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Parametric Definitions at the European Patent Office: Common Issues and How to Avoid Them

By Stephan Schultes, Senior Associate and Magnus Johnston, Partner

Chemical and materials related inventions lend themselves to being defined in terms of their physical structures and experimentally measurable properties. Inventions directed to porous membranes, for example, which are used to separate components of a mixture, can be readily characterized by the pore size and pore distribution of the membrane material. For other inventions, such as those employing bulk metallic glass materials, which have disordered atomic arrangement, a measurable property or combination of measurable properties such as yield strength, hardness and elasticity may be the most suitable way – and perhaps the only way – of defining the invention.

From a European patent law perspective, defining an invention in terms of such parameters in a patent application, particularly in the claims, merits careful consideration. A poorly defined parameter is at best likely to cause problems during examination of a patent application, and at worst could have potentially fatal consequences for the patent application. It is important to bear in mind in this regard that at its heart the grant of a patent is the grant of a monopoly, so it is right that patents should define the monopolized invention clearly.

What follows is a summary of issues that we see arise quite frequently in relation to parametrically defined inventions. Reference to some Board of Appeal case law of the European Patent Office is provided for the enthusiasts among us! But it is not necessary to read or consult these for the purpose of this article.

1. Common parameters – imprecise terminology

Commonly used parameters in the field of the invention are, on the face of it, clear. However, the use of imprecise terminology for such parameters can give rise to objections. To take an example, the “roughness” of a surface may be represented by the parameters Rz(DIN), R(max), Rz(ISO), Ry, R3z and R3zmax (among others). These parameters are all associated with the peak-to-valley heights of a surface profile, but they differ from each other by the way in which they are derived from the measured data. This means that, for the same surface profile, these parameters may have very different values.[i] As another example, the “average particle size” of a mixture of particles may encompass several different parameters, including volume surface mean diameter, arithmetic mean diameter, mass mean diameter, and volume mean diameter. For a material consisting of uniform particles, the values of these mean diameters will be the same so that, in this context, the term “average particle size” is reasonably clear. For a material containing particles of various sizes, however, the values of these mean diameters may differ widely from one another, and in this context the term “average particle size” gives rise to ambiguity.[ii] It is therefore important to ensure that the terminology used for the parameter is precise.

Definitions in standards issued by organizations such as the International Union of Pure and Applied Chemistry (IUPAC), the International Organization for Standardization (ISO) and the American Society for Testing and Materials (ASTM) can be used to more precisely define parameters. But even then it should be checked that the definition in the standard is unambiguous and preferably the date of the standard included in the patent application, particularly if the definition in the standard or the method by which it is to be measured change over time.

2. Common parameters – imprecisely defined measurement methods

It is good practice to include a description of the measurement device and method for determining the parameter in the patent application. This includes not only the general measurement approach, but also the specific conditions used for the measurements. This is particularly so if the specific conditions could affect the outcome of the measurement.

For example, if the crystallinity of a material can be determined by different methods (or using the same method but under different conditions), and these do not lead to comparable results, then omitting to describe the method and conditions under which the crystallinity was obtained may be fatal to the application.[iii]

Furthermore, it is important that the measurement method produces consistent values. For example, determining the “mean aspect ratio” from fifty randomly selected particles in a sample containing thousands of particles may produce a range of different values depending on which particles are selected. Problems can therefore arise if no details are provided of how this is achieved.[iv] As one might expect, the amount of detail required will be greater in cases where a parameter cannot be measured using a simple or readily available, or conventionally used apparatus in the technical field of the invention.[v]

As in the case of parameter terminology, standards can be useful to define measurement devices and methods. But it should be checked that the parameter used in the application is consistent with the standard, and that any variables that are not defined in the standard are taken account of in the application. For example, a parameter that defines a thermoplastic polymer composition in terms of a thermal conductivity as measured according to an identified standard, but neither the standard nor the application specifies the temperature at which the thermal conductivity is to be measured, may well be held to lack clarity. [vi]

3. “Unusual” parameters

Particular care needs to be taken when defining materials using parameters that are not commonly used in the field of the invention. The use of these so-called “unusual” parameters attracts additional requirements to those set out above for common parameters. In the case where an unusual parameter defines a measured property for which a recognized parameter exists in the technical field of the invention, then consideration should be given to describe in the application how the unusual parameter relates to the more commonly used parameter. The application must include details of an accessible apparatus for measuring the parameter, particularly if it is a proprietary apparatus. In the case that the unusual parameter defines a property that has not previously been measured in the field of the invention, then the application should clearly define the parameter and include a description of the measurement method.

4. Insufficiently defined parameters and measurement methods

Sometimes an ambiguity in a patent claim may lead to an insufficiency problem (i.e., a finding that the patent application lacks sufficient detail to enable the invention to be reproduced by a third party without an undue burden). Parameters and their measurement methods that are insufficiently defined raise issues that are closely related to and often overlap with those described above.[vii] However, they potentially pose greater risk, firstly because a finding of insufficiency may be incurable, and secondly because lack of sufficiency objections can be raised not only during examination of the patent application but also after a patent is granted, for example, in post-grant opposition or invalidity proceedings.

Typical objections arise where the level of variability associated with a given parameter is such that the invention cannot be reproduced. For example, the “half crystallization time” of a resin layer may be strongly influenced by the crystallisation temperature and the heating rate, leading to highly variable values of the half crystallization time. Accordingly, if information about the crystallisation temperature and the heating rate is not provided in the patent application, then the resin layer cannot be reproduced and the invention is consider to be insufficiently disclosed.[viii]

Even when parameters and their measurement methods are properly defined, issues relating to sufficiency can still arise, for example, if the application does not describe how to select suitable materials to ensure that the required properties are fulfilled, or if the invention cannot be reproduced over the entire range of claimed parameter values. For example, a distilled fuel oil defined in terms of wax crystals having “an average particle size less than 4000 nm” may give rise to lack of sufficiency objections if the application fails to describe how to obtain fuel oils of the claimed type containing wax crystals of an average particle size of less than 1000 nm.[ix]

5. Lack of experimental data

It follows from the preceding discussion that a patent application should provide enough experimental data to enable the invention to be reproduced. Some leeway is granted for submitting experimental data after a patent application has been filed, for example experimental data to confirm that the invention does indeed work across the claim scope to address an inventive step objection, or experimental data that compares the claimed process with related performance of the prior art. However, considerably less leeway is given if the problem identified is one of insufficiency. In some very limited instances, post-filed experimental data may be used to address a problem of insufficiency, but only if it supports and confirms what is already disclosed and taught in the application.

Despite these issues, the good news is that many hundreds of patents containing parameters are granted each year, and it is completely acceptable to use clearly defined parameters to define an invention. But particular care and attention is required. Here is a simple, non-exhaustive, check list covering a number of the issues to look out for and consider when drafting a patent application using parameters.

  • Can the invention be defined with and without using parameters?
    • If so, consider including both definitions
  • Is the parameter a common parameter in the field of the invention?
    • Double check with the inventors, check text-books, and the academic and patent literature
    • Is there a recognised standard, e.g., IUPAC, ISO, ASTM?
    • Double check the standard! Is there more than one version? Is there more than one way of measuring the parameter and could that affect the result?
  • Is the parameter an unusual parameter?
    • Extreme care should be taken!
      • Full details of the apparatus and method should be included in the patent application.
      • How readily can the unusual parameter be compared to a parameter more commonly used in the field of the invention?
      • Triple check that all conditions essential for determining the parameter are included in the patent application
  • Is the experimental data consistent with the parameters used to define the invention?
    • Check that the same methods and parameters are used to obtain and describe the experimental data
  • Is the extent of experimental data sufficient to support the claim substantially across its scope?

The Boards of Appeal decisions database can be found here.

[i] T 702/09

[ii] T 2086/11

[iii] T 0908/04

[iv] T 2086/11

[v] T 1352/07

[vi] T 1252/08

[vii] T 0061/14

[viii] T 1657/15

[ix] T 409/91

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