluminium Co of America's Application (1971) 41 AOJP 4259). Guidance from Baracuda (Pty) Ltd v Chauvier [1987] APO 3 suggests that a patent of addition cannot comprise a mere design optimisation of the main invention, while Fisons Ltd's Application [1983] APO 40 indicates that a patent of addition must disclose and claim matter substantially different from what was claimed in the parent. However, those decisions were peculiar to the ground of prior claiming under the 1952 Patents Act and are not to be taken as being indicative of the degree to which the subject matter of the patent of addition must be different from the main invention. Rather, for the purposes of the 1990 Act, the wording from Baracuda and Fisons supra is to be understood as synonymous with the requirement that the patent of addition be novel over the parent; see SNF (Australia) Pty Ltd v BASF Australia Ltd supra at [70]-[74].

Where a claim of the application for a patent of addition is directed to matter disclosed in the parent specification, either in the body of that specification or in the claims, an objection that matter which was actually part of the parent specification cannot be an improvement in, or modification of, the parent invention may apply. The only exception to this is the situation envisaged in 2.19.1.11 May be Both an Additional and Divisional.

Similar considerations apply where a claim of an application for a patent of addition is directed to matter which is inherent in the parent specification (see Aluminium Company of America's Application (1971) AOJP 4259).

Determination of “Improvement” and “Modification”

Elliott Brothers Application

The terms "improvement" and "modification" have been broadly judicially defined in relation to patents of addition in Elliott Brothers (London) Ltd.’s Application (1967) RPC 1. Thus, there is authority as to the extent or nature of the relationship required between the subject matter of the additional and the parent.

In relation to this case, Lloyd-Jacob J observed that:

“A modification is an alteration which does not involve a radical transformation and an improvement is a variation, whether by addition, omission or alteration, to secure a better performance, whilst retaining some characteristic part.”

The case was concerned with two patent applications claiming instruments for indicating a rate of turn in an aircraft, the claimed instruments having a number of features in common, but differing in the way in which the amount of movement of a certain component of the instrument was measured. During examination, it became apparent that all of the features that were common between the two instruments were also present in prior art instruments, and consequently the only features which could possibly be novel and inventive were the movement sensing mechanisms.

Lloyd-Jacob J considered that the nature of the invention of the parent (i.e. the "main invention") could not be properly understood without reference to the prior art, and when it was so understood, the second application, which the applicants wished to be a patent of addition of the first, had removed all of the novel features introduced by the first. Lloyd-Jacob J referred to this as "the most complete form of radical transformation possible" and held that the second application could not become a patent of addition to the first (Elliott Brothers (London) Ltd's Application supra at 5).

Therefore, the proper basis for determining if an application for a patent of addition is an improvement in, or modification of, the main invention is a comparison between the novel contribution which each claim makes over the prior art.

A generalisation of the facts of the Elliott Brothers case would be as follows:

Consider the “main invention”, i.e. the claimed invention, to comprise features A+B+C, where feature C represents the novel contribution. An application for a patent of addition is filed in respect of A+B+C+D. This application retains all of the features of the “main invention” and the addition of feature D makes this an improvement in the “main invention”. On the other hand, an application for a patent of addition for A+B+D, where feature D represents the novel contribution, leads to a different outcome. The novel feature C of the “main invention” has been removed, and consequently this is a new invention, rather than a modification of the “main invention”. D may also be considered a radical transformation or variation of C. The invention A+B+D is therefore more than an improvement in, or modification of, the main invention and is not suitable subject matter for a patent of addition.

Alternatively, an application for a patent of addition consists of claims directed to features A+B+C*, where feature C* represents the novel contribution. Provided C* is only a minor transformation or variation of feature C of the parent specification, then the invention A+B+C* is an improvement in, or modification of, the “main invention” and thus meets the requirements for a patent of addition. Of course, it must be determined on the facts of the case whether C* represents a minor transformation of feature C.

Although the above examples have dissected the claimed integers into parts, the words "modification" and "improvement" relate to the invention; they do not necessarily relate to individual integers of the claims. Thus, there may be one modification or one improvement of an invention, even though more than one integer has been changed.

Subsection 40(4) “Test”

It should be noted that sec 81(1) does not require that a patent of addition should be more limited in scope than the parent. An applicant or a patentee may use the provisions of the section to effectively broaden the parent. Thus, the patent of addition could be made broader than the parent by omission of a feature, the omission then constituting the modification (see Hughes Tool Company v. Ingersoll-Rand Company Limited (1977) FSR 406). Usually, if a claim could have been properly included in a parent specification without giving rise to an objection of lack of unity, that claim may be deemed to be for an improvement or modification.

Thus, if the claims of the complete specification are such that, had they been present in the parent complete specification, no breach of sec 40(4) would have occurred, then the application can proceed as an additional application. This means that the feature making the technical contribution over the prior art cannot be said to be defining a new invention. However, it should be noted that this "test" is for general guidance only, as there may be cases which, although not strictly falling within this rule, may properly invoke Chapter 7. This test is also unsuitable where a claim is debarred on the grounds specified in the cases referred to above (Georgia Kaolin Co. Ltd.'s Application supra, Welwyn Electrical Laboratories Ltd.'s Application supra, Aluminium Company of America's Application supra and Elliott Brothers (London) Ltd.'s Application supra).

It should also be noted that whilst certain claims may be properly included in an application for a patent of addition, they do not necessarily fit into one such application, i.e. sec 40(4) is fully applicable. Each application for a patent of addition may be made in respect of one improvement or one modification only. Different improvements or modifications may constitute different inventions and should, if that is the case, be made the subject of separate applications for patents of addition; the main invention cannot serve as a common element of novelty. However, where the invention which is the subject of the application for a patent of addition involves several changed integers (or steps), there is no objection if all those changed integers (or steps) are included in one claim, since all those changed integers (or steps) may constitute one modification of the invention. Examiners should clearly distinguish between improvements or modifications of the invention and improvements or modifications of individual elements of a claim.

In cases where the co-existence of independent claims in an application for a patent of addition would be objectionable under sec 40(4), the provision of alternative forms in the one claim is equally objectionable.

Note: The suitability of an application to proceed as an application for a patent of addition should be determined at the time when the specification of the application for the patent of addition is otherwise in order for acceptance (P. and S.'s Application (1952) 69 RPC 249). Any opinion on this matter expressed at an earlier date must be regarded as tentative only and subject to review at any time before acceptance. If the scope of the invention claimed in the parent specification is altered before acceptance, the invention of the application for a patent of addition must be capable of being considered as an improvement in, or modification of, the altered invention of the parent specification (see also 2.19.4 Amendments).

Failure to Meet Requirements for “Improvement” or “Modification”

If an application for a patent of addition does not meet the requirements of Chapter 7 because it is not an improvement in, or modification of, the main invention, examiners should object accordingly. Where the application for the patent of addition claims matter disclosed in the parent specification, a novelty objection in light of the parent may also apply (as discussed in “General Considerations” above).

In this situation, the applicant may decide to amend the patent request for the patent of addition so as to no longer invoke Chapter 7 (see 2.19.2.1 Examination Practice).