T 0810/15 17-10-2017

Main request (claims as granted)

1. Added subject-matter

The appellant raised objections under Article 100(c) EPC against claims 1 and 7.

1.1 Claim 1

1.1.1 Claim 1 as granted (see point I above) is based on claim 1 as filed which reads as follows:

"1. A prepreg containing a carbon fiber [A] and a thermosetting resin [B], and in addition, satisfying at least one of the following (1) and (2).

(1) a thermoplastic resin particle or fiber [C] and a conductive particle or fiber [D] are contained, and weight ratio expressed by [content of [C] (parts by weight)]/[content of [D] (parts by weight)] is 1 to 1000.

(2) a conductive particle or fiber of which thermoplastic resin nucleus or core is coated with a conductive substance [E] is contained."

The subject-matter of claim 1 as granted is limited to alternative (1) of claim 1 as filed, which has been further restricted with regard to the options for ingredients [C] and [D], namely that [C] is a thermoplastic resin particle and [D] a conductive particle.

This embodiment is directly and unambiguously derivable from the application as filed, which discloses (see page 5, lines 16-17):

"In this embodiment, it is preferable to use a thermoplastic resin particle as [C] and a conductive particle as [D]".

1.1.2 According to the appellant the "or" language of claim 1 as filed as well as the application as a whole specified that the prepreg contained a thermoplastic particle or fibre [C] and a conductive particle or fibre [D], wherein the weight ratio expressed by [content of [C] (parts by weight)]/[content of [D] (parts by weight)] was 1 to 1 000. Thus, the application as filed excluded a prepreg containing a thermoplastic particle and fibre [C] and/or a conductive particle and fibre [D].

By contrast, claim 1 as granted allowed for the additional presence of fibres of [C] and/or fibres of [D] in view of its open wording, namely the use of the expression "a prepreg containing" to define the prepreg.

1.1.3 The board does not agree.

The ratio [C]/[D] of claim 1 as filed is so defined as to comprise four embodiments:

fibre [C] - fibre [D],

fibre [C] - particle [D],

particle [C] - fibre [D] and

particle [C] - particle [D].

Claim 1 of the main request is limited to the last of these embodiments.

The board agrees with the appellant that claim 1 as granted allows for the additional presence of fibres of [C] and/or fibres of [D]. However, claim 1 as filed uses exactly the same open wording as claim 1 as granted to define the prepreg, namely "a prepreg containing". In fact, claim 1 as filed allows for the presence of further components for the embodiments comprised within the definition of the ratio [C]/[D], i.e. for the embodiment particle [C] - particle [D] the presence of fibres of [C] and/or fibres of [D]. Thus, claim 1 as filed and claim 1 as granted have the same degree of "openness" with regard to the presence of further components.

This was in fact also the respondent's position expressed both in writing and at the oral proceedings, namely that neither claim 1 as granted nor the application as filed, in particular the embodiment referred to on page 5, lines 16-17, excluded other particular components such as fibres of [C] and/or fibres of [D].

1.1.4 In view of the above, the subject-matter of claim 1 as granted does not extend beyond the application as filed.

1.1.5 The appellant argued that claim 1 as granted defined the weight ratio [C]/[D] in relation to the particles [C] and [D] only; any fibres of [C] and/or of [D] present were not taken into account for calculating the weight ratio [C]/[D]. Nevertheless, the fibres of [C] and [D] had the same properties as the particles of [C] and [D], so a weight ratio [C]/[D] defined only in relation to the particles of [C] and [D] would in the end be meaningless if fibres of [C] and [D] were additionally present. This would also support its view that claim 1 as granted contained added matter.

However, Article 100(c) EPC is purely a matter of disclosure. Since there is disclosure for the subject-matter of claim 1 as granted in the application as filed, the technical meaning of this disclosure may be examined at another stage, for example when assessing inventive step of the subject-matter of claim 1. In fact, this was also the position of the respondent at the oral proceedings.

1.2 Claim 7

1.2.1 Claim 7 as granted depends on claim 6, which depends on claim 1 (see section I above). According to the appellant, claim 7 combines the features of claims 6 and 7 for which there is no basis in the application as filed. In particular, the appellant objected to the combination of the localisation of 90 to 100 wt% of [C] and [D] in a 20% depth range from both surfaces of the prepreg in the thickness direction (claim 6) in combination with the localisation of 90 to 100 wt% of [C] and [D] in a 20% depth range from one surface of the prepreg in the thickness direction (claim 7).

1.2.2 The board does not agree.

As pointed out by the respondent, the specific embodiment of claim 6 defines the region of the prepreg which is to be occupied by particles [C] and [D]. This region is defined by the outer surfaces of the prepreg and by lines parallel to those surfaces located at 20% depth, with respect to the thickness, from the respective surfaces. This region is in two parts: a first 20% depth region associated with one surface and a second 20% depth region associated with the opposite surface. Thus, claim 6 covers arrangements in which [C] and [D] are present in only one of the regions or shared between both regions.

Claim 7, on the other hand, covers the arrangement in which [C] and [D] are present only in one of the regions. Therefore, claim 7 merely limits the feature of claim 6.

In the board's view, this reading of claim 6 is also the only meaningful one in view of the claim structure. Claim 6 sets out the arrangements of particles [C] and [D] in broad terms, whereas the claims referring back to claim 6 set out specific arrangements, namely particles [C] and [D] present in one region (claim 7) or both regions (claim 8).

If one were to follow the appellant's line of argument that already in claim 6 particles [C] and [D] have to be present in both regions, claim 8 would be completely superfluous.

1.2.3 In view of the above, there is no unallowable combination of features due to the dependency in claim 7, so that the objection of added matter to claim 7 has to be rejected.

2. Sufficiency of disclosure

2.1 The appellant contested the clarity of the terms "particle" and "conductive" used in the expression "conductive particle", and argued that since these terms were unclear, the skilled person was unable to carry out the claimed invention. The appellant also referred to paragraph [0035] of the patent in suit which mentioned the addition of a conductive filler in the form of a particle or a fibre. The skilled person would be unable to distinguish between a conductive particle and a conductive filler.

2.2 The board acknowledges that the patent in suit does not provide a clear definition for the term "particle". However, in the absence of any technical evidence to the contrary, the board concurs with the respondent that in most cases the skilled person can distinguish a particle from a fibre. In the particular case where the dimensions of a particle and a fibre converge, this appears not to affect the core of the invention but rather to create uncertainty at the "edges" of the dimensions for particle and fibre. In other words, this amounts to lack of clarity and not insufficiency.

2.3 Regarding the meaning of the term "conductive", it is beyond doubt in the light of the patent specification as a whole that it refers to electrical conductivity. The patent in suit explicitly discloses conductive particles to be used in the prepreg of the claimed invention (paragraph [0139] and tables 1, 3 and 4) to assure the conductive path between the fibres and the surface of the prepreg and to disperse the electrical charge from lightning also in the thickness direction (avoid insulation).

2.4 With respect to the contested distinction between a filler particle and a conductive particle, the skilled person finds appropriate guidance in the description (paragraph [0035]), which discloses that "The conductive filler mentioned here is a conductive particle or fiber having an average diameter smaller (generally 0.1 times or less) than the average diameters of the conductive particle [D]". It follows from this passage that the optional conductive filler, if present, is different from the conductive particle [D] of the claimed invention, otherwise the requirement for it to have a smaller (generally much smaller) average diameter would be meaningless.

2.5 In view of the above, the claimed invention is sufficiently disclosed.

3. Novelty

3.1 With its letter of 5 July 2016, in the appeal proceedings the appellant raised for the first time a novelty objection based on D14, which until then had never been used in the appeal proceedings.

During the opposition proceedings, only a novelty objection in view of D1 had been raised. Consequently, the decision under appeal dealt only with this novelty objection.

Thus the novelty objection based on D14 is late-filed and an amendment to the appellant's case.

3.2 The board notes that the novelty objection based on D14 triggered the filing of a great deal of contradictory evidence as to whether the prepreg disclosed in D14 ultimately contained thermoplastic particles [C] and/or conductive particles [D] (appellant: D50, D51 and D52; respondent: D48, D48-1, D48-2, D49, D49', D53 to D56, D56a', D57). At the oral proceedings the appellant even requested time to file a response to the evidence filed by the respondent on the day before the oral proceedings.

3.3 In view of the complexity of the novelty issue and the ramifications arising from this issue at a very late stage in the proceedings, and which could not be dealt with without adjournment of the oral proceedings, the board decided under Article 13(1) and (3) RPBA not to admit this objection into the proceedings.

3.4 The appellant argued that it had become aware of the relevance of D14 only during parallel opposition proceedings on a divisional application stemming from the patent in suit. However, this argument had to be disregarded, in particular because D14 was in the present opposition proceedings from the outset. Nor is a change of the representative in the appeal proceedings a valid argument.

4. Admissibility of D35 to D39

4.1 The appellant filed D35 and D36 as early as possible in the appeal proceedings, namely with the statement setting out the grounds of appeal. Both D35 and D36 relate to prepregs used in the field of aerospace technology and thus are more relevant than the other documents on file, taking into account the technical problem as defined by the respondent (see the section below concerning inventive step).

D35, in contrast to D13 which was filed with the notice of opposition, was explicitly directed to prepregs which were to be used in aerospace (page 140, left column, point 1, first to third paragraphs). Accordingly, D35 was filed in reaction to the argumentation of the opposition division, namely that the skilled person would not combine D13 with D8/D18 (the then closest prior art) because D13 did not relate to aerospace.

D36 was the PCT application corresponding to D7, filed with the notice of opposition. The content of D36 was identical to that of D7, except the passage concerning the amount of thermoplastic particles (page 10, second full paragraph) in the prepreg, namely 2 wt% or more, and a few other text passages. In view of this additional feature, D36 was more relevant than D7, as it suggested in combination with D35 the weight ratio specified in claim 1, namely [C]/[D] of 1 to 1 000, which the respondent considered a prerequisite for obtaining the alleged effects.

All in all, the filing of these documents was an immediate reaction to developments in the previous proceedings in order to support the reasoning to date and to fill gaps in the previously filed arguments. In view of the above, the board admitted these documents into the proceedings.

4.2 The respondent filed D37 to D39 in its observations on the grounds of appeal, in response to the appellant's argument, submitted with the grounds of appeal, that no technical effect had been demonstrated. D37 was submitted in order to show the excellent lightning protection provided by composites formed from the prepreg of claim 1 - i.e. containing conductive particles - compared with composites lacking conductive particles. D38 and D39 were submitted in order to provide evidence of the common general knowledge concerning lightning protection at the priority date of the patent. As these documents were filed in response to the appeal, they were also admitted into the proceedings.

5. Inventive step

5.1 According to the patent in suit, the prior art had difficulties in preparing carbon-fibre-reinforced materials having at the same time high impact resistance and conductivity in the thickness direction (paragraphs [0002] and [0003]). Therefore the purpose of the patent is to provide a prepreg and a carbon-fibre-reinforced composite having excellent impact resistance and (electrical) conductivity in the thickness direction (paragraph [0005]).

5.2 Closest prior art

The parties differed as to which document constituted the closest prior art: the appellant considered D36 and the respondent D33 to be the closest prior-art document.

5.2.1 D36 discloses a carbon fibre prepreg, wherein a carbon fibre bundle is impregnated with a base resin mainly composed of a thermosetting resin. Thermoplastic resin particles with a particle size of 150 mym or less, which account for 20 wt% or less, preferably 2-10 wt%, based on the weight of the entire prepreg, are distributed at a higher concentration in the surface zone of the prepreg than in the inside (claim 1; page 10, second full paragraph). Such a prepreg has excellent compression interlaminar shear strength (CILS) whilst maintaining good impact resistance (CAI), and can preferably be used as a structural member in aerospace, sport, civil engineering and architecture (page 23, "Industrial Applicability").

5.2.2 D33 discloses a polymer composite structure having an interlayer which is reinforced with shape memory alloy (SMA) particles, the use of which enhances the damage resistance and damage tolerance (i.e. compression after impact (CAI) strength) of the interlayer without negatively affecting its hot-wet compression. Such polymer composite materials are suitable for various applications, such as primary structure application in the manufacture of aircraft. However, D33 makes no use of thermoplastic particles dispersed on surface regions of the prepreg in order to improve its mechanical properties. D33 uses SMA particles for this purpose, which eliminate the need to use elastomeric resin particles. Additionally, the use of SMA serves to disperse the energy of an electric charge, such as from a lightening strike, more evenly throughout the composite structure. Reference is made to paragraphs [0004], [0009], [0031] and [0032].

5.2.3 D36, which - like the patent in suit - discloses the use of thermoplastic resin particles in order to provide excellent mechanical properties of the prepreg, such thermoplastic resin particles being distributed at a higher concentration within the surface zone of the prepreg than in the inside, is considered to be the closest prior art. In fact, D36 is quite similar to the prior art mentioned as the starting point for the inventors of the patent in suit.

The prepreg of claim 1 of the main request differs from the prepreg disclosed in D36 in that it contains (electrically) conductive particles and by consequence the weight ratio expressed by particles [C]/particles [D] is from 1 to 1 000.

5.3 Technical problem

5.3.1 The patent in suit discloses that the technical problem is to provide a prepreg and carbon-fibre-reinforced composite material having both excellent impact resistance and conductivity in the thickness direction (see paragraph [0005]). It further discloses that the above effects are achieved by the presence of conductive particles [D] in a specific weight ratio to the thermoplastic resin particle [C], which is expressed by [content of [C] (parts by weight)]/[content of [D] (parts by weight)] 1 to 1 000 (see paragraph [0006] and figure 2).

5.3.2 However, the desired technical effects of excellent impact resistance and conductivity in the thickness direction are not obtained over the whole breadth of the claimed subject-matter. As already observed above (see section 1.1.2), the claimed prepreg is defined in an open manner which allows thermoplastic resin fibres of [C] and conductive fibres of [D] to be present in its composition.

Such fibres will necessarily contribute to the impact resistance and conductivity of the prepreg in the thickness direction, similarly to the thermoplastic resin particles and conductive particles, and possibly render meaningless a ratio of [C]/[D], which relates to particles only. Reference is made to the application as filed (see table 5, examples 26 and 27), which shows that thermoplastic resin fibres [C] and conductive fibres [D] have a similar influence on impact resistance (CAI) and conductivity in the thickness direction as thermoplastic resin particles [C] and conductive particles [D] (see table 5, examples 1-6, 8-23). Table 5 shows that the compressive strength after impact (CAI) is 271 and 269 MPa for examples 26 and 27 respectively, which involve conductive fibres and thermoplastic resin fibres, while that of examples 1-6 and 8-23, which involve conductive particles and thermoplastic resin particles, varies between 265 and 343 MPa. Volume resistivity is 4.1x10**(4) and 4.7x10**(4) Omegacm for examples 26 and 27 respectively, while for examples 1-6 and 8-23, which involve conductive particles and thermoplastic resin particles, it varies between 1.1x10**(5) and 2.0x10**(3) Omegacm.

The apparent consequence of the presence of thermoplastic resin fibres and conductive fibres in addition to the conductive particles and thermoplastic resin particles in the prepreg is that the relationship between compressive strength after impact (CAI) and volume resistivity will not fall within the outlined area of the graph of figure 2 any longer, the latter having been drawn on the basis of prepregs containing exclusively thermoplastic resin particles and conductive particles, so that the claimed weight ratio, relating only to particles, will no longer have any technical relevance.

5.3.3 In view of the above considerations, the technical problem underlying the claimed invention in view of D36 has to be reformulated in a less ambitious manner, namely as merely the provision of an alternative prepreg.

5.4 Obviousness

5.4.1 The skilled person starting from the prepreg of D36 and aiming at an alternative prepreg would find in D35 the motivation to add electrically conductive particles in the thermosetting resin of the prepreg.

D35 relates to carbon-fibre-reinforced prepregs with an epoxy resin as thermosetting resin, like the prepregs of D36, and discloses that these prepregs are particularly useful in aerospace, again like the prepregs of D36. It further discloses that electrical conductivity is improved by dispersing fine metal particles between the layers of prepreg laminates (abstract; page 140, left column, lines 2-3 and 11-13; page 140, sentence bridging left/right columns; page 141, lines 3-6). Consequently, the skilled person confronted with the objective technical problem of providing an alternative to the prepreg of D36 would be motivated to combine D36 with D35 and would arrive at the subject-matter of claim 1 without the need to exercise inventive skill.

5.4.2 The respondent objected to the combination of these two documents because D35 was an academic paper with no specific experimental evidence regarding electrical conductivity. That is, however, no reason to disregard this disclosure: firstly, the EPC does not draw any distinction between various types of prior art; secondly, the experimental evidence of the patent in suit and of D37, filed by the respondent, corroborates the disclosure of D35, namely that the dispersion of metallic particles between prepreg layers increases the electrical conductivity of the laminate.

The respondent also argued that the disclosure of D35 contained a prejudice against the use of fine titanium particles in carbon-fibre-reinforced prepregs, and referred in this context to the tests carried out in D35 to evaluate the interlaminar fracture toughness. However, the respondent itself stated that the interlaminar fracture toughness is different from the CAI, the mechanical property of the prepregs of D36. Furthermore, the majority of the tests (three out of four) carried out in D35 to evaluate the interlaminar fracture toughness show that adding titanium particles in the prepreg has either an improved impact on the interlaminar fracture toughness or no impact at all (figure 7; page 142, right column, lines 30-32). More precisely, the experimental data of D35 show that prepregs with titanium particles compared with prepregs without such particles lead to improved composites in terms of mode I interlaminar fracture toughness GIC and GIR. In terms of mode II, this comparison shows that the composites are almost the same for the GIIC value. Regarding the insufficient interlaminar fracture toughness GIIR, D35 attributes it to poor adhesion between the fine titanium particles and the thermosetting resin (page 142, right column, lines 9-14 and 32-36). However, such insufficient adhesion of the conductive particles may also be detected in the prepregs of the patent in suit, which in such a case envisages a surface treatment as a possible remedy (see paragraph [0080]). All in all, D35 does not disclose that the presence of fine titanium particles in the prepreg renders it unacceptable and possibly even dangerous for aircraft use, contrary to the assertion of the respondent.

5.5 But even assuming, in favour of the respondent, that the objective technical problem underlying the claimed invention in view of D36 was the provision of a prepreg with electrical conductivity in the thickness direction while maintaining excellent impact resistance (CAI), for the reasons given above the skilled person would also find in D35 the motivation to add titanium particles (i.e. electrically conductive particles) to the prepreg known from D36 and thus improve the electrical conductivity of the prepreg in the thickness direction (page 140, left column, lines 24-30 and sentence bridging left/right columns) without reducing the impact resistance (CAI) of the prepreg of D36.

In this case, the claimed weight ratio of the thermoplastic resin particles [C] and the conductive particles [D] would be the unavoidable result of the the combination of D36 with D35. The appellant explained, without being contradicted by the respondent, that, when titanium particles with an average diameter of about 45 mym in an amount of 1.814 wt% or 1.663 wt%, as disclosed in D35 (page 141, left column, lines 3-6), are added to the carbon-fibre-reinforced prepreg of D36 with an epoxy thermosetting matrix and thermoplastic particles in its surface area in an amount of 2-20 wt% (page 10, lines 6-16), the ratio will lie within the claimed range of 1 to 1 000.

5.6 In view of the above, the subject-matter of claim 1 of the main request does not involve an inventive step.

New auxiliary request 1

6. This request was submitted during the oral proceedings before the board. Claim 1 of this request differs from claim 1 of the main request in that it specifies that the thermoplastic resin particle [C] is selected from the group of a thermoplastic resin particle or fibre and the conductive particle [D] is selected from the group of a conductive particle or fibre (see point XX above). This amendment introduced issues regarding clarity of the claim, at a very late stage in the proceedings, in view of the meaning of the terms "particle" (see patent in suit, page 6, lines 1-2; page 9, lines 1-3) and "fiber" (see patent in suit, page 69-10, lines 1-3), in particular as regards a precise distinction between the two terms. Consequently, this request was not admitted into the proceedings under Article 13(1) RPBA.

New auxiliary request 2

7. This request was also submitted during the oral proceedings before the board. Claim 1 of this request differs from claim 1 of the main request in that it requires that the prepreg does not contain a thermoplastic resin fibre or a conductive fibre (see point XX above). This additional limitation increased the complexity of the case in terms of clarity and added subject-matter at a late stage in the proceedings, with the consequence that this request was likewise not admitted into the proceedings under Article 13(1) RPBA.

Auxiliary request 12

8. As already mentioned above (see point VII), claim 1 of auxiliary request 12 comprises a feature taken from the description as filed (see page 35, lines 17-24) which reads:

"A prepreg for use in making a carbon fiber reinforced composite material for an aircraft structural member ...".

According to the case law of the EPO boards of appeal this is understood to mean a prepreg suitable for use in making a carbon-fibre-reinforced composite material for an aircraft structural member. However, as the appellant correctly observed during the oral proceedings, it is unclear for which structural member of an aircraft the prepreg is suitable, let alone for which type of aircraft, and which criteria the prepreg has to fulfil in order to be suitable for such a use. It is therefore unclear how this additional feature further limits the claimed prepreg. Under these circumstances, the board finds the subject-matter of auxiliary request 12 to be unclear, with the consequence that this request is not allowable.

9. Since none of the requests is allowable, the patent has to be revoked.