T 0732/92 12-07-1994

1. The appeal is admissible.

2. Main request

2.1. Nearest prior art document is document (D1) and not document (D2) since in the latter document the roller table is flat and does not contain an annular groove and since the rollers are not convexly shaped. Appellant's argument that Claim 1 is delimited over document (D2) is therefore not supported by the facts.

2.2. Claim 1 is completely delimited over document (D1) so that the roller mill claimed is novel, Article 54 EPC.

2.3. Starting from document (D1) the claimed invention seeks to improve the capability to retain material in the mill for a relatively long time, see EP-B1-0 208 033, Column 1, lines 23 to 27.

2.4. This problem is solved by the provision of an upstanding dam that extends radially inward at its upper position. The effect of this overhanging dam can be seen in the fact that the outward passage is obstructed so that the material to be crushed is kept within the clearance space for a long time.

2.5. The assessment of the question of inventive step leads to the following result:

2.5.1. From document (D3) which discloses a ball mill it is known that for reasons of good fine milling the material to be crushed has to be retained for a sufficient period of time within the mill. To achieve this a dam or a bulge, see reference "h" in Figure 1 thereof, is provided which has a height "h" and which is oriented radially inwardly, namely in a direction against the centrifugal forces acting on the particles to be ground. Background of this teaching of document (D3) is the attempt to obstruct the passage outwardly, see Figures 1, 2 and 4 as well as Claim 2 and page 2, paragraph 4 ("Damit nun ... nicht sofort verlassen kann ... der das Mahlgut zurückstaut...") of document (D3).

2.5.2. Following the principles developed in the decision T 176/84, published in OJ EPO 1986, 50, a technical field to be considered when assessing the issue of inventive step is a technical field in which identical or similar problems exist in respect of the problem underlying the claimed inventive.

2.5.3. As set out in paragraph 2.5.1 above document (D3) literally discloses the technical problem to be solved by the present patent specification so that document (D3) originates from a related technical field which has to be considered by a skilled person confronted with the problem of how in a roller mill the material can be retained for a relatively long time so that sufficient crushing of the material can take place.

2.5.4. Due to the fact that document(D3) addresses the problem of the patent in suit and also a solution in the meaning of Claim 1 the combination of documents (D1) as starting point of the invention and document (D3) would be envisaged by a skilled person.

2.5.5. In document (D3) a dam or bulge is taught which is of the height "h" and which acts as a means for obstructing the outward path of the mill. The centrifugal forces acting in a direction radially outwardly the known dam, see Figure 1, 2 and 4 of document (D3), also extends "radially inwardly" as claimed in the characterising clause of Claim 1 and thereby overhangs "to obstruct the passage outward from said clearance space of the material being crushed".

2.5.6. The above teaching can be derived from document (D3) without knowing the claimed invention so that the reproach of an ex post facto analysis (hindsight) expressed by Appellant's representative is not justified.

2.5.7. Since Claim 1 is not restricted to specific means for pressure loading the milling tools a convincing argument cannot be based in this difference between the subject- matter of Claim 1 and the teachings of documents (D3) and (D2).

2.5.8. The Board is therefore of the opinion that in contrast to the chain of arguments raised by the Appellant a skilled person could and would combine the teachings of documents (D1) and (D3) to immediately arrive at the subject-matter of Claim 1, since the effect of this combination was to be foreseen, namely an increase of the residence time of the material to be crushed in the mill.

2.5.9. Under these circumstances the subject-matter of Claim 1 cannot be seen as inventive so that granted Claim 1 is not valid, Article 56 EPC, and cannot justify maintaining the European patent No. 0 208 033 as granted. The main request consequently had to be rejected in the oral proceedings before the Board.

2.5.10. Appellant's argument that the claimed solution of the problem underlying the invention cannot be found in the prior art before the filing day of EP-B1-0 208 033 (history argument) and that the claimed roller mill is therefore nonobvious cannot be accepted since it is a novelty argument. Novelty is, however, not disputed.

Further arguments of the Appellant are also contradictory to the principles of T 176/84 and not convincing, namely the arguments of hindsight, non- compatibility of teachings of documents (D1) and (D3), unforeseeable technical effect, prior solutions of the problem of the claimed invention pointing away from the subject-matter of Claim 1, the age of document (D3), difference of crushing tools concerning Claim 1 and document (D3) as well as any differences in operation essentially when starting and stopping the crushing mill according to Claim 1 and document (D3) and the paths along which the crushed material finally leaves the mill. Not convincing to the Board was also Appellant's argument that an overhang in document (D3) would give rise to a conflict with the crushing tools (balls) since Figure 1, 2 and 4 thereof clearly demonstrate that the outward path of the crushed material is obstructed without any conflict with the balls as the crushing means.

3. Auxiliary request:

3.1. Claim 1 thereof is based on granted Claim 1 and on features defining in detail the clearance space between the rollers and the roller table, namely as a portion which is narrowing in an outward direction and as a portion of constant width.

3.2. Novelty was not under discussion in this respect so that the crucial question whether no not Claim 1 is patentable is that of inventive step.

3.3. The Board has come to the conclusion that the subject- matter of Claim 1 is based on an inventive step within the meaning of Article 56 EPC.

3.3.1. Claim 1 solves the problem of how to improve the possibility of retaining the material to be crushed sufficiently long in the roller mill.

3.3.2. Apart from a dam upstanding on the outer periphery of the groove provided in the table of the mill Claim 1 defines the clearance space as a two-part-stage, namely conically in an outward direction and of constant width thereafter.

3.3.3. It is obvious that the upstanding dam and the clearance space of constant width serve one and the same purpose, namely to enhance the residence time of the material to be crushed in the mill. The two-part clearance space in addition offers the possibility to choose the areas of coarse and of fine milling since the former is carried out in the narrowing clearance space and since the latter is carried out in the space of constant width. The dam in combination with the claimed clearance space thus contribute to the milling effect and make the mill versatile for a multitude of materials to be crushed.

3.3.4. In contrast to Respondent's findings the teaching of Claim 1 of the auxiliary request is more than the exercise of the knowledge of a skilled person.

3.3.5. There is no prior art document available which discloses an overhanging dam in a roller mill as claimed and there is also no prior art document available which in addition discloses the clearance space as claimed.

3.3.6. Document (D1) does not offer a narrowing clearance space and a clearance space of constant width since the radii indicated in Figure 5 thereof clearly demonstrate that no constant width is realised. Only by inadmissible hindsight does document (D1) teach a two-part clearance space as claimed.

3.3.7. Document (D2) is completely irrelevant in this context since not all features of the preamble of Claim 1 are realised there, see flat roller table and rollers for instance.

3.3.8. Document (D3) is a relevant document in combination with Claim 1 of the main request but not in combination with Claim 1 of the auxiliary request since in this context the milling tool of Claim 1, namely a roller, is of importance. The gap between these rollers and the roller table is specifically designed in two stages, one for the coarse milling and the other for the final fine milling, see EP-B1- 0 208 033 column 2 lines 37 to 50, and from document (D3) no information can be derived in this context let alone a combinatory effect achieved by a two-part clearance space as claimed and an overhanging dam.

3.3.9. Document (D6), see Figure 1 and 4, is very similar to document (D2) and therefore also irrelevant since the roller table and the rollers are not provided with an annular groove or a convex outer periphery.

3.3.10. Document (D7), see Figure 12 and 14(2), does at least not disclose a clearance space of constant width so that its contribution to the solution of the problem of how to enhance the residence time of the material to be crushed in the mill is not to be seen.

3.3.11. Document (D8) on the other hand also teaches away from the subject-matter of Claim 1 since its page 1, last two lines and single figure make it clear that no entry clearance space is foreseen but only a clearance space of uniform width. It is hindsight when the Respondent argues that the existence of a constant width clearance space leads to the claimed invention according to Claim 1.

3.3.12. Summarising the above arguments the Board is convinced that the teaching of Claim 1 is not rendered obvious by documents (D1) to (D3) and (D6) to (D8) even if the normal knowledge of a skilled person is duly considered.

3.3.13. Respondent's argument that the narrowing clearance space has only to safeguard the free entrance of the material to be crushed is not backed up by the facts since in this part of the clearance space coarse milling is already carried out.

Providing therefore a two-stage clearance space as claimed enables a skilled person to choose a balance between coarse and final fine milling depending on circumstances whereby the existence of a positive or negative slip between the rollers and the roller table can be clearly used to achieve an optimum milling result in both parts of the clearance space and this in combination with an overhanging dam which in itself is a means for influencing the milling result, see above remarks in combination with Claim 1 of the main request.

4. Claim 1 of the auxiliary request is as a consequence of the foregoing observations valid so that the patent can be maintained in amended form as submitted in oral proceedings.