T 541/09 – More On Weight Problems

All the parties filed appeals against the decision to maintain the opposed European patent on the basis of the second auxiliary request, but the patent proprietor finally defended this request.

Claim 1 of this request read (in English translation):

A process for the preparation of expandable styrene polymers having a molecular weight Mw in the range from 220000 to 300000 g/mol, characterised in that a blowing agent-containing styrene polymer melt having a temperature in the range from 160 to 240°C is conveyed through a die plate which is heated to a temperature that is in the range of 20 to 100°C above the temperature of the blowing agent-containing styrene polymer melt and which has holes the diameter of which at the die exit is in the range from 0.2 to 1.2 mm, and subsequently granulated.

The Board found this request not to comply with the requirements of A 83:

*** Translation of the German original ***

[4.1] The claimed invention concerns a process for the preparation of expandable styrene polymers. On the one hand, the process is defined by process steps comprising the extrusion of a blowing agent-containing styrene polymer melt through a heated die plate under certain temperature conditions, and the granulation if the extrudate. On the other hand, the process also characterises the product to be obtained via the process by means of a parameter. According to the claim, this product has to be an expandable styrene polymers having a weight average molecular weight Mw in the range from 220000 to 300000 g/mol.

The patent specification teaches, in particular in view of paragraphs [0005] and [0006], that the purpose of the teaching of the patent is to provide, by means of the claimed process, an expandable styrene polymer that can be foamed to give foams with ideal foam structure. The argumentation of [the patent proprietor] in its letter of November 25, 2009 […] allows to derive, together with the trial report I filed as an annex, that the claimed molecular weight Mw of the styrene polymer is essential for its foaming to final products having advantageous properties such as reduced post-shrinkage, even surface and homogeneous cell structure.

It follows that the molecular weight Mw of the process product according to the claim in the range from 220000 to 300000 g/mol, which is to be obtained according to the process, is an essential feature of the invention. This range has a width of 80000 g/mol, which is relatively narrow. Moreover, when the polymer is produced by means of extrusion of the departure polystyrene, it is necessary to take into account reductions of the molecular weight caused by thermal degradation reactions, which, according to paragraph [0008] of the patent specification can amount to 10000 g/mol and, according to the trial report I, which states that the Mw of PS 158 K is reduced from 280000 to 241000 g/mol, even 40000 g/mol. This loss of molecular weight alone comprises, as far as values are concerned, half the width of the claimed Mw range.

[4.2] The requirement under A 83 that the skilled person must be enabled to carry out the invention requires the skilled person to precisely determine the molecular weight Mw in order to obtain an expandable styrene polymer having a molecular weight Mw in the range from 220000 to 300000 g/mol within the meaning of the teaching of the patent in a target-oriented and reliable way. In particular, he has to choose a sufficiently high molecular weight Mw of the departure polymer in order to reach the claimed Mw range after the extrusion.

However, as the original documents of the application do not indicate any measuring method for determining the molecular weight Mw, the objection raised by [opponents 1 and 3], based on this lack of disclosure, that the skilled person is not enabled to carry out the invention, is a paramount criterion for the [present] decision.

[4.3] It is undisputed that there are several methods for determining the weight average molecular weight Mw of polymers, such as gel permeation chromatography (GPC), light scattering, ultracentrifugation. It is also undisputed that different measuring methods, when applied to the same sample, and different measurement conditions within a given measurement method, lead to different Mw values. This has been shown by the opponents in several documents (e.g. D55, D56, D67, D68, D69, D71).

[4.3.1] Thus it can be derived from Table 1.3.21 of D55 that the Mw determination of the standard polystyrenes NBS-705 et NBS-706 by light scattering, ultracentrifugation and GPC leads to significantly different results. The measurements carried out on NBS-705 and GPC give Mw values of 189000 and 159000 g/mol, respectively. The difference amounts to 30000 g/mol or about 20%. When Mw is determined for NBS-706 by means of ultracentrifugation (Mw 288000 g/mol) and GPC under certain measuring conditions (Mw 220000 g/mol) differences of 68000 g/mol (30%) are possible. Even when the same measuring principle (GPC) is used, differences of about 20% occur for different measuring conditions (Measurement series 2 and 3 of the Table).

D56 shows the dependence of the Mw value determined by GPC on the same samples on the sample concentration (Table 1).

The change of the calibration standard used in the GPC method also leads to significant differences in Mw as shown in D71 (where GPC is referred to as “Size Exclusion Chromatography“ or SEC) for different polystyrenes (SRM 706, SRM 705a, PS-1) using standards TSK and Shodex (Tables 2 to 7). On page 12 of D71 it is noted that the Mw values obtained with the Shodex calibration curve are about 10% higher than when the TSK calibration curve is used.

[4.3.2] It unambiguously follows from all this that the skilled person wishing to reliably determine the molecular weight Mw of the expandable styrene polymer according to the teaching of the patent needs precise information on how to proceed. The mere indication of a measuring method is not enough; indications regarding the precise measuring conditions are also needed. In particular in relative methods such as the common GPC method indications concerning the sample concentration, the calibration standard, the separation material and the eluent are required. The DIN-standard 55672-1 (D72) even requires an examination report (point 12).

[4.3.3] This is all the more true in the present case because the width of the Mw range that is relevant for the invention is relatively narrow (80000 g/mol) and because the differences of 20% or more that are observed when different measuring principles or conditions are used are of an order of magnitude that may amount to 50% of this width. Moreover, of one considers that there may be a reduction of the Mw value of up to 40000 g/mol between the initial product and the process product, due to thermal degradation (see trial report I), then it is practically impossible for the skilled person to obtain an expandable styrene polymer having the claimed Mw range within the meaning of the teaching of the patent in a targeted way if no details concerning the determination of the molecular weight are given.

[4.4] The argument of the [patent proprietor] according to which the polystyrene PS 158 K, which was characterised by a Mw of 280000 g/mol, could be used as a reference for the calibration is not persuasive. As a matter of fact, the data sheet for the polystyrene PS 158 K does not contain any indication regarding the molecular weight of the polymer sold by BASF. However, a commercial product without a precise specification of the molecular weight Mw appears not to be suitable for use as a calibration substance for this very parameter. Moreover, as shown in D64 and D67 to D69, GPC measurements carried out on PS 158 K sold by BASF in Korea and Europe (“PS Europa” and “PS Korea”) yield Mw measurements that, depending on the laboratory and on the measurements conditions, partly differ significantly from 280000 g/mol and fluctuate between 236000 and 27000 g/mol. Therefore, the skilled person is unable to correlate one particular measuring method and/or measuring conditions with the Mw value of 280000 g/mol to be obtained for PS 158 K.

[4.5] The further argument of the [patent proprietor], according to which polystyrene was a relatively simple molecule without significant branching of the polymer chain, so that the determination of its Mw was unproblematic, is not persuasive either. As already stated by [opponents 1 to 3], the styrene polymer to be used as the starting product according to the claim is not limited to a homopolymer but also encompasses, according to paragraph [0010] of the patent specification, a great number of copolymers such as ABS, SAN, ASA, MBS, MABS or blends thereof. The [patent proprietor] has not established that a particular measuring method suitable for a homopolymer is equally suitable for different copolymers. Rather, it is to be expected that at least certain measuring conditions (such as the PS reference, eluent, separating agent for GPC) have to be adapted.

[4.6] Summing up, it has to be noted that the differences of the measured Mw values of polystyrene of up to 30%, which have been established by [opponents 1 to 3], may exceed the claimed range width of 80000 g/mol, taking into account the not inconsiderable thermal reduction of the molecules of up to 40000 g/mol during the extrusion of the polystyrene starting material.

[4.6.1] Therefore, these considerable deviations in the determination of the molecular weight Mw, together with the narrow width of the claimed Mw range, not only lead to a lack of clarity of the scope of protection of the claims that normally has to be considered under A 84, but also concern the question of whether the invention can be carried out. When assessing this question, unclear parameters have to be taken into account, in view of T 608/07, in particular if

• the lack of clarity not only concerns the boundaries of the claimed range, and
• the lack of clarity results in undue efforts having to be made if the advantages of the invention are to be obtained.

[4.6.2] As far as the first criterion is concerned, the explanations under point [4.3] show that almost the whole Mw range from 220000 to 300000 g/mol is concerned.

[4.6.3] As far as the second criterion is concerned, it has already been explained under point [4.1] that the claimed range of molecular weights is an essential element of the invention and that the advantages of the invention (little post-shrinkage, even surface and homogeneous cell structure of the foamed final product) are only obtained if the expandable styrene polymer is within this relatively narrow Mw range. Therefore, in order to obtain these advantages within the meaning of the teaching of the patent in a targeted way, the skilled person must be certain that measured molecular weight values Mw for the styrene polymer that lie within the claimed domain do indeed qualify as values within the meaning of the invention. As this is not true, as has been shown in points [4.3] to [4.5], the reproduction (Nacharbeitung) of the teaching of the patent requires undue efforts of the skilled person wishing to obtain the advantages according to the invention. As a consequence, the requirement of A 83, according to which the invention has to be sufficiently disclosed, has not been complied with.

[4.6.3] Therefore, the main request, which is the only request on file, cannot be granted. […]

The patent is revoked.

Should you wish to download the whole decision (in German), just click here.

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