T 0417/13 - Particle size difficulties

Key points

• In this opposition appeal, the opponent alleges that claim 1 violates Article 83 because of the feature that the claimed paint comprises "solid [PCV] extender particles having an average particle size in a range from 20 to 60 microns", because of the particle size feature.
• The Board considers it a notorious fact about particle size measurements that "variations of the order of several magnitudes in the values obtained as results of the various methods are possible." 
• " The description of the application provides only very limited information that could lead to the selection of a particular method of measurement.  [...] The person skilled in the art has thus to rely on his common general knowledge for the selection of an appropriate method of measurement. [...]   
• However in this case patentee a way out. "The [patentee] has submitted ISO standard 1624 relating to sieving as a method of measurement for determining the size of PVC particles. [] The common general knowledge [] thus points towards sieving as the method of choice for determining the particle size of PVC particles." 
• The Board also sees a difference with T 225/93: " In the case underlying decision T 225/93 the prior art contained no indication of which method of measurement was suitable in particular for the calcium carbonate particles under consideration []. Unlike the situation in T 225/93, in the present case it has been determined that one particular method of measurement would have been chosen by the skilled person." 

EPO T 0417/13 -  link

3. Particle size measurements

In the board's judgment, the following physical and mathematical facts about particle size measurements are notorious, i.e. they were so well established in the art at the priority date that they cannot reasonably be disputed. First, there are different methods of measurement that are based on different physical properties of the particles to be characterised. Second, to a large extent the type of average used (e.g. type of mathematical average or type of base (number average versus weight average)) influences the results obtained. Variations of the order of several magnitudes in the values obtained as results of the various methods are possible. Since this knowledge is notorious, there is no need to discuss documents (2) (including (2a)), (3) and (4), all filed in order to establish the above facts.

4. Sufficiency of disclosure

4.1 In order to establish insufficiency of disclosure, it must be shown that the patent (application) does not disclose the invention in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art. If it is argued that insufficiency arises from a lack of clarity, it is generally not sufficient to establish a lack of clarity of the claims in order to establish insufficiency of disclosure. Rather, it is necessary to show that the patent as a whole does not enable the skilled person, relying on the description and on his common general knowledge, to carry out the invention (cf. T 1811/13, Reasons 5.1, and T 646/13, Reasons 3.1).

4.2 In the present case the size of the PVC particles is an important feature of the invention. The patent in suit, see paragraph [0046], states that various improved performance properties of the paint composition, such as burnish and mar resistance, scrub resistance and washability, are due to the size of the PVC extender particles. Thus a skilled person needs to be capable of establishing which PVC particles have the appropriate size, as defined in the claims.

It has been discussed above, see point 3, that the results for the particle size may vary to a large extent depending on the method of measurement.

The description of the application provides only very limited information that could lead to the selection of a particular method of measurement. In paragraph [0028] it is merely disclosed that the PVC particles may be obtained by suspension polymerisation and are commercially available from a number of suppliers. One useful PVC extender particle is said to be Geon 217, obtainable from Poly One Corporation. The only further information can be found in the examples, which use either Geon 217, of an average particle size of about 35 microns, or CP 501, of an average particle size of about 45 microns.

The person skilled in the art has thus to rely on his common general knowledge for the selection of an appropriate method of measurement.

4.3 It thus has to be determined whether this common general knowledge would point the skilled person to a specific method of measurement for the determination of the particle size of PVC particles.

The appellant has submitted ISO standard 1624 (document (7)) relating to sieving as a method of measurement for determining the size of PVC particles. ISO, the International Organization for Standardization, is a worldwide federation of national standard-setting bodies that publishes international standards for certain procedures. A person skilled in the art would be aware of the existence of these standards and would consult them when looking for usual methods of measurement.

The common general knowledge, as represented by document (7), thus points towards sieving as the method of choice for determining the particle size of PVC particles.

4.4 The respondent has alleged that, even with sieving, different values of average particle size would result, depending on the measurement conditions, but it has provided no experimental proof. It is thus not known to what extent the parameters selected for performing sieving will influence the particle size values obtained by that method. There is no evidence on file to show that the possible variations in results will be such that particles having an average particle size in a range from 20 to 60 microns according to any allowable variation of the standard method of measurement would not allow the skilled person to carry out the invention.

The respondent has further argued that dry sieving is difficult to carry out for particle sizes below 38 microns. However, a person skilled in the art, being aware of document (7), would consider using wet sieving if difficulties arose with dry sieving.

Concerning the type of average and variations in results depending on the selection of a certain type of average, the respondent has made no submissions which relate to sieving. The passage cited in document (5), paragraph 2.4.1, discusses molecular weight determination and not particle size measurements.

In the case underlying decision T 225/93 the prior art contained no indication of which method of measurement was suitable in particular for the calcium carbonate particles under consideration (Reasons 2.2). Unlike the situation in T 225/93, in the present case it has been determined that one particular method of measurement would have been chosen by the skilled person.

Decision T 805/93 discusses methods and conditions of measurement for determination of viscosities, mainly within the context of Article 84 EPC. The argumentation turns on the need to select the reactive compounds in order to obtain a reaction product having the claimed but unclear viscosity, and finds a lack of sufficiency of disclosure. There is no discussion in T 805/93 of the common general knowledge of the skilled person concerning viscosity measurements. The situation is thus not directly comparable with the present case.

4.5 Summing up, it can be concluded that in the present case of PVC particles the skilled person would not have considered using any method of measurement, but would have chosen a method relying on sieving, such as a method according to ISO standard 1624. There is no evidence on file that different measurement conditions in such a method would have led to the selection of PVC particles that would have prevented the skilled person from carrying out the invention as defined in the claims.

4.6 The subject-matter of the main request and of auxiliary requests 1-3 is sufficiently disclosed.