T 0068/93 (Phosphorodithioates/LUBRIZOL) 24-01-1995

1. The appeal is admissible.

Main request

2. Amendments

The Board is satisfied that the amended claims according to this request meet the requirements of Article 123(2) and (3) EPC.

2.1. The only feature objected to in respect of Article 123(2) EPC was the indication in Claim 1 that the amount of the active sulphur (component (C)) to be reacted is "more than 300 ppm as measured by IP-155". It is therefore sufficient to deal only with this issue in detail. In the Board's judgement the above mentioned feature follows directly and unambiguously from page 17, lines 8 to 12 of the description as filed (page 9, lines 10 to 13 of the granted patent). There it is stated that "By heating the combination of compounds (A) (B) and (C), substantially all of component (C) reacts with or is consumed ... and the resulting compositions are characterized by relatively low (for example, less than 300 parts per million as measured by IP-155) levels of active sulfur". This passage unambiguously implies - as the only technically meaningful consequence - that the starting mixture had to comprise more than 300 ppm of active sulphur, in each case measured according to IP-155.

2.2. The Board cannot accept the Respondent's objection that IP-155 was not the only method disclosed in the patent in suit for the determination of the active sulphur content and that, therefore, its incorporation into the present Claim 1 was arbitrary. While it is true that ASTM D 1662 was mentioned as a further method on page 15, lines 10 to 11 (page 8, lines 17 to 18 of the patent in suit), IP-155 is the (only) method expressly disclosed together with the said 300 ppm limit. Moreover, only the latter method was used in the examples whenever the amount of active sulphur was directly measured (see e.g. Examples 5 to 8). The Board concludes therefore, that this amendment does not extend the subject-matter of the patent beyond the content of the original application.

2.3. Neither is the Respondent's argument convincing that the gist of the invention was changed by incorporating into Claim 1 the feature of "more than 300 ppm" of active sulphur in the starting material, as the original disclosure did not contain any hint that the skilled person had to pay attention to the active sulphur content of the starting material. As already explained, the original disclosure contained an implicit teaching that the starting material had to comprise more than 300 ppm of active sulphur, as only this made a process technically meaningful which was aiming at a reduction of the sulphur content below this value.

2.4. This conclusion is not in contradiction with the finding of this Board in the decision T 526/92, where the incorporation of a particular parameter into the claims was not allowed, since the specification - apart from the examples - was completely silent on the parameter concerned, and the importance of this parameter to the alleged invention was not deducible from any part of the application documents (T 526/92, Nos. 5.1 and 5.3.1 to 5.3.6, not published in the OJ EPO). In contrast, the reduction of the active sulphur content is the very issue of the patent in suit (see e.g. page 2, lines 25 to 28; page 2, lines 7 to 11 as originally filed).

3. Novelty

3.1. Claim 1

3.1.1. Document (4) discloses a

"mixed metal salt of

(A) at least one acid of the formula

R1O

\

PSSH

/

R2O

wherein each of R1 and R2 is a hydrocarbon-based radical, and

(B) at least one carboxylic acid having the formula R3COOH which contains from about 5 to about 20 carbon atoms and wherein R3 is an aliphatic or alicyclic hydrocarbon-based radical; the ratio of equivalents of A and B being in between 2.5 : 1 and about 4.5 : 1; up to about 2 equivalents of metal being present per equivalent of acid; and the metal being at least one of Group I metals, Group II metals, aluminum, tin, cobalt, lead, molybdenum, manganese, and nickel" (Claim 1, columns 8 and 9).

According to Example 1, the mixed salt is obtained by reacting 1.63 equivalents of zinc oxide with 1 equivalent of di-(2-ethylhexyl)-phosphorodithioic acid and 0.25 equivalents of oleic acid in mineral oil (column 4, lines 16 to 18 in combination with column 3, lines 39 to 48). Document (4) is silent on the possibility of the presence of active sulphur (in the present context "active sulphur" designates sulphur in a form which can cause staining of e.g. copper, i.e. elemental sulphur or sulphur present in compounds of the formula R9-Sx-R10, wherein R9 and R10 are independently hydrogen or an organic group and x is a number greater than 2; see page 8, lines 16 to 25 of the contested patent). However, the Respondent contended that the skilled person would have known from common general knowledge that active sulphur was necessarily present in dialkyl-dithiophosphoric acids (= DDP acids), due to their preparation from P2S5. He concluded that Example 5 of document (4) anticipated the subject matter of present Claim 1, since oleic acid fell within the range of olefinically unsaturated compounds defined in the patent in suit as component (B) (page 7, lines 51 to 55 in combination with e.g. page 3, line 24).

3.1.2. The Appellant contested the existence of the alleged common general knowledge. The Respondent relied, in support of his respective allegation, only on the patent in suit. There it is stated that preparations of "phosphorodithioic acid usually involve the reaction of P2S5 and that "they often result in levels of active sulfur that are unacceptable ... due to the corrosive nature of active sulfur," (page 2, lines 14 to 16; emphasis added).

3.1.3. In the Board's judgement, the passage of the patent in suit quoted by the Respondent does not exclude the possibility that DDP acid may be free of active sulphur. Consequently, on the sole basis of the above statement in the patent in suit, it cannot be concluded that the DDP acid used according to document (4), in particular in Example 5, necessarily contained active sulphur.

3.1.4. Thus, the Respondent's burden of proving the assertion, on which his novelty objection was based, could not be discharged by this argument. Under these circumstances it is not necessary further to consider the relevance of the analytical data filed by the Appellant in respect to the active sulphur content of DDP acid Zn salts.

3.1.5. During the oral proceedings the Respondent suggested that the case be remitted to the first instance in order to give him an opportunity to provide experimental evidence demonstrating that the DDP acids mentioned in citation (4) inevitably contained more than 300 ppm of active sulphur, since, so he argued, he was taken by surprise by this restriction which was introduced into Claim 1 only in the course of the oral proceedings before the Board.

However, the Board did not accede to this suggestion, since the presence of active sulphur and its staining and corroding properties was the central issue of the patent in suit. The Respondent's above assertion was already raised during the opposition proceedings. It was however contested by the Appellant in his Statement of Grounds of Appeal, received on 18 March 1993. Therefore, the Respondent had almost two years to support his allegation by corroborating evidence.

In addition, the Board observes that the expression "non-staining amounts of active sulphur" was equated throughout the proceedings to a content of less than 300 ppm of active sulphur as measured by IP-155 (see the patent in suit, page 9, lines 10 to 17). Thus, the introduction of this feature into the claims could neither have taken the Respondent by surprise, nor did it change the situation in respect of the Respondent's burden of proof.

3.1.6. The Respondent further submitted that, as both the Example 5 of document (4) and the Example 15 of the patent in suit use the same language in respect to the content of active sulphur in the DDP acid, they must both relate to the same amount of active sulphur. He concluded that the lack of any information in Example 15 of the patent in suit - which on the other hand must refer to active sulphur containing DDP acid, if its technical relevance was to be acknowledged - was sufficient evidence that a skilled person would have understood that also the DDP acid of document (4) comprised active sulphur, even if this was not expressly stated.

3.1.7. This line of argument cannot discharge the Respondent's burden of proof either. According to the consistent case law of the Boards of Appeal the information available from a document has to be established on the basis of its whole content (see T 666/89, No. 5 of the Reasons for the Decision, OJ EPO 1993, 495, 501 and the further decisions cited there). This means that it is not allowable to take a particular example out of context. Therefore, as the patent in suit is mainly concerned with the removal of active sulphur, the only technically reasonable meaning of e.g. Example 15 is, that the starting DDP acid contained active sulphur, even if its amount was not specified. By contrast, document (4) is silent on the presence of active sulphur, which simply means that it comprises no information at all as to this feature. The Respondent's interpretation of this document, which is solely based on the knowledge of the patent in suit, is therefore the result of a typical ex- post facto analysis, which is not allowable.

3.2. Claim 15

3.2.1. Document (2) discloses lubricating oil additives formed from the reaction of (a) an alkylphenol, (b) sulphur, (c) an alkaline earth metal, and (d) an olefin (column 1, lines 41 to 46). The olefin reacts with the active sulphur so that the product is essentially free of the latter (column 1, lines 50 to 53). These products were tested in a base oil composition. In particular a lubricating oil composition was tested, comprising 1.1% of a product obtained by heating a sulphurised alkylphenol with 10% by weight of a mixture of about equal portions of C15-C18 1-olefins for 4 hours at 135°C in a base oil formulation comprising, inter alia, 18. mmols of a DDP acid zinc salt (the composition of test No. 18 in table II in columns 5 and 6; column 5, lines 16 to 21, in combination with column 5, lines 54 and 55, column 4, lines 43 to 50, and column 6, lines 9 to 11, and 18 to 23).

In the oral proceedings before the Board, the Respondent submitted that the ratio of olefin to DDP acid zinc salt in this lubricating oil composition fell within the range of this ratio valid for Claim 15 of the patent in suit. He concluded that the composition of Claim 15, which did not contain the lower limit for the active sulphur content of Claim 1, was therefore anticipated by document (2).

3.2.2. It is to be noted that according to document (2) the reaction of the active sulphur and the olefin does not take place in the presence of a DDP acid metal salt but that the latter is rather mixed with the reaction product of the olefin and the active sulphur comprised in sulphurised alkylphenols. Pointing to this difference, the Appellant contested that the product obtained according to the patent in suit and contained in the compositions of the present Claim 15 was the same as the mixture obtained according to and contained in the lubricating oils of citation (2). In the absence of any further evidence the Board finds that the Respondent, who has the burden of proof, did not sufficiently demonstrate that such difference was irrelevant and that the subject-matter of present Claim 15 was clearly and unambiguously disclosed in document (2), even if it would accept in the Respondent's favour, for the sake of argument, his submission that a skilled person would understand the expression "a zinc dithiophosphate" used there as having no other practical meaning than the different definition used for component A(I) in the patent in suit.

3.3. Hence, the Board concludes that neither document (4) anticipates Claim 1, nor document (2) anticipates Claim 15. The Board is also satisfied that none of the other citations on file discloses the subject-matter of any of the Claims 1 to 17. As novelty was not disputed on the basis of those other documents, no detailed comments are required.

4. Inventive step

4.1. It is stated in the patent in suit that preparations of DDP acids obtained according to the state of the art from P2S5 and an alcohol or a phenol may often comprise unacceptably high levels of active sulphur causing staining or corroding of copper or similar materials. Furthermore, sulphurisation of olefinically unsaturated compounds at relatively low temperatures (at about 140°C) according to the state of the art, tended also to leave unacceptably high levels of active sulphur in the product, whereas sulphurisation at higher temperatures (about 150 - 180°C) often led to very dark to black products, which were commercially unacceptable for use in lubricants or in functional fluids (page 2, lines 14 to 24).

4.2. Thus, although the Board accepts in principle the Respondent's position that, according to the patent in suit, the twin technical problem underlying to the claimed invention was

(i) to provide metal salts of phosphorus-containing acids, or of a mixture of such acids with carboxylic acids, with sufficiently low levels of active sulphur to avoid staining or corroding of copper or similar materials; and

(ii) to provide a process for sulphurising olefinic compounds at relatively low temperatures and relatively short reaction times, resulting in light coloured compositions, which would not stain or corrode copper or similar materials

(see page 2, lines 14 to 31), it wishes to state that the requirement of avoiding dark coloured products also existed in respect to part (i) of the above technical problem.

4.3. The only document before the Board relating to the reduction of active sulphur in accordance with part (i) of the above technical problem is citation (3) (see column 1, lines 35 to 38, and column 6, lines 55 to 66) which the Board, therefore, takes as the starting point for evaluating this aspect of the subject-matter of the patent in suit.

While there is no document in the proceedings referring to part (ii) of the technical problem, the Respondent, in the course of the oral proceedings, confirmed that the sulphurisation of olefinic compounds may lead to dark products. Thus, the Board is satisfied that the respective state of the art exists and that this part of the problem is realistically formulated in the patent in suit and may form the basis for evaluating inventive step.

4.4. The solution to the above technical problem consists according to Claim 1 in providing a composition made, in essence, by reacting particular metal salts of DDP acids, optionally in the presence of a carboxylic acid, with an olefinically unsaturated compound and more than 300 ppm of active sulphur under the reaction conditions and the reactant ratios as set out in Claim 1, which yield compositions containing less than 300 ppm of active sulphur.

The Respondent submitted that Examples 4, 17, 30, and 36 disclose a "red-amber liquid", a "brown liquid", "a brown-reddish liquid", and "an opaque, tan, gel-like material", respectively, as the reaction products obtained in accordance with the process used to define the compositions of Claim 1. However, the Board cannot accept the Respondent's conclusion that this shows that part (ii) of the existing technical problem was in fact not solved. In the Board's judgement, these examples, while indicating that the products concerned may be coloured, are no evidence that such colours are not lighter than those of the products of conventional sulphur clean-up processes using higher temperatures.

Therefore, and in view of the Examples 5 to 8 (page 10, lines 21 to 45 of the patent in suit), the Board is satisfied that both of the above-mentioned problems are solved.

4.5. It has now to be investigated whether or not the cited state of the art suggested to a skilled person the solution of the above-defined technical problem in the manner indicated by the present claims.

4.5.1. Document (3) discloses that the active sulphur content of the reaction product of

(a) a DDP acid with

(b) a hexavelant molybdenum oxide compound and

(c) hydrogen sulphide

may be reduced by including in the reaction mixture an olefinically unsaturated compound capable of reacting with active sulphur (column 1, line 55 to column 2, line 7, and column 6, line 62 to column 7, line 3).

The products obtained according to document (3) were said to be essentially free of "free sulfur" when having "less than 1.0 weight percent ... preferably less than 0.6. weight percent" of free sulphur (column 3, lines 21 to 24). Therefore, the tolerable active sulphur content aimed at according to this citation is much higher than that obtained according to the patent in suit.

Considering, furthermore, that molybdenum is the indispensable metal in the compositions disclosed in document (3) and that no quantitative data on their active sulphur content is available, the Board finds that this citation comprises no hint for the skilled person to the compositions of present Claim 1.

Moreover, since molybdenum compounds are dark coloured in any case, the problem of obtaining light coloured products did not arise there and, consequently, was not mentioned in this document.

4.5.2. The Respondent argued that it would, nevertheless, have been obvious for a skilled person to replace the molybdenum by other metals, e.g. those of present Claim 1. He relied in this connection upon documents (6) and (7) disclosing that the slow reaction of unsaturated polymers with sulphur may be accelerated by compounds such as zinc O,O-di-(n-butyl)-phosphorodithioate in the case of vulcanisation of EPDM (document (6), page 337, first paragraph, in combination with page 343, compound (36), and document (7), page 619, right hand column, last paragraph).

However, the Board finds it questionable whether a person skilled in the field of lubricants would have consulted publications in the field of synthetic rubber vulcanisation at all. Moreover, whereas document (6) discloses that a Zn salt of a DDP acid accelerates the reaction of sulphur with EPDM, it is neither concerned with the reduction of the sulphur content to such a degree that copper is not stained nor with the colour of the products obtained. In view of this difference in the respective technical problem, the Board finds that a skilled person would not have combined the teachings of documents (3) and (6) with a view to solving the existing technical problem underlying to the patent in suit.

4.5.3. The Respondent further submitted that the present Claim 1 reads also on e.g. compositions containing 299 ppm of active sulphur which were prepared from a starting mixture comprising 301 ppm of active sulphur. Such a minute reduction of active sulphur would not require the presence of a DDP acid salt, nor would it be surprising in view of the common general knowledge that practically all chemical reactions known to proceed rapidly at elevated temperatures would also occur slowly at lower temperatures. Thus, not all embodiments falling within the scope of present Claim 1, would involve an inventive step.

This argument is not convincing, because it is based on a construction of the meaning of Claim 1 which, in the Board's judgement, is rather artificial. However, if a claim refers to interrelated ranges of concentrations, it cannot normally be construed as comprising all arbitrarily chosen combinations falling within such ranges but has to be construed in the light of the description (see e.g. T 14/83, No. 9 of the Reasons for the Decision, OJ EPO 1984, 105). The Board finds that on that basis it is clear to a skilled person, that what is claimed is not just a marginal reduction of the active sulphur content of DDP acid salts, but one in the order of about 50 to 100 fold (see Examples 5 to 8) in a technically reasonable reaction time - depending on the reaction temperature. Thus, on its proper construction, the present Claim 1 does not comprise the allegedly obvious subject-matter. Hence, it is not necessary to investigate whether such subject-matter would in fact have been obvious in the light of the common general knowledge referred to.

4.5.4. As already explained, document (4) is not concerned with problems linked to active sulphur and, hence, contains no hint for the skilled person to the claimed solution. It could have amounted to an accidental anticipation only, as the Respondent conceded. It is not necessary, therefore, to deal further with this document in connection with the issue of inventive step.

4.5.5. In addition, the Respondent, relying on an experimental report of 11 March 1994, submitted that at a reaction temperature of 100°C (or below) no product was obtained meeting the requirements of Claim 1. The rating of the products obtained according to the experiments 3 and 4 - only these met the ratio set forth in the present Claim 1 for the components (A) and (B) - was 4A in the ASTM D130 test, which indicated (also in accordance with the Appellant's submission in the grounds of appeal; see the sentence bridging pages 5 and 6) an unacceptably high content of active sulphur of above 300 ppm (the patent in suit, page 9, lines 11 to 17). Therefore, so the Respondent argued, the subject-matter of Claim 1 comprised embodiments not solving the existing technical problem and, hence, not involving an inventive step.

The Board cannot accept this argument either. According to the uncontested submission of the Appellant, the olefin used in the Respondent's tests was highly branched and sterically hindered (first paragraph on page 2 of the Appellant's submission dated 13 January 1995). Taking into account that according to the Examples 5 to 8 of the patent in suit the reaction time for alpha-olefins was three hours at temperatures of 110°C and 120°C, respectively, the Board finds that, under these circumstances, the reaction time of six hours chosen in the above experiments 3 and 4 for the reaction of a sterically hindered olefin at a lower reaction temperature was not sufficiently long.

According to common general knowledge the reaction velocity is normally enhanced by a factor of about 2 to 3, if the reaction temperature is increased by 10 degrees centigrade. From this rule of thumb a skilled person, when reading the Examples 5 to 8 of the patent in suit, would have concluded that a reaction temperature of 100°C required at least about two to three times the reaction time given in these examples for the reaction of alpha-olefines and, of course, still longer reaction times in the case of sterically hindered olefins. Therefore, the Board concludes, that the Respondent's experiments were not persuasive and cannot be a valid basis for attacking inventive step (T 741/91, not published in the OJ EPO, No. 4.5 of the Reasons for the Decision).

4.5.6. It follows from the above that neither document (3) nor any other document on file, either in isolation or in combination renders the subject-matter of Claim 1 obvious. The subject-matter of Claims 14, 15, 16, and 17 concerning an additive concentrate and a lubricant or functional fluid comprising a composition of Claim 1, respectively a process for making the compositions of Claim 1, define the same invention in different patent categories. Dependent Claims 2 to 13 relate to specific embodiments of this invention. Therefore, these claims are likewise allowable.

Auxiliary request

5. The Appellant's main request being allowable, it is not necessary to further consider his auxiliary request.

6. The Respondent did not submit any observations regarding the adapted description. Nevertheless, the Board considered this matter on its own motion and has found that the description as amended meets the requirements of the EPC. In particular the Board finds in the circumstances of this case that all examples contribute to illustrating the subject-matter of the patent in suit and, thus, should be maintained in the specification as a valuable source of information for the public, although the majority is silent on the active sulphur content of the starting material and/or of the resulting products as measured by IP-155.