In this decision the Board examined the terms used in claim 19 of the patent as granted, which read:
19. A metal cyanide catalyst in the form of particles having an average particle size, as determined by transmission electron spectroscopy, of from about 5 to about 500 nm, prior to contact with an alkylene oxide.
 The contested feature of Claim 19 (“average particle size, as determined by transmission electron spectroscopy, of from about 5 to about 500 nm”) is made up of the following items of definition:
(a) (what) average particle size;
(b) (determined how) by transmission electron microscopy (TEM); and
(c) (expressed how) about 5 to about 500 nm.
[7.1] As regards the first item, it comprises two notions, “average” and “size”.
[7.1.1] The notion “size” is based on the assumption that a single dimensional property is indicative of the particle size. However, particles are three-dimensional objects, for which at least three parameters (length, breadth and height) are required to provide a complete description. The measurement of some one-dimensional property of a particle and the reference to a sphere in order to derive one unique number, namely of the sphere having the same response (diameter, cross-sectional area, volume, weight, sedimentation rate, etc.) as the particle under examination, is known as “equivalent sphere approximation”. In respect of this notion, Claim 19 does not specify which size is meant (larger/smaller dimension of the particle, diameter of a sphere having the same surface, cross-sectional area or volume, etc.).
[7.1.2] As to the notion “average” (mean), it is not in dispute that transmission electron microscopy (TEM) generates a two-dimensional image of the particles contained in the sample, wherefrom the particle are characterized. On this image, a number of sizes can be measured, such as maximum or minimum diameter of the particle, which are then summed and divided by the number of particles, to obtain a number-length mean. It is also possible to mathematically convert the diameters measured to obtain a volume or mass mean, whereby however the conversion increases the error of the measurement. As regards the “average”, Claim 19 does not specify what is meant (number-, volume-average, etc.). So it encompasses any of the common averages obtained from TEM.
[7.2] As to the second item of information, Claim 19 does not specify how the method of measurement, i.e. TEM, is actually carried out, e.g. as regards sampling, determination, measurement, treatment of data, etc.
[7.3] As regards the third item of information, it merely quantifies the concept of average particle size by a nanometric range. Since no statistical deviation is mentioned, the actual distribution of the particle sizes is thereby not defined.
[7.4] It follows from the foregoing that the definition of Claim 19, in particular the “average particle size”, is not as clear as possible. In this respect, the present decision is in line with decision T 1819/07 [3.5]. Thus, Claim 19 is to be construed.
The construed subject-matter of Claim 19
 Claim 19 concerns a metal cyanide catalyst in the form of particles having an average particle size, as determined by TEM, of from about 5 to about 500 nm, prior to contact with an alkylene oxide.
[8.1] In relation to the general process of manufacture, the patent in suit mentions that “the DMC catalyst complex can be prepared at such small particle sizes by precipitating it in the dispersed aqueous phase of a water-in-oil emulsion” […] and that “conditions are selected such that the aqueous phase forms droplets of about 500 nm or smaller in diameter” (emphasis added) […]. Since the particles are formed within those droplets, their maximum size (diameter) also lies within the upper limit of 500 nm. Hence, the feature “in the form of particles having an average particle size” is construed as implying that all particles have such an average size.
[8.2] For the range of 5 to 500 nanometres, as defined in Claim 19, the patent in suit does not generally define what average and what size are meant.
[8.3] Only in relation to the description of preferred embodiments does the patent in suit mention a volume average particle size, as follows:
(a) “The particles preferably have a volume average particle size from about 10 nanometres, such as from 40 nanometres, to 300 nanometres, more preferably 250 nanometres, especially to 200 nanometres, most preferably to 150 nanometres” […].
(b) “This catalyst has a volume average particle size of about 40 nanometres” […].
No details of how the volume average particle sizes have been computed from the measured values is disclosed.
[8.4] It follows from the foregoing that:
(a) The interpretation invoked by the appellants (the objected feature is not suitable to impart any limitation, it should not be considered) cannot be retained, as it disregards the whole disclosure of the patent (Case law, II.B.5.1).
(b) The interpretation invoked by the respondents (the objected feature concerns a volume average particle size) cannot be accepted either. The limitation “volume average particle size” appears in the description only in relation to preferred embodiments. So it cannot be read into Claim 1 also for the generic range of 5 to 500 nm (Case law, II.B.5.3.4).
[8.5] Hence, the average particle size defined in Claim 19 encompasses particles having any size ranging from 5 to 500 nm measured or computed and averaged from distributions commonly obtained with TEM equipment.
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