T 0764/01 23-08-2002

1. Scope of the appeal

In substance, the device claims 4 to 7 correspond to the device claims 1 to 4, on the basis of which the Opposition Division has decided to maintain the patent in amended form. Due to the prohibition of reformatio in peius (cf. decisions G 9/92, G 4/93 [OJ EPO 1994, 875]), neither the respondent nor the Board may challenge these claims (cf. T 856/92, not published in the Official Journal of the EPO).

2. Sufficiency of disclosure

The respondent has inter alia raised the ground for opposition under Article 100(b) EPC. In particular, he has submitted that the patent specification did not contain any information how the shear rate was calculated.

The shear rate is the gradient of the rate of flow transversely to the direction of flow. The Board agrees with the respondent that the velocity profile and hence the shear rate, depends inter alia on the size and shape of the cross-section of the channel. For various cross-sections, such as slits or perforated plates with circular openings, approximate formulae for the shear rate exist, which attempt to express the shear rate as a function of the parameter(s) that describe the cross-section, and of other parameters such as the length of the channel, the pressure difference through the opening and the viscosity of the fluid. However, flow rates, and thus shear rates, can be measured, so that the question which formula correctly calculates the shear rate, does not need to be answered.

In the description of the patent in suit, suitable ranges for the relevant process parameters for producing a foam with small and uniform bubbles are provided (cf. column 3, line 6, to column 5, line 18), namely: mesh-size of the fine-meshed screens, viscosity and shear stress of the reaction mixture, the required pressure of the reaction mixture prior to the passage through the screen and immediately prior to entering the screen. The pressure of the reaction mixture prior to the passage through the screen is dependent on the quantity of liquid carbon dioxide dissolved and must be in excess of the equilibrium pressure, so that the mixture is still homogeneous on entering the screen. By passing the reactive mixture through one or more fine-meshed screens, the foamable reactive mixture is subdivided into a large number of individual flows having a shear rate of above 500/s, resulting in a homogeneous density of bubble nuclei, which upon expansion produces a homogeneous low-density foam free from large voids or bubbles.

In the description of the patent in suit it is noted (cf. column 4, line 53, to column 5, line 13) that it is advantageous to use several fine-meshed screens in tandem with a view of increasing the shear time. If the shear time is too short, i.e. less than the relaxation time associated with the formation of bubble nuclei, and this may happen when only one screen is used, the resulting foam may not be sufficiently homogeneous. The respondent objected to the fact that no definitions of shear time and relaxation time were given in the patent in suit. The Board is of the opinion that definitions of shear time and relaxation time are not required to perform the invention, since these parameters do neither appear in the claims, nor elsewhere in the patent in suit, apart from the passage cited above, which is an attempt to explain why the use of more than one screen is beneficial.

The Board thus has no doubt that the process is disclosed in a manner sufficiently clear and complete for it to be carried out by the person skilled in the art (cf. Articles 83 and 100(b) EPC).

3. Allowability of the amendments and novelty

Claims 1 to 3 according to the sole request of the appellant correspond to claims 1 to 3 according to the first auxiliary request submitted before the Opposition Division. The Opposition Division held that these claims met the requirements of Articles 54, 123(2) and (3) EPC. The Board has duly examined this matter and has come to the same conclusion. Since novelty and allowability of the amendments were not challenged by the respondent, further substantiation of this matter is not considered necessary.

The amendments to the description, which were made with a view to bring the description into conformity with the new claims, also meet the requirements of Article 123(2) EPC. The claims according to the sole request are clear and supported by the description, so that the requirements of Article 84 EPC are also met.

4. Inventive step

4.1. The subject-matter of claims 1 to 3 relates to a process for the production of foams from at least two reactive components using carbon dioxide as expanding agent, comprising mixing at least one of the reactive components with carbon dioxide under pressure thereby producing a mixture containing liquid carbon dioxide, mixing the resultant mixture with the other reactive component to form a foamable reactive mixture at a pressure in excess of the equilibrium pressure of dissolved carbon dioxide, expanding the reactive mixture and curing the resultant foam product. Such a process is known from document D2 (cf. column 1, line 40, to column 2, line 6). This document, which can be considered as the closest prior art, does not disclose the use of a screen.

Liquid carbon dioxide has been used in the foaming art as an expanding agent for many decades (cf. document D2, which claims priority of an application filed in 1958), inter alia due to its environmental acceptability. However, the release of carbon dioxide from a foamable reactive mixture has been found to be difficult to control, since, firstly, carbon dioxide vaporizes relatively suddenly so that a very large increase in volume takes place in the reaction mixture, and, secondly, the reaction mixture tends to inhibit release of the carbon dioxide, which can be from 3 to 6 bar below the equilibrium vapour pressure at the relevant temperature, so that a sudden explosive release of carbon dioxide occurs with the result that large voids or bubbles are enclosed within the foam (cf. column 1, line 42, to column 2, line 4, of the patent in suit).

The problem the invention as claimed in claims 1 to 3 seeks to solve can thus be formulated as providing a process which produces a foam with small and uniform bubbles.

The invention as claimed in claims 1 to 3 is based on the finding that a large number of microscopic bubble nuclei are produced when the reaction mixture is exposed during expansion to high shear rates of above 500/s. This is achieved by passing the reaction mixture containing liquid carbon dioxide through at least one fine-meshed screen, so that the flow is subdivided into a large number of individual flows, and thereby expanded.

4.2. Document D1 discloses a process whereby an inert gas and an organic liquid foam precursor are passed together through a frothing zone, see column 2, lines 29 to 32. The inert gas may be carbon dioxide, but is normally air (see the Examples and column 2, lines 12 to 16). Document D1 does hence neither disclose that the inert gas is mixed with the reactive component before it enters the frothing zone, nor that it is initially mixed with only one reactive component and then with the other reactive component, i.e. a two-step mixing process. Document D1 also fails to disclose that the inert gas is in liquid form. Moreover, document D1 does not disclose the forming of a foamable reactive mixture at a pressure in excess of the equilibrium pressure of dissolved carbon dioxide.

The fine-mesh screens in the process known from document D1 are used to distribute the inert gas into the organic liquid foam precursor, whereby through the action of a large number of screens larger bubbles are divided into smaller ones. The process disclosed in document D1 is thus essentially a mechanical frothing process, although it is different from a conventional mechanical dispersion process, like, for example, beater and pump dispersion (cf. column 2, line 65, to column 3, line 9).

Summarizing, document D1 does not disclose that one of the reactive components is first mixed with carbon dioxide before the resultant "mixture containing liquid carbon dioxide" is mixed with the other reactive component to form a foamable reactive mixture, as required by claim 1. The expression "mixture containing liquid carbon dioxide" as used in claim 1 is defined in the patent in suit (cf. column 3, lines 10 to 13) as a homogeneous liquid under a pressure of at least 4 bar, wherefrom carbon dioxide is released after expansion to a pressure of less than at least 4 bar.

It follows from the above that document D1 is not at all relevant to assess inventive step of the invention as claimed in claims 1 to 3. Document D1 does not disclose the preparation of a foamable reactive mixture in the sense of the invention as claimed in claims 1 to 3, whereby bubbles are formed by evaporation, it rather discloses the mechanical preparation of a froth, viz. a liquid foam. Hence the skilled person had no incentive to employ the fine-meshed screen known from document D1 in the process known from document D2.

4.3. The subject-matter of claim 1 thus involves an inventive step. Claims 2 and 3 are appendant to claim 1 and relate to preferred embodiments of the process of claim 1. These claims thus similarly involve an inventive step.

5. The patent can thus be maintained as requested by the appellant.