T 143/06 – Clear & Close

Independent claim 1 of the main request read:

An uncoated nanocomposite dense sintered silicon carbonitride ceramic cutting tool, obtainable by cold pressing a spray-dried flowable granulate of a nanosized powder of α-Si3N4 and SiC, the mean particle size of α-Si3N4 and SiC being lower than 200 nm, containing an amount lower than 30% by weight of nanosized SiC particles, in the presence of an amount of from 3% to 6% of sintering aids Y2O3 and Al2O3 and of further additives consisting of polyethylene glycol with a molecular weight ranging of from 400 to 12000, by sintering the so obtained pressed products at a temperature of from 1800°C to 1900°C, for a time of from 0.5 to 2 hours and with an over-pressure of inert gas to a product having density close to the theoretical maximum and by machining the cutting tool from the so obtained sintered near net shape blank.

The Examining Division (ED) had found the expressions “close” and “near” to be unclear. The Board comes to a different conclusion:

Clarity of the claims (A 84)

[11] It has to be decided, whether the following features are sufficiently clear within the meaning of A 84, or not:

(i) a density “close to the theoretical maximum”;

(ii) “the sintered near net shape blank”.

[12] As to the first feature, the board notes that neither the claims nor the description contain an indication, how close the density is in respect to the theoretical maximum.

[12.1] According to the description, the sintered blanks are characterised by high densities […]. Such high densities are achieved by using the process for preparing the cutting tools set out in claims 1 and 7, respectively, particularly by cold pressing of the spray-dried flowable granulate of a nanosized powder of α-Si3N4 and SiC in the presence of Y2O3 and Al2O3 as sintering aids, followed by gaspressure assisted sintering […]. It has been found that the sintered blanks thus obtained have densities which are close to the theoretical maximum, which means that they contain little or no porosity […].

In the case of example 1, a value of 3.26 g/cm3 or “nearly 100 % of the theoretical full density” was achieved […]. Compared to the theoretical full density of 3.27 g/cm3, i.e. the theoretical density of a product having no porosity at all, this corresponds to about 99.7 % of the theoretical maximum […].

In example 2, nearly the identical result was obtained […], whereas in example 3, a density of “>98.5%”, i.e. at least 98.5 % of the theoretical maximum was found […].

[12.2] Ideally, the product of the sintering step is free of pores, so that a density of 100 % of the theoretical maximum is achieved. In practice, it will hardly be possible to reach the theoretical maximum. Minor deviations towards lower values will occur and may be tolerated, as long as the densities are “close” to the theoretical maximum. The examples 1 to 3 provide specific information on acceptable densities in terms of percents of the theoretical maximum, namely 99,7 % (examples 1 and 2) and > 98.5 % (example 3). In particular, the density of > 98.5 % in example 3 has to be regarded as representing a specific value, which is sufficiently close to the theoretical maximum of 100 %, to be qualified as acceptable.

In example 1, it is stated that after analysis and characterisation, the product was “found to be fully dense (nearly 100% of the theoretical full density) and pore free” […]. Thus, the density of the product is a functional feature of the process conditions and, as such, inextricably linked to these conditions. The density of the sintered product, which is obtained whenever the claimed process is carried out, is a property of said product, as opposed to the features of the process as such. In other words, it is a technical effect or a function of the process steps set out in claims 1 and 7, respectively.

Having regard to the specific densities obtained in examples 1 to 3, and in the absence of any evidence to the contrary, the board is of the opinion that it is justified to assume that, whenever the process features set out in claims 1 and 7 are put into practice, the resulting densities of the products will reach values of some 98.5 % or more, compared to the theoretical maximum. Such high values may be regarded without difficulty as being “close to” 100 %.

[12.3] In the board’s view it would not be appropriate to restrict the scope of the claims by defining a fixed numerical value of the minimum density, since the effect of the density on the mechanical properties of the sintered products is gradual.

In this respect, the examples 1 and 3 are informative: Whereas the product of example 1 with its density of about 99.7 % of the theoretical maximum gave rise to a hardness HV5 of 1785 ± 25 and a Palmqvist toughness of 7.0 ± 0.7 MPa m1/2, the somewhat reduced density of roughly 98.5 % of the theoretical maximum of the product of example 3 led to a hardness HV5 of 1552 ± 26 and a Palmqvist toughness of 6.5 ± 0.7 MPa m1/2 […]. Under these circumstances, the relative term “close to the theoretical maximum” can be considered as sufficiently clear in the context of the application read as a whole. Therefore no objection of lack of clarity arises under A 84.

[13] Another issue, which has to be examined, is whether the expression “the sintered near net shape blank” has a sufficiently clear meaning within the context of the present application, or not.

In this respect, the appellant referred to page 9, lines 3 to 7 of the description, where it is stated that in order to obtain a cost-effective manufacture of ceramic cutting tools, production of “near net shape items” is required.

What is meant by the term “near net shape” can be derived from the following explanation contained in the description:

“For the preparation of cutting tools meeting the dimensional specifications laid down in the standard ISO products, hard metal dies of appropriate geometry and dimensions are used such that the parts after sintering are of dimensions larger, by a controlled amount, than the required final tool dimensions in order to allow for machining to precise final dimensions” […].

[13.1] For practical reasons the amount of machining, which is required for bringing the sintered blanks into the final dimensions, is kept to a minimum in order to achieve an effective manufacture of the cutting tools, while avoiding unnecessary loss of material. Therefore the sintered blanks are only slightly oversized. This is illustrated by example 4, where special care was taken to adjust the size of the pressing die and the pressing pressure to the shrinkage characteristics of the powder during firing,

“such that slightly oversized cutting tool blanks were produced appropriate for the accurate diamond grinding of the standard tool geometry” […] (emphasis added by the board).

[13.2] Consequently, the term “near net shape” has to be construed to mean that the dimensions of the blanks are only slightly larger than the precise final dimensions of the cutting tools. Such a definition is in conformity with the recognised terminology in the technical field of ceramics.

It concurs also with relevant handbooks, for example the “Dictionary of Ceramic Science and Engineering” (H1), referred to by the appellant. There, the following definition of the term “near net shaping” is given: “Forming process designed to limit the amount of final grinding and polishing needed to meet specification” […] (emphasis added by the board).

[13.3] Having regard to the considerations set out above, it is clear that, although it is desirable to limit the amount of final machining, the degree of oversizing of the blanks may vary within wide ranges.

In the board’s view, it is acceptable to define the oversizing in relative terms such as “near net shape”, particularly because the degree of oversizing has no impact on the essential properties of the claimed cutting tools, namely the mechanical characteristics.

[13.4] For these reasons the board is satisfied that the feature “the sintered near net shape blank” is sufficiently clear within the context of the present application, so that no objection of lack of clarity arises under A 84.

[14] In the decision under appeal, the ED argued that the range of 50 to 200 nm for the particle size of the starting powder forms part of the essential features. Therefore, said range should have been included in the independent claims relating to the cutting tool and the process for its preparation. In this respect, the ED relied on a statement made by the applicant (now the appellant), according to which the present application teaches the preparation of an uncoated cutting tool material by using spray dried powder “obtained with raw materials based on silicon nitride - silicon carbide having a particle size distribution in the range of about 50-200 nm” […] (emphasis added by the board).

[14.1] The board notes that no corresponding statement is comprised in the application. In particular, nowhere in the application there is any disclosure of a lower limit of the particle size of 50 nm. According to claims 1 and 7, respectively, a “nanosized powder of α- Si3N4 and SiC, the mean particle size of α-Si3N4 and SiC being lower than 200 nm” (emphasis added by the board) is used in the spray-drying step.

[14.2] As far as the examples are concerned, it is indisputable that the treatment of the starting material in example 1 led to a nanosized powder having a mean particle size of α-Si3N4 and SiC lower than 200 nm, as required by claims 1 and 7, respectively […]. Nothing in example 1 or the remaining examples implies, however, that there was a lower limit of 50 nm of the particle size.

[14.3] It follows from the foregoing, that the statement made by the applicant in its letter […], according to which the silicon nitride and the silicon carbide have a particle size distribution in the range of “about 50-200 nm”, has to be regarded merely as an indication of a typical range of the distribution of the particle size. It cannot be derived from said statement, that the value of 50 nm represents the lower limit of the particle size of α-Si3N4 and SiC, let alone that this value is an essential feature of the claimed subject-matter.

[14.4] For these reasons the board is of the opinion that there is no need to include the feature of a range of 50 to 200 nm in the claims.

The board observes that, in any case, the specific range of 50 to 200 nm does not have a proper basis in the application as originally filed. Thus, its incorporation into the claims would contravene A 123(2).

[15] The board concludes that the set of amended claims 1 to 11 according to the main request, submitted together with the grounds of appeal, concurs with the requirements laid down in A 123(2) and A 84.

Boards also have generous days, huh?

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